Systematic Review Meta-analysis of single crowns supported ... · Conclusions: Single crowns...

Systematic Review

Meta-analysis of single crownssupported by short (<10 mm)implants in the posterior regionMezzomo LA, Miller R, Triches D, Alonso F, Shinkai RSA. Meta-analysis ofsingle crowns supported by short (<10 mm) implants in the posterior region.J Clin Periodontol 2014; 41: 191–213. doi: 10.1111/jcpe.12180.

AbstractAim: To assess the failures and complications of short (<10 mm) implantssupporting single crowns in the posterior region and its potential risk factors(RkF).Materials and Methods: Prospective studies were screened according to eligibilitycriteria, followed by contact with authors. Quality assessment was performedusing a standardized protocol. Mean implant failure proportion (FP), biologicaland prosthetic failure proportions (BFP/PFP) and marginal bone loss (MBL)including 95% confidence intervals were estimated using random-effects modelsfor meta-analysis.Results: Sixteen studies with a medium methodological quality (mean score:8 � 3; 2–14) had data collected. In summary, 762 short implants were followedup for up to 120 months in 360 patients (mean follow-up: 44 � 33.72 months;mean dropout rate: 5.1%). The means FP, BFP, PFP and MBL were 5.9% (95%CI: 3.7–9.2%), 3.8% (95%CI: 1.9–7.4%), 2.8% (95%CI: 1.4–5.7%) and 0.83 mm(95%CI: 0.54–1.12 mm) respectively. Quantitative analysis showed that placementin the mandible (p = 0.0002) and implants with length ≤8 mm (p = 0.01) increasedFP, BFP and MBL, whereas qualitative assessment revealed that crown-to-implant ratio did not influence MBL.Conclusions: Single crowns supported by short implants in the posterior regionare a predictable treatment option with reduced failure rates, biological/prostheticcomplications and minimal bone loss.

Luis Andr�e Mezzomo, Rodrigo Miller,Diego Triches, Fernando Alonso and

Rosemary Sadami A. Shinkai

Department of Prosthodontics, Post-Graduate

Program in Dentistry, Pontifical Catholic

University of Rio Grande do Sul, Porto

Alegre, Brazil

Key words: meta-analysis; partially

edentulous patients; posterior region; short

implants; single crown; systematic review

Accepted for publication 1 October 2013

The oral rehabilitation of short-spanedentulous areas or single missingteeth with endosseous implants canprovide optimal aesthetic and func-tional results, with good predictabil-ity (Jemt et al. 1991). However,limitations for implant placement inthe posterior region of the jaws oftenoccur when the alveolar ridge isresorbed due to periodontal diseaseand/or long-term edentulism. More-over, anatomical structures such asthe inferior alveolar nerve and the

maxillary sinus may be damagedwhen implants with conventionallengths are used (Renouard &Nisand 2005).

Several surgical techniques havebeen proposed to overcome these sit-uations and allow the placement ofimplant with conventional length,with varied success rates: sinus floorelevation (Summers 1994), verticalridge augmentation (Felice et al.2009), distraction osteogenesis (Chi-apasco et al. 2004), inferior alveolar

Conflict of interest and source offunding statement

The authors declare that they have noconflict of interests. The study wasfinancially supported by grants ofCAPES (Coordination of Improve-ment of Higher Education Personnel,Brazil), FAPERGS (Foundation ofResearch Support of the State of RioGrande do Sul, Brazil) and PUCRS(Pontifical Catholic University of RioGrande do Sul, Brazil).

© 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd 191

J Clin Periodontol 2014; 41: 191–213 doi: 10.1111/jcpe.12180

nerve lateralization (Garg & Morales1998) and placement of tilted(Krekmanov et al. 2000) or zygo-matic (Bedrossian et al. 2006)implants. Systematic reviews (Kot-sovilis et al. 2009, Annibali et al.2012) and randomized clinical trials(Felice et al. 2009, Esposito et al.2011a) stated that these complex sur-gical interventions significantlyincrease treatment duration, morbid-ity, risk of complications and costs.Therefore, implants of reducedlength (<10 mm) were suggested as amore accessible treatment option toboth patients and clinicians, withsuccessful results and low incidenceof biological and biomechanical com-plications (Morand & Irinakis 2007).

Early clinical evidences from ret-rospective (Friberg et al. 1991) andprospective (van Steenberghe et al.1990) studies stated that machinedsurface short implants had higherfailure rates than implants of conven-tional length. For this reason, shortimplants were initially suggested tobe used splinted to longer ones (tenBruggenkate et al. 1998). In the lastdecade, modified implant designs andmicrostructured implant surfaces thataugment the surface area have beenintroduced. The surface treatment isresponsible for a faster new bone for-mation and for the increase of thecontact area between bone andimplant, similar to the anchorage oflonger implants with smoothmachined surfaces (Hagi et al. 2004,Renouard & Nisand 2006). Hence,short implants with modified surfaceshave been recommended for regionsof poor bone quality and strongerforces, such as the posterior regionof the maxilla and/or mandible,reducing morbidity and costs of bonegrafting even for single-tooth replace-ments (Fugazzotto 2008c; Monjeet al. 2013).

There has been an increasing num-ber of systematic (Hagi et al. 2004,das Neves et al. 2006, Renouard &Nisand 2006, Kotsovilis et al. 2009,Esposito et al. 2010, Neldam & Pin-holt 2012, Menchero-Cantalejo et al.2011, Pommer et al. 2011, Sun et al.2011, Telleman et al. 2011, Annibaliet al. 2012, Monje et al. 2013) andnarrative (Lum 1991, Lee et al. 2005,Misch 2005, Morand & Irinakis 2007,Romeo et al. 2010) reviews on shortimplants being published in Medline-indexed journals. These studies

claimed that short implants should beconsidered as an alternative treatmentto advanced bone augmentation sur-geries, showing similar survival ratesto longer implants (das Neves et al.2006, Esposito et al. 2010, Pommeret al. 2011, Monje et al. 2013). Nev-ertheless, most of these reviews clus-tered the outcomes of short implantssupporting different types of recon-structions, from single crowns to fixedpartial dentures and overdentures.Also, they usually focused at assess-ing survival rates of the short implants(Kotsovilis et al. 2009), based pre-dominantly on heterogeneous datafrom both retrospective and prospec-tive studies (Renouard & Nisand2006, Neldam & Pinholt 2012, Anni-bali et al. 2012).

In despite of the evolution of themacro- and microtopography (sur-face) of the implants and the increas-ing success rates of short implants,there is still a lack of comprehensivesystematic reviews evaluating therisk factors (RkF) on the prognosisof the rehabilitation of the posteriorregion with single crowns supportedby short implants. Thus, the aim ofthis study was to answer the focusedquestion “In partially edentulouspatients presenting severe resorptionof the posterior region of the jaws,what is the effect of restoring short(<10 mm) implants with singlecrowns compared with single crownssupported by implants of conventionallength associated with bone grafts onthe failure rates of these implants andprostheses and what are the RkF forfailure and/or complications?”, by con-ducting a systematic review and ameta-analysis of prospective studiespublished in the dental literature upto October 2012.

Materials and Methods

Design

The methodological procedures ofthis review were based on the guide-lines proposed by the Cochrane Col-laboration (Higgins & Green 2001)and Needleman (2002).

Eligibility criteria and study selection

Inclusion criteria

Randomized controlled clinical trials(RCTs), controlled clinical trials(CCTs), prospective cohort studies

and case series where the test groupcomprised placement of short(<10 mm) implants supporting singlecrowns in non-augmented, healedjaw-bone, and the control groupcomprised placement of implants ofconventional length associated ornot to bone augmentation proce-dures and supporting single crownsin the posterior region of the max-illa/mandible of partially edentulouspatients, with a minimum of 10implants per group and at least a1-year post-loading follow-up; aclear report of (or report of dataallowing the calculation of) the totalnumber of short implants placed/surviving and the number of singlecrowns supported by short implantsin the posterior region with its likelyprognostic factors. In this study, animplant of length <10 mm was con-sidered as a short implant (Morand& Irinakis 2007, Telleman et al.2011), regardless of the level ofplacement.

Exclusion criteria

(1) studies with an unclear or mixeddesign; (2) literature reviews; (3) ret-rospective studies; (4) pre-clinical andin vitro studies; (5) case reports andcase series with less than 10 singlecrowns supported by short implantsper group; (6) length of the implants≥10 mm or unclear; (7) locationwhere short implants were placedwere not the posterior region orremained unclear; (8) studies with aninsufficient follow-up period; (9) stud-ies evaluating splinted fixed partial orcomplete dentures supported by shortimplants; (10) studies placing shortimplants in augmented area (eithersimultaneously or previously); (11)same population of a previous study(when multiple publications on thesame population and implants wereidentified, only data from the mostrecent report was used); (12) declina-tion of the main author to providefurther information; and (13) contactwith author failed.

Search strategy and data collection

Key words were selected from MeSHterms and descriptors from previousstudies to perform the specificsearch strategies for each database(Table 1). Electronic search wasperformed by two independent andcalibrated reviewers in a duplicated

© 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd

192 Mezzomo et al.

manner, at the following electronicdatabases: PubMed-Medline, Web ofScience, Cochrane Library, Proquest-Dissertations and Thesis, Lilacs,Ebsco-Dentistry and Oral SciencesSource, Scirus, Embase, Scopus andJournal Ovid. No restriction to theyear of publication was applied.Search was concluded in June 2012.The results were exported to the soft-ware EndNote Web� (ThomsonReuters, New York, NY, USA), whereboth title and abstract screenings,restricted to the English language,were performed.

Handsearch, which followed theguidelines of the Journal Handsearch-ing Programme (Cochrane OralHealth Group), was finalized in Octo-ber 2012. It was conducted within thetable of contents of 14 internationalpeer-reviewed journals for the periodsof time indicated in parentheses:Clinical Oral Implants Research (2001,2003–2012), International Journal ofOral and Maxillofacial Implants(2004–2012), Implant Dentistry (2004–2012), International Journal of Peri-odontics and Restorative Dentistry(2003–2012), Journal of Clinical Peri-odontology (2004–2012), Journal ofPeriodontology (2004–2012), ClinicalImplant Dentistry and Related Research(2003–2012), Journal of ProstheticDentistry (1999–2012), InternationalJournal of Prosthodontics (2001–2012),Journal of Oral and Maxillofacial Sur-gery (2003–2012), Oral Surgery, Oral

Medicine, Oral Radiology, Oral Path-ology and Endodontics (2004–2012),Journal of Dental Research (2004–2012), European Journal of Oral Im-plantology (2008–2012) and theJournal of Oral Implantology (2001–2012). The reference lists of thescreened original articles and reviewsalso underwent screening. In addition,corresponding authors were contactedfor missing, unclear or unpublisheddata.

Full-text screening was performedby two reviewers with no languagerestrictions. Professional translationwas provided when necessary. In caseof disagreement, the reviewers dis-cussed the issue to reach a consensus;if the divergence persisted, a thirdreviewer was consulted. Finally, thereviewers independently used a stan-dardized data-extraction form toclarify eligibility and collect the dataabout the overall characteristics ofeach included study and, finally, toassess the statistical analysis applied.

Outcome measures

• Implant failure proportion (FP):The primary outcome variablewas the percentage of implantsfailing out of the total numberplaced, after the first year ofprosthetic loading, and wasquantified as the FP. Failure wasdefined as removal of the implant

due to loss of osseointegration orprogressive marginal bone loss(Albrektsson et al. 1986).

• Biological failure proportion(BFP): This refers to the pres-ence of an implant with compli-cations of a biological nature (i.e.persistent pain, neuropathy and/or loss of function, persistentuncontrolled peri-implant inflam-mation and/or infection, implantmobility) (Albrektsson et al. 1986,Academy of Osseointegration2010). BFP was defined as theabsolute number of implants pre-senting one (or more) of theabove-mentioned complicationsdivided by the number of surviv-ing/prosthetically restored impla-nts. It includes late failures(Annibali et al. 2012).

• Radiographic marginal bone loss(MBL): This was studied as ameasure to evaluate the meanbone loss (Annibali et al. 2012)among the surviving/prostheti-cally restored implants.

