Prevalence of TMJ Disc Displacement in a Pre-Orthodontic Adolescent Sample

Transcription

1 Originl Article Prevlence of TMJ Disc Displcement in Pre-Orthodontic Adolescent Smple B. Nebbe, BDS, MDent, FFD(SA)Ortho, PhD ; P. W. Mjor, DDS, MSc, MRCD b Abstrct: This study evluted the prevlence of temporomndibulr joint (TMJ) disc displcement in preorthodontic dolescents (75 boys, 119 girls) by mens of mgnetic resonnce imging (MRI). One hundred thirty-eight consecutive subjects were recruited regrdless of TMJ signs or symptoms, wheres 56 other subjects were referred with ssocited signs or symptoms. Quntittive mesurements of disc displcement nd disc length were used to clssify the degree of internl derngement into 6 ctegories on the bsis of sgittl MRI slices of the joints. In ddition, sidewys disc displcement ws determined from coronl MRI imges of the joint. Unilterl nd bilterl norml disc position ws more prevlent in boys compred to girls. All forms of nterior nd rottionl disc displcement were more prevlent in the femle smple thn in the mle. Sidewys displcement ws more prevlent in girls thn boys nd occurred more frequently in lterl rther thn medil direction. This study supports previous studies in suggesting tht disc displcements occur frequently in preorthodontic dolescents. (Angle Orthod 2000; 70: ) Key Words: Adolescent; Temporomndibulr joint; Mgnetic resonnce imging; Prevlence INTRODUCTION Trditionlly, the prevlence of disese or disorder is estblished by mking use of epidemiologicl studies nd rndom selection of lrge smples of individuls with nd without disorder of interest. 1 The prevlence of temporomndibulr joint dysfunction (TMD) in the dolescent popultion hs been reported previously 2 4 nd vries considerbly depending on the smple selection, the criteri used to define disc displcement, nd the type of study conducted. Until recently, clinicl evlution of joint sounds ws used s stndrd to determine the prevlence of disc displcement in TMD subjects. Joint sounds were found to occur in 1% of smple of 3428 grde schoolchildren between 6 nd 12 yers of ge. 2 In nother study conducted by Gzit et l, 3 the prevlence of joint sounds in 369 individuls ged 10 to 18 yers ws reported to be 35.8%. In Reserch Associte, TMD Investigtion Unit, Fculty of Medicine nd Orl Helth Sciences, University of Albert, Edmonton, Albert, Cnd. b Professor, Division of Orthodontics, Director, TMD Investigtion Unit, Fculty of Medicine nd Orl Helth Sciences, University of Albert, Edmonton, Albert, Cnd. Corresponding uthor: Brin Nebbe, TMD Investigtion Unit, 4068 Dentistry/Phrmcy Center, Fculty of Medicine nd Orl Helth Sciences, University of Albert, Edmonton, Cnd T6G 2N8 (e-mil: bnebbe@hotmil.com). Accepted: My Submitted: October by The EH Angle Eduction nd Reserch Foundtion, Inc. review by Mintz, 5 the prevlence of joint sounds in dolescent individuls vried between 0% nd 35.8%, with n verge of 17.0%. These studies re further complicted by the findings of Egermrk-Eriksson et l 4,6 nd Nilner nd Kopp, 7 who showed positive ssocition between joint sounds nd ging in dolescent individuls. These findings highlight the importnce of defining specific criteri for evlution of the disorder of interest s well s defining the study popultion when the prevlence of disorder is investigted. Associtions between occlusl chrcteristics nd signs nd symptoms of TMD hve lso been ttempted in the dolescent popultion. In cross-sectionl evlution of 1342 subjects ged 6 to 17 yers, Riolo et l 8 showed tht functionl shift of the occlusion ws negtively ssocited with temporomndibulr joint (TMJ) nd muscle tenderness, tht open bite ws positively ssocited with TMJ nd muscle tenderness, nd tht joint noises were positively ssocited with clss II molr reltionship. In contrst, Keeling et l 2 were not ble to show ssocitions between molr reltionship nd TMJ sounds but did show ssocitions between joint sounds nd lrger mximl mouth opening, nterior dentl crowding, nd deeper incisor overbites. These studies mde use of different criteri to ctegorize joints s dysfunctionl or norml, nd the conflicting results highlight the need to estblish specific prmeters to define norml nd bnorml joint function or TMD. Numerous cuses of TMD hve been proposed, but some re more redily identifible thn others. Certin forms of 454

