[A comparative study on three-dimensional movement of anterior teeth between applying MDD appliances and applying three common fixed appliances in the initial alignment stage].

Typodont models of bilateral canines gingival displaced vertically for 3 mm and bilateral lateral incisors palatal displaced horizontally for 3 mm are made and every kind of the two kind models was divided into four groups: MDD, MBT, self-ligating and Tip-Edge. Each group of the two kinds of models had 5 models, so a total of 40 models for the two kinds of models were set up. The experimental models were aligned with a 0.30 mm of nickel titanium round wire in a water-bath with constant temperature 45 degrees C for 30 minutes. The three-dimensional digital images of the experimental models before and after the water bath were obtained by scanning with the three dimensional optical scanner ATOS. Geomagic software was used to overlap the digital images taken before and after the water bath treatment. The vertical changes of sign points of canines, the movements of sign points of lateral incisors in the sagittal plane and the horizontal plane were quantified by using the Color map. The data was then processed by a two-factor analysis of variance by using SAS 9.2 software package. Analysis of the results shows that the vertical changes of sign points of canines , the movements of sign points of lateral incisors in the sagittal plane and the horizontal plane of MDD group are all less than those in the other three groups, a statistically significant difference (P < 0.0001). And the size of the teeth displacement is directly related to the size of orthodontic force on the typodont models. Thus the preliminary results suggest that MDD appliance might have advantages of light force in the alignment stage, and that the possible relevant factors are the improvement of its sub-slot and the single ligation wing design.