Changes in Articular Eminence Inclination During the Craniofacial Growth Period

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1 Originl Article Chnges in Articulr Eminence Inclintion During the Crniofcil Growth Period Elis G. Ktsvris DDS, MSD Abstrct: The rticulr eminence of the temporomndibulr joint dicttes the pth nd type of condylrdisk complex movement. It hs been suggested tht steep rticulr eminence inclintion my predispose to temporomndibulr joint dysfunction. When using functionl pplinces in orthodontic therpy, the bite registrtion is gretly ffected by the rticulr eminence inclintion. Furthermore, the rticulr eminence morphology hs been relted to specific fcil types. Knowledge of how the rticulr eminence inclintion behves during the crniofcil growth period could help estblish more biologicl tretment modlities. We took silicone impressions of both left nd right rticulr fosse from 90 dried skulls. This smple consisted of three equl subgroups of skulls, ech group presenting deciduous, mixed, or permnent dentition. After the impression hd set, they were removed nd cut into sgittl sections 2.5 mm thick. The three middle sections were photocopied nd enlrged by 200%. The inclintion of ech section ws clculted trigonometriclly, nd the men vlue ws ssigned to the inclintion of the respective eminence. The dt indicted tht the inclintion of the rticulr eminence chnges rpidly until the completion of deciduous dentition, ttining more or less 45% of its dult vlue. By the ge of 10 yers, it ws 70% 72% completed, nd by the ge of 20 yers, it ws 90% 94% completed. In conclusion, normlly, the rticulr eminence inclintion shows symmetricl growth pttern, nd it grows t very rpid rte, ttining lmost hlf of its dult vlue by the ge of two yers. (Angle Orthod 2002;72:2 264.) Key Words: Temporomndibulr joint development; Articulr eminence slope; Growth INTRODUCTION The rticulr eminence is tht prt of the temporl foss over which the condyle-disk complex slides during the vrious mndibulr movements. It is often confused with the rticulr tubercle, which is n entirely different structure. The rticulr tubercle 1,2 is the smll bony projection t the lterl prt of the rticulr eminence tht serves s the origin of the temporomndibulr ligment. The rticulr eminence inclintion is defined s the ngle formed by the rticulr eminence nd the Frnkfort horizontl (FH) plne or ny other horizontl plne, such s the occlusl or pltl plne. It cn be mesured by two methods. 2,3 One method is to mesure the ngle between the best fit line on the slope of the eminence nd the FH plne (Figure 1), herefter referred to s method 1; the other Associte Professor in Orthodontics, Deprtment of Orthodontics, School of Dentistry, University of Athens, Athens, Greece. Corresponding uthor: Elis G. Ktsvris DDS, MSD, Deprtment of Orthodontics, School of Dentistry, University of Athens, 2 Thivon St, Goudi 11527, Athens, Greece. (e-mil: elkts@otenet.gr). This study is prt of reserch monogrph submitted to the School of Dentistry, Athens University, Accepted: November Submitted: August by The EH Angle Eduction nd Reserch Foundtion, Inc. method is to mesure the ngle between the FH plne nd line connecting the roof of the foss with the highest point of eminence (Figure 2), herefter referred to s method 2. It must be stressed tht lthough both ngles represent the rticulr eminence inclintion, the first ngle (best fit line FH) focuses primrily on the posterior surfce of the eminence, wheres the other ngle (foss roof eminence top, FH) focuses on the loction of the eminence crest reltive to the foss roof. The norml vlue of this ngle in dults hs been reported to be Articulr eminences hving inclintion vlues smller thn 30 hve been