Hard- and soft-tissue changes after adult Class II Division 1 orthodontic treatment: a retrospective CBCT-based...

Restoring facial balance is now central to adult orthodontic care, yet evidence describing hard-soft tissue coupling and short-term retention stability in non-growing adults with Angle Class II Division 1 malocclusion remains limited.

In this observational study, 236 consecutively treated adults (≥18 years) underwent clinically archived cone-beam computed tomography (CBCT) before treatment (T0) and within 2 weeks after debonding (T1). Ten hard- and five soft-tissue variables were measured on the T0 and T1 three-dimensional reconstructions and used for the treatment-change analysis. For the 12-month analysis (T2, n = 224) the T0 and T1 volumes were reformatted into orthogonally synthesized lateral cephalograms and re-measured, so that stability was assessed between two lateral cephalograms of the same geometrical type, the T2 record being the standardized digital lateral cephalogram taken at the routine retention review. Each T1-T2 change was judged against a variable-specific combined smallest detectable difference (SDD) derived from the method error of both cephalometric records, at group and at individual level. Paired tests with mean change, 95% CIs and Cohen's dz, correlations with multiplicity control, change-score correlations and multivariable linear regression evaluated change and hard-soft coupling.

From T0 to T1, ANB, U1-NA and L1-NB decreased and the interincisal angle increased (all P < 0.001), while SNA and SNB were unchanged. The nasolabial and mentolabial angles and chin thickness increased, and both lips retracted toward the aesthetic plane (all P < 0.001). Between T1 and T2 no variable showed a mean change that reached its combined SDD, and 92.5% to 98.7% of the T0-T1 change was still present at 1 year; 2.2%-6.7% of individual patients nevertheless crossed the SDD in the relapse direction. In adjusted models, maxillary incisor retraction remained independently associated with nasolabial-angle increase (B = -0.96° per degree; 95% CI -1.20 to -0.72) and with upper-lip retraction (B = +0.24 mm per millimeter; 95% CI +0.18 to +0.30), and mandibular incisor retraction with lower-lip retraction (B = +0.16; 95% CI +0.10 to +0.22). Adjusted R ² ranged from 0.146 to 0.397 and the maximum variance inflation factor (VIF) was 1.76.

In non-growing adults, treatment was accompanied by predominantly dentoalveolar correction and by coupled soft-tissue change that was maintained at 1 year at group level, no mean change exceeding the error of the method. The coupling was consistent on average but explained a minority of the between-patient variance, and a small proportion of individuals showed measurable rebound, so the individual soft-tissue response remains difficult to predict. These observational data describe association and short-term stability, not causal benefit.