[Influence of canine vertical position on smile esthetic perceptions by using 3D digital facial reconstruction]

To verify the impact of alterations in the vertical position of maxillary canine on smile esthetic perceptions, in order to find an optimal canine position.

A volunteer's dentition and facial images were scanned by intra-oral scanning and three-dimensional facial scanning, which were then calibrated. In virtue of dental computer-aided design software, the canine vertical positions were symmetrically modified in a variable of 0.5 mm, creating 4 new 3D virtual digital smile faces varying from 1.0 mm of intrusion to 1.0 mm of extrusion. A total of 5 3D virtual digital smile faces were evaluated from the front and 45°to the right sides by 60 dentists and 60 laypersons on a visual analog scale. The data were input into SPSS 20.0 software package, ANOVA of repeated measurement was used to compare the differences in the assessment scores between two groups and rank sum test was used to analyze the differences from different evaluation angles.

Alterations in the vertical position of maxillary canine had significant influence on the esthetic evaluation of the smile(P<0.05); there was significant difference between the dentists' and laypersons' esthetic evaluations after the canine vertical position being modified(P<0.05), there was no significant difference on the evaluations of smile esthetics from different evaluation perspectives(P>0.05).

The most attractive smile was the one with canine cusp 0.5 mm vertically higher than the incisal edge of the lateral incisor. The smile is not attractive when the cusp of canine is vertically lower than the incisal edge of lateral incisor. These results can be used as references in the esthetic treatment planning for anterior maxillary teeth.