Abstract
This study to evaluate the effects of different hydrofluoric acid (HF) concentrations and thermal cycling on the shear bond strength (SBS) of brackets to ceramic. Cylinders of ceramic were divided into 10 groups (n=15), according to HF concentrations: 1-1%;2-2.5%;3-5%;4-7.5%;5-10% (storage 24 h); 6-1%;7-2.5%;8-5%;9-7.5%; and, 10-10% (thermal cycling). All cylinders were etched for 60s and received one layer of silane. Metallic brackets were bonded to the cylinders using Transbond-XT, light activated for 40 s, using a LED (Radii Plus) and stored in deionized water at 37o C for 24h. The groups 6 to 10 were submitted to thermal cycling (7,000 cycles - 5o/55oC). SBS was performed in an Instron at crosshead speed of 1.0 mm/min. Data were submitted to two-way ANOVA and Tukey's post-hoc test (α=0.05). The Adhesive Remaining Index (ARI) was evaluated at 40x magnification. The different HF acid concentrations influenced on the SBS of the brackets to ceramic (p<0.05). The thermal cycling decreased the SBS of the brackets to ceramic for all acid concentrations (p<0.05). The ARI showed a predominance of scores 0 for all groups, with an increase in scores 1, 2 and 3 for the group storage for 24 h. In conclusion, the different HF acid concentrations 5.0%, 7.5% and 10% influenced on the SBS of brackets to ceramic. The thermal cycling decreased significantly the SBS of brackets to ceramic.
Highlights
Glass ceramic material has been used in restorative dentistry and may serve as substrates for bonding orthodontic brackets
Different hydrofluoric acid (HF) acid concentrations applied on ceramic surface promoted different results, indicating that the first hypothesis was rejected
Others study showed that fewer microporosities were found with low HF concentration with reduced contact area between ceramic and bonding materials, resulting in little mechanical interlocking and lower bond strength [22]
Summary
Glass ceramic material has been used in restorative dentistry and may serve as substrates for bonding orthodontic brackets. The ideal bonding to ceramic surface is obtained with hydrofluoric acid (HF) etching and silane application [1]. The effect can continue for several days, causing increased tissue damage at a later stage. The severity and damage are directly related to the acid concentration, exposure time, and penetration to the exposed tissue [6]. HF is not applied on soft tissue, less concentrated HF would cause less injury in accidental contact situations [4]. Little is known about the effect of increased or decreased HF concentrations on the bonding ability of the brackets to ceramic. HF acid application is followed by silane coupling agent on the ceramic surface before to applying bonding material and may increase the bonding strength between ceramic and orthodontic brackets
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