Mechanobehavior and mandibular growth in children with Class II skeletal malocclusions

To evaluate if mandibular growth was influenced by the mechanobehavior (magnitude and frequency) of temporomandibular joint (TMJ) loading, the hypotheses tested were: Time 1 (T1) mechanobehavior and age correlated with changes (Δ) in lengths of (1) ramus (CoAS-Go) and (2) mandible (CoP-Gn) at Time 2 (T2) after Herbst appliance therapy (HAT).

Subjects had Class II skeletal malocclusions for which HAT was planned and gave informed consent to participate. Anatomy, including CoAS-Go and CoP-Gn, were derived from cone-beam computed tomography at both timepoints. T1 loading magnitudes were measured as TMJ energy densities (ED, mJ/mm3) using dynamic stereometry, loading frequencies were measured as jaw muscle duty factors (DFs, %) from at-home electromyography (EMG) recordings made by subjects, and mechanobehavior scores (MBS; MBS = ED2xDF, (mJmm3)2 %) were calculated for each TMJ. Generalized additive models tested for effects of T1 MBS and age on ΔCoAS-Go and ΔCoP-Gn.

Fifteen subjects (eight females, seven males) with T1 age of 12.7 ± 1.3 years completed protocols and HAT of 12.0 ± 1.1 months. Subjects produced 37 daytime and 42 night-time electromyographic recordings of 6.3 ± 1.1 and 8.9 ± 1.3 hours, respectively. Normalized changes in ramal and mandibular lengths vs T1 overall MBS and age showed significant nonlinear relationships (P = .003 and < .0001 with adjusted R2= 0.54 and 0.74, respectively), where relatively larger MBS and younger age showed larger changes in ramal and mandibular lengths after HAT.

Initial mechanobehavior and age were significantly correlated with changes in lengths of the ramus and the mandible after Herbst appliance therapy.