UCSF

Objective:This study evaluates the perception of transverse jaw asymmetries in patients with varying degrees of sagittal jaw relationships. Secondly, it determines the asymmetry perception threshold in which raters are able to distinguish the deviation in mandibular asymmetry that affect their aesthetic and symmetry perception. In addition, the study seeks to compare that ratings between orthodontists and oral surgeons.

Methods:Our sample consisted of 30 anonymized CBCT scans of adults (ages 11-30 years old). The reference images obtained from the CBCT’s were categorized by Class I, Class II, and Class III using ANB angles values of -4.9 degrees to 5.8 degrees. ANB angle is routinely used for orthodontic treatment planning, it represents the difference between the SNA and SNB angles, providing an indication of the sagittal jaw discrepancy between the maxilla and mandible. An ANB angle ranging from 2+/-2 degrees is considered Class I discrepancy; ANB angle greater than 4.0 is considered to be a skeletal Class II discrepancy; an ANB angle less than 0 degrees is considered a skeletal Class III discrepancy. CBCT data (4 males, 2 females) were processed into 3D models lacking several confounding facts (ex: hair style and color, skin complexion, and eye color) were stripped away in the CBCT images.. Next, images were manipulated in the transverse direction via Morpho J software, using landmarks pogonion and gnathion to alter mandibular symmetry at intervals of 0%, 25%, 50%, 75% and 100%. Lastly, 153 orthodontists, 141 oral surgeons, 68 lay persons, and 59 other dental professionals rated the aesthetics and asymmetry of each model using a scale of 1-10 mm Visual Analog Scale (VAS) for asymmetry and a scale of 1-100 mm Visual Analog Scale (VAS) for aesthetics. No information was provided on the ethnicity, age, and biological sex of each CBCT model, allowing the raters to focus on shape.

Results:As a general trend with our overall data of 421 assessors, our results indicate that in Class I, Class II and Class III faces, increasing mandibular asymmetry within a particular ANB angle was correlated with lower VAS scores for facial symmetry and aesthetics, therefore, the majority of shape changes were negatively perceived by raters. However, the data indicates that the severity of the skeletal sagittal relationship was increased, as in Class I, Class II and Class III relationships, as measured by ANB, is not indicative of decreasing perception of aesthetics and symmetry. The data concluded that when rating aesthetics, Class III faces were scored the highest followed by Class II then Class I faces. For symmetry, Class III faces were scored the highest followed by Class I then Class II faces. In addition, the threshold point with which raters are able to distinguish the deviation in mandibular esthetics and asymmetry affect aesthetic perception ranged from 50-75% mandibular deviation. When correlating symmetry and aesthetics, the data indicates that the severity of the skeletal sagittal relationship was increased, as in Class I, Class II and Class III relationships, as measured by ANB, there is not a linear decrease in perception of mandibular aesthetics and asymmetry. In Class I, symmetry and aesthetics were similarly affected, in Class II, aesthetic perception was more affected than symmetry and lastly in Class III, symmetry was more affected than aesthetics. More specifically, when evaluating 0% mandibular deviation to 100% mandibular deviation, the perception between symmetry and aesthetics, the percentage drop in VAS score ranged from 19-33%. Next, the VAS scores of orthodontists vs. oral surgeons were compared. In our Class I, Class II, and Class III faces, oral surgeons rated the faces with an overall higher VAS score than orthodontists, indicating that orthodontists may be more particular and discerning of all faces. Conclusions: The data indicates that increasing or decreasing anteroposterior jaw position does not have the strongest impact on facial esthetics and symmetry. Our findings did not support the idea that balanced jaw associations are the most consistent predictor of perception of facial aesthetics and symmetry. We hypothesized that individuals will find patients with transverse jaw asymmetries and increased or decreased anteroposterior relationships less aesthetic than those with transverse jaw asymmetries and normal sagittal relationships. The data indicates that the severity of the skeletal sagittal relationship was increased, as in Class I, Class II and Class III relationships, as measured by ANB, is not indicative of decreasing perception of aesthetics and symmetry. However, our overall results indicate that within a particular ANB angle, the majority shape changes were negatively perceived, in which, increasing mandibular asymmetry was correlated with lower VAS scores for facial aesthetics and symmetry. Additional analysis indicating that is not a linear decrease in perception between symmetry and aesthetics, the range being from 19-33% decrease in VAS score from 0% mandibular deviation to 100% mandibular deviation.

Lastly, out of all of the subgroups of data collected, the orthodontic group were the most particular and discerning all of the original faces by scoring the lowest VAS scores for all subgroups. We conclude that inconsistencies seen in our results could be attributed to confounding factors such as soft tissue characteristics that may alter perception of aesthetics and asymmetry.