chrcterized s flt, wheres those hving vlues greter thn 60 hve been chrcterized s steep. However, this distinction hs not been universlly ccepted since Ichikw nd Lskin 5 nd Grnd 6 hve, bsed on subjective criteri, divided rticulr eminence inclintions into flt, moderte, nd protubernt types. The fltness or steepness of the rticulr eminences dicttes the pth of condylr movement, s well s the degree of rottion of the disk over the condyle. The steeper the rticulr eminence, the more the condyle is forced to move inferiorly s it shifts nteriorly. This results in greter verticl movement of the condyle, mndible, nd mndibulr rch upon opening. 7 It hs been reported tht during mouth 2

2 CHANGES IN ARTICULAR EMINENCE SLOPE DURING GROWTH 259 MATERIALS AND METHODS FIGURE 1. The rticulr eminence inclintion presented s the best fit line (method 2). FIGURE 2. The rticulr eminence inclintion presented s the rooffoss nd eminence-top line (method 2). opening, the posterior disk rottion is more prominent in joints with steep rticulr eminence thn in joints with less steep eminence. 8,9 Furthermore, becuse of the rotry movement of the disk on the condyle s the whole complex moves forwrd, the totl bodily movement of the condyle, in reltion to the foss, exceeds tht of the rticulr disk. This difference increses s the steepness of rticulr eminence increses. It hs been suggested tht steep rticulr eminence predisposes to disk interference problems. Once these problems occur, the effect of inclintion is ugmented. 4 The rticulr eminence inclintion hs been studied in reltion to its height, 10 fcil morphology, 11,12 posterior loss of teeth, 13,14 tooth inclintion, nd temporomndibulr joint derngement However, studies on rticulr eminence growth re scnt. The purpose of this study ws to ssess the inclintion of the rticulr eminence during the crniofcil growth period. The mterils consisted of 90 dry skulls from Asitic Indin individuls selected from greter skull collection stored t the Orthodontic Deprtment of Philips University in Mrburg, Germny. The cuse of deth of the individuls ws unknown. The selection of skulls ws bsed on the following criteri: good generl condition (no dmge), no pprent skull symmetry, no bony pthology, good condition of the dentition, nd stge of the dentition development. These skulls were divided into three groups, A, B nd C, ech of which ws composed of 30 skulls. Group A skulls hd deciduous dentition; group B skulls hd mixed dentition (first molrs nd mxillry nd mndibulr incisors present); nd group C skulls hd permnent dentition. For every skull, the dentl ge ws ssessed by the method of Schour nd Mssler. 31 No sex determintion ws undertken. The procedure used for ech skull hs been described elsewhere. 32 Briefly, fcil bow (Denttus, Sweden) ws stbilized on ech skull by inserting the er sets into the coustic metus nd the plne indictor into the right infrorbitl formen (DMG-Hmburg, Germny). Using silicone-type mteril, we took impressions of both temporomndibulr fosse. Cre ws tken to level the bse of the impression to be prllel to the FH plne. The mteril ws sliced with common egg slicer (Westmrk, Germny). The surfces fcing the midsgittl plne of the three middle sections were photocopied on 200% scle. In ech photocopy, line from the top of the rticulr eminence ws drwn prllel to the upper surfce of the impression, nd hence, prllel to the FH plne. Two dditionl lines were drwn: one line ws the best fit line on the posterior surfce of the rticulr eminence (nterior surfce of the foss) (Figure 1), nd the other line connected the deepest point of the roof of the foss nd the top of rticulr eminence (Figure 2). These two lines, together with the FH plne, formed the ngles