Age and Gender Specific Effect of Lip Form on Maxillary and Mandibular Incisal Display with Lips at Rest in Elderly Indian Population: A Cross-sectional Study

Introduction: Maxillary and mandibular incisal display at rest and smile is an integral part of dento-facial aesthetics. Its correlation with lip form and the effect of age and gender has not been studied in elderly Indian population. Dental photography has been given a great importance in prosthodontics and the study of various aesthetic parameters on digitalised photographs can act as additional diagnostic tool. Aim: To determine correlation between lip form and incisal display in elderly subjects and to determine age and gender related changes. Materials and Methods: A cross-sectional study was conducted in the Department of Prosthodontics, Karnavati School of Dentistry, Gandhinagar, Gujarat, India, from November 2020 to September 2021. The study sample comprised of digital photographs taken in natural head position of 324 elderly Indian subjects (180 males &144 females) and they were divided into 4 age groups: Group I consisting of 157 subjects aged (31- 45 years), Group II consisting of 107 subjects aged (46-55 years), Group III consisting of 47 subjects aged (56-65 years) and Group IV consisting of 13 subjects aged >65 years. The various parameters (lip form, maxillary and mandibular incisal display) were then analysed using Image J (Fiji app) image analysis software. The statistical analysis was done using Pearson correlation (significant when p<0.05), scatter plot, and Independent t-test (significant when p<0.05) and one-way Analysis Of Variance (ANOVA) post-hoc Tukey-Kramer test to compare the parameters of different groups. Results: The results of this study showed that there is a significant correlation between lip form and maxillary & mandibular incisal display at rest (r=0.388, p=0.001). Females have more incisal display for a particular type of lip form as compared to male subjects. A statistically significant difference was found in maxillary incisal display and lip form between male and female groups (T=-5.934, p-value=0.001 and T=-2.367, p-value=0.019 respectively) but no statistically significant difference was found in mandibular incisor display between male and female groups (T=1.832, p-value=0.068). Hence, females above 30 years of age had more maxillary incisal display as compared to males but almost same mandibular incisal display. Also, straight lip form was more common among elderly male subjects (63.6% as compared to females 36.4%) but females had moderate lip form most commonly (52.1% as compared to males 47.9%). High lip form was reported equally in both male and female subjects with 50% in each group. Conclusion: It has been concluded from the study that for a particular type of lip form (either straight, moderate or high), females have more average incisal displays as compared to males. A strong correlation exists between lip form and incisal display in elderly Indian population. Hence, lip form can be used as a definitive parameter to determine Incisal displays in prosthetic rehabilitation to get optimum aesthetic outcomes.