Micro Surgical Instruments for Root-End Cavity Preparation Following Apicoectomy a Literature Rev

Endod Dent Traumatol 2000; 16: 47–62 Copyright C Munksgaard 2000Printed in Denmark . All rights reserved

Endodontics &Dental Traumatology

ISSN 0109-2502

Review article

Microsurgical instruments for root-endcavity preparation following apicoectomy:a literature reviewvon Arx T, Walker WA. Microsurgical instruments for root-end T. von Arx1, W. A. Walker III2

cavity preparation following apicoectomy: a literature review. Departments of 1Periodontics and 2Endodontics,Dental School, The University of Texas HealthEndod Dent Traumatol Endod Dent Traumatol 2000; 16: 47–62.Science Center at San Antonio, Texas, USAC Munksgaard, 2000.

Abstract – Root-end cavities have traditionally been prepared bymeans of small round or inverted cone burs in a micro-handpiece.Since sonically or ultrasonically driven microsurgical retrotips be-came commercially available in the early 1990s, this new techniqueof retrograde root canal instrumentation has been established as anessential adjunct in periradicular surgery. At first glance, the mostrelevant clinical advantages are the enhanced access to root endsin limited working space and the smaller osteotomy required forsurgical access because of the various angled designs and small sizeof the retrotips. However, a number of experimental studies com-paring root-end preparations made with microsurgical tips to thosemade with burs have demonstrated other advantages of this newtechnique, such as deeper cavities that follow the original path ofthe root canal more closely. The more centered root-end prepara-tion also lessens the risk of lateral perforation. In addition, the ge-ometry of the retrotip design does not require a beveled root-endresection for surgical access thus decreasing the number of exposed

Key words: apicoectomy; microsurgicaldentinal tubules. A controversial issue of sonic or ultrasonic root-endinstrument; retrotip; root-end cavity preparation;

preparation is the formation of cracks or microfractures, and its ultrasonic; sonicimplication on healing success. The present paper reviews experi- Thomas von Arx, Department of Oral Surgery,mental and clinical studies about the use of microsurgical retrotips Dental School, Freiburgstrasse 7, 3010 Berne,in periradicular surgery and discusses many issues raised in pre- Switzerland

vious papers. Accepted September 3, 1999

Preservation of natural teeth is one of the ultimategoals of modern dentistry. In the case of periradicularpathosis, potential pathogens are usually eliminatedby non-surgical root canal treatment with subsequentobturation and coronal restoration. However, in somecases, the periradicular lesion does not heal or it flaresup, indicating the persistence of noxious agents withinthe physical confines of the canal system. If conven-tional endodontic retreatment is neither indicated nor

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feasible, endodontic surgery may become the last re-sort for salvaging the affected tooth.

One of several treatment options in endodonticsurgery is periradicular surgery, which includes threecritical steps to eliminate persistent endodontic patho-gens: 1) surgical debridement of pathological perirad-icular tissue, 2) root-end resection (apicoectomy), and3) retrograde root canal obturation (root-end filling).The goals of root-end resection are listed in Table 1.

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The objectives of retrograde obturation are shown inTable 2.

A root-end cavity is conventionally prepared bymeans of a round or inverted cone bur in a micro-handpiece. However, this technique of apical prep-aration has a number of limitations (Table 3). Alterna-tive root-end preparation techniques like slot prepara-tion using a fissure bur or reverse instrumentationusing modified K-files or Hedstrom files in specialholders or hemostats were advocated in the 1980s (1–3). These methods have circumvented some of thelimitations inherent to the conventional technique,but have not become standard procedures in perirad-icular surgery.

Richman (4) reported the first documented appli-cation of ultrasound in periradicular surgery in 1957using an ultrasonic chisel to cut bone and resect api-cal tooth tissue. The first root-end preparation bymeans of modified ultrasonic inserts following apico-ectomy is attributed to Bertrand et al. (5). Flath &Hicks (6) also reported the application of ultrasonicsand sonics for root-end cavity preparation in two casepresentations. They used cut-off and bent or pre-curved files that were driven by ultrasonic or sonicdevices. In an experimental study in extracted humanteeth, Sultan & Pitt Ford (7) compared root-end prep-aration with either hand-held or ultrasonically acti-vated files. At the beginning of the 1990s, commer-cially produced microsurgical tips became available

Table 1. Objectives of root-end resection (apicoectomy)

– Surgical removal of apical delta (root canal ramifications)– Enhancement of access to apex– Creation of a working surface for retrograde preparation– Facilitate debridement of periapical tissue– Observation of resected root end for presence of vertical fractures

Table 2. Objectives of root-end obturation

– Removing irritants during root-end cavity preparation– Preventing penetration of microorganisms and their by-products from the

root canal into the periapical region– Optimizing conditions for periapical tissue healing including regeneration

of attachment apparatus

Table 3. Limitations inherent to the conventional bur technique for root-endcavity preparation

– Axis of preparation not parallel to root canal– Risk of perforation of lingual dentin wall– Insufficient depth of root-end cavity– Difficult in limited working space– Requires a root-face bevel of 45æ or more– Enlarged area of patent dentinal tubules due to acute angle of bevel– Reduced surgical site visibility

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for endodontic surgery (8–11). Other terms used forthese microinstruments are retrotips or retroprep tips.Since the introduction of these retrotips, a numberof experimental and clinical studies have investigateddifferent aspects of their application in periradicularsurgery. The objectives of the present paper are toreview the literature as of July 1999 and to discussthe reported results. The review is divided in two sec-tions: (I) experimental studies and (II) clinical studies.The multitude of experimental studies further war-ranted subdivision into the following sections:– Geometry and cleanliness of root-end preparations

prepared with retrotips– Cutting ability of retrotips– Sealing ability of root-end fillings placed into cavi-

ties prepared with retrotips– Root-face alterations following root-end prepara-

tion with retrotips– Fracture of retrotips.Experimental studies have also been summarized intables for quick references.

Experimental studies1. Geometry and cleanliness of root-end preparationsprepared with retrotips (Table 4)

Wuchenich et al. (12) published the first experimentalstudy on ultrasonic root-end preparation using micro-surgical tips. The objective of their study was toevaluate the depth, parallelism and cleanliness ofroot-end cavities prepared by ultrasonic tips com-pared to conventional apical preparations made byburs. Twenty teeth from two human cadavers wereinstrumented and obturated with gutta-percha andsealer. Following flap reflection and osteotomy, theapical third of each root was resected. Subsequently,root-end cavities were prepared either with an ultra-sonic retrotip (Excellence in Endodontics, San Diego,CA) or with an inverted cone bur driven by a slow-speed micro-handpiece. Following extraction, theteeth were sectioned longitudinally and sputter-coatedwith gold for SEM analysis. Ultrasonic root-end prep-arations were found to be at least 2.5 mm deep andclosely followed the root canal space. Cavity wallsshowed many patent dentinal tubules with littledebris. In contrast, preparations made with the burwere offset to the long-axis of the root by 45æ to 60æand had only an average depth of 1 mm. In addition,the tubules of the cavity walls were covered with aheavy smear layer.

Gutmann et al. (13) evaluated three different tech-niques of root-end cavity preparation. Sixty single-rooted extracted human teeth were prepared and ob-turated with subsequent root-end resection at a 45æangle. Three groups of 20 teeth each were treatedas follows: Group 1 had a 2–3-mm deep root-endpreparation prepared using a round bur in a slow-

Retrotips in apicoectomy

Table 4. Summary of experimental studies evaluating geometry and cleanliness of root-end cavities prepared with retrotips

Paper Tested issues Material Evaluation Root-end treatment Results

Wuchenich Depth, cleanliness and Teeth of Scanning electron Retroprep with Minimum depth 2.5 mm, direction ofet al. 1994 parallelism of root-end human microscopy ultrasonic retrotips cavity parallel to canal space, cavity walls(12) preparations cadavers (CT, EIE) (nΩ10) with minimal debris

Retroprep with a .331/2 inverted Mean depth 1 mm, direction of cavitycone bur in a slow-speed deviated 45–60æ from long axis of themicrohead handpiece (nΩ10) root, cavity walls with heavy debris layer

Gutmann Amount of debris, and Extracted SEM analysis with Retroprep with a Debris score: 2.33et al. 1994 smear layer human gradation scoring round bur (nΩ20) Smear score: 3.98(13) teeth 1–4 (1Ωleast, Retroprep with a round burπ Debris score: 2.16

