| Lingual orthodontia appliance was brought in during the 70s last century. Now it has become a recognized orthodontia system. Because of its invisible orthodontia idea and well received treatment result, more orthodontists have accepted this technique and more patients prefer this way of treatment. The study of the biomechanical characters of the lingual appliances above, has a lot of meaning for us to use the lingual appliances,. This study has four parts.Part 1 The design and the exploitation of the tester for the orthodontia frictionThrough self designing, we have invented the tester for the orthodontia friction. It creates the condition for the friction experiment below, and it also has set up the base for the inventing of the computerized accurate multifunctional friction tester.Part 2 The study of the influence from the ligating ways on the friction of the edgewise slot.We obtain the sliding friction between the different edgewise slot of lingual brackets/different ways of ligating and the arch wire and the brackets in the passive situation. And we evaluated the influence of the ways of ligating to the friction and obtained such result:(1) Different design of the bracket and different ways of ligate leads to different ligating force, so the frictions are quite different from each other. GAC self-ligating bracket has the least ligating force, so as the sliding friction, However, conventional ligating bracket such as the Kurz bracket and the STB bracket has more ligating force than the self-ligating bracket, so as the sliding friction.(2) For the GAC self-ligating bracket in the passive situation. there are small friction between the bracket and the 0.016 " NiTi wire; 0.016" stainless steel wire; 0.016×0.022" NiTi wire and 0.016×0.022" stainless steel wire. Since the clip has no ligating force towards the arch wire, the sliding friction is too small to be count.(3) Compare with the Kurz lingual brackets, the STB lingual brackets' slot has less friction with the thin round arch wire, but when it comes to the stainless steel rectangular wire, the frictions are almost the same. But the friction between the STB bracket and the NiTi rectangular wire are significantly more the the Kurz lingual bracket.Part 3 The study of the influence from the ligating ways on the friction of the ribbon arch slot.We obtain the sliding friction between the different ribbon arch slot of lingual brackets/different ways of ligating and the arch wire and the brackets in the passive situation. And we evaluated the influence of the ways of ligating to the friction and obtained such result:(1) Different design of the bracket and different ways of ligate leads to different ligating force, meanwhile, it can create different pressure from the arch wire towards the wall of the slot, so the frictions are quite different from each other. Using the round arch wire, Forestadent 3D Torque-Lingual self-ligating lingual bracket has the least ligating force, so as the sliding friction, however, for the conventional ligating, the 3B Xu lingual bracket has the most sliding friction. The 3M individual lingual bracket with a special design for the low friction has the medium ligating force, so the three ribbon arch lingual brackets have different sliding friction.(2) There is significant relation between the types of the arch wire for the Forestadent 3D Torque-Lingual self-ligating bracket in the passive situation. There are certain friction between the bracket and the 0.016" NiTi wire; 0.016" stainless steel wire; and 0.016×0.022" stainless steel wire. However, the 0.016×0.022" NiTi wire and the slot has a great ligating force because of the clip, the sliding friction has increased significantly to 132 gram.(3) Compare with the 3M individual lingual bracket,3B Xu lingual bracket shows the greater sliding friction with the thin round wire or the thick rectangular wwire. It has proved that the low friction expending arm of the 3M individual lingual bracket does decrease the friction between the arch wire and the bracket.Part 4 The study of the influence from different types of bracket on the frictionWe studied the different types of the bracket with the arch wire in a certain angle, and the sliding friction between the four different brackets and 0.016" stainless steel wire/0.022×0.016" stainless steel wire. Analyze the influence from types of the bracket, size of the arch wire, and the angle between the bracket and the arch wire on the sliding friction, and obtained such result:(1) The friction of four types of brackets shows that in the passive situation, the friction stay the same, in the motive situation, as the increase of the angle, the friction increases, and have a linear relationship. Different bracket with the same stainless steel rectangular wire, the slopes of the angle towards the sliding friction are different, and it is related to the types of the brackets.(2) In the passive situation, the design and the feature of the slot of the edgewise and ribbon arch do not influence the sliding friction. Using the lingual bracket with the expending arm which has the function of decreasing the friction, such as STB lingual bracket,3M individual lingual bracket, the sliding friction between the bracket and the thin round wire (NiTi wire or stainless steel wire) can be decreased significantly.(3) In the motive situation,0.022×0.016" stainless steel wire sliding in a certain angle with the Kurz bracket; STB lingual bracket and domestic Xu lingual bracket, the slope of the angle towards the sliding friction are close to each other. However when the 3M individual bracket and the 0.022×0.016" stainless steel wire have a certain angle as 3-9°, the slope of the angle towards the sliding friction is the biggest. It shows that the 3M golden alloy individual bracket has a big sliding friction with the stainless steel rectangular wire in the motive situation.
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