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QUANTITATIVE ASSESSMENT OF CLASS II MALOCCLUSION IN MIXED DENTITION by Pius Jwn-Young Kim Divisionof Graduate Orthodontics Submitted in partial llfilment ofthe requirements for the degree of Master ofClinical Dentistry Faculty of Graduate Studies The University of Western Ontario London, Ontario February 1997 BPius Joon-Young Kim 1997 National Library Biblioth&que nationale du Canada Acquisitions and Bibiiographic Services Acquisitions et sewices bibliographiques 395 Wellington Street OltawaON K1AON4 395, rue Wellington OtmwaON K1AON4 Canada Canada L'auteur a accorde m e licence non exclusive pennettant a la Biblioth6qge nationale du Canada de reproduke, prgter, dktri'buer ou reproduce, loan, distn'bute or sell copies ofhismer thesis by any means vendre des copies de sa these de and in any form or format, making forme que ce soit pour mettre des this thesis availab1e to interested exemplaires de cette thkse a la persons. disposition des personnes int&e&es. The author has granted a nonexclusive licence allowing the National Library of Canada to The author retains ownership ofthe copyright in hidher thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced with the author's permission. L'auteur consewe la propriete du &oit d'auteur qui protkge sa these. Ni la these ni des extraits substantiek de celle-ci ne doivent &re imprimts ou autrernent reproduits sans son autorisation. Abstrret The purposeofthis study was to investigate cepbalometrically the facial components associated with Class II malocclusions and compare the &dings with previously published studies. The sample consisted of 46 msks and 59 fbdes in mixed dentition (range: 8.0- 11-0 years) with Class I1 molar and cuspid relationships. Lateral cephalometric radiographs for these subjects were obtained tiom the files o f the Graduate Orthodontic Clinic, at the University of Western Ontario (London, Ontario). In 40 of these subjects, posteroanterior (P-A) cephalometric radiographs were also available to investigate the rmutillomandibular transverse skeletal relationships. A wide variation was evident fiom the various measurements. In comparison to the established cephalometric norms, the maxilla was more prognathic in 35.2% of the subjects based on SNA and 21 -0% based on A point to nasion perpendicular measurements. The mandible was retrogrdic in 76.2% based on SNB and 55.2% based on pogonion to nasion perpendicular measurements. The lower f- height was short to normal in 26.7% and exoessive in 73.3% ofthe subjects mpechely. The Pearson correlation coefficients between the transverse dimensions of maxilla and to the lower anterior face height were 0.40 and 0.46, respectively. Compared to cephalometric norms, the maxillary incison were protrusive in 23.8% with reference to A point vertical and 98.1% with respect to A pointpogonion line while the madicbular incisors were retnrsive to A point-pogonion line in 44.8% of the sample. Key words: Class I1 Malocclusion, Mixed Dentition, Cephalometry, Facial dimensions I would like to atpress my sincere gratitude to my thesis advisor and the chairperson of the orthodontic program, Dr. AH. hrlamaadras for his constant support, guidance and encouragement in this study. I would like to extent my thanks to the following members of my cornminee, Dr. D.W. Banting, Dr. TF. Foley, Dr. W.S. Hunter and Dr.J. R Murray for their valuable and constructive comments- Special thanks to my classmates, Drs. P.J. Karl and U P .Meehan and their f d e s for the support and Wendships during the past three years. I would like to acknowledge alI the staff members and personnel involved with the Graduate Orthodontic Program at the University of Western Ontario. A special gratitude to Mrs. P.J. Blake for her technical support with this thesis. To my wife, Sylvia and our children, Rachel, Kathryn and William, for their love, encouragements and shariag this memorable time in our lives together. finally, to my mother and late fhther, who d a d and made everything possible for our education. Page Certificate ofE x m i d o n . . ... - . . . .. . . . ... . - .. . .. . . . . . . . . . . .. . . . . . . . . . . ii Abstra~t.................................................~.......... ..- ur Acknowledgments . . . . . . . . . .. . . . . . . . . . . . . . . . . .. .. . .. . . . . . . . . . . . . . . . . . . iv Table ofContents . . .. ,, , , . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . - . . . . . .. . . .. . v List of Tables . . . . . . . - . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi ,, , ,, ListofFigures ....................................................... vii List of Appendices . . . . .. . . . .. . . . . . . . . . . . . . . . . . .. . ... . . . . . . . .. . . . . . . . . . ix Introduction . . . . . . . . . . . . . . . . . . . , . . - . . . . . . . . .. . . ... . . , . , . . . . . . . . . . . . . - 1 Materials and Methods . . . . . . . . . . . . . - . . . . . . . . . . . . . .. . .. . . . . . . . . . . . . . . . . 