2 ADOLESCENT TMJ DISC DISPLACEMENT disc displcement result in TMD nd re often ssocited with considerble suffering nd loss of joint function. Disc displcement is redily identified with mgnetic resonnce imging (MRI) of the joint. The technique is noninvsive, pin free, of miniml risk potentil, nd free of ionizing rdition exposure, nd it cn be pplied to both dysfunctionl nd control subjects. 9 The prevlence of disc displcement in the symptomtic dult popultion hs been shown to be pproximtely 30%, wheres the prevlence in symptomtic ptients rnges from 77.0% 11 to 82.0% 12 when MRI ws used to determine disc position. In study to determine the prevlence of MRI-determined disc displcement in 51 children between the ges of 8 nd 15 yers who presented with mlocclusions, the prevlence of disc displcement ws shown to be 11.8%. 13 Although this ws smll smple of children, it did include individuls with both norml nd bnorml disc position nd did not rely on smple of ptients presenting for tretment of TMD-relted symptoms. The prevlence of disc displcement is nturlly expected to be higher in ptients thn in symptomtic individuls nd, therefore, prevlence studies should not be bsed on bis smple selections, s my hve occurred in previous studies. The purpose of the present study is to report on the prevlence of disc displcement in preorthodontic dolescent smple drwn to determine the ssocitions between disc displcement nd crniofcil morphology. This study reports on the prevlence of vrious forms of disc displcement identified by mking use of newly estblished nd tested quntittive technique for evlution of MRI-determined disc position. MATERIALS AND METHODS One hundred thirty-eight consecutive subjects were recruited from the grdute orthodontic progrm t the University of Albert nd from privte orthodontic prctice in the re before they underwent orthodontic tretment. The group consisted of subjects with nd without cliniclly detectble TMJ signs nd symptoms (cpsulr pin, joint sounds, mstictory muscle tenderness, limited mndibulr rnge of motion, nd devition on opening). Prcticing orthodontists in the Edmonton re were sked to screen preorthodontic ptients for signs nd symptoms of TMD nd to refer individuls with TMJ symptoms for MRI evlution if consent ws given. A totl of 56 other subjects were recruited in this wy. No individuls with history of juvenile rheumtoid rthritis were included in the study. MRIs of the TMJs were obtined on ll 194 subjects (75 boys nd 119 girls) between the ges of 10 nd 17 yers, regrdless of TMJ disc position. All individuls consented to inclusion in the study, nd the study ws pproved by the Joint Dentistry/Phrmcy Humn Ethics Committee. MRIs of the TMJs were performed without sedtion by 455 using 1.0 T mgnet (Shimdzu Corportion 3, Tokyo, Jpn) nd unilterl 76-mm surfce receiver coil. Axil scout imges were obtined to identify the condyles. Bilterl closed-mouth sgittl sections were obtined perpendiculr to the long xis of the condyle, nd coronl imges were obtined prllel to the condylr long xis. Closed mouth imges were obtined with polyvinylsiloxne (President Jet-Bite, Coltene/Whledent Inc, Mhwh, NJ) centric occlusion bite registrtion. To prevent muscle ftigue, bilterl open-mouth sgittl imges were produced by mking use of Burnett cliper (Medrd, Pittsburgh, P) set t 10 mm below the mximl voluntry interincisl mouth opening. Subjects were instructed to rest the nterior teeth on the bldes of the cliper. T1-weighted 500/20 (TR ms: TE ms) pulse sequences were performed on ll subjects by using 3-mm slice thickness, 140-mm field of view, NEX of 2, nd imge mtrix of pixels. An experienced mxillofcil rdiologist subjectively determined the disc position from the coronl nd sgittl MRI slices of the joints. Of the 194 subjects imged (387 joints), only 35 joints were excluded becuse of poor MRI qulity, possibly s result of motion rtifcts. Six ctegories of disc position were identified, ll exhibiting disc reduction on mouth opening. Disc position ctegories Ctegory 1: norml disc position. In the closed-mouth position, the intermedite zone of the disc ws interposed between the hed of the condyle nd the posterior slope of the rticulr eminence, with the nterior nd posterior bnds eqully spced on either side of the condylr lod point in bow tie ppernce (Figure 1). 