| Objective:After root canal treatment,the loss of dental tissue and other reasons will lead to the decline of the anti-folding ability of teeth,resulting in the occurrence of tooth fracture.The new endodontic access cavity based on the concept of minimally invasive emphasizes the retention of more tooth tissues,such as peri-cervical dentin and marginal ridge,in order to increase the fracture resistance of endodontically treated teeth.This experiment studied the changes of the fracture resistance of the maxillary first premolar used new endodontic access cavity based on the concept of minimally invasive endodontics,and explored the effects of peri-cervical dentin and marginal ridge on the fracture resistance of the endodontically treated teeth,so as to provide an experimental basis for the clinical selection of appropriate endodontic access cavity to reduce the incidence of tooth fracture after root canal treatment.Method:A total of 88 intact adult maxillary first premolars in vitro were collected.No caries and fillings were required,and no hidden cracks and root cracks were observed under microscope.According to the loss of marginal ridge,they were randomly divided into groups A-E,including complete marginal ridge,missing one side marginal ridge,missing two sides marginal ridge,missing one side marginal ridge was repaired and missing two sides marginal ridge was repaired.In each group,they were randomly divided into group 1and group 2 according to the endodontic access cavity,group 1 used the traditional endodontic access cavity,and group 2 used the contracted endodontic access cavity based on the concept of minimally invasive,Group F was the control group without any treatment.After all the detached teeth were fixed,CBCT images were taken,and the endodontic access cavity was designed and measured on CBCT.The measured values were transferred to the detached teeth for opening and root canal preparation using the Pro Taper Gold root canal preparation system.After preparation,the experimental group and the control group were used to conduct the compression test with universal mechanical tester.By observing the maximum load that the samples could bear and the direction and position of the fracture line,the fracture resistance and fracture mode between different groups were compared.Results:1、The maximum load when the isolated teeth of each group are fractured is:Group A1:(684.85 ± 64.87)N;Group A2:(710.88 ± 55.78)N;Group B1:(480.69 ± 56.91)N;Group B2:(493.69 ± 51.03)N;Group C1:(310.33 ± 46.44)N;Group C2:(314.32 ± 51.44)N;Group D1:(596.81 ± 54.04)N;Group D2:(611.34 ± 50.01)N;Group E1:(573.69 ± 50.15)N;E2 group:(500.55 ± 32.95)N;Group F(control group):(890.81 ± 70.97)N.The data of each group were less than the control group(p < 0.05).The difference was statistically significant,indicating that the fracturel resistance of the premolars in each experimental group was less than that of the intact teeth in the control group.2、Group A2 > group A1,group B2 > group B1,group C2 > group C1,group D2 > group D1,group E2 > group E1,the difference was not statistically significant(p >0.05),indicating that the contracted endodontic access cavity based on the concept of minimally invasive can not significantly improve the fracture resistance of maxillary first premolar after root canal treatment compared with the endodontic access cavity.3、Group A1 > group B1 > group C1,group A1 > group D1 > group B1,group A1 > group E1 > group C1,the difference was statistically significant(p < 0.05).It showed that when the traditional endodontic access cavity was used,the loss of marginal ridge would reduce the fracture resistance of maxillary first premolar after root canal treatment,while the repair of missing marginal ridge could restore the fracture resistance,but it was still lower than that when the marginal ridge was intact.4 、 Group A2 > group B2 > group C2,group A2 > group D2 > group B2,group A2 >group E2 > group C2,the difference was statistically significant(p < 0.05).It showed that when the contracted endodontic access cavity based on the concept of minimally invasive was used,the loss of marginal ridge would reduce the fracture resistance of maxillary first premolar after root canal treatment,while the repair of missing marginal ridge could restore the fracture resistance,but it was still lower than that when the marginal ridge was intact.5、All the isolated teeth in the control group had mesial and distal fractures,and most of the isolated teeth in the experimental group also had mesial and distal fractures,only one isolated tooth in group B1 had buccal and lingual fractures,and one isolated tooth in group A2 had buccal lingual + mesial and distal fractures There was no significant difference among the groups(p > 0.05),which showed that the fracture line of maxillary first premolar was mesial and distal fracture.6、In the control group,the isolated teeth were broken irreparably.Most of the isolated teeth in the experimental group also had irreparable fracture,and only one isolated tooth in the C1 group had repairable fracture at dentin level.There was no significant difference among all groups(p > 0.05),indicating that the fracture of maxillary first premolars after root canal treatment was difficult to repair.Conclusion:1、The contracted endodontic access cavity based on the concept of minimally invasive can not improve the fracture resistance of isolated teeth,so it should be used as appropriate in clinical practice.2、The damage of marginal ridge will reduce the fracture strength of teeth after root canal treatment,and the repair of the lost marginal ridge can enhance the fracture strength to a certain extent,suggesting that the marginal ridge should be retained as much as possible in clinical practice.3、The most common fracture mode of maxillary first premolars after stress is mesial and distal fracture from crown to root,and the fracture is mostly below the cemento-enamel junction,which is difficult to repair. |
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