The effects of Twin block treatment on skeletal and dental changes in Class II Division 1 malocclusion

Class II Division 1 malocclusion is one of the most common orthodontic issues, characterized by a retrusive mandible and protrusive maxilla, leading to an increased overjet and often affecting the patient’s facial aesthetics and function. In the past decade, the Twin-block functional appliance has become increasingly popular for treating this type of malocclusion. The Twin-block appliance is a removable orthodontic device designed to encourage mandibular growth and correct jaw discrepancies by repositioning the mandible forward, thereby improving the skeletal and dentoalveolar relationships between the maxilla and mandible. This study aimed to evaluate the skeletal and dentoalveolar changes in patients with Class II Division 1 malocclusion who were treated with the Twin-block appliance.

Material and Methods

The study involved a cephalometric analysis of 34 patients with Class II Division 1 malocclusion who underwent treatment with the Twin block appliance. Cephalometric analysis is a diagnostic tool in orthodontics that involves taking precise measurements of the bones and teeth in the head, allowing orthodontists to assess the skeletal and dental relationships before and after treatment. The study used the same reference system for measurements before and after treatment to ensure consistency. The skeletal and dentoalveolar facial structures of these patients were compared to those of individuals with excellent occlusion, known as the Bolton standards. These individuals served as the control group to account for natural growth changes over time.

Results

The results showed that the Twin-block appliance led to significant improvements in both skeletal and dentoalveolar relationships. The length of the mandible, measured from the Articulare (a point located on the mandible’s posterior edge) to the Pogonion (the most anterior point of the chin), increased by an average of 4.6 mm in the treatment group. In contrast, the control group (Bolton standards) showed an average mandibular growth of only 2.2 mm over the same period. This indicates that the Twin-block appliance significantly stimulates mandibular growth, contributing to the correction of Class II Division 1 malocclusion.

Furthermore, the study found a substantial improvement in the skeletal relationship between the maxilla and mandible, as evidenced by the reduction in the ANB angle. The ANB angle is a cephalometric measurement used to assess the anteroposterior relationship between the maxilla and mandible; a smaller angle indicates a more favorable jaw relationship. In the treatment group, the ANB angle decreased by 2.3 degrees, suggesting a considerable improvement in the alignment of the upper and lower jaws.

The overjet, which refers to the horizontal distance between the upper and lower front teeth, was also significantly reduced by 4.7 mm in the treatment group. Additionally, the postnormal molar position (the relationship between the upper and lower molars) was corrected by 3.6 mm, further contributing to an improved occlusion.

Conclusions

The study concluded that the Twin-block appliance is highly effective in treating Class II Division 1 malocclusion, primarily by promoting mandibular growth. Over a 12-month treatment period, the appliance increased mandibular length by an average of 2.4 mm more than natural growth alone would have achieved. The study also found that approximately 40% of the overjet correction was due to skeletal changes, while the remaining 60% was due to dentoalveolar changes, indicating that the appliance effectively influences both skeletal and dental structures.

Correction of the postnormal buccal segments was achieved through a combination of distal movement of the upper molars and forward migration of the lower molars. Specifically, the upper molars moved distally by 0.7 mm dentoalveolar and 0.3 mm skeletal, while the lower molars advanced by 0.9 mm dentoalveolar and 1.7 mm skeletal. These findings underscore the Twin-block appliance’s ability to produce comprehensive corrections in both the skeletal and dental aspects of Class II Division 1 malocclusion, making it a valuable tool in modern orthodontic practice.

Source: Pubmed