• Prosthetic failure proportion(PFP). Defined as the presenceof an implant with complicationsof a prosthetic nature (i.e. frac-tured veneering materials, frac-tured or loosened prostheticcomponents) (Academy of Osseo-integration 2010). PFP wasdefined as the absolute number ofimplants presenting one (or more)of the above-mentioned complica-

Table 1. Key words and MeSH terms used for electronic search*

Population Intervention/comparison Outcome Type of non-includedstudies

OR OR OR ORMeshTooth extraction,partially edentulousjaw, alveolar boneatrophy, boneresorption, bruxism,bite force

AND

MeshDental implants,implant-supporteddental prosthesis,single-tooth dentalimplant, bonesubstitutes, bonegrafting

AND

MeshDental prosthesis failure,survival rate,complications, patientsatisfaction, quality of life

NOT

MeshIn vitro, animals,review, case reports,retrospective

Key wordsPosterior atrophicmandible

Key wordsShort implant†, boneaugment†

Key wordsSuccess rate, dentalimplant fail†, radiographicbone loss, radiographicbone density loss, primarystability, crown-to-implantratio

Key wordsPre-clinical

*According to the PICO scheme (P, population or problem of interest; I, intervention under investigation; C, comparison of interest; O,outcomes considered most important in assessing results) (Needleman 2002).†means truncation, that is to say, whatever is the suffix after it, the word keeps the main radical.


Single posterior short implants 193

tions divided by the number ofsurviving/prosthetically restoredimplants (Annibali et al. 2012).

• Risk factors (RkF) associated toimplant and prosthesis failure: Thepotential factors that could com-promise the short- and long-termsuccess of the implant-prostheticreconstruction, such as systemic(uncontrolled diabetes, smoking,etc.), and local conditions (implantlocation, poor bone quality, insuf-ficient primary stability, presenceof bruxism, as well as an unfa-vourable C/I ratio). The RkFswere evaluated either qualitativelyor quantitatively (for the dichoto-mous co-variables).

Quality assessment

The levels of evidence of the includedstudies were assessed according to themethodology applied, confoundingfactors, ethical aspects, funding, con-flict of interest, unit of analysis forstatistics (patient or implant) andexternal validity. At the end, an esti-mated risk of bias (low, medium orhigh) was assigned to each of theincluded studies by the reviewersusing the forms “Quality Assessmentof a RCT” and “Quality Assessmentof a Cohort Study”, with some adap-tations (Table 2). These validity toolsconsist originally of nine and eightitems, respectively, which have to bescored with a plus “+”, a minus “�”,or a question mark “?” (Tellemanet al. 2011). For the present review,nine additional items have beenadded to the forms. Thus, studiesscoring 0–7, 8–13 and 14–18 plusses(in proportion to the original) wereconsidered of high, medium and lowrisk of bias respectively. One reviewerperformed the quality assessment andgenerated the scores for the includedarticles. No blinding for author,institute or journal was applied.

Quantitative data analysis

Percentage of agreement amongreviewers was expressed as Cohen’sunweighted r. Data were presentedat the implant level. Dropouts/lossesto follow-up were excluded from theanalysis and thus the total numberof implants was represented by thosethat completed at least one year offollow-up.

All statistical analyses and assess-ment of heterogeneity among studieswere carried out using a commer-cially available software (Compre-hensive Meta-Analysis�; CMA,Biostat, Englewood, NJ, USA). Theoutcomes FP, BFP, PFP and MBLwere meta-analysed according to therandom-effects models (a consider-able heterogeneity among studieswas anticipated). Considering thatthe outcomes evaluated as propor-tions (FP, BFP, PFP) had valuesvery close to zero, a transformationof the data had to be carried out forappropriate calculations. The CMAsoftware automatically converts pro-portions into the logit scale for themeta-analyses calculations, and even-tually transforms the values back tothe original proportion scale in thefinal results presentation.

Risk factors were considered co-variates and their influence on themain outcomes were evaluated. Con-tinuous covariates, such as patient’sage and gender, implant location,length and diameter, surgicalapproach, type of prosthetic reten-tion and follow-up period had theirproportions converted into percent-ages [from 0.0% (0.000) up to 100%(1.000)] and thus meta-regressionanalysis were run as fixed-effectmodels. The further covariates, suchas timing of prosthetic loading, typeof implant-abutment connection,surface topography, presence ofbruxism as well as periodontal dis-ease, smoking and systemic diseasesstatus, were dichotomized into “pres-ence/absence,” or “1/0,” respectively,and thus subgroup analyses were runas mixed effect models. The level ofsignificance was set at 5%(p < 0.05).

Results

Search yielding and screening process

Electronic search yielded 4514, 535and 56 references for title, abstractand full-text screening respectively.Hand-search yielded additional 44studies – 15 from the journals, 5from the author themselves and theother 24 from the reference lists ofarticles and reviews. In summary,100 articles were eligible for full-textscreening. Disagreements were usu-ally caused by slight differences ininterpretation and were easily

resolved in a consensus discussion.Percentage of agreement expressedas Cohen’s unweighted r achievedscores of r = 0.76 and 0.97 forabstract and full-text screening,respectively, among the reviewers(Fig. 1) (Jekel et al. 2005).

Results of contact with authors

Due to limited information providedin some original articles (forinstance, some studies did not detailindividual failure scores for the dif-ferent implant lengths), 31 authorswere contacted and additional infor-mation was sought through electronicmail for 39 articles. Reminders weresent to the authors on a weekly basisup to a point that either the requesteddata could be obtained or the contactwas considered as failed. At theend, the authors of 12 articles (30.7%)kindly provided the requestedanswers.

Quality assessment of the studies

Table 2 summarizes the qualityassessment results. The scores of theincluded studies (mean: 8 � 3;range: 2–14) indicated a mediummethodological quality and a highmethodological unconformity. Factorsthat most increased the risk-of-biaswere the lack of a standardization ofthe treatment that patients underwentand a lack of a report of the samplesize calculation. Ethical aspects werenot entirely reminded as long asHelsinki Declaration was reported atonly two studies. On the other hand,informed consent form was obtainedfor the majority of the studies,whereas ethical committee approvalwas sought for six studies. Further-more, reasons for dropouts weredisclosed at only nine studies. Onceany RCT addressing the strict eligibil-ity criteria of the present review wasfound, the form “Quality Assessmentof a RCT” was not used.

Study characteristics

The overall characteristics of theincluded studies are described inTable 3. Twenty-one articles wereincluded, accounting for 16 prospec-tive parallel-designed studies – 10cohorts and six case series. Due tothe strict inclusion criteria, thissystematic review failed to identify


194 Mezzomo et al.

Table

2.

Quality

assessm

entoftheincluded

studies(n

=16)†

Question(+

�?)

Study#

12

34

56

78

910

11

12

13

14

15

16

1.Hasasample

size

calculationand

power

beenreported?§

�+

��

��

+�

��

��

��

�+

2.Hasbaselinehomogeneity

been

achieved?§

++

�+

+�

��

�+

++

��

++

3.Haseligibilitycriteria

beenclearly

described?§

++

++

++

+�

++

++

++

++

4.Hasahighrisk

ofbiasonpatient’s

selectionbeenexcluded?‡

�+

��

++

++

�+

++

++

�+

5.Hastheinterventionbeenclearly

described?‡

�+

�+

�+

+�

�+

++

��

�+

6.Are

allpatients

treatedaccordingto

thesameintervention?‡

��

��

��

��

��

��

��

��

7.Are

theoutcomes

clearlydescribed?‡

��

��

�+

+�

�+

++

?�

��

8.Are

themethodsusedto

assessthe

outcomeadequate?‡

��

�+

��

��

++

++

��

�+

9.Is

blindingusedto

assessthe

outcome?

Ifnot,does

thishaveno

effect

ontheevaluationoftheresults?

‡

�+

�+

+�

��

+�

��

�+

��

10.Is

calibrationusedto

assessthe

outcome?

Ifnot,does

thishaveno

effect

ontheevaluationoftheresults?

§

��

�+

��

��

+�

��

��

++

11.Is

theoutcomeassessordifferent

from

theoperator?

§�

��

++

+�

�+

��

��

�+

+

12.Hasthefollow-upbeencompleted?‡

��

++

�+

+�

�+

++

+�

��

13.Candropouts

beexcluded

sufficiently?‡

+�

��

+�

++

+�

��

++

++

14.Hastheoriginalprotocolnotbeen

violated?§

?+

+�

�+

+�

�+

�+

��

�+

15.HastheSTROBEstatementbeen

mentioned

andfollowed?§

�+

��

��

+�

��

��

��

�+

16.Havetheethicalconsiderations

(HelsinkiDeclaration,Inform

edConsentandEthicsCommittee

approval)beenconsidered?§

�+

�+

�+

+�

++

++

++

�+

17.Are

themost

importantconfounders

orprognostic

factors

identified?‡

+�

��

++

��

�+

�+

++

�+

18.Theauthors

havedeclarednoconflict

ofinterests?

§?

++

?�

�+

�+

+?

+�

�+

+

Score

(total+)

410

49

79

11

28

11

811

66

614

Riskofbias*

High

Medium

High

Medium

High

Medium

Medium

High

Medium

Medium

Medium

Medium

High

High

High

Low

*Studiesscoring0–7,8–13and14–18plusses

wereconsidered

asofhigh,medium

andlow

risk

ofbiasrespectively.

†Adaptedfrom

Tellemanet

al.(2011).

‡Originalitem

s.§Item

sadded

bytheauthors

ofthepresentreview.



any controlled clinical trial, eitherrandomized or not, that is, usingimplants of conventional length insites with or without bone augmen-tation as a control. Therefore,within-study comparison of shortand long implants was not possible.Likewise, odds ratio and relative riskcould not be calculated throughmeta-analysis. Seventy-nine studiesdid not meet the inclusion criteria,either before or after contactwith authors, and were excludedfrom this analysis (supplementarymaterial).

The studies #2 (Cannizzaro et al.2012) and #9 (Nicolau et al. 2013), aswell as the study #16 (Telleman et al.2012), which were originally designedas randomized controlled trials evalu-ating different loading protocols anddifferent implant-abutment platformsof short implants, respectively, hadthe results of groups test and controlclustered into only one group and sowere reclassified as cohort studiesaccording to the criteria of the pres-ent review. Likewise, studies #1 (Bro-card et al. 2000), #4 (Deporter et al.2001a), #11 (Romeo et al. 2002), #13(Stanford et al. 2010) and #14 (Striet-zel & Reichert 2007), which wereoriginally classified as prospectivecohort studies and where shortimplants supporting single crowns in

the posterior region represented aportion of the whole sample size,were reclassified as case series(Table 3).

The article from Deporter et al.(2001a) concerned the same popula-tion and implants of the papers fromDeporter et al. (1999, 2000, 2002)and Rokni et al. (2005), whereas thearticle from Tawil et al. (2006) con-cerned the same patients andimplants as the paper from Tawil &Younan (2003). Thus, data fromthese reports were used to supple-ment each other but accounted foras studies #4 (Deporter) and #15(Tawil), respectively, in the meta-analysis. The paper of Rokni et al.(2005) comprised the population andimplants from two studies – Deport-er et al. 2001a, 2012, in the maxillaand the mandible respectively. Thus,their results were separated for bothstudies.

Population characteristics

The sample size and age (mean;range) of the population of theincluded studies are listed in Table 3.In some reports, especially in largecohort studies where implants of dif-ferent lengths were used, it wasalmost impossible to distinguish thesample of patients who have received

implants with length <10 mm. Thus,the actual population of patientsreceiving short implants was surelylarger than the 360 patients reportedamong the ten studies that dealtexclusively with short implants.Meta-regression analysis revealedsignificant effects for the variableage on both outcomes BFP andMBL (p = 0.0142 and 0.00000117respectively), as well as for the vari-able gender (percentage of females)on the MBL (p = 0.000) (Table 4).

Implant characteristics

The characteristics of the implants(location, length, diameter andsurface) of the included studies aresummarized in Table 3.

Implant location

The means FP, BFP and MBL forimplants placed in the mandiblerevealed by fixed effect meta-regres-sion were significantly higher thanthat for implants in the maxilla(p = 0.0002, 0.00375 and 0.0000-00117 respectively) (Table 4). Due tothe small number of studies report-ing if short implants were placedeither in the premolar or in themolar area (n = 6), statistical analy-sis over the site of placement couldnot be performed. Except for study#15 (Tawil), which did not find sig-nificant differences in terms of fail-ures and complications betweenimplants placed in molar as com-pared to premolar positions, theother original studies did not reportrelevant information.

Implant length

The distribution of the implants withregards to the length was as follows:8 9 5 mm (8/803, 0.99%), 57 9 6mm (57/803, 7.09%), 53 9 6.5 mm(53/803, 6.60%), 247 9 7 mm (247/803, 30.76%), 154 9 8 mm (83/803,19.18%), 201 9 8.5 mm (201/803,25.03%) and 83 9 9 mm implants(83/803, 10.33%). Dropouts andlosses to follow-up (n = 41) wereconsidered neither as failed nor assuccessful implants. Therefore, 762implants were available for meta-analysis. All but one study (#11)stated that short implant lengthobtained similar if not superior sur-vival rates with minimal bone lossthan those reported for other implantlengths.

