Evaluation of the Shear Bond Strength of Methacrylate-based Composite, Resin-modified Glass Ionomer Cement, and Fuji IX Glass Ionomer Cement with Biodentine as a Base

INTRODUCTION

Regeneration is the new treatment strategy in the fields of pediatric endodontics for preservation and protection of the dental pulp.¹ The shortcomings associated with mineral trioxide aggregate (MTA) has led to the development of various new calcium silicate-based materials. One such material is Biodentine (Septodont, France); designed as a dentine substitute for resin composite restorations, pulp capping, and endodontic repair material. It consists of tricalcium silicate, calcium carbonate, zirconium oxide, and a water-based liquid containing calcium chloride as the setting accelerator and water-reducing agent. It has a good sealing ability, high compressive strength, short setting time, greater biocompatibility, bioactivity, and biomineralization properties.2

Resin composites and glass ionomer cements (GICs) are very popular in restorative dentistry because of their esthetic qualities. But they cannot be placed directly over freshly mixed MTA because they can affect its setting, and the etching and rinsing of the unset MTA may dislodge the MTA. However, the setting time of Biodentine is 12 minutes, the resin composites and GICs can be layered over set Biodentine after 12 minutes, which might enable single-visit procedures. Therefore, it is important to identify materials that are compatible in relation to the interface between the two different materials.3

Any material which is used as a base or cavity liners, are described as materials that are used as a layer to seal the dentin floor from the invasion of bacteria and irritants as well as for thermal insulation. These materials should possess an adequate seal, prevent leakage, and remain intact under dislodging forces like masticatory pressure and also be adhesive to the dentine.⁴ But the strength with which restorative materials bond to Biodentine is unclear. The longevity of adhesive restorations depends on the bond strength between the restoration and the base. Therefore, it is important to know the bond strength of various available restorative materials with Biodentine as a substitute and repair material.⁵ Thus, the aim of the study was to evaluate the shear bond strength (SBS) of methacrylate-based (MB) composite, resin-modified GIC (RMGIC), and Fuji IX GIC when used with Biodentine.

MATERIALS AND METHODS⁵

This in vitro study was conducted in the Department of Pedodontics and Preventive Dentistry, College of Dental Sciences, Davangere, Karnataka, India. Following were the materials used in the study: Biodentine (Septodont, France), GIC (GC Fuji IX, GC, Tokyo, Japan), RMGIC (Fuji type IX), and MB composite resin.

RESULTS

Based on the data collected, mean and standard deviation of bond strengths of three groups in the study were as follows. Highest bond strength of 1.495 ± 0.05 MPa was observed in group I (i.e., MB composite), followed by group II with 1.139 ± 0.02 MPa (i.e., RMGIC type II), and the lowest bond strength of 0.80 ± 0.05 MPa observed in group III (Fuji IX GIC) (Table 1).

Observation showed that the significant value (p value) of F-statistic is *0.000 < 0.05 (i.e., at 5% level of significance/95% confidence level of the test). This implies that the three groups under study statistically differ significantly in their respective bond strengths.

Furthermore, the difference between groups w.r.t. bond strength taken two groups at a time was performed using Tukey’s post hoc test. The outcomes are shown in Table 2. Here, also the significant value (p value) of F-statistic is 0.000 < 0.05 in each set of comparison for mean bond strength between two groups under study. Thus, the three groups under consideration are three distinct groups with significantly different bond strengths with highest bond strength being observed in group I, i.e., Biodentine samples with MB composite (Table 2).

DISCUSSION

In restorative treatments involving the exposure of pulp, since clinical findings and histological events do not often coincide, prediction of severity and type of the pulpal damage are almost impossible. Thus, the clinician should make every effort to protect the pulp vitality. Treatment modalities like pulp capping aim to preserve pulp vitality by elimination of caries (bacteria) and using biocompatible products to provide a strong barrier against the bacterial microleakage.¹ Calcium hydroxide is the popular pulp-capping agent. However, other biocompatible materials, such as mineral trioxide aggregate, calcium-enriched cement, and Biodentine, have gained popularity recently.⁶ After pulp capping, the tooth requires a proper final restoration and most often composite is the first choice especially in the esthetic zone. Whereas, cases in which lack enough enamel preparation, RMGIC can be a good alternative restorative material. In such restorations, the bond between pulp-capping agents and composite resin or RMGIC plays a crucial role in the sealing provided by the restoration and finally leads to the success of the treatment.⁷ Therefore, the bond strengths of composite, RMGIC, and GIC to Biodentine surface were evaluated in the current study.

