Biomechanische Untersuchungen an thermoplastisch geformten Schienen

Abstract

Many clinical treatments with removable thermoplastic appliances have been documented in dental literature. Yet, the forces produced by these appliances have not been investigated systematically so far. Hence the aim of the study was to quantify the forces delivered by a special type of thermoplastic appliance described by Sheridan. Traditional aligner appliances are using a series of aligners to move teeth. The method applied in this study moves teeth through pressure points, so called bumps. These bumps are created by special pliers, which are pressed in the aligner. The aim of the study was to measure the forces generated by bumps when tipping a maxillary central incisor in vitro in detail. Further on it was investigated whether these forces change when the bumps` depth and position were altered. Moreover another aim was to evaluate whether the pliers` shape and the occlusal forces acting during swallowing affect the forces delivered by removable thermoplastic appliances. To simulate swallowing, a weight was positioned on top of the aligners during the measurements. The following results can be stated: Bumps produce a complex system of forces during tipping. When deconstructing the force vector into its components, this results in horizontally and intrusively acting forces. The measured forces in the present study were much higher than the ideal forces recommended for orthodontic treatment in dental literature. Compared to other studies, the forces in this trial were also much higher, however only some exceeded the forces measured in a parallel study which evaluated forces during tipping a maxillary central incisor with traditional thermoplastic appliances. When the bumps were deepened, horizontal and intrusive forces occurred, which were statistically significantly higher. Depending on the position of the bumps, varying forces were generated, although the bumps` depth remained unchanged. Yet no homogeneous influence of the bumps` position on the strength of the measured forces could be found. The shape of the pliers only affected the measurements in some cases. However, the trend could be observed that the thin pliers produced higher forces than the thick one. When simulating swallowing the resulting forces were also higher in tendency. However, in the statistical analysis the results were also only partly significant. In conclusion, the present study showed that even flat bumps produce high forces. This finding should be taken into account when thermoplastic aligners are used in orthodontic therapy.