An In‑vitro Evaluation of the Shear Bond Strength to Dentin and Microhardness of Different Restorative Materials Placed by Different Techniques

Abstract

Background: The mentioned advantages of bulk‑fill composite resin and high-viscosity glass ionomer restorative materials have  increased their use in restorative dentistry in recent years; accordingly, the bonding of these materials to dental tissues and their  mechanical properties have become more important.

Aim: This study aimed to evaluate the effects of different application methods on   Vicker’s hardness and shear bond strength of three different restorative materials.

Methods: In this in‑vitro study; Teflon molds were   used for the microhardness test. In the control group, reinforced high-viscosity glass ionomer, high-viscosity glass ionomer, and flowable   bulk‑fill composite resin were applied by the manufacturer’s instructions. In other groups, preheating, ultrasonic activation,  and both  preheating and ultrasonic activation were applied, respectively (n = 14). Microhardness values of the upper surfaces of the  specimens  were measured with Vicker’s hardness measuring device. For the shear bond strength test, 84 intact human molar teeth were  used. The  teeth were sectioned two in the mesiodistal direction (n = 14). The materials were applied to the dentin using the same  placement  protocols as those used in the hardness test. After the specimens were maintained at 37°C for 24 h, the shear bond strength  test was  performed using a universal test device.

Statistical Analysis Used: The data were analyzed using SPSS 26.0 at a 95% confidence  level. The  Mann–Whitney test was also used for the statistical analysis of the data (P = 0.05).

Results: Preheating the  restorative materials  significantly decreased the shear bond strength in the flowable bulk‑fill composite resin group (11.77 ± 4.46 MPa)  compared with that in  the control group (12.14 ± 4.23 MPa) (P < 0.05) but significantly increased the shear bond strength in the  reinforced high‑viscosity glass  ionomer group (3.91 ± 2.93 MPa) (P < 0.05).

Conclusions: It can be concluded that preheating before  application may increase the shear  bond strength of reinforced high-viscosity glass ionomer.