Endodontically treated teeth are challenging regarding their longevity and success rate, due to their
lower fracture resistance than vital teeth. The lower fracture resistance and lower stiffness of
endodontically treated teeth is mainly due to loss of tooth structure mainly due to caries, cavity
preparation and endodontic instrumentation. The restoration of endodontically treated teeth for a long
time has been post and core and a crown as a protection for the remaining tooth stucture but it has been
found out that the extra preparation for post insertion and crown restoration loses tooth structure and
hence it is less conservative. With the development of adhesive dentistry and new ceramics the partial
coverage restorations as inlay and onlays have been encouraged in such cases. This in-vitro study
evaluated the fracture resistance of endodontically treated teeth restored with inlays, onlays and fiber
post retained crowns. All restorations were fabricated from lithium disilicate (E-max). Twenty one
freshly extracted caries free mandibular molars of similar dimensions that followed the inclusion criteria

were collected. All samples were embedded in epoxy resin to a level of 2 mm below the cemento-
enamel-junction simulating bone with polyvinyl-siloxane layer between the roots and the epoxy resin

acting as a periodontal ligament. A biogenetic copy was made to all the teeth. Access cavities and
endodontic treatment till obturation were done to all the teeth. Samples were divided randomly
according to the restoration type to inlays, onlays and fiber post retained crowns. All the samples
received mesiooccluso-distal cavity of an isthmus dimensions of 5mm deep and 3mm wide with 8 ̊
divergence angle. The inlay group received MOD cavity design with a proximal box of 1mm dimension.
The onlay group received MOD cavity design with proximal box with 1mm dimension and 2mm
occlusal reduction with chamfer finish line buccaly and lingualy. The fiber post retained crown group
had MOD cavity design that received fiber post in the distal canal after gutta percha removal leaving
5mm of apical gutta percha and the post extended occlusaly 2mm below the occlusal surface and luted
with dual cure self adhesive resin cement, composite core buildup and preparation for E-max crown was
made with 2mm occlusal reduction 8 ̊ convergence angle and a 1mm chamfer finish line circuling the
preparation cervically. All samples were digitally scanned using (MyCrown, Fona) digital scanner and
twenty one lithium dislocate restorations were constructed as inlays, onlays and conventional crowns.
Samples crystallization and glazing were done according to manufacturer instructions. Restoration
surface treatment was done according to the manufacture instruction while tooth surface treatment was
done using total etch protocol and cemented using dual cure etch and rinse resin cement under a
standard load of 5kg and light cured. The samples were kept in distilled water for 24 hours at 37 oC.
Cyclic fatigue and thermo-cyclic tests were performed after 24h from cementation using a chewing

simulator for 75,000 cycles at 5̊C and 55̊C to simulate 6 months of service. After completing thermo-
dynamic fatigue tests all samples were subjected to a constant vertical load of 1mm/min till failure in a

universal testing machine. The failure modes were evaluated using digital microscope at 35X
magnification. The results were collected and statistically analyzed.