الفهرس 
Endodontically treated teethOnly 14 pages are availabe for public view
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Abstract
Statement of problem: Coronal rehabilitation of endodontically treated posterior teeth is still a controversial issue.Objective: This in vitro study was conducted to evaluate the influence of fatigue loading on fracture resistance of computer aided design/computer aided manufacturing (CAD-CAM) fabricated endocrowns restoring endodontically treated molars using different machinable blocks.Materials and methods: Forty freshly extracted human intact lower right first molars were root canal treated and were prepared in a standardized method by removing intact crown 1 mm above the CEJ with extension cavity of 3mm in depth.The specimens were divided into 4 groups (n = 10) to receive CAD/CAM fabricated endocrowns using four materials. Anatomically shaped endocrowns groups were manufactured using polymer infiltrated ceramics (VITA ENAMIC blocks: group VE) and super translucent zirconia (Katana Zirconia STML: group KZ). Layered endocrowns groups were manufactured using Lithium disilicate ceramics (IPS e.max CAD veneered with IPS e.max Ceram: group EM) and polyether-ether ketones (BioHPP veneered with Visio.Lign: group BH). Cervico-occlusal thickness of restoration was 5.5mm at functional cusps and 6mm at non-functional cusps.Cementation of the specimens were done using dual cure resin adhesive (Panavia F2). Half of the specimens of each group were subjected to fracture resistance test by a universal testing machine, while the other half subjected to thermocycling(15000 cycles, 5-55 C, 30 sec dwell time) and chewing simulator in ACTA pneumatic fatigue tester with a load from 50 N to 150 N and the load was applied for 600,000 cycles to simulate 2.5 years with a loading frequency 6 HZ. Specimens that survived cyclic loading were loaded to failure on universal testing machine to calculate the residual fracture strength after fatigue. Scanning electron microscopy was performed to analyze failure modes to reveal if it was restorable or nonrestorable fracture. Data were analyzed using ANOVA analysis of variance and Bonferroni post hoc test (α=0.05).Results: Materials used, layering technique and fatigue loading had an effect on the fracture resistance. Regarding the material used, the initial fracture resistance of all test groups showed statistical significance difference. KZ group had the highest value (1810.20± 119.56 N) and BH had the lowest value (579.50± 76.15 N).Regarding the layering technique, the initial fracture resistance of anatomically shaped endocrowns (1505.850±342.03 N) was significantly higher than those of layered specimens (894.45±332.25 N). In addition, fracture resistance after fatigue loading of anatomically shaped endocrowns (1345.01±342.03 N) was significantly higher than those of layered specimens (807.35±316.8 N). Regarding the fatigue loading the reduction of fracture resistance was significant for KZ and BH groups and non-significant to VE and EM groups (1588.30±216.25 N), (502.60±11.53 N),(1101.70±77.05 N) and (1112.10±74.12 N) respectively. Failure modes of KZ and EM groups showed high percentage of non-restorable fractures, while VE and BH groups showed high percentage of restorable fractures.Conclusion: Yttrium-stabilized zirconia (YSZ) showed the highest fracture resistance after fatigue loading although its mode of failure was non-restorable.Poly infiltrated ceramics is the proper material to be used as an endocrown material because of its high resistance to masticatory loading. Even if failure occurred, mode of failure is restorable.