Occlusal Morphology 1 Year after Orthodontic and Surgical-Orthodontic Therapy

Transcription

1 Originl Article Occlusl Morphology 1 Yer fter Orthodontic nd Surgicl-Orthodontic Therpy A Quntittive Anlysis of Cliniclly Successful Ptients Cludi Dellvi ; Luis Toms Hunc Ghislnzoni b ; Redento Perett c ABSTRACT Objective: To evlute morphologic chrcteristics of occlusion (contct points, contct res, nd frequency of contct) in cliniclly successful ptients 1 yer fter orthodontic nd surgiclorthodontic therpy followed by pssive retention. Mterils nd Methods: Twenty-two orthodontic nd 18 surgicl-orthodontic ptients were nlyzed. All ptients were treted with stndrd edgewise technique by the sme orthodontist. Contct points nd res were evluted using new method of digitl imge nlysis of occlusl impressions. Polivinylsyloxn impressions were tken, scnned, nd turned into gry-scle imges. The physic reltionship of light bsorbnce through the polivinylsyloxn for known thickness ws clculted to determine contct res (less thn 50 m of thickness) nd ner contct res (less thn 350 m of thickness). Results: The contct re ws significntly lrger in the orthodontic thn in the surgicl-orthodontic ptients (Student s t-test, P.05). The surgicl-orthodontic group hd significntly fewer contct points thn the orthodontic group only t 150 m of thickness. In both groups of ptients, the first molr hd the lrgest contct surfce. Occlusl support ws distributed minly in the posterior regions with n importnt role involving the first molrs. Conclusion: Surgicl-orthodontic ptients pper to hve smller contct surfces nd fewer contct points thn orthodontic ptients do. However, there were no differences in the number of teeth in contct with opposing teeth. KEY WORDS: Occlusion; Retention; Orthognthic surgery INTRODUCTION Clinicl success fter orthognthic therpy cn be defined s combintion of six fctors: (1) ptient (nd ptient s fmily) stisfction, (2) correct occlusl reltionship (one tooth ginst two), (3) stbility 1 yer fter tretment, (4) incisl/cnine guide with posterior disclusion in protrusive nd lterl movements, (5) ptient comfort when chewing, nd (6) no pin in the temporomndibulr joint (TMJ). 1 3 Reserch Assistnt, Deprtment of Humn Morphology, University of Miln, Miln, Itly. b Postgrdute Student (DDS), Deprtment of Humn Morphology, University of Miln, Miln, Itly. c Postgrdute student (MD, PhD), Deprtment of Humn Morphology, University of Miln, Miln, Itly. Corresponding uthor: Dr Cludi Dellvi, Deprtment of Humn Morphology, University of Miln, Vi Mngiglli 31, Milno, Itly (e-mil: cludi.dellvi@unimi.it) Accepted: Jnury Submitted: October by The EH Angle Eduction nd Reserch Foundtion, Inc. These objectives cn be ssessed using Andrews s 4 six keys to define the best occlusion when finishing cse. It is cliniclly ccepted tht occlusion control is trnsferred from pplinces to ptient s neuromusculr system t the end of tretment. Unfortuntely, the modlity of occlusl ssessment is still unknown. It cn be supposed tht there is good integrtion between new occlusl morphology nd musculr function when occlusion shows stbility long time nd the follow-up is negtive for TMJ pin. It is of clinicl interest to define ntomic prmeters to ssess the evolution of ech cse during the period of occlusl recovery (1 to 3 yers fter tretment). Sullivn et l 5 found fewer contct points in postorthodontic ptients thn in control subjects, with the number of contcts incresing with time. Further long in retention, occlusion is dynmic condition influenced by the nturl tendency to relpse, occlusl forces, the neuromusculr system, nd the retention pplinces themselves. Occlusl recovery involves mny fctors, nd vrition in contct points is re- DOI: /

