A Comparative Evaluation of Masticatory Performance and Occlusal Load Distribution in Class II Adolescent Patients...

To evaluate masticatory performance and occlusal load distribution in Class II division 1 adolescent patients treated with bilateral maxillary first‑premolar extractions or a fixed functional appliance (Mandibular Protraction Appliance IV, MPA IV), each compared independently against Class I subjects serving as a common functional reference.

In this single‑centre prospective cohort study, 54 adolescents (24 males, 30 females; mean age 15.6 ± 1.4 years) were allocated to three groups (n = 18 each): Group I, Class II patients with maxillary prognathism treated by bilateral maxillary first‑premolar extractions and fixed appliance mechanotherapy; Group II, Class II patients with mandibular retrognathism treated with a fixed functional appliance (Mandibular Protraction Appliance IV, MPA IV) followed by fixed appliance mechanotherapy; Group III, Class I subjects with normal overjet/overbite, serving as controls. Masticatory performance was assessed at baseline (T0) and after completion of active treatment (T1) using a β‑carotene colorimetric test (20 standardized chewing cycles), reported as normalized optical density (OD; M⁻¹cm⁻¹), with a normalized percentage score derived as Performance (%) = (E₁/E) × 100 for standardization against a seasonal reference OD (E). Occlusal load distribution at centric occlusion (maximum intercuspation) was recorded with T‑Scan III (Tekscan Inc., Boston, MA) and expressed as percentage force in anterior and posterior segments bilaterally. A mixed‑model repeated‑measures analysis of variance (ANOVA) evaluated the time × group interaction; paired t‑tests assessed intra‑group changes; one‑way ANOVA with post-hoc Bonferroni correction assessed inter‑group differences.

At T0, masticatory performance was significantly lower in both Class II groups than in controls (p < 0.001). Performance increased significantly in Groups I and II (Δ0.29 and Δ0.49 M^-1cm^-1; p < 0.001) at T1. Post‑treatment, anterior force distribution increased in both Class II groups. Posterior loading decreased bilaterally in the extraction group, whereas in the fixed functional group, it decreased on the right side but increased slightly (non‑significantly) on the left. Overall normalization toward the Class I pattern was more pronounced, though not uniform across all segments, in the fixed functional group.

When each Class II treatment group was compared independently against Class I controls, both extraction‑based camouflage and fixed functional mandibular advancement significantly improved masticatory performance and occlusal load distribution, bringing values closer to those of individuals with Class I occlusion. Fixed functional therapy yielded a larger functional gain and a more physiologic occlusal loading pattern than premolar extraction camouflage; however, this difference must be interpreted cautiously, given that the two treatment groups differed in their underlying skeletal phenotypes, precluding attribution of the inter-group difference to treatment modality alone.