| Objective: The cracked tooth has not obvious early symptoms,that easily ignored and thus delay treatment.The tooth fracture is the severe consequence.Cracked tooth treatment of non-involved pulp can prevent the cracked line expand downward.At present,direct filling and onlay have been used as a common treatment method to repair cracked teeth with living pulp in clinically.In this study,the most commonly used three different materials onlays were selected.And direct filling with resin and amalgam as a control.After the experimented cracked teeth were repaired in vitro and the anti-fracture properties were compared between them,it would be the appropriate materials in theoretical basis for dentists to choose.Methods: 70 single-rooted extracted maxillary premolars for orthodontic extraction were selected.The criteria for the tested teeth include single-root,completely formed apices,caries-free and without visible fracture lines or cracks.Curette and polishing brush were used to clean the periodontal soft tissues,after that teeth were immersed in 4% saline solution at room temperature.A 3mm depth cracked line from mesial marginal ridge to distal marginal ridge was made by the specific diamond burs(minimally invasive bur).Then these teeth were randomly divided into 7 experimental groups(n=10)as follows: Group A-the normal tooth group.Group B-the experimented cracked line but without filling group.Group C-the direct resin filling control group.Group D-the direct silver amalgam control filling group.Group E-the cobalt-chromium alloy onlay group.Group F-the ultimate ceramic onlay group.Group G-the IPS e.max Press porcelain onlay group.After all the groups were repaired,they were embedded in a self-consolidating plastic block with a side length of 3 cm.Then test on the electronic universal testing machine,and the3-mm-diameter stainless steel cone was used to pressed on the occlusal surface.At the same time,it should loaeded in the same direction as the long axis of the tooth,andcontacted with the buccolingnal bevel.The test parameter was set as a force of 0.5 mm /min continuously until the sample specimen cracked.Recorded the maximum load at fracture and observed the type of sample fracture.In accordance with the location of the fracture,fractured morphology were divided into two categories: type I(located over the CEJ of the crown),type II(located underneath the CEJ of the root),the corresponding data was recorded and by statistical.Results: 1.All test results were analyzed by One-Way ANOVA: the flexural strength of group B was significantly lower than the other groups(P <0.05).The flexural strength of group E was significantly higher than that of group F and group G(P <0.01),while the difference between group F and group G was not significant(P> 0.05).The difference between the flexural strength of group C and group D was not significant too(P> 0.05).2.Type of fracture-Type II from high to low as follows: group E 100%;group B 80%;group D 70%;group C,group G 60%;group A,group F 20%.Conclusion:1.Direct filling and indirect onlay repair methods can increase the fracture resistance of cracked tooth that has been prepared the cavity.Fracture resistance between different materials are still some differences in each group.2.The fracture resistance of cobalt-chromium alloy onlay was the most stronger group.The type of destruction in these group was all the cusp and tooth fracture under stress force.3.The fracture resistance of ultimate ceramic onlay group was lower than the IPS e.max Press porcelain onlay group.Fractured morphology were mostly prosthesis broken protected the remaining healthy tooth tissue under stress. |
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