2 26 DELLAVIA, GHISLANZONI, PERETTA lted to overbite/overjet modifictions. 6 In conventionl orthodontic tretment, there is 14% ugment in the number of contct points t 3 months, 7 which becomes 56% t 1 yer. 8 Severl methods hve been proposed to mesure contct res. Unfortuntely, most of these systems re opertor dependent. 9 The polyvinyl-siloxne impression method is virtully opertor independent with gret repetbility. 10 The mteril is fluid before setting, thus hving nil resistnce to mndibulr closure force without modifying the proprioceptive senstion during clenching. Contct points nd surfces hve been studied by digitl imge nlysis of silicon impression thickness in control subjects nd compred to subjects with mlocclusion 11 nd to postorthodontic ptients. 12 In ddition, the interprettion of digitl dt obtined with the scnning of the impressions, where described, ppers imprecise. 11 To dte, few dt bout occlusl morphology in post surgicl-orthodontic ptients re vilble. 13 The objective of the current study is to describe the chrcteristics of occlusion in surgicl-orthodontic ptients compred to conventionlly treted orthodontic ptients 1 yer fter the end of the orthodontic therpy, pplying new method of computing res nd points of contct nd ner contct from polyvinyl-siloxne occlusl impressions. MATERIALS AND METHODS Forty ptients ged 14 to 32 yers were nlyzed: 22 ptients (6 men, 16 women; men ge 20.0 yers, SD 6.3, rnge 14 28) were treted with orthodontic therpy (ORTHOs) nd 18 ptients (6 men, 12 women; men ge 24.8 yers, SD 4.4, rnge 18 32) were treted with surgicl nd orthodontic therpy (SURGs). Before the therpy, the orthodontic group ws composed of 4 skeletl Clss I mlocclusion ptients (0 ANB 4 ), 15 ptients with Clss II tendency, nd 3 ptients with Clss III tendency. The surgicl group ws composed of 3 ptients with Clss II tendency nd 15 ptients with skeletl Clss III mlocclusion. In both groups, most of the subjects hd norml verticl dimension (fcil index 60% 70%); only few cses of open nd deep bite were observed. Surgicl ptients were treted with combined mxillry Le Fort I nd sgittl mndibulr osteotomies. All subjects were treted with stndrd edgewise technique by the sme orthodontist. The orthodontic therpy ended bout 6 months fter surgery. After the completion of the orthodontic tretment, the verticl dimension showed only miniml vrition, while ll ptients finished with skeletl Clss I occlusion (men ANB of ORTHOs ; SURGs ), except for four surgicl ptients with Clss II tendencies. After tretment, the ptients occlusion ws stbilized with Begg plque in the upper rch nd spring retiner in the lower rch. At the first-yer recll, ptients completed self-dministered questionnire specificlly designed to mesure their stisfction (esthetic ppernce, comfort when chewing, bsence of pin in the TMJ). All ptients were stisfied. In ddition, the orthodontist ssessed correct occlusl reltionship (one tooth ginst two), incisl/cnine guide with bck disclusion in protrusive nd lterl movements, nd stbility 1 yer fter tretment. The current mesurements were performed t the first yer fter the beginning of retention (12 months fter orthodontic tretment completion for both groups, 18 months fter surgery for the surgicl ptients). All subjects gve their informed consent to the experiment. All procedures were noninvsive nd performed with miniml discomfort to the subjects. All occlusl impressions were performed by single opertor. The study protocol ws pproved by the locl ethics committee. Estimtion of Occlusl Contct Ares nd Points Occlufst Rock (Zhermck Inc, Trieste, Itly) silicone-bsed registrtions of occlusion were obtined in