Fig. 1. Flow chart of the search and screening processes of the primary studies. Somearticles have been excluded during full-text screening because of more than one singlereason.


196 Mezzomo et al.

Table

3.

Characteristics

ofthepopulation,interventionsandoutcomes

ofthestudies(n

=16).

Study

Population

characteristics

Implant

location(n)

Implant

characteristics

Implant

length

(n)

Implant

diameter

(n)

Surgical

parameters(n)

Prosthetic

parameters(n)

Follow-up

inmonths

Riskfactors

included/

assessed

(yes/no)

Outcomes

(n)

Proportions

Mean

(CI:lower-

upper

limit)

Reference

Number

(#)

First

Author

(Yearof

publication)

Type

Design

1.nofpatients

total(♂

;♀)

2.nofpatients

inthisreview

2.Age(m

ean

inyears)

3.Age(range

inyears)

1.Maxilla

2.Mandible

3.Premolars

4.Molars

5.Total

1.Company

2.Surface

1.≤6

mm

2.6mm

<x<8mm

3.8mm

≤x<10mm

1.Narrow

(Ø3.3–Ø

3.5

mm)

2.Regular

(Ø3.75–Ø

4.3

mm)

3.Wide

(Ø4.8–Ø

6.0

mm)

1.Tim

ing

ofim

plant

placement

(immediate/

early/late)

2.Flapraised

3.Primary

closure

4.Approach

(1-versus

2-stages)

5.Criteria

forsuccess

1.Loadingprotocol

(immediate/early/

conventional)

2.Typeofveneering

3.Typeofretention

(cem

ented-versus

screw

retained)

4.Im

plant-abutm

ent

connection

(internalversus

external)

1.Mean

2.Range

1.System

ic

disease

2.Smoking

3.Bruxism

4.Periodontal

disease

5.Bonequality

6.Primary

stability

7.Crown-

to-implant

ratio(m

ean)

1.Drop-outs/

losses

to

follow-up

2.Failures

(early;late)

3.Biological

complications

4.Radiographic

marginalbone

loss

(mean)

5.Prosthetic

complications

1.Failure

proportion

(FP)

2.Biological

failure

proportion

(BFP)

3.Radiographic

marginalbone

loss

(mean)

4.Prosthetic

failure

proportion

(PFP)

#1

Brocard

(2000)

Case

series

Parallel

1.n=

440(184;256)

2.n=?

3.53years

4.16–9

0years

1.n=

7*

2.n=

25*

3.N/R

4.N/R

5.n=

32*

1.IT

I

(Straumann�)‡

2.TPS�

(Titanium-

plasm

a-spray)

1.n=

1*

2.n=

0

3.n=

31*

1.n=

0

2.n=

32

3.n=

0

1.Late

(32)

2.Yes

(?)

3.N/R

4.N/R

5.Albrektsson

etal.1986,

Buseret

al.

1997,

1.Conventional(32)

2.Porcelain-fused

tometal(32)

3.N/R

4.Internal(32)

1.N/R

2.13–63*

1.Yes

2.Yes

3.Yes

4.No

5.N/R

6.N/R

7.N/R

1.N/R

2.n=0;n=0

3.n=0

4.N/R

5.n=0

1.0.015

(0.001–0

.201)

2.0.015

(0.001–0

.201)

3.N/A

4.0.015

(0.001–0

.201)

#2

Cannizzaro

2012

Cohort

Split-mouth

1.n=

30(15;15)

2.n=27

3.35years

4.18–5

7years

1.n=

29

2.n=

24

3.n=25

4.n=28

5.n=

53

1.Biomet

3I�

§

2.Nanotite

�

(dualetched

andpartially

covered

with

nanoscale

calcium

phosphate

crystal)

1.n=

0

2.n=

53

3.n=

0

1.n=

0

2.n=

20

3.n=

40

1.Im

mediate

(18);

Late

(35)

2.Yes

(13);

No(40)

3.N/R

4.1-stage(53)

5.Im

plant

removalor

implant

fracture

(mobilityand/

orinfection)

1.Im

mediate

(26);

Early(27)

2.Porcelain-fused

tometal(53)

3.Cem

ented

retained

(53)

4.External(53)

1.N/R

2.12–48

1.No

2.Yes

3.Yes

4.No

5.Yes

6.Yes

7.N/R

1.n=0

2.n=2;n=0

3.n=5

4.0.34mm

5.n=3

1.0.038

(0.009–0

.139)

2.0.098

(0.041–0

.215)

3.0.340

(0.244–0

.436)

4.0.039

(0.010–0

.144)

#3

Corrente

(2009)

Cohort

Parallel

1.n=

48(22;26)

2.n=35

3.45years*

4.N/R

1.n=

35

2.n=

0

3.N/R

4.N/R

5.n=

35

1.Endopore

�, *,¶

2.Porous

Sintered�

1.n=

5*

2.n=

30*

3.n=

0

1.n=

0

2.n=

21*

3.n=

14*

1.Late

(35)

2.N/R

3.N/R

4.2-stages

(35)*

5.N/R

1.Conventional(35)

2.Porcelain-fused

tometal(35)*

3.Cem

ented

retained

(30);

Screw

retained

(5)*

4.External(35)

1.20

2.12–36

1.No

2.Yes

3.N/R

4.N/R

5.N/R

6.N/R

7.N/R

1.n=0

2.n=1;n=0

3.n=0*

4.1.5

mm

†

5.n=0

1.0.029

(0.004–0

.177)

2.0.014

(0.001–0

.191)

3.1.500

(1.334–1

.666)

4.0.014

(0.001–0

.191)

#4

Deporter

2001a

Case

series

Parallel

Deporter

etal.

(1999,2000,

2002);Rokni

etal.(2005)

1.n=

50(25;25)

2.n=?

3.53.7

years

4.25–7

6years

1.n=

70

2.n=

0

3.N/R

4.N/R

5.n=

70

1.Endopore

�,¶

2.Porous

Sintered�

1.n=

2

2.n=

44

3.n=

24

1.n=

40

2.n=

74

3.n=

21

1.Late

(70)

2.Yes

(70)

3.N/R

4.2-stages

(70)

5.N/R

1.Conventional(70)

2.Porcelain-fused

tometal(70)

3.N/R

4.External(70)

1.34.6

2.5.1–6

8.6

1.No

2.No

3.N/R

4.No

5.N/R

6.Yes

7.Mean1.5

1.n=0

2.n=1;n=0

3.n=0

4.0.038mm

5.n=0

1.0.014

(0.002–0

.094)

2.0.007

(0.000–0

.104)

3.0.038(�

0.014

to0.090)

4.0.007

(0.000–0

.104)



Table

3.(continued)

Study

Population

characteristics

Implant

location(n)

Implant

characteristics

Implant

length

(n)

Implant

diameter

(n)

Surgical

parameters(n)

Prosthetic

parameters(n)

Follow-up

inmonths

Riskfactors

included/

assessed

(yes/no)

Outcomes

(n)

Proportions

Mean

(CI:lower-

upper

limit)

Reference

Number

(#)

First

Author

(Yearof

publication)

Type

Design

1.nofpatients

total(♂

;♀)

2.nofpatients

inthisreview

2.Age(m

ean

inyears)

3.Age(range

inyears)

1.Maxilla

2.Mandible

3.Premolars

4.Molars

5.Total

1.Company

2.Surface

1.≤6

mm

2.6mm

<x<8mm

3.8mm

≤x<10mm

1.Narrow

(Ø3.3–Ø

3.5

mm)

2.Regular

(Ø3.75–Ø

4.3

mm)

3.Wide

(Ø4.8–Ø

6.0

mm)

1.Tim

ing

ofim

plant

placement

(immediate/

early/late)

2.Flapraised

3.Primary

closure

4.Approach

(1-versus

2-stages)

5.Criteria

forsuccess

1.Loadingprotocol

(immediate/early/

conventional)

2.Typeofveneering

3.Typeofretention

(cem

ented-versus

screw

retained)

4.Im

plant-abutm

ent

connection

(internalversus

external)

1.Mean

2.Range

1.System

ic

disease

2.Smoking

3.Bruxism

4.Periodontal

disease

5.Bonequality

6.Primary

stability

7.Crown-

to-implant

ratio(m

ean)

1.Drop-outs/

losses

to

follow-up

2.Failures

(early;late)

3.Biological

complications

4.Radiographic

marginalbone

loss

(mean)

5.Prosthetic

complications

1.Failure

proportion

(FP)

2.Biological

failure

proportion

(BFP)

3.Radiographic

marginalbone

loss

(mean)

4.Prosthetic

failure

proportion

(PFP)

#5

Deporter

2012

Cohort

Parallel

Rokniet

al.

(2005)

1.n=

24(8;16)

2.n=24

3.49.6

years

4.20–7

2years

1.n=

0

2.n=

35

3.N/R

4.N/R

5.n=

35

1.Endopore

�,¶

2.Porous

Sintered�

1.n=

0

2.n=

32

3.n=

16

1.N/R

2.N/R

3.N/R

1.Late

(35)

2.Yes

(35)

3.N/R

4.2-stages

(35)

5.N/R

1.Conventional(35)

2.Porcelain-fused

tometal(35)

3.Screw

retained

(41)

4.External(35)

1.N/R

2.12–120

1.No

2.No

3.N/R

4.No

5.N/R

6.N/R

7.Mean1.4

1.n=7

2.n=2;n=0

3.n=0

4.1.21mm

5.n=0

1.0.071

(0.018–0

.245)

2.0.019

(0.001–0

.236)

3.1.210

(1.060–1

.360)

4.0.019

(0.001–0

.236)

#6

DeSantis2011

Cohort

Parallel

1.n=

46(21;25)

2.n=12

3.N/R

4.36–7

8years

1.n=

6

2.n=

23

3.n=11

4.n=18

5.n=

29

1.Nobel

Biocare

�**

2.TiU

nite�

(anodically

oxidized

surface)

1.n=

0

2.n=

20

3.n=

9

1.N/R

2.N/R

3.N/R

1.Late

(29)

2.Yes

(29)

3.Yes

(29)

4.2-stages

(29)

5.Albrektsson&

Zarb

(1998)

1.Conventional(29)

2.Porcelain-fused

tometal(29)

3.Cem

ented

retained

(29)

4.External(29)

1.24.6

2.12–48

1.No

2.Yes

3.No

4.No

5.N/R

6.Yes

7.N/R

1.n=0

2.n=4;n=0

3.n=1

4.0.6

mm

5.n=1

1.0.138

(0.053–0

.315)

2.0.040

(0.006–0

.235)

3.0.600

(0.522–0

.678)

4.0.040

(0.006–0

.235)

#7

Mal� o

2011

Cohort

Parallel

1.n=

127(31;96)

2.n=74

3.53years

4.23–7

8years

1.N/R

2.N/R

3.N/R

4.N/R

5.n=

74

1.Nobel

Biocare

�**

2.TiU

nite�

(anodically

oxidized

surface)

1.n=

0

2.n=

74

3.n=

0

1.n=

0

2.n=

74

3.n=

0

1.Late

(74)

2.Yes

(74)

3.Yes

(74)

4.2-stages

(29)

5.Malo

clinic

survival

criteria

1.Conventional(74)

2.Porcelain-fused

tometal(74)

3.N/R

4.External(74)

1.12

2.N/R

1.No

2.Yes

3.No

4.Yes

5.N/R

6.Yes

7.N/R

1.n=8

2.n=10;n=0

3.n=1

4.1.27mm

5.n=0

1.0.152

(0.084–0

.259)

2.0.018

(0.003–0

.116)

3.1.270

(1.095–1

.445)

4.0.009

(0.001–0

.125)

#8

Nedir2004

Cohort

Parallel

1.n=

30(10;20)*

2.n=30*

3.51.1

years*

4.32.8–7

3.3

years*

1.Both

(?)

2.Both

(?)

3.n=19*

4.n=17*

5.n=

36

1.IT

I

(Straumann�)‡

2.TPS�

(titanium-

plasm

a-spray)

andSLA

�

(sand-blasted,

large-grit,

acid-etched)

1.n=

0

2.n=

0

3.n=

36

1.n=

0

2.n=

27*

3.n=

9*

1.Late

(36)

2.N/R

3.N/R

4.1-stage(36)*

5.Buseret

al.

