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Journal of Cranio-Maxillo-Facial Surgery 43 (2015) 1694e1699

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Journal of Cranio-Maxillo-Facial Surgery

journal homepage: www.jcmfs.com

Coronectomy of mandibular third molars: A clinical protocol to avoidinferior alveolar nerve injury*

Giuseppe Monaco, Elisabetta Vignudelli*, Michele Diazzi, Claudio Marchetti,Giuseppe CorinaldesiDepartment of Oral and Maxillofacial Surgery (Head: Prof. C. Marchetti), University of Bologna, Via San Vitale 59, 40125, Bologna, Italy

a r t i c l e i n f o

Article history:Paper received 13 March 2015Accepted 14 July 2015Available online 29 July 2015

Keywords:CoronectomyGuidelinesProtocolThird molarsSurgery

* The work is attributed at the Department of OrUniversity of Bologna, Via San Vitale 59, 40125, Bolog* Corresponding author. Tel.: þ39 051 2088155; fax

E-mail address: elisabetta.vignudelli@unibo.it (E. V

http://dx.doi.org/10.1016/j.jcms.2015.07.0061010-5182/© 2015 European Association for Cranio-M

a b s t r a c t

Coronectomy is a surgical procedure for the treatment of mandibular third molars in close proximity tothe mandibular canal. Unfortunately, often the surgical protocol is not described step by step and it isdifficult for the clinician to assess the key factors that are important for the success of this procedure. Theaim of this paper is to propose and describe a standardized surgical protocol to improve the success ofthe technique. The treatment approach, for the most common types of third molars impaction is ana-lysed. Each step of the surgical procedure is described in details and a new type of crown section isproposed. The presented protocol is proposed in order to define a clinical practitioner's guide that couldhelp the surgeon who approaches coronectomy for the first times.

© 2015 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rightsreserved.

1. Introduction

Coronectomy is a surgical procedure indicated when, as esti-mated from radiographs, the roots of the thirdmolars are close to orviolate the canal of the inferior alveolar nerve (IAN) (Long et al.,2012).

This technique was first proposed in 1984 (Ecuyer and Debien,1984) as an alternative surgical procedure to complete third mo-lars extraction. Since then, several papers have been published onthis technique (Long et al., 2012; Freedman, 1997; Knutsson et al.,1989; Pogrel et al., 2004; O'Riordan, 2004; Renton et al., 2005;Leung and Cheung, 2009; Hatano et al., 2009; Cilasun et al., 2011;Dolanmaz et al., 2009; Monaco et al., 2012; Sencimen et al., 2010;Goto et al., 2012; Leung and Cheung, 2012; Gleeson et al., 2012).

A systematic review based on randomized clinical trialsconcluded that coronectomy could be used for the treatment ofhigh neurological risk third molars and the authors suggested howthe risk of failure may be reduced by an improvement of the sur-gical procedures (Long et al., 2012).

al and Maxillofacial Surgery,na, Italy.: þ39 051 225208.ignudelli).

axillo-Facial Surgery. Published by

Unfortunately, often the surgical protocol is not described stepby step and so it is difficult for the clinician to assess the key factorsthat are important for the success of this procedure (Renton et al.,2005; Hatano et al., 2009; Cilasun et al., 2001).

In the present paper, we evaluated the results obtained in 100cases of coronectomy where the same surgical protocol, with in-dications for the treatment of different patterns of molar inclusion,was employed. In addition, we propose a specific section of thecrown, in order to avoid the risk of one of the most potentialdangerous complications: intra-operative root mobilization (Longet al., 2012; Renton et al., 2005; Leung and Cheung, 2009; Hatanoet al., 2009; Cilasun et al., 2001; Gleeson et al., 2012).

The following protocol is an attempt to define a clinical practi-tioner's guide that can be useful to the surgeon who approachescoronectomy for the first time (Fig. 1).

The operative steps evaluated were radiographic diagnosis, flapdesign, osseous surgery, crown section, suturing, postoperative rootmigration, and management of postoperative complications.

2. Material and methods

The study population was composed of 98 healthy patientsreferred to the Department of Oral and Maxillofacial Surgery of theDental Clinic, Alma Mater Studiorum, University of Bologna, Italyfor mandibular third molars evaluation.

Elsevier Ltd. All rights reserved.