Different mechanical tests have been used to assess the bonding performance of restorative materials. Although with its drawbacks, shear testing has been widely used to evaluate the bonding ability of adhesive materials to dental structure. This method is easier to perform than the microtensile method. Especially in regards to GICs, which present low bond strength, other tests may be difficult to apply.8

There was a significant difference between bond strengths of the composite resin, RMGIC, and GIC groups. According to the results, the bond strength of composite to Biodentine was higher followed by RMGIC and least with GIC. The higher bond strength to composite may be because the 37% phosphoric acid removes the smear layer and leading to a clean surface which in turn increases the micromechanical bond, hence high bond strength.9

In RMGIC samples, no significant difference was observed among the SBSs of substrate. This may be because the bond between RMGIC and the substrate must be mostly chemical and micromechanical having less effect. This hypothesis is supported by a study performed by Ajami et al.,³ where the type of the failure seen is mostly of the adhesive type. Thus, we can conclude that the bond strength between RMGIC and substrate was lower than the cohesive strength. However, the current study did not attempt to check the cohesive strength of the materials independently, and therefore, further studies on the difference of cohesive strength are recommended.3

It was reported that etch-and-rinse adhesives can increase the SBS of composites to MTA. Odabaş et al. evaluated the SBS of composite to Biodentine after two time intervals (i.e., 12 minutes and 24 hours) and other results showed that the SBS value increased for the 24-hour period.¹⁰ Bachoo et al. reported that the initial setting reaction of Biodentine takes approximately 12 minutes after mixing the powder and the liquid. However, it takes up to 2 weeks to achieve complete maturation of Biodentine.¹¹ For this reason, in the current study, Biodentine specimens were stored for 24 hours at 100% humidity to allow complete hardening of the materials.

Another contributing factor for the low bond strength value is lack of pressure during placement of the self-adhesive resin cement. Application of pressure during cement placement is necessary to avoid bubbles and open spaces on the interface, and may affect the longevity of the self-adhesive resin cement.5

Not much information is available in the literature about the bond strength of Biodentine to restorative materials. Ajami et al. evaluated the SBS of RMGIC to calcium enriched mixture (CEM) was 2.69 MPa.³ Altunsoy et al. evaluated the SBS of X-tra base with Futurabond DC to MTA was 1.8 MPa.¹² In the current study, SBS of MB composite to Biodentine was 1.49 MPa, which is much lower than the value of previous studies.

Similar results to our current study were observed by Chitnis et al., who compared the bond strength between GIC, polyacid modified composite resin (PMCR), and resin-based composite and found that resin-based composite had significantly higher shear bond values than the other materials.¹³ In contrast to our current study, Prabhakar et al. observed that RMGIC exhibited higher bond values when compared to PMCR and resin-based composite.¹⁴ While Almuammar et al. observed that PMCR had higher shear bond than GIC and RMGIC, but less than resin-based composites.15

In the previous studies, approximately half of the specimens exhibited adhesive failure, and the remaining half of the specimens exhibited cohesive failure in the pulp-capping materials.¹⁶ However, in the current study, specimens showed cohesive or mixed failure and the failures occurred within the layer of Biodentine and adhesive failure did not occur. This finding does not necessarily reflect the true interfacial bond strength between the adhesive resin and the pulp-capping material. However, it can be said that calcium silicate-based materials used in the current study may present higher SBS to composite, RMGIC, and GIC if cohesive failure would not occur. It is reported that the bond is acceptable when fracture occurs inside each material rather than in the bonded interface (i.e., cohesive rather than adhesive).

Another important point to be noted is that the materials were not tested immediately after their initial setting, which is the real clinical scenario. Here, the samples were stored without any load up to 24 hours before loading, which may have influenced the results.¹² It should also to be kept in mind that the current study was performed using only one setting time.

Thus, the drawbacks of this study on the basis of the methodology are that we have used only one setting time for the SBS evaluation, and the adhesive systems have different setting times, and we did not consider alternative bonding systems, and the study was designed as an in vitro evaluation. Future studies are needed to investigate the effects of different bonding protocols on the surface and structural characteristics of Biodentine to provide an insight into the adhesive mechanisms of the different bonding systems and Biodentine.

CONCLUSION

Within the limitations of the current study, it was concluded that the bonding of composite to Biodentine appears superior when compared to RMGIC and type IX GIC. However, only initial setting time was taken in the study and further studies are recommended before considering for clinical use.

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