Abstract
BackgroundThe ideal built-in tip and torque values of the straight wire appliance reduce the need for wire bending and hence reduce chair time. The vertical position of the bracket on the tooth surface can alter the torque exerted on the tooth. This is a result of the altered surface curvature observed at each vertical position. To further clarify the role of vertical bracket positioning on the applied torque and the resultant stresses in the periodontal ligament (PDL), we designed a mandibular first premolar using finite element modeling.MethodsCone beam computed tomography of 52 patients (83 lower first premolars) was selected to be included in the study. Curvature was measured for points along the labial surface with increasing distances (0.5 mm increments) from the cusp tip by calculating the angle between tangents drawn from these points and the axis joining the cusp tip and the root apex. The mean values for each distance were calculated, and a finite element model was designed incorporating these mean values. The resultant stress and hydrostatic pressure in the PDL were calculated using finite element analysis.ResultsThe labial surface of the mandibular first premolar demonstrated a 26.39° change from 2.5 to 6 mm from the cusp tip. The maximum Von-Mises stress and hydrostatic pressure in the PDL were observed at the root apex for all of the bracket positions, and these values demonstrated, respectively, a change of up to 0.059 and 0.186 MPa between two successive points.ConclusionsIt can be concluded that the variation in the vertical position of the bracket can have an important effect on the torque and subsequently on the stresses and pressures in the PDL.
Highlights
The ideal built-in tip and torque values of the straight wire appliance reduce the need for wire bending and reduce chair time
The inclusion criteria for the cone beam computed tomography (CBCT) images were radiographies obtained from healthy individuals who were 15 to 30 years old, who did not suffer from any syndrome known to cause altered tooth morphology, and who had a normal class I occlusion
Buccal surface curvature The intraclass correlation coefficient (ICC) was used to determine the agreement between the two measurements made by the OMFR
Summary
The ideal built-in tip and torque values of the straight wire appliance reduce the need for wire bending and reduce chair time. The vertical position of the bracket on the tooth surface can alter the torque exerted on the tooth. This is a result of the altered surface curvature observed at each vertical position. To further clarify the role of vertical bracket positioning on the applied torque and the resultant stresses in the periodontal ligament (PDL), we designed a mandibular first premolar using finite element modeling. Considering that SWA brackets contain the necessary information for the desired tooth position (i.e., tip, torque, height, and rotation) [5], the only variables are tooth morphology and the position. A sequel of orthodontic treatment, has been linked to the amount of torque applied to a tooth [13,14,15]. Studies evaluating the relationship between torqueing force and root resorption arrived at the same conclusion, that is, higher torque magnitudes result in elevated resorption [13,15]
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