4Ωgreatest amount) acid etching (nΩ20) Smear score: 2.27

Retroprep with ultrasonic retrotip Debris score: 1.70(nΩ20) Smear score: 2.74

Engel & Size of preparation, Extracted Visual and metric Retroprep with .1 round bur with Mean postop canal area 2.8 mm2, prepSteiman canal debridement, human teeth analysis of slow-speed (nΩ10) time 80 s, one root fractured1995 (14) time required for (only roots photomicrographs Retroprep with .1 round bur with Mean postop canal area 3.4 mm2, prep

preparation, root with 2 canals slow-speedπ10 s use of ultrasonic time 95 s, one root fracturedfractures selected) retrotip (Neosonic) (nΩ10)

Retroprep with Neosonic ultrasonic Mean postop canal area 2.2 mm2, prepretrotip (nΩ10) time 85 s, one root fractured

Gorman Presence of debris, Extracted Photomicrographs at Retroprep with .1 round bur with Debris score: 1.2et al. 1995 and smear layer human teeth ¿600 magnification slow-speed and refinement with Smear score: 2.2(15) with a single (scores 0–3 recorded ultrasonic retrotip

canal for amount of debris (Neosonic) (nΩ10)and smear layer) (0Ω Retroprep with .1 round bur alone Debris score: 1.7least, 3Ωgreatest (nΩ10) Smear score: 2.7amount)

Retroprep with ultrasonic retro-tip Debris score: 1.5(Neosonic) (nΩ10) Smear score: 1.5

Mehlhaff Preparation depth, Bilaterally Bony crypt measured in Retroprep with ultrasonic tips Mean depth 2.51 mm, 2.6% ofet al. 1997 deviation of cavity matched cadavers before tooth (CT-5 and CT-1, EIE) (nΩ38) specimens showed prep deviation from(16) from long axis of root, pairs of teeth extraction, all other long axis, mean bevel 16.0æ, mean size

size of bony crypt and in human parameters measured of bony crypt 4.3¿5.2 mmbevel angle of resection cadavers on radiographs Retroprep with round bur in high- Mean depth 2.05 mm, 100% ofneeded for access projected at ¿10 power speed handpiece (nΩ38) specimens showed prep deviation from

long axis, mean bevel 35.1æ, mean sizeof bony crypt 4.7¿6.3 mm

Lin et al. Enlargement of cavity, Extracted Stereomicroscopic Retroprep with ultrasonic retrotip 326% enlargement, 17.6% loss,1998 (17) loss of tooth structure, human teeth quantitative analysis (CT-5, EIE ) (nΩ10) 0.43 mm wall thickness

width of remaining Retroprep with .8 bur in micro- 616% enlargement, 30% loss,dentin wall handpiece (nΩ10) 0.17 mm wall thickness

speed handpiece. Group 2 received the same treat-ment, but a 10% citric acid and 3% ferric chloridesolution was subsequently applied for 60 s to flush theapical cavity. In group 3, an ultrasonic retrotip wasemployed to prepare a 2–3-mm deep apical cavity.All specimens were then split longitudinally and thetwo halves were analyzed by SEM. The preparationswere evaluated in the apical, middle, and coronalportions for the amount of superficial debris at ¿100magnification and the amount of remaining smearlayer at ¿780 magnification. Each specimen wasgraded using a scoring system. Group 3 (ultrasonic

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retrotip) had significantly less superficial debris(P∞0.05). However, group 2 (burπacid etching) sig-nificantly (P∞0.05) showed the least amount of smearlayer and the greatest amount of clean dentin andpatent tubules, especially in the apical one-third ofthe cavity. No technique effectively removed thesmear layer in the coronal one-third of the prepara-tion.

Engel & Steiman (14) compared three differenttechniques of root-end cavity preparation. Thirty ex-tracted human roots containing two canals were se-lected to examine isthmus instrumentation. Following

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conventional root canal preparation and obturation,the apical third of the root end was resected perpen-dicular to its long axis. Three different root-end prep-aration techniques were analyzed: In group 1, prep-arations were made with a round bur in a slow-speedhandpiece. In group 2, the teeth were prepared ident-ically to group 1, but an ultrasonic retrotip was ad-ditionally applied for 10 s. In group 3, only the ultra-sonic instrument was used for root-end preparation.All root ends were stained with methylene blue dyeand photographed at ¿20 magnification before andafter retrograde instrumentation. Ultrasonically pre-pared cavities were found to be significantly smallercompared to the other two techniques (P∞0.02 and0.001). In contrast, the ultrasonic instrumentation re-sulted in less canal debridement with some residualgutta-percha remaining on the walls. Preparationtime did not significantly differ between the conven-tional and the ultrasonic technique (P±0.20).

Gorman et al. (15) performed a similar study with30 extracted human teeth. Following standard rootcanal instrumentation, canals were obturated with lat-erally condensed gutta-percha and sealer. The rootends were then resected at a 45æ angle 3–5 mm fromthe apex. Three different techniques were used tomake 3-mm deep root-end preparations. In group 1,a round bur in a straight handpiece was used followedby ultrasonic instrumentation (Neosonic, Amadent,Cherry Hill, NJ) to refine the preparation. In group2, only the bur was used and teeth in group 3 wereprepared by ultrasonic instrumentation alone. Thesamples were then sputter-coated with gold-palladiumprior to SEM analysis. Photomicrographs at ¿600magnification were analyzed for the following par-ameters: presence of debris, smear layer, smoothnessand uniformity of preparation. The amount of debrisand smear layer was graded with scores from 0 (none)to 3 (heavy). Mean scores were calculated per par-ameter and group from the original data and areshown in Table 4. Statistically, the ultrasonic groupperformed significantly better than both other groupswith respect to smear layer removal (P∞0.01). Thecombination of bur and ultrasonic showed the leastamount of debris. No differences between the tech-niques were observed for smoothness or uniformity ofthe preparations.

Mehlhaff et al. (16) compared ultrasonic and burpreparations in three human adult cadavers to simu-late in vivo conditions. They selected 29 bilaterallymatched pairs of teeth for a total of 76 root-end prep-arations. Full-thickness flaps were reflected and anosteotomy performed. The size of the bony crypt andthe root bevel angle were determined by the need foraccess and visualization to attempt a 3-mm deep root-end preparation. Thirty-eight roots were preparedwith ultrasonic tips (CT-1 and CT-5, EIE) and 38roots were prepared using a round bur in a high-

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speed handpiece. Preparations were then filled withamalgam enabling subsequent radiographic measure-ments. After measuring the bony crypt, the remainingbuccal cortical bone was removed and the teeth wereextracted. Radiographs were then taken in a mesio-distal and bucco-lingual direction. The following par-ameters were measured radiographically using a digi-tal micrometer: depth of preparation, deviation ofpreparation from long axis of root, and bevel angleof root resection. None of the 76 specimens showeda root perforation. Only one (2.6%) ultrasonic prep-aration deviated from the long axis, whereas all burpreparations were at an acute angle to the root canal.Mean measurements of cavity depth were significant-ly greater for ultrasonic (2.51 mm) compared to bur(2.05) preparations. Also, a statistically significant dif-ference was found for the mean angle of root-end re-section (35.1æ for bur vs 16æ for ultrasonic prepara-tions) and for the bony crypt size (all P∞0.0001).

Lin et al. (17) measured different geometrical par-ameters of root-end cavities prepared by ultrasonicscompared to the conventional technique. Twentyroots from extracted human maxillary molars con-taining two canals and an isthmus were instrumentedand then obturated with gutta-percha and sealer.Subsequently, 3-mm root-end resections were madeperpendicularly to the long axis of the root. In group1, 3-mm deep root-end preparations including theobturated canals and the isthmus were carried outwith an ultrasonic retrotip (CT-5, EIE) and in group2 with a bur in a slow-speed micro-handpiece. Theroot ends were analyzed prior to and after instrumen-tation under a stereomicroscope. Images were cap-tured using a CCD camera for quantitative com-puter-aided evaluation. The mean increase for thecross-sectional area was 616% for cavities made byburs vs 326% for cavities prepared by ultrasonics. Amean loss of tooth structure of 30% was calculated forbur preparations compared to only 17.6% followingultrasonic instrumentation. Three out of 10 bur speci-mens showed root perforations in the isthmus area.All postoperative data were statistically significantlydifferent between the two groups (P∞0.0001). Themain concern with the bur preparations was thatroot-end preparations were irregularly shaped andpoorly centered with little dentin remaining at theisthmus area.

