An In vitro Study to Assess the Effectiveness of the Shear Bond Strength of Mineral Trioxide Aggregate with Different Adhesive Systems.

PURPOSE OF THE STUDY: Mineral trioxide aggregate (MTA) is a biocompatible material and has excellent sealing ability. It is proved and claimed that it provides double seal due to its physical sealing ability as well as ability to induce cementogenesis that provides biological seal. AIM AND
OBJECTIVES: The aim of the study was to assess the shear bond strength of MTA with three different types of adhesive systems: (1) self-adhering flowable composite, (2) etch and rinse (ER) adhesive system, and (3) self-etch (SE) adhesive system.
MATERIALS AND METHODS: Ninety MTA specimens were prepared using cylindrical acrylic blocks, having a central cavity with 2 mm depth and 4 mm diameter. MTA was mixed and placed in the prepared cavity and was covered with moist cotton pellet and temporary filling material (Cavit). They were further divided into three groups which were further divided into two subgroups. After the bonding agents was applied, the composite resin was placed over the MTA surface. The specimens were then tested for shear bond strength; statically analysis was done. RESULT: After 24 h, the mean value of ER group was found to be significantly higher than SE and the self-adhering composite groups. Among the 45 min groups, there was no significant difference observed.
CONCLUSION: In single visit, after 45 min, self-adhering flowable can be used successfully as a final restorative material in place of conventional flowable composite without using any alternative adhesive system over MTA. Copyright:

INTRODUCTION

Mineral trioxide aggregate (MTA) was initially presented as a root perforation repair material in 1993.[1] The material is composed primarily of calcium, silicon, bismuth, and oxygen. MTA is a biocompatible material[12] and has excellent sealing ability. Research has well claimed the ability of MTA to provide double seal due to its physical sealing ability as well as ability to induce cementogenesis that provides biological seal. It also has the ability to set in the presence of moisture. Despite several advantages, prolonged setting time, and compulsion to place wet cotton pellet over MTA in some procedures to complete the setting reaction is a major drawback that necessitates multiple visits and increased chair time.[3] Conventionally, glass ionomer cement can be layered over partially set MTA after 45 min to complete the procedure in a single visit. Its advised that the restorative procedure might be postponed at least for 96 h after mixing MTA to allow the material to achieve its optimum physical properties.[4] Recent studies have also suggested that composite resin with a bonding agent can be restored over MTA almost immediately after the placement of MTA. When hydration during MTA setting process is guaranteed, there are no particular issues related to composite resin restoration even if it is performed almost immediately after MTA filling. However, during acid etching, just before composite placement reduces the compressive strength and surface microhardness of MTA. Dyad Flow, a new generation flowable composite, is an amazing self-adhering composite and is designed to bond to tooth structure without the need for an independent adhesive or an etching step. The reduction in the number of steps can lead to lesser chances of procedural errors and lesser chair side time and results in more patient comfort during placement and hence are less technique sensitive than total etch and self-etch (SE) adhesives. Studies in the past have evaluated the physical properties, bond strengths, and marginal leakage of self-adhering composite to tooth, but no study has compared the bond strength of self-adhering composite with SE and etch and rinse (ER) adhesive systems when placed over the MTA.[5678910] The aim of this study is to assess the shear bond strength of MTA with three different types of adhesive systems: a self-adhering flowable composite, a SE adhesive system, and an ER adhesive system.

MATERIALS AND METHODS

Preparation of mineral trioxide aggregate specimens[1]

The materials used in the study are enlisted in Table 1. Ninety MTA specimens were prepared using cylindrical acrylic blocks. In each block, central cavity was created in each block measuring the materials used and applied as recommended by the manufacturing company. The materials used are listed in Table 1.

Table 1

Materials used, composition, and method of application

Product name (manufacturer)	Composition	Application
ProRoot MTA (Dentsply Tulsa Dental, USA)	Tricalcium silicate, bismuth oxide, dicalcium silicate, tricalcium aluminate, calcium sulfate dehydrate, or gypsum	Mix MTA with distilled water according to manufacturer’s instruction
DF (Kerr, Orange, CA, USA)	GPDM, HEMA, prepolymerized filler (20 μm), barium glass filler (0.7-1 μm), nano-sized colloidal silica (10-40 nm), nano-sized Ytterbium fluoride (40 nm), zinc oxide (pH 1.9)	Brush a thin layer (<1.5 mm) of Dyad Flow for 15-20 s and light cured for 20 s and subsequent layer added
Brilliant flow (Coltene Whaledent, Switzerland)	Methacrylates, barium glass, silanized amorphous silica, hydrophobic	Apply the material using applicator tip and light cured
Prime and bond NT (Dentsply, Konstanz, Germany)	Di-trimethacrylate resin, PENTA, functionalized amorphous silica, photoinitiator, stabilizers, cetylamine hydrofluoride, acetone	Apply 35% phosphoric acid etchant for 15 s. rinse and blot dry. Apply adhesive. Gentle air stream. Light polymerize for 20 s
All bond 7 (Coltene Whaledent, Switzerland)	Primer: MDP, HEMA, hydrophilic dimethacrylate, dl-camphorquinone, water bond: MDP, HEMA, BIS-GMA	Apply, wait for 20 s, light cure the bond for 10 s

MTA: Mineral trioxide aggregate, MDP: Methacryloxydecyl dihydrogen phosphate, HEMA: Hydroxyethyl methacrylate, GPDM: Group practice diabetes management, PENTA: Dipentaerythritol penta acrylate monophosphate, BIS-GMA: Bisphenol A-glycidyl methacrylate, DF: Dyad Flow

The shear bond strength was observed for MTA with adhesives 4 mm in diameter and 2 mm in depth. The MTA was mixed according to the manufacturer's instructions on the box, was placed into the central cavity in the acrylic blocks, and was covered with a moist cotton pellet and temporary filling material (Cavit; 3M ESPE America, Norristown, PA, USA). Nearly 50% of the specimens were stored for 45 min, and the remaining 45 specimens were stored for 1 complete day for 24 h at 37°C temperature and 100% humidity. After removing the Cavit and moist cotton, the MTA surface was not rinsed or polished. Ninety samples were divided into three groups according to the type of adhesive system used, and these groups were further divided into two subgroups (n = 15) according to the different time intervals. The divisions of groups are listed in Table 2.