G. Monaco et al. / Journal of Cranio-Maxillo-Facial Surgery 43 (2015) 1694e1699 1695

Study inclusion criteria were: age between 18 and 70 years old;the presence of at least one high neurological risk third mandibularmolars that needed extraction for previous episodes of pericor-onitis or periodontal disease distal to the second molar (Monacoet al., 2012).

The exclusions criteria were: patients with systemic conditionthat preclude surgical treatment, the use of antibiotics or anti-inflammatory agents for 14 days before surgery and third molarwith caries, endodontic disease or premature apexes.

The variables evaluated were

� Neurological damage evaluated at sutures removal as the pres-ence of hypoesthesia, hyperaesthesia or dysaesthesia of thelower lip and mental region on the operated side. The presenceof any alteration of lingual sensitivity was also evaluated.

� Failed coronectomy considered as any intra-operative rootmobilization

� Re-operation rate evaluated as the need of the second surgery totreat the retained roots. The reason and the type of secondsurgery were also recorded.

Fig. 1. Decision flow-chart (NAI: Inferior Alveolar Nerve).

2.1. Surgical technique

2.1.1. Indications and contraindications

Coronectomy treats vital high-risk mandibular molars (Leungand Cheung, 2009; Dolanmaz et al., 2009; Monaco et al., 2012).Most of the criticisms of this technique concern the fate of thesectioned roots and the possibility of the development of pulpaldiseases (Assael, 2004). The key factors to avoid these complica-tions are the maintenance, before and during the procedure, of thevitality and immobility of the roots (Renton et al., 2005; Leung andCheung, 2009; Monaco et al., 2012; Johnson et al., 1974; Plata andKelln, 1976; Whithaker and Shankle., 1974.)

For these reasons, this technique is not indicated for the treat-ment of high-risk third molars affected by caries, endodontic dis-ease, premature roots or mobility.

On the other side coronectomy is indicated for the treatment ofhigh-risk third molars affected by pericoronitis or causing peri-odontal disease on the adjacent mesial tooth.

2.1.2. Radiographic diagnosis

In most reports, the diagnosis of a close relationship betweenthe IAN and third molar roots was made based only on panoramicX-ray examination (Freedman, 1997; Pogrel et al., 2004; Rentonet al., 2005; Leung and Cheung, 2009; Dolanmaz et al., 2009;Leung and Cheung, 2012). The criteria selected for coronectomywere the presence of some radiographic markers (darkening of theroot, diversion of the canal, narrowing and interruption of theradiopaque border) that are considered highly predictive of closecontact between IAN and third molar roots.

In some studies (Hatano et al., 2009; Cilasun et al., 2001;Monaco et al., 2012; Goto et al., 2012), after assessment of thesemarkers on panoramic X-rays, a more accurate topographic diag-nosis was made by using cone-beam computed tomography (CT).These cases showed the best results in terms of avoidance of intra-operative root mobilization with a rate ranging from 0 to 5%(Hatano et al., 2009; Cilasun et al., 2001; Monaco et al., 2012).However, in case of root mobilization root removal was recom-mended (Renton et al., 2005; Leung and Cheung, 2009; Gleesonet al., 2012).

In this regard coronectomy can be executed based on the in-formation obtained by panoramic X-ray, however a CT scans ex-aminations allows the clinician with less surgical experience amore accurate diagnosis and appropriate choice of therapy,although it does expose the patient to radiation and is associatedwith increased cost (Monaco et al., 2004). Moreover, in case ofintra-operative root mobilization, a CT scan offers a three-dimensional evaluation of the root morphology and the relation-ship between roots and mandibular canal that could help the cli-nicians to perform roots removal with a reduced risk.

2.1.3. Flap design

The flap design should be related to the type of inclusion. Somestudies reported the use of a buccal mucoperiosteal flap withoutspecifying whether this flap presents a buccal-releasing incision(Leung and Cheung, 2009; Cilasun et al., 2011; Dolanmaz et al.,2009). In other studies, the authors reported the execution of alingual flap to facilitate crown sectioning, although in some caseswas associated with lingual nerve injury (Pogrel et al., 2004;Renton et al., 2005).

Pogrel (Pogrel et al., 2004) suggested to perform the flap designaccording to the crow section technique. He proposed the execu-tion of both buccal and lingual flaps in case of crown section with

G. Monaco et al. / Journal of Cranio-Maxillo-Facial Surgery 43 (2015) 1694e16991696

fissure burs, while a buccal flap alone in case of crown grindingwith round burs.

