| Background:Defected teeth becomes fragile and easy to fracture after root canal treatment and usually restored with post and core crown, post and core crown can repair defected tooth and less easy to fractured. Cast metal post system and fiber post and composite system werecommonly used. There was no answer how to choose the systems.Objectives:Comparative evaluation of the reinforcing effect of different post systems in the restoration of endodontically treated human molar with different defect of the crown.Materials and Methods:110 extracted human molars were endodontically treated, and they were used for three different experiments.40 maxillary molars were used in the first experiment,and were divided into 4 experimental groups for differet defect of the crown. Each group was prepared according to numbers of residual walls ranged from 1 to 4 and named with A B C and D. Then each group was divided into two subgroups with one restored with fiber posts and the other with cast metal posts.Each tooth was restored with a complete metal crown. Then a quasi-statically load was applied in a universal testing machine 30°to the long axis with a crosshead speed of 1 mm/min until fracture.40 maxillary molars were used in the second experiment,and were divided into 4 experimental groups for the uniform height of the residual coronal dentin.defined as 0-,1-,2-, or 3-mm from the cemento-enamel junctionand named with A B C and D.Then each group was divided into two subgroups with one restored with fiber posts and the other with cast metal posts.Each tooth was restored with a complete metal crown. Then a quasi-statically load was applied in a universal testing machine 30°to the long axis with a crosshead speed of 1 mm/min until fracture.The last 30 mandible molars were used in the third experiment. All molars were decoronated 2mm above the cementoenamel junction and divided into 3 experimental groups according to the length of post space preparation:3mm,5mm and 7mm. and named with A B and C. Each group was divided into two sub-groups with one restored with fiber posts and the other with cast metal posts.Each tooth was restored with a complete metal crown. Then a quasi-statically load was applied in a universal testing machine 30°to the long axis with a crosshead speed of 1 mm/min until fracture.Fracture mode was analyzed for all the samples. Results from the four test groups were compared and analysed using one-way ANOVA test and the Post-hoc Bonferroni test to demonstrate differences between pairs of groups. Results of sub-groups were compared and analysed using t test.Results:It is better to restore the molar with fiber post with the decreasing number of the residual wall of tooth. It is better to restore the molar with cast metal post with the crown tissue lost. It is better to restore the molar with fiber post if there were residual crown tissue of tooth. It is better to restore the molar with fiber post if the post was short. It is better to restore the molar with cast metal post if the post was long.The second experiment results revealed that the fracture resistance of the tooth in A 1, B1, C1 and D1 sub groups were 1.230±0.114、1.497±0.074\1.433±0.234 and 3.108±0.313KN respectively and in A2, B2, C2and D2 sub group were 1.198± 0.061、1.632±0.128、2.128±0.475 and 3.471±0.543KN respectively. There were no significant difference between A1, B1, and C1 sub groups. The fracture resistance of D1>A1, B1, and C1 sub groups. There were no significant difference between A2 and B2 sub groups, the same to B2 and C2 sub groups. The fracture resistance of A2< B2 sub groups and D2> A2, B2, C2 sub groups. There were no significant difference between the two sub groups in A, B, and D groups. The fracture resistance of C2 was significantly higher than C1 sub group.The third experiment results revealed that the fracture resistance of the tooth in A 1, Bl and C1 sub groups were 1.433±0.351、4.476±0.166 and 3.583±0.803KN respectively and in A2, B2 and C2 sub group were 2.128±0.713、2.092±0.267 and 2.310±0.518KN respectively. There were no significant difference between sub groups of fiber post. There were no significant difference between B1 and C1 sub groups. The fracture resistance of C1> A1 sub groups and B1> A1 sub groups. The fracture resistance of B1 and C1 was significantly higher than B2 and C2 sub groups respectively. There were no significant difference between the two sub groups in A groups.Conclusion:It is better to restore the molar with fiber post if the number of the residual walls was less than 3. It is better to restore the molar with cast metal post if the number of the residual walls was more than 3. It is better to restore the molar with cast metal post if the residual tissue of the teeth was less than 1 mm. It is better to restore the molar with fiber post if the residual tissue of the teeth was more than 1 mm. It is better to restore the molar with fiber post if the post was shorter than the crown. It is better to restore the molar with cast metal post if the post was longer than the crown. |
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