The Effects of Amalgam Contamination and Different Surface Modifications on Dentin Shear Bond Strength When Using Different Adhesive Protocols

Abstract

Purpose: To evaluate the effect of amalgam contamination, different surface treatments, and adhesive protocols on dentin shear bond strength (SBS) to bulk-fill composite resin material.

Materials and methods: Eighty teeth were fixed in molds, and the dentin was exposed and then polished. Sixty teeth were restored by amalgam and thermocycled to 10,000 cycles (5°C and 55°C, 30-second dwell time). The rest were restored with composite materials without amalgam predecessor. The samples were divided into G1 (with dentin pretreatment with 2% chlorhexidine gluconate), G2 (0.5 mm of dentin was removed), G3 (no surface modification), and G4 (samples were restored with bulk-fill composite). The bonded specimens were subdivided based on the adhesive protocol of the universal adhesive system used into etch-and-rinse and self-etch groups. Acid etching was done using 32% phosphoric acid. Composite resin was used for build-up using mold and glass. Specimens were cured and left for 24 h in distilled water at room temperature for polymerization reaction, underwent thermocycling for 5000 cycles, and were subjected to knife-edge shear bond testing. Descriptive statistics, independent t-tests, and one-way analysis of variance followed by pairwise comparisons were used to analyze the results.

Results: The highest mean SBS values were found in the control group where acid etching was used (24.46±2.24 MPa), followed by self-etching in the same group (21.92±2.54 MPa). Lower SBS values were associated with the amalgam-contaminated group. The lowest values were found in the dentin refreshment group when the self-etching mode was used (13.59±1.73 MPa). Chlorhexidine treatment improved the mean SBS value compared with the no treatment or dentin refreshment groups for both adhesive protocols.

Conclusion: Amalgam contamination may affect SBS values. Acid etching improved SBS for non-contaminated dentin. Chlorhexidine improved SBS for amalgam-contaminated dentin as a surface treatment but had no significant effect.

Keywords: chlorhexidine; dentin refreshment; resin-based composite; universal adhesive system.

Figure 1

Shear bond strength (MPa) in all tested groups.

Figure 2

Distribution of adhesive failure types among experimental groups.

Figure 3

A photograph of the different types of failure. (A) Adhesive failure, (B) cohesive in composite, (C) cohesive in dentin, and (D) mixed.

Figure 4

A photomicrograph of two different specimens with different magnifications that are bonded using the etch-and-rinse protocol in which the formation abundant resin tags are clear.

Figure 5

A photomicrograph of two different specimens with different magnifications that are bonded using the self-etch adhesive protocol showing demineralized dentin with no to little resin tags.