Abstract
The aim of this study was to evaluate the effect of different number of thermal cycles on the shear bond strength (SBS) of metallic orthodontic brackets bonded to feldspathic ceramic by a composite resin. Twenty-five ceramic cylinders were etched with 10% hydrofluoric acid for 60 s and received two layers of silane. Brackets were bonded to the cylinders using Transbond XT and assigned to 5 groups (n=5): Group 1 - Control group (without thermal cycling); Group 2 - 500 thermal cycles; Group 3 - 5,000 thermal cycles; Group 4 - 7,000 thermal cycles and Group 5 - 10,000 thermal cycles. Light-activation was carried out by Radii Plus LED. SBS testing was carried out after 24 h of storage in deionized water and thermal cycling (5/55 oC and 30 s dwell time). Five brackets were bonded to each cylinder, totalizing 25 brackets for each group. Data were submitted to one-way ANOVA and Tukey's test (α=0.05). The Adhesive Remnant Index (ARI) was evaluated at 8× magnification. The SBS (MPa) of control group (9.3±0.8), 500 (9.0±0.7) and 5,000 (8.4±0.9) thermal cycles were significantly higher than those after 7,000 (6.8±0.6) and 10,000 (4.9±1.0) thermal cycles (p<0.05). The ARI showed a predominance of Scores 0 (adhesive failure) prevailed in all groups, as shown by the ARI, with increased scores 1 and 2 (mixed failures) for control group and 500 thermal cycles. In conclusion, thermal fatigue may compromise the bonding integration between metallic brackets and ceramic restorations. For in vitro testing, use of at least 7,000 cycles is advised to result in significant fatigue on the bonding interface.
Highlights
In the last years, use of restorative materials like dental ceramic has increased as result of their optimum esthetic and mechanical properties [1], and as substrates for bonding of brackets in clinical situations [2]
The clinical success and long-term durability of the bond strength between orthodontic brackets and the ceramic surface using composite resin may be influenced by several factors, such as thermal cycling, fatigue, artificial ageing and mechanical properties of composite resin, silane and adhesive bonding [11]
The quality and durability of this bond is determined by the specific treatment used to produce chemical and micromechanical retention to the ceramic material [13] and bonding mechanisms between bracket/bonding materials [2]
Summary
Use of restorative materials like dental ceramic has increased as result of their optimum esthetic and mechanical properties [1], and as substrates for bonding of brackets in clinical situations [2]. The ceramic/composite and composite/tooth structure interfaces have been addressed in clinical studies as factors for ageing processes [4] to determine the clinical long-term success. The bond among orthodontic brackets, composite and ceramic is an important factor for durability and clinical success. The bonding of brackets to the tooth is commonly evaluated by tensile or shear bond strength tests. The shear bond strength test is the most used to evaluate the bonding of brackets to the tooth [2,3]. It is most recommended because it reproduces the stresses caused at the bonding resin/enamel and bonding resin/bracket interfaces during alignment, leveling and sliding movements in the orthodontic treatment. The durability may be influenced due to heavy forces produced by archwire [2], the action of water-saliva storage [6], thermal and mechanical cycling test to simulate the oral conditions prior to mechanical tests [5,7]
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