mximum intercusption. This polyvinyl-siloxne ws chosen becuse of the ese of dispensing nd ppliction, good viscosity, fst setting time (1 minute), detil of impression, nd hrdness nd rigidity once set. The impression mteril ws injected on the occlusl plte of ll the teeth of the lower rch with disposble syringe. Ech subject ws seted upright in dentl chir, mintining the nturl hed position. Ptients were sked to bite down firmly into mximum intercusption for 20 seconds nd to keep this position with light force until the mteril hd set. An imge of ech occlusl registrtion ws obtined with Hewlett Pckrd ScnJet 6100C/T scnner (Plo Alto, Clif). A stndrd record t known thickness ws used to check the sme light power for ech scnning. The softwre progrm Adobe Photoshop ws used to convert the imge into luminnce (gryscle) imge nd to mnully insulte the pltform re of ech tooth (Figure 1). Since the opcity of the mteril increses proportionlly to thickness, clibrtion step wedges of polyvinyl-siloxne of known thickness were used to estblish the reltionship between ech level of the 256 gry scle nd the thickness of the occlusl registrtion (Tble 1; Figure 2). Thickness ws mesured us-

3 MORPHOLOGICAL OCCLUSION IN POSTORTHODONTIC PATIENTS 27 Figure 1. Scnned imge of the occlusl registrtion (mndibulr surfce fcing downwrd) in one orthodontic ptient. On the left side is n exmple of mnul insultion of ech single tooth. ing dibse control plne with comprtor. The men error ws 20 m. The clibrtion step wedges were scnned nd nlyzed with Imge Pro Plus softwre (Medi Cybernetics Inc, Silver Spring, Md). A gry-scle vlue ccording to the pixel density ws obtined (ie, the thickness of the smple). Using physicl theoreticl pproch to the phenomenon of light bsorbnce through mteril, we defined n eqution tht fit with our dt s ( 0,000993x) x 0,19099 y 455,614 e where x is the vlue of thickness in micrometers nd y the luminosity in gry-scle vlues. According to previous studies with silicone impressions, 10,14 ctul contcts were defined s res of contct with thickness t or below 50 m, nd ner contcts were defined s those with thickness t or below 350 m. Contct res nd points were considered t 50, 150, 250, nd 350 m fter clculting the gry-scle equivlent of the threshold thickness. In ddition, the frequency of contct ws computed evluting the presence of t lest one contct point on ech tooth. An symmetry index for contct res nd points ws clculted ccording to the following formul: Tble 1. Thickness nd Luminosity With Error Mesures (Rnge nd SD) for Ech Clibrtion Step Wedge Step Wedge, n Thickness, m Rnge Luminosity, GS SD GS indictes gry-scle vlue. Figure 2. Reltion between thickness in m (x) nd luminosity in gry scle (y). right side left side Asymmetry Index 100 right side left side The bsolute vlues of the symmetry index were lso used to void right- or left-side prevlence. For ech ptient, the reltive weight of every tooth/group of teeth contct re ws blnced on the totl re. The sme procedure ws performed for the number of contct points. The repetbility of the procedure (impression, scnning, nd mnul insultion of single teeth) ws tested, repeting the exmintion 4 times in 6 control subjects. A good repetbility ws ssessed, s the men coefficient of vrition ws 2.3% (rnge, 0.6% 5.1%) for contct res nd 4.8% for contct points, (rnge, 1.2% 8.4%). Sttisticl Anlyses For ech subject, the re nd number of contcts for ech tooth were computed. The skewness nd kurtosis showed tht the totl re nd the number of contcts were normlly distributed within ech group. Descriptive sttistics (men, stndrd devition, nd coefficient of vrition) were clculted for ech vrible (ge, contct re, nd points). The men vlues of ech vrible were compred in the two groups of ptients using Student s t-test for independent smples. Comprisons between groups were computed by two-wy fctoril nlysis of vrince (ANOVA) test to evlute the effect of therpy (fctor 1) nd the loction of the teeth in the rch (eg, nterior/posterior; fctor 2). The interction be-

