Compressive Strength Of Dental Ceramics

Iso 6872 dentistry ceramic materials specifies the requirements for ceramic materials used in dentistry and also defines the basic methods for flexural strength testing.

Compressive strength of dental ceramics.

Dental ceramics possesses very good resistance to the compressive stresses however they are very poor under tensile and shear stresses 1 11 22. 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. Typical values of compressive strength of some restorative dental materials are given in table 5 1. 65 7 993 997 jul 1986.

Dental porcelain has very stable chemical properties and outstanding esthetics which are unlikely to be influenced by time. 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. However the tensile strength of dental porcelain is very low 20 60 mpa. In addition the surface microcracks caused by various reasons during manufacturing are the starting sites of catastrophic fracture.

Ceramics materials are used in modern dentistry in a variety of different applications including fillings crowns veneers implants and dental brackets. 35 fair hurst cw loc kwood pe ring le rd twiggs sw. 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.

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. This imparts brittle nature to the ceramics 23 24 25 and tend to fracture under tensile stresses. Alumina for example has a tensile strength of 20 000 psi 1138 mpa while the compressive strength is 350 000 psi 2400 mpa. Even the pressure strength of dental ceramics are between 350 550 mpa the draw strength value is 20 60 mpa.

Ceramic material used in dentistry is a glassy matrix that is produced via sintering and it contains leucite crystals. More recently the flexural strength has been reported as 240 mpa compared with a value of 115 mpa for alumina reinforced porcelain oilo 1988.