Shear Bond Strength of an Endodontic Tricalcium Silicate-Based Putty to Different Adhesive Systems at Different Time Intervals

Majedah Al-Homaidhi^*

^*Correspondence: Majedah Al-Homaidhi, Department of Pediatric Dentistry and Orthodontics, College of Dentistry, King saud university, Saudi Arabia, Email:

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Introduction

Calcium silicate-based cements (CSCs) are a group of biomaterials that have been introduced into the market as an alternative to calcium hydroxide [1]. They are currently the material of choice for regeneration and repair treatments in endodontics due to their biocompatibility, bioactivity, sealing properties, and ability to induce reparative hard tissue formation [2].

The original tricalcium silicate-based product, known as mineral trioxide aggregate (MTA), was introduced to dentistry in 1993 by Torbinejad, et al. [3]. However, MTA has different limitations, such as discoloration of tooth structure, difficult handling, premixing, and long working time, which might require several appointments to complete treatment [4,5]. Therefore, several CSCs were introduced into the market, such as premixed tricalcium silicate-based putties, which were introduced in 2010 to overcome these limitations of MTA [6,7].

Premixed tricalcium silicate-based putties have the advantages of being easy to handle, premixed, hydrophilic, and offer immediate placement of the final restoration [8].

With CSCs a leakage-free restoration should be used to ensure a successful treatment [9,10]. Therefore, several studies have been conducted to evaluate the bonding of CSCs with different restorative materials (composite, glass ionomer, and amalgam) [9-12].

Kayahan et al. [11] evaluated the effect of acid etching on the compressive strength and surface microhardness of ProRoot MTA and recommended delaying the final restoration when acid etching is required for at least 4 days after mixing the MTA. In addition, the use of an intermediate material or liner, such as flowable composite or resin-modified glass ionomer, has also been suggested to avoid condensation forces [12].

A new composite known as self-adhering flowable composite (SAFC) has been introduced to the market by combining an all-in-one bonding system and flowable composite resin [13]. It has the advantage of fewer application steps where etching and bonding are eliminated to simplify the adhesive procedure [13]. Oz et al. [14] compared the long-term clinical performance of SAFC and flowable composite in Class I cavity restoration and concluded that SAFC exhibited a clinical performance like the conventional flowable applied with an etch-andrinse adhesive.

NeoPUTTY (NuSmile, Houston, TX, USA) is a new fastsetting pre-mixed hydraulic calcium silicate putty that has been introduced to the market. The adhesion of restorative materials to NeoPUTTY has not been extensively studied. To date, no published papers have evaluated the shear bond strength of NeoPUTTY with SAFC or RMGIC. Therefore, this in vitro study aimed to test the shear bond strength of two different restorative materials, SAFC (Vertise™ Flow, Kerr, Orange, CA, USA) and RMGIC (GC Fuji II LC®, GC, Japan), with NeoPUTTY and to assess whether the proper time to perform the restorative procedure is immediately or 24 h after the placement of NeoPUTTY.

Materials and Methods

This study was conducted after obtaining approval from the College of Dentistry Research Centre, Deanship of Scientific Research, King Saud University (No. FR-0604). A total of 80 polytetrafluoroethylene (Teflon) molds were prepared with a central hole measuring 4 mm in diameter and 2 mm in depth, fully filled with NeoPUTTY (NeoPUTTYTM, NuSmile, Houston, TX, USA), and the surface was smoothed using a spatula.

The samples were then randomly assigned to two groups based on the restorative material used: self-adhering flowable composite (SAFC) (Vertise™ Flow, Kerr, Orange, CA, USA) or resin-modified glass ionomer cement (RMGIC) (GC Fuji II LC®, GC, Japan). The samples in each group were then subdivided into two sub-groups (n=20) based on the setting procedure duration: immediately and after 24 h as follows:

• Group 1: SAFC, immediately.

• Group 2: RMGIC, immediately.

• Group 3: SAFC, after 24 h.

• Group 4: RMGIC, after 24 h.

In groups 1 and 2, the bonding procedures were carried out immediately after placing the Neo PUTTY, while groups 3 and 4 were incubated at 37°C and 100% humidity for 24 h after placing them vertically in a plastic container with wet gauze and secured tightly with a lid.

For the bonding procedure, a customized silicone mold with a thickness of 2 mm was fabricated for use in the bonding procedure. A 3-mm circular hole was made in the centre of the mold. The mold was placed at the centre of the Neo PUTTY.

In groups 1 and 3, the SAFC was bonded to NeoPUTTY following the manufacturer’s instructions. In groups 2 and 4, the RMGIC was bonded to the Neo PUTTY after applying the cavity conditioner (GC cavity conditioner, GC, Japan). All samples were light-cured using a previously calibrated LED light-curing device (Bluephase G2; Ivoclar Vivadent, Schaan, Liechtenstein) according to the manufacturer’s instructions. After removing the mold, the samples were cured again for 20 s and incubated at 37°C and 100% humidity for 24 h before the shear bond strength test. All materials used are listed in Table 1.

