The Fracture Behavior Of Premolar Teeth With Class Ⅱ Cavities Restored By Polyethylene Fiber

Objective:To evaluate the effect of five restorative techniques and polyethylene fiber on the fracture load and fracture mode of endodontically treated single-rooted maxillary premolars with classⅡcavities in vivo,and to provide some alternative for non-vital teeth with minor loss of coronal dentin.Methods:60 extracted human single-rooted maxillary premolars were distributed into six groups. Group 1 remained untreated and served as control group. The other five groups were endodontically treated and prepared with standardized MO (mesio-occlusal) cavities. Group 2 were restored with composite resin. Group 3 were restored with quartz fiber posts and direct composite resin, and group 4, the polyethylene fiber post systems and direct composite resin filled. Cavity surface were covered with flowable resin in group 5, and polyethylene fiber was placed into the bed of resin in a buccal to lingual direction before the composite restoration was placed. In group 6, the teeth were restored with composite resin, then a groove 2-mm wide and 1.5-mm depth was prepared on the ccclusal surface of the restorations between the cusp and buccal to lingual side. The groove overlap the buccal and lingual sides by 3 mm. Polyethylene fiber was inserted in the groove in combination with flowable resin and covered with composite resin just as group 5. All specimens were thermocycled for 10000 cycles between 5 oC and 55 oC and then were loaded in an universal testing machine until failure. Data were recorded and submitted to ANOVA and Tukey post hoc test. All specimens fracture modes were evaluated.Results:The mean load necessary to fracture the samples in each group was: G1: 1191.04±362.59^a, G2: 578.81±117.87^b, G3: 909.33±250.20^c, G4: 831.56±220.16^c, G5: 900.66±185.57^c, G6: 1161.31±184.26^a. The incidence of repairable fracture mode were: 20%^a,20%^a,50%⁹(ab),80%^bc,100%^c,100%^c。Different superscript letters demonstrate significant difference between groups.Conclusion:The use of quartz fiber posts and polyethylene fibers in premolars with classⅡcavities can significantly increase the fracture load. Especially when the fibers were used over or under the MO composite restorations, the fracture mode can also be significantly improved.