An in vitro study of the influence of remaining coronal tooth structure on the fracture resistance of endodontically-treated maxillary premolars.

Abstract

Objectives: This in vitro study investigated the relationship between the cross-sectional area and the location of remaining coronal tooth structure and the fracture resistance of restored endodontically-treated teeth. Materials and Methods: Fifty-five extracted maxillary premolars received root canal treatment and crown preparation and were randomly divided into 11 groups of five teeth each according to the number and the site of the missing axial wall(s). Impressions of the prepared teeth were taken and poured with epoxy resin to construct a die for each tooth that was then sectioned 1mm above the finish line. The surface area was measured using ImageJ software (version 1.41n. Developed by Wayne Rasband. National Institutes of Health, USA.1 All 55 prepared teeth were then restored with composite resin cores, and cast metal crowns. Specimens were thermocycled between 5°C and 55°C for 500 cycles, prior to testing. A universal testing machine was used to apply a compressive load at a crosshead speed of 1mm/min to the palatal surface of the buccal cusp of the crown at an angle of 45 degrees to the long axis of the tooth until failure. Results were analyzed using one-way ANOVA and t-tests. Results: Specimens with all axial walls intact (only access cavity) had mean fracture strength of 1380.5±393.9N. Groups that have a missing palatal wall with one or two proximal walls showed the lowest mean failure loads of 398.4N ± 149.5N and 344.7N ± 91.2N respectively. The coefficient of determination (R²) between the surface area and the fracture resistance was 0.52. Conclusions: For restored endodontically-treated upper premolars there is a positive linear relationship between the remaining dentine surface area and fracture strength. Residual dentine location influences the fracture resistance with the palatal wall having a major role in resisting force.