nd, respectively. Both of these ngles present mesure of rticulr eminence inclintion. The vlues of these ngles were estimted. Using n electronic digitl cliper (54496 Pro-Mx Cliper, Ted Pell Inc., Redding, CA) with resolution of 0.01 mm, the distnces AB nd BC nd A1B1 nd B1C1 (Figures 1 nd 2, respectively) were recorded. The vlues of ngles nd were then clculted trigonometriclly s tn ( ) BC/AB nd tn ( ) (B1C1/A1B1). The men vlue of the three clculted ngles ws ssigned s the inclintion of the corresponding rticulr eminence. The findings were tbulted nd processed further with SPSS for Windows softwre (7.5 Relese SSPS, Inc., Chicgo, IL). The left nd right sides were plotted seprtely ginst the dentl ge. Using the lowest procedure (SPSS), which is loclly weighted regression sctter plot

3 260 KATSAVRIAS TABLE 1. Descriptive Sttistics for All Groups Men SD SEM Minimum Mximum Men SD SEM Minimum Mximum Deciduous Dentition Type Mixed Permnent Vlues re men rticulr eminence inclintion ngles in degrees. TABLE 2. Unpired t tests Between nd Side for All Groups Type of Dentition df t Vlue P Deciduous Mixed Permnent Deciduous Mixed Permnent smoothing method, ech growth curve ws smoothed to 50%. Error of the study Twenty-four skulls (eight from ech group) were selected t rndom, nd the whole methodology ws repplied. Testing for systemtic errors ws performed using pired t- test, wheres testing for rndom errors ws done using the Dhlberg formul. The t-test t the.05 level ws not significnt. The rndom error for the mesurements for the inclintion clculted s the ngle between FH nd the best fit line on the posterior surfce of the rticulr eminence ws 1.66 (4%). The rndom error for the mesurements for the inclintion clculted s the ngle between FH nd the line of deepest point of the roof of the foss nd top of the rticulr eminence ws 0.43 (1.5%). Sttistics Descriptive sttistics re presented in Tble 1. Dt were nlyzed by pplying n unpired t-test between left nd right sides (Tble 2) nd using nlysis of vrince to ssess significnt differences between ge groups (Tble 3). Significnt differences between groups were further nlyzed using multiple comprison tests, such s the Tukey-HSD TABLE 3. Anlysis of Vrince Between Groups Side F P Clcultions for ech side include dt from groups A, B, nd C. TABLE 4. Tukey-HSD Test Group A Group B Group C side side side side Sttisticl significnce * ** Vlues re men rticulr eminence inclintion ngles in degrees. * Sttisticl significnce between groups A B. ** Sttisticl significnce between groups A C nd B C. test (Tble 4). The levels of significnce used were P.05. RESULTS In generl, there ws sttisticlly significnt increse in the rticulr eminence inclintion when plotted ginst ge. Detils for ech method of rticulr eminence inclintion mesurement re presented. Articulr eminence inclintion mesured s the best fit line on its posterior surfce (method 1) The men rticulr inclintion ws 26 t ge 2, 42 t ge 10, 56 t ge 20, nd 59 t ge 30. The inclintion hd ttined 40% of its finl size by ge 2, 70% by ge 10, nd 94.5% by ge 20, nd gined the remining 5.5% by the ge of 30 (Figure 3). Articulr eminence inclintion mesured s the ngle of FH plne to the line of deepest point of the roof of the foss nd the top of the rticulr eminence (method 2) The men rticulr eminence inclintion ws 20 t ge 2, 30 t ge 10, 36 t ge 20, nd 40 t ge 30. There ws no sttisticlly significnt difference between the right nd left sides, lthough smll differences were noted. At ge 2, the inclintion hd ttined 50% of its finl vlue, while t ge 10 it hd ttined 72.5% of its finl vlue. During the next 10 yers, the eminence inclintion ttined 90% of its finl vlue, cquiring the remining 10% during subsequent yers (Figure 4).

