An evaluation of the Stresses Generated in a Bonded Orthodontic Attachment by Three Different Load Cases Using the Finite Element Method of Stress Analysis

Abstract

The objective of the investigation was to develop a clinically valid three-dimensional computer model of the orthodontic bracket-cement-tooth continuum, and determine the magnitude and distribution of stresses generated by three different load cases. A three-dimensional finite element model of the bracket-cement-tooth system was constructed consisting of 15,324 nodes and 2,971 finite elements. The stresses induced in the bracket-tooth interface by a masticatory load, a peel force and a twisting couple were recorded. The maximum principal stresses resulting from occlusal and 'twisting' forces are distributed toward the lute periphery. Peel forces, applied to the bracket tie wing, are concentrated beneath the bracket stem. Twisting forces result in the highest enamel stresses. The quality of orthodontic attachment can be explained by the magnitude and distribution of major principal stresses within the cement and impregnated bracket base. Shear and shear/peel forces are most likely to induce crack propagation within the adhesive layer. However, when a twisting action is used to remove orthodontic brackets, enamel failure is most likely. A clearer insight into the complexity of the bracket-cement-tooth system has been provided by numerical and finite element investigations. Further investigations, evaluating the influence of bracket base designs and orthodontic cement physical and geometric properties are indicated. Refereed Scientific Paper

Finite element sub-modeling analyses of damage to enamel at the incisor enamel/adhesive interface upon de-bonding for different orthodontic bracket bases

“…A de-bonding shear force can detach the bracket more easily than the other forces, with the lowest risk of enamel loss. This finding is consistent with the work of Rossouw and Terblanche (1995) and Knox et al (2000), who found that (1) the shear mode was safer for de-bonding brackets than the tensile mode, and (2) torque more often caused damage to the enamel than did shear.…”

“…Bracket detachment is usually caused through shear peeling, tensile forces or torque (Wang et al, 1997;Kapur et al, 1999;Rix et al, 2001) by clinicians. Many studies have focused on the stress distribution at an enamel/adhesive/bracket interface in various detached loading modes, but no comprehensive survey of the enamel damage associated with the micro-interlocking mechanism between resin tags has been carried out (Rossouw and Terblanche, 1995;Knox et al, 2000;Valletta et al, 2007;Chen et al, 2008). A reduction in the size of the brackets and their bases has also been proposed to produce a smaller retentive area, which Fig.…”

In vivo debonding strength and enamel damage in two orthodontic debonding methods

“…However, ARI and Ca scores were identical in both methods despite the differences in debonding forces. The explanation to this dichotomy is that cracks probably initiated at the adhesive layer and propagated to either the bracket/adhesive or the adhesive/enamel interfaces (Knox et al, 2000). Since metal brackets bonded with light-cure bonding material were examined in this study, the strength (complete polymerization) of the adhesive material was initially weaker at the bracket/adhesive than at the enamel/adhesive interface, as light-cured Table 2 Correlations between adhesive remnant index (ARI), calcium remnant (Ca) and debonding strength (DS) for each tooth (1 -5) in the two debonding methods.…”

“…Greater tooth damage may found in twisting disengagement techniques than in shear/peel (Knox et al, 2000). Excessive debonding strength (>11.3 MPa) causes enamel cracks that are less likely to appear when lower forces are applied (7.3 MPa) (Bishara et al, 1995).…”

Effect of tooth layers' segmentation on pattern of stress distribution in bracket- adhesive- tooth system

“…Stress distribution in bracket-adhesive-tooth system has been known as a good parameter to estimate and compare the bond strength of different systems [2,3]. Primary studies had used two dimensional finite element models to obtain stress distribution in systems [4,5]. Subsequent studies performed three dimensional analyses that were more accurate, nevertheless most of these efforts led to low quality three dimensional models because they did not consider the reality of tooth structure, its irregularity and asymmetry.…”