1991,Buser

etal.1997,

Cochran

etal.2002

1.Conventional(36)

2.Porcelain-fused

tometal(36)*

3.Cem

ented

retained

(36)*

4.Internal(36)

1.N/R

2.N/R

1.Yes

2.Yes

3.N/R

4.N/R

5.N/R

6.N/R

7.Mean1.62

1.n=1*

2.n=0;n=0

3.n=1

4.N/R

5.n=2*

1.0.014

(0.001–0

.187)

2.0.029

(0.004–0

.177)

3.N/A

4.0.057

(0.014–0

.202)


198 Mezzomo et al.

Table

3.(continued)

Study

Population

characteristics

Implant

location(n)

Implant

characteristics

Implant

length

(n)

Implant

diameter

(n)

Surgical

parameters(n)

Prosthetic

parameters(n)

Follow-up

inmonths

Riskfactors

included/

assessed

(yes/no)

Outcomes

(n)

Proportions

Mean

(CI:lower-

upper

limit)

Reference

Number

(#)

First

Author

(Yearof

publication)

Type

Design

1.nofpatients

total(♂

;♀)

2.nofpatients

inthisreview

2.Age(m

ean

inyears)

3.Age(range

inyears)

1.Maxilla

2.Mandible

3.Premolars

4.Molars

5.Total

1.Company

2.Surface

1.≤6

mm

2.6mm

<x<8mm

3.8mm

≤x<10mm

1.Narrow

(Ø3.3–Ø

3.5

mm)

2.Regular

(Ø3.75–Ø

4.3

mm)

3.Wide

(Ø4.8–Ø

6.0

mm)

1.Tim

ing

ofim

plant

placement

(immediate/

early/late)

2.Flapraised

3.Primary

closure

4.Approach

(1-versus

2-stages)

5.Criteria

forsuccess

1.Loadingprotocol

(immediate/early/

conventional)

2.Typeofveneering

3.Typeofretention

(cem

ented-versus

screw

retained)

4.Im

plant-abutm

ent

connection

(internalversus

external)

1.Mean

2.Range

1.System

ic

disease

2.Smoking

3.Bruxism

4.Periodontal

disease

5.Bonequality

6.Primary

stability

7.Crown-

to-implant

ratio(m

ean)

1.Drop-outs/

losses

to

follow-up

2.Failures

(early;late)

3.Biological

complications

4.Radiographic

marginalbone

loss

(mean)

5.Prosthetic

complications

1.Failure

proportion

(FP)

2.Biological

failure

proportion

(BFP)

3.Radiographic

marginalbone

loss

(mean)

4.Prosthetic

failure

proportion

(PFP)

#9

Nicolau2011

Cohort

Parallel

1.n= 266(118;148)

2.n=?

3.46.3

years

4.N/R

1.Both

(?)

2.Both

(?)

3.N/R

4.N/R

5.n=

38*

1.IT

I

(Straumann�)‡

2.SLActive�

(sand-blasted,

large-grit,

acid-etched

active)

1.n=

0

2.n=

0

3.n=

38

1.N/R

2.N/R

3.N/R

1.Late

(38)

2.N/R

3.N/R

4.1-stage(38)

5.Resem

blesto

Albrektsson

etal.1986,

1.Conventional(38)

2.Porcelain-fused

tometal(38)

3.Cem

ented

retained

(28);

Screw

retained

(6)*

4.Internal(38)

1.N/R

2.18–2

4

1.Yes

2.Yes

3.Yes

4.N/R

5.N/R

6.N/R

7.N/R

1.n=2*

2.n=2;n=0

3.n=0

4.0mm*

5.n=0

1.0.056

(0.014–0.197)

2.0.014

(0.001–0.191)

3.N/A

4.0.014

(0.001–0.191)

#10

Perelli2011

Cohort

Parallel

1.n= 40(15;25)

2.n=?

3.N/R

4.N/R

1.n=

0

2.n=

21

3.n=12

4.n=9

5.n=

21

1.Endopore

�,¶

2.Porous

Sintered�

1.n=

1

2.n=

20

3.n=

0

1.n=

0

2.n=

47

3.n=

8

1.Late

(21)

2.Yes

(21)

3.Yes

(21)

4.2-stages

(21)

5.N/R

1.Conventional(21)

2.Porcelain-fused

tometal(21)

3.N/R

4.External(21)

1.60

2.N/R

1.No

2.Yes

3.N/R

4.No

5.N/R

6.N/R

7.N/R

1.n=0

2.n=0;n=4

3.n=6

4.1.5

mm

†

5.n=0

1.0.190

(0.073–0.412)

2.0.353

(0.168–0.596)

3.1.500

(1.265–1.735)

4.0.028

(0.002–0.366)

#11

Romeo

(2002)

Case

series

Parallel

1.n= 109(40;69)

2.n=?

3.41.3

years

4.19–68years

1.N/R

2.N/R

3.N/R

4.N/R

5.n=

14

1.IT

I

(Straumann�)‡

2.TPS�

(Titanium-

plasm

a-spray)

1.n=

0

2.n=

0

3.n=

14

1.N/R

2.N/R

3.N/R

1.Late

(14)

2.N/R

3.N/R

4.1-stage(14)

5.Albrektsson

etal.1986,

Buseret

al.

1991;Van

Steenberghe

1997

1.Conventional(14)

2.Porcelain-fused

tometal(14)

3.N/R

4.Internal(14)

1.84

2.N/R

1.No

2.Yes

3.No

4.No

5.N/R

6.N/R

7.N/R

1.n=0

2.n=0;n=0

3.n=0

4.N/R

5.n=0

1.0.033

(0.002–0.366)

2.0.033

(0.002–0.366)

3.N/A

4.0.033

(0.002–0.366)

#12

Rossi2010

Cohort

Parallel

1.n= 35(13;22)

2.n=35

3.51years

4.28–70years

1.n=

15

2.n=

25

3.n=14

4.n=26

5.n=

40

1.IT

I

(Straumann�)‡

2.SLActive�

(sand-blasted,

large-grit,acid-

etched

active)

1.n=

40

2.n=

0

3.n=

0

1.n=

0

2.n=

19

3.n=

21

1.Late

(40)

2.Yes

(40)

3.Yes

(40)

4.1-stage(40)

5.N/R

1.Early(40)

2.Porcelain-fused

tometal(40)

3.N/R

4.Internal(40)

1.24

2.N/R

1.No

2.Yes

3.N/R

4.No

5.Yes

6.Yes

7.Mean1.5

1.n=2

2.n=2;n=0

3.n=19

4.0.43mm

5.n=0

1.0.053

(0.013–0.187)

2.0.056

(0.014–0.197)

3.0.430

(0.270–0.590)

4.0.014

(0.001–0.182)



Table

3.(continued)

Study

Population

characteristics

Implant

location(n)

Implant

characteristics

Implant

length

(n)

Implant

diameter

(n)

Surgical

parameters(n)

Prosthetic

parameters(n)

Follow-up

inmonths

Riskfactors

included/

assessed

(yes/no)

Outcomes

(n)

Proportions

Mean

(CI:lower-

upper

limit)

Reference

Number

(#)

First

Author

(Yearof

publication)

Type

Design

1.nofpatients

total(♂

;♀)

2.nofpatients

inthisreview

2.Age(m

ean

inyears)

3.Age(range

inyears)

1.Maxilla

2.Mandible

3.Premolars

4.Molars

5.Total

1.Company

2.Surface

1.≤6

mm

2.6mm

<x<8mm

3.8mm

≤x<10mm

1.Narrow

(Ø3.3–Ø

3.5

mm)

2.Regular

(Ø3.75–Ø

4.3

mm)

3.Wide

(Ø4.8–Ø

6.0

mm)

1.Tim

ing

ofim

plant

placement

(immediate/

early/late)

2.Flapraised

3.Primary

closure

4.Approach

(1-versus

2-stages)

5.Criteria

forsuccess

1.Loadingprotocol

(immediate/early/

conventional)

2.Typeofveneering

3.Typeofretention

(cem

ented-versus

screw

retained)

4.Im

plant-abutm

ent

connection

(internalversus

external)

1.Mean

2.Range

1.System

ic

disease

2.Smoking

3.Bruxism

4.Periodontal

disease

5.Bonequality

6.Primary

stability

7.Crown-

to-implant

ratio(m

ean)

1.Drop-outs/

losses

to

follow-up

2.Failures

(early;late)

3.Biological

complications

4.Radiographic

marginalbone

loss

(mean)

5.Prosthetic

complications

1.Failure

proportion

(FP)

2.Biological

failure

proportion

(BFP)

3.Radiographic

marginalbone

loss

(mean)

4.Prosthetic

failure

proportion

(PFP)

#13

Stanford

2010

Case

series

Parallel

1.n= 549(242;307)

2.n=?

3.57years

4.18–84years

1.n=

33*

2.n=

19*

3.N/R

4.N/R

5.n=

52*

1.Astra

Tech�††

2.Osseospeed�

(nanoetched)

1.N/R

2.N/R

3.N/R

1.N/R

2.N/R

3.N/R

1.Late

(52)

2.N/R

3.N/R

4.1-stage(52)

5.N/R

1.Conventional(52)

2.Porcelain-fused

tometal(52)

3.N/R

*

4.Internal(52)

1.12

2.N/R

1.No

2.Yes

3.N/R

4.No

5.N/R

6.N/R

7.N/R

1.n=4

2.n=1*;n=0

3.n=0

4.N/R

5.n=0

1.0.021

(0.003–0.425)

2.0.010

(0.001–0.191)

3.N/A

4.0.010

(0.001–0.146)

#14

Strietzel

&

Reichert2007

Case

series

Parallel

1.n= 133(66;71)

2.n=3(1;2)*

3.48years*

4.18–61years

1.n=

5*

2.n=

7*

3.N/R

4.N/R

5.n=

12*

1.Camlog�

‡‡

2.Promote

�

(abrasive

particle-

blasted,

thermalacid-

etched

micro-

structured)

1.n=

0

2.n=

0

3.n=

12

1.N/R

2.N/R

3.N/R

1.Late

(12)*

2.N/R

3.N/R

4.2-stages

(12)

5.Buseret

al.

1997,Cochran

etal.2002

1.Conventional(12)

2.Porcelain-fused

tometal(12)*

3.Cem

ented

retained

(7);

Screw

retained

(5)*

4.Internal(12)

1.21.9

2.N/R

1.No

2.Yes

3.N/R

4.No

5.N/R

6.N/R

7.N/R

1.n=1

2.n=0;n=0*

3.n=3*

4.1.1

mm

5.n=0*

1.0.042

(0.003–0.425)

2.0.042

(0.003–0.425)

3.1.100

(0.568–1.632)

4.0.042

(0.003–0.425)

#15

Tawil(2006)

Case

series

Parallel

Tawilet

al.

(2006)

1.n= 111(45;66)

2.n=28

3.53.6

years

4.22–80years

1.N/R

2.N/R

3.N/R

4.N/R

5.n=

116

1.Nobel

Biocare

�**

2.Machined-

surface

1.N/R

2.N/R

3.N/R

1.N/R

2.N/R

3.N/R

1.Late

(116)

2.N/R

3.N/R

4.1-stage(13);

2-stages

(103)

5.“Surviving

implant

presentedno

clinicalor

radiographic

signsof

failure”

1.Conventional

(116)

2.Porcelain-fused

tometal(116)

3.N/R

4.External(116)

1.53

2.12–1

08

1.N/R

2.N/R

3.N/R

4.no

5.N/R

6.yes

7.mean1.48

1.n=15

2.n=1;n=0

3.n=0

4.0.71mm

5.n=15

1.0.010

(0.001–0.067)

2.0.005

(0.000–0.074)

3.0.710

(0.583–0.837)

4.0.150

(0.092–0.234)

#16

Tellemanet

al.

