Comparative evaluation of shear bond strength of a bioactive material to composite resin using three different universal bonding agents: An in vitro study.

Background: Calcium silicate-based cements or bioceramics have revolutionized and simplified pulp-capping procedures due to its versatility and accessibility. Aim: This study aimed to assess the shear bond strength (SBS) of a bioceramic material to composite resin at two aging periods and with three universal adhesives. Materials and
Methods: Forty-eight samples of Biodentine with a height of 2 mm and internal diameter of 4 mm were prepared. After 12 min of mixing, 24 samples were randomly selected and divided into four subgroups: Group I: Single Bond Universal, Group II: Palfique Universal Bond, Group III: G-Premio BOND, and Group IV: Control. Composite resin was restored over Biodentine after the application of universal adhesives using a cylindrical plastic mold of 2 mm height and 2 mm internal diameter. This process was repeated 24 h after mixing on the remaining 24 samples of Biodentine. The universal testing machine was used to measure the SBS of the fractured specimens, followed by stereomicroscopic evaluation. One-way ANOVA test and Bonferroni post hoc test were used to statistically analyze the data.
Results: Highest SBS values were observed in Group III at 12 min and 24 h of the setting of Biodentine. Conclusions: Compared to the 12-min group, SBS was higher at 24 h. Group III exhibited higher bond strength than other subgroups. Copyright:

INTRODUCTION

The goal of restorative treatment is to preserve and protect healthy dental tissues by constraining microbial invasion.[1] A conservative and minimally invasive approach is possible due to the advent of bioactive materials, which help maintain pulpal vitality and stimulate reparative dentin formation.[2] These materials should have specific characteristics such as radiopacity, insolubility, dimensional stability, biocompatibility, and adequate adhesive ability to both the dentin and restorative materials.[3]

Although calcium hydroxide (Ca[OH] 2) has been regarded as the gold standard, high solubility and insufficient adherence to dentin have reduced its usage as a liner.[4] Nowadays, it is being replaced by new generations of materials with more predictable clinical outcomes.

Mineral trioxide aggregate (MTA) has been preferred as a pulp space barrier due to its biocompatibility and regenerative physiognomies.[5] MTA has significant drawbacks including a long setting time, complex handling characteristics, and potential for discoloration.[6]

Biodentine, a calcium silicate-based cement, has shown to overcome the inadequacies of MTA. It is a bioactive dentin substitute, which offers greater viscosity, ease of handling, and a reduced setting time.[7]

Studies have shown that Biodentine can be adhesively bonded after the initial set of 12 min. It can also be placed as a bulk restorative material in pulp-capping procedures and layered with a definitive restoration within 6 months. A single-sitting procedure is always preferred since the patient may not return for a second appointment. Self-etch adhesives are attractive to practitioners since they can be used without the rinse phase, have reduced application time and technique sensitivity.[8]

Hence, this in vitro study was carried out to assess the shear bond strength (SBS) of Biodentine to composite resin at two aging periods and with three different universal bonding agents.

MATERIALS AND METHODS

In this study, universal adhesive systems, Single Bond Universal (3M™ ESPE™, USA), Palfique Universal Bond (Tokuyama), and G-Premio BOND (GC Corporation, Japan) were tested and used as recommended by the manufacturers [Figure 1a].

Figure 1

Photographs of methods: (a) Materials used in the study. (b) A sample loaded on a universal testing machine. (c) A sample after fracture

Specimen preparation

Forty-eight acrylic blocks containing a central hole of 2 mm height and 4 mm diameter were prepared. These holes were filled with Biodentine™ (Septodont, Saint-Maur-des-Fossés, France), according to manufacturer instructions, and smooth surfaces were obtained with amalgam condenser and ball burnisher. The specimens were then stored at 37°C with 100% humidity for 12-min and 24-h to encourage setting.

After the allotted time had elapsed, 24 samples were chosen randomly and distributed into four groups of six specimens each:

Group I: Single Bond Universal (3M)

Group II: Palfique Universal Bond (Tokuyama)

Group III: G-Premio BOND (GC)

Group IV: Control (No adhesive).

In Groups II, III, and I, the corresponding adhesive agent was applied over Biodentine, whereas in Group IV, no adhesive system was applied.

Composite resin, Filtek™ Z350 XT (3M™ ESPE™), was restored using a cylindrical plastic matrix with a height of 2 mm and internal diameter of 2 mm and light-cured.

The same steps were repeated for the remaining 24 samples after 24 h of mixing.

Shear bond strength measurement

All specimens were subjected to shear loading in a universal testing machine (Tecsol-TSI-BDS) by securing them on a jig placed on the platen of the testing machine [Figure 1b]. They were sheared with a rectangular-shaped plunger at a crosshead speed of 1.0 mm/min using a 2kN load cell [Figure 1c]. Shear bond strength (SBS) in megapascal (MPa) was gauged by dividing the highest load at failure by the specimen surface area.

Fracture analysis

The debonded fracture test specimens were examined at ×25 magnification under a stereomicroscope (Stemi DV4: Carl Zeiss, Gottingen, Germany) to characterize fracture mode.

The fracture modes were classified as follows:

Adhesive failure – the failure was at the interface between the restorative material and Biodentine® (bonding area)

Cohesive failure – the failure was a fracture within the Biodentine® or restorative material

Mixed failure – the failure was a combination of interfacial separation and partial cohesive loss of the Biodentine® and, or restorative material [Figure 2].