14 Ctegory 2: slight disc displcement. The intermedite zone of the disc ws slightly nteriorly displced from between the osseous rticulr components. The hed of the condyle opposed the posterior bnd of disc (Figure 2). Ctegory 3: moderte disc displcement. The intermedite zone of the disc ws completely displced from between osseous rticulr structures. The hed of condyle ws in contct with the junction between posterior bnd of the disc nd the bilminr zone (Figure 3). Ctegory 4: full disc displcement. The entire rticulr disc ws nteriorly displced reltive to the posterior slope of the rticulr eminence nd hed of the condyle. The bilminr zone of the disc ws interposed between the osseous rticulr structures nd occupied the nrrowest joint spce. The disc reduced on mouth opening (Figure 4). Ctegory 5: full disc displcement with severe loss of morphology. Identicl description to ctegory 4, but without reduction of the disc on mouth opening nd morphologicl ltertion of the disc evident (Figure 5). Ctegory 6: nonctegoricl disc position. MRI imges produced were of poor dignostic qulity nd could not be interpreted for disc position.

3 456 NEBBE, MAJOR FIGURE 1. Sgittl closed-mouth mgnetic resonnce imge depicting norml disc position. FIGURE 2. Sgittl closed-mouth mgnetic resonnce imge depicting slight disc displcement. The subjective ctegoriztion of disc position ws used in discriminnt nlysis to determine whether quntittive mesurements of disc length nd disc displcement could be used to clssify the position of the disc on ech sgittl MRI slice of the joint. 15 Quntittive mesures of disc length nd disc displcement were obtined with reference plnes trnsferred from corresponding lterl cephlometric rdiogrphs for ech subject; this ided in stndrdiztion of joint position nd mesurement technique. 15 Discriminnt nlysis reveled tht ctegoriztion into the subjectively determined ctegories by using the quntittive mesures of disc length nd disc displcement ws fesible. In boys, 70 left joints nd 68 right joints were vilble for nlysis. In girls, n equl number of right nd left joints (107) were vilble for nlysis. The newly defined discriminnt ctegory per slice of the joint ws used to determine the degree of disc displcement in ech joint. A joint ws ssigned to these ctegories only if ll slices within the joint were ssigned the sme discriminnt ctegory (Figure 6). Joints tht did not hve consistent discriminnt score ssigned to ech slice throughout the joint were ssigned to 1 of 2 groups. Anterolterl disc displcement. The medil pole of the disc hs lost its ttchment or hs become elongted. The degree of disc displcement in the medil prt of the joint exceeds tht noted in the lterl region of the joint when discriminnt scores of sgittl MRI slices re used for clssifiction. In this sitution, the bulk of the displced disc is

4 ADOLESCENT TMJ DISC DISPLACEMENT 457 FIGURE 3. Sgittl closed-mouth mgnetic resonnce imge depicting moderte disc displcement. FIGURE 4. Sgittl closed-mouth mgnetic resonnce imge depicting full disc displcement. locted in n nterolterl position when the teeth re in intercusption (Figure 7). Anteromedil disc displcement. The degree of disc displcement in the lterl region of the joint ws more severe thn in the medil region of the joint, s determined by the discriminnt score ssigned. This mens tht the disc exhibits rottionl displcement, with the bulk of the disc locted in the medil region of the joint in the closed-mouth position (Figure 8). Sidewys disc displcement hs recently been identified by Tski et l 12 when mking use of coronl MRI imges. In joints ffected by sidewys disc displcement, the rticulr