4 Results ........,.....,.,............,............................... 6 Discussion ...........,.................................,............. 9 Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Tables ........,..........,....,....-....-.,.................,.,...- 16 Figures ............................................................ 24 Appendices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 References . . . . . . . . .. . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. , . . . 46 Vita ............................................................... 50 Table 1 Standard errors of manual measurements 2 Lateral cephelomeaic measurements d subgroup measurements by gender Maxillary and mandibular transverse dimensions (mm) and me& ratios between maxillary basal to man&bdar basal dimensions; total sample and subgroup measurements by gender M d a r y length end mandibular length measurements (rnm), and 9 year old cephalometric norm fiom Bolton, Burlington and Michigan Growth studies with associated percent enlargements Pearson correlation coefficients for various cephalometric skeletal variables Pearson correlation coefficients for rmucillary and mandibular transverse dimensions to lower anterior face heights 21 Correlations between measurements from condylion and articulare to A point and gnathion 22 Subgroup measurements with angle ANB < 4.5" versus angle 23 ANB > 4.5" LIST OF FIGURES Figure 1, Lateral cepbalometric landmarks 2. Angular measurements for lateral cephalometric radiographs Linear measurements for lateral cephalomemc radiographs Frontal (posteroanterior) cephalometric landmarks with linear measurements Distniution of maxillary position, measured with angle SNA Distribution of maxillary position, measured by linear distance fiom nasion perpendicular to A point Distribution of mandibular position, measured with angIe SNB Distribution of mandibular position, measured by linear distance fiom nasion perpendicular to B point Distribution of mandibular position, measured by the angle between Frankfort plane and mandibular plane Distribution of linear vertical dimension, fkom anterior nasal spine to menton Distribution of mandibular position in vertical and anteroposterior dimensions, measured by the posterior angle between basion-nasion plane and pterygomaxillaxy-gnathion plane Distribution of vertical mandibular position, measured by the angle between sella-aasion plane and mandibular plane vii 35 List of Figures cont'd. 13, Distributionof maxillary incisor position in anteroposteriorposition, measured tiom A point vertical to most facial sudhce of maxillary incisor Distniution of maxillary incisor position in anteroposterior position, measured fiom A pointpogonion line to incisal tip of maxillary incisor Distribution of mandibularincisor position in anteroposteriorposition, measured &omA pointpogonion line to incisal tip of mandiiular incisor LIST OF APPENDICES A Definitions of l a n a , angles and planes utilized 39 B Cephelometric norms fiorn various analyses 40 C Corrected linear measurements of the sample (1 1%) 41 D Mardllary length and mandibular length, corrected measurements of the sample and corrected cephalometric nonns fiom Bolton, Burlington and Michigan Growth studies 42 E List of individuals in the sample from the Graduate Orthodontic Clinic, UWO Introduction The prevalence ofclass I1 malocclusions is reported fiom 15% to 38.6% in children 6 to 11 years of age? A broad spearurn of treatment philosophies and modalities are available for the treatment of Class II malocclusions. These include various dentofacial orthopedic appliances for growing individuals, extraction of bicuspids, or orthognathic surgery where the growth potential is limited or udavourable. It is important to recognize and address variations in size, position, form and proportions of the dentofacial complex in the diagnosis of Class II malocclusions. It has been suggested by various investigators that the Class 11malocclusion is not a single entity, but rather a combination of various skeletal and dental components.zCD In 1941, ~aldridge'proposed four possible conditions associated with Class 11malocclusions: 1. Over-development of the maxilla in conjunction with a mandible being n o d in position and size. .. 