Initial forces generated by three types of thermoplastic appliances on an upper central incisor during tipping

Abstract

The force properties of thermoformed appliances have not been systematically investigated. Therefore, the aim of the present study was to quantify the forces delivered by thermoplastic appliances manufactured from three different materials, with the same thickness, on a central upper incisor, during tipping. Five identical appliances were manufactured from three different materials all with a thickness of 1.0 mm (Ideal Clear, Erkodur, and Biolon). For measuring the forces, an isolated measuring tooth, as part of a standardized resin model incorporated in a newly developed measuring device, was tipped in nine 2.7 arc minute (0.04629 degree) steps, from 0 to 0.416 degrees in the vestibular and palatal directions around a rotational axis through the virtual apex, after positioning an appliance on the model. For statistical analysis, the force components Fx/tipping and Fz/intrusion at a displacement of +/-0.151 mm from the incisor edge were determined. Means and standard deviations (SDs) were calculated. The Kruskal-Wallis test for overall effects and the Wilcoxon two-sample test for individual group pairings were used (P < 0.05 significance level). The mean Fx forces ranged from -2.82 N (SD 0.62) to 5.42 N (SD 0.56). The mean Fz forces were between -0.14 N (SD 0.52) and -2.3 N (SD 0.43). The highest intrusive forces were measured during vestibular displacement of the measuring tooth. The forces delivered by the Biolon appliance were found to be much greater (P < 0.01) than those of the other materials. The forces delivered by the materials investigated were mostly higher than those stated in the literature.

Initial Forces and Moments Delivered by Removable Thermoplastic Appliances during Rotation of an Upper Central Incisor

“…[17][18][19] Nevertheless, the forces at the lower range of activation are of lesser relevance, because the amount of movement is adapted to the width of the periodontal ligament (0.1-0.3 mm). 20,21 As postulated before, 5,6 a self-protecting mechanism might be responsible for a low rate of root resorption, even with appliances with an initial activation range of over 0.2 mm. 4,[17][18][19] This mechanism is probably based on the reduced fit of the appliance during increased activation.…”

“…16 Comparable values and Fz values about three times higher than those measured in the present study have been reported before, for the same materials, during tipping of 0.151 mm. 5 These intrusive force can be explained by a local deformation of the inclined inner surfaces of the appliance ( Figure 5) and with a reduced fit during progressive axial rotation, which tends to deform the appliance like a bow, by raising it in the anterior region. As a consequence, a reactive force Fz is generated that acts vertically on the tooth.…”

“…5 It was constructed for modular use and is composed of a quadrangular frame rigidly coupled on a base-plate by four posts. A resin bowl can be reversibly fixed in the frame by a locking screw.…”

“…2,3 Even though the movement of teeth with thermoplastic appliances has been clinically documented, the force delivery properties of these appliances have only been evaluated in a few in vivo 4 and in vitro studies of tipping movement. 5,6 The aim of the present study was to evaluate the forces and moments exerted by removable thermoplastic appliances produced by three different, hard thermoplastic materials, with the same thickness, on a maxillary central incisor during rotation in vitro.…”

Forces and moments delivered by novel, thinner PET-G aligners during labiopalatal bodily movement of a maxillary central incisor: An in vitro study

“…10 Although such study design allows a basic comparison between the various plastic materials, it must be noted that results cannot be transferred to the clinical situation because of the simplified specimen geometry that ignores relevant mechanical effects such as regional reinforcement of the plastic material due to thermoforming on dental models. 11,12 The latter has been considered in later investigations examining force-andmoment application of aligners thermoformed on dentition models. Results clearly indicated that the teeth are overloaded when following the recommendations regarding tooth displacements in the setup and aligner materials.…”