| The physical and mechanical properties of endodontically treated teeth such as the modulus of elasticity, the mean tensile strength and shear strength are poor. So endodontically treated teeth are known to present a higher risk of biomechanical failure than vital teeth. Once the root fracture happens, the tooth often has to be extracted. Many researchers emphasize that one goal of the post-core restoration is to preserve the remaining tooth structure. However, very little is known about the resistance to fracture of endodontically treated teeth restored with newly developed post systems, for example, the glass fiber-reinforced post.Objective: This in vitro study compared the effects of 4 different post-core designs on the fracture resistance and fracture patterns of crowned, endodontically treated maxillary incisors, providing experimental basis for clinical application of glass fiber-reinforced post.Material and methods: A total of 30 recently extracted , sound human maxillary incisors of similar size were used for the study. They were divided into 5 groups of6 teeth each randomly. After endodontically treated, they were given the following treatments: Group A: prefabricated glass fiber-reinforced post and composite core, Group B: coventional Ni-Cr cast metal post and core, Group C: prefabricated titanium post and composite core, Group D: Parapost casting technique system post and core, Group E: intact endodontically treated teeth, no further tooth preparation. Teeth groups A, B, C and D were prepared, remaining 2.0mm dentine ferrule, then metal crowns were fabricated and cemented with zinc phosphate cement. Each specimen was embedded in acrylic resin 2.0mm below the cementoenamel junction (CEJ), and then secured in a universal testing machine with a special jig. A compressive load was applied at the palatal junction of incisor third and middle third of crown with 135-degree angle to the long axis of the tooth until fracture, at a crosshead speed of 1.0mm/min. Fracture loads (N) and patterns (restorable or catastrophic) were recorded.Results: 1. The failure loads obtained from destruction test were as follows: group A～474.59±40.40N, group B～525.85±41.11N, group C～516.84±48.13N, group D～531.27±53.24N, and group E～437.18±39.77N. 2. One-way analysis of variance (1-way ANOVA) results indicated that there was significant difference of destruction test values among the five groups (P<0.01). Multiple comparison (SNK) results indicated thatno significant differences were detected among the group A, B, C and D (P>0.05). Neither did group A and group E. But group B, C and D exhibited significantly higher resistance to fracture than group E (P<0.05). 3. The fracture modes included horizontal root fracture, oblique root fracture and vertical root fracture. Fractures were classified as restorable if located in the cervical third of the root and catastrophic if located below. In group A, all the teeth showed restorable root fracture. The fracture line extended from the lingual margin of metal crown toward the labial area where the specimen embeded in acrylic resin. In group B, one tooth showed oblique fracture, from the mesiodistal margin of metal crown to the labial area where the specimen embeded in acrylic resin, while the other 5 teeth were complex root fractures. The fracture lines extended from the lingual margins of metal crowns and the labial areas where the specimen embeded in acrylic resin to the root apex at vertical angles. In group C, 3 teeth showed oblique fractures just like group A, and 2 teeth showed complex fractures like group B. There was a horizontal fracture located in the middle third of the last tooth root. In group D, 5 teeth showed complex fractures like group B, the last tooth was horizontal fracture located in the middle third of root. In group E, all the teeth showed restorable root fractures. The fracture lines extended from the lingual load spots of crowns to the labial area where the specimenembeded in acrylic resin. 4. A Fisher exact test was p... |