In order to reduce the risk of lingual nerve lesions, a lingual flapis not recommended even if this results in crown sectioning beingmore time-consuming (Leung and Cheung, 2009; Monaco et al.,2012; Robinson and Smith, 1996).

Flap design should be related to the type of inclusion to obtain aprimary tension-free closure. A mucoperiosteal buccal flap with areleasing incision distal to the second molar is suggested in case ofpartially impacted third molar. A mucoperiosteal buccal flap with areleasing incision mesial to the second molar instead, is advisablein case of completely impacted third molar.

These flap designs facilitate primary closure of the surgicalwound, improving post-surgical healing bone formation coronal tothe sectioned roots (Monaco et al., 2012), and minimize the risk ofpost-operative infections (Pogrel et al., 2004; O'Riordan, 2004;Hatano et al., 2009; Cilasun et al., 2011; Monaco et al., 2012).

2.1.4. Osseous surgery

In a recent study, it was stated that bone surgery should beperformed only in case of deeply impacted teeth, when the bonycrest prevent an easy crown sectioning with fissure burs. In thisstudy, the authors did not report any case of intra-operative rootmobilization (Monaco et al., 2012).

Bone resection, when necessary, should not be performed belowthe cemento-enamel junction (CEJ), in order to minimize the risk ofroot mobilization, especially in cases of conical roots with lowretention in bone (Renton et al., 2005).

The depth of inclusion and the type of impaction (vertical orhorizontal) should determine the quantity of bone removed.

Two different surgical protocols are proposed, according to thetype of inclusion.

- Third molars in vertical or disto-angular inclusion

A tooth with vertical inclusion is defined as having an inclina-tion of its axis minor than 25� compared to the axis of the mesialtooth.

When the third molar crown is erupted more than 50% abovethe CEJ of the second molar, it is possible to perform the crownsection with no ostectomy.

If the third molar crown is 50% or more apical to the CEJ of thesecond molar, osseous surgery is necessary. To reduce the risk ofroot mobilization it is important not to expose the entire thirdmolar crown.

- Third molars in mesial or horizontal inclusion

In these cases, the procedure is more problematic and bonesurgery is always needed to visualize the third molar crown. Usu-ally, the amount of ostectomy is similar to that necessary for acomplete tooth removal.

2.1.5. Crown section

The crown section is a crucial point of the technique because it isnecessary to remove all enamel remnants because enamel seems toinhibit bone healing over the sectioned roots.

In this stage, attention should be made to not mobilize the rootfragments. In some studies (O'Riordan, 2004; Leung and Cheung,2009; Cilasun et al., 2011) the authors proposed a completecrown section to minimize the risk of root mobilizing during theremoval of the crown. Nevertheless this procedure presents higherpossibilities of lingual nerve injury since this lesion could be

determined by a fissure bur or by the elevator used for lingual flapprotection (Pogrel et al., 2004).

Some authors have proposed a partial crown section with afollowing crown fracture after the insertion of an elevator in thesection line (Pogrel et al., 2004; Renton et al., 2005). This procedureis safer with regard to the lingual nerve, but the crown fracturecould lead to root mobilization and, therefore, to the failure of theprocedure (Cilasun et al., 2011).

Leung et al. suggested making more sections to weaken thethird molar crown and so minimize the risk of root mobilization(Leung and Cheung, 2009).

In order to overcome these problems, two surgical protocols areproposed, according to the type of inclusion.

- Third molars in vertical or distoangular inclusion

The section is performed in a bucco-lingual and mesio-distaldirection, using a fissure bur on a high-speed drill. The mesio-distal section needs a bur inclination of 45� in lingual direction,in order to section the lingual part of the crown apically to the bonycrest without any other procedures. This section could start1e2 mm coronal to the buccal bony crest and after this first cut, thepart of the tooth between the buccal bone and the section is grin-ded with a round bur. In this way, it is possible to visualize the partof the tooth that needs to be sectioned to remove the crown.

A second section in the bucco-lingual direction perpendicular tothe first cut is made. This section permits to weakening of thecrown and, at the same time, allows determination of the depth ofthe first section (Figs. 2 and 3).

The crown is gently fractured using an elevator inserted be-tween the buccal bony crest and the tooth. The pressure of theelevator is on the buccal plate and not on the root, to avoid mobi-lizing the latter.