2012

Cohort

Parallel

1.n= 92(15;77)

2.n=92

3.50.6

years

4.18–70years

1.n=

61

2.n=

85

3.n=74

4.n=72

5.n=

146

1.Biomet

3I�

§

2.Nanotite

�

(dualetched

andpartially

covered

with

nanoscale

calcium

phosphate

crystal)

1.n=

0

2.n=

0

3.n=

146

1.n=

0

2.n=

110

3.n=

36

1.Late

(146)

2.N/R

3.N/R

4.1-stage(146)

5.N/R

1.Conventional

(146)

2.Porcelain-fused

tometal(146)

3.Cem

ented

retained

(146)

4.Internal(146)

1.12

2.N/R

1.No

2.No

3.N/R

4.No

5.Yes

6.N/R

7.N/R

1.n=1

2.n=9;n=0

3.n=7

4.0.61mm

5.n=0

1.0.062

(0.033–0.115)

2.0.044

(0.020–0.095)

3.0.610

(0.513–0.707)

4.0.004

(0.000–0.056)

Overall


200 Mezzomo et al.

Table

3.(continued)

Study

Population

characteristics

Implant

location(n)

Implant

characteristics

Implant

length

(n)

Implant

diameter

(n)

Surgical

parameters(n)

Prosthetic

parameters(n)

Follow-up

inmonths

Riskfactors

included/

assessed

(yes/no)

Outcomes

(n)

Proportions

Mean

(CI:lower-

upper

limit)

Reference

Number

(#)

First

Author

(Yearof

publication)

Type

Design

1.nofpatients

total(♂

;♀)

2.nofpatients

inthisreview

2.Age(m

ean

inyears)

3.Age(range

inyears)

1.Maxilla

2.Mandible

3.Premolars

4.Molars

5.Total

1.Company

2.Surface

1.≤6

mm

2.6mm

<x<8mm

3.8mm

≤x<10mm

1.Narrow

(Ø3.3–Ø

3.5

mm)

2.Regular

(Ø3.75–Ø

4.3

mm)

3.Wide

(Ø4.8–Ø

6.0

mm)

1.Tim

ing

ofim

plant

placement

(immediate/

early/late)

2.Flapraised

3.Primary

closure

4.Approach

(1-versus

2-stages)

5.Criteria

forsuccess

1.Loadingprotocol

(immediate/early/

conventional)

2.Typeofveneering

3.Typeofretention

(cem

ented-versus

screw

retained)

4.Im

plant-abutm

ent

connection

(internalversus

external)

1.Mean

2.Range

1.System

ic

disease

2.Smoking

3.Bruxism

4.Periodontal

disease

5.Bonequality

6.Primary

stability

7.Crown-

to-implant

ratio(m

ean)

1.Drop-outs/

losses

to

follow-up

2.Failures

(early;late)

3.Biological

complications

4.Radiographic

marginalbone

loss

(mean)

5.Prosthetic

complications

1.Failure

proportion

(FP)

2.Biological

failure

proportion

(BFP)

3.Radiographic

marginalbone

loss

(mean)

4.Prosthetic

failure

proportion

(PFP)

10cohorts

6case

series

16parallel-

designed

Publication

yearrange:

2000–2012

1.n= 2000(805;

1195)

2.n=360

3.49.87�

21.78

years

4.16–9

0years

1.n=261

2.n=264

3.n=155

4.n=170

5.n=803

(mean

length

=7.65mm)

1.See

above

2.Machined

surface:

1study

(116

implants);

roughsurface:

15studies

1.n=

65(8.1%)

2.n=

300(37.36%)

3.n=

438(54.54%)

1.n=

21(4.14%)

2.n=

356(70.22%)

3.n=

130(25.64%)

1.Im

mediate

(18);

Late

(785)

2.Yes

(288);

No(40)

3.Yes

(164)

4.1-stage

(466;59.98%);

2-stage

(311;40.02%)

5.See

above

1.Im

mediate/

early(90);

Conventional

(480)

2.Porcelain-fused

tometal(731)

3.Cem

ented

retained

(183;76.25%);

Screw

retained

(57;33.75%)

4.External

(433;53.92%);

Internal

(370;46.08%)

1.44�

33.72

2.12–120

months

1.Yes:

3studies

2.Yes:

12studies

3.Yes:

3studies

4.Yes:

1study

5.Yes:

7studies

6.Yes:

6studies

7.Yes:

5studies

(mean

1.5

�0.8;

n=297)

1.n=

41

(rate:5.1%)

2.n=

39(35;04)

(rate:5.1%)

3.n=

40

4.0.835�

0.49mm

5.n=

21

1.0.059

(0.037–0

.092)

2.0.038

(0.019–0

.074)

3.0.835

(0.545–1

.125)

4.0.028

(0.014–0

.057)

CI,confidence

interval;N/R

,notreported;N/A

,notavailable.

*Inform

ationretrieved

after

contact

withthecorrespondingauthorofthestudy.

†Valuecalculatedforthisreview

from

theraw

data

oftheoriginalarticles.

‡IT

I/Straumann�AG

(Waldenburg,Switzerland).

§Biomet

3I�

(Palm

Beach

Gardens,FL,USA).

¶ Endopore

�(InnovaCorporation,Toronto,Canada).

**Nobel

Biocare

�(G

othenburg,Sweden).

††Astra

Tech(M

€ ondal,Sweden).

‡‡Camlog�(W

imsheim,Germany).



For statistical purposes, implantswere divided into two subgroups. Inthe first scenario, Groups 1 and 2were defined as implants ≤6 mmlong and 6 mm<x < 10 mm long,respectively. Six studies wereincluded in Group 1, accounting for65 implants (8.09%). Meta-regres-sion analysis with fixed-effect modelsfailed to identify statistically signifi-cant difference between the twogroups on the outcomes FP, BFP,mean MBL and PFP (p = 0.445,0.956, 0.423 and 0.426 respectively)(Table 4).

In the second scenario, Groups1 and 2 represented implants≤8 mm long and 8 mm<x < 10 mmlong, respectively. Ten studies wereincluded in Group 1, accountingfor 365 implants (45.45%). Meta-regression analysis with fixed-effectmodels revealed statistically signifi-cant inter-groups differences on FP,BFP and MBL (p = 0.019, 0.00351and 0.000367, respectively) (Table 4),whereas PFP was not significantlyinfluenced (p = 0.275).

Implant diameter

Due to the small sample size and forstatistical purposes, the narrow-diameter (ø3.3–ø3.5 mm) were clus-

tered with the regular-diameter(ø3.75–ø4.3 mm) implants, account-ing for Implant Diameter Group 1(n = 377; 74.36%), whereas thewide-diameter (ø4.8–ø6.0 mm) groupaccounted for Implant DiameterGroup 2. Meta-regression analysisresulted in no statistically significantdifference between the two groupson both FP and BFP (p = 0.067 and0.0847 respectively) (Table 4). Onthe other hand, regular-diametershort implants presented significantlyless radiographic MBL and incidenceof prosthetic complications (PFP)(p = 0.000 and 0.000347 respectively)than the wide-diameter implants(Table 4).

Implant surface

One study (#15) used machine-sur-faced implants (116 implants,14.44%); the other 687 implants(85.56%) had different types ofrough surfaces of different manufac-turers. The overall results of the sub-group analysis for all short implantsshowed FPs of 7.0% (95% CI: 4.6–10.7%) for rough surface implantsand 1.0% (95% CI: 0.1–6.7%) forthe machined surface implantsrespectively. FP, BFP and MBLwere not significantly influenced by

surface treatment (p = 0.05, 0.135and 0.424 respectively). The inci-dence of prosthetic complications(PFP), on the other hand, was signif-icantly influenced by the type ofimplant surface (p < 0.001)(Tables 3, 4).

Surgical parameters

Due to limited information(Table 3), a quantitative analysis ofthe surgical protocols used in theoriginal articles could not be per-formed. A qualitative assessmentfailed to identify any relevant impactof the timing of implant placement,elevation of a mucoperiostal full-thickness flap and primary woundclosure on implant failure and/orbiological complications.

In relation to the surgicalapproach (one- versus two-stage),fixed effect meta-regression analysisrevealed no statistically significantdifference on the FP and BFP ofshort implants (p = 0.784 andp = 0.068 respectively). However, themean MBL was significantly affectedby the variable one- versus two stage(p = 0.0000799) (Table 4).

Post-operative surgical complica-tions were rare. Seven studies did

Table 4. P-values from the statistical analysis (covariates 9 outcomes)

Covariates Outcomes

Failureproportion

(FP)

Biologicalfailure

proportion(BFP)

Radiographicmarginal bone

loss(MBL)

Prosthetic failureproportion

(PFP)

Population characteristicsAge (mean) 0.193 0.0142* <0.001* 0.060Gender (males versus females) 0.155 0.428 <0.001* 0.198

Implant characteristicsLocation (mandible versus maxilla) <0.001* <0.01* <0.001* –Implant length (6 mm) 0.445 0.956 0.423 0.426Implant length (8 mm) 0.019* <0.01* <0.001* 0.275Implant diameter (narrow/regular versus wide) 0.067 0.0847 <0.001* <0.001*Implant surface (rough versus machined) 0.050 0.135 0.424 0.000*

Surgical parametersSurgical Approach (one- versus two-stage) 0.784 0.068 <0.001* –

Prosthetic parametersType of retention (screw- versus cemented retained) 0.986 – – 0.622Type of implant-abutment connection (external versus internal) 0.542 0.976 0.184 0.590Timing of Loading (immediate/early versus conventional) 0.568 0.172 <0.01* 0.910Follow-up (mean in months) 0.801 0.0323* <0.001* 0.0229*

Risk factors included (yes versus no)Systemic disease 0.235 0.285 – –

Smokers 0.537 0.656 0.362 –

Bruxism 0.016 0.586 0.081 0.930Periodontal disease 0.011* 0.385 <0.001* –

*Statistically significant.(–)Calculations not run due to the lack of a clinical correlation or insufficient data.


202 Mezzomo et al.

not report it, whereas other fivereported no surgical complicationswith short implants, such as vestibu-lar or lingual bone dehiscence or epi-sodes of paraesthesia. Study #14(Strietzel & Reichert 2007) reportedpremature mucosal dehiscences intwo implants placed with a sub-merged approach (one in the leftposterior maxilla and one in the leftposterior mandible) (informationprovided by the author). There wasa report of one single implant placedin the mandible that had a sensationalteration that abated after 8 weeksin study #8 (Nedir et al. 2004). Inthe study #11 (Romeo et al. 2002),perforation of the cortical of themandibular canal with inferior alve-olar nerve lesion occurred; however,this complication was related to alonger implant.

Criteria for implant success

In despite of the lack of standardiza-tion of the success criteria adoptedamong the studies (Table 3), theyusually included the followingaspects as determinants: (1) absenceof pain or discomfort or any negativesubjective sensation, (2) absence ofclinically detectable implant mobility,(3) absence of any recurrent peri-implant mucositis and/or peri-im-plantitis accompanied by bleeding onprobing of the peri-implant sulcusand (4) absence of continuous peri-implant radiolucency. Three studies(#2, #7 and #15) adopted their ownsuccess criteria. Mal�o et al. 2011 (#7)was the only study that has consid-ered the aesthetic outcomes achievedwith the prostheses.

Prosthetic parameters

In total, 731 single crowns werefollowed up for at least 1 year(Table 3). The majority of theimplants followed a conventionalloading protocol, except on studies#2 (Cannizzaro et al. 2012) and #12(Rossi et al. 2010). Data were thencategorized into two subgroups –immediate/early loading (Group 1)versus conventional loading (Group2). Mixed-effect subgroup analysisrevealed that FPs for groups 1 and 2were 4.8% (95% CI: 2.2–10.3%) and6.3% (95% CI: 3.6–10.9%), respec-tively (Table 3), and this differencewas not statistically significant

(p = 0.568) (Table 4). BFPs were7.3% (95% CI: 3.6–14.5%) and 3.3%(95% CI: 1.3–8.0%) for groups 1 and2 respectively. This difference wasnot statistically significant (p = 0.172)(Table 4). The means radiographicMBL of the two types of loadingprotocol were 0.364 mm (95% CI:0.281–0.446 mm) and 0.940 mm(95% CI: 0.581–1.300 mm) (groups 1and 2 respectively). This differencereached statistical significance(p = 0.002) (Table 4).

Porcelain-fused to metal as aveneering material was a constantbetween the included studies and,thus, no statistics were applied.Provisional prostheses were used ineight out of the sixteen studies, for297 implants. Data on the type ofretention (screw- versus cementedretained) were available in eightstudies (Table 3). Fixed effect meta-regression revealed no statisticallysignificant differences between thetwo types of crown retention on theoutcomes FP and PFP (p = 0.986and 0.622 respectively) (Table 4).

At least four different types ofimplant-abutment connection werereported. External hexagon, internalhexagon, internal morse taper and,finally, internal triple-cam tube wereused in 433 (53.92%), 146 (18.18%),212 (26.4%) and 12 (1.49%)implants respectively. They werethen dichotomized into two sub-groups – external versus internalconnection. The mixed-effect sub-group analysis showed estimatedFPs of implants of 6.8% (95% CI:3.4–13.4%) and 5.2% (95% CI: 3.2–8.5%) for external and internalimplant-abutment connections resp-ectively. These results were not sta-tistically different for any of theoutcomes FP, BFP, MBL and PFP(p = 0.542, 0.976, 0.184 and 0.590respectively) (Table 4).

Studies where comparisonsbetween splinted or non-splintedcrowns were made are noteworthy.Study #7 (Mal�o et al. 2011) claimedthat both types of prosthetic recon-structions supported by 7-mm shortimplants are successful in the shortterm. Studies #4 and #5 (Deporteret al. 2001a, 2012) found thatsplinted implants showed signifi-cantly greater (0.2 mm more) crestalbone loss than non-splintedimplants, and these differences werestatistically significant. On the other

hand, study #6 (De Santis et al.2011) found significantly higherimplant success rates for fixed pros-theses supported by short implants(98.3%), compared to the 93.1% forsingle crowns.

