In Vivo Strain Alterations in Mandibular Molars after Root Canal Treatment Procedures

Introduction: The aim of this investigation was to determine the coronal strain variations in mandibular molars under an in vivo bite load after root canal treatment procedures. Methods: The coronal strain in carious mandibular first molars with symptomatic irreversible pulpitis (experimental group) was compared with that of intact contralateral teeth (control group) in patients 20-40 years old. Experiments were conducted in 2 stages. In stage 1, the maximum bite force on the first molar region was determined on the experimental and control teeth using a customized load cell. In stage 2, strain gauges were bonded to the buccal aspect of teeth, and the strain was recorded after the application of a bite load on the intact (control) teeth; and the experimental teeth before and after endodontic access cavity preparation, cleaning/shaping procedures, root filling, and composite core restoration. Results: The mean maximum bite force on the experimental teeth (91 +/- 48 N) and the contralateral control teeth (91 +/- 49 N) was not significantly different (P = .989). The preoperative strain (microstrain) in the experimental teeth was significantly higher (125 +/- 36, P = .001) than in the contralateral intact teeth (46 +/- 17). Access cavity preparation significantly increased the strain (327 +/- 98, P = .019) on the experimental teeth compared with the preoperative strain. Cleaning/shaping (355 +/- 113) and root filling (346 +/- 89) did not significantly increase (P = 1.00) the strain compared with the strain determined after endodontic cavity preparation. Composite core restoration in the experimental teeth (106 +/- 41) resulted in a significant reduction in the strain compared with the values recorded after an endodontic access cavity (P = .002) and was similar to the preoperative strain values (P = 1.00) but was significantly higher than the strain values in contralateral intact teeth (P = .001). Conclusions: The coronal strain on the buccal surface of mandibular first molars significantly increased with access cavity preparation, which did not increase further after cleaning/shaping or root filling. A significant reduction in the strain induced by root canal treatment steps was evident after composite core restoration.