Influence of different indentation load and dwell time on Knoop microhardness tests for composite materials

Abstract

Various microhardness test methods with different indentation loads and dwell times have been used to evaluate the hardness of composite materials. However, there is still no agreement on the ideal test method for composites. The aim of this study was to determine the influence of different indentation load and dwell time on Knoop Hardness Number (KHN) of three different kinds of light-cured composites. A mold was fabricated to make cylindrical specimens of three different composite resins (TPH, Tetric Ceram, Surefil), and 45 cylindrical composite discs were prepared. Hardness tests on the materials were performed with three different loads at two different dwell times. One-way analysis of variance and LSD did not reveal a statistically significant difference between TPH and Surefil with 50 gf at both dwell times. However, on the other matched load and time groups, Surefil exhibited higher KHN than TPH and Tetric Ceram. Our results suggest that the indentation load is critical for micro-indentation hardness tests and as the results are directly affected, further studies are needed to standardize the micro-indentation test load.