The definition of failure applied in clinical studies may affect the reported statistics. Demarco "et al" note: "Failed restorations or restorations presenting small defects are routinely treated by replacement by most clinicians. Because of this, for many years, the replacement of defective restorations has been reported as the most common treatment in general dental practice..." Demarco "et al" observe that when both repaired and replaced restorations were classified as failures in one study, the Annual Failure Rate was 1.9%. However, when repaired restorations were reclassified as successes instead of failures, the AFR decreased to 0.7%. Reclassifying repairable minor defects as successes rather than failures is justifiable: "When a restoration is replaced, a significant amount of sound tooth structure is removed and the preparation hole is enlarged". Applying the narrower definition of failure would improve the reported longevity of composite restorations: Composite restorations can often be easily repaired or extended without drilling out and replacing the entire filling. Resin composites will adhere to the tooth and to undamaged prior composite material. In contrast, amalgam fillings are held in place by the shape of the void being filled rather than by adhesion. This means that it is often necessary to drill out and replace an entire amalgam restoration rather than add to the remaining amalgam.