Follow-up

Table 3 summarizes the details ofthe follow-up periods of the includedstudies. Deporter et al. 2012 (#5)observed 38 implants in the posteriormandible for 120 months. Themajority of the short implant losses(FP) occurred before loading(89.74%). However, the fixed effectmeta-regression analysis failed toidentify statistically significant corre-lation (p = 0.801) between greaterfollow-up periods and reducedimplant FPs (Table 4). On the otherhand, the incidence of biological/prosthetic complications (BFP/PFP)as well as the MBL tend to statisti-cally increase over the time(p = 0.0323, 0.0229 and 0.00000013respectively) (Table 4).

Peri-implant health parameters

The health of the peri-implant tis-sues is crucial for the long-termimplant survival/success (Anneret al. 2010). However, details onthese parameters were scarce andusually assessed in a non-standard-ized manner among the primarystudies. Four studies (#2, #3, #5 and#15) did not assess any peri-implanthealth parameter at all. Plaque score,bleeding on probing and pocketprobing depth were assessed at onlyfive, four and five studies respec-tively. Presence of peri-implantitis,which presents clear signs and symp-toms, was mentioned in eight out ofthe sixteen studies (#1, #6–8, #10,#11, #13 and #16). Due to the lim-ited information available and to thelack of standardization, neitherquantitative nor qualitative analysiscould be performed correlating thesevariables to the outcomes.

Risk factors

The information about the RkF onthe prognosis of short dentalimplants is described in Table 3 andthe corresponding p values (when-ever applicable) are listed in Table 4.For the patient-related covariates



systemic disease, smoking status,bruxism and periodontal disease, theactual implant sample size could notbe extracted from the original arti-cles because of very limited informa-tion. Therefore, studies weredichotomously categorized into twosubgroups for statistical purposes –those that included versus those thatdid not include the covariate accord-ing to their eligibility criteria. Forthe implant-related covariates bonequality, primary stability and crown-to-implant ratio, meta-regressioncould not be performed due torestricted data available. Therefore,conclusions about their influence onthe outcomes were based exclusivelyfrom the interpretation of the rawdata of the original articles.

Systemic disease

Pregnants, immunodeficients,patients under medication and thoseundergoing radiotherapy of the headand neck were excluded from all thestudies. Subgroup analysis revealedthat the mean FP among studies thatincluded systemically compromisedpatients was slightly lower than theoverall mean presented in the meta-analysis [3.5% (95% CI: 1.1–10.4%)versus 5.9% (95% CI: 3.7–9.2%)respectively. However, the FP wasnot statistically significant comparedto those studies that did not includesystemically compromised patients[7.3% (95% CI: 4.6–11.3%)] (p =0.235) (Tables 3, 4). Furthermore,the mean BFP was not statisticallydifferent between studies thatincluded versus studies that did notinclude systemically compromisedpatients (p = 0.285) (Table 4).

Smoking status

The FP revealed by mixed-effectsubgroup analysis from studies inwhich smokers were included washigher [7.1% (95% CI: 4.2–11.7%)]compared with those in which smok-ers were excluded [5.5% (95% CI:2.9–10.0%)]; however, the differ-ences of means FP, BFP and MBLof studies where smokers wereincluded were not statistically signifi-cant when compared to studieswhere smokers were not included(p = 0.537, 0.656 and 0.362 respec-tively) (Table 4).

In study #12 (Rossi et al. 2010),two implants failed in two heavysmokers, and the failure rate

obtained in that study might havebeen determined by this confoundingrisk factor. Besides that, in the largecohort study of Strietzel & Reichert(2007) (#14), a significant associationbetween heavy smoking (>10 ciga-rettes/day) and the frequency ofimplant loss was found.

Bruxism

The FP revealed by mixed-effectsubgroup analysis from studies inwhich bruxers were included waslower [4.0% (95% CI: 1.6–9.8%)]compared to those in which bruxerswere not included [14.0% (95% CI:8.5–22.1%)]. This difference was sta-tistically significant (p = 0.016)(Table 4). On the other hand, themeans BFP, MBL and PFP of stud-ies that included bruxers in theirsample were not statistically differentfrom those studies that did notincluded bruxers (p = 0.586, 0.081and 0.930 respectively) (Table 4).Particular attention should be givento the study of Tawil et al. (2006)(#15). Authors found that althoughmore serious prosthetic complica-tions such as veneering fracturesand screw-loosenings occurred inthe bruxer-group, there was no sta-tistical difference in the proportionof complications between the differ-ent groups examined (bruxer-, occa-sional bruxer- and the non-bruxergroup).

Periodontal disease

Patients usually underwent periodon-tal treatment before the commence-ment of the studies and wereincluded in a strict maintenance pro-gramme that included professionaloral hygiene on a regular basis. TheFP revealed by mixed-effect sub-group analysis from one study inwhich periodontal patients wereincluded (#7) was higher [15.2%(95%CI: 8.4–25.9%)] compared withthose in which periodontal patientswere not included [5.5% (95% CI:3.3–9.1%)]. These results were statis-tically significant (p = 0.011)(Table 4). Furthermore, the meanBFP of studies that included peri-odontal patients were not statisti-cally different from those studiesthat did not included periodontalpatients (p = 0.385), whereas themean MBL was statistically signifi-cant between the two categories ofstudies (p = 0.001) (Table 4).

Bone quality

The bone quality of the recipient sitewas assessed intra-surgically for 185implants only, whereas radiographicbone quality assessment was not per-formed at all. Types II and III bone(Lekholm & Zarb 1985) were themost common sites where shortimplants were placed in the posteriorregion (n = 66 and 70 respectively).

This study found contradictoryresults of the effects of low bonequality on the failure rates and cres-tal bone level changes of shortimplants. Nicolau et al. 2013 (#9)found a 100% survival rate forimplants placed in bone of low qual-ity (type IV). Likewise, study #14(Strietzel & Reichert 2007) failed toidentify any association between lowbone quality and higher failure ratesof short implants. On the otherhand, failures were more criticalwhen machined-surface implantswere used in bone of lower quality(Tawil, study #15).

Primary stability

Primary stability was assessed bymeans of three methods among theincluded studies: insertion torque,damping capacity/subclinical mobil-ity (Periotest�) and resonance fre-quency analysis (RFA). Regardinginsertion torque, there seemed tohave a lack of standardization of theparameters in terms of N�cm, as aconsequence of the different implantbrands used. In some cases, anadapted surgical protocol (under-preparation) of the implant sites wasused to facilitate implant placementwith a higher insertion torque (#2),to obtain adequate primary stabilityin sites of poor bone density.

One single study assessed primarystability by means of dampingcapacity (Periotest�). Deporter et al.(2001a) found no relationshipbetween Periotest� values (PTVs)and the different implant lengths(mean PTV = �2.39). Single crownsobtained better PTVs when com-pared to splinted crowns supportedby short implants. The authors con-cluded that splinting is not a neces-sary prerequisite for the success ofshort rough-surfaced implants. Like-wise, the ISQ (implant stability quo-tient), as assessed by means of RFA,was measured only by the study ofRossi et al. (2010). The mean value


204 Mezzomo et al.

after 6 weeks was higher comparedwith the initial registration [74.8 �6.1 (60–84) versus 70.2 � 9 (42–84)respectively], and the difference wasstatistically significant. A positivecorrelation was found between inser-tion torques and RFA values, whilenegative correlations were foundbetween bone morphology and RFAvalues.

Crown-to-implant ratio

Four studies adopted, for descriptiveanalysis, three categories of C/Iratio: C/I ratio ≤ 1, C/I ratio = 1.1–2.0, and C/I ratio > 2 (#4, #5, #8and #15). No evidences of the effectof the C/I ratio on the outcomeimplant failure have been found;however, the findings suggest thatthere is not a significant effect of theC/I ratio on the crestal bone levelsof either rough-surfaced (#4, #5) ormachined-surface implants (#15).Rossi et al. (2010) found that themean clinical C/I ratio increasedfrom the time of delivery of the

prosthesis to the 2-year follow-upfrom 1.5 � 0.3 to 1.8 � 0.6 mm –that is, the lever arm increased.However, according to Deporteret al. (#4, #5), a C/I ratio of ≥1.5 isnot detrimental to the continuedhealth of a rough-surface implant.

Tawil et al. (2006) (#15) assessedthe effect of the C/I ratio on theprosthetic outcomes. They claimedthat this variable did not prove tobe a major biomechanical risk fac-tor, as long as the occlusion isproperly adjusted and occlusal con-tacts are placed as closely as possi-ble to the emerging axis of theimplant, that is, when force orienta-tion and load distribution arefavourable.

Outcomes

The overall means for the implantFP, BFP, radiographic MBL andPFP are listed in Table 3 and thegraphic representation of the meta-analysis are illustrated in Fig. 2.

Implant failure proportion

The pooled FP (according to therandom-effects model) was 5.9%(95% CI: 3.7–9.2%) (Table 3;Fig. 2). The heterogeneity betweenstudies was found as moderate(<50%). The majority of the implantlosses occurred before prosthesisplacement (89.74%), varying from2.1% at the 1-year follow-up (Stan-ford et al. 2010) to 7.1% after10 years of observation (Deporteret al. 2012). Telleman et al. (2012)found 66% (n = 6) of the failuresbefore loading.

Peri-implantitis, premature load-ing and implant fracture have beensought as the reason for failure infour (#6, #7, #10 and #15), two (#13and #15) and two (#15 and #16)studies respectively. Other reasonsreported in the original articlesincluded insufficient residual crestheight (study #3), surgical error, acombination of a narrow alveolarridge and lack of buccal keratinizedgingiva (study #5), osteoporosis,

(a)

(c)

(b)

(d)

Fig. 2. Forest plot of the outcomes (mean follow-up 44 � 33.72 months). (a) failure proportion (FP); (b) biological failureproportion (BFP); (c) radiographic marginal bone loss (MBL); and (d) prosthetic failure proportion (PFP).



severe bruxism, overheating of thesite at the time of preparation andunknown reason (study #15) and,finally, implant placed in type 2 bonethat was lost after 7 years of loading(study #16).

Biological failure proportion

The reported BFP varied from 0.5%(Tawil & Younan 2003, mean fol-low-up: 53 months) to 35.3% (Perelliet al. 2011, mean follow-up:60 months). When the observationalperiod was increased (mean follow-up, 120 months) (Deporter et al.2012), the BFP decreased dramati-cally (0.7%). Pooled BFP (accordingto the random-effects model) was3.8% (95% CI: 1.9–7.4%) (Table 3;Fig. 2). The heterogeneity betweenstudies for the outcome BFP washigh (55%).

The most common biologicalcomplications were: increased pocketprobing depth (>4 mm) in 19implants (study #12), followed by

peri-implantitis (n = 6, studies #2,#11, #12 and #15), increased plaquescores (n = 4, study #16), loss ofosseointegration after loading (n = 4,study #10), increased bleeding scoresand perimucositis (n = 3, studies #16and #2 respectively), and neuropa-thy/loss of function (n = 1, study#8).

Radiographic marginal bone loss

Pooled MBL (random-effects model)was 0.835 mm (95% CI: 0.545–1.125 mm) (Table 3; Fig. 2). Figure 3represents the scatter plots of the rele-vant clinical covariates that signifi-cantly influenced the outcome MBL.The heterogeneity between studies forMBL was very high (98%).

The studies of Deporter et al.(2001a, 2012) (#4 and #5) found thatlonger and splinted implantsappeared to favour greater crestalbone loss. On the other hand, study#14 (Strietzel & Reichert 2007)found that the difference of mean

bone loss between long and shortimplants was not significant. Deport-er et al. (2012) found no statisticallysignificant changes in the meancrestal bone level from baseline tothe end of the observation time. Inthe study by Tawil & Younan (2003)8.9% of the sites lost more than1.5 mm (ranging from 1.6 to3.18 mm). A greater bone loss alsopresented a strong correlation withthe deeper placement of themachined collar of some shortimplants (Nicolau et al. 2013, study#9) and when two or more adjacentimplants were placed (study #16).

When a within-comparison ofshort implants was made (Tawil,study #15), no statistically significanteffect of the prosthetic variablesocclusal table, C/I ratio, mesial anddistal cantilever, and type of occlusalpattern on the mean mesiodistalbone loss could be found(p = 0.242). Regarding the design ofthe implant-abutment platform, Tell-

(a) (b)

(c) (d)

Fig. 3. Scatter plots of the meta-regression analysis for the most clinically relevant covariates that resulted in statistically significantdifferences on the outcome marginal bone loss (as reported in ten studies). The “x”-axis of each panel expresses the percentages foreach covariate (from 0.02 up to 0.98). (a) Implant location (mandible): the straight line across the studies (circles) represents analmost perfect positive cause–effect relationship (slope = 0.8126), for example, the larger the sample of implants placed in the man-dible, the greater the mean bone loss; (b) implant length (≤8 mm or >8 mm): although positively correlated, the variable “length8 mm” was not a major risk factor (slope = 0.20002); (c) implant diameter: negatively correlated, for example, the larger thenumber of regular-diameter short implants, the lower the mean bone loss (slope = �0.4546); and (d) surgical approach (one versustwo-stage): as well as the variable “length 8 mm”, this variable was positively correlated although it was not a major risk factor(slope = 0.1428).


