Inlays and onlays are used when there is mild decay or damage on a tooth, but not enough to require a full crown, though are still very durable; onlays and inlays can last up to 30 years! Unlike traditional metal fillings which can reduce the strength of your teeth by up to 50%, modern inlays and onlays help strengthen your teeth by up to 75%! They also prevent further bacteria damage to a cavity hole by blocking it up so efficiently.