11. Mamllary teeth are forward in relation to the maxilla. The relationship of the maxilla to mandiiiile is normal. iii. The mandible is underdeveloped or smaller than normal in size. The maxilla is normal. iv. The mandible is in a posterior position with respect to a normal maxilla. In 1948, Elsasser and Wylie6 suggested an additional condition associated with Class II malocclusion. v. The maxilla and mandible are average in size and position but the mandibular dental 2 arch is posteriorly placed on the mandiiufar base. Some studies,zGc18have reported that the major component of Class II malocclusion is the skeletal mandibular retmsion. Protrusive skeletal maxilla has been suggested by some hrvestigatodvWDas a primary causative k t o r in Class 11rnalocdusion, while have attributed Class I1 malocclusion to a maxilla that is either neutral or slightly retrognathic. Interestingly, EElsasser and Wylie6 reported a neutral maxillary position for females but a prognathic maxilla for males. Sassouni2' summarized the interaction of size, position, form and proportions of various dentofacial structures of verticai and horizontal deviations. He descnied and classified vertical disproportions (skeletal open-bite and skeletal deep-bite) with anteroposterior disproportions (skeletal Class I1 and skeletal Class III malocclusions). Moyers et al* used sophisticated cluster analyses to subgroup 697 Class I[ subjects. They described six horizontal and five vertical facial types and proposed an arborization to subgroup C l w II malocclusions with similar skeletal and dental characteristics. They concluded, "AU vertical types are not found with each horizontal type, but there is a strong relationship between horizontal and vertical features permitting identification of Ween subtypes with distinguishing features." An increase of the anterior face height in Class II malocclusion has also been reported by some investigator^.^^*^^'^ Sujmimposed on various skeletal relationships is the position of dentoalveolar units in their respective basal bones. Many s t ~ d i e s ~ *have " * ~reported protrusive maxillary dentition within the maxillary basal bone. ~ t h e r ~ ' ~ * 'observed "" a retrusive position of the mandibular dentoalveolar units within the basal mandible in Class II maloccfusion. 3 Fisk et ai" in 1953, and McNamara4 in 1981, reviewed and reported on Class II malocclusions. McNamara investigated 277 subjects with Class II malocclusion in mixed dentition stage. He concluded that the most common components in a Class II malocclusion include; ( i J skelaal retrusion, (ii) neutral positioning of skeletal rmodlla, and (iii) excessive lower face height. Some investigatof~~~ have discussed the conflicting and inconsistent reports of Class II malocclusions in the Literature. Facton that may contribute to these variations include but are not limited to: 1. variations in age of samples studied .11.. sexual dimorphism ILL ... differences in the methods of investigations iv. lack of valid statistical analysis and interpretations v. insufficient sample size@) vi. lack of stable reference plane vii. natural variation of Class II malocclusion^ In considerations of the above factors and many diversified opinions respecting the constitution of Class II malocclusion, the purpose of this study was to investigate cephalometricaUy which facial components are associated with Class I1 malocclusion and compare the findings with previously published studies. hlrteriais and Method@ Lateral beadfilms of 46 males and 59 females were cepbalometridy analyzed. The subjects ranged in age &om 8 years, 0 months to 1 1 years, 0 months, with an average age of 9 years, 10 months. All 105 l a t d cepbalometric radiographs ofthese subjects were obtained from the files of the Graduate Orthodontic C h i c at the University of Western Ontario (London, Ontario, Canada). The Class II occlusal relationship was determined fiom the headfilms and study models with at leest endsn molar and cuspid relationships. Although all subjects included in this study were class%edas Class II malocclusion, 99 exhibited Class 11, Division 1 and 6 exhibited Class II, Division 2 characteristics. In 40 of these subjects, posteroanterior (P-A) cephalometric radiographs were available to investigate the maxiuoman'bular transverse skeletal relationships. Initially, each film was traced by one investigator and digitized using a computer cephalometric program' Due to unforeseen technical dficdties, the digitized data were discarded and each tracing was nmeasuredby the same investigator manually with Mitutoyo dial caliperAwith accuracy of 0.05 mm and a protractor with accuracy of 0.5". The landmarks, angles and planes utilized in this study have been previously reported2' and their definitions can be found in Appeadix A Various cephalometric measurements were analyzed with Student's t-test and Pearson correlation coefficient (SPSS for MS WINDOWS Release 6.1.3). bentofacid Planner, version 6.5 1;RDT 1212 Saiptel Digitizer, Columbus, Ohio; Packard &U 586 Computer ^MTI Corporation, Japan The eniargernent fhctor at the midsagittal plane was 11.0%. Reliability of Method The error mdy for landmark identification and measurement involved retracing and remeasuring 28 l a t d and 15 P-A cephalometricradiographs with a 4 week interval W e e n first and second measures. The error variance was computed using both standard errors of the mean and Dahlberg's formula? where d is the Merence between duplicate measures and n is the number of duplications. m!!