Fracture Resistance Of Maxillary Premolars With Mesial Occlusal Cavity Restored With CAD/CAM Ceramic Restorations

Objective:To assess the influence of fracture resistance of CAD/CAM ceramic restoration selection for maxillary premolars with mesial occlusal cavity and its effect on the crack propensity.Methods:Thirty-two intact and single-rooted human maxillary first premolars,freshly extracted because of orthodontic treatment within half a year recently,were randomly assigned into four groups(n=8).The control group A consisted of sound unprepared teeth.Teeth in the other 3 groups were endodontically treated and all received cavity preparation designs: MO(mesio-occlusal preparation).Postendodontic restorations were: inlay(B),onlay(C),fullcrown(D)with CAD/CAM milling lithium disilicate reinforced ceramics.Specimens then were embedded vertically in a mould filled with auto-polymerizing acrylic resin to a level of 2 mm apical to the cemento-enamel junction.Then all the specimens were subjected to fracture failure tests by a universal testing machine,loaded with an incremental force at a speed of 1.0mm per min on the buccal surface of the palatal cusps at an angle of 30° to the long axis of the tooth.The fracture loads were recorded and analyzed by One-way ANOVA(α=0.05).Fracture modes were recorded based on the degree of tooth structure involvement.Results:The mean of fracture load is expressed by (?)±s.The group A presented the highest fracture resistance values(778.00±56.14N)and the group B presented the lowest fracture resistance values(425.13±56.28N).The One-way ANOVA showed that there were significant differences(P<0.001)between group B and group A,C,D;no significant difference was found between group C and group A,D(P>0.05),or between group D and group A(P>0.05).The group B and C was mainly in the form of repairable fracture,and the group D was mainly in the pattern of unrepairable fracture.Conclusions: 1.Postendodontic maxillary premolars with mesial occlusal cavity can recover the strength of the lost dental tissue,when restored with onlay or fullcrown with CAD/CAM milling lithium disilicate reinforced ceramics.2.Under the conditions of this in vitro study,onlay with CAD/CAM milling lithium disilicate reinforced ceramics can be used as the first choice to restore endodontically treated maxillary premolars with mesial occlusal cavity.