4 28 DELLAVIA, GHISLANZONI, PERETTA Tble 2. Contct Are nd Points in the Orthodontic nd Surgicl-Orthodontic Ptients Mesurement Orthodontic (n 22) x SD CV, % Surgicl-Orthodontic (n 18) x SD CV, % Student s t-test Are, mm 2 50 m *** 150 m * 250 m * 350 m * Points (n) 50 m ns 150 m * 250 m ns 350 m ns ns indictes not significnt. * P.05; ** P.01; *** P.001. tween the two fctors ws lso computed. A 2 test ws used to compre the gender distribution nd the frequency of contct of ech tooth nd group of teeth between the two groups of ptients. A correltion coefficient ws computed to ssess the influence of ge on contct res nd points. For ll nlyses, the level of significnce ws set t 5% (P.05). RESULTS Significnt ge differences were found between the two groups of ptients. The ORTHOs were younger thn the SURGs (Student s t-test, P.05). No difference in gender distribution ws found between the two groups ( 2 test). Within ech group, no significnt effect of ge ws found on contct res nd points (correltion coefficient, P.05). Tble 2 reports the men re nd points of contct ( 50 m) nd ner contct t 350 m nd t intermedite thickness. There ws gret intrgroup vribility, with the coefficient of vrition rnging from 33% to 60% for the res nd 16% to 43% for the number of points. The ORTHOs contct re ws significntly lrger thn the SURGs re t ll levels (Student s t-test, P.05; Figure 3). The contct points were significntly different only t 150- m thickness (P.05). The men vlues of re nd contct points seprtely for ech tooth re reported in Tble 3. The mndibulr first molr hd the lrgest contct re in both groups nd the highest number of contct points in the ORTHOs. Differences between the contct re nd points on the right nd left sides were not sttisticlly significnt for the overll ptients nor for the two groups (Student s t-test). For the overll ptients, the men index of symmetry ws 3% for res (SD 29%) nd 1% for points (SD 22%). The men bsolute vlues of the index were 24% for res (SD 17%) nd 16% for points (SD 15%). In the observed ptients, 390 of the 556 (70%) nlyzed mndibulr teeth (two ptients hd their first premolrs extrcted) were in contct with their mxillry opponents: men of 9.8 mndibulr teeth were in contct with their opponents (SD 2.6). There were no differences between the two groups. Of the 390 teeth in contct, 196 contcts occurred on the right side nd 194 on the left side. The nterior teeth (incisors nd cnines) were in contct in 45% of the OR- THOs (60 of 132) nd in 52% of the SURGs (56 of 114). The posterior teeth (premolrs nd molrs) were in contct in 88% of the ORTHOs (152 of 172) nd in 85% of the SURGs (122 of 152). On verge, the teeth with the highest frequency of contct were the first molr (95% ORTHOs; 100% SURGs) nd the second molr (98% ORTHOs; 89% SURGs). There were no significnt differences between the two groups in the frequency of contct of single (Tble 3) or grouped (nterior, posterior) teeth ( 2 test). The contct re nd points reltive weight per group of teeth in the ORTHOs nd in the SURGs re listed in Tble 4. Between the two groups of ptients, no differences were found in the distribution of contct Figure 3. Men contct re of ech single tooth in orthodontic (OR- THOs) nd surgicl-orthodontic ptients (SURGs). On the x-xis re the mndibulr teeth; on the y-xis is the contct re (thickness 50 m) in mm 2.