& The standard errors for the m u d reproducibilityare found in Table 1. The largest standard ertor for angular measurement was the mandibular plane angle at 0.2P,and for linear measurement, pogonion to nasion perpendicular at 1.01 mm. The corresponding Dahlbergs standard errors wen 0.99" and 3.77 nun, respectivelyrespectively These large values of error of measurements were most likely due to difllidty in locating the reference landmarks, namely orbitale and porion." Uncorrected cephalometric measurements are reported for comparison with other published data.4*24v2744 The summary of cephalometric values and subgroups for males and females are presented in Table 2. The mean SNA for r n d a r y position was 8 1.2" (Figure 5). The A point to nasion perpendicular was -0.44 rnm (Figure 6). Both of these values indicate average to mildly retrusive madary position compared to the ideal cephalornetric norms (AppendomBU*27-M). The mean SNB (Figure 7) and pogonion to nasion perpendicular (Figure 8) measurements were 75.3" and -9.49 mm respectively, suggesting moderate skeletal mandibular retrusion with respect to anterior cranialbase. The means of vertical measurements,the rnandr'bular plane angle (Figure 9) and lower anterior face height (Figure 10) wen 25.0" and 65.77 mm, respectively. The facial growth axis was 87-90 (Figure 11). The angle between SN-GoGn was 33.3" (Figure 12). The mean madllary basal width was 63.21 mm. The mean mandibular basal widths were 81.25 mm and 90.50 mat the antegod and gonial points respectively, as determined from the P-A cephalometric measurements of 40 subjects (Table 3). 7 Dentally, the maxillary incisors were on average, 5-95 mm ahead of A point perpendicular (Figure 13). The mean distance between d a r y incisors to A pointpogoaion line mgure 14) was 8.62 nrm. The mean distance between mandibular incisors to A point-pogonion line (Figure 15) was 4-16mm behind this line. The r m x i h y and mandibular lengths were measured &om condylion and artidare. For maxilla, the mean measurements were 90.78 mm and 87.81 mm fiom A point to condylion and to artidare, respeaively. The mean mandiiular lengths were 109.39 mm and 101.77 mrn h m gnathionto condylion and to artidare, respectively (Table 2). The sample maxillary and mandibular lengths were compared to other published studies24s (Table 4). In Table 5, various cephalometric skeletal variables fiom lateral cephalometric radiographs were correlated. SpeciGcdly, the correlation values between the anteroposterior position of maxilla to vertical dimension were not stathically significant, with r values of 0.07 between SNA and LAFH, and 0.09 between A point to nasion perpendicular and LAFH. In Table 6, Pearson correlation coefficients were calculated between maxillary and mandibular transverse dimensions and lower anterior face height. The r value was 0.40 for maxillary transverse dimension to LAFH. In mandible, the r values were 0.43 and 0.46 for mandibular basal 1 (AG-GA) to LAFH and mandibular basal 2 (GO-GO)to L m respectively. In Table 7, Pearson correlation coefficients were calculated to determine the relationships of- and mandibular length measurements fiom articulare and condylion. For maxillary length measurements, the r value was 0.93. For mandibular length measurements, the r value was 0.91. 8 In Table 8, various cephalomeaic values between the skeletal Class I1 (ANB > 4.5") and the skeletal Class I (ANB 5 4.5")ere compared. The correctedd u e s for various lhreer measurements are in Appendices B and C for comparison with other published data with different enlargement fkctors. The published magnification factors were subtracted from the reported values of various growth studies. Y Discussion Describ'mg craniofiwiai associations, various i n v e s @ t t ~ n ~have ' ~ *stated ~ that the mean values and wious ldfttiStical analyses represent oniy the overall average picture. Also, absolute values are not as important as the variability seen among individual^?^ Only by examidon of individual cases can one truly appreciate the extent of the variation seen within each class of maloodusion. Therefore, comparisons of means and conclusions derived from statistical analysis should be tempered by the concept of individual variations. This study and many other^^*^^*'^"*^^* have previously reported an extensive variation of the dentofacial complex. Hence, most of the cephalometric variables were presented in histograms to demonstrate the variability associated with each of the measurements. Consistent with previous report^:^*^^" the most significant component of Class II malocclusion was the mandibular retrusion. The mandible was retrognathic in 76.2% with SNB as reference measurement. When the pogoclion to nasion perpendicular measurement was dyed, 55.2% demonstrated a retrognathic mandible. These values concurred with McNamara's report4 of 78.5% and 60.W with respect to SNB and pogonion to nasion have reported that the glenoid perpendicular measurements respectively. Investigator~~*'~ fossa in