DiscussionSix studies have evaluated the geometry and cleanli-ness of root-end preparations made with microsurg-ical instruments (12–17). All studies compared thenew microsurgical technique to the conventional burtechnique. All but two studies were performed on ex-tracted human teeth. This has certainly simplified theroot-end preparation procedure compared to a clin-ical situation. The studies by Wuchenich et al. (12)


and by Mehlhaff et al. (16) were conducted in humancadaver teeth. Therefore, they are of particular inter-est, since they tried to simulate the clinical approach.Both studies found that preparations made with ultra-sonic retrotips are deeper and more parallel to theroot canal than those made by burs. These findingsare consistent with the concept that root-end prepara-tions should be 3-mm deep and follow the originalpath of the root canal (18). These requirements aremore easily achieved if straight line access can begained during the use of the root-end preparation in-strument.

One experimental study also demonstrated that thebevel of root-end resection needed for surgical accessto the root canal is significantly smaller for microsurg-ical tips than for conventional burs (16). Theseauthors also made a special effort to select bilaterallymatched pairs of teeth to exclude variations of toothposition and morphology that might have influencedthe outcome.

The amount of debris and smear layer productionwas addressed in three studies (12, 13, 15). The re-moval of debris and smear layer is of clinical import-ance, since they may serve as an avenue for leakageand prevent intimate contact of the root-end fillingwith the cavity walls. Root-end preparations, irrespec-tive of the technique used, resulted in a significantaccumulation of dentin debris and root canal fillingmaterials in the base of the root-end preparation (13).This material might serve as a reservoir of future con-tamination if coronal leakage occurred. Two studiesalso reported difficulty in removing gutta-percha withultrasonic instrumentation (13, 14). However, thismight be explained by the fact that the tested ultra-sonic retrotips used in these studies had a smoothworking tip without abrasive properties. Therefore, agutta-percha thermoplasticizing rather than a cuttingeffect was created. Diamond-coated retrotips withbetter cutting abilities might be advantageous in this

Table 5. Summary of experimental studies evaluating the cutting ability of retrotips


Waplington Displacement Extracted Light stereo- Ultrasonic tip CT-1 Amplitude range 26.5 to 46.5 mm,et al. 1995 amplitude of tips, human teeth microscope, (isthmus prep tip) depth of cut range 50 to 290 mm(21) cutting ability of tips profilometry Ultrasonic tip CT-2 Amplitude range 40.5 to 70.0 mm,

(depth of dentin cut) (main prep tip) depth of cut range 130 to 610 mm

Ultrasonic tip CT-3 Amplitude range 31.0 to 53.5 mm,(main prep tip) depth of cut range 70 to 470 mm

Devall et al. Cutting ability of sonic Bovine bone, Stereomicroscope with Sonic retrotips powered by sonic Cutting depth:1996 retrotips with respect 1-mm thick calibrated eyepiece handpiece (MM 1500) Full±half power; parallel±(22) to power setting, sections reticle at ¿50 perpendicular tip orientation;

orientation of tip, magnification narrow±wide tip; short±loading of tip, length long; 50±25 g load.of tip, and tip size(depth of cut)

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respect (19). Abedi et al. (20) suggested removing thegutta-percha with heat-carrying instruments beforeapplying the ultrasonic tip. In terms of smear layerremoval, ultrasonic tips performed better than burs.However, a considerable number of specimensshowed moderate to heavy smear layers (13, 15). Theimportance of using a citric acid and ferric chloridecombination to remove the smear layer prior toplacement of the root-end filling was therefore em-phasized. However, this etching agent failed to effec-tively remove the smear layer in the root-end prep-aration other than in its apical one-third (13).

The microsurgical technique clearly preservedmore tooth structure than the conventional technique(14, 17). Ultrasonic instrumentation was found to pro-duce less enlargement of the canal. Preparations werewell centered and thicker dentin walls were main-tained in ultrasonically prepared teeth compared tobur preparations. A more conservative root-end prep-aration is essential to prevent apical perforations orfractures, especially in deeply fluted or invaginatedroots with an isthmus.

2. Cutting ability of retrotips (Table 5)

Waplington et al. (21) investigated the cutting abilityof three ultrasonically driven retrotips in nine freshlyextracted human teeth. The teeth were sectioned lon-gitudinally and polished to produce a flat surface ontowhich the surgical tips could be applied. The ultra-sonic handpiece (Neosonic) had an operating fre-quency of 29 kHz. Three different tips with two geo-metrical designs were tested. The activated ultrasonictips were applied for 1 min using a load of 20 g at sixdifferent power settings. The depth of the dentin cutwas measured using a two-dimensional surface profi-lometry technique and ranged from 50 mm to 610mm. For all tips, the depth of cut increased in a linearmanner along with the displacement amplitude which

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Table 6. Summary of experimental studies evaluating the sealing ability following root-end cavity preparation with retrotips


Saunders Apical seal of EBA root- Extracted Stereomicroscopic Retroprep with a round bur Mean leakage score for 7 days: 0.7et al. 1994 end fillings following human teeth evaluation of dye (nΩ40; 20π20) Mean leakage score for 7 months: 2.2(23) three methods of root- penetration (gradation Retroprep with a round burπacid Mean leakage score for 7 days: 1.2

end preparation; analysis scoring 0–4; 0Ωno etching (nΩ38; 20π18) Mean leakage score for 7 months: 2.6after 7 days and 7 leakage; 4Ωleakage ±2

Retroprep with ultrasonic retrotip Mean leakage score for 7 days: 1.1months mm)(nΩ38; 19π19) Mean leakage score for 7 months: 3.1

O’Connor Apical seal of EBA and Extracted Stereomicroscopic Retroprep with ultrasonic, 0æ bevel, 44% of specimens with leakageet al. 1995 amalgam root-end human evaluation of dye Super-EBA retrofilling (nΩ17) beyond retrofilling(24) fillings following two teeth penetration Retroprep with ultrasonic, 0æ bevel, 87% of specimens with leakage

methods of root-end amalgam π cavity varnish for beyond retrofillingpreparation retrofilling (nΩ17)

Retroprep with .2 bur, 45æ bevel, 56% of specimens with leakageSuper-EBA retrofilling (nΩ17) beyond retrofilling

Retroprep with .2 bur, 45æ bevel, 100% of specimens with leakageamalgam π cavity varnish for beyond retrofillingretrofilling (nΩ17)

Lloyd et al. Apical leakage of Extracted Microscopic metric Retroprep with .8 round bur 45æ/amalgamΩ1.08 mm penetration1997 amalgam or Diaket human teeth evaluation of linear dye (nΩ4¿20) 45æ/DiaketΩ0 mm penetration(25) root-end fillings penetration 0æ/amalgamΩ1.4 mm penetration

following two different 0æ/DiaketΩ0.02 mm penetrationmethods of root-end Retroprep with sonic retrotip 45æ/amalgamΩ1.2 mm penetrationpreparation and two (MicroMega) (nΩ4¿20) 45æ/DiaketΩ0.13 mm penetrationdifferent resection angles 0æ/amalgamΩ0.37 mm penetration

0æ/DiaketΩ0.26 mm penetration

Chailertvanitkul Coronal seal of EBA Extracted Time delay for Retroprep with Mean leakage score 2.0et al. 1998 root-end filling human teeth contamination with a .8 round bur (nΩ17)(26) following two different polymicrobial marker Retroprep with ultrasonic tip CT3 Mean leakage score 0.7

methods of root-end (gradation score 0–4; (EIE) (nΩ18)preparation 0Ωno leakage at

60 days; 4Ωleakagewithin 1–15 days)

itself correlated with the power setting. The analyzedtips were capable of removing dentin across the fullpower range; however, a medium to high power set-ting was suggested to optimize their efficiency.

Devall et al. (22) performed an in vitro experimentin which they evaluated the effect of different vari-ables on the cutting ability of retrotips powered by asonic handpiece (MicroMega, Prodonta SA, Geneva,Switzerland). The following factors were investigated:power setting (half or full power), width (.35 or .55)and length (2 mm or 3 mm) of retrotip, tip orientation(parallel or perpendicular to long axis of handpiece),and tip loading (25 g or 50 g). One-millimeter thicksections of bovine bone were instrumented for 10 s.The depths of the cuts measured with a stereomicro-scope at ¿50 magnification ranged from 0.2 mm to0.45 mm. All factors tested had a significant effect onthe cutting performance of the sonic retrotips(P∞0.05). The most significant effect was determinedfor the power setting (P∞0.001). The parallel orien-

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tation of the tips produced deeper cuts than the per-pendicular orientation. The narrow tips cut morethan the wide tips, and the short more than the long.The least significant variable upon the cutting abilitywas load applied to the retrotip.