206 Mezzomo et al.

eman et al. (2012) found significantlyless peri-implant bone loss after1 year in function for platform-switched implants 8.5 mm in length.Study #12 (Rossi et al. 2010) foundthat short (6 mm) implants loaded inan early phase of the healing (after6 weeks) supported single crownswith a minimal loss of marginal alve-olar bone after 2 years. Moreover,surgical variables such as implantlocation, implant diameter, microbi-ological status, mucosal thickness,and type of bone apparently playedno significant role on the peri-implant bone loss (Telleman et al.2012).

Prosthetic failure proportion

Incidence of reported prostheticcomplications was very low. PooledPFP (random-effects model) was2.8% (95% CI: 1.4–5.7%) (Table 3;Fig. 2), and the heterogeneitybetween studies was moderate(<50%). Eleven studies did notreport any biomechanical complica-tions, whereas the study of Brocardet al. (2000) did not find prostheticcomplications. Cannizzaro et al.(2012) reported one decementation,one veneer fracture and one case offood impaction. De Santis et al.(2011) mentioned one case of occlu-sal overloading, whereas Nedir et al.(2004) reported one case of decemen-tation and one single case of abut-ment fracture. On the study of Tawil& Younan, where external-hexagonimplant-abutment connection wasused, six cases of fracture of theveneering material and nine cases ofscrew loosening occurred.

Discussion

In this study, a systematic review ofprospective studies was conducted toanswer the clinical question whethersingle crowns supported by shortimplants could be successfully usedto restore the posterior region ofpartially edentulous patients. Meta-analyses revealed means FP, biologi-cal/prosthetic failure proportionsand marginal bone loss of 5.9%,3.8%, 2.8% and 0.083 mm, respec-tively, for implants <10 mm longsupporting single crowns in the pos-terior region of partially edentulouspatients. These results are compara-ble with those from clinical studiesreported for longer implants placed

in the same region supporting FPDs(Romeo et al. 2006) or previousreviews assessing survival of longerimplants placed in augmented bone(Aghaloo & Moy 2007). Hence, pros-theses supported by short implantsseem to be an acceptable alternativefor single-tooth replacement in par-tially edentulous patients with mini-mal bone height, compared toconventional rehabilitation proce-dures and advanced surgery since atleast 94% of the short implants anal-ysed were successfully restored andpresented minimal biological/pros-thetic complications.

Primary outcomes

The majority of the studies consultedwere limited at mentioning thecumulative survival rates ofimplants, which provide informationon how the risk of failure at theimplant level varies over time. How-ever, it does not inform about theabsolute failure rate and the charac-teristics of the implants lost (Nel-dam & Pinholt 2012). For instance,the handling of the recipient sitemay play an important role fordetermining early failures of shortimplants, as long as any small devia-tion of the handpiece during drillingmay enlarge the crestal portion ofthe prepared socket. This, in turn,may compromise the anchorage ofthe implant (primary stability),resulting in a higher likelihood forfailure.

In this review, a mean MBL of0.83 mm was found for the entirefollow-up period. Within the limitsof the little amount of data, mar-ginal bone loss around shortimplants did not exceed the criteriaaccepted for standard implants.Nevertheless, it should be noted that2- to 3 mm of bone loss around a6 mm long implant corresponds tonearly half of the entire implantlength, and therefore should beinterpreted differently (Annibaliet al. 2012). Limitations found onthe different methods of assessmentwere that the reading of the radio-graphs might have been impaired byanatomical limitations of the jaws(Mal�o et al. 2011). Moreover, radio-graphs only reflected a two-dimen-sional situation of the real situationin the patient and any informationof the buccal and lingual aspects of

an implant can be elucidated (Nico-lau et al. 2013).

Since the majority of the studiesaims at assessing survival rates ofshort dental implants only, the lowincidence of complications of biolog-ical and/or prosthetic nature, asexpressed by means of BFP and PFP(3.8% and 2.8% respectively),should be interpreted with caution.Reports on the incidence of compli-cations after the osseointegration/prosthetic loading stages are scarceor even absent. Hence, it is likelythat reporting biases including, butnot limited to publication bias, couldhave a substantial impact on thefindings of this review. It should beemphasized that, to precisely esti-mate the influence of such determi-nants, the original data sets shouldbe accessed in order to perform theanalyses on an individual level. Inthe present review, an attempt toretrieve such information has beenmade, but was impaired by the lackof consistent data on the originalstudies. Therefore, the potential forreporting bias and the possibleimpact on our findings will need tobe considered carefully.

Implant characteristics

In this study, a combination of stricteligibility criteria was set and thismay have led to findings others thanthose reported in the previousreviews assessing short implants.One relevant finding of this meta-analysis was that the incidence offailures/complications and marginalbone loss of maxillary short implantswere lower than those of mandibularshort implants. This is contrary toprevious clinical (Adell et al. 1990,Buser et al. 1997) and review (Tell-eman et al. 2011, Monje et al. 2013)studies, which have shown that thefailure rates for the upper jaw weresignificantly higher. The above-men-tioned results could be attributed tothe comparisons established, inmany instances, between anteriorversus posterior regions of the jaws,with different types of prostheticreconstructions. The opposing find-ings of the present review, in turn,could be attributed to the fact thatthe incidence of failures and compli-cations of short implants supportingsingle crowns in the posterior regionof both jaws may not be influenced



by the bone quality or implantlength only. These variables havesomehow been compensated bythe enhancements of the surfacetopography (rough-surfaces) of theimplants. Since in the present reviewthe majority of the implants had arough surface (85.56%), our findingscorroborate those reported byanother meta-analysis that reportedthat, in partially edentulous patients,implants with a rough surface hadsignificantly higher success rates inthe maxilla than in the mandible(Cochran 1999). Furthermore, pros-thetic-related factors, such as occlu-sal table, cantilever extension,distance to the temporo-mandibularjoint and the inclination of the cuspsmay also explain the higher failureand complication proportions foundin the mandible.

The definition of a short implantis still controversial and appears tochange over time. Both lengths<10 mm (Morand & Irinakis 2007)and <8 mm (Renouard & Nisand2006) have been considered short.This last one is closer to the mostrecent discussions in the dental com-munity – that an 8-mm implant isno longer considered a shortimplant. Hence, in this study, twosubgroups have been created andmeta-regression failed to identify sig-nificant differences between implants≤ and >6 mm long in all the out-comes assessed. It is likely that thelarger the sample would be (only8.09% of the implants were ≤6 mmlong), the greater would be the inci-dence of failures and complications,probably leading to different results.On the other hand, with a largersample size, meta-regression foundstatistically significant differencesbetween implants ≤8 mm and>8 mm long in all the outcomes butPFP.

Longer implants used to be sug-gested to ensure sufficient surfacearea for bone contact, leading tomore favourable results within thesame implant system (van Steenber-ghe et al. 1990). However, the suc-cess of short implants should not becompared with the success of longerimplants placed in the native jaw-bone of good quality, but should becompared with the success rate ofthe advanced surgical techniquesnecessary to place standard implantsin resorbed implants in posterior

jaws (Del Fabbro et al. 2012).Although distinct, the FP for bothsituations in the present review areconsistent with clinical evidences of6 mm implants used in differentareas of the jaw with different typesof prostheses (ten Bruggenkate et al.1998) as well as with those forlonger implants placed in augmentedbone (Del Fabbro et al. 2012),regardless of the length (≤6 mm or≤8 mm). However, isolated variablessuch as implant length should not beover-emphasized and multifactorialrequirements such as overall implantcharacteristics, surgical and pros-thetic variables and systemic condi-tions should be respected.

Another issue is to what extentan increase of the implant diametercompensates (das Neves et al. 2006)or not (Pommer et al. 2011) thelength reduction. Mal�o et al. (2007),Pommer et al. (2011) and Neldamand Pinholt (2012) found that widerimplants showed less favourableresults than the implants of regulardiameter for all lengths. This state-ment found agreement with our find-ings, once the regular diameter shortimplants presented significantly lessradiographic MBL and incidence ofprosthetic complications (PFP). Itcan be speculated that a regular plat-form can better withstand the masti-catory forces due to the increasedwidth of the buccal and lingual bonewalls, resulting in lower incidence ofcomplications of the prosthetic com-ponents and lower transmission ofstresses to the crestal bone. Thus,although the compensation for areduced length with an implant ofwider diameter may seem obvious,the results may not be that encour-aging.

Systematic reviews (das Neveset al. 2006, Renouard & Nisand2006, Neldam & Pinholt 2012; Pom-mer et al. 2011, Annibali et al. 2012,Monje et al. 2013) found that arough surface increases survival ratesof short implants when compared tomachined-surface implants. Thisstatement is not in agreement withour findings, where rough-surfaceshort implants presented higher FPs(0.07 versus 0.01). However, this dif-ference was not statistically signifi-cant, as well as the means BFP andMBL for both surfaces. It is likelythat the larger the sample ofmachined-surfaced implants (approx-

imately 15% of the whole sample)would be, the greater would be theFP. The findings of this review areconsistent with a recent publishedsystematic review (Telleman et al.2011), where no statistically signifi-cant difference between the survivalrates of implants with either a rough-or a machined-surface was noted.

Compared with longer implantswith identical design and surfacetopography, short implants have lessbone-to-implant contact due to thedecreased implant surface. However,the new developments of the surfacemicro-topography and chemistry,such as roughness and hydrophilic-ity, induced a greater amount ofbone in contact with the implantsurface and a faster bone formationduring healing of rough-surfacedshort implants when compared tomachined-surface ones. This, in turn,results in better maintenance ofimplant stability, despite the reducedimplant length (Hagi et al. 2004,Blanes 2009, Kotsovilis et al. 2009,Rossi et al. 2010, Monje et al. 2013).Thus, the surface configuration ofthe implants may be a more signifi-cant factor than implant length indetermining survival.

Surgical parameters

Although a qualitative analysis didnot identify an impact of the surgicaltechniques on failures and/or biolog-ical complications and the report ofmorbidity and incidence of post-operative complications was low, theMBL seemed to be significantlyhigher with non-submerged implantsthan with submerged ones. This isnot consistent with previous clinicalfindings (Cecchinato et al. 2004) thatclaimed that the bone level change inpartially edentulous patients seemedto be unrelated to whether initialsoft-tissue healing had occurredunder submerged or non-submergedconditions.

Prosthetic parameters

A relevant finding of this structuredreview was that, contrary to whatwas considered to be a rule, shortimplants can be predictably and suc-cessfully restored with single crownsand may not require splinting ofmultiple implant units. The low inci-dence of implant failure (5.9%) and


208 Mezzomo et al.

biological/prosthetic complications(3.8% and 2.8% respectively) isencouraging and may shift the para-digm towards simpler restorationswith minimally invasive proceduresfor partially edentate in the posteriorregions of the jaws. Prosthetic vari-ables may have influenced the out-comes – for instance, implantsconventionally (3+ months) loadedpresented increased MBL comparedto implants loaded either immedi-ately or early. Furthermore, the vari-ables type of retention (screw- versuscemented retained) and type ofimplant-abutment connection (inter-nal versus external) failed to reachstatistical significance for any of theoutcomes assessed. However, largersamples of the above-mentionedvariables should be evaluated inorder to draw conclusions moreprudently.

A minimum of 1 year after load-ing was determined as the thresholdfor this review. From studies ontotally edentulous jaws, most failureswere detected during the first year ofservice, which is crucial for the sur-vival of short implants (Lindh et al.1998, Mal�o et al. 2007). This patternwas also observed with longerimplants that are lost during thehealing phase, abutment connectionor during the first year of loading.One notable finding of this study isthat most of the implant failuresoccurred before single crown instal-lation (89.74%), and no major com-plications occurred over time. Thisfinding is in agreement with previoussystematic reviews (das Neves et al.2006, Neldam & Pinholt 2012; Anni-bali et al. 2012). Moreover, ourfindings showed that the incidenceof biological and prosthetic compli-cations, as well as peri-implantmarginal bone loss seemed to behigher with greater follow-up peri-ods.

Risk factors

Peri-implantitis was found to be arisk factor for short implant loss.One millimetre of bone loss aroundthe neck of an implant shorter than8 mm means a loss of 12.5% ofbone support (Neldam & Pinholt2012). However, only half of theincluded studies reported peri-im-plantitis as the cause of failure, andthese data were not usually related

to the length or to the location ofthe implant. Furthermore, means FPand MBL of patients with periodon-tal disease were found to be higherthan those of healthy patients. How-ever, no differences were found withregards to biological complications.

