| Objective: This in vitro study compared the effects ofdifferent post-core systems on the fracture resistance and failurepatterns of crowned endodontically treated maxillary caninesand evaluated their restorative effect, providing experimentalbasis for clinical application.Materials and methods: A total of 24 recently extractedhuman maxillary canines of similar size were used for the study.The crowns of all teeth were sectioned at 2.0mm above thelabial cement-enamel junction (CEJ), perpendicularly to thelong axis of the teeth. All teeth were divided into four groups ofsix teeth each randomly. After endodontically treated, the teethwere restored with the following posts and cores: Group A:quartz fiber reinforced post and composite core; Group B:carbon fiber reinforced post and composite core; Group C:zirconium post and heat pressed ceramic core; Group D:conventional Ni-Cr cast metal post and core. All the teeth wereprepared, remaining 2.0mm dentine ferrule and 1.0mm shoulderat the CEJ, after all the posts and cores being cemented withC&B cement. And then, the metal crowns were fabricated andcemented with C&B cement. Each specimen was embedded inacrylic resin 2.0mm below the CEJ and then secured in aCMT7104 universal load-testing machine with a special jig. Acompressive load was applied at the palatal junction of incisorthird and middle third of crown with 135degree angle to thelong axis of the tooth until fracture , at a crosshead speed of1.0mm/min. Fracture loads (N) and patterns (restorable orcatastrophic) were recorded.Results: (1) the mean failure loads obtained fromdestruction test were as follows: group A (quartz fiber reinforcedpost and composite core): 620.7±73.2N, group B (carbon fiberreinforced post and composite core): 630.9±73.4N, group C(zirconium post and heat pressed ceramic core): 908.9±69.5N,group D (conventional Ni-Cr cast metal post and core):865.0±75.8N. (2) One-way analysis of variance (1-way ANOVA)results indicated that there was significant difference ofdestruction test values among the four groups (P <0.05).Multiple comparison (SNK) results indicated that nosignificant differences were detected between the group A and B,neither did group C and D (P>0.05). But group C and Dexhibited significantly higher resistance to fracture than group Aand B (P<0.05). (3) The fracture of specimens showed thatthere were only teeth failure in group A, B and D, while ingroup C, the fractures involved posts and teeth. The fracturemodes of the teeth included horizontal root fracture, obliqueroot fracture, vertical root fracture and complex root fracture.The fracture modes were classified as restorable fracture andcatastrophic fracture, which were located in the cervical thirdand in the middle or apical third of the root, respectively. Ingroup A, five teeth showed oblique root fracture in the cervicalthird with fracture lines extending from the palatal margin of themetal crown toward the labial surface where the specimenembedded in acrylic resin and oblique fracture in the middlethird of one teeth root (Fig.8 group A and Fig.9). In group B,five teeth showed oblique root fracture in the cervical third quitesimilar to those found in the group A and one oblique fracture inthe middle third of one teeth root with cracks extending apical(Fig.8 group B and Fig.10). In group C, all the teeth showedfavorable root fracture, and all zirconium posts fractured wherethey exited the cores (Fig.8 group C and Fig.11). In group D,Three different failure types were recorded including horizontalfracture in the middle third of one teeth root, the obliquefracture of one tooth in the apical third and four complex rootfractures like in group A (Fig.8 group D and Fig.12). (4) AFisher exact test was conducted for statistical evaluation of thefracture patterns. The results showed the differences werestatistically significant among the four groups (P < 0.05).Multiple comparison results indicated significant differencesbetween group D and group A,B,C (P<0.05).There was nosignificant difference among the group A ,B and C (P>0.05).Conclusions: 1 With 2.0mm dentine ferrule, the toothrestored with the three metal-free post-core systems (quartzfiber reinforced post with composite core, carbon fiber... |
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