5 MORPHOLOGICAL OCCLUSION IN POSTORTHODONTIC PATIENTS 29 Tble 3. Tooth Men Are, Points, nd Frequency of Contct for Ech Mndibulr Tooth in the Two Groups of Ptients Orthodontic (n 22) Surgicl-Orthodontic (n 18) Are, mm 2 Points Frequency, % Are, mm 2 Points Frequency, % Centrl incisor Lterl incisor Cnine First premolr Second premolr First molr Second molr Frequency, % indictes the frequency of presence in contct. re nd number of contct points reltive weights; in ddition, the interction between the two fctors ws not significnt (ANOVA two-wy test). No effect of the loction of the teeth in the rch (nterior nd posterior teeth) ws found, nd the interction of the loction fctor with the therpy fctor ws not significnt. DISCUSSION The photo-occlusion technique is opertor independent. It is computerized, semiutomtic imge nlysis system tht recognizes the occlusl contcts nd ner contcts ccording to threshold thickness/luminosity previously identified. In the present investigtion, the silicon ws preferred to other mterils since it ppered to be the most precise, repetble, nd opertor-independent mteril to exmine occlusl morphology. 9,11 A pilot study ws conducted so tht the opertor could become fmilir with the experimentl procedure. The current protocol ws similr to the one defined by Owens et l, 11 but the clibrtion curve describing the intensity of light expressed in gry scle ws more ccurte for thicknesses greter thn 50 m. The present curve represents n optiml pproximtion of light behvior through the impression mteril for vlues of thickness (lrger thn 50 m) concerning contct nd ner-contct points. These concerns minimized bis. Tble 4. Contct Are nd Points Reltive Weight (in Percentges) per Group of Teeth (Blnced on Totl Are/Points) in the Two Groups of Ptients Teeth Group Orthodontic (n 22) Are % Points % Surgicl-Orthodontic (n 18) Are % Points % Incisors Cnines Premolrs Molrs Anteriors Posteriors b Incisors nd cnines. b Premolrs nd molrs. In the present study, the orthodontic ptients were significntly younger thn the surgicl ones. All of the ORTHOs underwent therpy fter the pubertl growth pek, in the lst phse of growth, while the SURGs cn be definitely considered n dult smple. The ge difference is due to the necessity of growth ending before performing surgicl tretment. The influence of ge cnnot be excluded in occlusl recovery independent from the therpy. Most investigtions refer to dolescent subjects, which llows us to compre our orthodontic group with results of previous studies. 12,15 Nevertheless, contct nd ner-contct surfces t 50 nd 350 m were independent from gender nd ge in ccordnce with Gurdspsri et l. 10 Previous studies 16,17 found 7 to 12 contct points for hemimndibles in helthy subjects. Similrly, contct points for hemimndibles were found in the present work. Dincer et l 12 compred 20 untreted subjects with 20 orthodontic ptients fter 9 months of retention. They found no differences in the number of contct points between ptients nd controls. The current dt in the orthodontic group were comprble with these findings 12 nd led us to investigte wether the occlusion in surgicl-orthodontic ptients t the end of tretment is comprble with occlusion of pure orthodontic ptients. The men contct re ppers to be relted to the therpy. The ORTHOs contct re nd ner-contct re re significntly lrger thn the SURGs vlues. A possible explntion of these results could be the chnge of chewing hbits of ll ptients undergoing surgicl tretment. After surgery, ptients report certin difficulty when grinding food nd discomfort when biting hrd foods, such s bred nd crrots. This senstion improves with time, until disppering 1 to 2 yers fter surgery. Mstictory efficiency mesured with stndrd sieve techniques in surgicl ptients ws found to be lower thn in control subjects. 18 The postsurgicl functionl sitution ws generlly better thn the presurgicl one. The mstictory cycles were less vrible, showing higher stbility of occlusion. 19,20 Other investigtions found reltion be-

