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.

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 has similar thermal conductivity and coefficient of thermal expansion to enamel and dentine and exhibits high compressive strength. 35 fair hurst cw loc kwood pe ring le rd twiggs sw. Typical values of compressive strength of some restorative dental materials are given in table 5 1.

In addition the surface microcracks caused by various reasons during manufacturing are the starting sites of catastrophic fracture. Alumina for example has a tensile strength of 20 000 psi 1138 mpa while the compressive strength is 350 000 psi 2400 mpa. Dental porcelain has very stable chemical properties and outstanding esthetics which are unlikely to be influenced by time. However the tensile strength of dental porcelain is very low 20 60 mpa.

More recently the flexural strength has been reported as 240 mpa compared with a value of 115 mpa for alumina reinforced porcelain oilo 1988. 65 7 993 997 jul 1986. It can be identified as a sort of ceramic that is not totally transformed into glass phase. 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.

This imparts brittle nature to the ceramics 23 24 25 and tend to fracture under tensile stresses. Note that the proportional limit ultimate compressive strength and elastic modulus of enamel are greater than the corresponding values for dentin. Ceramic material used in dentistry is a glassy matrix that is produced via sintering and it contains leucite crystals. Dental ceramics possesses very good resistance to the compressive stresses however they are very poor under tensile and shear stresses 1 11 22.

Ceramics materials are used in modern dentistry in a variety of different applications including fillings crowns veneers implants and dental brackets. Even the pressure strength of dental ceramics are between 350 550 mpa the draw strength value is 20 60 mpa.