Compressive Strength Of Dental Ceramics

Compressive strength is therefore a useful property for the comparison of dental amalgam resin composites and cements and for determining the qualities of other materials such as plaster and investments.

Compressive strength of dental ceramics. Fatigue of dental ceramics in a simul ated oral environmen t j dent res. 35 fair hurst cw loc kwood pe ring le rd twiggs sw. Dental ceramics possesses very good resistance to the compressive stresses however they are very poor under tensile and shear stresses 1 11 22. Iso 6872 dentistry ceramic materials specifies the requirements for ceramic materials used in dentistry and also defines the basic methods for flexural strength testing.

However the tensile strength of dental porcelain is very low 20 60 mpa. Alumina for example has a tensile strength of 20 000 psi 1138 mpa while the compressive strength is 350 000 psi 2400 mpa. For a metal the compressive strength is near that of the tensile strength while for a ceramic the compressive strength may be 10 times the tensile strength. It can be identified as a sort of ceramic that is not totally transformed into glass phase.

Note that the proportional limit ultimate compressive strength and elastic modulus of enamel are greater than the corresponding values for dentin. Even the pressure strength of dental ceramics are between 350 550 mpa the draw strength value is 20 60 mpa. This imparts brittle nature to the ceramics 23 24 25 and tend to fracture under tensile stresses. 65 7 993 997 jul 1986.

A value of 152 mpa has been quoted for the modulus of rupture of dicor glass ceramic dentsply international york pn usa adair and grossman 1984. It has similar thermal conductivity and coefficient of thermal expansion to enamel and dentine and exhibits high compressive strength. Dental porcelain has very stable chemical properties and outstanding esthetics which are unlikely to be influenced by time. In addition the surface microcracks caused by various reasons during manufacturing are the starting sites of catastrophic fracture.

More recently the flexural strength has been reported as 240 mpa compared with a value of 115 mpa for alumina reinforced porcelain oilo 1988. Typical values of compressive strength of some restorative dental materials are given in table 5 1.