6 30 DELLAVIA, GHISLANZONI, PERETTA tween chewing efficiency/number of teeth in contct nd re of ner contct. 21 The smller re nd the fewer contct points observed in the SURGs thn in the ORTHOs could be explined by the lower dynmic stimulus to mstiction of surgicl ptients during the occlusl recovery period. Since considerble chnge in bite force, which is not primrily relted to jw movement, occurs fter orthognthic surgery, 22 these chnges my explin significnt proportion of the differences between the groups in the number nd size of contct res. This fctor in conjunction with the inherent compressibility of the periodontl ligment my explin the differences observed when the teeth were held in occlusion. Furthermore, the lck of ny wy of stndrdizing the occlusl force my lso hve influenced the findings. Nevertheless, n incresed number of contcts in post surgicl-orthodontic ptients 6 months fter surgery ws reported by Athnsiou. 13 In the current work, ptients were evluted 18 months fter surgery, nd t this time, their recovery period my be not concluded yet. The bsolute vlues of the symmetry index found for the re nd the number of contct points indicte certin degree of individul symmetry, in ccordnce with the work of McDevitt nd Wrreth. 6 The bsence of contct between the upper nd lower nterior teeth occurred in 53% of the nlyzed ptients. Similr findings in young control subjects were reported by McNmr nd Henry (40%). 15 A 15% lck of contct ws observed mong the posterior teeth of the nlyzed subjects. Possible explntions could be the strightening of the curve of Spee, the ugment of the upper curve, nd the overtretment of overbite/ overjet. The higher frequency of contct of the centrl incisor in SURGs thn in ORTHOs my be ccounted for by the totl horizontl nterior relpse nd postopertive counterclockwise rottion of the mndible observed in surgicl Clss III ptients (most SURGs) fter bilterl sgittl split osteotomy. 23 The number of contcts on first molrs in the OR- THOs is comprble to the findings of Dincer et l 12 in norml subjects. Molrs re the teeth more frequently in contct with their opponents, which underlines their role in keeping occlusl stbility. Further studies in lrger smples re needed to define the morphologic occlusl chnges in orthodontic nd surgicl-orthodontic ptients fter 1 yer of retention. Although there were differences between the groups in terms of the size nd number of contcts, there were no differences in the number of teeth in contct with opposing teeth. Furthermore, there were no differences in the frequency of contcting teeth when this ws further nlyzed by grouped teeth (nterior or posterior). The wy the orthodontists finish cses, in ccordnce to the literture, 2 4 is probbly wht determines the number of teeth in contct with their opponents. In contrst, the size nd number of contcts could be relted to the neuromusculr system recovery peculir of ech ptient. CONCLUSIONS The nlyzed surgicl-orthodontic ptients hd smller contct surfces nd fewer contct points thn orthodontic ptients did. There were no differences in the number of teeth in contct with opposing teeth. REFERENCES 1. Mscrenhs AK, Vig K, Joo BH. Prents stisfction with their child s orthodontic cre: comprison of orthodontists nd peditric dentists. Peditr Dent. 2005;27: Mhony D. Refining occlusion with muscle blnce to enhnce long-term orthodontic stbility. Gen Dent. 2005;53: Clrk JR, Evns RD. Functionl occlusion: I. A review. J Orthod. 2001;28: Andrews LF. The six keys to norml occlusion. Am J Orthod. 1972;62: Sullivn B, Freer TJ, Vutin D, Bsford KE. 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7 MORPHOLOGICAL OCCLUSION IN POSTORTHODONTIC PATIENTS Athnsiou AE, Melsen B, Kimmel P. Occlusl tooth contcts in nturl norml dult dentition in centric occlusion studied by photocclusion technique. Scnd J Dent Res. 1989;97: Iwse M, Sugimori M, Kurchi Y, Ngumo M. Chnges in bite force nd occlusl contcts in ptients treted for mndibulr prognthism by orthognthic surgery. J Orl Mxillofc Surg. 1998;56: Kobyshi T, Honm K, Shingki S, Nkjim T. Chnges in mstictory function fter orthognthic tretment in ptients with mndibulr prognthism. Br J Orl Mxillofc Surg. 2001;39: Youssef RE, Throckmorton GS, Ellis E III, Sinn DP. Comprison of hbitul mstictory cycles nd muscle ctivity before nd fter orthognthic surgery. J Orl Mxillofc Surg. 1997;55: Julien KC, Buschng PH, Throckmorton GS, Dechow PC. Norml mstictory performnce in young dults nd children. Arch Orl Biol. 1996;41: Proffit WR, Turvey TA, Fields HW, Phillips C. The effect of orthognthic surgery on occlusl force. J Orl Mxillofc Surg. 1989;47: Politi M, Cost F, Cin R, Polini F, Robiony M. Stbility of skeletl Clss III mlocclusion fter combined mxillry nd mndibulr procedures: rigid internl fixtion versus wire osteosynthesis of the mndible. J Orl Mxillofc Surg. 2004;62: