Anteroposterior displacements of the jaws and incisors relative to the forehead during growth: A longitudinal cephalometric analysis of untreated subjects with Class I occlusions.

Abstract

Objective: To assess anteroposterior (AP) displacements of the jaws and incisors relative to the forehead in untreated growing subjects with normal (Class I) occlusions.

Materials and methods: Serial lateral cephalograms from 74 untreated subjects (37 female, 37 male) with Class I dental relationships were obtained from the AAOF Craniofacial Growth Legacy Collection. Mean age at T1 was 9.9 years; T2 was 17.6 years. T1 tracings were secured over millimeter graph paper with Frankfort Horizontal aligned horizontally. Superimpositions were guided by anterior cranial base structures, then shifted along Frankfort Horizontal so that glabella on T1 and T2 shared a common vertical plane (Glabella-Vertical [GV]). AP displacements of Point A (Pt A), Point B (Pt B), maxillary central incisor's FA point (U1FA), and mandibular central incisor's FA point (L1FA) were measured relative to GV. Changes in occlusal plane (OP) inclinations were also measured.

Results: Average AP displacement at Pt A was -0.47 mm; Pt B +0.71 mm; U1FA +0.32 mm; and L1FA +0.82 mm. OP inclination decreased 2.3⁰ on average. Displacement of L1FA was significantly different between genders (M, +1.16 mm; F, +0.47 mm; P = 0.04). No significant differences between genders were found for any other variable.

Conclusions: AP jaw and incisor positions were effectively static relative to GV during normal growth between ages 9 and 18 with untreated Class I occlusions. On average, no site underwent AP displacement relative to GV that exceeded 1 mm. The OP tended to rotate counterclockwise. In subjects with Class I dental relationships, pretreatment jaw, and incisor positions do not undergo significant AP changes relative to GV during growth after 9 years of age regardless of gender. GV could thus serve as a reliable AP diagnostic landmark in growing patients.