On the brittleness of enamel and selected dental materials

Although brittle material behavior is often considered undesirable, a quantitative measure of "brittleness" is currently not used in assessing the clinical merits of dental materials.

To quantify and compare the brittleness of human enamel and common dental restorative materials used for crown replacement.

Specimens of human enamel were prepared from the third molars of "young" (18< or =age< or =25) and "old" (50< or =age) patients. The hardness, elastic modulus and apparent fracture toughness were characterized as a function of distance from the DEJ using indentation approaches. These properties were then used in estimating the brittleness according to a model that accounts for the competing dissipative processes of deformation and fracture. The brittleness of selected porcelain, ceramic and micaceous glass ceramic (MGC) dental materials was estimated and compared with that of the enamel.

The average brittleness of the young and old enamel increased with distance from the DEJ. For the old enamel the average brittleness increased from approximately 300 microm(-1) at the DEJ to nearly 900 microm(-1) at the occlusal surface. While there was no significant difference between the two age groups at the DEJ, the brittleness of the old enamel was significantly greater (and up to four times higher) than that of the young enamel near the occlusal surface. The brittleness numbers for the restorative materials were up to 90% lower than that of young occlusal enamel.

The brittleness index could serve as a useful scale in the design of materials used for crown replacement, as well as a quantitative tool for characterizing degradation in the mechanical behavior of enamel.