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Class II subdivision malocclusion types and evaluation of their asymmetries

ORIGINAL ARTICLE
Class II subdivision malocclusion types and
evaluation of their asymmetries

Guilherme Janson,a Karina Jerônimo Rodrigues Santiago de Lima,b Donald G. Woodside,c Angelos Metaxas,d Marcos Roberto de Freitas,a and José Fernando Castanha Henriquesa
Bauru, São Paulo, Brazil

Introduction: The primary objective of this study was to determine, by means of frontal photographic evaluation, the distribution of the 2 main types of Class II subdivision malocclusions. The secondary objective was to compare the dentoskeletal asymmetries in these 2 types with a group of normal-occlusion subjects by using submentovertex and posteroanterior radiographs. Methods: The experimental group included 44 untreated Class II subdivision malocclusion subjects with a mean age of 15.3 years. The control group included 30 subjects with normal occlusions with a mean age of 22.4 years. All had full complements of permanent teeth up to the first molars and had not received orthodontic treatment. Type 1 Class II subdivision malocclusion is coincidence of the maxillary dental midline with the facial midline and deviation of the mandibular midline. Type 2 has the opposite characteristics. The frontal photographs were evaluated subjectively by 2 examiners. In the submentovertex and posteroanterior radiographs, symmetry was assessed by measuring the relative difference in the spatial positions of dentoskeletal landmarks between the right and left sides. Independent t tests were used to compare the dentoskeletal asymmetries of types 1 and 2 with the normal-occlusion group. Results and Conclusions: The results showed that 61.36% had type 1, 18.18% had type 2 Class II subdivision malocclusion, and 20.45% had mixed characteristics. The predominant asymmetric dentoalveolar characteristics of both types of Class II subdivision malocclusions were evident when individually compared with a normal-occlusion control group. There was a tendency for the type 1 subjects to have greater mandibular asymmetry than type 2, as compared with the control group.
(Am J Orthod Dentofacial Orthop 2007;131:57-66)

aProfessor, Department of Orthodontics, Bauru Dental School, University of São Paulo, Bauru, São Paulo, Brazil.
bGraduate student, Department of Orthodontics, Bauru Dental School, University of São Paulo, Bauru, São Paulo, Brazil.
cProfessor, Department of Orthodontics, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada.
dAssociate professor. Department of Orthodontics, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada.
Supported by FAPESP (São Paulo State Research Foundation) Process #01/ 02964-0.
Based on research by Dr Karina Jerônimo Rodrigues Santiago de Lima in partial fulfillment of the requirements for the degree of master of science in
orthodontics at Bauru Dental School, University of São Paulo, Bauru, São Paulo, Brazil.
Reprint requests to: Dr Guilherme Janson, Department of Orthodontics, Bauru Dental School, University of São Paulo, Alameda Octávio Pinheiro Brisolla
9-75, Bauru, SP, 17012-901, Brazil; e-mail, jansong@travelnet.com.br.
Submitted, October 2004; revised and accepted, February 2005. 0889-5406/$32.00
Copyright © 2007 by the American Association of Orthodontists.
doi:10.1016/j.ajodo.2005.02.031

Some studies have already demonstrated that the primary factor contributing to Class II subdivision malocclusion is the distal positioning of the
mandibular first molar on the Class II side.1-3 A secondary contributor is the mesial positioning of the maxillary first molar on the Class II side.2 Consequently, a mandibular dental midline deviation to the Class II side is more frequent than a maxillary dental midline deviation to the opposite side in posteroanterior (PA) radiographs of patients with these types of malocclusions. 2 Following this rationale, 2 types of Class II subdivision malocclusion can be observed: type 1, characterized by distal positioning of the mandibular first molar on the Class II side, and type 2, characterized by mesial positioning of the maxillary first molar on the Class II side. Accordingly, there is an optimal treatment approach for each type of Class II subdivision
malocclusion that the clinician should incorporate into the available options.4 Even though significant skeletal asymmetries have not been found in Class II subdivision malocclusions compared with normal-occlusion subjects, there is speculation that they could occur if types 1 and 2 were individually compared with subjects in a normal-occlusion group.2 Therefore, based on these considerations, it would be interesting to investigate the prevalence of these 2 types of Class II subdivision malocclusions and to study whether the contribution of skeletal asymmetries would be greater when the 2 types are independently compared with normal-occlusion subjects. The primary objective of this study was to determine the prevalence of the 2 main types of Class II subdivision malocclusions among patients with such malocclusion through evaluation of frontal photographs. The secondary objective was to determine the degree of dentoskeletal asymmetries in these 2 types of malocclusion compared with a group of normal-occlusion subjects in submentovertex (SMV) and PA radiographs.