Table 2

Different groups at different time intervals for bond strength test

Group 1: Dyad Flow	Group 2: SE	Group 3: ER
45 min	45 min	45 min
24 h	24 h	24 h

SE: Self-etch, ER: Etch and rinse

In the SE and ER groups, the corresponding adhesive system was applied over MTA according to the instructions following which a conventional flowable composite Flow (Coltene Whaledent, Switzerland) was placed over MTA surface with the help of cylindrical plastic tube having an internal diameter of 2 mm and a height of 3 mm. Light curing was done with a quartz–tungsten–halogen (QTH) light-curing unit (DENTSPLY, USA) at an intensity of 600 mW/cm2 for 20 s. In the DF Group, the self-adhering composite was placed over MTA in small increments. Light curing was done using a QTH light-curing unit (Spectrum 800, DENTSPLY Caulk Milford, DE, USA) at an intensity of 600 mW/cm2 for 20 s and then the remaining height of the plastic tube was filled with the second pour, and light curing was done. The specimens were stored at 37°C temperature and 100% humidity for 24 h to encourage setting.

Shear bond strength measurement

The specimens were mounted in a universal testing machine (Instron Corp, Canton, MA). A crosshead speed of 0.5 mm/min was applied to each specimen using a knife-edge blade until the bond between the MTA and composite failed. The means and standard deviations were calculated. Shapiro–Wilks test was used for normality. The mean bond strengths of the groups were compared using one-way analysis of variance and Tukey's honestly significant difference test with significance level, P < 0.05 was used.

RESULTS

The means and standard deviations of the shear bond strengths are given in Table 3. There was no significant difference between Dyad Flow and SE groups at both the time intervals. However, there is a significant difference between the mean bond strengths at 45 min and 24 h for the ER group, when compared with SE and Dyad Flow groups.

Table 3

Mean shear bond strength values in MPa

Time interval	Dyad Flow (MPa)	SE (MPa)	ER (MPa)
45 min	3.5±1.19	3.9±1.30	5.5±1.47
24 h	4.7±1.36	4.9±1.44	6.9±0.98

SE: Self-etch, ER: Etch and rinse

DISCUSSION

MTA has been used since many years successfully as a material for use in perforation repair and retrograde filling, and eventually, it was recommended for pulp capping, pulpotomy, and as an apical barrier in the treatment of immature teeth with nonvital pulps and open apices as pulp capping agents in vital pulp therapy. Following pulp capping, direct resin composites can be used for final restoration. Research has recommended that the application of ER and SE adhesive over MTA is postponed for 96 h.[89] The most common method to evaluate adhesive properties of restorative materials is bond strength assessment. Recent studies have evaluating the bond strength of adhesives to MTA, using various bonding systems, concluded that superior MTA-composite bond strength can be achieved with an ER adhesives at 24 h in comparison to SE system.[68] SE adhesives are gaining popularity because of simplified bonding procedures and reduced technique sensitivity. The SE approach uses acidic adhesive monomers that at the same time demineralize and infiltrate into the dentin. The intensity of the interaction of SE adhesive systems with dentin was mostly dependent on the acidity and aggressiveness of the primer used.[1011121314] The manufacturer of Dyad Flow has mentioned that it has a pH of 1.9, and One Coat 7.0 (Coltene Whaledent, Switzerland), a mild SE adhesive, has a reported pH of 2.0. Thus, Dyad Flow can be expected to interact with the dental substrate in a manner similar to that of a mild SE adhesive. Our study has also the results of this study showed that there is no significant difference between the bond strength of Dyad Flow, SE adhesive, and ER adhesive after 45 min. However, the bond strength of the composite to MTA was significantly higher for the ER group after 24 h. Previous studies have evaluated the bond strengths of adhesives to MTA using various bonding system. Although acid etching reduces the surface microhardness of MTA and weakens the structure of the material, the results of these studies[11516] have shown that superior MTA/composite bond strength can be achieved with ER adhesives in comparison However, according to this study, there is no significance difference between Dyad Flow — SE and ER group at 45 min. The mild etching efficacy of Dyad Flow (pH 1.7) in comparison to aggressive phosphoric acid in ER group might be a reason for lower bond strength value at 24 h. Dyad Flow and SE adhesive have pH of 1.7 and 1.8, respectively, and due to similar etching effectiveness, the bond strength values are almost same which is similar to the study done by Tyagi et al.[1]

CONCLUSION

There is no significant difference in the mean bond strength values for Dyad Flow — SE and ER groups at 45 min. However, there was a significant difference observed in the mean bond strength values for adhesives in ER group when compared to Dyad Flow and SE adhesives at 24 h. Thus, to complete the clinical procedure in a single visit and to reduce the clinical steps, Dyad Flow can be used as an alternative to SE or ER adhesives as a definitive restoration after 45 min.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.