Abstract: Objective To evaluate the effect of different restoration methods on fracture resistance of endodontically treated
teeth. Methods Fifty intact extracted maxillary first premolars were randomly divided into 5 groups. Medial-occlusal cavity
models were established in all the test groups (B-E) according to the same standard, followed by treatments with defect
exposure only, defect filling with light cured composite resin, indirect resin inlays, or light cured composite resin combined
with Biosplint fiber. Each specimen was tested using a universal test machine at 1.00 mm/min until fracture and the fracture
load was recorded. The load angle was 45 degree to the long axis of the teeth, and the load was pointed to the middle of the
lingual surface on the buccal cusp. The fracture resistance was analyzed statistically. Results The mean load to cause fracture
of the samples in each group group A to E was 1.27 ± 0.41, 0.23 ± 0.17, 0.55 ± 0.31, 0.89 ± 0.40, and 0.98 ± 0.34 kN, respectively,
showing significant differences between the groups. Conclusion The fracture resistance of the teeth is reduced after
endodontic therapy, but can be increased significantly by restoration with composite resin inlay or light cured composite resin
combined with Biosplint fiber.