INTRODUCTION
Calcium silicate-based dental cement known as mineral trioxide aggregate (MTA) has gained popularity especially in endodontic dentistry because of its physical and regenerative characteristics.1,2 Mineral trioxide aggregate is one of the most successfully used materials in clinical procedures, such as indirect pulp capping, apexification, and root-end filling material.3-6 Despite its unique combination of favorable properties, MTA has some critical shortcomings, such as prolonged setting time, high solubility, and difficulty in handling.7
To overcome the disadvantages of MTA, biodentine, a new calcium silicate-based cement, is used as dentin substitute for resin composite restorations, pulp capping, and endodontic repair material. It has improved sealing ability, higher compressive strengths, and short setting time.8,9
Resin composites were very popular in restorative dentistry. They cannot be placed directly over MTA because it affects its setting and can dislodge the material. However, it has claimed that the setting time of biodentine is 12 minutes. So hypothesis is that resin composites can be layered overset biodentine which might enable single-visit procedures.10 Therefore, the present study is to evaluate the bond strength of methacrylate-based composite and fiber-reinforced composite when used with biodentine.
MATERIALS AND METHODS
Specimen Preparation
Acrylic blocks (n = 30) with 2 mm high and 5 mm diameter central holes were prepared. In all 30 samples, the holes were fully filled with biodentine. The specimens were stored at 37°C in 100% humidity for respectively, 15 minutes and 96 hours for setting.
Placement of Restorative Material
After the setting, biodentine samples are randomly divided into two groups. Group I: Methacrylate-based composite; group II: Fiber-reinforced composite. In both the groups, corresponding adhesive system was applied over biodentine according to manufacturer’s instructions as displayed in Table 1. Each resin composite was placed at the center of biodentine by placing the packing material into cylindrically shaped plastic tubes with internal diameters of 2 mm and height of 2 mm. The composite resins were cured with light-emitting diode for 20 seconds as per manufacturer’s instructions. After the polymerization, the plastic tubes were removed carefully and specimens were stored at 37°C in 100% humidity for respectively, 15 minutes and 96 hours for setting.
Table 1
Manufacturer and application details of the materials used in the study
Shear Bond Strength Test
Each block was secured in a universal testing machine. A chisel-edge plunger was mounted on to the movable cross-head of testing machine and positioned so that the leading edge was aimed at the biodentine®. The force required to remove the restorative material was measured in Newtons.
RESULTS
Table 2 shows the descriptive statistics of shear bond strength for each group. The highest and lowest bond strength values were recorded for the fiber-reinforced composite with biodentine and methacrylate-based composite with biodentine respectively.
DISCUSSION
Dental restorative filling composite resins have been introduced to the dental community in the 1960s. Since then after many significant material improvements, restorative composite still suffers lack of mechanical properties and problems related to polymerization shrinkage. Clinical studies have shown that direct fillings fail predominantly because of occlusal wear (or) secondary caries.11
Table 2
Descriptive statistics of shear bond strength for each group
| Group | Number | Mean ± SD | p-value |
| Fiber-reinforced composite | 15 | 3.19 ± 0.37 | <0.0001a |
| Methacrylate-based composite | 15 | 1.48 ± 0.21 | |
| aHighly significant; SD: Standard deviation | |||
However, the fracture of restorative composite is also a common reason for replacement. Due to failures of this kind, it is still controversial whether restorative composites should be used in large, high-stress-bearing applications, such as in direct posterior restorations. The relatively high brittleness and low fracture toughness of current composites still hinder their use in large stress-bearing areas.
Recently, short fiber-reinforced composite was introduced as dental restorative composite resin. The composite resin is intended to be used in high-stress-bearing areas, especially in molars. The results of the laboratory mechanical tests revealed substantial improvements in the load-bearing capacity, the flexural strength, and fracture toughness of dental composite resin reinforced with short E-glass fiber fillers in comparison with conventional particulate filler restorative resin.11
In this study, fiber-reinforced composite showed highest bond strength when compared with methacrylate-based composite. The result of our present study is in accordance with previous studies conducted by Abouelleil et al12 which stated that everX Posterior performed relatively better. The study concluded that the fibers have played a role in increasing the material stiffness and resistance to bending force during testing and probably during function. The enhancement of material properties was explained due to the stress transfer from matrix to the fibers and also due to the action of fibers in stopping crack propagation through the material.12
In this study, fiber-reinforced composite showed highest bond strength with biodentine. It is unknown whether a chemical union exists between Biodentine™ and the overlying resin composite restoration; however, previous research found that the functional monomer 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP), present in the adhesive used in this study binds to calcium in tooth structure. Theoretically, it could be assumed that the 10-MDP monomer may bind chemically to the calcium in Biodentine™, hence, promoting chemical adhesion in addition to micromechanical attachment.13
In the present study, methacrylate-based composite showed lower bond strength when compared with fiber-reinforced composite; it might be because of less filler volume percentage and also because of absence of fibers which inhibit crack propagation.