Comparison of the effects of clear aligners and twinblock appliances in functional treatment of class II malocclusion

In this thesis, the aim was to compare the effects of mandibular advancement with Twinblock, a conventional functional appliance, and with clear aligners in growing patients with skeletal Class II malocclusion due to mandibular retrognathia. The effects on skeletal, dental, soft tissue, airway, and hyoid bone position were evaluated through cephalometric measurements, while alterations in the trabecular bone structure of the mandible were assessed using the fractal analysis (FA) method. The MA group (Invisalign MA; Align Technology, San Jose, California, USA) consisted of 16 patients (12 females, 4 males; mean age: 11.80 ± 1.0 years), while the Twinblock group included 18 patients (9 females, 9 males; mean age: 12.10 ± 0.90 years). Lateral cephalometric and panoramic radiographs were obtained at the beginning of treatment and at the end of functional therapy. In the lateral cephalometric analysis, a total of 47 measurements were performed, including 18 skeletal, 16 dental, 4 airway, 3 hyoid, and 6 soft tissue parameters. FA was conducted by calculating the fractal dimension (FD) in eight regions: condyle, angulus, and corpus on both right and left sides of panoramic radiographs, and the symphysis region on lateral cephalometric radiographs. Data analysis was performed using MedCalc Statistical Software version 12.7.7 (MedCalc Software bvba, Ostend, Belgium; http://www.medcalc.org; 2013). The normality of continuous variables was tested with the Shapiro–Wilk test. For intragroup comparisons, the Mann–Whitney U test was used for independent continuous variables not conforming to a normal distribution, while the Wilcoxon signed-rank test was applied for dependent continuous variables in intergroup comparisons. A significance level of p<0,05 was considered statistically significant. According to cephalometric analysis, no significant changes were observed in the SNA° and A-VRD values in either group (p>0,05), whereas a significant decrease in the A-Ndik value was found in the MA group (p=0,017). In the mandible, both the MA and Twinblock appliances led to an increase in sagittal parameters, although the SNB° value showed a greater increase in the Twinblock group (p=0,021). Effective mandibular length (Co-Gn) increased in both appliances (p<0,05), with no significant difference between the groups (p>0,05). Corpus length (Go-Me) increased significantly with the MA appliance, while ramus length (Ar-Go) increased significantly with the Twinblock appliance (p<0,05). Both appliances induced retrusion, retroclination, and extrusion of the maxillary incisors (p<0.05), with no significant difference between the groups (p>0,05). In the mandibular incisors, the Twinblock appliance caused significant proclination (L1-NB°=6 ± 3) (p<0,05), whereas no significant change was observed with the MA appliance. The vertical position of the mandibular incisors remained unchanged with the Twinblock appliance (p>0,05), while significant intrusion was observed in the MA group (p=0.011). Airway measurements increased with both appliances; however, the oropharyngeal distance showed a greater increase in the Twinblock group (p<0,05). The sagittal position of the hyoid bone did not change with either appliance (p>0,05). In terms of vertical position, no significant change was observed in the MA group (p>0,05), whereas a superior position was detected in the Twinblock group (p<0,05). Regarding soft tissues, both appliances retruded the upper lip and increased the convexity angle (p<0,05). Soft Tissue A' point demonstrated significant changes in the MA group (p=0.021), while the Soft Tissue Pog' showed significant anterior movement only in the Twinblock group (p=0,004). The trabecular structure of the mandibular condyle, angulus, and corpus regions remained unchanged (p>0,05). The FD of the symphysis region increased in both groups (p<0,05), with no significant difference between them (p>0,05). In conclusion, both MA and Twinblock appliances were effective on the mandible in the correction of Class II malocclusion. However, the Twinblock was found to be more effective in increasing the SNB° value. The effects of the two appliances on the maxillary incisors were similar, whereas the MA appliance provided better control over the mandibular incisors. Both appliances demonstrated positive effects on the airway and soft tissues; nevertheless, greater improvement in oropharyngeal measurements was observed in favor of the Twinblock. The hyoid bone was positioned superiorly with the Twinblock appliance. Both appliances exerted similar effects on mandibular trabecular bone structure.