A comparative evaluation of dental luting cements by fracture toughness tests and fractography

In recent years there has been a shift from traditional methods of investig ating dental materials to a fracture mechanics approach. Fracture toughness (K-1C) is an intrinsic material property which can be considered to be a m easure of a material's resistance to crack propagation. Glass-ionomer cemen ts are biocompatible and bioactive dental restorative materials. bur they s uffer from poor fracture toughness and are extremely susceptible to dehydra tion. The main objective of this study was to evaluate the fracture toughness of three types of commercially available dental cements (polyacid-modified com posite resin, resin-modified and conventional glass ionomer) using a short- rod chevron-notch test and to investigate and interpret the results by mean s of fractography using scanning electron microscopy. Ten specimens of each cement were fabricated according to manufacturers' instructions, coated in varnish, and stored at ambient laboratory humidity, 100 per cent relative humidity, or in water at 37 degreesC for 7 days prior to preparation for te sting. Results indicated that significant differences existed between each group of materials and that the fracture toughness ranged from 0.27 to 0.72 MN/m(3/)2. It was concluded that the resin-modified glass-ionomer cement d emonstrated the highest resistance to crack propagation. Fractographs clear ly showed areas of stable and unstable crack growth along the fractured sur faces for the three materials examined.