Does the mode of mandibular advancement affect the treatment effects on molar relationship?

Abstract

AIM: This prospective clinical study compared the molar relationship effect between mandibular stepwise advancement and maximum jumping. SUBJECTS AND METHOD: The headgear activator group (HGA-S) had stepwise advancement (n = 24, mean age = 11.9 ± 1.2 years) of 4 mm every 3 months with individualised bite opening following the condylar translatory pathway, whilst the HGA-M group (n = 31, mean age = 11.2 ± 1.5 years) had maximum jumping with edge-to-edge 6 mm interincisal opening. Active treatment was 12 months (T0-T12) for the HGA-S group and 6 months (T0-T6) for the HGA-M group followed by 6 months (T6-T12) of retention. Molar relationship effects were analysed from lateral cephalograms (Pancherz, 1982) taken at start of treatment (T0), 6 months (T6) and 12 months of treatment (T12). The results were adjusted to similar observation lengths. Growth changes were obtained from the pre-treatment HGA-M group. RESULTS: The molar relationship was unchanged with 6 months’ growth. With the initial 6 months’ treatment (T0-T6) the molar relationship improved 2.8 mm (P < 0.001) and 3.2 mm (P < 0.001) with HGA-M. With HGA-S, jaw base relationship improved 2.1 mm (P < 0.001) whereas the molars were unaffected. With HGA-M, jaw-base relationship improved (1.5 mm; P < 0.01), maxillary molars distalized (–1.1 mm; P < 0.01) and mandibular molars mesialized (0.6 mm; P < 0.01). During the second 6 months (T6-T12) of active treatment, the molar relationship improved with HGA-S (1.9 mm; P < 0.001) mainly due to an improved jaw base relationship (1.4 mm; P < 0.05). After HGA-M retention, the molar relationship was unaffected, due to an insignificant jaw base relationship effect and relapse of the maxillary molars. During the total 12-month observation period, the effect on the molar relationship was significantly larger (P < 0.05) with HGA-S than HGA-M. CONCLUSION: With mandibular stepwise advancement there seem to be more skeletal and less dental effects contributing to the improved molar relationship.