It is observed clinically that some years after MOD restoration of molar and premolar teeth, cuspal failures commonly occur. The period between restoration and failure is usually from eight to fifteen years. Evidence has been found, both from observations of fractured cusps and from a mathematical model of an idealized molar tooth, that allows a clear description of the mechanism of these slow failures. Suggested changes in clinical practice are recommended if such failures are to be prevented in the future.