their sampleswas posteriorlypositioned, while other^^^"^^^ have reported that the smaller size and funn of the mandible were the significant factors in mandibular retrusion. Based on embryological and biochemical studies, McNamara4postulated a possible etiology of skeletal mandibular retrusion. He stressed the developmental difrence between the condylar cartilage, which is secondary in origin embryologically, and other primary cartilaginous skeletons of both the craniofkcial and the appendidar skeletons. Furthermore, 10 he discussed the condylar d a g e respond to alterations in the environment similar to that of periosteum and these altered hctioaal environments may aEict the size and shape of mandible. Although the mean SNA value for maxilla of 81.2" indicated orthoguathism, if not slight maxillary retrognathisrn, the range of values obsemd indicated that the number of subjects exhiiited various degrees of maxillary prognathism (Figwe 5). These observations support McNamara's findings4. Not only was the mandible retrognathic, but more often than not, the mardlla was deficient in the anteroposterior dimension. MaxiUary retrusion was also reported by others.10i41g Consistent with Solow and Kreiborg's (1977) which suggested the inhibition of the forward development of the nasomaxillarycomplex in mouth breathers due to stretchmg of the fjlciel soft tissue layer, McNamara discussed the association of maxillary retrusion in conjunction with excessive vertical development in his repon.' To investigate this relationship, the anteroposterior maxillary position measurements, SNA, A point to nasion perpendicular were related to the vertical dimensions, lower anterior face height, facial axis, mandibular plane angle, and the angle between SN to mandibular plane. The r values ranged fkom -0.37 to 0.15 (Table 5) and thus, do not support the relationship between the mx&y retmion and excessive vertical development with this sample of Class II malocclusions. ~ ~ sample ~ ' ~ of Class I1 malocclusion exhibited Consistent with other ~ t u d i e s , this longer Lower face height than the McNamaragscephalometric norm for this age, of 6062 mmw Similarly, the mean facial axis value was less, at 87.9". However, other vertical measurements, mandibular plane angle and SN-GoGn angle were comparable to the 11 cephalometric mxms o f ~ c ~ a m a f a~ickettsfi ," and ~ i e d e l s These . ~ Merences in various cephalometric measurements demonstrated the variability due to different methods of measurements. Interestingly, the lower face height pigwe 10) showed a tendency to skewness toward the shorter lower f'hce height vatues (i.e. Lebard skewness; a median value is greater thpn the mean value), while the kcid axis (Figure 11) demonstrated an asymmetrical distniution pattern. The mandibular incisors were more retruded by 1.5 m m than McNarnara's sample4 (+I .3 mm versus -0.16 mm with respect to A point-pogonion line). In contrast, maxillary incisors with respect to A point-pogonion and A point vertical were remarkably similar but slightly more protruded than McNamata's sample. The distribution patterns of incisor positions were demonstrated in Figures 13-15. The majority of upper incisor positions to A point-pogonion Line were closely distributed about the mean value of 8.62 mm ( 74.3% of sample between values, 6.00 to 11.00 mm ), whereas the lower incisor positions were not appeared to be normally distributed. The upper incisor to A point vertical appeared to be normally distributed about the sample mean value of 5.95 mm. The relative inaeases in protrusion of maxillary incisors and remsion of mandibular incisors in Class I?malocclusion were partially due to the retruded mandible, which is causing the posterior positioning of the A point-pogonion reference line.' Similarly,a protrusive maxilla will have the same relative effect as a retrusive mandiile. The size of anatomic pogonion will also modify the position of A point-pogonion reference line. In a Class I1 malocclusion, a dimensionally large pogonion will place both the mandibular incisors and the mdIary incisors in relatively more retrusive position. 12 Clinically, orthodontists have postulated that there may exist a relationship between the constricted skeletal basal dimensiona d the iaaepse m lower anterior f- height. Linder- A.ronson3' described in detail, f m e s of adenoid f m in a typical mouth breather. These subjects have changed their jaw, tongue a d head postures such that they exhibit a long lower face height secondary to ova-enrpted posterior teeth, narrow maucilla, increased overjet, clockwise (down and back) rotated mandible. In the present sample, the mean maxillary width (JR-K)was 6321 mm and 81-25 mrn for the mean mandibular width (AG-GA). The Rickett's P-A cephalometric analysip has values for the normal transverse dimensions for maxilla (TR-JL) and mandible (AG-GA) at 61.9-62.5 mm and 76.1-77.5 mm for 9 to 10 years old children, respectively. Therefore, the