disc is displced either medilly or lterlly reltive to the condyle nd pprently shows no component of nterior disc displcement. To determine the prevlence of sidewys disc displcement in the current study, sgittl nd coronl imges were subjectively ssessed to determine the presence of medil or lterl sidewys displcement tht my hve occurred. No quntittive score ws ssigned to this type of disc displcement. Dt nlysis The percentge prevlence of disc displcement ws determined independently for right nd left joints seprtely for girls nd boys nd ssessed independently on the bsis of symptomtic referrl or consecutive referrl from referring orthodontists nd grdute orthodontic progrms. These dt were further utilized to determine the prevlence of bilterl joint involvement by mking use of the discriminnt ctegories. Unilterl norml disc position in n ipsilterl joint nd contrlterl disc displcement were lso determined for boys nd girls. The prevlence of bilterl or unilterl joint involvement ws determined for 104 girls nd 68 boys for whom bilterl MRI dt were vilble.

5 458 NEBBE, MAJOR FIGURE 5. Sgittl closed-mouth mgnetic resonnce imge depicting full disc displcement with loss of morphology. RESULTS The percentge prevlence of norml nd disc displcement ccording to the discriminnt scores per joint re presented in Tbles 1 nd 2 for nonconsecutive nd consecutive subjects included in the study, respectively. From these dt, it is evident tht pproximtely 50% of the mle consecutive joints were norml, with miniml joint-side bis. A slightly smller percentge of norml disc position ws evident in the nonconsecutive smple. Norml femle joints rnged from 23% to 29%, with little difference in percentge prevlence between consecutive nd nonconsecutive groups (Figure 1). Full disc displcement with loss of morphology occurred more frequently in girls thn in boys in this smple of dolescents (Figure 5). Bilterl norml joints were more common in boys thn in girls, wheres bilterl full disc displcement with loss of morphology ws fr more prevlent in girls thn in boys (Tble 3). Bilterl occurrence of the intermedite stges of disc displcement ws poorly represented in both boys nd girls in this dolescent smple when only the sgittl slice informtion meeting requirements for discriminnt ctegoriztion ws ssessed. The occurrence of unilterl norml disc position with contrlterl disc displcement of ny form ws more prevlent in boys t 36.36% for the nonconsecutive group nd 26.31% for the consecutive group, compred with girls, who showed 18.0% for the nonconsecutive group nd 18.5% for the consecutive group (Tble 3). Regrdless of sex or joint side, nteromedil disc displcement ws more prevlent thn nterolterl displcement (Tble 4). Overll, girls exhibited more rottionl disc displcement thn boys. The prevlence of sidewys disc displcement for boys nd girls, s determined from coronl imges of the joints, is presented in Tble 5. Figure 9 depicts lterl sidewys disc displcement s seen on coronl MRI imges of the TMJ. DISCUSSION The smple under considertion ws recruited to determine whether MRI-determined disc position could be ssocited with ltertion in crniofcil morphology. Although this ws not the topic of discussion in this investigtion, this smple of preorthodontic subjects llowed for ssessment of the prevlence of disc displcement in subjects referred directly for symptomtic joint ssessment nd the prevlence of disc displcement ssessment in subjects referred consecutively from the grdute orthodontic progrm. Subjects recruited for this study included individuls with nd without cliniclly detected signs nd symptoms of TMD. It ws ttempted to derive study smple on the bsis of clinicl signs nd symptoms tht would be eqully distributed between symptomtic nd symptomtic ssignment. This seems to hve been chieved in the consecutive mle smple, in which pproximtely 50% of the mles hd either right or left TMJs with norml ctegoriztion. Only 40.4% of the consecutive boys, however, were bilterlly norml ccording to discriminnt nlysis ssignment of TMJ ctegory. In nonconsecutive symptomtic boys, norml joint ctegoriztion ws slightly lower, t 36.4% for right nd 40.1% for left joints. Bilterl norml disc position in the nonconsecutive group ws observed in only 18.2% of the boys. Noticebly fewer bilterl norml joints were seen in the nonconsecutive symptomtic mle smple under investigtion. In the consecutive femle smple, only pproximtely 25% to 29% of the joints were norml on either the left or

