The widespread use of porcelain in restorative dentistry is generally due to its esthetic appearance even though it is brittle. The transverse strength, or modulus rupture, averages around 108 MPa (16,000 psi) for aluminous porcelain and 88 MPa (13,000 psi) for feldspathic porcelain. The tensile strength, as determined by diametral compression, is approximately 29 MPa (4,200 psi) for opaque feldspathic porcelain and 40 MPa (5,800 psi) for gingival feldspathic porcelain. The compressive strength is reported to be 340 MPa (50,000 psi) for a feldspathic porcelain. These mechanical strength properties of dental porcelain confine its use to low stress-bearing restorations or to those restorations with a metal substrate.