The type, number, and arrangement of teeth in the mouth is called dentition. Dentin is the hard layer of tissue immediately under the tooth's enamel. Dentino-enamel junction (DEJ) is where the dentin and enamel meet on the crown of a tooth.
It is important to know as much as possible about the physical properties of dentin, because it is the most abundant tissue present in the human dentition. Knowledge of its physical properties helps us understand what material best serves as its substitute when dentin is lost due to cavities, fracture, or removal as a dental treatment. Various restorative materials possess different physical properties that dictate preparation, design, and usage.
The dentin that is protected by the harder enamel structure is what affords dentition its resilience and toughness over the patient's lifetime of biting and chewing. Many of our concepts of the biomechanical properties of dentin have changed in the last 30 years. We know that it is more elastic than previously believed. But pre-existing flaws in dentin can cause teeth to fail at stresses far less than their theoretical strength. Therefore, dental materials which add stiffness, used to replace tooth structure help to preserve long-term function of the tooth. With this in mind, we must set aside outdated concepts which have influenced the choice of or against cast gold for restorations, its preparation and its design.
It is also important to understand that the critical junction between enamel and dentin, the DEJ, transfers stress from the enamel to the dentin. This inhibits cracks in enamel from spreading and resulting in catastrophic fracture of the tooth. Cracks which start in enamel are arrested once they reach the DEJ within the mantle dentin (dentin closest to the DEJ).
Conservation of tooth structure is of paramount importance in restoring long-term function. Both the quantity of remaining tooth structure and the type of restorative material placed has a significant impact on the distribution of stress to that tooth. Restorative materials such as cast gold, which impart less stiffness to the tooth result in greater flexibility - they do a better job of distributing stress.