| Summary: | Nojoud Alshehri, Mohammed Bin-Shuwaish Restorative Dental Sciences Department, College of Dentistry, King Saud University, Riyadh, Kingdom of Saudi ArabiaCorrespondence: Nojoud AlshehriCollege of Dentistry, King Saud University, Kingdom of Saudi ArabiaTel +966 11 489 4865Email alshehri.nojoud@gmail.comPurpose: 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
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