An In Vitro Study Evaluating The Effect Of The Ferrule Design On The Fracture Resistance Of The Endodontically Treated Teeth Restored With Different Post-and-Core Materials

Post-and-core crown had been a conventional method of restoringendodontically treated teeth when inadequate tooth structure remained andthe resistance and retention of the restoration could be gained by theplacement of the posts in the root canals. If enough tooth structure remainedin the coronal roots, the design of the ferrule would strengthen the fractureresistance of the endodontically treated teeth restored with dowel crowns. Iffor the subgingival roots, some methods should be done first to expose thecervical section of the roots, such as gingivectomy, crown lengthening or theforced eruption method, but few studies were found for the restoration of thesubgingival roots recently. This study used the prepared endodonticallytreated root models with simulated crown lengthening procedure and theforced tooth eruption method respectively to study the effects of differentferrule designs on the fracture resistance of the endodontically treated teethrestored with different post and core systems.PartⅠEffect of ferrule length on fracture resistance ofendodontically treated teeth restored with differentpost-and-core materials Objective: To investigate the effect of a crown-lengthening ferrule on thefracture resistance of endodontically treated teeth restored with two dowel-core systems.Methods: Thirty-two extracted mandibular first premolars were eachsectioned perpendicular to the long axis at a point 1.0 mm occlusal to thebuccal cementoenamel junction. Following endodontic treatment, the teethwere assigned randomly to 4 groups: cast Ni-Cr alloy dowel-core with noferrule (Group A1), cast dowel-core with 2.0 mm ferrule (Group A2),prefabricated carbon fiber-reinforced dowel-resin core with no ferrule(Group B1), and fiber-reinforced dowel-resin core with 2.0 mm ferrule(Group B2). The simulated crown lengthening procedure was done toprovide the ferrule design. Each specimen was embedded in a self-curedacrylic resin block from 2.0 mm apical to the margins of a cast Ni-Cr alloycrown, and then loaded at 150 degrees from the long axis in a universaltesting machine at a crosshead speed of 1.0 mm/min until fracture. Datawere recorded and analyzed using ANOVA and Fisher's exact tests, withα=0.05.Results: Mean failure loads (KN) for A1, A2, B1, B2 Groups were: 1.46(S.D. 0.45), 1.07 (0.21), 1.13 (0.30), 1.02 (0.27). Teeth restored with castdowel and core with no ferrule designs demonstrated significantly higherfracture loads(P＜0.05). There were significant differences in fracturepatterns restored with different dowel materials. Conclusion: Simulated crown lengthening with a 2.0 mm ferrule resulted inreduced fracture strengths for endodontically treated teeth restored usingtwo dowel-core systems and cast metal crowns. The fiber-reinforceddowel-resin core system reduced the severity of the root fractures.PartⅡEffect of various ferrule lengths on the fractureresistance of endodontically treated teeth restored withprefabricated fiber post-and-core systemObjective: To investigate the effect of various ferrule lengths on the fractureresistance of endodontically treated teeth restored with prefabricated carbonfiber post-and-core system.Methods: Thirty-two extracted endodontically treated mandibular firstpremolars were sectioned perpendicular to the long axis at a point 1.0 mmocclusal to the buccal cementoenamel junction (CEJ). All the preparedendodontically treated root models were divided into four groups accordingto the ferrule lengths from 0 mm to 3.0 mm with 1.0 mm interval each(Group A, B, C and D). The simulated crown lengthening procedure wasdone to provide the ferrule design. After restoration with prefabricatedcarbon fiber post-and-core system, each specimen was embedded in aself-cured acrylic resin block from 2.0 mm apical to the margins of a cast Ni-Cr alloy crown, then loaded at 150 degrees from the long axis in auniversal testing machine at the crosshead speed of 1.0 mm/min untilfracture. Data were recorded and analyzed using ANOVA and Fisher's exacttests, withα=0.05.Results: Mean failure loads (KN) for A, B, C, D Groups were: 1.13(S.D.0.15), 1.27(0.18), 1.02(0.11) and 1.05(0.12). Compared to Group C andGroup D, Group B demonstrated significantly higher fracture strengths(P＜0.0S).Conclusion: Simulated crown lengthening with a ferrule length more than2.0 mm resulted in reduced fracture strengths for endodontically treatedroots restored with prefabricated carbon fiber post-and-core system and castmetal crowns.PartⅢEffect of the forced eruption and ferrule design onthe fracture resistance of the endodontically treated teethrestored with prefabricated fiber post-and-core systemObjective: To investigate the effect of different ferrule lengths on thefracture resistance of the endodontically treated teeth restored withprefabricated fiber post-and-core system.Methods: Twenty-four extracted endodontically treated mandibular first premolars were sectioned perpendicular to the long axis at a point 1.0 mmocclusal to the buccal cementoenamel junction (CEJ). All the preparedendodontically treated root models were divided into three groups accordingto the ferrule lengths from 0 mm to 2.0 mm with 1.0 mm interval each(Group A, B and C). The simulated forced eruption method was done for theferrule design in the cervical tooth structure. After restoration withprefabricated carbon fiber post-and-core system, each specimen wasembedded in a self-cured acrylic resin block from 2.0 mm apical to themargins of a cast Ni-Cr alloy crown, then loaded at 150 degrees from thelong axis in a universal testing machine at the crosshead speed of 1.0mm/min until fracture. Data were recorded and analyzed using ANOVA andFisher's exact tests, withα=0.05.Results: Mean failure loads (KN) for A, B, C Groups were: 1.13(S.D. 0.15),1.63(0.14) and 1.92(0.19). There were significant differences among thethree groups (P＜0.05).Conclusion: The combination of the simulated forced eruption and moreapical crown margin placement to provide a ferrule more than 1.0 mm onthe endodontically treated teeth resulted in the significant benefit onstrengthening the fracture resistance of the endodontically treated roots.