Abstract: [Abstract] Objective To explore the influence of different glass-fiber post lengths and the content of fiber on teeth fracture resistance, and investigate the optimal glass-fiber post length and the content of fiber when apply fiber post restorative treatment．Methods Forty-two intact single canal mandibular premolars were collected from orthodontic patients．All the teeth were endodontically treatment after cut off the crowns from the 2mm above cemento—enamel junction．Divided the mandibular premolars randomly into three experimental groups (A, B, C) 14teeth a group．The experimental groups were post lengths of 10mm(1onger than 1／1 clinical crown length),8mm(1／1 clinical crown length)and6mm (shorter than 1／1 clinical crown length) respectively with 3# fiber Post drill．Each experimental group was averagely divided into two subgroups (A1, A2, B1, B2, C1, C2 )．Group A1, B1,and C1were restored with the 42% glass fiber post, group A2, B2, C2 with 75% glass fiber post．And then,all of them were restored with resin cores and metal crowns．Fracture resistance was measured with universal testing machine and recorded the root fracture pressure data and the mode of all the teeth．Results Fracture resistance of group A of restoration was significantly lower than that of B group and C group(P<0.05)．Fracture resistances of group B was significantly lower than that of C group (P<0.05)．Conclusion Within a certain range, the longer the length of pile, tooth fracture resistance is greater when we use them to restore dental defects.The fracture resistance of fiber content75% is better than the fiber content42%．

Key words: Glass fiber post, Fiber post length, Elasticity Modulus, Fracture resistance, Fracture mode