6 ADOLESCENT TMJ DISC DISPLACEMENT 459 FIGURE 6. Discriminnt ctegories of disc position. () Posterior bnd of disc; (b) nterior bnd of disc. right side, nd only 15.4% hd bilterl norml disc position. Even fewer nonconsecutive symptomtic girls presented with norml disc position, nd bilterl norml disc position ws ssessed in only 12.8% of this smple. Full disc displcement nd full disc displcement with loss of morphology occurred with greter prevlence in the nonconsecutive symptomtic femle smple thn in the consecutive femle smple. Girls showed higher prevlence of full disc displcement thn boys for nonconsecutive symptomtic nd consecutive smples. On the whole, bilterl disc displcement, whether full disc displcement or full disc displcement with loss of morphology, ws more prevlent in girls thn in boys, but boys exhibited more bilterl norml joints thn girls. Boys seemed to be more ffected by unilterl joint involvement thn were girls. This my be relted to the etiology of the displcement. From evlution of clinicl history obtined from our subjects, trum to the mndible nd joint seems to be more prevlent in boys thn in girls. A history of trum my be ssocited with the greter prevlence of unilterl disc displcement in boys thn in girls. Possibly other mechnisms re responsible for bilterl disc displcement in girls. It hs been suggested in niml studies tht joint lxity involving ny joint occurs more commonly in girls thn in boys. 16,17 These findings my represent sex-limited expression of joint lxity tht is relted to ltered collgen synthesis, which is ffected either by the level of circulting estrogen or the concentrtion of estro-

7 460 NEBBE, MAJOR FIGURE 7. Anterolterl disc displcement. () Posterior bnd of disc; (b) nterior bnd of disc. FIGURE 8. Anteromedil disc displcement. gen receptors within joints. 18 It is suggested tht individuls with joint lxity s result of ltered collgen synthesis re t greter risk of developing bilterl TMD when subjected to etiologicl fctors such s trum, joint overextension, or joint overuse. 19 Anteromedil disc displcement involving stright nterior displcement of the lterl region of the disc nd sidewys shift of the displced lterl pole of the disc in medil direction ws shown to be more prevlent thn nterolterl disc displcement. These findings re comprble to those of Tski et l, 12 who termed these displcements prtil nterior displcement of the disc in the lterl prt of the joint nd prtil nterior displcement of the disc in the medil prt of the joint, respectively. In keeping with the overll higher level of disc displcement identified in girls, the prevlence of nteromedil nd nterolterl rottionl disc displcements ws higher in girls thn in boys. Rottionl disc displcement did not, however, show ny side-specific bis in either boys or girls. These forms of rottionl disc displcement were the most prevlent of ll forms of displcement identified. This my be n indiction tht disc displcement in single region of the joint is common compred with the disc displcement throughout the joint needed to stisfy the strictly pplied discriminnt ctegories of disc displcement. TABLE 1. Percentge Prevlence of Disc Displcement in Symptomtic Nonconsecutive Adolescent Smple Ctegory of Disc Position Norml disc position Slight disc displcement Moderte disc displcement Full disc displcement Full disc displcement with loss of morphology Other Boys Girls Disc position per joint ws determined by mking use of ll sgittl mgnetic resonnce imging slices per joint. All slices per joint hd to be similrly scored to be plced into 1 of the 6 ctegories. Joints with slices hving different scores ssigned to the slices were plced in the Other ctegory, which ws