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INTRODUCTION: This study aims to understand the relationship between midline deviations and the inherent asymmetry that can be observed in a human face. MATERIALS AND METHODS: A cross-sectional study was conducted using a frontal smile photograph of a female which was altered on Adobe Photoshop software version 23.0 into eight different photographs by deviating the dental midlines by 2 mm, 4 mm, and 6 mm towards and away from the facial flow line (FFL). 4 mm of chin deviation was incorporated in all the pictures except for the first picture in which the midline and chin were kept symmetric. Orthodontic residents evaluated those photographs on an interrupted visual analogue scale (VAS) with 0 being the least attractive and 10 being the most. Simple linear regression was applied to observe factors associated with VAS score. RESULTS: Highest score was observed for picture with midline and chin on (MLCon) with a score of 9.4 ± 0.7, followed by picture with midline on and chin deviated (MLon) 8.7 ± 0.8. The deviations towards green zone received higher scores in comparison to deviations towards red zone. Linear regression revealed highly statistically significant differences between the constant and the rest of the pictures. CONCLUSIONS: The formation of green and red zones by the FFL influences the perception of midline deviation as judged by orthodontic residents. Midline when deviated towards the green zone, was judged to be more aesthetic than when shifted towards the red zones.
RESUMO
Objective@#To explore the application effect of a four-dimensional smile design as the leading and facial streamline as the reference system in the aesthetic restoration of anterior teeth.@*Methods@# A case of scattered space in anterior teeth was treated with a four-dimensional smile design and digital aesthetic restoration with ultrathin porcelain veneer. The digital information of the patients was obtained through oral and facial scanning, and a four-dimensional smile design and prediction were carried out. After the treatment plan was jointly determined by doctors and patients, minimally invasive abutment preparation was carried out, and ultrathin porcelain veneer was made and bonded in place. After the operation, the esthetic degree and marginal fit were observed and reexamined one year after the repair.@* Results @#The edges of the ultrathin ceramic veneers were naturally tight, and the color was coordinated, with satisfying pink and white esthetics. The face was more harmonious and natural when smiling. One year after the restoration, the facial aesthetics were wonderful, the abutment teeth and periodontal tissues were healthy, and the patients were satisfied. The results of the literature review showed that the fitting of temporal facial scanning and intraoral scanning data can accurately predict four-dimensional smile aesthetics, simulate the real state of the dynamic smile and pronunciation process, and combine it with facial streamlines to design a natural and coordinated personalized smile for patients with asymmetric faces. However, for patients with occlusal changes, unstable occlusion or temporomandibular joint disorder, it is necessary to add data fitting, such as electronic facial arch and cone beam CT, to more accurately simulate postoperative mandibular movement.@*Conclusion@# With a four-dimensional smile design as the leading and facial streamline as the reference system, the whole process digital design assisted the restoration of asymmetric anterior teeth with ultrathin porcelain veneer and had a good effect. The postoperative smiling of patients is harmonious and beautiful, which is in line with the expected effect. Patient participation and satisfaction are high; thus, this method is worthy of clinical promotion.
