Objectives: Myofunctional appliances stimulate mandibular growth in Class II malocclusion with a retrognathic mandible. The twin-block appliance is favored over other appliances for comfort and it can advance the mandible in a single-step or two-step protocol. Although many studies have been conducted comparing the effects of single-step and two-step advancement in the twin block, its biochemical impacts remain unclear. This study compares salivary alkaline phosphatase (ALP) (a bone-turnover marker) during single-step versus two-step twin-block therapy in growing Class II patients to compare treatment-related skeletal remodeling differences biologically. Material and Methods: This study involved 40 Class II patients aged 10–14 years with overjet >7 mm. Patients were randomly divided into two groups: Group 1 including twin block with single-step advancement ( n = 20) and Group 2 including twin block with two-step advancement ( n = 20). Salivary ALP was measured at baseline and monthly for 6 months (M0–M6). Skeletal changes were assessed through pre-treatment and post-treatment lateral cephalograms. Results: In Group 1, ALP showed a gradual rise from 837 IU/L (M0) to a peak of 876 IU/L (M3) then fell to 847 IU/L (M6). Group 2 increased from 862 IU/L to 919 IU/L (M4), declining to 880 IU/L (M6). Both groups ended with higher ALP than baseline. Comparison of skeletal and dental parameters between both the groups showed a significant difference in Sella Nasion A point angle (SNB), A point Nasion B point angle (ANB), total mandibular length, and lower incisor proclination. Conclusion: These findings indicate that while the two-step protocol resulted in a slightly stronger and more sustained ALP response, the differences were not sufficient to demonstrate statistical superiority over the one-step protocol within the observed sample. Overall, the pattern of skeletal and dental outcomes indicates that the two-step advancement protocol delivers greater skeletal correction while producing fewer dentoalveolar changes than the single-step approach.
Badu et al. (Sun,) studied this question.