further nlyzed for direction of disc displcement TABLE 2. Percentge Prevlence of Disc Displcement in Consecutive Adolescent Smple Ctegory of Disc Position Norml disc position Slight disc displcement Moderte disc displcement Full displcement Full disc displcement with loss of morphology Other Boys Girls Disc position per joint ws determined by mking use of ll sgittl mgnetic resonnce imging slices per joint. All slices per joint hd to be similrly scores to be plced into one of the 6 ctegories. Joints with slices hving different scores ssigned to the slices were plced in the Other ctegory, which ws further nlyzed for direction of disc displcement

8 ADOLESCENT TMJ DISC DISPLACEMENT 461 TABLE 3. Percentge Prevlence of Bilterl nd Unilterl Disc Displcement Joint Sttus Bilterl sttus Norml Slight disc displcement Moderte disc displcement Full disc displcement Full disc displcement with loss of morphology Unilterl sttus b Symptomtic Boys, % Girls, % Consecutive Boys, % Girls, % Disc position per joint ws determined by mking use of ll sgittl mgnetic resonnce imging slices per joint. All joints previously clssified into one of the 6 ctegories were used to determine bilterl clssifiction. Unilterl joint ctegory ws determined by combining norml-only joints with either moderte disc displcement, full disc displcement, or full disc displcement with morphologicl ltertions. b One side norml, other side disc displced TABLE 4. Percentge Prevlence of Anteromedil nd Anterolterl Disc Displcement for All Joints Ctegory of Disc Position Anterolterl disc displcement Anteromedil disc displcement Boys Symptomtic Girls Boys Consecutive Girls Disc position per joint ws determined by mking use of ll sgittl mgnetic resonnce imging slices per joint. All joints previously clssified s Other in Tble 1 were evluted to determine direction of disc displcement when full ctegory could not be ssigned throughout the joint TABLE 5. Percentge Prevlence of Medil nd Lterl Sidewys Disc Displcement Disc Displcement Lterl Medil Boys Right, % Left, % Girls Right, % Left, % Disc position determined by subjective evlution of coronl mgnetic resonnce imges of joints. Anteromedil or nterolterl disc displcement my be viewed s form of slight or moderte disc displcement if the functionl effects of disc displcement re considered. A rottionl disc displcement functions similrly to slight or modertely displced disc in tht during some phse of the mstictory cycle, the disc is displced, wheres during nother phse, the disc is once more interposed between the osseous rticulr surfces. Rottionl displcements my be n intermedite stge of disc displcement in which only one collterl discl ligment is elongted nd the other collterl ligment my not yet hve elongted sufficiently to llow for the developed of full disc displcement throughout the joint. If nteromedil nd nterolterl displcements re considered s slight or moderte disc displcements, then it my be pprecited tht these 2 ctegories do form continuum in the distribution of disc displcements identified. The prevlence of sidewys disc displcement in girls FIGURE 9. Coronl mgnetic resonnce imge of TMJ depicting sidewys disc displcement. ws higher thn tht in boys nd ws more common in lterl direction, s identified by lterl bulging of the joint cpsule on coronl MRI imges. Lterl sidewys disc displcement ws more prevlent in the left TMJ thn the right for both boys nd girls, wheres medil sidewys disc displcement ws more common in the right TMJ. Only 1 boy exhibited medil sidewys disc displcement, nd this

