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Statement of problem The biomechanical properties of post systems may become more important as the amount of remaining tooth structure decreases, thus different materials may influence the characteristic strength of fatigued endodontically treated teeth. Purpose The purpose of this study was to assess the characteristic strength and probability of survival of endodontically treated teeth restored with different intraradicular post systems. Material and methods Forty human maxillary canines with similar root lengths were randomly divided into 4 groups (n=10): cast post and core, stainless-steel prefabricated post, carbon-fiber post, and glass-fiber post. Cores and metallic crowns were fabricated for all specimens. Restored teeth were exposed to mechanical fatigue (250 000 cycles) in a controlled chewing simulator. Each intact specimen was mounted in a special device and aligned at a 45-degree angle to the long axis of the tooth. A universal testing machine was used to apply a static load at a crosshead speed of 0.5 mm/min until specimen failure. The maximum value was recorded in newtons (N). Probability Weibull curves (2-sided 90% confidence bounds) were calculated for each group, and a probability of survival as a function of load at failure was plotted for the groups. Results A significantly higher characteristic strength was observed for groups carbon-fiber post (755.82 N) and cast post and core (750.6 N) ( P <.05) compared with glass-fiber post (461.35 N) and stainless-steel prefabricated post (524.78 N) groups. All the roots in the cast post and core group demonstrated catastrophic fracture, whereas the remaining groups had no root fractures. Conclusions Prefabricated posts made of glass fiber and stainless steel showed significantly lower characteristic strength and probability of survival than cast post and core, whereas crowns with carbon-fiber posts presented a single load similar to the fracture values of cast posts. [ABSTRACT FROM AUTHOR]

Statement of problem The mechanical stability of the implant-abutment connection is of fundamental importance for successful implant-supported restorations. Therefore, understanding removal torque values is essential. Purpose The purpose of this study was to evaluate the reverse torque values of indexed and nonindexed abutments of the Morse Taper system. Material and methods Twelve Morse taper implants with their respective abutments were divided into 2 groups (n=6): group NI, nonindexed abutments; and group IN, indexed abutments. Each abutment received a sequence of 2 consecutive torques for insertion (15 Ncm) at an interval of 10 minutes, and 1 reverse torque, all measured with a digital torque wrench. The Student t test with a 5% significance level was used to evaluate the data. Results Statistical analysis showed no significant difference in reverse torque values between nonindexed and indexed abutments ( P =.57). When comparing insertion torque and reverse torque values between the groups, group NI presented a mean torque loosening percentage of 8% ( P =.013), whereas group IN presented a loosening of 15.33% ( P <.001). Conclusion The use of indexed abutments for the Morse taper system presented similar biomechanical stability when compared with nonindexed abutments, both with a significant reduction in reverse torque values. [ABSTRACT FROM AUTHOR]

Statement of problem: Glass fiber posts are commonly used to provide adequate support and retention for the restoration of endodontically treated teeth, but their resistance to dislodgement depends on their adhesion to root dentin. Purpose: The purpose of this study was to assess the effect of cement type on the pull-out bond strength of fiber posts. Material and methods: Seventy maxillary canines were endodontically treated and then divided into 7 groups according to the cement used for fiber post cementation as follows (n=10): RelyX Unicem, BisCem, RelyX Luting 2, RelyX ARC, Panavia F, Enforce, and Allcem. The specimens were subjected to a pull-out bond strength test in a universal testing machine at a crosshead speed of 0.5 mm/min. The results, in newtons, were analyzed with 1-way ANOVA and the Tukey post hoc test (α=.05). Results: RelyX Unicem (472.3 ±8.9 N), BisCem (506.6 ±9.2 N), RelyX ARC (498.0 ±8.2 N), Panavia F (502.3 ±7.0 N), and Allcem (470.0 ±11.3 N) presented significantly higher bond strength than RelyX Luting 2 (241.8 ±9.70 N) and Enforce (309.5 ±6.3 N) cements (mean ±SD; P<.05). Conclusions: Except for Enforce, all resin cements produced pull-out bond strength values twice that of resin modified glass ionomer cement. However, all cements promoted adequate retention to fiber posts to withstand functional loads. [Copyright &y& Elsevier]

Statement of problem: Endodontically treated teeth are known to have reduced structural strength. Glass fiber posts may influence fracture resistance and should be evaluated. Purpose: The purpose of this study was to evaluate the influence of glass fiber post length on the fracture resistance of endodontically treated teeth. Material and methods: Forty intact human maxillary canines were selected and divided into 4 groups, the control group consisting of teeth restored with a custom gold cast post and core, with a length of two-thirds of the root. Other groups received prefabricated glass fiber posts in different lengths: group 1/3, removal of one-third of the sealing material (5 mm); group 1/2, removal of one-half of the sealing material (7.5 mm); and group 2/3, removal of two-thirds of the sealing material (10 mm). All the posts were cemented with resin cement, and the specimens with glass fiber posts received a composite resin core. All the specimens were restored with a metal crown and submitted to a compressive load until failure occurred. The results were evaluated by 1-way ANOVA, and the all pairwise multiple comparison procedures (Tukey honestly significantly difference test) (α=.05). Results: The ANOVA showed significant differences among the groups (P<.002). The Tukey test showed that the control group presented significantly higher resistance to static load than the other groups (control group, 634.94 N; group 1/3, 200.01 N; group 1/2, 212.17 N; and group 2/3, 236.08 N). Although teeth restored with a cast post and core supported a higher compressive load, all of them fractured in a catastrophic manner. For teeth restored with glass fiber posts, the failure occurred at the junction between the composite resin core and the root. Conclusion: The length of glass fiber posts did not influence fracture load, but cast post and cores that extended two-thirds of the root length had significantly greater fracture resistance than glass fiber posts. [Copyright &y& Elsevier]