Table 1: Materials, compositions, and instructions for use.

Finally, the shear bond strength of the samples was determined in MPa using a universal testing machine (Instron5965, Instron, England) with a knife-edged rod at a crosshead speed of 0.5 mm/min.

To determine the fracture pattern the samples were examined using a stereomicroscope (Nikon Stereomicroscope 100 m Microscope, SMZ 1000, SMZ800, Swift, CA, USA) with a digital camera (Nikon digital cameraDXM1200F). The failure modes were categorized as follows:

• Adhesive failure: failure between NeoPUTTY and restorative materials.

• Cohesive failure: cohesive failure within the NeoPUTTY.

• Cohesive failure: cohesive failure within the restorative materials.

• Mixed failure: both adhesive and cohesive.

All data were processed using the Statistical Package for the Social Sciences software (version 21.0; SPSS Inc., Chicago, IL, USA). Comparisons between groups were analyzed using a one-way analysis of variance (ANOVA) and the post-hoc test. Statistical significance was set at P<0.05.

Results

The mean, standard deviations, and minimum and maximum values of shear bond strengths (MPa) of SAFC and RMGIC to NeoPUTTY are listed in Table 2.

Table 2: Descriptive statistics of the shear bond strength of the four experimental groups.

Table 3: Comparison of the four experimental groups with respect to s

Table 3 shows comparison of the four groups with respect to shear bond strength by using one-way ANOVA test, which revealed a statistically significant difference between all the groups (p=0.000).

The post hoc test was used to evaluate the differences between groups (Table 4). The results showed that the SAFC after 24 h (p=0.0000) had the highest bond strength values compared to the other groups. This was followed by the RMGIC after 24 h (p=0.000). The lowest shear bond strength values were obtained by the immediate placement of RMGIC (p=0.000).

The percentages of samples exhibiting the four failure modes in each group are shown in Figure 1. Mixed and cohesive failure within the NeoPUTTY were the predominant modes among all the groups.

Figure 1. The percentages of samples exhibiting the four failure modes in each group.

Discussion

Shear bond strength is a measure of the strength between two materials and estimates the local stress that the bonding layer can withstand. A higher shear bond strength means better bonding between the two interfaces and increases retention, which results in lesser microleakage [15]. Therefore, the shear bond strength was used in this study to evaluate the adhesive properties of SAFC and RMGIC with NeoPUTTY.

NeoPUTTY had the advantage of immediate placement of the final restoration. Therefore, in this study we select to place the material either immediately or after 24 h to check if there will be a difference in the values with time, since the initial setting time of NeoPUTTY is approximately 4 h at 37°C [16].

The results of the present study revealed a significantly higher mean shear bond strength with the SAFC than with the RMGIC when comparing the groups at the same time intervals. These results confirmed the previous report obtained by Doozaneh et al. [17] when they compared the shear bond strength of SAFC and RMGIC with MTA and a calcium-enriched mixture.

In the present study, the highest bond value was obtained with SAFC after 24 h. This could be explained by the presence of a phosphate functional monomer (GPDM), which may interact with the calcium ions in the NeoPUTTY and create a chemical bond between the SAFC and NeoPUTTY, resulting in a higher bond strength than RMGIC [18,19].

Ajami et al. [20] evaluated the shear bond strength of composite resin and giomer with MTA at different time intervals. In the composite resin groups, the shear bond strength values increased with time, whereas they decreased with the giomer. However, in the present study the value of shear bond strength increased with time in both materials, which might suggest further investigation to compare RMGIC versus the giomer bond with CSC.

When using the RMGIC, the manufacturer recommends conditioning the surface with a GC cavity conditioner before placing the restoration. Gulati et al. [15] evaluated the effect of using a conditioner on the shear bond strength between RMGIC with MTA and dentin and recommended that conditioning increases the bond strength between RMGIC and dentin with no significant effect on the RMGIC to the MTA shear bond strength value. Therefore, a cavity conditioner was used.

In this study, after testing the shear bond strength, all specimens were evaluated under a microscope to determine the mode of failure. Most failures observed were predominately cohesive within NeoPUTTY or the mixed failures. This finding is consistent with a previous study by Hursh et al. [21]. This mode of failure may indicate a failure in the material before adhesion or could be due to the smaller and uniformly sized particles in the fast-set putty [22].

The results of this study provide information that can aid clinicians in selecting the best material used in clinical practice. Based on our findings, using SAFC with NeoPUTTY is preferred over RMGIC. In addition, delayed adhesion of the final restoration was recommended.

The most important limitation of this study is that bonding was performed only between the two materials. In the clinical setting, a bonding interface between restoration and dentin and that between CSC and dentin are also present. Therefore, bonding to dentin should be considered and evaluated.

Conclusion

Within the limitations of the study, the shear bond strength was significantly higher at placement after 24 h than immediately with both materials. The bond strength of SAFC is higher than that of RMGIC. Thus, SAFC is recommended for use with NeoPUTTY instead of RMGIC.

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