Perception thresholds of dental and gingival asymmetries by orthodontists, dentists, and laypeople when observing close-up smile images using eye tracking technology.

Introduction: This study aimed to investigate the perception thresholds of dental and gingival asymmetries in close-up smile images for orthodontists, dentists, and laypeople.

Methods: Seven sets of close-up smile images were created, in which gingival and dental asymmetries were intentionally incorporated using a software-imaging program. The alterations included unilateral changes to the gingival border and incisal edge of the central and lateral incisors and crown width of the lateral incisor. Combination sets of both dental and gingival asymmetries together were also created. Eye-tracking technology was used to assess visual attention by measuring the fixation duration of the area of the alteration of each image by 195 participants in 3 groups: orthodontists, dentists, and laypeople. Statistical analysis was performed using analysis of variance with Bonferroni adjustment for multiple comparisons, to determine the perception thresholds for each group.

Results: Orthodontists and dentists perceived asymmetry of the gingival border of the central incisor at threshold levels of 1 mm, whereas laypeople perceived this asymmetry at 1.5 mm. Dentists and orthodontists were more sensitive to alterations in the gingival border of the lateral incisor, with a threshold of 1 mm, compared with laypeople, who had a threshold of 2 mm. Wear on the central incisor was perceptible at 1 mm for all groups, whereas wear on the lateral incisor was perceptible at 0.5 mm for orthodontists and dentists and 1 mm for laypeople. The perception threshold values for lateral width discrepancy were 2 mm for orthodontists, 3 mm for dentists, and 4 mm for laypeople.

Conclusions: On the basis of the perception thresholds found in this study, greater visual attention is drawn toward gingival asymmetries located closer to the midline and dental asymmetries that alter the smile arc.