DiscussionTwo studies have been published which determinedthe cutting characteristics of microsurgical instru-ments, one evaluating ultrasonically (21) and theother sonically powered retrotips (22). The depth ofthe cuts was strongly correlated with the power settingfor all tested microsurgical retrotips. The study onultrasonic retrotips also clearly showed a linear in-crease of the displacement amplitude with increasingpower settings. But the amount of oscillation is notsolely determined by the power setting, but also bythe tip design, especially by the angulation and posi-tion of bends. This correlation was also demonstratedin the study evaluating the cutting ability of sonic re-


trotips where a tip orientation parallel to the driverhead resulted in more cutting, probably because ofthe vertical rather than horizontal oscillation of thepowered tip with respect to the driving handpiece.However, in a clinical situation, access to root endsrequires bent instruments with a horizontal oscillationplane relative to the cutting end of the working tips.The recorded cutting depths were minimal, rangingfrom 0.05 mm to 0.61 mm for ultrasonic retrotips andfrom 0.2 mm to 0.45 mm for sonic retrotips. How-ever, this is not a shortcoming since a conservativecavity preparation reduces the risk of perforation ormicrofracture of the root end. No studies have beenpublished on the cutting characteristics of retrotipswith roughened or coated working ends. It would beclinically relevant to know whether such instrumentsenhance canal debridement compared to retrotipswith a smooth working end, and how such instru-ments alter the root-end morphology.

3. Sealing ability of root-end fillings placed into cavitiesprepared with retrotips (Table 6)

Saunders et al. (23) evaluated the apical seal of root-end fillings following three different techniques ofroot-end preparation. The root canals of 116 ex-tracted human teeth were instrumented and obtu-rated with gutta-percha and sealer. Subsequently, rootends were resected at a 45æ angle. In group 1, a 2–3-mm deep root-end preparation was made using around bur in a slow-speed handpiece. Teeth in group2 received the same treatment, but the apical cavitywas subsequently flushed with a 10% citric acid and3% ferric chloride solution for 60 s. In group 3, anultrasonic retrotip was employed to prepare a 2–3-mm deep apical cavity. All cavities were then obtu-rated with EBA cement. Apical dye leakage of indiaink was analyzed after 7 days (in 59 teeth) and after7 months (in 57 teeth) using a stereomicroscope at¿6 magnification. A gradation score of 0–4 was ap-plied for each specimen depending on the depth ofdye penetration. No statistically significantly differentleakage was found between the three preparationtechniques at either time point. However, 7-monthspecimens showed significantly more leakage than 7-day specimens irrespective of the preparation tech-nique (P∞0.01). In addition, the ultrasonic techniqueproduced significantly more cracks at the root endthan the conventional bur technique (P∞0.001).

O’Connor et al. (24) investigated the apical leakageof amalgam and EBA root-end fillings with twomethods of root-end preparation. Seventy-six ex-tracted human teeth were instrumented and obtu-rated with laterally condensed gutta-percha. How-ever, no sealer was used to simulate a poorly obtu-rated root canal. Four groups each containing 17teeth were treated as follows: in groups 1 and 2, per-

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pendicular root-end resections were made 3 mm fromthe apex with subsequent ultrasonic (Neosonic) prep-aration of a 3-mm deep cavity. In groups 3 and 4,specimens were resected at a 45æ bevel 3 mm fromthe apex and root-end preparations were made with around bur in a micro-handpiece. For root-end filling,Super-EBA cement was used in groups 1 and 3, andamalgam with cavity varnish in groups 2 and 4. After4 months, root-end filled teeth were coated with nailpolish except for the cut root face and suspended inan aqueous solution of 1% methylene blue dye for 2weeks. After longitudinal separation, dye penetrationwas graded under a stereomicroscope at ¿6 magnifi-cation as either acceptable (no leakage beyond root-end filling) or unacceptable (leakage beyond root-endfilling). Irrespective of root-end bevel and cavity prep-aration technique, Super-EBA root-end fillings dem-onstrated significantly less dye penetration than amal-gam and varnish. Although the ultrasonic prepara-tions tended to show less leakage than burpreparations, no statistically significant difference wasfound between the two techniques (P±0.05).

Lloyd et al. (25) analyzed the apical seal of tworoot-end filling materials following two root-end prep-aration techniques. The crowns of 172 recently ex-tracted human teeth were removed and the canalswere instrumented and obturated using gutta-perchaand sealer. The teeth were then randomly assigned toeight treatment groups (each with 20 teeth) combin-ing three variables such as bevel of root-end resection(0æ or 45æ bevel), cavity preparation (round bur orsonic retrotip (MicroMega), and root-end filling(amalgam or Diaket). Specimens were then coatedwith sticky wax and nail varnish and placed into indiaink for 2 weeks. Following demineralization of theteeth, the maximum linear dye penetration wasexamined at ¿10 magnification. No significant differ-ence in leakage was observed between the two cavitypreparation techniques or between the two resectionangles. Amalgam fillings exhibited significantly morelinear leakage than Diaket irrespective of the twoother variables. In addition, root-end preparationsmade with sonic retrotips resulted in significantlymore root canal enlargement compared to cavitiesprepared by burs (P∞0.05).

Chailertvanitkul et al. (26) evaluated the coronalleakage of EBA root-end fillings following two root-end preparation techniques in extracted human teeth.Root canal treatment included instrumentation andobturation with gutta-percha and sealer. After a stor-age period of 6 months in artificial saliva containingGentamycin, the root-ends were resected 3–4 mmperpendicularly to the long axis and crowns were re-moved. In group 1, at least 3-mm deep root-endpreparations were made using a round bur, while ingroup 2, an ultrasonic tip (CT-3, EIE) was employedfor root-end preparation. Super-EBA cement was

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placed into the root-end cavity. Instead of assessingdye penetration from the apical aspect, specimenswere attached to a coronal chamber containing mi-crobial markers of anaerobic streptococci and Fusobac-terium nucleatum. The cut root surface was placed in‘‘Brain Heart Infusion Broth’’ (BHIB) in an apicalchamber. The time taken for the broth to becometurbid following bacterial penetration and contami-nation was recorded as an indicator of leakage. Scor-ing (0–4) was based on the number of days for leakageto occur. After 90 days, the ultrasonic group showedsignificantly fewer specimens with complete leakagethan the bur group (P∞0.05).

DiscussionFour studies (23–26) have evaluated the sealing abilityof root-end fillings placed into ultrasonically orsonically and conventionally prepared root ends. It isdifficult to compare the studies because of the vari-ations of treatment parameters such as different leak-age methods (apical or coronal leakage, dye or poly-microbial penetration, leakage distance or time re-quired for leakage), various root-end filling materials(amalgam, amalgam π varnish, EBA, Diaket), anddifferent bevels of root-end resection (0æ or 45æ). Inaddition, the period after placing the root-end fillinguntil dye or microbial exposure and the duration ofexposure showed considerable variability (Table 7).

The study by Chailertvanitkul et al. (26) should beregarded as the most clinically relevant with respect tomethodology of leakage assessment and time intervalsselected. It is the only study to analyze coronal leak-age using a polymicrobial marker. The purpose ofplacing a root-end filling material is to prevent pene-tration of microorganisms and irritants from the rootcanal system into periradicular tissues (27). Therefore,the assessment of the coronal seal of root-end fillingmaterials is clinically more relevant than the determi-nation of the apical seal (28). In addition, a short set-ting time for the root-end filling prior to an immedi-ate, but extended period of exposure is a more de-manding model and better simulates the clinicalsituation. The study by Chailertvanitkul et al. (26) wasthe only one to demonstrate significantly less (coronal)leakage of root-end fillings following ultrasonic root-

Table 7. Summary of experimental studies evaluating delayed exposure toleakage tracers

Time period between Length ofroot-end obturation exposure to

Study and exposure to tracer tracer

Saunders et al. 1994 (23) 7 days or 7 months 90 hoursO’Connor et al. 1995 (24) 4 months 2 weeksLloyd et al. 1997 (25) N/A 2 weeksChailertvanitkul et al. 1998 (26) 1 day Up to 90 days

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end preparation compared to bur preparation. Allother leakage studies (23–25) found no statistically sig-nificant differences between root-end preparationtechniques within the limits of apical dye penetrationstudies.

