Effect of two different deproteinizing agents on microtensile bond strength between resin composite and deep dentin using two restorative protocols : An in-vitro study /

Abstract

Bonding to deep dentin is considered a challenging procedure due to few intertubular dentin, increased number of dental tubules and difficult moisture control. One of the difficulties in achieving optimal hybridization in etch and rinse adhesive systems is the incomplete penetration of adhesive system into demineralized dentin leaving the collagen fibrils susceptible to enzymatic degradation. Deproteinization is a suggested method introduced to dissolve the organic smear layer and increase the mineral/organic ratio aiming to improve resin monomer infiltration and increase bond strength with dentin. Two deproteinizing agents, sodium hypochlorite (NaOCl) and bromelain enzyme showed the ability to remove collagen fibers from acid etched dentin. However, sodium hypochlorite showed several side effects such as the formation of a fragile zone, intolerable taste, unfavourable odour and cytotoxicity. While bromelain enzyme showed a deproteinizing effect without the side effects associated with sodium hypochlorite. The study used two different bulk-fill resin composite materials, a packable nanohybrid bulk-fill resin composite and a bulk fill flowable resin composite as a liner, to investigate their microtensile bond strength to deproteinized deep dentin. A total of 45 sound extracted human molars were selected for this study. The selected teeth were equally divided into one control group and four experimental groups (n=9). Group 1 (control): Acid etching + Bonding agent + Packable nanohybrid bulk-fill RC, Group 2: Acid etching + 10% NaOCl + Bonding agent + Packable nanohybrid bulk-fill RC, Group 3: Acid etching + 10% NaOCl + Bonding agent + bulk-fill flowable RC + Packable nanohybrid bulk-fill RC, Group 4: Acid etching + 10% bromelain enzyme + Bonding agent + Packable nanohybrid bulk-fill RC and Group 5: Acid etching + 10% bromelain enzyme + Bonding agent + bulk-fill flowable RC + Packable nanohybrid bulk-fill RC. The selected molars were embedded in self-cured acrylic resin blocks, occlusal surface was flattened to expose deep dentin, and resin composite was applied according to their corresponding groups. Teeth were sectioned to obtain marked central beams with a surface area (0.9 mmx 0.9 mm±0.1 mm for both dimensions and a height of 5.5±1. Marked beams were stored for 24 hours at 37oC in distilled water then subjected to microtensile bond strength testing using a universal testing machine. Their failure modes were also examined. The results showed that there was a statistically significant difference between the microtensile bond strength values of different groups (P-value <0.001, Effect size = 0.704). Pair-wise comparisons between groups revealed that Group 1 recorded the highest microtensile bond strength with a non-statistically significant difference from Group 4, but statistically significantly higher than other groups. Group 5 showed the least microtensile bond strength value of all tested groups. Failure mode examination showed different types of failure between the tested groups. The main failure mode in Group 1 and 4 was cohesive failure while Group 2, 3 and 5 adhesive failure mode predominated.