Modern endodontic principles part 7: the restorative interface

Following successful endodontic therapy the tooth must be restored. This restoration process has several justifications:

Of these functions, protection of the underlying tooth structure should be recognized as essential in preventing endodontic failure. It is known that the longevity of a root-treated tooth is directly related to the amount of remaining sound tooth material¹ and there is frequently extensive loss of natural tooth structure in endodontically-treated teeth.² Previous beliefs that the mechanical weakening of endodontically-treated teeth was due to the difference in moisture content when compared to vital teeth has been disproved.³ It has been shown that endodontic access and treatment only reduces the stiffness of teeth by 5%, compared to a 63% reduction in stiffness following preparation of an MOD cavity.⁴ It is now accepted that cuspal deflection and thickness of the residual walls and cusps are more important factors. As cavity size increases, especially after endodontic access, and the marginal ridges are lost, structural stability decreases. Thus, the presence of a marginal ridge is now considered a far more influential factor upon tooth strength than an endodontic access cavity.⁵ However, it must be noted that non-vital teeth do appear to have reduced tactile sensitivity and therefore have the potential to be loaded to a greater degree before the biofeedback mechanism is initiated.⁶