Methods: Sixty intact extracted premolars were collected and endodontically treated. These teeth were divided into six groups and assigned to different combinations of two simulated alveolar bone conditions (normal and reduced bone height) and three post-core systems (fiber post, titanium post, and cast post-and-cores). The normal bone height and reduced bone height were set as 2 and 6 mm apical to cementoenamel junction respectively. Composite cores were built in the fiber- and titanium- post restored groups, then all teeth were covered with nonprecious alloy crowns. The tooth displacements under an oblique force on the palatal cusp were evaluated by the digital-image-correlation method. Marginal integrity before and after thermocycling and mechanical loading (TCML) tests was quantitatively assessed using the replicas methods. Finally, the teeth received an oblique load to examine the fracture strength and modes.
Results: The displacements in teeth with reduced bone were greater than those with normal bone height. Normal bone groups tended to bend under loads with the fulcrum at the palatal margin. The cast post groups showed less reduced marginal integrity rate than the other post groups. Two-way ANOVA test showed that the influence of post-core systems at the marginal integrity was more significant than bone height. With the same bone level, fiber post group showed the least fracture strength. The normal bone groups showed greater fracture strength than reduced bone groups for all post-core systems.
Conclusion: The cast post-and-core helps to maintain marginal integrity after loading. The teeth with impaired bone support exhibited greater displacements under loads and decreased fracture resistance. Both alveolar bone height and post systems are associated with the stability and the marginal adaptation of the endodontically-treated teeth. Supported by NSC 96-2320-B-006-034-MY3, Taiwan.