Histobacteriology and pulp reactions to long-term dental restorations

The prevention of degeneration and necrosis of the endodont is one of the main goals of dental treatment. Kerschbaum and Voss (1979, 1981) described that 15% of teeth showed negative results to sensitivity testing 10 years after crown preparation. Pulpal responses to dental treatment depend on many factors including thermal injury, transsection of the odontoblastic process, vibration, desiccation of dentin, pulp exposure, smear layer, remaining dentin thickness and used materials. The knowledge concerning endodontic reactions in short and medium term observation is mainly based on research by Klötzer and Langeland. Histological assessment of reactions is a well accepted method for biocompatibility testing (i.e. ISO/TR 7405). It is consistent to apply its principles to the evaluation of endodontic reactions of teeth with long term restorations. As pulpal injury is furthermore due to microleakage between filling material and the wall of the cavity the analysis of infected dentin tubules seems to be important. A consideration of the location of the tubules and of the severity of the invasion is necessary. Using a classification (grade 1-6) comprising the parameters of degenerative and regenerative reactions and bacterial invasion, 24 teeth restored with different types of fixed prosthodontic restorations were investigated. The restorations were between 0-6, 7-12 and 13-18 years in situ. Serial sections (5 microns) were stained with haematoxylin-eosin, azan, according to Goldner and J. Hopkins. 22 of 24 teeth showed typical degenerative reactions. Negative sensitivity testing occurred in teeth with no pain and no or partial necrosis. The histobacteriological assessment showed bacterial invasion of the dentin tubules of 21 teeth. From this investigation it was concluded that the proposed classification shows sufficient sensitivity for the evaluation of progressive endodontic changes of long-term restored teeth. Furthermore it was shown that bacterial invasion must be considered as a possible co-factor for the described degenerative character of the pulpal tissue.