Fig 1. Frontal facial evaluation.

MATERIAL AND METHODS

The experimental group consisted of 44 untreated subjects (23 male, 21 female) with Class II subdivision malocclusions, with a mean age of 15.3 years (SD, 3.73 years; range, 11.9-31.9 years), selected from the files of the orthodontic department at Bauru Dental School, University of São Paulo, São Paulo, Brazil. The control group comprised 30 subjects (10 male, 20 female) with normal occlusions, selected from students and employees who offered to participate in the study, with a mean age of 22.42 years (SD, 5.6 years; range, 15.1-41.1 years).
The selection criterion for the 2 groups was the presence of all maxillary and mandibular permanent teeth up to the first molars. The patients in the experimental group had complete Class I molar relationships on 1 side of the dental arches with a full Class II relationship on the opposite side. Additional criteria included no previous orthodontic treatment, no lateral mandibular shift during closure, no facial trauma or medical condition that could have altered the growth of the apical bases,5 and no crowding (or at most, symmetrical crowding up to 3 mm in the maxillary or mandibular dental arch).2 These criteria were evaluated in clinical histories and examinations. Photographs of the 44 subjects with Class II subdivision malocclusions were taken with a camera (F801, Nikon, Tokyo, Japan) with a 105-mm macro lens (Nikon) and a ring flash (SB21B, Nikon). The photographs were taken in centric occlusion with the patients smiling broadly to allow observation of the maxillary and mandibular dental midline deviations in relation to a reference line as described by Jerrold and Lowenstein.6 The distance from the lens to the patient was standardized at 1 m with the head in natural position. After processing, the photographs were magnified and printed. The maxillary and mandibular dental midline deviations were evaluated in relation to an imaginary line drawn through the center of glabella, perpendicular to the ground6 (Fig 1). According to this method, some midline variations are possible. A possible variation occurs when only the maxillary midline is off to 1 side. The initial visual facial evaluation of the maxillary midline to the imaginary centered plumb line shows its ectopic position. Another midline variation is when the facial and maxillary midlines are coordinated, but the mandibular midline is eccentric.6 Two calibrated examiners (K.J.R.S.L. and A.R.P.A.) classified the subjects into the 2 main types of Class II subdivision malocclusion.
A subject was classified as type 1 when the maxillary dental midline was coincident to the facial midline and the mandibular dental midline was deviated,
and as type 2 when the mandibular dental midline was coincident to the facial midline and the maxillary dental midline was deviated.
Two radiographs were obtained from each subject: 
SMV and PA. The anatomic tracings were manually made on acetate paper and digitized (Numonics Accu- Grid XNT, model A30TL.F, Numonics, Montgomeryville, Pa). These data were then stored on a computer and analyzed with Dentofacial Planner 7.0 (Dentofacial Planner Software, Toronto, Ontario, Canada). The SMV radiographs were obtained according to the literature.7,8 The machine used for the SMV radiograph was the TUR D800 (Hermann Matern, Dresden,  Germany), with Kodak X-Omat K film (Kodak, Rochester, NY) with an exposure time of 0.125 seconds, 70 kV, and 32 mA. The distance from the focal point to the ear rods was set at 152 cm, and the distance from the ear rods to the film was set at 16 cm; this yielded a magnification factor of 9.55%. During exposure, the subjects kept their teeth in centric occlusion under light pressure, and the head was positioned with the Frankfort plane perpendicular to the floor. Cephalometric structures, landmarks, lines, and variables were obtained according to the analysis of Ritucci and Burstone,9 to which some modifications for this study were added. The tracings of the SMV radiograph included foramen magnum, foramen spinosum, metallic ear rods, mandible (including condyles, gonial angles, and coronoid processes), posterior cranial vault, zygomatic arches, anterior cranial vault, pterygomaxillary fissures, vomer, maxillary and mandibular first molars, and maxillary and mandibular central incisors. The landmarks are defined and illustrated in Figure 2. The method of Forsberg et al7 and Ritucci and Burstone9 evaluates the asymmetry of craniodental structures in relation to various coordinate systems. In our study, we used this method with some modifications. The coordinate systems were the mandibular, the
cranial floor, the zygomaxillary complex, and the dental. The coordinate systems consisted of 2 axes perpendicular to each other. The anteroposterior and the lateral positions of all pertinent structures were evaluated in relation to these axes. The transcondylar axis was established in the mandibular coordinate system, passing through the condylar midpoints. This axis was used to evaluate symmetry in the anteroposterior plane of dentoalveolar and skeletal structures to the mandible. In addition, the symmetry of the transverse positioning of these structures was evaluated by using the intercondylar
axis drawn perpendicular to the transcondylar axis from its midpoint. Similarly, the transspinosum and interspinosum axes were constructed for the cranialfloor coordinate system; the transpterygomaxillary and interpterygomaxillary axes were constructed for the zygomaxillary coordinate system; and the transmaxillary molar, transmandibular molar, intermaxillary molar, and intermandibular molar axes were constructed for the maxillary and mandibular dental coordinate systems, respectively. For paired structures, the distance to the reference axis was determined for both landmarks, and the difference in horizontal distance was calculated. For unpaired points, the horizontal distance to the midline was determined. There were 53 variables for the SMV radiograph. Figure 3 illustrates the mandibular coordinate system variables. PA radiographs were obtained according to the method of Harvold,10 with the forehead and nose lightly touching the film cassette. The machine used for this radiograph was the Roentax 10090 (EMIC, Electro Medicina Ind. Com. Ltda, São Paulo, Brazil), with Kodak X-Omat K film and an exposure time of 1 second, at 90 kV(p) and 25 mA. In these radiographs, the distance from the focal point to the ear rods was standardized at 152 cm, and the distance from the ear rods to the film was fixed at 16 cm; this yielded a magnification factor of 8.91%. During exposure, the subjects kept their teeth in centric occlusion. The tracings of the PA radiograph included the following structures: orbits, contours of the nasal cavity, crista galli, zygomatic arches, mandibular contour from 1 condyle to the other, left and right maxillary contours, lateral aspects of the frontal bone, lateral aspects of the zygomatic bones, maxillary and mandibular central incisors, and maxillary and mandibular first
molars. The landmarks are defined and illustrated in Figure 4. The cephalometric measurements were obtained according to the method of Grummons and Van De Coppello11 (Fig 5). For paired structures, the distances to the reference midline were determined for both landmarks, and the difference between the distances was calculated. For unpaired points, the horizontal distance to the midline was determined. This part of the analysis yielded 18 variables (Table VI). For the 2 radiographs, absolute values were used for the differences between the measurements of the right and left sides, and for the horizontal distances to the reference midplanes. This kept any positive and negative values from canceling themselves out in the calculation
of actual means for each group.12 For the evaluation of intraexaminer error, 20 randomly selected SMV and PA radiographs were retraced, redigitized, and remeasured by the same examiner (K.J.R.S.L.). The casual error was calculated according to Dahlberg’s formula13 (S2  d2/2n) and the systematic error with paired t test,14,15 at P .05.