Statement of problem: Since the introduction of glass fiber posts, irreversible vertical root fractures have become a rare occurrence; however, adhesive failure has become the primary failure mode. Purpose: The purpose of this study was to evaluate the push-out bond strength of glass fiber posts cemented with different luting agents on 3 segments of the root. Material and methods: Eighty human maxillary canines with similar root lengths were randomly divided into 8 groups (n=10) according to the cement assessed (Rely X luting, Luting and Lining, Ketac Cem, Rely X ARC, Biscem, Duo-link, Rely X U100, and Variolink II). After standardized post space preparation, the root dentin was pretreated for dual-polymerizing resin cements and untreated for the other cements. The mixed luting cement paste was inserted into post spaces with a spiral file and applied to the post surface that was seated into the canal. After 7 days, the teeth were sectioned perpendicular to their long axis into 1-mm-thick sections. The push-out test was performed at a speed of 0.5 mm/min until extrusion of the post occurred. The results were evaluated by 2-way ANOVA and the all pairwise multiple comparison procedures (Tukey test) (α=.05). Results: ANOVA showed that the type of interaction between cement and root location significantly influenced the push-out strength (P<.05). The highest push-out strength results with root location were obtained with Luting and Lining (S3) (19.5 ±4.9 MPa), Ketac Cem (S2) (18.6 ±5.5 MPa), and Luting and Lining (S1) (18.0 ±7.6 MPa). The lowest mean values were recorded with Variolink II (S1) (4.6 ±4.0 MPa), Variolink II (S2) (1.6 ±1.5 MPa), and Rely X ARC (S3) (0.9 ±1.1 MPa). Conclusions: Self-adhesive cements and glass ionomer cements showed significantly higher values compared to dual-polymerizing resin cements. In all root segments, dual-polymerizing resin cements provided significantly lower bond strength. Significant differences among root segments were found only for Duo-link cement. [Copyright &y& Elsevier]

Statement of problem: Root fracture is one of the most serious complications following restoration of endodontically treated teeth. Purpose: The purpose of this study was to compare the fracture strengths of endodontically treated teeth using posts and cores and variable quantities of coronal dentin located apical to core foundations with corresponding ferrule designs incorporated into cast restorations. Material and methods: Fifty freshly extracted canines were endodontically treated. The teeth were randomly divided into groups of 10 and prepared according to 5 experimental protocols. Control group: teeth with custom cast post and core; 0-mm group: teeth without coronal structure (no ferrule); 1-mm, 2-mm, and 3-mm groups: teeth with 1 mm, 2 mm, and 3 mm of remaining coronal tooth structure (1-, 2-, and 3-mm ferrule), respectively. All specimens in 0-mm through 3-mm (noncontrol) groups were restored with a prefabricated post (Screw-Post) and composite resin (Z100) core located superior to the different tooth structure heights. All teeth were restored with complete metal crowns. The fracture resistance (N) was measured in a universal testing machine at 45 degrees to the long axis of the tooth until failure. Data were analyzed by 1-way analysis of variance and Tukey test (α=.05). Results: Significant differences (P<.001) were found among the mean fracture forces of the test groups (control group: 818.2 N; 0-mm, 1-mm, 2-mm, and 3-mm groups: 561.0 N, 627.6 N, 745.3 N, and 907.1 N, respectively). When the mode of failure was evaluated, all failures in the control group occurred due to root fracture, and all failures in the 0-mm group occurred due to core fracture. The majority of failures in the other groups occurred due to crown cementation failure. Conclusion: The results of this study showed that an increased amount of coronal dentin significantly increases the fracture resistance of endodontically treated teeth. [Copyright &y& Elsevier]

This study evaluated the fracture resistance of endodontically treated teeth restored with prefabricated carbon fiber posts and varying quantities of coronal dentin. Sixty freshly extracted upper canines were randomly divided into groups of 10 teeth each. The specimens were exposed to 250,000 cycles in a controlled chewing simulator. All intact specimens were subjected to a static load (N) in a universal testing machine at 45 degrees to the long axis. Data were analyzed by 1-way analysis of variance and Tukey test (α = .05). Significant differences (P < .001) were found among the mean fracture forces of the test groups (positive control, 0 mm,1 mm, 2 mm, 3 mm, and negative control groups: 1022.82 N, 1008.22 N, 1292.52 N, 1289.19 N, 1255.38 N, and 1582.11, respectively). These results suggested that the amount of coronal dentin did not significantly increase the fracture resistance of endodontically treated teeth restored with prefabricated carbon fiber post and composite resin core. [Copyright &y& Elsevier]