Endodontically treated teeth are thought 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.(ABSTRACT
TRUNCATED AT 250 WORDS)