Composites are monitored in clinical studies by using United States Public Health Service (USPHS) categories  of interest: color matching, interfacial staining, secondary caries, anatomic form (wear), and marginal integrity .
Changes in restorative treatment patterns, the introduction of new and improved restorative materials and techniques, effective preventive programs, enhanced dental care, and growing interest in caries-free teeth have greatly influenced the longevity of dental restorations; however, failure of restorations is a major problem in a practice treating primarily permanent teeth. Studies show that 60% of all operative work done is attributed to the replacement of restorations . Composites have improved since their introduction, and their survival rates are improving. Clinical studies to evaluate the latest composite technologies have not been published; therefore most of the survival data are on older composite compositions.
In the 1970s, degradation or wear was considered the main reason for failure of composite restorations. Improvements in filler technology and formulation of composite materials have resulted in new reasons for replacement. Twenty years later, studies revealed secondary caries to be the new cause of failure. The main factors responsible for the change in reasons for replacement include improved clinical technique based on more adequate teaching of posterior composites at dental schools, and on gained experience through trial and error of clinicians in practice . Advancements in composite properties and adhesive technology also contributed to these changes.
In comparison of survival probability between amalgam and composite, a time period involving 3, 4, 5, and 7 years was considered . In permanent teeth, the following values were measured: 3 year, 97.2% (amalgam) to 90% (composite); 4 year, 96.6% (amalgam) to 85.6% (composite); 5 year, 95.4% (amalgam) to 78.2% (composite); and 7 year, 94.5% (amalgam) to 67.4% (composite).
In summary, longevity of composite restorations depends upon factors involving the materials, the patient, and the dentist. The request for these esthetic, tooth-colored restorations will continue to increase, and patients must be educated about the expected life of these restorations as well as their advantages and disadvantages, so they can make an informed decision on a treatment option.