Effect Of Different Forms Of Resin Onlays On The Fracture Resistance Of Endodontically Treated Premolars

Objective In this study,resin onlays with different forms was used to repair endodontically treated premolars.And the fracture resistance of premolars after restoration was compared.Hoping to provide partial reference for oral clinical work.Methods A total of 120 maxillary first premolars were collected and randomly divided into 12 groups.Different premolar preparation was performed according to the groups:A1～A4 were the occlusal surface defect group(O),B1～B4 were the distalocclusal surface defect group(DO),and C1～C4 were the mesio～occlusal-distal surface defect group(MOD).Each group has four subgroups.Subgroup 1 is:only covering functional cusp+retention depth 2 mm;Subgroup 2:full coverage of the tooth cusps+retention depth of 2 mm;Subgroup 3:only covering functional cusp+retention depth of 3 mm;Subgroup 4 was:full coverage of the tooth cusps+retention depth of 3 mm.After tooth preparation,FiltekTMZ350XT nanocomposite resin was used to make onlays for premolars restoration,and the onlays were cemented by Rely X U200 adhesive.The cemented samples were soaked in a 37℃ incubator for preservation about 24 hours.Before the experimental test,the samples were treated with root embedding and perfusion.The fracture strength.of each group was tested respectively,and the final force value and failure mode was recorded.Results Group A2(occlusal surface defect+retention depth of 2mm+full coverage of the tooth cusps)had the highest average breaking force value(1973.4±269.4N).The type of tooth preparation had statistical significance on tooth fracture resistance(p<0.05);Among them,the type of cusp coverage and the type of tooth defect had statistical significance on tooth fracture resistance(p<0.05),while the 2mm and 3mm retention depth had no statistical significance(p>0.05),but the 3mm groups were more prone to irreparable failure than the 2mm groups.There was no significant difference in the proportion of failure modes among all groups(p>0.05).Conclusion In this experiment,the type of cusp coverage had a significant impact on the fracture resistance of the restored teeth,and all cusps coverage had a stronger fracture resistance than only functional cusp coverage.The more defects the tooth had,the worse its fracture resistance was.The retention depth of 3mm and 2mm groups had no significant effect on the fracture resistance of premolars after restoration.