| Dento-maxillofacial deformities is decided as by the World Health Organization (WHO) one of the three major oral diseases, and orthodontic treatment is one of the important means to solve dentofacial deformities. For orthodontic doctors , it is the biggest challenge to improve the treatment efficiency and make the treatment process become more comfortable.Direct at the diversity of malocclusion symptoms; the complication of appliance power system; and the features of internal rules and needing time of tooth movement. Regardless of appliance techniques, we are required to follow the "step by step" principle, and divide the entire treatment process into several relatively independent and interrelated phases, complete a specific purpose of each phase, also create the conditions for the follow-up phase.The nature of the fixed appliance is to us through the "power " treatment and allows teeth to produce a shift in the right direction. Based on different movement methods of tooth fixed appliance can be divided into: 1: Differential tooth movement technology. Representative of the appliance are: Begg filaments appliance technology and Tip-Edge differential straight wire appliance. 2. the whole tooth movement technology. Representative of the appliance are: edgewise technique, straight wire appliance and the self-locking brackets straight wire appliance.MBT appliance is as the basis for Andrew-Roth straight wire appliance system improvement, and take the introduction of the Begg appliance close extraction space slide method, but in the clinical practice of orthodontic surgeons come to realize the limitations of the technology,①in the early treatment, teeth move as whole with the greatest root first impedance and the demand higher anchorage;②while correcting many of the objectives, the teeth are also prone to adverse movement. Which incisor temporary deepen overbite and pour lip is a relatively common problem.Tip-Edge appliance, also known as differential straight wire appliance, stems from edgewise appliance, which was invented on the basis of applying differential power to move teeth in the traditional straight wire system. As a kind of straight wire appliance, through a unique bracket design, Tip-Edge appliance has the advantages of both traditional straight wire appliance and Begg appliance. It overcomes the shortcomings of the straight wire appliance, thus contributing to the movement of the orthodontic teeth and reducing the demand on the anchorage.MDD applianceis also fully integrated the advantages of both traditional straight wire appliance and Begg appliance. Also, it is designed on the basis of overcoming their respective shortcomings. Its innovative design is reflected in the following aspects:It can move teeth by light force from the direction of far and near without using of mouth force or implanting anchorage to strengthen it.It is easy to control the roots of teeth on the buccolinqual and the direction of far and near without using additional wires.Because the difference of the appliances' structures ,in the treatment process, there is a clear difference about the teeth movement when using straight wire appliance and standard edgewise appliance, some adverse teeth movements are prone to occurrence,including the anterior labial dipping and overbite deepening.Therefore, it is very important that using the straight wire appliance controls incisors' movement in the stage of alignment and leveling, especially, controls the anterior labial dipping and overbite. This study ia based on the experimental model of deep overbite Typodont, comparing the three directional movement trends of incisors when using different fixed appliance syetem on the stage of alignment and leveling. It also provides the clinical application of MDD brackets with certain references and basis.First , experimental comparison about incisors' 3D moving trends when using MDD and MBT appliance system on the stage of alignment and leveling.Choose 10 Angel II classification I maxillary and mandibular Typodont models, and randomly divide them into 2 groups: group MDD and group MBT.Five samples in each group are bonded MDD and MBT appliance, respectively. Use 0.014,0.016,0.018 inch diameter nickel titanium round wire to align and level the maxillary and mandibular longitudinal jaw curve.Every time replace the wires ,put them into 45 C°thermostatic water bath for 20 min ,then cool them with cooling water. Scan the experimental models with ATOS mobile optical scanner before and after the water bath.Coincide with the digital images of experimental models and initial models after the water bath and conclude corresponding landmarks in the X, Y, Z triaxial movement,and conduct t-test with SPSS17.0 to the measurement data..The movement trend of the two groups in the X, Y, Z three-axis is: When using a 0.014 inch NiTi round wire, the incisors of the two groups moved. But the difference of the incisors moveing trends between group MBT and group MDD is unconspicuous. When using 0.016 inches NiTi round wire, the moving trend of incisors in group MBT increased, while the group MDD did not change significantly. When using 0.018 in. NiTi round wire, the variation tendency of group MBT is more obvious than the one of group MDD. Judging from the whole process of alignement and leveling,the insiors' amount of movement in group MBT is apparently larger than in group MDD, and there is a statistically significant difference(P<0.05).Second, experimental comparison about incisors' 3D moving trends when using MDD and Tip-Edge appliance system on the stage of alignment and leveling.Choose 10 Angel II classification I maxillary and mandibular Typodont models,and randomly divide them into 2 groups: MDD group and Tip-Edge group.Five samples in each group are bonded MDD and Tip-Edge appliance, respectively.Bend a Australian wire of diameter 0.016 in. to an angle of 30°2-3cm in front of the four 1st molar buccal tubes. Use an anchorage curve to align and level the maxillary and mandibular longitudinal jaw curve. Place the bows into the slot, then pull them with classⅡintermaxillary traction, force 0.5 N.Put them into 45 C°thermostatic water bath for 20 min ,then cool them with cooling water. Scan the experimental models with ATOS mobile optical scanner before and after the water bath. Once again put them into thermostatic water bath for 20 min , then cool them with cooling water. Test them with three-axis,and use the suite to coincide with the digital images of experimental models and initial models after the water bath and conclude corresponding landmarks in the X, Y, Z triaxial movement, conduct t-test with SPSS17.0 to the measurement data. The movement trend of the two groups in the X, Y, Z three-axis is: after 20 min.water bath, the moving tendency of both two groups incisors is obvious, after 40min. water bath, move more apparent.Judging from the whole process of alignement and leveling, there is no statistically significant differences about the incisors' moving tendency between the two groups (P> 0.05).In summary,as far as the Typodont models are concerned,when using less than or equal 0.014 inch NiTi round wire , there is no significant difference in teeth three-dimensional movement between group MBT and group MDD ;when using 0.016 inch NiTi round wire ,compared with group MDD,overbite is intensive in group MBT and promote incisors forward; when using 0.018 inch NiTi round wire, compared with group MDD, overbite is intensive in group MBT, and promote the incisors forward more obviously . The special design of MDD bracket reduces the function of deepening overbite. but it needs further clinical trials whether the anterior teeth can reciprocate when using MDD bracket to align the anterior teeth. Experimental study found that, there is no significant difference about the control of 3D movements when using MDD bracket and Tip-Edge bracket in the stage of alignment and leveling. |