- Third molars in mesial or horizontal inclusion

The crown section is made in the bucco-lingual direction, usinga procedure identical to that described for complete removal(Checchi and Monaco, 2001). This section must be wide enough toallow a gently fracture of the crown.

A second section of the mesial fragment is made in a disto-mesial direction, to obtain two smaller pieces that can beremoved separately.

Then, using a round bur on a surgical high-speed drill, it isimportant to grind the third molar root as described for thirdmolars in a vertical inclusion.

2.1.6. Root grinding

After crown removal, it is important to reduce the remainingroot at least 2e3 mm below the bony crest (Renton et al., 2005;Leung and Cheung, 2009). The roots grinding is performed usinga round bur or a drill and to reduce vibrations, a high speed isrecommended. This is a fundamental step for each inclusionpattern in order to make a smooth surface without dentinal orenamel spikes and to reduce the rate of retained root exposure(Garver and Fenster, 1980). The post-operative migration ofretained roots is a common and well documented finding in liter-ature (Leung and Cheung, 2009, Dolanmaz et al., 2009; Monacoet al., 2012; Leung and Cheung, 2012). In a vertical third molar,root migration could lead to root eruption, whereas root migrationof a horizontal third molar could lead to contact with the distalsurface of the second molar. In these cases a second surgery toremove remaining fragments may be necessary.

Fig. 2. In vertically impacted wisdom tooth two sections are needed: one in a mesio-distal direction and the second in a buccal-lingual direction.

Fig. 3. Clinical view of a correct crow section.

Fig. 4. Radiographic examination before sutures. The crown section needs to be cor-rect due to the presence of enamel mesial spike.

Fig. 5. Radiographic examination after crown section reshaping.

G. Monaco et al. / Journal of Cranio-Maxillo-Facial Surgery 43 (2015) 1694e1699 1697

2.1.7. Socket washing

No endodontic treatment of the retained root is required. Theendodontic treatment of retained root could increase the risk ofpost-operative complication due to the prolongation of the surgicaltime (Sencimen et al., 2010). We recommend only a socket washwith saline solution.

2.1.8. Radiographic control

Before suturing it is important to make a periapical radiographto control the crown section. In order to promote the integrations ofretained roots it seems to be important to remove all enamel anddentinal asperities that could affect the bone healing over thefractured surface (Figs. 4 and 5) (Garver and Fenster, 1980).

2.1.9. Sutures

A systematic review based on randomized clinical trials did notreport any indication about the type of sutures needed for thistechnique (Long et al., 2012). Nevertheless, in most studies, theauthors agree on the primary closure of the wound (Pogrel et al.,2004; Hatano et al., 2009; Cilasun et al., 2011; Monaco et al.,2012; Sencimen et al., 2010), based on the hypothesis that a pri-mary tension-free closure could help the blood clot stabilizationimproving the post-operative healing. In addition, a primaryclosure could minimize the risk of alveolus contamination andpost-operative infection (Dolanmaz et al., 2009).

The flap designs proposed in this protocol are helpful to try toobtain a primary closer but in case of partially impacted thirdmolar, when the buccal flap is sutured to the lingual side, it canresults in a temporary reduction of fornix depth that is usuallyresolved 1 year after surgery.

It is important to underline that the recommendation of a pri-mary closure is only a clinical indication based on authors'

G. Monaco et al. / Journal of Cranio-Maxillo-Facial Surgery 43 (2015) 1694e16991698

experience because there are not clinical trials that investigate thistopic. Further clinical randomized studies are necessary to confirmthe necessity of a primary closure and its relationships to the long-term success of the coronectomy.

3. Results

The presented protocol is routinely used at the Unit of Oral andMaxillofacial Surgery of the University of Bologna by surgeons withdifferent surgical skills. This surgical protocol has been used toperform 100 coronectomies on 98 healthy patients with a meanage, 28.99 ± 8.9 years. Any nerve damage or failed coronectomies(0%) has been registered in the sample. A second surgery to extractthe retained roots was needed in 5 cases (5%): 1 case of pulpitis and4 cases of root eruption into the oral cavity due to post-operativeroots migration. A second corrective surgery without retainedroots extraction was necessary in 4 (4%) other cases: in 3 cases toremove enamel remnants that prevented bone formation aroundthe roots and in 1 case to decrease gingival hyperplasia distal to thesecond molar.