Smoking did not seem to be astrict exclusion criterion among theselected studies (approximately 3/4of the studies included smokers intheir sample). The higher incidenceof implant loss among smokersfound on the qualitative analysis ofthe current review could also be seenin previous clinical (Strietzel &Reichert 2007, Rossi et al. 2010, Pi-eri et al. 2012) and review (Monjeet al. 2013) studies. However, theresults of the meta-analysis failed toreach statistical association for noneof the outcomes assessed (FP, BFPand MBL) and the variable smoking.

Our results showed that systemicdisease did not characterize as a riskfactor for implant failure and/orcomplication. However, it should bekept in mind that the patients withsystemic diseases were eitherexcluded from the analysis or hadtheir pathologies (diabetes, hyperten-sion) treated and stabilized withinnormal biological parameters beforethe commencement of the studies.Thus, these findings are not conclu-sive.

The findings of the present reviewshowed that the incidence of implantfailures was even higher in the stud-ies that did not include bruxers intheir sample. However, it failed toidentify significant differences onbiological/prosthetic complications(BFP/PFP) and MBL between thetwo groups. Limited informationabout parafunction (bruxism) andoverloading as potential RkF wasmentioned, whereas individual bitingforce was not mentioned at all.These factors are particularly impor-tant in the posterior region of thejaws, where the most distal positionusually involves greater masticatoryload than the anterior one. Thisload, in turn, could be intensified inan individual with stronger muscularstrength (biotype). It is possible thata larger sample of bruxers includedwould have resulted in different find-ings. Even necessary, we believe thata larger sample of patients withparafunction to run a clinical studyis almost unfeasible. Thus, state-

ments about bruxism as a risk factorare mostly based on the report offew cases. This is the case of thestudy of Tawil & Younan (2003),who claimed that attention shouldbe given to the nature of the compli-cations themselves – bruxers usuallypresented more serious prostheticcomplications than non-bruxers.

Among the RkF, poor bone qual-ity in association with short implanthas been suggested to play a majorrole on the prognosis than prostheticfeatures (das Neves et al. 2006).Short implants are mostly placed inthe posterior zone (types III and IV)and does not appear to withstandthe same forces as dense bone usu-ally found in the interforaminalregion of the mandible (types I orII). Hence, short implants were notrecommended in poor quality bone(Romeo et al. 2006). Although thequality of the bone has been men-tioned in some of the included stud-ies, the total number of sites withvarious bone quality classificationswas not available. In addition, boneclassification criteria were not uni-form, making direct comparisonsdifficult. Therefore, the actual effectof bone quality on the prognosis ofshort implants supporting singlecrowns in the posterior region of thejaws remains unknown.

Primary implant stability is aprerequisite for the success of anyloading protocol of implants (Nico-lau et al. 2013). Very few studies(Deporter et al. 2001a, Rossi et al.2010) have reported the primary sta-bility of short implants, as assessedby different methods. Qualitativeanalysis suggested that shortimplants performed similar to longerimplants as revealed by PeriotestValues and Resonance FrequencyAnalysis. However, insufficient dataand a lack of standardization didnot allow us to draw definitiveconclusions.

The limited data available in thepresent systematic review failed toidentify quantitatively any associa-tion between implant failure andincreased crown-to-implant ratio (C/Iratio). Two original studies (Deporter2001a, Tawil et al. 2006) evaluatedthe clinical C/I ratio by means ofmeasurements on working casts.Rossi et al. (2010) found that themean clinical C/I ratio, as measuredin radiographs (which truly consid-



ered the endosseous portion of theimplant), increased up to the 2-yearfollow-up. In other words, theclinical C/I ratio, which should beconsidered for conclusions, is not aconstant along the time and theinfluence of this aspect may bealtered over time. A qualitativeanalysis suggested that the C/I ratiohas no significant effect on crestalbone levels and that a C/I ratio of1.5 or greater is not detrimental tothe success of a short implant. Spe-cial care should be taken whendeveloping the patient’s occlusal pat-tern, properly adjusting the occlu-sion and avoiding contact in lateralmovements. Thus, a more favourableforce orientation and load distribu-tion can be achieved and the C/Iratio may not be a major biome-chanical risk factor.

In the case of conventional fixedprosthodontic restorations, it is gen-erally recommended that a ratio oftwo lengths of root structure embed-ded in healthy bone should be usedfor one length of crown (i.e. c/rratio = 1:2 or 0.5). If this is not pos-sible, an increased number of abut-ment teeth should be used (Rokniet al. 2005). This law has beenextrapolated to the implant dentistryfor many years. Particularly in theposterior region of the jaws, wherethere is limited bone height andshort implants are used, a very out-sized crown needs to be fabricatedto reach occlusion. This results in ahigher C/I ratio. A C/I ratio >1:1 isconsidered harmful for any implant(Romeo et al. 2006), and C/I ratiosbetween 0.5 and 1 have been pro-posed to prevent crestal bone lossand eventually implant failure. Nev-ertheless, recent evidences from asystematic review (Blanes 2009) anda clinical study (Blanes et al. 2007b)showed that implant restorationswith C/I ratios >2 may not influenceimplant survival rate and the inci-dence of prosthetic complications.The introduction of the surfacetreatment of short implants has beensuggested to largely offset the exis-tence of inadequate crown-implantratios (Menchero-Cantalejo et al.2011).

Strategy and strength of evidence

A modified validity tool with theaddition of nine items has been used

for the quality assessment in thepresent review (Telleman et al.2011). The inclusion of itemsaddressing issues not explored in theoriginal version of the chart hasbeen discussed and decided amongthe review team in an attempt toincrease its scope and identify possi-ble methodological biases. The qual-ity assessment revealed a moderatemethodological quality and a highunconformity of the studiesincluded. However, the interpreta-tion of these findings should be donewith caution, as long as our charthas not been validated elsewhere andthus may present some potential lim-itations. Moreover, the results wereobtained from observational studiesand the highest level of evidence(randomized controlled study) hasnot been achieved. This is in agree-ment with previous reviews (Renou-ard & Nisand 2006, Kotsovilis et al.2009, Monje et al. 2013), when noRCTs assessing the outcomes ofshort implants have been found.There is controversy over the valid-ity of evidence from non-randomizedstudies; they are more susceptible toselection, performance, detection,attrition and publication bias (Pom-mer et al. 2011).

Although no specific randomizedcontrolled trials meeting the eligibil-ity criteria of the present review havebeen found, some studies that wereexcluded from the data compilationand meta-analysis are noteworthy.In these clinical trials, short implantswere randomly placed in non-aug-mented bone and were compared tolonger implants placed in verticallyaugmented mandibles (Felice et al.2010, Esposito et al. 2011a) andmaxillae (Cannizzaro et al. 2009,Pieri et al. 2012). The results indicatethat when the bone height over themandibular canal or below the max-illary sinus is reduced, short implantspresent good and similar results inthe short- and mid-term to longerimplants placed in vertically aug-mented bone. The studies agreedthat short implants could be aninteresting alternative to verticalaugmentation since the treatment isfaster, cheaper and associated with alower incidence of complications.Even promising, these preliminarypost-loading results must be con-firmed by trials with larger samplesizes and longer follow-ups.

Finally, statistical analyses in thisreview were restricted to implant-based failure data and this limitationis in agreement with recentlypublished systematic reviews withmeta-analysis (Kotsovilis et al. 2009,Pommer et al. 2011, Telleman et al.2011, Monje et al. 2013). Theauthors would have preferred to per-form a patient-based analysis, asevents (implant loss) tend to clusterwithin the same patients. However,the use of patient-based statisticalanalysis was hampered by the lackof adequate patient-based failuredata and to the fact that some of thestudies included in this review arenot exclusively about short implants.

On the other hand, the presentsystematic review applied meticulousstrategies of searches, screenings,data compilation and analysis toprevent or minimize bias. Norestrictions to the database, lan-guage and year of publication wereapplied. This may have contributedto the high number of referencesfound. Contact with the authorsallowed the obtaining of some miss-ing, unpublished, or unclear data ina form compatible for meta-analysis.Furthermore, some exclusion criteriawere used to prevent potential con-founders and, therefore, systematicbias. For instance, we thought con-venient to not include retrospectivestudies; we opted for selecting onlythose prospectively designed. Conse-quently, no significant heterogeneityamong selected studies was found inthe meta-analyses for the outcomesFP and PFP, as well as no evidenceof publication bias existed. On theother hand, the studies presentedhigh and very high heterogeneity forthe outcomes BFP and MBL respec-tively. This inconsistency may beexplained by the lack of standardi-zation on how the outcomes areassessed and reported. In the caseof MBL, subgroup analysis andmeta-regressions had a greater rele-vance, because they assess every sin-gle co-variable that may beresponsible for the overall very highheterogeneity.

Conclusion

Within the limitations of the presentsystematic review with meta-analysis,it is suggested that single crownssupported by short implants are an


210 Mezzomo et al.

acceptable and predictable option inthe short- and long-term treatmentof the atrophic jaws. It should beconsidered as an alternative toadvanced bone augmentation surger-ies, with a favourable advantage/riskratio. Low failure proportions(5.9%), low incidence of biologicaland prosthetic complications (3.8%and 2.8% respectively) and minimalbone loss are reported after a meanfollow-up period of 40 � 33.72months. Some advantages of thetechnique can be listed: (1) avoid theneed for bone grafting to placelonger implants; (2) less postopera-tive morbidity; (3) reduced treatmenttime; (4) reduced costs; and (5)restricting the need of sophisticatedcomputerized radiographic exams.

In summary, it can be concludedthat

• the installation of single crownssupported by short dentalimplants in the maxilla has abetter prognosis over installationin the mandible;

• surface topography and surgicaltechnique did not affect the fail-ure proportion and incidence ofbiological complications of shortimplants;

• peri-implantitis, heavy smokingand persistent periodontal diseaseare RkF for the loss of a shortimplant;

• the actual effect of systemic dis-ease, bone quality and primarystability on the prognosis ofshort implants supporting singlecrowns in the posterior region ofthe jaws remains unknown;

• increased C/I ratios of shortimplant-supported single crownsdid not influence marginal boneloss and cannot be associatedwith increased implant failurerates and the occurrence of tech-nical complications;

• surgical handling of the recipientsite is critical for short implants,as long as it may seriouslycompromise implant stability.

Recommendations for further research

In spite of the increasing number ofpapers on short implants being pub-lished, it must be noted that the over-all levels of evidence provided by theliterature are still insufficient. Ran-

domized controlled trials specificallyaddressing single crowns supportedby short implants placed in originaljawbone compared with those oflonger implants placed in augmentedbone, with longer follow-up timesand larger samples are necessary tovalidate the current findings. Further-more, it is desirable that future stud-ies could address, in a patient-basedanalysis, factors such as minimallength, prosthetic design, implant sta-bility, bone quality, smoking statusand presence of bruxism that maylead or not to an increased risk of fail-ures and/or complications.

Acknowledgements

The authors acknowledge Dr. Rodri-go Ribeiro for the conduction of themeta-analysis. We thank allcolleagues who kindly replied thee-mails, clarifying relevant issues andeven providing unpublished data:Dr. Nathalie Nurdin and Dr. RabahNedir (Switzerland); Dr. Frank Stri-etzel (Germany); Dr. Dietmar Wengand Mrs. Renee Stach (Germany);Dr. Juan Iba~nez (Argentina); Dr.Jefrey Ganeles (USA) and Dr. SvenKnapinski (Switzerland); Dr. G�erardBrunel (France); Dr. Michele Perelli(Italy); Dr. Daniele De Santis (Italy);and Dr. Douglas Deporter (Can-ada).

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Supporting Information

Additional Supporting Informationmay be found in the online versionof this article:

Table S1. List of excluded articlesand reasons.

Address:Luis Andre MezzomoDepartment of Prosthodontics, Faculty ofDentistry, Pontifical Catholic University ofRio Grande do Sul, 6681 Ipiranga Avenue,91530-001 Porto Alegre,BrazilE-mail: [email protected]

Clinical Relevance

Scientific rationale for the study:There is a lack of evidences on theprognosis of single crowns sup-ported by short implants in theposterior region of the jaws.Principal findings: Single crownssupported by short implants in the

posterior region show a high predict-ability, with a low incidence of fail-ures and complications.Practical implications: Clinicians cansafely use short implants to supportsingle crowns for the rehabilitationof partially edentulous patients.However, comparisons to longer

implants associated to bone aug-mentation prior to placement arelimited and the treatment optionthat shows better results in thelong term is still unknown.



Systematic Review Meta-analysis of single crowns supported ... · Conclusions: Single crowns...

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