Lead Author Affiliation

Doctor of Dental Surgery

Lead Author Program & Year

DDS Year 2

Presentation Category

Research

Introduction/Context/Diagnosis

• Dentofacial asymmetries can present substantial challenges to orthodontic treatment.1 They, which can be congenital, developmental, and acquired, are based on discrepancies in the two halves of the face with reference to size, form, and arrangement of facial landmarks. • Class II subdivision malocclusions show more than half-step Class II occlusion on one side of the dental arch and Class I molar occlusion on the other side of the dental arch. They attribute to 50% of all Class II malocclusions and are one of the most frequent dental asymmetries in the orthodontic population.2 • Cone-beam computed tomography (CBCT) can be used to examine skeletal and dental asymmetries in Class II subdivision malocclusions and other morphological features of the craniofacial structures of facial asymmetry.3 • Mandibular asymmetry (skeletal) was the primary factor that contributed to Angle Class II subdivision malocclusions. Class II side had shorter total mandibular length and ramus height and deviated mandibular dental midline landmarks (pogonion and menton). Mandibular dental landmarks were positioned more latero-posterio-superiorly.4

Methods/Treatment Plan

Design: • Retrospective study; records collected from University of the Pacific, Arthur A. Dugoni School of Dentistry Graduate Orthodontic Clinic

Inclusion Criteria: • Have complete initial records and photographs • Have intraoral scans with occluded models • Have initial full-volume CBCT • Have all permanent dentition • Have at least 3mm of Class II molar relationship on one side and Class I molar on the other side • Have all premolars and molars present

Exclusion Criteria: • Have syndromes or history of cleft lip or palate • History of prior orthodontic care • Impacted canines

Sample: • 108 subjects • 61 females and 47 males • Age range between 10-63 years; Average: 21 years • Class II side: 54 Lt (50%) and 54 Rt (50%)

Method: • Two calibrated judges located 33 landmarks and generated a 3D analysis for each patient using Anatomage InVivo6® 3D imaging software.

Statistics: • Paired t-test was used to determine if there are significant differences between Class I and Class II skeletal and dental measurements for all subjects (N=108) and for only those with skeletal asymmetry (Me deviation >2mm to Class II side: Asymmetry group, N =34). • Pearson correlation/linear regression analyzed degrees of skeletal asymmetry and Class II malocclusion for proportionality.

Results/Outcome

• Midline landmarks, Menton and Pogonion, had similar distribution while ANS showed less deviation. (Figure 1)

• In the skeletal asymmetry group, Class II side had shorter Ramus and Mandibular total lengths.

• There was a positive correlation (r=0.37, p=0.03) between mandibular body length difference and degree of Class II malocclusion (U6-L6 AP diff). When the mandibular body length is shorter on the Class II side, molars presented more Class II. (Figure 2)

• There was a positive correlation (r=0.65, p<.0001) between L6 anterior-posterior position difference of the Class I and Class II sides and the degree of Class II malocclusion. The more anterior L6 on Class I side or the more posterior L6 on the Class II side, the greater degree of Class II malocclusion. (Figure 3)

Significance/Conclusions

• 31.5% of subjects showed significant skeletal asymmetry defined as Me deviation > 2mm to Class II side. • There was no significant difference in skeletal size between Class I and Class II sides for the whole cohort (N = 108). However, there was a significant difference in total mandibular length between Class I and Class II sides in the asymmetry group (N = 34). This appeared to result from shorter ramus length on the Class II side. • Degree of Class II malocclusion did not show a strong correlation to skeletal asymmetry and was most affected by dental L6 AP position. However, it did show a statistically significant weak positive correlation with mandibular body length difference between Class I and Class II sides.

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Evaluation of Skeletal and Dental Asymmetries in Patients with Angle Class II Subdivision Malocclusion with 3-Dimensional Analysis of Cone-Beam Computed Tomography

• Dentofacial asymmetries can present substantial challenges to orthodontic treatment.1 They, which can be congenital, developmental, and acquired, are based on discrepancies in the two halves of the face with reference to size, form, and arrangement of facial landmarks. • Class II subdivision malocclusions show more than half-step Class II occlusion on one side of the dental arch and Class I molar occlusion on the other side of the dental arch. They attribute to 50% of all Class II malocclusions and are one of the most frequent dental asymmetries in the orthodontic population.2 • Cone-beam computed tomography (CBCT) can be used to examine skeletal and dental asymmetries in Class II subdivision malocclusions and other morphological features of the craniofacial structures of facial asymmetry.3 • Mandibular asymmetry (skeletal) was the primary factor that contributed to Angle Class II subdivision malocclusions. Class II side had shorter total mandibular length and ramus height and deviated mandibular dental midline landmarks (pogonion and menton). Mandibular dental landmarks were positioned more latero-posterio-superiorly.4