Evaluation of Microhardness of Bulk-base Composite Resins According to the Depth of Cure

Abstract

Composite resin becomes an essential material in pediatric dentistry. However, incremental filling of composite resin to minimize the polymerization shrinkage takes time. To reduce the polymerization shrinkage, clinicians and researchers have focused on bulk-filling materials. Bulk-base composite resin is newly introduced as bulk-filling composite resin. The purpose of this study was to evaluate microhardness profile of bulk-base composite resin according to the depth of cure. A high flow bulk-base material and a low flow bulk-base material were used for experimental group, and a conventional composite resin was used for control group. Each group consist of 20 specimens, 3.5 × 3.5 × 5.0 mm mold was used to make specimen. Specimens were sectioned at the 2 mm and the 3 mm depth with milling machine. Microhardness profile was measured at the surface, 2 mm depth, 3 mm depth, and 4 mm depth. Microhardness of control group showed statistically significant difference (p < 0.05) according to the polymerization depth. In contrast, experimental group showed no statistically significant difference, except between 0 mm and 4 mm at HFB, 0 mm and 2 mm, 0 mm and 3 mm at MFB. At the surface and the 2 mm depth, the control group showed higher microhardness than the experimental groups (p < 0.05). However, at the 4 mm depth, the experimental groups showed significantly higher microhardness (p < 0.05). The results from this study, the bulk-base composite resin showed higher microhardness at the 4 mm and lower microhardness at the surface and the 2 mm depth. Therefore, if bulk-base resin overcomes the mechanical weakness, it could be considered using in pediatric dentistry.

Comparison of Surface Microhardness of the Flowable Bulk-Fill Resin and the Packable Bulk-Fill Resin according to Light Curing Time and Distance

“…A direct method is to measure the amount of monomer, and one of the indirect methods is a comparison using microhardness 19,20) . Microhardness is a physical property that represents the characteristics of a material and represents the magnitude of the force that a material resists permanent deformation that occurs when an external force is applied to a minute part 21) . Therefore, in this study, Vickers Hardness Number was used to measure the physical properties of Bulk-Fill resin.…”

“…In the study using the bulk-base resin, a significant difference in surface microhardness change was found from 4 mm in the case of the high flow bulk resin. In addition, it was reported that there was a significant change in surface microhardness between 0 mm and 2 mm of Medium Flow Bulk resin, but no significant change in surface microhardness was found between 2 mm and 3 mm, and 3 mm and 4 mm 21) . This…”