Saunders et al. (23) reported that root ends thathad been acid-etched showed leakage from the cutroot face into the dentinal tubules, indicating that thesmear layer produced during resection had been re-moved. Since all teeth in that study had a resectionangle of 45æ, this was indirect proof that many tubulesbecame patent following a beveled root-end resection.This is of clinical concern, because microorganismsresiding in the tubules might move through patentopenings into the periapical area. In addition, patenttubules may serve as a pathway of communicationbetween the root canal and the periradicular tissueunless the root-end filling extends beyond the mostcoronal point of the resection bevel (29, 30). Thesefindings were recently corroborated by a study evalu-ating the influence of resection angle on the apicalseal (31). Standardized resections either perpendicularto the long axis of the root or at an angle of 45æ weremade followed by ultrasonic root-end preparationand placement of Super-EBA cement. Apical dyepenetration from the cut root surface into the dentinaltubules and along the interface of the cavity walls andthe root-end filling was investigated. Results showedless infiltration both in dentin and along the root-endfilling with the perpendicular resection plane. In sum-mary, all these observations emphasize the need toperform a perpendicular rather than a beveled resec-tion.

The studies comparing different root-end fillingmaterials showed more leakage with amalgam com-pared to cements (Diaket or EBA). However, it is be-yond the scope of this review to discuss root-end fill-ing materials.

4. Root-face alterations following root-end preparation withretrotips

Abedi et al. (20) determined the effects of bur andultrasonic preparation on the root apex followingroot-end resection. Forty-seven extracted humanteeth with standardized root-end diameters were in-strumented and obturated using gutta-percha andsealer. Following root-end resection, epoxy resin rep-licas were made from polyvinylsiloxane impressions.Each root was also photographed at ¿30 magnifi-cation. The root ends of one group were prepared bymeans of a fissure bur, whereas the other group re-ceived root-end preparations with an ultrasonic tip(CT-2, EIE) driven by either an Enac (Osada ElectricCo., Tokyo, Japan) ultrasonic unit or a Neosonicultrasonic unit. Photographs and root replicas weremade of all specimens and pre- and postoperative


replicas and original specimens were sputter-coatedwith gold for SEM analysis. The following parameterswere assessed: cracks present before and/or afterroot-end preparation, percentage increase of cavitysize following preparation, correlation between pres-ence of cracks and width of thinnest dentin wall aftercavity preparation. A significantly lower incidence ofcrack formation was found after bur preparationcompared to ultrasonic preparation (P∞0.05). No dif-ference was observed for the two ultrasonic units.Cavities prepared by burs showed a larger mean in-crease compared to ultrasonically prepared cavities,but without correlation to crack formation. However,cracking correlated with the remaining width of den-tin walls, with 95% of cracks found in the thinnestpart of the cavity wall. When the remaining dentinwall was thinner than 1 mm 75% of ultrasonicallyprepared root-ends developed cracks, whereas thisphenomenon was never observed in bur preparations.

Layton et al. (32) evaluated root ends after apico-ectomy and after ultrasonic instrumentation at lowand high power settings. Thirty unobturated and bi-laterally matched extracted human teeth were re-sected perpendicularly 3 mm from the root tip. Subse-quently, 3-mm deep root-end cavities were preparedusing ultrasonic tips (CT-1 and 5, EIE). The prepara-tions in group 1 were made at the lowest power set-ting, whereas in group 2, the highest power settingwas applied. Before and after cavity preparation, theroots were immersed in methylene blue dye. There-after, the root surfaces were analyzed under a stereo-microscope at ¿20 and ¿63 magnification. Differ-ences in the numbers and types of cracks followingroot-end preparation compared to those seen afterroot-end resection were recorded. In the low-power-setting group 40% of teeth and in the high-power-setting group 47% of teeth developed cracks afterultrasonic root-end preparation compared to 20%and 17%, respectively, observed after root-end resec-tion only. While there was a significant difference(P∞0.05) for the overall greater percentages of teethwith cracks seen after ultrasonic preparation com-pared to resection only, no statistically significant dif-ference was found between the two power settings.However, significantly more cracks per tooth wereobserved in the high-power-setting group, whencracking did occur. Cracks radiating from the canalspace were far more often seen than intradentincracks.

Frank et al. (33) examined the effects of five differ-ent root-end preparation techniques on root apices.Sixty extracted human roots were resected 2–3 mmfrom the apex. Using a microscope at ¿16 magnifi-cation, no existing fracture lines were detected afterstaining the resected root ends with methylene blue.The following apical preparation techniques were ap-plied: group 1 no preparation (controls), group 2 a

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round bur in a high-speed handpiece, group 3 around bur in a slow-speed handpiece, group 4 a sonicretrotip (MicroMega), group 5 an ultrasonic retrotip(EIE) with a medium power setting, and group 6 anultrasonic retrotip (EIE) with a high power setting.After root-end preparation, the root tips were againstained and examined at ¿10 magnification for thepresence of infractions. The frequency of infractionsis listed in detail in Table 8. The highest number ofinfractions was observed in ultrasonically preparedroot-ends with a high power setting. In addition, bi-concave roots were more susceptible to infractionsthan oblong or round root-ends. Also root tips with adiameter of less than 3 mm developed more infrac-tions than those with a diameter of 3 mm or greater.However, no statistically significant difference wasfound for the occurrence of infractions based on root-tip morphology.

Lloyd et al. (34) analyzed chipping and crackingfollowing root-end cavity preparation using a sonicretroprep tip or a bur. Eighty extracted human teethwere instrumented and obturated using thermoplasti-cized gutta-percha and sealer and divided into fourgroups of 20 teeth each. In group 1, a perpendicularresection 3–4 mm from the apex was made with sub-sequent root-end preparation using a sonic retrotip(MicroMega). In group 2, the same instrument wasused for cavity preparation, but the root ends wereresected at a 45æ bevel. Teeth in groups 3 and 4 wereresected like those in groups 1 and 2 respectively, butcavities were prepared with a round bur and an in-verted cone bur in a handpiece. The cut root facesand the prepared root-end preparations were thenreplicated in resin and were sputter-coated with goldfor SEM analysis. Each specimen was photomicro-graphed at ¿20 magnification to evaluate crackingand at ¿80 magnification to evaluate chipping of thecavity margins. No significant difference between thefour groups was observed for the incidence of crack-ing, (range 0% to 15%). Four out of a total of fivecracks in 80 specimens were seen after sonic instru-mentation. However, the authors were not sure ifthese lateral canals had been exposed during the re-section process. Unfortunately, no root replicas wereobtained following resection alone. Bur preparationshad significantly less chipping of the cavity marginsthan sonic preparations (P∞0.001). Regardless of thecavity preparation technique, teeth with a perpen-dicular resection showed significantly fewer alter-ations than those with a beveled resection (P∞0.005).

Waplington et al. (35) evaluated the incidence ofroot face alterations following ultrasonic cavity prep-aration over a full range of power settings in compari-son to conventional bur preparation. Fifty-five ex-tracted human teeth were instrumented and obtu-rated with gutta-percha and sealer. Root ends wereresected perpendicularly to the long axis of the root

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Table 8. Summary of experimental studies evaluating root-face alterations following root-end cavity preparation with retrotips


Abedi Crack formation Extracted Light and scanning Retroprep with fissure bur (nΩ24) Cracks formed or deteriorated in 33%;et al. following root-end human teeth electron microscopy cavity increase 480%1995 cavity preparation, using the resin Retroprep with ultrasonic CT-2 tip in Cracks formed or deteriorated in 70%;(20) increase of cavity size replica technique Enac unit (nΩ11) or in Neosonic unit cavity increase 200% (Enac)

(nΩ12) and 333% (Neosonic)

Layton et al. Evaluation of frequency Extracted Immersion of prepared Retroprep with ultrasonic tip (EIE) at 40% of teeth showed a total of 161996 and types of cracks human teeth roots in methylene blue lowest power setting (nΩ30) cracks(32) following ultrasonic (bilaterally solution; Retroprep with ultrasonic tip (EIE) at 47% of teeth showed a total of 26

root-end preparation matched) stereomicroscopic highest power setting (nΩ30) cracksanalysis at ¿20 and¿63 magnification

