| Recently, the indications of post-core crown have been enlarged with the further study. Many researchers have made researches on the post-core crown restoration after the residual roots drawn from subgingiva to supragingiva or crown lengthening. However, nothing is known about the post-core crown restoration after the reconstruction of the subgingival oblique fracture of dental corona and root.Objective: This in vitro study compared the effects of the post-core crown restoration after the reconstruction or not of three types of oblique fracture of dental corona and root on the fracture resistance and fracture patterns of crowned, endodontically treated maxillary incisors, providing experimental basis for clinical application.Methods: A total of 42 recently extracted, sound human maxillary incisors of similar size were used for the study. they were divided into 7 groups of 6 teeth each randomly. After endodontically treated, they were given the following treatment: Group A: the post-core crown restoration after the reconstruction of the oblique fracture from lingual surface to labial surface, Group B: the direct post-core crown restoration after the oblique fracture from lingual surface to labial surface, Group C: the post-core crown restoration after the reconstruction of the oblique fracture from labial surface to lingual surface, Group D: the direct post-core crown restoration after the oblique fracture from labial surface to lingual surface, Group E: the post-core crown restoration after the reconstruction of the oblique fracture from mesial surface to distal surface, Group F: the direct post-core crown restoration after the oblique fracture from mesial surface to distal surface, Group G: the group without the oblique fracture of dental corona and root. All external debris was removed with an ultrasonic scaler. After the oblique fracture of the teeth, the highest point of the oblique plane is 2.0mm above the cementoenamel junction(CEJ), while the lowest point is 1.5 mm below the cementoenamel junction(CEJ),namely parallel to the top of the alveolar ridge. The teeth of group G were only incised horizontally 2.0mm above the CEJ. The casting Ni-Cr alloy post-core crowns would be finished after preparing root canals, but teeth groups A, C and E just prepared root canals 24 hours later after the reconstruction. Light cured composite resin and two dentin pins with a diameter of 0.5mm were used for materials of the reconstruction in this experiment. After being reconstructed, teeth groups A, C and E were similar to group G. Each specimen was embedded in acrylic resin 2.0mm below the cementoenamel junction, and then secured in a universal testing machine with a special jig. A compressive load was applied at the palatal junction of incisor third and middle third of crown with 135-degree angle to the long axis of the tooth until fracture, at a crosshead speed of 1.0mm/min. the fracture loads (N) and patterns ( restorable or catastrophic) were recorded.Results: 1 The failure loads obtained from destruction test were as follows: Group A: 506.98±36.58N, Group B: 335.74±26.41N, Group C: 469.32±37.21N, Group D: 259.30±14.18N, Group E: 397.19±36.83N, and Group F: 347.54±33.90N, Group G: 501.91±26.84N. 2 One-way analysis of variance (One-way ANOVA) results indicated that there was significant difference of destruction test values among the seven groups (P<0.01). Multiple comparison (SNK) results indicated that no significant differences were found among the group A, C and G or between E and F (P>0.05). Neither did group E and C. But there was significantly higher resistance to fracture between group A and B or group C and D, at the same time, group B, D, E and F exhibited statistical differences than group G (P<0.05). 3 The results of fracture pattern showed that there were restorable and catastrophic fractures in each group, which are located in cervical third of the root and below respectively. Moreover, the catastrophic fractures were majority. Conclusions: 1 The reconstruction of the oblique... |
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