4 CHANGES IN ARTICULAR EMINENCE SLOPE DURING GROWTH FIGURE 3. The growth curve of the rticulr eminence inclintion, presented s the best fit line, seprtely for left nd right sides. Ech curve ws smoothed through the lowest (50%) method ( loclly weighted regression sctter plot smoothing method) of the SPSS sttisticl softwre. FIGURE 4. The growth curve of the rticulr eminence inclintion, presented s the foss-roof nd eminence-top line, seprtely for left nd right sides. Ech curve ws smoothed through the lowest (50%) method ( loclly weighted regression sctter plot smoothing method) of the SPSS sttisticl softwre. DISCUSSION In summrizing the findings of the present study, it is cler tht the inclintion of rticulr eminence hs very rpid growth rte during development of the deciduous dentition, ttining lmost hlf of its dult vlue by the ge of two yers. It then continues to grow, lthough t reduced rte, until the ge of 30 yers. Viewed in conjunction with the development of djcent res such s the middle crnil foss nd the muscles of mstiction, it seems plusible tht this initil very rpid growth is intended to prepre temporomndibulr joint morphology to withstnd the lod of future mstictory function. The fct tht it gins the 261 remining percentge over long period of time denotes susceptibility but lso n opportunity for therpeutic intervention. It should be recognized tht the skulls used in our study, strictly speking, were not rndomly selected. As stted, these skulls were selected on the bsis of condition, symmetry, nd type of dentition. It should be further recognized tht the stge of dentition development does not necessrily correspond to the stge of skeletl development. However, we feel tht these shortcomings did not in ny wy ffect the relibility of our results. Furthermore, one my question the representtiveness of these skulls to the modern popultion. However, becuse the study concentrted on the chnges of rticulr eminence inclintion during the crniofcil growth period, the findings re not likely to be ffected by this possible flw. It is well known tht the rticulr eminence is strongly convex, nteroposteriorly, nd slightly concve, mediolterlly. This profile leds to vrition in inclintion from point to point. Thus, one could question the vlidity of our method since we considered the rticulr eminence inclintion to be the men vlue of three consecutive sections tken 2.5 mm prt. However, the fct tht these three sections belong to the centrl prt of the eminence nd cover distnce of 7.5 mm out of mm 33 enbles us to consider the men vlue of these sections s good representtive smple of mesurement. One my wonder why we used two different methods to clculte the rticulr eminence inclintion. One method, the best fit line method (method 1), is mesure of the inclintion of the posterior surfce of the eminence. The other method, the foss roof eminence top method (method 2), is mesure of the reltionship of the eminence top reltive to the foss roof. It is obvious tht the second method is gretly ffected by the eminence height development, wheres the first method is the fctor tht dicttes the type of condylr pth. Mny methods hve been used in mesuring the rticulr eminence inclintion. These methods include impressions done with modeling cly, 14 direct mesurements, 5,16 rthrogrms, 26 pnormic rdiogrphs, 29 tomogrphic rdiogrphs (both corrected nd uncorrected), 23,24,34 cephlometric rdiogrphs, 15,27,35 scled photogrphs, 36 cephlometry using intensifying screens, 37 protrusive condylr pth, 38 nd wx. 39 The method used is very importnt fctor, s it influences the results. Modeling cly nd wx hve been criticized s being vulnerble to distortion nd shrinkge. Pnormic rdiogrphs of the joint re distorted, mking it very difficult to ccurtely nd relibly interpret its morphology. 40 The protrusive condylr pth 38 is n indirect method of mesuring the steepness of the eminence. However, whether the protrusive condylr pth trcing cn ccurtely revel the rticulr eminence inclintion is questionble. Cephlometry, photogrphy, nd uncorrected tomogrms cnnot overcome the ntomic difficulties of the region. It should be

