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The aims of this study were to analyse lip line heights and age effects in an adult male population during spontaneous smiling, speech, and tooth display in the natural rest position and to determine whether lip line height follows a consistent pattern during these different functions. The sample consisted of 122 randomly selected male participants from three age cohorts (20-25 years, 35-40 years, and 50-55 years). Lip line heights were measured with a digital videographic method for smile analysis, which had previously been tested and found reliable. Statistical analysis of the data was carried out using correlation analysis, analysis of variance, and Tukey's post hoc tests. Maxillary lip line heights during spontaneous smiling were generally higher in the premolar area than at the anterior teeth. The aesthetic zone in 75 per cent of the participants included all maxillary teeth up to the first molar. Coherence in lip line heights during spontaneous smiling, speech, and tooth display in the natural rest position was confirmed by significant correlations. In older subjects, maxillary lip line heights decreased significantly in all situations. Lip line heights during spontaneous smiling were reduced by approximately 2 mm. In older participants, the mandibular lip line heights also changed significantly and teeth were displayed less during spontaneous smiling. Mandibular tooth display in the rest position increased significantly. Upper lip length increased significantly by almost 4 mm in older subjects, whereas upper lip elevation did not change significantly. The significant increasing lip coverage of the maxillary teeth indicates that the effects of age should be included in orthodontic treatment planning.

Age-related changes of the dental aesthetic zone at rest and during spontaneous smiling and speech