Frank et al. Infractions of dentin Extracted Root-tips stained with No retroprep (control group) (nΩ15) 0% with infractions1996 following five different human methylene blue before Retroprep with .1 bur and high- 33.3% with infractions(33) methods of root-end teeth and after retroprep, speed handpiece (nΩ9)

cavity preparation visual analysis of Retroprep with .1 bur and slow- 11.1% with infractionsphotographs at ¿10 speed handpiece (nΩ9)magnification

Retroprep with sonic retrotip (nΩ9) 22.2% with infractions

Retroprep with ultrasonic tip at 11.1% with infractionsmedium power (nΩ9)

Retroprep with ultrasonic tip at 55.6% with infractionshigh power (nΩ9)

Lloyd et al. Degree of chipping Extracted SEM analysis with Retroprep with sonic tip, no bevel Mean chipping score: 1.651996 and cracking following human teeth photomicrographs at (nΩ20) Cracking 15%(34) four methods of root-end ¿20 and ¿80 Retroprep with sonic tip, 45æ Mean chipping score: 2.2

preparation magnifications. bevel (nΩ20) Cracking 5%Chipping-scoring 1 Retroprep with round and inverted Mean chipping score: 1.1(best) – 3 (worst), cone burs, no bevel (nΩ20) Cracking 0%cracking yes or no

Retroprep with round and inverted Mean chipping score: 1.55cone burs, 45æ bevel (nΩ20) Cracking 5%

Waplington Cracks and chipping of Extracted SEM analysis of resin Retroprep with CT-1 or CT-2 No cracks; marginal chipping scoreet al. 1997 cavity margins human teeth replicas of preparations ultrasonic tips at five different power for CT-1Ω1.24 and for CT-2Ω1.57(35) (at ¿50 magnification) settings (10 groups, nΩ5)

Score 1–3 for chipping Retroprep with .1 rotary bur in No cracks; marginal chipping scoreΩcontra-angle handpiece (nΩ5) 1.0

Beling et al. Cracks following root- Extracted Immersion in methylene Retroprep of uninstrumented and After resection: 5 cracks in 4 teeth, after1997 end preparation in human teeth blue, analysis with unfilled teeth with CT-5 and CT-1 retroprep: 6 cracks in 4 teethΩ1 new(36) unfilled and filled teeth stereomicroscope at (EIE) ultrasonic tips (nΩ20) crack (5% of teeth developed cracks)

¿20-¿63 magnification Retroprep of instrumented and After resection: 5 cracks in 2 teeth, afterobturated teeth with CT-5 and CT-1 retroprep: 7 cracks in 4 teethΩ2 new(EIE) ultrasonic tips (nΩ20) cracks (10% of teeth developed cracks)

Min et al. Number, width and Extracted Confocal microscopy No retroprep (control group) 50% with cracks; max width 23 mm;1997 length of cracks human molar and histologic (nΩ10) max length 254 mm; max depth 653 mm(37) following different teeth examination Retroprep with .331/3 inverted 60% with cracks; max width 84 mm;

root-end preparation of 6-mm thick serial cone bur in microhead handpiece max length 494 mm; max depth 906 mmtechniques sections of the root- (nΩ10)

ends Retroprep with ultrasonics (EIE) at 100% with cracks; max width 52 mm;lowest power (nΩ10) max length 620 mm; max depth 1432 mm

Retroprep with ultrasonics (EIE) at 100% with cracks; max width 66 mm;intensity 5 (nΩ10) max length 615 mm; max depth 1740 mm

Calzonetti Microfractures Human Examination of pre- Retroprep with ultrasonic tip AP4– No microfractures observedet al. following root-end cadaver and postop impressions 90 and Enac unit (nΩ26)1998 cavity preparation teeth with a stereomicroscope Retroprep with ultrasonic tip CT-1 No microfractures observed(38) and SEM and Mini-endo unit (EMS) (nΩ26)

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Table 9. Comparison of ultrasonic/sonic and bur application with respect to different parameters of root-end cavity preparation (REP)

Parameter Comparison Studies

Depth of cavity Ultrasonic±Bur Wuchenich et al. (12), *Mehlhaff et al. (16)Parallelism of cavity to canal space or long axis of root Ultrasonic±Bur Wuchenich et al. (12), Mehlhaff et al. (16)Amount of smear layer Ultrasonic±Bur Wuchenich et al. (12), *Gutmann et al. (13), *Gorman et al. (15)Amount of superficial debris Ultrasonic±Bur Wuchenich et al. (12), *Gutmann et al. (13)

Ultrasonic∏Bur *Gorman et al. (15)Canal debridement Bur±Ultrasonic *Gutmann et al. (13), *Engel & Steiman (14)Root perforation Ultrasonic±Bur *Lin et al. (17)Remaining thickness of dentinal wall Ultrasonic±Bur *Lin et al. (17)Loss of tooth structure Ultrasonic±Bur *Engel & Steiman (14), *Lin et al. (17), Abedi et al. (20)

Bur±Sonic *Lloyd et al. (25)Root-face alterations (cracks, microfractures) Ultrasonic∏Bur Waplington et al. (35)

Bur±Ultrasonic *Abedi et al. (20), *Saunders et al. (23), *Min et al. (37)Chipping of cavity margins Bur±Ultrasonic *Waplington et al. (35)

Bur±Sonic *Lloyd et al. (34)Time needed for preparation Ultrasonic∏Bur *Engel & Steiman (14)

Bur±Ultrasonic Gutmann et al. (13)Bevel angle needed for REP Ultrasonic±Bur *Mehlhaff et al. (16)Size of bony crypt needed for REP Ultrasonic±Bur *Mehlhaff et al. (16)Apical leakage of retrofilling Ultrasonic∏Bur *Saunders et al. (23), *O’Connor et al. (24)

Sonic∏Bur *Lloyd et al. (25)Coronal leakage of retrofilling Ultrasonic±Bur *Chailertvanitkul et al. (26)

Comparison: ±performed better than, ∏performed similar to.Studies: *preceding author’s nameΩstatistics were performed.

3 mm from the apex. Root-end preparations werecreated at five different power settings and with twodifferent tip designs (CT-1 and 2, EIE). This resultedin 10 experimental groups with five teeth each. Theremaining five teeth received a conventional root-endpreparation with a rotary bur in a contra-angle hand-piece. Tips and burs were marked at 3 mm to obtainstandardized cavity depths. Replica models were thenmade using a silicone impression material and epoxyresin to reproduce root-end preparation details.Photomicrographs were taken at ¿50 magnificationunder an SEM. Cracking was assessed as present orabsent, whereas chipping of the cavity margin wasscored from 1–3 (1Ωnone, 2Ωmodest, 3Ωsevere). Nocracks were evident in any of the specimens. How-ever, all ultrasonically prepared cavities showed chip-ping of the margins. The CT-2 tip produced signifi-cantly more chipping than the CT-1, and both tipsproduced significantly more chipping with increasedpower settings. No marginal chipping was observedin any of the bur preparations.

Beling et al. (36) investigated cracks in ultrasonic-ally prepared root ends of teeth with or without in-strumentation and obturation. Forty extracted humanteeth were divided into two groups. In group 1, theteeth were left uninstrumented. In group 2, root ca-nals were instrumented and obturated with gutta-per-cha, lateral condensation and sealer. Subsequently, allteeth were perpendicularly resected at 3 mm from theapex. Root-end preparations were then made in allteeth using ultrasonic retrotips (CT-1 and 5, EIE) atthe lowest power setting. Roots were inspected for

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cracks at the cut root surface with a stereomicroscopeat ¿20 to ¿63 magnification after resection aloneand after root-end preparation. To aid in detection ofcracks, teeth were placed in a methylene blue dyesolution for 48 h. After root-end resection, five crackswere observed in four unobturated teeth and fivecracks were present in two obturated teeth. Onlythree more cracks developed after ultrasonic root-endpreparation: one crack in an unfilled tooth, and twonew cracks associated with two filled teeth. All cracksforming after ultrasonic instrumentation were incom-plete canal cracks. No statistically significant differ-ences were found between any of the groups.

