Force delivery modification of removable thermoplastic appliances using Hilliard precision thermopliers for tipping an upper central incisor

OBJECTIVES: To evaluate the force delivered by removable thermoplastic appliances (RTAs, aligners), altered with Hilliard precision thermopliers, on an upper central incisor to tip it in the palatal and vestibular directions. MATERIALS AND METHODS: A total of 10 aligners made from Ideal Clear® (polyethylene terephthalate glycol copolyester, PET-G) with a thickness of 1 mm were used in force analysis. Different-sized spot-thermoformed protuberances (bumps) were generated by activating the thermoplier (thin and thick) up to 30°, 60° and 90° in the centre of the palatal and vestibular surfaces of the aligner in 15° steps. The tipping (Fx) and intrusive (Fz) force components were measured on the isolated upper central incisor as part of a standardized resin model, with or without vertical loading by a weight equivalent. RESULTS: Thermoplier activation at 30°, 60° and 90° resulted in different bump heights. The analysis revealed significantly higher Fx and Fz values with increasing bump heights for every activation step in all cases (p < 0.0001, respectively). Overall, the values of the Fx force component were higher than those observed for Fz. Significant differences between the palatal and vestibular tipping procedures were found depending on the resulting force components when the thin thermoplier was used; in contrast, the thick thermoplier resulted in a larger dispersion of the force magnitudes. CONCLUSIONS: Aligners modified with Hilliard precision thermopliers showed altered biomechanical parameters. This approach could be an option for treatment modification. CLINICAL RELEVANCE: The instrumental examination provided informative results for daily practice, as activation, force dosage and different force values under chewing pressure can be estimated more precisely based on the determined force levels.