Figure 2

Images of fractured samples showing: (a) Adhesive failure; (b) Superficial cohesive failure in biodentine; (c) Mixed failure and stereomicroscopic images of the failure mode; (d) Adhesive failure; (e) Superficial cohesive failure in Biodentine; and (f) Mixed failure

Statistical analysis

The collected and tabulated data were subjected to statistical analysis using the Statistical Package for the Social Sciences (SPSS) software version 23 (IBM, Chicago, US). To detect dissimilarities in bond strength among the experimental groups, one-way analysis of variance was used.

RESULTS

Mean shear bond values and the standard deviations are given in Table 1. It was observed that between the two-time intervals, bond strength after 24-h was considerably greater than 12-min. In addition, the bond strength of subgroup III was notably more than other groups at both time intervals.

Table 1

Summary of shear bond strength in two main groups (24 h and 12 min) and four subgroups (1, 2, 3, and 4)

Bonding agent	n	Shear bond strength in MPa (mean±SD)
		12 min	24 h
Single bond universal	6	5.390±0.340	9.860±1.585
Palfique universal bond	6	3.378±1.442	12.111±3.053
G-Premio BOND	6	11.305±0.980	21.640±2.336
Control	6	1.141±0.442	1.560±0.984

SD: Standard deviation

Fracture failure

In the stereomicroscope analysis, superficial cohesive failure was observed in Biodentine in the 12-min groups and deeper cohesive failure was observed in the 24-h groups [Table 2]. None of the specimens failed cohesively within the composite resin.

Table 2

Fracture modes of the specimens after shear bond strength test

	Total	Single bond universal		Palfique universal bond		G-Premio BOND		Control
		12 min	24 h	12 min	24 h	12 min	24 h	12 min	24 h
Adhesive	18	2		2		2		6	6
Mixed	10	2			2	4	2
Cohesive in biodentine	20	2	6	4	4		4
Cohesive in composite resin	0

DISCUSSION

One of the main goals of restorative dentistry is to preserve pulp vitality and pulp-capping procedures are critical to clinical success. For the efficacious outcome of the treatment, a hermetic seal preventing bacterial infiltration is a prerequisite. The bond between the restorative material, tooth, and the pulp-capping agent is crucial to avoid radiographic and clinical failures.[9] Such a bond between the restorations also helps to spread the occlusal forces evenly. Adhesion studies revealed that minimum bond strength of 17–20 MPa to enamel and dentine is sufficient to resist shrinkage and reduce marginal gaps.[10]

Biodentine is the first all-in-one bioactive material popularly used for damaged dentin replacement. During its setting, the compressive strength increases to 100 MPa in the 1sth, 200 MPa after 24 h and progresses over time reaching 300 MPa after 1 month, which is similar to natural dentine, which is around 297 MPa.[11]

Biodentine shows low physical characteristics ensuing initial mixing. Studies have shown that the shrinkage stress at the surface of matured Biodentine during polymerization of different bonding agents was around 2.89 to 3.49 MPa. This stress may be the reason for high cohesive disintegration and reduced bond strength in the 12-min groups. When composite resin is compacted over a thin layer of freshly mixed Biodentine, it leads to fractures and cracks within the material. Therefore, a better option is to cover Biodentine with an interim restoration and permanent restore in the following visit.

The longevity of restoration depends on the quality of adhesive bond between Biodentine and composite resin. It remains indistinct as to which adhesive agent achieves better bonding with Biodentine. Previous studies emphasize that etch and rinse adhesives perform better than self-etch adhesives. Research has also shown that self-etch adhesives provide higher bond strength or that the bonding strategy is irrelevant.[12]

To simplify the application process and reduce technical errors, one-step self-etch adhesives have been developed. Studies have shown that the acidic monomers used in self-etch adhesives play an important role in bonding to enamel and dentin.[13] The differences in pH of the adhesives used in this study led to varying degree of biomaterial dissolution since pH value is known to strongly affect the solubility of the smear layer and the depth of demineralization of underlying dentin. Previous studies have stated that micromechanical retention and bond strength increases with increase in surface porosity of tricalcium silicate-based cements.[14]

Previous studies have found that the functional monomer, 10-methacryloyloxydecyl dihydrogen phosphate, which is present in some SE adhesives, binds to calcium in tooth structure and promoting chemical adhesion in addition to the micromechanical attachments. The bifunctional silane molecule bonds chemically to silica-containing constituents and has the methacrylate functionality that allows chemical reactions with the adhesive substrate. Silanes also enhance the wetting ability of the adhesive system and promote adhesion.[15]

With regard to fracture modes, a bond is considered acceptable when fracture occurs within the object rather than at the adhesive interface. The main type of failure observed in this study was cohesive failure in Biodentine, as was seen in previous studies.[16] Cohesive failure occurs when the bond strength is higher than the internal strength of the substrate.[17]

CONCLUSIONS

Further research is needed to better understand the adherence of Biodentine to various adhesive systems. However, it is clear that sufficient bond strength is attained without an acid-etching procedure, as universal adhesives applied on Biodentine indicate effective bond values. This makes it easier to use in noncompliant patients with a reduced number of procedural steps and the risk of saliva contamination.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.