Digitized three-dimensional analysis of normal dento-labial relationships

Abstract

The lips and their relationship with the positions of anterior teeth considerably affect a person's smile and facial esthetics in general. In this study, the changes in lip dimensions and position in three-dimensions during the period between adolescence (12 boys and 12 girls aged 13–15 years) and young adulthood (10 men and 11 women aged 20–24 years) in normal, untreated subjects were measured, along with the age-related modifications in the clinical crown dimensions of maxillary and mandibular anterior teeth. The three-dimensional coordinates of selected soft-tissue facial and dental landmarks were directly digitized on the subjects using a non-invasive electromagnetic instrument. From the landmark coordinates, the total vermilion and upper lip heights; mouth width; intercanine and interincisor distances; clinical crown heights and widths of anterior teeth; interlabial, nasolabial, mentolabial, dentolabial and inciso-occlusal angles were calculated. Mean values for each sex and age group were computed and compared using two-way factorial analysis of variance. Results have shown that soft-tissue growth in the lip area has not subdued in adolescent males, while it has slowed in females; moreover, there was some degree of eruption of the maxillary anterior teeth in adolescent males, thus modifying dento-labial relationships. On average, males have a tendency toward a wider, thinner, and flatter lip area with growth. The various growth phenomena still to take place in adolescent males should be taken into consideration when commencing treatment: enucleation of four premolars may for example enhance a natural tendency toward a flatter lip area.