Endodontically treated teeth are though to be more susceptible to fracture as a result of the loss of tooth vitality and tooth structure. This study was designed to compare the contributions of endodontic and restorative procedures to the loss of strength by using nondestructive occlusal loading on extracted intact, maxillary, second bicuspids. An encapsulated strain gauge was bonded on enamel just above the cementoenamel junction on both the buccal and lingual surfaces, and the teeth were mounted in nylon rings leaving 2 mm of root surface exposed. Under load control, each tooth was loaded at a rate of 37 N per s for 3 s and unloaded at the same rate in a closed loop servo-hydraulic system to measure stiffness. A stress-strain curve was generated from each gauge prior to alteration of the tooth and after each procedure performed on the tooth. Cuspal stiffness, as a measure of tooth strength, was evaluated on one of two series of sequentially performed procedures: 1. (a) unaltered tooth, (b) access preparation, (c) instrumentation, (d) obturation, and (e) MOD cavity preparation; or 2. (a) unaltered tooth, (b) occlusal cavity preparation, (c) two-surface cavity preparation, (d) MOD cavity preparation, (e) access, (f) instrumentation, and (g) obturation. Results on 42 teeth indicate that endodontic procedures have only a small effect on the tooth, reducing the relative stiffness by 5%. This was less than that of an occlusal cavity preparation (20%). The largest losses in stiffness were related to the loss of marginal ridge integrity. MOD cavity preparation resulted in an average of a 63% loss in relative cuspal stiffness. The results indicate that endodontic procedures do not weaken teeth with intact marginal ridges.
Bibliographical noteFunding Information:
This research was supported in part by a Grarlt-ln-Aid of Research from the Endowment and Memorial Foundation of the American Association of Endodontists. The opinions, assertions, materials, and methodologies herein are private ones of the authors and are not to be construed as official or reflecting the views of the American Association of Endedontists or the Endowment and Memorial Foundation. This research was presented at the 45th Annual Meeting of the American Association of Endedontists, Anaheim, CA, where it won first place in the Graduate Student Presentations. This work was based on a thesis submitted to the Graduate School of the University of Minnesota in partial fulfillment of the requirements for the MS degree. This study was also supported by Grant DE 08732 from the National Institute for Dental Research, Bethesda, ME).