Effect of increasing occlusal vertical dimension on lower facial form and perceived facial esthetics: A digital...

Increasing occlusal vertical dimension (OVD) is often indicated in complex prosthodontic rehabilitations to gain restorative space and improve the occlusal relationship and esthetics. The effect of increasing occlusal vertical dimension on lower facial height (distance from subnasale to soft-tissue menton) and perceived facial esthetics is not well understood.

The purpose of this clinical study was to investigate the effect of incremental increases in the occlusal vertical dimension on lower facial height and perceived facial esthetics by using a digital approach.

Twenty-five participants with Class I jaw relationship and no loss of OVD participated in the study. Custom mandibular devices were digitally designed and 3-dimensionally printed to increase the OVD by 3, 6, and 9 mm in each participant. Three-dimensional facial scans and frontal photographs were made with the participants wearing a specific device to achieve the desired OVD increase. The lower facial height, total facial height (distance between nasion to soft-tissue menton), nasolabial angle, lip width, and lip height were digitally measured on facial scans. All measurements were recorded in a computer-aided design (CAD) software program and were repeated 3 times. Subsequently, frontal photographs of 10 participants were randomly selected for survey. Three groups each of 10 prosthodontists, general dentists, or laypersons participated in the survey and were asked to detect OVD difference in 2 photographs of the same participant and to rank facial esthetics at varying OVDs. One-way repeated measures ANOVA (α=.05) for the facial measurements and descriptive statistics for the survey results were used.

Lower facial height, the ratio of lower facial height to total facial height, lip height, and nasolabial angle increased with an OVD increase, whereas lip width decreased (P<.001). Bonferroni corrected paired t tests revealed all groups of OVD increase to be significantly different from each other (P<.001) except for an OVD increase to 6 mm versus 9 mm in lip height (P=.540) and lip width (P=.019), respectively. Prosthodontists, general dentists, and laypersons could detect a +3 mm OVD increase 63.9%, 62.5%, and 56.5% of the time, respectively. The participants' original OVD was considered the most esthetic (60.0%, 45.0%, and 68.0%) by prosthodontists, general dentists, and laypersons, respectively.

Increased OVD increases lower facial height, the ratio of lower facial height to total facial height, lip height, and nasolabial angle but decreases lip width. Prosthodontists are more sensitive to a smaller increase in OVD, closely followed by general dentists and then laypersons. In case of no loss of OVD, a vertical increase as small as 3 mm can be detected by both dentists and the general public and perceived as less esthetic. The larger the increase in OVD, the more detectable the difference and the less the faces are perceived as esthetic.