differences between mandibular base to maxillary base are, 14.2 nunfor 9 years and 15.0 mm for 10 year n o d subjects. The mean dEerence for the same rneesuremeats in this sample was 18.04 mm This large Merence may also be due to a large m a n d i i width compared to a n o d maxillary transverse width. However, Moyers' t e e has the normal bigonial width measurements for this age group as 92.13 to 94.60 mm for males and 88.50 to 90.61 mm for females. The bigonial width measurements of the sample were 92.26 mm for males and 89.19mm for females, which were comparable to Moyers' cephalometric norms. Furthermore, the skeletal width ratios, maxillary basaVrnandibular basal 1 (JR-JL/ AG-GA), for this sample of Class I1 malocclusion was 0.705 0.04 (Table 3). This ratio value is less than 0.73-0.74 reported by Ghafari et al." They reported that this ratio may be more accurate indicator than the absolute differences between maxillary and mandibular widths. Hence, this Class II sample had on average, a constricted maxilla The Pearson correlation d c i e n t values between the transverse maxilla 13 and mandibular dimensions to lower anterior face height were &om 0.40 to 0.46 (Table 6). Thus,no clinicaUy significant conelation was present between the transverse dimensions and lower anterior tkce height, at least in this sample.' ~ o y and d other i n ~ e s t i g a t o f lhave ~ ' ~obsewed, in general, Class I1 patients have smaller hces or components of craniofacid dimensions. The values for lower anterior face height, maxillary and mandibular lengths were compared to published reports by McNamara et and an Rid0 et ala (TabIe 4). There were no significant differences for any of the measurements of the sample of Class II malocclusions as compared to previous reported data.24a Therefore, this study does not support the observations made by the previous a~thors,~ 4'3*'6" that the Class II malocclusions exhibit smaller dimensions, at least with lower anterior face height, maxillary and mandibular lengths. However, all linear dimensions for males were larger compared to females (Tables 2,3,4). This observation of sexual dimorphism supports tindings of other investigator^."'^ The Pearson correlation coefficients for maxillary length and mandibular length measurements fiom condylion and articulare were 0.93 and 0.9 1, respectively (Table 7). Such values are highly clinically significant,' and thus support the interchangeability of measurements for maxillary and mandibular length measurements from candylion or artidare. These values m higher than previously reported data by Foley and Mamandra~,~~ 0.59 to 0.75 for Co-GniAr-Gn measurements at diierent age groups of Class I females. Others have reported correlation values any where from 0. I6 to 0.64 by CoUins," 0.87 by Pollard and Mamandras" and 0.70 to 0.87 by Love et al." Finally, to examine if there was any difference between the skeletal Class 11 14 (ANB>4.S0) versus Class 1 skeletal with dental Class II relationships ("Pseudo Class ~ " 9 , the sample was divided into 2 subgroups (Table 8). The mean SNB measurements were 75-722.8"and 75.122.8" for skeletal Class 1and skeletal Class II subgroups, respectively. The main difference between these 2 subgroups was not the position of the mandible but rather the position of the maxilla with respect to anterior cranial base (SNA values of 78.7+3.2" for skeletal Class I and 81-9-12-7" for skeletal Class LC). Similar observation was reported by Blair," in comparing Class I versus Class II, Division 2 malocclusions with respect to SNA measurement Furthermore, the A point was 2.53 mm fbrther posterior in the skeletal Class I subgroup compared to skeletal Class II subgroup, with respect to nasion perpendicularplane in this study. Other significant cephalometric differences between theses two subgroups were; (i) the fUcia axis angle was greater, (ii) the mandibular plane angle was smaller and (iii the upper incison were fUrther posteriorly positioned with respect to A pointpogonion line in skeletal Class I malocclusion- It is abundantly clear that a great deal of variation exists among Class II type of malocclusion. Detailed examinations, appropriate diagnosis and carefbl treatment planning are of paramount importance. Treatment modalities should parallel and reflect the nature of the Class II maloccIusions. A skeletal imbalance should be differentiated &om a dental disharmony and only then can one plan appropriate treatment toward improving form and hction. Summanr and Conclusions The purpose of this study was to investigatethe components of Class I1 malocclusion, using lateral cephalometric radiographs fiom patients at the Graduate Orthodontic Clinic, University of Western Ontario. The following obsewations and conclusions can be drawn &om this investigation: Extensive variations of the skeletal and the dental patterns were associated with Class II malocclusion in this study. The most significant component to Class