in 18.6% of first molars and 9.6% of second molars.These findings were about half of those reported instudies by Seidberg11 (33%) and Pomerantz andFishelberg (28.2%).12 Fogel et al13 evaluated the use of2.5× magnification telescopes with fiberoptic head-lamps for locating ML canals in maxillary first molarsin vivo. After access preparation, a groove, approxi-mately 1 mm in depth, was made along the floor of thepulp chamber lingual to the MB canal orifice,following the developmental groove between the MBand palatal canals. They found that 148 of 208 (71.2%)MB roots had 2 treatable canals.12 Several techniqueshave been recommended in the English-language liter-ature, with respect to locating the ML canal. Neaverthet al14 discussed a method of minor canal detection inthe MB root in a clinical investigation of 228 maxillaryfirst molars. They described a heart-shaped accessopening, a distal approach because of the dentinal shelfpresent on the mesial, and countersinking the floorlingual to the major canal to locate the minor canalorifice. Weller and Hartwell15 have stated that there isan increased probability of finding this canal if theinitial access is changed from a classical triangularshape to a more rhomboidal shape. They also advisedthat the developmental groove between the MB andpalatal canals be explored, often by deepening it, tolocate a fourth canal. In a retrospective study of 1134maxillary molars treated with the modification of arhomboidal access, the authors were able to detect 4canals in 39% of maxillary first molars and 21.4% ofsecond molars. Stropko16 found 73% to 93% MB2 in arecent clinical study that examined 1732 maxillarymolars. In Kulild and Peters’17 study of first and

190

One of the goals of nonsurgical root canal treatment islocation and debridement of all canals wheneverpossible.1-3 In the treatment of maxillary molars,locating and negotiating a mesiolingual (ML) canal inthe mesiobuccal (MB) root (also referred to as minor,lateral, secondary, accessory, second mesial, or MB2)may have implications to the long-term prognosis.4

Research in vitro has demonstrated wide variation inthe prevalence of the ML canal. Hess5 evaluated thenumber of canals in 513 extracted maxillary first andsecond molars and found that 54% had 4 canals.Pineda and Kuttler6 reported finding 4 canals in 51.5%of first and second maxillary molars combined.Weine,7 using maxillary first molars, located 4 canalsin 62%. In an SEM analysis of maxillary molars, Gillesand Reader8 found 70% to 90% of ML canals in MBroots. Most recently, Weine et al9 examined 293extracted maxillary first molars from a Japanese popu-lation and found that 68% demonstrated more than 1canal in the MB root.9

The relative success of finding an ML in an in vivosetting has been poor. Hartwell and Bellizzi,10 in areview of treatment records involving 714 maxillaryfirst and second maxillary molars, found a fourth canal

The influence of dental operating microscope in locating themesiolingual canal orificeLynne A. Baldassari-Cruz, DDS,a Jeffrey P. Lilly, DDS, MS,b and Eric M. Rivera, DDS, MS,c

Iowa City, IowaUNIVERSITY OF IOWA

Objective. The purpose of this study was to evaluate the influence of using the dental operating microscope (DOM) for detec-tion of the mesiolingual (ML) canal orifice in extracted maxillary molars compared with unaided vision (no loupes or head-lamps).Study design. Using a clinical simulation model system, we mounted 39 maxillary molars in a dentoform and placed theminto a mannequin. After rubber dam placement and preparation of standard access, 2 attempts were made to locate the MLcanal with unaided vision. Then the teeth were examined by using a DOM. Finally, all teeth were sectioned, stained, and eval-uated with the DOM for actual presence of an ML canal.Results. ML canal orifices were detected in 20 of the teeth with a sharp explorer and mirror. In the remaining teeth, 12 MLcanal orifice were located by using the DOM. Qualitative nonparametric comparisons were used. Conclusions. The results of this study indicate that the DOM provides increased opportunity for the dentist to detect canal orifices.(Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2002;93:190-4)

aAssistant Professor, University of Iowa, Iowa City. bAdjunct Faculty, University of Iowa, Iowa City; in private practice,Des Moines, Iowa.cAssociate Professor and Head, Department of Endodontics,University of Iowa, Iowa City. Received for publication Sep 21,2000; returned for revision Nov 13,2000; accepted for publication Jun 19, 2001.Copyright © 2002 by Mosby, Inc.1079-2104/2002/$35.00 + 0 7/15/118285doi:10.1067/moe.2002.118285

ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY Baldassari-Cruz, Lilly, and Rivera 191Volume 93, Number 2

second maxillary molars, a second canal was located inthe coronal half of 95.2% of the roots, by hand instru-ments in 54.2%, after modifying the access in 31.3%and after sectioning and viewing with a measuringmicroscope in 9.6%.

Location of root canals has previously been evalu-ated in vivo and in vitro in research articles by usingdental loupes, fiberoptic head lamps, scanning electronmicroscopy, and sectioning for microscopic observa-tion.1,7,11,16-30 The DOM provides enhanced illumina-

tion and magnification for dental procedures on bothhard and soft tissues, giving advantage to designingand reflecting gingival tissue flaps.1,16-19 The dentaloperating microscope has been associated withobtaining favorable treatment results in a study in vivoof endodontic surgery with improved postoperativesymptoms.16,18 Literature describing the use of thedental operating microscope for nonsurgical routineprocedures is limited. Very recently, a study in vitrousing the DOM for gutta percha removal showed no

Fig 1. A, Drawing of access to demonstrate typical location ofmesiolingual (ML) canal in relationship to mesiobuccal (MB),distobuccal (D), and palatal canals in a maxillary molar.Photographs of maxillary molar before (B) and after (C) MLcanal trench preparation.