Min et al. (37) examined serial histologic sectionsof root ends prepared either with ultrasonics or con-ventionally to detect structural alterations. Forty rootsof extracted human molar teeth were divided in fourgroups of 10 each. The apical 3 mm of each root wasresected at a 90æ angle. Group 1 included the controlteeth without root-end preparation. In group 2, a 2-mm deep root-end preparation was made with an in-verted cone bur in a microhead handpiece. Group 3received 2-mm deep root-end preparations with ultra-sonic tips (CT-3 and 5, EIE) at the lowest power set-ting. The same ultrasonic instruments were used ingroup 4 at an intensity level midway between the low-est and highest power settings. All roots were thenetched with 37% phosphoric acid to remove thesmear layer before they were placed in a fluorescentdye (Eosin Y) solution for 30 min. The specimenswere analyzed for structural alterations using a con-focal microscope. Thereafter, serial histological sec-

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tions of 6-mm thickness obtained from the most apical2 mm and at the 3-mm and 4-mm levels were stainedwith hematoxylin and eosin. The sections were exam-ined for the number, width, length, and depth of frac-tures under light microscopy at ¿40 and ¿100 mag-nification. The data of the histologic analysis up tothe 2-mm levels are listed in Table 8. The controlgroup and the group with the bur preparations hadsignificantly fewer fractures than both ultrasonicgroups. Also, the fracture width was significantlysmaller in the control group compared to the findingsin both ultrasonic groups. However, no differenceswere found for crack length or depth between thefour groups. At the 3- and 4-mm levels, only the pres-ence or absence of fractures was recorded, and nosignificant differences were found between the fourgroups.

Calzonetti et al. (38) investigated the incidence ofmicrofractures following root-end preparations incadaver teeth. In situ impressions were used for SEManalysis of root-face alterations. The canals of 52roots of bilaterally matched teeth were prepared andobturated with gutta-percha and sealer. After 7 days,flaps were reflected and roots were exposed followingosteotomy. Root ends were then resected 3 mm fromthe apex and flushed with 35% phosphoric acid.Using customized minitrays, polyvinylsiloxane im-pressions were made of the cut root faces before root-end cavity preparation. Cavities were prepared usingtwo different ultrasonic instruments (AP4–90, Enac;and CT-1, EIE). The tips were activated with watercoolant for 2 min. Thereafter, impressions were takenas described above. Pre- and postoperative im-pressions were sputter-coated with platinum subse-quently examined under a stereomicroscope (¿20)and with a scanning electron microscope (¿25, ¿50,¿100). Root faces showed some irregularities andgrooves due to the ultrasonic tip ‘‘skidding’’. How-ever, no microfractures were seen in any of the speci-mens. The authors concluded that under the con-ditions of the study, ultrasonic root-end cavity prep-aration did not cause root dentin microfractures inendodontically treated teeth.

DiscussionSince the introduction of microsurgical retrotips, themajority of experimental studies on these instrumentshave evaluated root-end alterations possibly inducedby apical instrumentation. All eight studies addressingthis subject were in vitro studies (20, 32–38). One studywas performed in human cadavers (38), while theother seven were conducted in extracted humanteeth. It is difficult to transfer the results obtainedfrom extracted teeth to the completely different en-vironment of the clinical situation. The periodontalligament may act as a dampening and absorbing fac-tor preventing the propagation of cracks following vi-

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bratory root-end preparation with sonics or ultrason-ics. It has also been claimed that tooth desiccationand brittleness following extraction and SEM prep-aration may produce artifactual microfractures (38).

Calzonetti et al. (38) found no cracking formationin ultrasonically prepared root ends in cadaver teethincluding smaller roots of molar teeth. However, itmust also be mentioned that the retrotips were acti-vated at low power settings and no data were givenfor the depth of the preparations. In fact, the CT-1tip used in one group has been shown to have a lowoscillation amplitude with a low cutting ability (21).Under the limitations mentioned above for in vitrostudies using extracted human teeth, the results ofCalzonetti et al. (38) were corroborated by the studyof Waplington et al. (35) in which efforts were madeto obtain standardized 3-mm deep cavities. Again, nomicrofractures were observed with ultrasonic retrotips(CT-1 and 2, EIE) tested over a full power range.However, significantly more chipping of the cavitymargins were observed in ultrasonic than in bur prep-arations. This finding was corroborated by Lloyd etal. (34), who also found little evidence of chipping inbur preparations, while sonic preparation producedsignificant chipping of the cavo-margins. However, itis questionable whether this surface alteration altersthe success rate of clinical treatment since the chip-ping is shallow and does not extend into the cavity.In addition, removing more tissue in the plane of re-section can easily refine a chipped cavity margin.

The depth of possible microfractures was evaluatedhistologically by Min et al. (37). The observed cracks(maximum depth 1.74 mm) never reached the depthof the cavity (2 mm) following ultrasonic root-endpreparation. It is important that cracks present in50% of the resected teeth without apical preparationhad a depth of 0.65 mm. It cannot be excluded withcertainty that these preexisting cracks propagated thedevelopment of deeper cracks following ultrasonic in-strumentation. The role of preoperative cracks on thesuccess of periradicular surgery warrants further in-vestigation. The use of extracted teeth limits the inter-pretation of the results because of the absence of peri-odontal support. A better approach would be to do anexperimental in vivo study in a suitable animal model.

5. Fracture of microinstruments

Walmsley et al. (39) investigated whether the break-age of ultrasonic root-end preparation tips is relatedto the tip design. Ten different tips were tested in anultrasonic unit (Enac) at the highest power setting.Tips were evaluated by SEM before and after com-pletion of the experiment. Extracted human teethwere instrumented, but left unobturated. The rootswere then resected 2–3 mm from the apex. To ensurethat a constant load was applied while the tip was


activated, each tooth was attached on a pan balance.Root ends were prepared for three 5-min periods withan initial load of 100 g that was increased by 100 gfor each preparation period. Two retrotips and anamalgam condenser tip broke while two other instru-ments demonstrated bending of the working tip. Allbroken instruments had a working tip angle greaterthan 45æ. Breakage always occurred approximately 2–3 mm from the end at a bend in the retrotip.

DiscussionA single study (39) addressed the problem of instru-ment fracture when ultrasonically driven microsurg-ical instruments were used for root-end cavity prep-aration. Angulation of retrotips increases the trans-verse oscillation and decreases the longitudinaloscillation, putting the greatest strain on the bend ofthe instrument. It is therefore recommended not toput excessive load on the activated retrotips.Walmsley et al. (39) also suggested reducing the angu-lated design and producing thicker instruments to re-sist breakage. However, a straighter design will re-strict access to difficult to reach areas, and thickerinstruments prevent instrumentation of fine root ca-nals and isthmuses.

Clinical studies

The first clinical study evaluating ultrasonic root-endpreparation was published in 1996 by Sumi et al. (40).They examined clinically and radiographically theoutcome of periradicular surgery of 157 teeth in 86patients. Root-end resection was performed almostperpendicular to the long axis of the root and 3- to3.5-mm deep apical cavities were prepared with anultrasonic tip (type not specified). The preparationswere filled with gutta-percha and Super-EBA cement.The bony crypt was irrigated with saline containingantibiotics prior to wound closure. A postoperativeradiograph was taken 2 or 3 days later. Follow-upexaminations including radiographs were performedevery 6 months. The follow-up period ranged from 6months to 3 years. Success was defined as the absenceof clinical symptoms and disappearance or regressionof the periapical radiolucency compared to the post-operative radiograph. In all, 92.4% of the teeth wereclassified as successful.

A year later, the same authors published a prelimi-nary report on the use of a specialized ultrasonic tipfor root-end preparation with a congruous titanium-inlay for root-end obturation (41). One hundred andeight teeth were treated in 48 patients with follow-upperiods ranging from 1 month to 12 months. Again,an almost perpendicular apical resection was per-formed with subsequent ultrasonic root-end prepara-tion. The cavity was obturated with a titanium inlayand sealed with Super-EBA cement. Further treat-

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ment, examinations, and success criteria were identi-cal to the study mentioned before. For 56 teeth, thefollow-up period exceeded 6 months and no failureswere recorded.

Bader & Lejeune (42) published the first clinicalstudy comparing ultrasonic and conventional root-end preparations. The study comprised 320 teeth as-signed to four groups of 80 teeth each. Four differenttechniques of periradicular surgery were evaluated.Perioperative medication was identical for each groupand included amoxicillin for 8 days and a steroid for3 days. Postoperatively, patients received an analgesicand chlorhexidine mouthwash. The following treat-ment options were investigated. In groups 1 and 2, amicrobur was used for root-end preparation followingroot-end resection. In groups 3 and 4, root-end prep-arations were made with ultrasonic tips (EMS). In ad-dition, the exposed radicular dentin in groups 2 and4 were irradiated with a CO2 laser for 5 s. All root-end preparations were then filled with IRM. After12 months, all cases were reevaluated clinically andradiographically. Teeth without clinical signs andshowing radiographic healing were classified as suc-cessful. Success rates for ultrasonically treated teeth(95% in group 3 and 90% in group 4) were signifi-cantly better than those treated with microburs (65%in group 1 and 68% in group 2). The laser treatmenthad no apparent effect on the success rate.