II malocclusion was the mandibular retrusion, The distribution o f m d a y position was slightly more retrusive than protrusive in this sample ofclass 11 malocclusion. The vertical skeletal measurementswere slightly higher than the cephalometric norms for this age group. There were no correlations b e w e n maxillary or mandibular transverse dimensions and lower anterior face height. This study does not support the smaller tscial dimensions reported in previous studies with respect to maxillary length, mandibular length and lower anterior facial height. This study supports the sexual dimorphism in facial dimensions. Clinically sigdicant correlations exist for m d a r y and mandibular length measurements from articuIare or condylion and thus support the interchangeability of these landmarks in these measurements. Table 1 Standard errors of manual measurements Measurements Standam of the mean ("1 = 0.1 1 (0) 0.08 SN-GoGn (") 0.14 A point to nasion perpendicular (mm) 0-34 pogonion to nasion perpendicular (mm) t -01 lower anterior face height (mm) 0.15 mandibular plane angle (") 0-27 facial axis (0) 0.13 upper incisor to A point vertical (mm) 0-12 upper incisor to A point-pogonion(rnm) 0.19 lower incisor to A point-pogonion (mm) 0.25 condylion-A point (rnm) 0.18 artidare-A point (mm) 0.10 condylion-gnathion (mm) 0.14 artidare-gnathion (mm) 0.10 d a r y basal (IR-JL) (mrn) 0.25 mandibular basal 1 (AG-GA) (mrn) 0-44 mandibular basal 2 (GO-GO)(mrn) 0.26 Table 2 Lateral cepbatometric measurements and subgmap mcwunmeats by gender SNA (O) 81.2 * 3.1 81.1 * 3.4 81.2 2.9 SNB (O) 75.3 2.8 75.1 3.0 75.4 2.7 SN-GoCn (O) 33.3 =t 5.2 32.9 5.2 33.6 5.2 Md Plane (O) 25.0 24.8 * 4.7 25.2 5.2 5.0 64.41 * 4.7St* Table 3 M u i l l v g .ad mandibular transverse dimensions (ma) and mean ratios between m a d b y basal to mandibuhr b u r l dimension; total sample and subgraup measurements by gender max basal 1-( mand basal 1 (AC-CA) maad basal 2 (GO-GO) LAFH (ANS-Me) Total n=40 8 Q n=17 as23 63.21 4.14 64-40+ 3 -45 62.33 * 4.45 80.47 * 4.77 81.25 * 4.95 82.30 5- 14 90.50 * 5.32 92.26 * 5-57 66.3 1 5.33 67.73 5-28 0.70 0.04 * 0.70 0.04 0.70 0.05 * 0.04 0.78 * 0.04 0.78 0.05 * 89-19 4-83 65.26 5.24 I mar bas& mand basal 1 max basal 0.78 mand b a d 2 J~ Table 6 Pwsoa corrda@ioncoeffidents for mlrillrry and mandibular tm~wversedimensions to lower anterior f.cc heigbts I LGE'EI (ANS-Me) max basal 1 - (AG-GA) - I KAB~~D) - Table 7 Comlrtionr between measurements fmm comdylion and articdare to A point and gnathion Subgroup measurements with angle ANB a 4.5' venus angle A N '> 4.S0 A to N L (mm) Pg to N I (mm) UI to A I (mm) UI to A-Pg (mm) LI to A-Pg (mm) Ar-A (mm) Ar-Gn (mm) Co-Gn (mm) Figurn I Lateral cephalomenie landmarkr Angulat mcisurements for IateraI ctphalometric radiographs 1. 2. 3. 4. 5. SNA SNB SN-GoGn Mandibular plane angle Facial axis Figure 3 Linear meaSunments for lateral cephalometric radiographs I. 2. ApoiattoN~ Pg to N L 3. 4. 5. UI to A point vertical UI to Apg L I to Apg 6. Ar-A point 7. Ar-Gn 8. Co-A point 9. Co-Gn 10. ANSMe Figure 4 Frontal(postemanteriot) cephalonettic landmarks with linear measurements 1. 2. 3. M a r i U ~ yb u d (JR-JL) Mandibular basal L (AGGA) Mandibular basal 2 (GO-GO) Figure 5 Dbtribution o f m a d a y position, measured with angle SNA N = 105 Mean = 81.2' S.D. = 3. lo SNA Figure 6 Distribution of muill.ry position, measured by linear distance from nuion perpendicular to A point A point to nasion perpendicular Distribution of mandibular position, measured with angle SNB. SNB Distributionof mandibular position, measured by linear distance fmm nrsion pvpcadiculv to B point N = 105 Mean = -9.49 m m S,D. = 5.29 m m Pogonion to nasion perpendicular Figure 9 Distribution of mandibulr position, measured by the angle between Franklor&plane and mandibular plane N = 105 Mean = 25.0" S.D. = 5.00 Mandibular plane angle Figure 10 DMbutioa of lincu vertical dimension, N = 105 Mean = 65.77 mm S.D. = 4.91 mm Lower anterior face height Figure 11 Distribution of mandibular position in v d d and antemposterior dimensions, m&red by the posterior angle between basion-nuiou p h e and pttrygomadhy-gnathion plane Facial axis angle Distribution of vertical mandibular position, measured by the mgk betwan s&-nuion plant and mandibular plane N= 105 Mean = 33.3' S.D. = 5.2' Angle between SN-GoGn ,l'n--T Figure 13 Distribution of mmrilllry incisor position in anteroposterior dimension, measured from A point vertical to most facial sudace o f maxillary incisor N = LO5 Mean = 5.95 mm S.D. = 2.23 m m Figure 14 Distribution o f m u i l l v y incisor position in antemposterior position, measured from A point-pogonion Uae to incM tip of muillmy incisor N = 105 Mean = 8.62 mm S.D. = 2.82 mm Upper incisor to A-Pg line Figure 15 Distributioa o f mandibular incisor position in anternposterior dimension, measured from A point-pogonion line to inciul tip of mandibulu incisor N = 105 Mean = 4.16 mm S.D. = 2.46 mm Lower