5 262 KATSAVRIAS relized tht, in using rdiogrphic technique, it is very importnt to select one tht is cpble of imging the rticulr eminence t the sgittl plne, where the condyle-disk complex trnsltes. This requires the projection x-rys to be individully corrected ccording to the ngultion of the width (long xis) of the condyle nd foss. The siliconetype mteril used in our study, we believe, offered relible mens of rticulr eminence impression. Hence, the clcultion of the rticulr eminence inclintion ws relible becuse the physicl properties of this mteril re well known in our profession. It hs been reported tht t birth, there is no rticulr eminence, mking the first months of life the only period during which the mndible cn be moved forwrd or lterlly without ny inferior movement Tking this for grnted, it follows tht the rticulr eminence develops lmost entirely postntlly. The fct tht the congenitl bsence of condyles is ccompnied by rticulr eminence underdevelopment or bsence 44 denotes strong functionl dependence, view tht is further supported by the findings of Pirttiniemi et l. 35 They concluded tht rticulr eminence development is ffected more by function thn by skull bse chrcteristics. Demirjin 45 concluded tht rticulr eminence growth is ffected more by function thn by genetics. However, Iki et l 11 nd Ingervll 12 supported the view tht fcil morphology ffects rticulr eminence inclintion. Assuming functionl dependence, it is worth serching for the functions ffecting its development. A widely held view hs been tht development is relted to the presence of overbite nd overjet in the humn dentition. 46 Humn mstiction requires both incising nd grinding functions. Incision requires seprtion of the posterior teeth, wheres grinding requires lterl mndibulr movements tht re free of incisor or cnine interference. These ctions cn only be chieved by permitting the condyles to slide forwrd nd downwrd, nd this requirement is fulfilled by the rticulr eminence. However, ccording to Johnson nd Moore, 47 this type of mndibulr movement cn be chieved even in the bsence of n rticulr eminence. Furthermore, it hs been noted tht in jw joints of ncient forms of hominids nd gret pes, ll of the incisors meet edge to edge during mximum intercusption. It is obvious tht our dt cnnot enlighten the bove mentioned rguments. However, knowledge of the wy in which the rticulr eminence grows is considered to be very importnt, s such knowledge will help to estblish nd pply more biologicl therpeutic orthodontic modlities, especilly in cses of Clss II mlocclusion. For instnce, it is well known tht cses of Clss II division 2 mlocclusion re chrcterized by steep nd high rticulr eminences. However, it is not known which fctors influence this development or if the lingul inclintion of the upper incisors hs ny prticiption. Extending this line of thinking, it is lso unknown if the chrcteristics of the rticulr eminence hve ny effect in treting cses of Clss II mlocclusion with functionl pplinces. Unfortuntely, s ws stted, reports deling with the growth-relted chnges of rticulr eminence inclintion re scnt. To the best of our knowledge, these reports include those of Nickel et l, 36 Ricketts, 34 Scott, 48 Angel, 49 nd Humphreys. 50 Humphreys 50 stted tht until the ge of six, the foss is shllow, nd the rticulr eminence is bsent. The eminence then begins to grow t very slow rte until the ge of 10, when it receives mrked nd sudden impetus in growth. Its growth is prcticlly complete by the 12th yer of life. Our findings do not support Humphreys findings nd, since no detils were given in tht study, we cnnot determine the reson for such divergence. Our findings, however, gree in generl with those of Nickel et l, 36 who stted tht the eminence hs cquired more thn 50% of its mture size by the ge of three. The method they used to mesure the rticulr eminence inclintion is similr to the method of the best fit line on its posterior surfce tht we used in the present study (method 1). However, our findings revel tht by the ge of 3, the rticulr eminence inclintion hs cquired 42% of its mture vlue. There seems to be n overestimtion in the findings of Nickel et l, 36 which is probbly function of the method used. Ricketts, 34 using smple of 200 joints from individuls with Clss I nd Clss II mlocclusions, concluded tht t ge 7.5 yers, the inclintion ws 46 (77.9% of its mture form), nd t ges 12.5, 18.5, nd 22 yers, the inclintion ws 52 (88%), 57 (96,6%), nd 59, respectively. It is obvious tht Rickets 34 men vlues re lrger thn ours, but it should be noted tht his mesurements were obtined using no individully corrected temporomndibulr joint lmingrms. A remining unnswered question is the point t which growth of the rticulr eminence inclintion stops. Riesner 