Fig 2. Structures and landmarks of SMV radiograph: 1, metallic ear rod point—medial center of each ear rod; 2, gonion point—midpoint mediolaterally on posterior border of each gonial angle; 3, medial condylar point— tangent point to each medial condylar border of line drawn parallel to each mandibular body line; 4, lateral condylar point—tangent point to each lateral condylar border of line drawn parallel to each mandibular body line; 5, condylar midpoint—midpoint between lateral and medial condylar points on each condyle; 6, distal mandibular first molar point—most distal point in line with central groove on each mandibular first molar; 7, distal maxillary first molar point—most distal point in line with central groove on each maxillary first molar; 8, coronoid process point—most anterior point relative to transcondylar axis on each coronoid process; 9, mandibular midline—most anterior point of mandibular
body; 10, (skeletal point) mandibular dental midline— point of contact between mesial surfaces of crowns of mandibular central incisors; 11, maxillary dental midline— point of contact between mesial surfaces of crowns of maxillary central incisors; 12, foramina spinosa points—geometric center of each foramen spinosa; 13, angulare—most anterior points relative to transpterygomaxillary axis of triangular opacities at external orbital angle where upper and lower orbital rims meet and zygomatic arch inserts; 14, buccale—point on internal surface of each zygomatic arch where arch turns medially and directly starts on backward sweep; 15, pterygomaxillary fissure—most medial and posterior point of each pterygomaxillary fissure; 16, zygion points—intersections of lateral borders of zygomatic arches with line parallel to transpterygomaxillary axis drawn across section of greatest bizygomatic width; 17, basion—most anterior point relative to transspinosum axis on border of foramen magnum; 18, opisthion— most posterior point relative to transspinosum axis on border of foramen magnum.