B

C

192 Baldassari-Cruz, Lilly, and Rivera ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGYFebruary 2002

significant difference in the debris remaining in thecanal compared with re-treatment without the use ofthe DOM.31

The purpose of this study was to evaluate whether theadjunctive use of the DOM would increase detection ofML canal orifice in the MB root of extracted maxillaryfirst and second molars, when not found with unaidedvision in an in vitro mannequin setting.

MATERIAL AND METHODSThirty-nine extracted maxillary first and second

molars were used in this study. The extracted teethwere stored in a 1% thymol solution for 2 months. Theteeth were mounted into a dentoform with acrylic,which extended 5 mm below the cementoenamel junc-tion, then mounted onto a dental chair mannequin(Columbia Dentoform, Long Island, NY). Radiographsof all teeth were made while in the dentoform by usingan XCP, 70 KVP, 10 mA, and 0.4 second of exposure.Angulations of 20° mesial and 0° vertical were used toincorporate the best reproducibility for analyzing canalmorphology of the MB root.9,15,18,19 Without the use ofmagnification or headlamps (unaided vision), standardendodontic access was performed by using a high-speed hand-piece with a 557 fissured bur, sharpexplorer, mirror, and 2.5% sodium hypochlorite irriga-tion. After the MB, distobuccal, and palatal canals werelocated, an attempt was made to locate the ML canalagain with unaided vision by using only a sharpexplorer and a mirror. If the ML canal was not located,a 700L bur was placed 2 to 3 mm into the orifice of theMB canal and a trench was prepared at that depthtoward the lingual and slightly mesial into and through

the mesial dentinal shelf.2,3 This trench was againexplored with unaided vision by using only a sharpexplorer and a mirror to locate an ML canal. Fig 1, A isa drawing of a standard access with typical canal loca-tions demonstrated. Fig 1, B and Fig 1, C show accessbefore and after trench preparation at 3× magnification.These images were made with a digital camera system(Canon model number EOS D30, Tokyo, Japan). A MLcanal orifice was either located or not located. If not,the teeth were then evaluated by using a Zeiss DOM(Carl Zeiss, Inc, Oberkochen, Germany) at 25× magni-fication to search for the ML canal. Again, an ML canalwas either located or not located (Fig 2). The MB rootsof all teeth were then sectioned in an axial plane 5 mmbelow the cementoenamel junction, then stained withmethylene blue dye (Fig 3). All sections were exam-ined by using the DOM at 25× magnification to deter-mine the actual presence or absence of the ML canal

Fig 2. Methodology flow chart.

Fig 3. A and B, Schick image demonstrating the ML canal inMB root after laboratory sectioning and staining at 25×.

ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY Baldassari-Cruz, Lilly, and Rivera 193Volume 93, Number 2

orifice. Each tooth served as its own control. Two eval-uators, both second-year endodontic residents,performed all the examinations and proceduresinvolved in the study. Both evaluated all teeth for MLcanal detection.

RESULTSFig 4 summarizes the results of this study. With the use

of only a sharp endodontic explorer and mouth mirror(unaided vision, no adjunctive use of illumination ormagnification), 20 ML canal orifices were detected outof the 39 teeth, representing 51%. After evaluation of thesame 39 teeth with the DOM, an additional 12 ML canalorifices were detected in the remaining 19 teeth (63%).In other words, these 12 canal orifices were not locatedwithout the use of the DOM. Overall, 82% of ML canalswere detected in 39 experimental teeth by using bothmethods of discovery. In the lab, after sectioning andstaining all the teeth, 3 additional ML canals were iden-tified in the remaining 7 teeth. These 3 canals were notdetected with unaided visual examination or with theDOM. A total of 35 ML canals were identified out of 39experimental teeth.

DISCUSSIONThe DOM has become more popular for surgical and

nonsurgical endodontics.16-18,29 Some reasons for thisincreased use may be choice of magnification and avariable intensity of light, which is focused down theshaft of the optic piece, parallel to the field of magnifi-

cation. This allows the most direct illumination of themagnified image.16-18,29 It has been reported that thesebenefits are somewhat balanced by the steep learningcurve to become familiarized with and proficient inDOM use.19

The ML canal in MB roots of maxillary molars canbe extremely challenging to locate. To accomplish this,one must be well trained in the knowledge of pulpmorphology to know typical location and number ofexisting canals.2-28 Different methods of access modi-fication to increase frequency of locating the ML canalhave been demonstrated.2,11,14,26 The modification ofthe access cavity to include a trench preparation fromthe mesiobuccal canal in mesial palatal direction,where the ML canal may typically be found, increasedthe frequency of ML canal orifice detection. Combinedwith the knowledge of root canal system morphologyand accessibility, enhanced vision to the area allowsthe operator to achieve maximum results. ML canaldetection was increased by the addition of the DOM inour study, from 51% to 82% in 39 test teeth. Fogel etal13 located and treated 71.2% of ML canals with theaddition of enhanced vision by using fiberoptic head-lamps and 2.5× loupes. In our study, with the additionof the DOM we located 82% of the ML canals in 39maxillary molars. Negotiation of detected canals wasnot part of this study. The nonparametric statistics ofquantifying the numbers of detected ML canals foreach category was in agreement with both operators.

CONCLUSIONSOur study demonstrated that the adjunctive use of the

DOM increased the ability for the dental clinician tolocate an ML canal.

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Reprint requests:

Lynne A. Baldassari-Cruz, DDSDepartment of Endodontics, DSB 435 SUniversity of Iowa College of DentistryIowa City, IA 52242-1001lynne-baldassari-cruz@uiowa.edu