Characteristics and Dynamics of Smile in Patients With Skeletal Class II Malocclusion Versus Class I Malocclusion Using Still Digital Video Captures: A Three-Group, Cross-Sectional, Comparative Study.

Background Smiling is one of the effective ways for people to express their feelings. It is an integral part of the diagnosis and planning and a key point of the treatment objectives in orthodontic care. Many factors are associated with a pleasant smile, such as correct anatomy, gingival health, and teeth proportion. Therefore, different malocclusion classes can affect the characteristics of smile esthetics. This study aimed to evaluate the effect of skeletal class II malocclusion on the characteristics and dynamics of the smile in the sagittal and frontal planes. Methodology The study sample included 60 patients comprising three groups of malocclusion classes, namely, Class I, Class II division 1, and Class II division 2. A video recording was taken for 5-10 seconds for each patient using a specific camera mounted at a fixed distance from the imaged face. Two facial expressions were captured for each patient, one representing the lips at rest and the second representing the unrestricted natural smile. The facial still images were derived from the streaming video recording, and two images were chosen for each plane (the frontal plane and the sagittal plane) for each patient. In total, 12 variables were assessed on these captured images. One-way analysis of variance (ANOVA) was used to detect significant differences between the three groups. Results There were statistically significant differences in some of the measured variables. The mean values of thickness of the upper lip, commissure height, gum width, maxillary incisor display, and interlabial gap were greater in the Class II division 1 group than in the other two groups. The proclined incisors were evident in the Class II division 1 group, while the retroclined incisors were evident in the Class II division 2 group. Conclusions The skeletal Class II malocclusion influences the characteristics of the smile, either assessed on the anterior or lateral imaging angles, in addition to its influence on the resting position of the lips. Orthodontists should always analyze patients' facial expressions, including those related to the upper and lower lips at rest and when patients smile naturally. Depending on the results of this analysis, treatment planning could be built to improve the characteristics of the natural smile in patients with Class I and Class II malocclusions.