Polymerization behavior within adhesive layer of one- and two-step self-etch adhesives: A micro-Raman spectroscopic study

Polymerization shrinkage of light-cured conventional and bulk-fill composites -The effect of cavity depth and post-curing

Volumetric shrinkage (VS) of conventional, bulk-fill, and core build-up resin-based composites (RBCs) of various thickness (1-5 mm) was measured using the modified bonded-disk method with confocal laser scanning microscopy. Additionally, the bottom-to-top ratio of Vickers hardness (%VH) was measured. Conventional RBCs exhibited significantly higher VS than bulk-fill and core build-up RBCs (p<0.05). As specimen thickness increased, VS relative to volume (%VS) and difference in VS at each depth (VS_depth) decreased. For conventional RBCs, there was a significant drop in VS_depth between 1 mm and 2 mm (p<0.05), and another drop was observed between 3 mm and 4 mm (p<0.05) where %VH decreased below 90%. For bulk-fill and core build-up RBCs, VS_depth decreased significantly between 2 mm and 3 mm (p<0.05), but %VH exceeded 90% even in 5 mm deep cavities. These results indicated that post-curing contributed to lower shrinkage in deeper layers, and that conventional RBCs were not adequately polymerized at the depth of over 3 mm.

Sodium p-Toluenesulfinate Enhances the Bonding Durability of Universal Adhesives on Deproteinized Eroded Dentin

The effects of deproteinization using sodium hypochlorite (NaOCl) and the subsequent application of an antioxidant (sodium p-toluenesulfinate, STS) onto the bonding durability of universal adhesives on eroded dentin were investigated. Untreated sound dentin served as the control, whereas eroded dentin, which had been prepared by pH-cycling in 1% citric acid and a remineralization solution, was either untreated, deproteinized with a 10% NaOCl gel or deproteinized with the 10% NaOCl gel and subsequently treated with an STS-containing agent. The dentin surfaces were bonded using a universal adhesive (Clearfil Universal Bond Quick, Scotchbond Universal or G-Premio Bond), and the micro-tensile bond strength (µTBS) test was performed after 24 h or 10,000 thermal cycles. The µTBS data were statistically analyzed using a three-way ANOVA and Tukey’s HSD post hoc tests. The lowest µTBS was measured on untreated eroded dentin (p < 0.001). Deproteinization of eroded dentin resulted in µTBS similar to untreated sound dentin (p > 0.05), but the highest µTBS was obtained if deproteinization was followed by the application of STS. Thermocycling significantly decreased µTBS in all groups (p < 0.001), except for STS-treated deproteinized eroded dentin (p > 0.05). This indicated that deproteinization, followed by the application of STS, could enhance the bonding durability of universal adhesives on eroded dentin.

Effect of anaerobic cure of self-etch adhesive on degree of conversion and shear bond strength

OBJECTIVE

The main aim was to evaluate the effect of postponing the curing of the adhesive layer until the first layer of composite resin is applied-hereby oxygen-inhibited layer (OIL) formation and its detrimental effect on the degree of conversion (DC) of self-etch adhesives should be prevented. For this purpose, the degree of conversion and shear bond strength of four current market self-etch adhesives were evaluated, assessing the effect of curing the adhesives anaerobically and then under two different thicknesses of composite resin, and compare this to the samples cured alone and in air.

MATERIALS AND METHODS

The degrees of conversion were obtained by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, after the samples were prepared on a glass slide. The samples were either light-cured in air or anaerobically under a clear matrix strip alone, under 2 mm of cured composite resin or under 4 mm of cured composite resin. To determine the shear bond strength (SBS), extracted molars were halved and set in acrylic. Prefabricated cured cylinders of composite resin (TPH 3, 2.4 mm in diameter) of two different lengths are placed over the adhesives under the following conditions: light-cured conventionally (2-mm-long cylinder) and light-cured anaerobically under the uncured end of the piece of composite resin (using both 2- and 4-mm-long cylinders as separate treatments). After another incubation for 24 h at 37 °C, the samples were subjected to shearing using the Bisco Shear Bond Strength Tester.

RESULTS

The degree of conversion of the one-step self-etch adhesives was not statistically different when cured anaerobically under a clear matrix strip or cured anaerobically under 2 mm of composite resin. These results were greater than those cured under 4 mm. Shear bond strength between samples cured in air and anaerobically were similar under 2 mm of composite resin tubes, while those cured anaerobically under 4 mm of resin showed lower shear bond strength.

CONCLUSION

When cured anaerobically, one-step self-etch adhesives show a greater degree of conversion and no significant difference in degree of conversion and shear bond strength when compared to those cured in air under the same thickness of composite resin.

CLINICAL RELEVANCE

The results obtained from DC and SBS analysis show promise in placing the uncured adhesive under the composite resin and curing both the adhesive and restoration material simultaneously.

Analysis of micro-shear bond strength of self-etch adhesive systems with dentine: An in vitro study

BACKGROUND

Success or failure of a composite restoration largely depends on its bonding to enamel/dentine. Several better adhesive systems have been developed during the last few years due to rapid advancement in the technology. Recent self-etched adhesives have fewer clinical steps and are less technique sensitive.

METHODS

Ninety extracted human permanent molars were collected, grounded and finished to prepare flat dentine-bonding surfaces on their occlusal surface. All specimens were divided into three groups (n = 30) on the basis of three adhesive systems Adper Easy Bond (AE), Beautibond (BB) and Xeno IV (XE). These adhesive systems were applied on prepared mid-dentine-bonding surface. A restorative resin was added with the help of a transparent tube of 2 mm height and 1.7 mm internal diameter and cured. Fifteen specimens in each group were loaded to failure in an Instron Universal Testing Machine after storage for 24 h at 37 °C to check micro-shear bond strength. Another fifteen specimens from each group were thermocycled 500 times at 5 °C and 55 °C with dwell time of 1 min in each bath followed by loading to failure. The data obtained was analyzed with SPSS version 21 at significance level of <05.

RESULTS

After 24 h, micro-shear bond strength of BB was higher (26.04 MPa) than XE (23.69 MPa) and AE (21.50 MPa). After thermocycling, micro-shear bond strength decreased significantly in BB (P = .001) and XE (P = .03).

CONCLUSION

The micro-shear bond strength of BB was highest among three groups, which decreased after thermocycling.