51 reported tht the foss grows until ge 25, wheres Angel 49 reported tht growth continues until ge 33. However, Moffet 52 showed tht grdul increse in size of eminence occurs until the ge of 40. The disgreement bout when rticulr eminence inclintion growth ends is reflected in the fct tht reported dult vlues for the inclintion show gret dispersion. For instnce, Nickel et l 36 reported n dult vlue of 45, while Moffet 53 reported 42.8 ( 10 ) for whites, 39.2 ( 10 ) for shell mound Indins, 36.5 for West Africns, nd 33.9 for Austrlin borigines. Ichikw nd Lskin 5 reported dult vlues of 65.9 ( 7.7 ) for steep eminences, 54.8 ( 10.4 ) for moderte eminences, nd 47.4 ( 12.3 ) for flt eminences. Pnmekite et l 26 reported vlue of 36.4 ( 4.9 ); Kerstens et l, ( 21.7 ); Hll et l, ; Ricketts, nd Widmn, ( 4.2 ). It hs been reported tht the temporomndibulr joint undergoes continuous morphologic lter-

6 CHANGES IN ARTICULAR EMINENCE SLOPE DURING GROWTH tion, nd tht this ltertion is medited by dentl occlusion. 3 If this is true, then it seems difficult to differentite rel growth chnges from those chnges of n dptive nture. However, considering tht crniofcil growth more or less stops round ge 20, it seems logicl to ssume tht growth chnges of the temporomndibulr joint should lso stop round this ge. It follows tht ll subsequent chnges should be considered s dpttions to ltered functions. On the other hnd, it hs been reported tht sutures round the temporomndibulr joint, such s the petrooccipitl, squmosl, nd occipitomstoid sutures, fuse round ge This feture forced us to regrd ge 30 s the ge of mturtion. The differences between right nd left sides were not sttisticlly significnt. These findings re in ccordnce with those of Dorier et l, 55 Weinberg, 56 nd Ichikw nd Lskin, 5 but contrdict those of Lindblom, 57 who climed tht left temporomndibulr joints were lrger thn right temporomndibulr joints. In summry, the rticulr eminence inclintion, regrdless of the method of mesurement, hs period of very rpid chnge during development of the deciduous dentition. Chnges in this inclintion then slow, nd growth of the rticulr eminence seems to follow growth pttern very similr to tht of fcil development. The fct tht the rticulr eminence inclintion develops lmost exclusively postntlly denotes strong functionl dependence. Wht remins to be investigted is the interction of growth of the rticulr eminence inclintion with fcil structures nd the role, if ny, of rticulr eminence inclintion in temporomndibulr joint dysfunction. In ddition, further investigtion is needed into the role of the rticulr eminence inclintion in treting cses of Clss II mlocclusion with functionl pplinces nd pproches for guiding the development of the rticulr eminence inclintion. CONCLUSIONS Bsed on the findings of this work, the following conclusions cn be drwn: 1. Under norml conditions, the rticulr eminence inclintion hs symmetricl pttern of growth, mening tht there is no sttisticlly significnt difference between the development of the right nd left sides. 2. By the ge of two, the rticulr eminence inclintion cquires 40% to 50% of its finl vlue. The percentge figure depends on the method by which the inclintion is mesured. 3. The inclintion reches bout 71% of its finl vlue by the ge of 10, 92% by the ge of 20, nd full inclintion by the ge of Although the eminence belongs to the crnium, its growth pttern more closely resembles tht of the fce. 5. The fct tht 50% of the eminence s dult inclintion vlue is ttined over long period denotes not only 263 vulnerbility, but lso possible opportunity for therpeutic intervention. REFERENCES 1. Ktsvris E, Doukoudkis A. The Norml Temporomndibulr Joint. Athens, 2001 [in Greek]. 2. Ktsvris E. Chnges of Articulr Eminence Inclintion During Crniofcil Growth Period [in Greek]. Reserch monogrph, Athens, Greece, University of Athens: Hinton RJ. Chnges in rticulr eminence morphology with dentl function. Am J Phys Anthropol. 1981;54: Bell WE. Clinicl Mngement of Temporomndibulr Disorders. Yer Book Medicl Publishers, Chicgo, IL; 1982: Ichikw W, Lskin DM. Antomic study of the ngultion of the lterl nd midpoint inclined plnes of the rticulr eminence. Crnio. 1989;7: Grnd FM. A Crniometric Study of the Articulr Tubercle of the Temporl Bone [mster s thesis]. Sn Antonio, Tex: University of Texs; Okeson JP. Mngement of Temporomndibulr Disorders nd Occlusion. 4th ed. 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