Fig 3. Measurements from SMV radiograph. Mandibular coordinate system variables. Anteroposterior: 1, gonion to transcondylar axis; 2, coronoid process point to transcondylar axis; 3, distal mandibular first molar point to transcondylar axis; 4, distal maxillary first molar point to transcondylar axis.  Transverse: 5, gonion to intercondylar axis; 6, coronoid process point to intercondylar axis; 7, distal mandibular first molar point to intercondylar axis; 8, distal maxillary first molar point to intercondylar axis; 9, mandibular midline to intercondylar axis; 10, mandibular dental midline to intercondylar
axis; 11, maxillary dental midline to intercondylar axis.

Fig 4. Structures and landmarks of PA radiograph. 1, most lateral point on outline of nasal orifice in region of each pyriform aperture; 2, superolateral reference point located at lateral aspect of each frontozygomatic suture; 3,lateral aspect of each zygomatic arch centered vertically; 4, point at depth of concavity of each lateral maxillary contour at junction of maxilla and zygomatic buttress; 5, buccal cusp tip of each maxillary first molar; 6, buccal cusp tip of each mandibular first molar; 7, point on superior surface of head of each condyle centered mediolaterally; 8, point at each gonial angle of mandible; 9, point at each antegonial notch; 10, menton— most inferior point on anterior border of mandible at symphysis; 11, most superior point of crista galli located ideally in skeletal midline. 12, tip of anterior nasal spine; 13, mean contact point between each maxillary and mandibular first molar; 14, midpoint between
maxillary central incisors; 15, midpoint between mandibular central incisors.

Fig 5. Angular and linear measurements from PA radiograph: 1, Z plane angle—angle between Z plane and crista galli-anterior nasal spine line; 2, occlusal plane angle—angle between occlusal plane and crista gallianterior nasal spine line; 3, antegonial plane angle— angle between antegonial plane and crista galli-anterior nasal spine line; 4, antegonial angle—angle between mandibular ramus and mandibular body; 5, anterior nasal spine deviation—horizontal distance between anterior nasal spine and X-line (vertical line, representing medial plane, drawn at right angle to Z plane through root of crista galli)40,41,44; 6, mandibular deviation— horizontal distance between menton and X-line; 7, maxillary dental midline deviation—horizontal distance
between dental maxillary midline and X-line; 8, mandibular dental midline deviation—horizontal distance between dental mandibular midline and X-line; 9, frontozygomatic suture to X-line distance—horizontal distance between frontozygomatic suture and X-line; 10, condylion to X-line distance—horizontal distance between condylion and X-line; 11, zygoma distance—distance between zygomaxillary arch and X-line; 12, pyriform aperture to X-line distance—horizontal distance between lateral wall of pyriform aperture and X-line; 13, maxillary buttress to X-line distance—horizontal distance between maxillary buttress and X-line; 14, antegonial notch to X-line distance—horizontal distance between antegonial notch and X-line; 15, maxillary first molar height—vertical distance between maxillary buttress and buccal cusp tip of maxillary first molar; 16, condylion to antegonial notch distance—size of mandibular
ramus from condylion to antegonial notch; 17, condylion to menton distance—mandibular length from condylion to menton; 18, menton to antegonial notch distance—mandibular body size from menton to antegonial notch.

Statistical analyses

Distributions of the Class II subdivision malocclusion types on the photographs were expressed in percentages in relation to the total sample. The test of
differences between percentages was used to compare the distribution of types in the sample. Independent t tests were used to independently compare the radiographic dentoskeletal asymmetries between types 1 and 2 of Class II subdivision malocclusion with the normalocclusion group. The results were regarded as statistically significant at P .05. All analyses were performed with software (Statistica for Windows, release 5.0A, Statsoft, Tulsa, Okla).

RESULTS

Only 2 variables had statistically significant systematic errors, and casual errors varied from 0.27 to 2.41. Twenty-seven subjects (61.36%) had type 1 Class II subdivision malocclusions, 8 (18.18%) had type 2, and 9 (20.45%) had combinations of both characteristics and were excluded from the asymmetry evaluation (Table I). Means and standard deviations for the differences between the right and left sides for all variables in the 2 groups and the results of the t test between them and the normal-occlusion group are listed in Tables II through VI. The primary contributors to asymmetric
anteroposterior relationships in types 1 and 2 of Class II subdivision malocclusion were dentoalveolar. There was a tendency for type 1 to have greater mandibular asymmetry than type 2, compared with the control group.

