Properties of Composite Materials Used for Bracket Bonding

Ana Caroline Silva Gama,Jose Bauer,Alessandro Dourado Loguercio,Ceci Nunes Carvalho,Andre Guaraci De Vito Moraes,Lilyan Cardoso Yamasaki

doi:10.1590/0103-6440201302184

Abstract

The purpose of this study was to evaluate in vitro the shear bond strength to enamel, flexural strength, flexural modulus, and contraction stress of one orthodontic composite and two flowable composites. Orthodontic brackets were bonded to 45 human maxillary premolars with the composites Transbond XT, Filtek Z-350 flow and Opallis flow and tested for shear bond strength. For measurement of flexural strength and flexural modulus, specimens were fabricated and tested under flexion. For the contraction stress test, cylindrical specimens were tested and an extensometer determined the height of the specimens. The data were subjected to one-way ANOVA and Tukey's test (α=0.05). The shear bond strength values were significantly lower (p<0.05) for the flowable composites compared with the orthodontic composite. For the flexural strength, no statistically significant difference was found among the composites (p>0.05) while the flexural modulus was significantly higher (p<0.05) for Transbond XT than for Filtek Z-350 flow and Opallis flow. The orthodontic composite presented significantly lower contraction stress values than the flowable composites (p<0.05). The light-activated orthodontic composite material presented higher flexural modulus and shear bond strength and lower contraction stress than both flowable composites.

Highlights

Several factors might affect the bond strength of bracket to enamel, leading to debonding, such as acid etching and drying time, adhesive application mode and time and photoactivation time [1]
These materials are very similar to the composite resins used in restorative dentistry [5], which has led to the indication of flowable composites for bracket bonding instead of orthodontic composites [6,7,8,9,10]
Flowable composites are usually less expensive than orthodontic composites [9] and their low modulus of elasticity could act as an “elastic layer” [12], preventing stress concentration at the tooth/bracket interface during light-activation and allowing a better dissipation of the stresses generated during occlusal movements [13]

Summary

Introduction

Several factors might affect the bond strength of bracket to enamel, leading to debonding, such as acid etching and drying time, adhesive application mode and time and photoactivation time [1]. Activated resin composites have been widely used in Orthodontics These composites require mixing of two pastes, which could induce incorporation of air bubbles into the material. Other disadvantages include longer working time, slower polymerization reaction and lower mechanical properties because the incorporation of oxygen in the mass inhibits the polymerization [3]. For these reasons, light-activated orthodontic composite materials have been ever more frequently used for bracket bonding to dental enamel [4]. Flowable composites are usually less expensive than orthodontic composites [9] and their low modulus of elasticity could act as an “elastic layer” [12], preventing stress concentration at the tooth/bracket interface during light-activation and allowing a better dissipation of the stresses generated during occlusal movements [13]

Objectives

Methods

Conclusion