Fracture Resistance Of Endodontically Treated Teeth With Flared Root Canal Restored By Different Post And Core Systems After Rehabilitation

Objective: This in vitro study compared the effects of endodontically treated teeth with flared root canal restored by different post and core systems after intraradicular rehabilitation or not on the fracture strength and fracture patterns. The two factors were evaluated to provide experimental basis for clinical application.Methods: A total of 45 recently extracted, sound human maxillary incisors of similar size were used for the study. They were divided into 9 groups of 5 teeth each randomly based on the treatments of different root canal shapes and post-core systems. Group A1: normal root canal with cast Ni-Cr alloy post and core, Group A2: normal root canal with cast Au-Pd alloy post and core, Group A3: normal root canal with prefabricated glass fiber-reinforced post and composite core, Group B1: flared root canal with cast Ni-Cr alloy post and core, Group B2: flared root canal with cast Au-Pd alloy post and core, Group B3: flared root canal with prefabricated glass fiber-reinforced post and composite core, Group C1: rehabilitated root canal with cast Ni-Cr alloy post and core, Group C2: rehabilitated root canal with cast Au-Pd alloy post and core, Group C3: rehabilitated root canal with prefabricated glass fiber-reinforced post and composite core. All the teeth were prepared, remaining 1~2mm dentine ferrule and 0.5mm shoulder at the enamelo-cemental junction, then covered by the cast Ni-Cr alloy full crowns. Each specimen was embedded in acrylic resin 2mm below the enamelo-cemental junction, and then secured in a universal testing machine with a special jig. A compressive load was applied 3mm below the palatal incisor edge of the crown with 135-degree angle to the long axis of the tooth until fracture, at a crosshead speed of 1mm/min. Fracture loads(N) and patterns (restorable or catastrophic) were recorded.Results: 1 The failure loads(N) obtained from the test were as follows: A1, 531.32±44.14; A2, 501.38±58.23; A3, 516.94±40.95; B1, 288.60±51.95; B2, 382.80±60.69; B3, 365.58±49.62; C1, 514.36±59.83; C2, 473.20±77.01; C3, 486.08±51.85.2 Two- way analysis of variance (2-way ANOVA) results indicated that the factor of root canal shapes had significant effect on the fracture strength(P<0.05), but the factor of post-core systems didn't (P>0.05). The two factors didn't have the interaction in the test(P>0.05). Multiple comparison(SNK) results indicated that there were significantly higher failure loads in the Group C than Group B(P<0.05). There was no statistical difference between the Group A and C (P>0.05). Group B2, B3 exhibited higher fracture strength than Group B1(P<0.05), but no sign- ificant difference was observed between Group B2 and B3 (P>0.05). There was no statistical difference between either two groups among the other six groups(P>0.05). 3 The fracture patterns were classified as restorable fracture and catastrophic fracture, which were located in cervical third of the root and below, respectively. In Group A1, all the five teeth showed catastrophic root fractures. In Group A2, B1, B2, C1, one restorable root fracture and four catastrophic root fractures were showed. In Group A3, all the five teeth showed restorable root fractures. In Group B3, C3, four restorable root fractures and one catastrophic root fracture were showed. In Group C2, two restorable root fractures and three catastrophic root fractures were showed. 4 A Chi-square test was conducted for statistical evaluation of the fracture patterns. The results showed that the difference was significant among the Group 1, 2, 3(P<0.05). The partitions ofχ2 method results indicated that there was significant difference between the group 1, 2 and 3(P<0.0125). But there was no significant difference between the Group 1and 2( P>0.0125).Conclusions: 1 The endodontically treated teeth with flared root canal could be reinforced the fracture resistance after intraradicular rehabilitation. 2 After intraradicular rehabilitation, there was no significant difference of the fracture resistance of endodontically treated teeth, restored by different post and core systems. 3 The glass fiber-reinforced post and composite core system has the superiority of restorable root fractures. 4 With the flared root canal, the endodontically treated teeth restored by cast Ni-Cr alloy post and core system showed the lowest fracture strength.