A comparative assessment of the forces and moments generated at the maxillary incisors between conventional and self-ligating brackets using a reverse curve of Spee NiTi archwire

Abstract

Abstract Objectives To compare the intrusive forces and labio-palatal moments generated at the maxillary incisors by a 0.017 x 0.025 inch reverse curve NiTi wire using self-ligating and conventional brackets. Methods Ten 0.017 x 0.025 inch reverse curve NiTi archwires were used with each of the following 0.022 inch bracket systems: Titanium Ortho (Ormco/Sybron, CA, USA), In-Ovation R (GAC International, NY, USA) and Damon System 3MX (Ormco/Sybron, CA, USA). The wires were inserted on bracketed maxillary Frasaco models, with segmented maxillary incisors. Simulated intrusion from 0.0-1.0 mm was performed on the Orthodontic Measurement and Simulation System, which recorded the intrusive forces and the labio-palatal moments at 0.05 mm increments. The data were analysed with the ANOVA and Scheffe tests. Results The intrusive forces were significantly different between all bracket types. The highest force was recorded with the conventional Titanium Orthos brackets (8.2 N), followed by the Damon 3MX brackets (6.3 N) and the In-Ovation R brackets (5.5 N). The moments were found to be significantly different between the conventional and the self-ligating brackets, but not between the two types of self-ligating brackets. The highest moments were recorded with the self-ligating brackets (16.6-16.9 N/mm), followed by the conventional brackets (10.8 N/mm). Conclusions The intrusive forces exerted on the maxillary incisors by a 0.017 x 0.025 inch reverse curve NiTi archwire during the final 1 mm of levelling are very high and beyond the necessary intrusive force level for these teeth. Lower intrusive forces, but higher labio-palatal moments, were recorded with the self-ligating brackets.