Determination Of The Strains Generated By Invisible Appliance With Different Thickness And Different Designed Displacement

Objective:To study how the invisible appliance works and to guide the process of manufacture and the clinical application of invisible appliance. We compared the orthodontic force value of invisible appliance with different thickness and different designed displacement.Methods:Ten sets of invisible appliances were prepared of 1.0mm and 0.75mm thickness respectively and lingual displacements of Omm, 0.2mm and 0.3mm were measured respectively. The appliances were put into the light-cured maxillary resin model before orthodontic treatment. 9 regions on the labial surface and 2 regions on the lingual surface were selected as measuring points. The strains were measured at different measuring points with resistance strain gauge and strain gauge. All the statistical analysis were conducted by SPSS 15.0 statistical package.Results:Ⅰ. In 1.0mm invisible appliances, after the upper left central incisor moved 0.2mm lingually, there were 10 points whose strain values were higher than that before the treatment, and 9 of them were significantly higher than that before the treatment(p<0.05). In 0.75mm invisible appliances, after the upper left central incisor moved 0.2 mm lingually, there were 11 points whose strain values were higher than that before the treatment, and 9 of them were significantly higher than that before the treatment (p<0.05). The strain values of the 11 measuring points were different from each other and the strain distribution showed no obvious pattern.Ⅱ. In 1.0mm invisible appliances, after the upper left central incisor moved 0.3 mm lingually, there were 10 points whose strain values were higher than that before the treatment, and 8 of them were significantly higher than that before the treatment (p<0.05). On the other hand, the strain value at 1 point was lower than that before the treatment, the differences were insignificant(p>0.05). In 0.75mm invisible appliances, after the upper left central incisor moved 0.3 mm lingually, there were 10 points whose strain values were higher than that before the treatment, and 9 of them were significantly higher than that before the treatment (p< 0.05). The strain value at 1 point was lower than that before the treatment, however, the differences were insignificant (p>0.05). The strain values of the 11 measuring points were different from each other and the strain distribution showed no obvious pattern.Ⅲ.Both In 1.0mm invisible appliances and in 0.75mm invisible appliances, the strain values at 11 points were higher after the upper left central incisor moved 0.3 mm lingually compared to 0.2 mm, and 9 of those points showed significant differences (p<0.05) in 1.0mm invisible appliances, while 7 of those points showed significant differences (p< 0.05) in 0.75mm invisible appliances.Ⅳ. During the process of upper left central incisor moved 0.2 mm and 0.3mm lingually, with the same designed displacement the strain values at 8 measuring points of 0.75mm appliances were higher than that 1.0 mm appliances, and 6 of the significant differences were found (p<0.05) Additionally, the strain values at 3 points were lower in the former than that in the latter, however, the differences were insignificant (p>0.05)Conclusions:Ⅰ. The invisible appliance generated higher strain after the treatment, and showed treatment effect, During the treatment, the strain values were different from each point, and the strain distribution showed no pattern.Ⅱ. The invisible appliance generated higher strain values after the upper left central incisor moved 0.3 mm lingually compared to 0.2mm.Ⅲ. The strain values generated by 0.75mm invisible appliances were higher than that by 1.0 mm invisible appliances.