Effects of fixed twin-block and forsus fatigue resistant device on mandibular third molar angulation – A comparative study

Abstract

INTRODUCTION: Fixed functional appliances such as fixed twin-block (FTB) and forsus fatigue resistant device (FRD) improve Class II skeletal relationships by increasing the length of the mandible, which subsequently leads to an increase in the retromolar space. This would bring about a positional and angular change in the mandibular third molar. These appliances also produce forward movement of the mandibular buccal segments, which has also been cited as an important factor providing space and therefore improving the angulation and eruption potential of the third molars. OBJECTIVE: To evaluate and compare the effects of FTB and forsus FRD treatment on mandibular third molar angulation. MATERIALS AND METHODS: Pretreatment and posttreatment lateral cephalograms and orthopantomograms of 25 patients with Class II division 1 malocclusion treated with FTB were compared with those of 25 patients treated with forsus FRD. Sagittal and vertical skeletal relationships and mandibular length were assessed on lateral cephalogram, whereas linear parameters such as retromolar space; space width ratio (SWR); distance of Xi point from the distal surface of the lower second molar; and angular parameters such as α, β, and ϒ; and gonial angles were measured using orthopantomograms. Intragroup comparison was done using paired t-test, while unpaired t-test was done for intergroup comparison of the observed changes. RESULTS: Mandibular length increased significantly in the FTB group, whereas mesialization of the mandibular dentition was significantly high in the FRD group. Both groups showed a significant increase in retromolar space, SWR, Xi point to 7 distance, α angle, and a decrease in β angle. These changes were significantly more pronounced in the FTB group. CONCLUSION: There was a significant improvement in the third molar angulation following treatment with fixed functional appliances, which was comparatively more in the FTB group than that in the FRD group, owing to an increase in mandibular length.