Structural reliability and bonding performance of resin luting agents to dentin and enamel

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Abstract

This study evaluated the bonding performance and structural reliability of indirect resin composite restorations luted to dentin and enamel. Four resin luting agents were tested in the study, namely three total-etch materials (Allcem; Allcem Core; and RelyX ARC) and one self-adhesive material (RelyX U200). The materials were characterized with degree of conversion (DC) and pH analyses, and used to lute resin composite restorations to dentin or enamel (n = 6). The restorations were prepared for microtensile bond strength (μTBS) testing (DL500). Data were analyzed with ANOVA or Kruskal-Wallis and Tukey/SNK (α = 0.05). Weibull analysis was used to verify the structural reliability and characteristic strength of dental bonds. While RelyX ARC exhibited greater DC, RelyX U200 was the most acidic material of the study. Allcem and RelyX U200 demonstrated greater and lower μTBS, respectively, at both dentin and enamel. Comparing μTBS of dentin and enamel, RelyX ARC and RelyX U200 produced higher bonds in dentin. RelyX U200 showed ~100% of adhesive failures, differing from other groups. Structural reliability was higher for Allcem Core in dentin and for RelyX U200 in enamel; the characteristic strength was higher for Allcem and lower for RelyX U200. Conventional resin luting agents performed better than the self-adhesive material, at both dentin and enamel. Among the conventional materials, Allcem demonstrated an overall greater bonding ability and lower probability to failure. DC and pH of resin luting agents did not influence on their bonding performance.

Introduction

Dental bonding of indirect restorative materials or intracanal post systems using resin luting agents can be achieved by following two distinct adhesive strategies: conventional/total-etch or self-adhesive [1]. While the former require the application of an acidic substance followed by adhesive agents prior to the bonding procedure in order to allow proper demineralization and resin infiltration to the substrate; the latter eliminates the pre-use of any adhesive system, since the luting agent itself possesses the ability to demineralize and infiltrate dentin and enamel with resin monomers [2]. Despite their adequate clinical applicability, the current literature still diverges on which adhesion strategy would perform better when bonding indirect composite restorations [3,4], so that new studies on this topic are still necessary, attempting to compare the bonding performance of different materials to both dentin and enamel.

Bond strength testing has been broadly considered for verifying the adhesion/retention of restorative materials to the tooth. However, these tests usually lack in standardization, leading to great variation data [[5], [6], [7]]. In light of improving the reliability and interpretation of bond strength tests, studies have been applying Weibull statistics as an additional measure of strength data, offering a strong theoretical basis of understanding the structural reliability and strength properties of fractured samples, especially in dental applications [8]. To date, there are only few studies focusing on the evaluation of the structural reliability of dental bonds obtained with the application of resin luting agents.

Hence, the present study aimed to evaluate the bonding performance and structural reliability of resin composite indirect restorations luted to dentin or enamel using distinct resin luting agents. The hypothesis of the study was that conventional resin luting agents would present higher bonding performance than self-adhesive materials, regardless of the dental substrate.

Section snippets

Materials and methods

This study evaluated two variable factors: dental substrate (dentin or enamel) and resin luting agent (total-etch or self-adhesive). Four materials were investigated: three total-etch (Allcem; Allcem Core; and RelyX ARC) and one self-adhesive (RelyX U200). Information on their manufacturer, chemical composition, inorganic filler fraction, and bonding protocol is given in Table 1. All materials were applied following the manufacturer's instructions.

Results

DC was higher (p ≤ 0.007) for RelyX ARC (78.4% ± 1.9) than Allcem Core (64.9% ± 1.7), Allcem (56.6% ± 3.3), and RelyX U200 (56.4% ± 5.6), which have not differed between each other (p ≥ 0.067). Concerning pH, RelyX U200 showed the lowest value (2.2 ± 0.1), which was lower than the other materials (p < 0.001). Allcem Core (4.9 ± 0.3) and RelyX ARC (4.8 ± 0.4) showed similar pH values (p = 0.880) and higher than Allcem (3.8 ± 0.1) (p ≤ 0.003).

Fig. 1A shows the bond strength results of the study.

Discussion

In this study, three conventional (total-etch) luting agents were tested (Allcem, Allcem Core, and RelyX ARC), opposed by only one self-adhesive material (RelyX U200). It has been hypothesized that the former would present greater bonding performance than the latter, which was indeed accepted. While RelyX U200 presented nearly 46–57% less adhesion ability to dentin as compared to conventional materials, the reduction of adhesiveness was even greater in enamel (47–64%). One may consider that the

Conclusions

In this in vitro study, total-etch resin luting agents performed better than the self-adhesive material, at both dentin and enamel, with Allcem resulting in an overall greater bonding ability and lower probability to failure. Degree of conversion and pH of the luting agent did not seem to influence on the bonding performance of resin luting agents.

Acknowledgments

This study was supported in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) Finance Code 001; under grant number: 88882.346901/2019-01.

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