The regenerative capability found in most other tissues is not possessed by teeth. Hence, enamel or dentin once lost as a result of caries, trauma, wear, and restorative materials must be replaced to restore form and function. Teeth require preparation to receive restorations, and these preparations must be based on fundamental principles from which basic criteria can be developed to help predict the success of restorative treatment.

Periodontitis is an inflammatory disease affecting the periodontium i.e. the tissues that surround and support the teeth. Periodontitis manifests as progressive loss of the alveolar bone around the teeth, and if left untreated, can cause loosening and subsequent loss of teeth. Periodontitis is initiated by microorganisms that adhere to and grow on the tooth's surfaces, besides an over -aggressive immune response against these microorganisms. The primary goal of periodontal therapy is to preserve the natural dentition by accomplishing and preserving a healthy functional periodontium. Many treatment modalities have been introduced to improve the therapeutic result of periodontal treatment which may also damage the periodontiumiatrogenically.

Missing teeth should be replaced as soon as possible to maintain arch integrity and thereby avoid both morphologic and functional derangements in the occlusion. Otherwise, changes occur that upset the masticatory system, such as extrusion of the teeth opposing the edentulous areas along with their alveolar housing, their supporting tissues and ultimately the maxillary sinus. Concurrently with extrusion, shifting of the interproximal contacts and migration of the adjacent teeth occur, thereby impairing function and causing disharmony. Good oral health cannot be achieved when changes in tooth position alter the coronal contour and occlusion interfering with mutual support, which encourages food impaction and retention, further leading to osseous defects.

The toxicity and tissue reactions to dental materials are receiving more attention as a wide variety of materials are used and as federal agencies demonstrate more concern in this area. A further indication of the importance of the interaction of materials and tissues is the development of recommended standard practices and tests for the biological interaction of materials.

The tooth, the pulp tissue within it and its supporting structures should be viewed as one biologic unit. The interrelationship of these structures influences each other during health, function and disease. The interrelationship between periodontal and endodontic diseases has aroused much speculation, confusion and controversy. The endodontium and periodontiumare closely related and disease or damage of one tissue may lead to the involvement of the other.