Analysing Torque Expression with Different Bracket Positions and Crown-Root Angles of Maxillary Central Incisor

Abstract

Background: Torque expression in orthodontics is critically influenced by bracket positioning and anatomical variations in crown-root angulations of maxillary central incisors. Understanding these relationships is essential for optimal treatment outcomes and precise tooth positioning.

Objective: To evaluate the effect of vertical bracket positioning and varying crown-root angles on torque expression in maxillary central incisors using finite element analysis.

Methods: Three-dimensional finite element models of maxillary central incisors with crown-root angles of 165°, 170°, 175°, and 180° were constructed. Brackets were positioned at three vertical heights (3mm, 4.5mm, and 6mm from the incisal edge). A standardized 30° labial root torque was applied, and torque expression was measured for each configuration.

Results: Torque expression increased significantly with bracket height from the incisal edge across all crown-root angle variations (p < 0.001). Maximum torque expression was observed at 6mm bracket height: 24.8 ± 2.1° for 165° crown-root angle, 22.4 ± 1.8° for 170°, 19.6 ± 1.5° for 175°, and 17.2 ± 1.3° for 180°. Minimum expression occurred at 3mm height: 12.4 ± 1.1° for 165°, 11.2 ± 0.9° for 170°, 9.8 ± 0.8° for 175°, and 8.6 ± 0.7° for 180°. Crown-root angle showed significant inverse correlation with torque expression (r = -0.89, p < 0.001). The difference between maximum and minimum torque expression remained constant at approximately 12° regardless of crown-root angle variation.

Conclusion: Bracket positioning significantly influences torque expression, with higher bracket placement yielding greater torque delivery. Crown-root angle variations substantially affect torque expression, with more acute angles demonstrating enhanced torque transmission. These findings provide critical insights for individualized orthodontic treatment planning and bracket positioning protocols.