DISCUSSION

The age differences of the groups did not seem to be a problem because Melnik,16 in his study of mandibular asymmetry, verified that it is equally probable for asymmetry to improve or to worsen with growth. Therefore, considering the almost complete maturation of the Class II subdivision group and the equal probability of improvement of craniofacial asymmetry with growth, the age difference between the groups should not interfere with this type of evaluation. According to the photographic evaluation results, 61.36% of the patients had type 1 Class II subdivision malocclusions reflecting more distal positioning of the mandibular first molars in the Class II sides. Type 2 Class II subdivision malocclusions were evident in 18.18% of the subjects,
reflecting more mesial positioning of the maxillary first molars on the Class II sides. The other 20.45% had a combination of both characteristics and were not included in the asymmetry evaluation (Table I). The percentage difference between the 2 types was statistically significant. This clinical finding confirms previous results of cephalometric investigations that had found more distal positioning of the mandibular first molar on the Class II side as the primary contributor to the asymmetric malocclusion, and the more mesial positioning of the maxillary molar on the Class II side as the secondary contributor.1-3 If the mandibular first molar is more frequently distally positioned, the mandibular dental midline will be deviated toward the Class II side with a greater frequency as well, and this results in a greater percentage of type 1 Class II subdivision cases. These results also resemble previous
reports that found deviations of the mandibular dental midline in relation to the midsagittal plane as the primary contributor to the asymmetric Class II
malocclusion2 and also that deviation of the mandibular dental midline was more frequent than deviation of the maxillary dental midline in this type of
malocclusion.17
The clinical method of analysis we used, although subject to criticism, is useful in identifying the primary anomaly in relation to the patient’s soft-tissue frontal view, which is of utmost importance in diagnosis because the frontal appearance is evident at first.11,18,19 Perhaps this method could provide
slightly different results when compared with cephalometric evaluations of midline deviations in individual analyses, as will be further discussed. However, clinical manifestations of the asymmetries are more important than cephalometric data, especially nowadays.20-22 In addition, these results agree with previous cephalometric findings.1-3 Sound concerns could be raised if the results had been contradictory to previous observations.

SMV radiographs

Clinically distinguishing Class II subdivision malocclusion in 2 types did not greatly modify the primary dentoalveolar factors that contribute to this asymmetric malocclusion, previously reported,1-3 as shown in Table II. The anteroposterior asymmetry degrees of the mandibular and maxillary molars in the 2 types were statistically greater than in the normal-occlusion group, as was observed previously in undistinguished Class II subdivision malocclusion samples.1-3 Only a small difference could be observed in the level of significance between the groups; ie, in the type in which asymmetry
would be expected for a molar, the level of significance was greater than for the other type. Tables III and IV show significantly greater anteroposterior asymmetry for only the mandibular molars in both types of subdivision malocclusions in relation to normal occlusion. This means that the primary characteristic of type 2 subdivision malocclusion (asymmetry of the maxillary molars) did not manifest in this evaluation and that, in this type, asymmetry of the mandibular molars also plays an important role, as previously shown.23 This could be because of the small number of subjects in this malocclusion type, requiring subsequent investigations with a larger sample. Skeletally, in the zygomaxillary coordinate system, there was greater asymmetry of the
anterior cranial vault in relation to the transpterygomaxillary axis for type 2 in relation to normal occlusion. However, this structure is not amenable to
changes with orthodontic treatment, and therefore this asymmetry can be considered of minor importance. Nevertheless, transversally, slight differences in skeletal asymmetries were suggested. In the mandibular coordinate system, the asymmetry of the coronoid process point to the intercondylar axis was statistically smaller in type 2 than in the normal-occlusion group, whereas type 1 had similar asymmetry to the control group. In the cranial-floor coordinate system, the mandibular skeletal structures had statistically greater asymmetry in type 1 than in the normal-occlusion
group, whereas type 2 had similar asymmetries as the control group. Therefore, this suggests the association of mild mandibular asymmetry in type 1 subdivision malocclusion, and that type 2 patients have more symmetrical mandibles. Additionally, the middle cranial fossa was more symmetrical in type 2 than in the normal-occlusion group. This further reinforces that midface skeletal asymmetry does not contribute to Class II subdivision malocclusions as previously found.2

