Effect Of Retaining Position Of Mandibular Incisor Dentine Collar On The Flexural Strength Of Fiber Post-core Restoration

Objectives:In order to provide a scientific basis for the clinical restoration of mandibular incisor Post and Core Crown PCC,the effects of different dentin shoulder and collar positions on the flexural strength of five groups of mandibular incisor were tested and analyzed by in vitro mechanical testing method.Methods:Forty single Root Canal mandibular incisors extracted due to periodontal disease were collected for Root Canal Therapy(RCT),and randomly divided into 5 groups:group A:shoulderless group;Group B:Dental shoulder and collar with intact single wall of labial side;Group C:dental shoulder and collar with intact lingual single wall;Group D:group with intact dentin shoulder and collar with single wall near the middle;Group E:retain a full ring of dentin neck shoulder collar group.The dentin shoulder collar was prepared with a height of 2mm and a thickness of 1mm.Fiber Post FP,Composite Resin Core CRC and metal crown were used to repair.The finished resin post-core crown of the lower anterior tooth is completely embedded in the self-coagulation resin with a height of 3 cm and a thickness of 2cm from the base from 2mm below the cement-enamel junction CEJ,and the embedding model is fixed on the electronic universal tester.Static loading force was applied at a loading speed of 0.5mm/min until the tooth was broken.The corresponding fracture load and fracture mode of each isolated tooth sample when the tooth was broken were measured and recorded.Results:1 Comparison of load values between each experimental group:There were significant differences between A and B,C,D and E groups(P<0.05),which was statistically significant;There were significant differences between B,C and D groups(P<0.05),which was statistically significant;There was no significant difference between group B and group E(P>0.05),which was not statistically significant.There was significant difference between group C,group D and group E(P<0.05),and there was significant difference between group D and group E(P<0.05),which was statistically significant.The mean value of group B and E was greater than that of group A,C and D.2 Comparison of the flexural strength of each experimental group2.Comparison of the flexural strength of each experimental group.\2 Average fracture load of each group:One-way variance test showed that there were significant differences in the fracture loads among the five groups(P<0.05),which was statistically significant.The mean value of fracture load in group A is the smallest,while that in group E is the largest.3 Comparison of the fracture modes of each group of specimens:There were 2 cases of irreparable fracture in group A and group C.B and E are all repairable fractures.One case of irreparable fracture was found in group D.The repairable and irrepairable fractures were 87.5%and 12.5%respectively in the whole sample.(Group A:No shoulder collar group;Group B:Dental shoulder and collar with intact single wall of labial side;Group C:dental shoulder and collar with intact lingual single wall;Group D:group with intact dentin shoulder and collar with single wall near the middle;Group E:retain a full ring of dentin neck shoulder collar group)Conclusion:1 The retention of intact dentin collar at different positions of mandibular incisors directly affects the flexural strength of post-core crown restoration;2 The flexural resistance of the mandibular incisor with a complete dentine collar on the neck and a complete dentine collar on the stressed side is the strongest.3 The fracture pattern of the intact dentine shoulder collar on the stressed side of the mandibular incisor is conducive to the secondary restoration.