Exploring bracket torque expression: A comparative in vitro study of new self-ligating bracket designs and archwire geometries

Objective: This in vitro study aimed to evaluate the torque expression efficiency when it is integrated into the bracket slot versus the bracket base. Additionally, the impact of archwire geometry (rectangular vs. rhomboid) on torque expression has been examined.

Material and methods: The torque expression was evaluated in a full arch printed maxillary model, focusing on tooth #11, which was positioned within an alveolus filled with Typodont wax. Three different types of brackets were utilized: conventional metallic bracket (Minidiamond™), self-ligating bracket with torque in base (Damon Q2™), and a new self-ligating bracket design with torque in slot (Damon Ultima™). Two variations of archwires were used: rectangular and rhomboid stainless steel, measuring 0.019×0.025 inches and 0.019×0.0275 inches, respectively, from ORMCO™. The study included seven groups: six experimental groups and a control group, with 15 measurements in each group, totaling 105 torque measurements. Optical impressions were taken of the tooth's original position and its final position after torque expression. STL files were superimposed using GEOMAGIC software to calculate the percentage of torque expression.

Results: The self-ligating bracket with torque in slot (Damon Ultima™) shows significantly higher torque expression than the self-ligating bracket with torque in base (Damon Q2™) with a rectangular stainless steel archwire (P=0.00015). The Ultima™ bracket also demonstrates higher torque expression than both the Q2™ and conventional 22° brackets with a rhomboid stainless steel archwire (P<0.003). No significant difference in torque expression was found between the rectangular and rhomboid stainless steel archwires for any bracket group (P>0.05).

Conclusions: The self-ligating bracket with torque in slot shows comparable torque expression effectiveness to the conventional bracket, outperforming the self-ligating bracket with torque in base. Archwire geometry does not significantly impact torque expression.