Abstract
The aim of this in vitro study was to evaluate the effect of different bur types and acid etching protocols on the shear bond strength (SBS) of a resin modified glass ionomer cement (RM-GIC) to primary dentin. Forty-eight clinically sound human primary molars were selected and randomly assigned to four groups (n=12). In G1, the lingual surface of the teeth was cut with a carbide bur until a 2.0-mm-diameter dentin area was exposed, followed by the application of RM-GIC (Vitremer - 3M/ESPE) prepared according to the manufacturer's instructions. The specimens of G2, received the same treatment of G1, however the dentin was conditioned with phosphoric acid. In groups G3 and G4 the same procedures of G1 and G2 were conducted respectively, nevertheless dentin cutting was made with a diamond bur. The specimens were stored in distilled water at 37 degrees C for 24h, and then tested in a universal testing machine. SBS data were submitted to 2-way ANOVA (= 5%) and indicated that SBS values of RM-GIC bonded to primary dentin cut with different burs were not statistically different, but the specimens that were conditioned with phosphoric acid presented SBS values significantly higher that those without conditioning. To observe micromorphologic characteristics of the effects of dentin surface cut by diamond or carbide rotary instruments and conditioners treatment, some specimens were examined by scanning electron microscopy. Smear layer was present in all specimens regardless of the type of rotary instrument used for dentin cutting, and specimens etched with phosphoric acid presented more effective removal of smear layer. It was concluded that SBS of a RM-GIC to primary dentin was affected by the acid conditioning but the bur type had no influence.
Highlights
One of the major challenges in dentistry has been to find an ideal restorative material that has physical properties similar to those of tooth structure, adhesion to dentin and enamel, in addition to resistance to degradation in the oral cavity[27]
There is a possibility of not rejecting the hypothesis of an equal effect between the different cutting rotary instruments used, in addition to the interaction of the instrument with the dentin surface conditioner. (Table 2)
The SEM micrographs revealed the formation of smear layer in all specimens, regardless of the type of rotary instrument used for dentin cutting
Summary
One of the major challenges in dentistry has been to find an ideal restorative material that has physical properties similar to those of tooth structure, adhesion to dentin and enamel, in addition to resistance to degradation in the oral cavity[27]. Manual instruments and a large amount of energy is generated locally, which results in denatured collagen and chemically and physically altered surfaces This procedure produces smear layer, which can influence the adhesion between the tooth structure and dental materials[8]. Polyacrylic acid is one of the most used pre-treatment substances after cavity preparation and promotes an increase in the bond strength between the conventional GICs and dentin[11,13] Many cleaning solutions, such as polyacrylic acid and phosphoric acid in different concentrations have been investigated as a pre-treatment to RM-GICs, in order to improve their adhesion to the dentin surface[9,17,18,21]. The purpose of this in vitro study was to evaluate the shear bond strength of a RM-GIC to primary dentin, after cutting with diamond or carbide rotary instruments with or without phosphoric acid conditioning
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