Centroid analysis of twin-block appliance treatment for Class II Division 1 malocclusion

Centroid points were used as a stable baseline to assess treatment changes in twin-block appliance therapy because of their reduced variance.

Cephalometric radiographs were taken before and after treatment with the twin-block appliance on 30 consecutive patients with Class II Division 1 malocclusions. A control group was generated from standard Bolton outlines, with each treated case matched individually for age and treatment time. The center of area of the whole skull, cranium, face, and upper and lower face outlines was calculated. Angular and linear measurements were made for standard cephalometric points relative to the less variable centroid reference points. The results were compared to the natural growth change in the matched control group using a Mann-Whitney U test for statistical significance.

The treatment effect was also calculated by subtracting the natural growth change from the treatment change. This was then compared to twice the method error to see if the treatment change was clinically significant. There was both a statistically and clinically significant improvement in the dental base relationship due to a forward mandibular skeletal response and maxillary dentoalveolar retraction of the maxillary incisors.

Centroid analysis provided more stable reference points, giving a clearer picture of twin-block appliance outcome.