incisor to A-Pg line Appendix A Definition o f landmarks, angles and planes utilized Nasion (N): Thejunction ofthe t i o n t o d suture at the most posterior point on the curve of the bridge of the nose. PterygomaxiUaty The intersecfion of the inferior border offoramen rotundurn with the posterior w d of the pterygomaxillary fossa. Point (Pt): A Point (A): The point in the median sagittal plane where the lower fiont edge of the anterior4 spine meets the &ont wall of the maxillary alveolar process. B point (B): The deepest midline point on the mandible between idadentale and pogonion. Pogonion (Pg): The most anterior point on the symphysis of the mandible in themedian plane determined by a line fiom nasion tangent symphysis. Gnathion (Gn) : The most anterior and iaferior point on the contour of the bony chin symphysis. Determined by biseaing the angle fonned by the mandibular plane and a line through nasion to pogonion. Menton (Me): The most inferior point on the symphysis of the mandiile in the median plane. Gonion (Go): The external angle of the mandible, located on the lateral and P-A cephafograms by bisecting the angle formed by tangents to the posterior border of the ramus and the Senor border of the mandible. Merior Gonion (I-): A point at a tangent to the inferior border of the mandible near gonion. The lowest point on the anterior margin of the foramen magnuqon the midsagittal plane. Anterior Nasal Spine (ANS): The most anterior position of the maxilla at the lower margin of the anterior aperture of the nose. Porion (Po): The most superior point of the bony external auditory meatus. Condylion (Co): The most superior posterior point of the average of the tight and left condylar head. Upper lacisor Tip 0: The incisal tip of the d q central incisor. Lower Incisor Tip O: The incisal tip of the mandibular central incisor. Upper Incisor Apex (UIA): The root apex of the maxillary central incisor. If root formation is not complete,then the midpoint ofthe fomriag root is used. Lower Incisor Apex (LLA): The root apex of the mandibular central incisor. If root formation is not complete, then the midpoint of the fonning root is used. Orbitale (Or): The lowest on the average ofthe right and left borders of the bony orbit. Posterior Nasal Spine (PNS): The most posterior point of the bony hard palate. The point of intersection of the inferior cranial base sUTface and the averaged posterior surfhces of the mandibular borders. SeUa Turcica (S): The centre of the pituitary fossa of the sphenoid bone. Jugale Bilateral points on the jugal process at the intersection of the outline ofthe tuberosity of the maxilla and the zygomatic buttress. Antegonion (AG,GA): The deepest point of the antegonial notch. (JWu: Andes SNA: The angle formed by the points S, N and A. SNB: The angle formed by the points S, N and B. Facial Axis: The posterior inferior angle formed by the intersection of basionnasion plane facial axis plane (Pt-Gn). The angle formed by the points A, N and B. The angle formed by the intersection ofthe S-Nplane and the Go-Gn plane. Mandibular Plane Angle: The angle formed by the intersection of the Frankfort plane and the Go-Gn plane. Frankfort Horizontal: A line joining porion and orbitale. A line joining basion and nasion. Facial Axis: A Line joining pterygoid point and gnathion Mandibular Plane: A line joining menton and inferior gonion. A line joining sella and nasion. Lower Anterior A line j o h g anterior nasal spine and menton. Face Height: Mandibular (# 1) Length (Co-Gn): A linejoining condylion to gnathion. Mandibular (#2) Length (Ar-Gn) : A linejoining articulare to gnathion. M a r y (#1) Length (Co-A): A linejoining condylion to A point. Maxillary (#2) Length (Ar-A): A line joining hculare to A point. M d a r y Basal Width (JR-JL): A line joining J(R) to J(L). Mandibular Basal 1 Width (AG-GA): A linejoining AG-GA Mandibular Basal 2 Wldth (GO-GO): A Linejoining Go@)-Go&). Appendix B Cepbdometric norms from various anrlyse-' Measurtments SNA (0) SJVB("1 SN-GOGn (O) A point to mion perpendicular (mm) pogonion to nasion perpendicular (mm) lower fjlce height (mm) mandibular plane angle (0) facial axis (") upper incisor to A point vertical (mm) upper incisor to A point-pogonim (am) lower incisor to A poiat-pogonion (mm) condylion-A point (mm) articulare-A point (mm) condylion-gnathion (mm) artidare-gnathion(mm) max basal (JR-JL) (mm) maad basal 1 (AG-GA) (mm) mand basal 2 (Go-Go) (mm) Normal values List of individuals inthe sample fiom the Graduate Orthodontic Clinic. UWO Lateral cephalometric radiographs N=105 Chart numbers P-A cephalometric radiographs N=40 Chart numbers 139 175 351 386 467 497 644 696 1105 1466 148 181 354 395 472 499 654 701 1309 1493 150 233 357 449 482 SO5 664 741 1395 1518 151 244 382 464 495 542 691 996 1463 1626 I , References Proffit WR.Contemporary Orthodontics. Mosby Year book, Inc. St. Louis l993;Znd edition pg.6-9,85. 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