| The restoration of endodontically treated teeth is a common aspect of dental practice that involves a range of treatment options of varing complexity, such as the length, diameter, design of post, the materials of post and core, the ferrule, etc. The challenge may be complicated by substantial loss of coronal tooth structure and the ability to predict restorative success.Many study suggest that the 360 degrees circumferential 2-mm ferrule would enhance the fracture resistance of endodontically treated teeth. If there is no circumferential 2-mm ferrule available, some authors also suggest that the upper central incisors with incomplete ferrule exhibited higher loads when the remaining coronal tooth structure located in palatal aspect than in facial aspect. Because of the differences of contour and load aspect between incisor and premolar, it is uncertain about how the location of remaining tooth structure affect the fracture resistance of mandibular premolar. Some in vitro studies and theoretical analysis suggest that the presence of 2mm circumferential ferrule rendered the design of post and core nonsignificant. But it is yet uncertain about how the design of post and core affect the fracture resistance of teeth if there is incomplete ferrule.The purpose of this study was to compare fracture resistance of endodontically treated mandibular premolars with different ferrule restored with two different post-and-core systems.In this study, 48 extracted mandibular premolars were endodontically treated. The teeth were randomly divided into 6 groups(A-F) with 8 teeth in each group. All teeth were sectioned 2mm above the CEJ. In group A and group B, the 360 degrees circumferential 2-mm ferrule were remained; In group C and group D the one half of tooth structure were removed buccally; in group E and group F, the one half of tooth structure were removed lingually.Then the teeth in group A, C and E were restored with cast post and core, and the teeth in group B, D and F were restored with prefabricated post and resin core. All teeth were restored with metal crowns. A universal testing machine compressively loaded the tooth specimens from the middle of the occlusal surface at a speed of 2mm/min at an angle of 30 degrees to the long axis of teeth until failure occurred.Results:The median failure load of group A to F was:1.1324KN,0.9811KN,0.8060KN,0.6495KN,0.7843KN,0.5563KN. There was no significant difference between group A and B, group C and E, group D and F(P>0.05). There was significant difference between group AB and others, also between group C and D, group E and F(P<0.05). The major failure mode was the root frature. Only the resin cores exhibited repairable fractures.Within the limits of this in vitro study,the following conclusions were drawn:1.The mean fracture strength of endodontically treated mandibular premolars with 360 degrees circumferential 2-mm ferrule was higher than those with incomplete ferrule. The mean fracture strength was not significant different between teeth restored with cast post and core and prefabricated post and resin core when 2mm circumferential ferrule was present.2.If the ferrule was incomplete, the mean fracture strength of endodontically treated mandibular premolars was not significant different restored with the same post and core system whether the remaining tooth structure located in the buccal or lingual aspect.3.If the ferrule was incomplete, the mean fracture strength of endodontically treated mandibular premolars restored with cast post and core was higher than those restored with prefabricated post and resin core. But both of them were higher than the maximal clenching force. The fracture forms were favorable in those teeth restored with core material of lower modulus. |
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