Rubinstein & Kim (43) investigated the outcome ofultrasonically prepared root ends in a prospectivestudy over a period of 14 months. Ninety-four teeth(32 anterior teeth, 31 premolars, and 31 molars) weresubjected to periradicular surgery under a surgicaloperating microscope. All root ends were resectedperpendicular to the long axis and were subsequentlyprepared with appropriate ultrasonic tips (EIE) to adepth of at least 3 mm. For root-end filling, Super-EBA cement was used in all cases. All patients re-ceived antibiotics for 7 days starting 2 days preopera-tively. Recall radiographs were taken at 3-month in-tervals. Criteria for success were clinical function, ab-sence of symptoms, and the presence of a restoredlamina dura on the radiograph. A very high successrate of 96.8% was reported at the completion of thestudy after 14 months. A positive correlation was alsoobserved between the healing time and the smallerosteotomy sizes.

The first longitudinal results with an ultrasonictechnique for root-end preparation were reported byTestori et al. (44). In 95 root ends, preparations weremade with an ultrasonic tip (EIE) and filled with Su-per-EBA cement. Previously, 207 apices had beenprepared with the standard technique using a smallround bur. Root-end preparations in these teeth werefilled with amalgam. Therefore, the healing obtainedfor a certain root-end preparation technique couldnot be separated from the effect of the root-end filling

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material. Recall radiographs after a mean follow-upperiod of 4.6 years (range 1–6 years) were assigned tofour healing groups: complete, incomplete, and un-certain healing, and failure. The long-term successrates were 85% for the ultrasonic group and 68% forthe conventional group.

von Arx & Kurt (45) published the first clinicalstudy reporting the use of a sonic device for root-endcavity preparation. In a prospective study of 50 teeth,apical preparations were made with sonic and dia-mond-surfaced retrotips (KaVo SONICretro, KaVoGmbH, Biberach, Germany) following a 0æ bevel re-section 3 mm from the root tip. The apical prepara-tions were at least 2 mm deep. All root-end prepara-tions were filled with Super-EBA cement. Antibioticswere not routinely administered. Patients were fol-lowed for 1 year and standardized radiographs weretaken preoperatively, postoperatively and at the com-pletion of the study. Periapical healing assessment wasbased on anamnestic, clinical, and radiographic cri-teria and was categorized either as successful, im-proved, or failing. A mean percentage of 93% wascalculated for the osseous regeneration seen on radio-graphs after 1 year. 82% of all cases were classified assuccessful, 14% as improved, and 4% as failures.

Discussion

A literature search produced five clinical studies onultrasonic (40–44) and one study (45) on sonic root-end cavity preparation. Although the number of pub-lished clinical articles is not overwhelming, the out-come reported in these studies was extremely goodwith success rates ranging from 82% to 96.8%. Twostudies compared the ultrasonic technique with theconventional bur technique (42, 44). However, nei-ther study is a true comparative investigation, sincethe surgeons switched to the new technique when itbecame available, and analyzed the data of bur prep-arations retrospectively. In addition, Testori et al. (44)used two different root-end filling materials for thetwo different preparation techniques: amalgam in burprepared teeth and Super EBA-cement in ultrasonic-ally prepared teeth. In the other ‘‘comparative’’ study,all teeth received IRM root-end fillings (42). Signifi-cantly higher success rates of 95% and 90% were re-ported for the ultrasonic groups, with or without lasertreatment, compared to 65% and 67.5%, respectively,for the conventional group.

In general, it is difficult to attribute the high successrates of the reviewed clinical studies solely to the newroot-end preparation technique. Parallel to the use ofmicrosurgical instruments for apical preparation, themore frequent use of Super-EBA cement as a root-end filling material and new surgical visibility aidssuch as the surgical operating microscope may havepositively affected the outcome. In fact, all but one

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study used Super-EBA cement for root-end cavity ob-turation. It has been demonstrated experimentallyand clinically that this cement has properties leadingto successful healing when used as a root-end fillingmaterial (46–48).

The high success rates reported in the reviewedclinical articles also indicate that possible root-facealterations like cracks or microfractures followingsonic or ultrasonic instrumentation do not necessarilycompromise healing. The fractures, if present at all,probably do not reach the coronal level of the root-end filling which still provides a hermetic seal to po-tentially noxious agents within the root canal. Mostof these clinical studies also emphasized the advan-tage of a root-end resection perpendicular to the longaxis of the root. The avoidance of an angled rootsurface decreases the number of dentinal tubules thatform patent pathways from the canal following steepbeveled resections (49). This seems to be a major fac-tor in successful healing. In this respect, it has beenshown that a perpendicular resection requires a shal-lower root-end filling to prevent leakage (30).

The study by Rubinstein & Kim (43) is of particu-lar interest, because of the high success rate of 96.8%in a study population comprising 66% posterior teeth(33% molars and 33% premolars). The authors notedthat 80% of the molars presented with isthmuses. Themesial roots of mandibular first molars presented thehighest frequency of isthmuses (90%). The identifi-cation of isthmuses by surgical operating microscopeand the removal of isthmus tissue using a microsurg-ical retrotip appear to have been key factors in thehigh success rate.

The ability to remove isthmus tissue without com-promising the thickness of the remaining dentin wallsis one of the most essential improvements of using thenew microsurgical technique for root-end prepara-tion.

Only one of the reviewed clinical studies evaluateda sonic device for apical preparation (45). Utilizingvery strict healing criteria, 82% of the cases wereclassified as successful. Including the 14% of caseswith radiographic improvement, the success rate ap-proximated studies which defined success as disap-pearance or regression of the periapical radiolucencyin the absence of clinical manifestations.

The lack of experimental and clinical studies com-paring sonic and ultrasonic root-end instrumentationdoes not allow us to draw conclusive judgments onwhich type of device is superior.

Concerns have been raised regarding the produc-tion of aerosol and splatter when using ultrasonic orsonic scalers and inserts in periodontal procedures(50–53). No study has so far addressed this topic inperiradicular surgery using sonically or ultrasonicallypowered instruments. A microsurgical retrotip drivenby such devices will certainly produce an aerosol con-


taining blood and bacteria, considering the openworking field with a reflected flap during periradic-ular surgery. Studies would seem indicated to deter-mine whether a health hazard exists for patients andoffice staff during ultrasonic or sonic instrumentationof root-ends in periradicular surgery although the useof universal standard surgical precautions such asgloves, eye protection, masks, and gowns should pro-tect office personnel.

Conclusions

- Experimental in vitro studies performed in extractedhuman teeth and in human cadaver teeth have dem-onstrated several advantages of ultrasonic or sonicroot-end preparation compared to conventional burpreparation. These advantages include a deeper root-end preparation, alignment in the original path of theroot canal, and a reduced risk of lingual perforation.

- With respect to the cleanliness of the root-endcavity, ultrasonic preparations demonstrated smalleramounts of smear layer compared to bur prepara-tions. However, the latter showed less superficialdebris and better canal debridement of gutta-percha.

- The development of cracks and microfracturesfollowing sonic or ultrasonic root-end instrumentationis still controversial. It is unknown whether cracks af-fect the healing success. However, undisputedly morechipping of cavity margins occurs following sonic orultrasonic compared to bur preparation.

- Apical leakage studies using a dye tracer showedno statistically significant differences between the tworoot-end preparation techniques. However, a coronalleakage study with a polymicrobial marker demon-strated a significantly better seal of ultrasonically pre-pared cavities compared to those made with a bur.

- Only a limited number of clinical studies havebeen published on periradicular surgery using micro-surgical retrotips. All these studies reported high suc-cess rates for periradicular healing with follow-upperiods ranging from 6 to 14 months.

- No controlled clinical prospective studies or ex-perimental in vivo studies have been published com-paring the new microsurgical technique to the con-ventional technique.

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Micro Surgical Instruments for Root-End Cavity Preparation Following Apicoectomy a Literature Rev

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