A note on the temperature dependence of the flexural strength of a porcelain

Objectives: The purpose of this study is to determine the temperature dependence of the flexural strength of a dental porcelain (IPS-Classic Dentin; manufacturer: Ivoclar, Liechtenstein) with temperature between its glass transition (Tg=581.7 °C) and room temperature. Methods: The flexural strength was measured in three-point bending tests on an Instron 4204 testing apparatus. The strength values were determined for the temperatures T=20, 300, 400, 450, 500, 550, and 600 °C. Results: In the temperature interval 20≤T≤400 °C the flexural strength decreased slightly from not, vert, similar80 to not, vert, similar73 MPa (mean values), as temperature increased. That is a decay of less than 10%. At higher temperatures the flexural strength increased to a maximum of not, vert, similar98 MPa at 500 °C, probably due to the closure of microcracks in the surface on account of the onset of viscous flow. A further increase of the temperature delivered again decreasing strength values. At its glass transition temperature the porcelainʹs flexural strength was not, vert, similar76 MPa which is only about 5% less than the value at room temperature. Significance: In order to be able to evaluate the risk of fracture of ceramometallic crowns and bridges due to high temperature gradients and accompanying large transient thermal stresses in the veneer during the fabrication process, flexural strength values at high temperatures must be known. This study was carried out to fill this knowledge gap because to the authorsʹ knowledge there was little published in the literature.