Influence of reverse torque values in abutments with or without internal hexagon indexes.

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.

Fracture resistance of endodontically treated teeth restored with glass fiber posts of different lengths.

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.

Push-out bond strengths of different dental cements used to cement glass fiber posts.

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.

Seven-Year Follow-up of Full-Arch Prostheses Supported by Four Implants: A Prospective Study.

PURPOSE: To evaluate biologic and prosthetic outcomes of implant-supported mandibular full-arch fixed prostheses treated with the All-on-4 treatment concept after 7 years. MATERIALS AND METHODS: Patients were selected to receive full-arch fixed immediate prostheses supported by four implants up to 72 hours after surgery. The following biologic aspects were evaluated: Plaque Index (PI) and Bleeding Index (BI), implant stability by resonance frequency, and marginal bone loss (MBL) measured with the aid of periapical radiographs. The prosthetic complications evaluated were related to screw loosening, framework or acrylic teeth fractures, or fractures of implants. The means of implant stability and MBL were subjected to analysis of variance and the Tukey test (P < .05). For PI and BI, the Friedmann test was used (P < .05). RESULTS: Sixteen patients (12 women and 4 men; mean age: 59.1 years) received 64 implants, and in all patients, two implants were positioned axially at the incisor region and two distally tilted implants at the region of the second premolars or molars. Patients were evaluated immediately after surgery and at 1, 2, and 7 years. Fifteen patients attended the recall after 2 years; one patient could not attend the scheduled follow-up visit and was excluded from the sample. In the 7-year evaluation, the sample size decreased to 12 patients; one could not attend because of a severe disease, and two were deceased. The cumulative implant survival rate was 100%. There was a significant (P < .0162) decrease in PI at the 1- and 7-year evaluations (71.87% and 47.92%, respectively), while the BI was the same at 1 and 7 years (43.75%). There was no statistical difference in MBL (P = .12) and implant stability (P = .48) between axial and tilted implants (P = .48). The survival rate of prostheses was 100%. The following technical complications were observed: tooth fracture occurred in one patient (6.25%); loosening of prosthetic screws and abutments were observed in three patients (18.75%); after 5 years, three patients (18.75%) had changed the denture acrylic teeth because of the replacement of the removable total maxillary prostheses with fixed implant prostheses. CONCLUSION: For the 12 patients who attended the recall after 7 years, implant loss was not found, the implant stability was high, MBL was low, and prosthetic complications were easily solved. Thus, it can be concluded that rehabilitation with implant-supported mandibular full-arch fixed prostheses with four implants has proved to be a treatment with a high survival rate.

Fracture resistance of endodontically treated teeth with different heights of crown ferrule restored with prefabricated carbon fiber post and composite resin core by intermittent loading.

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 (alpha = .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.