Comparisons of soft tissue chin thickness in adult patients with various mandibular divergence patterns

Abstract

Objective: To evaluate the association between soft tissue at the chin (STC) thickness and mandibular divergence.

Materials and methods: Nongrowing patients seeking orthodontic treatment (n = 190; 113 women and 77 men), who had an average age of 26.94 years (range = 18.10-53.50 years), were stratified in four subgroups based on cephalometric mandibular plane inclination to anterior cranial base (MP/SN): low = MP/SN ≤ 27° (n = 48); medium-low = 27° < MP/SN ≤ 32° (n = 60); medium-high = 32° < MP/SN < 37° (n = 37); and high = MP/SN ≥ 37° (n = 45). The STC thicknesses were measured at pogonion (Pog), gnathion (Gn), and menton (Me). Group differences were evaluated with two-way analysis of variance and Student's t-test. The Pearson product moment correlation gauged associations between parameters.

Results: The STC values were greater in men than women (P < .02) and were smaller in the high group (7.47 ± 2.42 mm) than in all other groups at Gn (mean values = 9.00 mm < STC < 9.58 mm; P < .001) and at Me (high group = 6.30 ± 1.89 mm; other groups = 7.15 mm < STC< 7.57 mm; P = .011).

Conclusion: The STC is thinner at Gn and Me in hyperdivergent facial patterns, apparently in contrast to Pog. This differential thickness warrants focused research as it implies that it is possible (1) to vertically grow hard tissues impinging on the inferior soft tissue envelope in patients with severe hyperdivergence and (2) to plan for genioplasty in such patients when more advancement of the chin might be needed to compensate for the increased vertical height.

Keywords: Adult; Chin; Divergence; Mandible; Soft tissue; Thickness.

Figure 1.

To the left, lateral cephalogram studied angular measurements: Mandibular plane (menton-gonion); palatal plane (anterior nasal spine-posterior nasal spine); sella-nasion angle; true horizontal. To the right, measurements of skin thickness at the chin were evaluated: hard tissue pogonion and the distance to its horizontal projection on the soft tissue (Pog-Pog'), distance from hard tissue gnathion to soft tissue gnathion (Gn-Gn'), and the distance from hard tissue menton to its vertical projection on the soft tissue (Me-Me').

Figure 2.

Mean measurements of soft tissue at the chin in groups low, medium (medium-low + medium-high), and high for men (M) and women (F).