Methods: Forty maxillary central incisors were randomly divided into 2 control groups (Group 1 and 2: 5 teeth of each) and 3 experimental groups (Group 3, 4 and 5: 10 teeth of each). Group 1: filled access opening with resin composite, Group 2: restored with quartz fiber post without resin composite core, Group 3, 4 and 5: restored with quartz fiber post in different heights (2, 4, 6 mm, respectively) in 6 mm resin composite core. Specimens were loaded with 130 degree at the palatal surface of all-ceramic crown by the universal testing machine at a crosshead speed of 0.5 mm/min. The highest fracture load and mode of failure of each were recorded.
Results: The highest fracture resistance force was observed in Group 2 (290.38±48.45 N) and respectively decreased in Group 1 (238.98±26.26 N), Group 5 (228.35±58.79 N), Group 4 (221.43±38.74 N) and the least was observed in Group 3 (199.05±58.00 N). According to one-way ANOVA and Duncan's test (p≤.05), there was no statistically significant increase in the force from Group 3 to Group 5 and the force in Group 2 was significantly higher than that of the experimental groups.
Conclusion: 1.There is no statistical significance in force among the experimental groups. 2.The tooth structure is critical factor in fracture resistance.