9 462 NEBBE, MAJOR ffected left TMJ. In joints with sidewys component to the disc displcement, the sgittl MRI imges did contin n re of reduced signl intensity nterior to the condyle, inferior to the height of the rticulr eminence, nd superior to the lterl pterygoid muscle insertion into the condyle neck in the region of the nterior joint recess. This re of reduced signl intensity ws interpreted to be the elongted medil or lterl collterl discl ligment mintining communiction between the displced disc nd the corresponding condylr pole of ttchment (Figure 10). The prevlence of medil sidewys disc displcement for boys in this study is significntly less thn tht previously reported by Tski et l 12 in their evlution of ptients nd symptom-free individuls. In ddition, the present study reports significntly higher prevlence of lterl sidewys disc displcement in girls compred with the findings of Tski et l. 12 The ge of the individuls included in the respective studies my be fctor responsible for the differences observed between the 2 studies. The prevlence of disc displcement identified in this smple of dolescent individuls should not be extrpolted to the generl orthodontic popultion or to the popultion t lrge. This study is not representtive of these popultions becuse it ws not selected on rndom bsis. The study, however, does recognize tht disc displcement is prevlent in the dolescent popultion nd is more prevlent in the femle smple. The present study shows tht disc displcement involving the TMJ ffects individuls presenting for orthodontic consulttion. Disc displcement my be ssocited with ltered fcil morphology or mlocclusion, nd these my be clinicl tretment chllenge if norml fcil growth is nticipted with disc displcement Furthermore, disc displcement my be ssocited with the development of clinicl symptoms of crniofcil pin once the dptive cpcity of the joints is reduced when ctive growth is complete. A filure to identify individuls with disc displcement my hve medicolegl implictions if symptoms pper fter orthodontic tretment hs been completed. In ddition, the use of only sgittl MRI slice informtion my not identify the full prevlence of disc displcement becuse the lterl or medil sidewys disc displcements, seen on coronl MRI imges, my not be visulized on the sgittl imges. CONCLUSIONS FIGURE 10. Sgittl mgnetic resonnce imge of temporomndibulr joint depicting elongted collterl ligment ssocited with sidewys disc displcement. The prevlence of disc displcement in this study smple of preorthodontic dolescent individuls ws shown to be higher in girls thn in boys. Unilterl disc displcement ws more common in boys thn in girls, but no side-specific bis in the prevlence of disc displcement ws identified. Anteromedil disc displcement ws shown to occur more commonly thn nterolterl disc displcement. These rottionl disc displcements were the most common form of disc displcement ffecting joints nd were most likely included in the moderte disc displcement group. ACKNOWLEDGMENTS We thnk the TMD Investigtion Unit, Mgnetic Resonnce Centre of Edmonton, Edmonton Dignostic Imging nd the Reyburn Mc- Intyre Fund for Dentistry, University of Albert, Edmonton, Albert, Cnd. REFERENCES 1. Moses AJ. Scientific methodology in temporomndibulr disorders. Prt I: epidemiology. J Crniomndib Prct. 1994;12: Keeling SD, McGorry S, Wheeler T, King GJ. Risk fctors ssocited with temporomndibulr joint sounds in children 6 to 12 yers of ge. Am J Orthod Dentofcil Orthop. 1994;105: Gzit E, Liebermn M, Eini R, Hirsch N, Serfty V. Prevlence of mndibulr dysfunction in yer-old Isreli schoolchildren. J Orl Rehbil. 1984;11: Egermrk-Eriksson I, Crlsson GE, Ingervll B. Prevlence of mndibulr dysfunction nd orofcil prfunction in 7-, 11- nd 15-yer-old Swedish children. Eur J Orthod. 1981;3: Mintz SS. Crniomndibulr dysfunction in children nd dolescents: review. J Crniomndib Prct. 1993;11: Egermrk-Eriksson I, Ingervll B, Crlsson GE. The dependence of mndibulr dysfunction in children on functionl nd morphologic mlocclusion. Am J Orthod. 1983;83: Nilner M, Kopp S. Distribution by ge nd sex of functionl disturbnces nd disese of the stomtognthic system in yer-olds. Swed Dent J. 1983;7: Riolo ML, Brndt D, TenHve TR. Associtions between occlusl chrcteristics nd signs nd symptoms of TMJ dysfunction in children nd young dults. Am J Orthod Dentofcil Orthop. 1987;92: Cirbus MT, Smilck MS, Beltrn J, Simon DC. Mgnetic resonnce imging in confirming internl derngement of the temporomndibulr joint. J Prosthet Dent. 1987;57: Kircos LT, Ortendhl DA, Mrk AS, Arkw M. Mgnetic res-

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