A randomized clinical trial of two alternative designs of Twin-block appliance.

OBJECTIVE: To test if placing a Southend clasp on the upper and lower incisors during Twin-block appliance treatment will control their angulation and enhance skeletal correction. DESIGN: Prospective, randomized, controlled clinical trial (ISRTCTN 45965219). SETTING: Orthodontic Department, Royal Preston District General Hospital, Preston, UK. PARTICIPANTS: Fifty-two consecutive patients aged 9-30 years undergoing treatment for Class II division 1 malocclusion (ANB>5°, OJ>6 mm). METHODS: Two alternative designs of Twin-block appliance were allocated randomly. One with a Southend clasp on the upper and lower central incisors and one without. The appliances were identical in all other aspects. OUTCOMES: Skeletal and dental changes measured on before and after treatment lateral cephalometric radiographs. RESULTS: There was a statistically significant change in ANB angle between the Southend group (-3·5°) and the Non-Southend group (-2·6°) (P = 0·004). The change in upper incisor angulation was -6·1° for the Southend group and -12·0° for the Non-Southend group, which was statistically significant (P = 0·005). The change in lower incisor angulation was 3·0° for the Southend group and 6·9° for the Non-Southend group, which was statistically significant (P = 0·005). CONCLUSIONS: The presence of a Southend clasp on the upper and lower incisors during Twin-block treatment limited their tipping which enhanced the skeletal correction.