[Dynamic esthetic analysis of the anterior teeth in normal occlusion in individuals aged 18-49 years]

Objective: To investigate the relationship between age, sex, length of upper lip and the exposure of maxillary central incisor. Methods: A total of 304 participants in normal occlusion (154 males, 150 females, aged 18-49 years) were recruited in this study from patients, visited the Medical Examination Center, Affiliated People's Hospital, Shanxi Medical University from January 2019 to August 2020. Participants were divided into 18-29 years old group (104, 53 males, 51 females), 30-39 years old group (110, 56 males, 54 females) and 40-49 years old group (90, 45 males, 45 females). Facial photography was used to record the facial state during the mandibular postural position, "che" pronunciation position and posed smile. The upper lip length, upper lip thickness and the exposure of maxillary central incisor were measured by ImageJ. The differences of measurement items in each group and the gender differences of each measurement item were analyzed. The length of upper lip and the exposure of upper central incisor in the mandibular postural position were analyzed by Pearson correlation. Results: In the mandibular postural position, the length of upper lip was (21.9±2.2), (22.5±2.5) and (23.1±2.2) mm in the 18-29 years old, 30-39 years old and 40-49 years old groups, and the length of upper lip in the 40-49 years old group was significantly larger than that in the 18-29 years old group (P<0.05). The exposure of upper central incisor in the 40-49 years old group during the mandibular postural position, "che" pronunciation position and posed smile [(1.4±1.2), (4.7±2.4), (7.7±2.4) mm, respectively] were significantly lower than those in the 18-29 years old group [(2.3±1.4), (5.5±2.2) and (8.8±2.0) mm] (P<0.05). The exposure of upper central incisor in the 30-39 years old group during the mandibular postural position and posed smile [(1.8±1.4), (8.2±2.0) mm, respectively] was significantly lower than those in the 18-29 years old group (P<0.05). With the increase of age, the exposure of upper central incisor decreased gradually. In the same group, the exposure of upper central incisor in the female during the mandibular postural position and "che" pronunciation position (except 40 to 49 years old group) were significantly larger than those in the male (P<0.05), and there was no statistically significant difference between the sexes in the posed smile (P>0.05). There was a significant linear correlation between the exposure of upper central incisor and the length of upper lip at the mandibular postural position in normal occlusion aged 18-49 (r=-0.325, P<0.01). Conclusions: Gender factor should be considered in the esthetic design of anterior teeth. The exposure of anterior teeth in the mandibular postural position and "che" pronunciation position is more valuable than that in the posed smile. The length of upper lip in normal occlusion aged 40-49 was significantly shorter than that aged 18-29, and the exposure of upper central incisors was significantly reduced.