Dental coordinate system

Anteroposteriorly, type 1 patients had greater asymmetry of the molars than did those in the normalocclusion group. Greater asymmetry of the mandibular molars was expected because of the nature of Class II subdivision in this type, but not of the maxillary molars. This demonstrates that there might also be slight contribution of the maxillary molars to the asymmetry in this malocclusion type.23 On the other hand, type 2 seems to have symmetrical mandibular-molar anteroposterior positioning and asymmetrical maxillary-molar anteroposterior positioning, in relation to the normal
occlusion group, reflecting its expected characteristics. Transversely, type 1 patients demonstrated significantly greater mandibular dental midline deviations to the mandibular intermolar axis than did the control group; type 2 subjects did not have this characteristic (Table V). This reflects greater arch form asymmetry in type 1 subdivision malocclusions and more symmetrical arch forms in type 2. This would be expected because type 1 is caused by asymmetry of the mandibular molars. However, the mandibular molars in both types were more asymmetrically positioned in relation to the mandible than in the normal occlusion group because the mandibular midline deviation to the mandibular intermolar axis was significantly greater than in normal-occlusion subjects. Both types showed greater maxillary dental midline deviations to the maxillary intermolar axis than did the control group. Although
this was expected in type 2, it was not in type 1, demonstrating some asymmetry of the maxillary arch in this group as well. Additionally, the asymmetrical
positioning of the maxillary molars in both groups also caused the mandibular midlines to show greater devi-ations to their intermolar axes than did the normalocclusion group. From our results, it can be seen that the characteristics of each type are not always clearly manifested in every coordinate system. However, the primary characteristics of each type prevail most of the time.

PA radiograph results

The statistically greater asymmetry of the mandibular dental midline deviations in type 1 compared with the normal-occlusion group confirms the predominant characteristic in this malocclusion type—distal positioning of the mandibular first molar on the Class II side, with accompanying deviation of the mandibular dental midline, as also shown in the tables. In type 2 subjects, the mandibular dental midlines had similar deviations as the normal-occlusion group but less mandibular skeletal asymmetry (antegonial notch to X-line distance) than the control group; this was surprising. This reinforces that this malocclusion type has relatively symmetrical mandibular bones and dentitions. However, greater maxillary dental midline deviations to X-line than the control group were not observed and could not reinforce the primary contributory factor to this malocclusion type—ie, a mesially positioned maxillary first molar accompanied by maxillary midline deviation. Therefore, it seems that this result in the PA radiograph does not agree with the
photographic evaluation method used to divide the sample into 2 groups. However, slight differences between a frontal visual inspection and the PA radiograph might occur because the subjects were not similarly standardized for both evaluations. In the photographic evaluation, the patients were evaluated subjectively by the operator as to the best natural frontal view. In the PA radiograph, the subjects were standardized by the cephalostat. The external auditory meatus might have slight anteroposterior asymmetry11,24 that could rotate the head and consequently affect evaluation of the structures in relation to the midsagittal plane. This could have accounted for the different results obtained. Additionally, small asymmetries of the overlying soft tissues could have also contributed to this difference. Perhaps this also explains some diverging results of the SMV evaluation that were
unexpected. However, a patient’s clinical or photographic frontal evaluation is more important than a radiographic evaluation.20-22 Nevertheless, because there were few type 2 subjects, these results should be regarded with caution. The other variables in the 2 groups did not have significant differences in relation to the normal-occlusion group; this is similar to previous results of undistinguished Class II subdivision samples.1,2 Despite clinically dividing Class II subdivision malocclusions into types 1 and 2, the main factors contributing to asymmetry were dentoalveolar, as previously
found in undistinguished Class II subdivision malocclusions.1-3 In our study, skeletal asymmetries were mild. These results did not strongly support speculations of finding skeletal asymmetries in the different types of Class II subdivision malocclusions.2 However, they suggested slightly greater mandibular skeletal asymmetries in type 1 than in type 2 Class II subdivision malocclusions. Further studies, with larger samples, especially of type 2 Class II subdivision malocclusions, are necessary to confirm these tendencies.

CONCLUSIONS

The frequencies of Class II subdivision malocclusion types from the frontal photographic evaluation were type 1, 61.36%; type 2, 18.18%; and a type with
combined characteristics, 20.45% (not evaluated regarding the asymmetries). The predominant asymmetric dentoalveolar characteristics of types 1 and 2 of Class II subdivision malocclusions were evident when individually compared with a normal-occlusion control group. There was a tendency for type 1 patients to have greater mandibular asymmetry than type 2 patients, as compared with the control group.

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