This result could be related to the standardized surgical protocolthat permits, also for clinicians with less surgical experience, toobtain positive outcomes.

4. Discussion

Coronectomy of high riskerisk third molars is, nowadays, a welldocumented surgical alternative with low rate of complications(Long et al., 2012).

The questions about this technique regard the fate of retainedroots that could became symptomatic due to the crown section,pulp necrosis or infection (Assael, 2004).

The pain in the first postoperativeweek is a controversy topic. Insome studies the post-operative pain was observed to be less thanwhat occurs after complete extraction (Leung and Cheung, 2009;Monaco et al., 2012). In one study, it was reported that post-operative pain was greater in the coronectomy group than in theextraction group, and this occurrence was explained with the “tightprimary closure of the wound that could have caused high pressureinside the wound, thus acute pain” (Hatano et al., 2009). Moreover,limited grinding of the root can lead to insufficient removal of pulptissue and consequently greater postoperative pain (Monaco et al.,2012). Cilasun et al. (Cilasun et al., 2011) reported one case of re-intervention after 10 days due to post-operative pain.

Monaco et al. reported that the post-operative pain is generallylimited at the first two post-operative days and its intensity is lessthan a score of 4 in a horizontally visual analog scale (VAS) fromzero (no pain) to ten (unbearable pain) (Monaco et al., 2012).

The need of antibiotic therapy to avoid post-operative infectionis also a questioned topic related to this technique. A recent sys-tematic review failed to draw a definitive conclusion due to the lackof homogeneity in antibiotic prescription (Long et al., 2012). In ourexperience, 2 g of amoxicillina and clavulanic acid 1 h before sur-gery and 1 g every 8 h for 4 days after surgery were able to mini-mize the numbers of post-operative infection (Monaco et al., 2012).In case of post-operative infection, the management of thiscomplication is similar to the one reported for complete extraction(Monaco et al., 2012). Infection of the socket is reported with at anincidence of 0%e11% (O’Riordan, 2004; Renton et al., 2005; Leungand Cheung, 2009; Hatano et al., 2009; Cilasun et al., 2011;Dolanmaz et al., 2009; Monaco et al., 2012) and wound primaryclosure is indicated to minimize this risk (Knutsson et al., 1989;O'Riordan, 2004; Hatano et al., 2009; Cilasun et al., 2011; Monacoet al., 2012).

On the contrary, the post-operative migration of retained rootsis a common event (Leung and Cheung, 2009; Dolanmaz et al.,2009; Monaco et al., 2012; Leung and Cheung, 2012). Studies inwhich the rootmovementwas evaluated by panoramic radiographsreported migration of 2.9 mm (Leung and Cheung, 2012) to 4 mm(Dolanmaz et al., 2009) after 24 months.

When root migration was evaluated using periapical radio-graphs, the mean movement was 2.0 mm at 6 months (Monacoet al., 2012).

When evaluated by CT the average root movement was 3 mm 1year after coronectomy (Goto et al., 2012).

Female gender and age under 26 years seems to be related to astatistically significant major migration (Renton et al., 2005;Monaco et al., 2012; Goto et al., 2012). The post-operative migra-tion led to the eruption of the root fragment in the oral cavity with arate between 0 and 1.3% (Long et al., 2012). If the eruption in oralcavity occurs, the extraction of retained roots is indicated to avoidinfection (Long et al., 2012).

It is important to inform the patients of this event and a clinicaland radiograph examination at 3, 6, and 12 months post-operatively is useful to evaluate the need for re-intervention.

Regardless of the low rate of complications, patients need to beinformed of all the possible complications regarding thisprocedure:

- nerves injuries- intra-operative roots mobilization- pain- swelling- bleeding- socket infection- necessity of a second surgery for retained roots extraction due toinfection or migration

5. Conclusion

Nowadays, coronectomy is a surgical option for the treatment ofvital high risk thirdmandibular molars. A correct case selection andan appropriate learning curve are important for improving clinicalsuccess. The choice of this technique should be planned beforesurgery and the correct protocol must be used.

The clinical protocol described above can improve clinical out-comes and may be of interest to clinicians who do not haveextensive experience in this field.

Conflict of interest statementNone.

Funding supportThe authors declare that they didn't receive any sources of

support in the form of grants.

Acknowledgements

The authors are grateful to Dr. Giselle De Santis and Dr. AlbaKellezi for their contribution to preparing the manuscript.

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