1,720,962 research outputs found
Bond Strength to Cubic Zirconia and Lithium-disilicate. A Preliminary Study
No full textObjectives: Bonding to polycrystalline ceramics is a concern in fixed prosthodontics. Aim of this study was to determine the micro-SBS of two MDP-based cements to cubic-zirconia (ZIR) and lithium-disilicate (L-DIS).
The null hypothesis was that mean micro-SBS did not vary among tested groups.
Methods: Twenty plates 12x12x2mm of Katana-UTML, (Kuraray-Noritake), and 20 of IPS e.max CAD LT, (Ivoclar-Vivadent) were used as substrates. They were assigned to 4 groups (n=40) according to the combination with two resin-cements: PanaviaV5 (PV5) + Clearfil-Ceramic-Primer-Plus, (groups PV5/ZIR and PV5/L-DIS); PanaviaSA (PSA) self-adhesive cement, (groups PSA/ZIR and PSA/L-DIS).
The ceramics were pre-treated following the cements manufacturer instructions: ZIR-tablets were sandblusted (Al2O3 powder, 50mm); L-DIS-tablets were conditioned (35% H3PO4, K-Etchant Syringe).
Four cylinders (1.7mm diameter, 2mm height) of resin-cement were applied on each plate with vertical load (1Kg) and light-cured (20sec).
All samples were stored in water (37°C, 24h) and tested for micro-SBS (Instron-machine). Failed surfaces were analyzed under optical-microscope and failure pattern was determined (adhesive, cohesive or mixed). Percentage of actual-failed/total adhesive surface was calculated with dedicated software (Zeiss ZEN). Mean micro-SBS values were measured (MPa) and statistically analyzed (Kruskall-Wallis-test, Dunn’s test, a=0.05).
Results: The null hypothesis that micro-SBS did not vary among the groups was rejected, (p<0.05). Mean values varied from 7.7±1.9MPa (PSA/L-DIS) to 19.6±1.7MPa (PV5/ZIR). All groups were statistically different, except PSA/ZIR vs PV5/L-DIS, (p>0.05). Both cements presented significantly higher bond strength to ZIR than L-DIS substrate. For each substrate, PV5 showed higher bond strength than PSA. Adhesive failures were mostly observed in all groups. Mean percentage of actual-failed adhesive surface varied from 69.5% (PSA/ZIR) to 85.1% (PV5/L-DIS).
Conclusions: ZIR treatment with MDP-based primer helped obtaining improved adhesion. L-DIS treatment with H3PO4 should be further investigated and compared with the conventional HF treatment. Micro-SBS measurements after longer aging conditions are needed to evaluate the bonding stability
Influence of artificial aging on the fracture strength and stiffness of Targis/Vectris fixed partial dentures.
No full textOBJECTIVE: To evaluate the effect of artificial aging on the fracture strength and stiffness of fiber-reinforced composite fixed partial dentures (FPDs). METHOD AND MATERIALS: Twelve FPDs were replicated using Targis/Vectris resin composite (Ivoclar Vivadent) and randomly divided in 2 groups. Group A was artificially aged for 900 hours in a weathering machine using dry/wet cycles and 534 W/m2 irradiations with wavelengths ranging from 300 to 800 nm. Group B (control) was stored in 100% relative humidity at 37 degrees C +/- 1 degree C for 900 hours. The FPDs were luted on metal abutments with Variolink II resin cement (Ivoclar Vivadent). The flexure stress was applied on the pontic at a descending speed of 1.0 mm/min until complete failure. Fracture strength, stiffness, and number of cracks produced on the FPDs were statistically analyzed. RESULTS: Targis veneering material in the control group fractured at a mean of 913 +/- 130 N, whereas in the aged group it failed at a mean of 722 +/- 154 N (P = .042). The mean fracture load of aged FPD frameworks was slightly lower than that of the controls: 1,532 +/- 237 N and 1,578 +/- 257 N, respectively (P = .758). The stiffness at 400 N was not significantly different between the 2 groups. The number of cracks at Targis failure was higher in aged groups. CONCLUSION: Accelerated aging significantly reduced the strength of the Targis veneering composite, increasing its brittleness; however, it had no effect on the inner Vectris framework
Accuracy of Digital Impression for Full-arch Implant-supported Prostheses
No full textObjectives: Although CAD/CAM technology offers uninterrupted digital workflow, concerns still remain about the accuracy of digital-impression procedure, particularly for full-arch implant rehabilitations. Inaccuracies may affect the long-term success of both prosthetic-rehabilitations and implants. The aim of this study was to determine the accuracy of an intraoral-scanner (TDS, 3M ESPE) creating a metrological model as reference system for digital-impressions.
Methods: A CT-scan of an edentulous mandible was randomly selected to obtain a SLM-titanium-model, which received 6 implants (Premium3.80; Sweden&Martina) in 3.6, 3.5, 3.3, 4.3, 4.5, 4.6 teeth positions. Each implant was connected to a metal scan-body, then their position was spatially determined using an opto-mechanical coordinate measuring machine (OCMM, CNC 300, Optical Gaging Products). The system integrates a video, a touch and a laser probe to determine the spatial coordinates (X-Y-Z axes) of each scan-body center-point. The data were processed with a 3D-modeling-software (Rhinoceros® 5.0) obtaining a reference system called “calibration-model”.
Four differently experienced operators took 5 digital-impressions each; then, the .stl files were processed with the modeling-software. Each impression was described by 6 scan-body center-points to be compared, for accuracy determination, with the calibration-model. The data were statistically analyzed with 1-way-ANOVA test, multiple comparison Scheffè test and Intraclass Correlation Coefficient (ICC), (p<.05).
Results: The mean error (accuracy) between the calibration-model and the 20 digital-impressions was 63±31μm, as determined combining the errors in the X-Y-Z axis coordinates. The operators experience degree did not influence the mean accuracy of the data obtained with the scanning-procedure (p>.05). The reproducibility of the scanning-procedure was assessed at a good level, as the ICC value was 0,593.
Conclusions: The accuracy determined on the digital-impressions was clinically acceptable, well within the maximum admitted mismatch reported for implant-supported prostheses fitting (150μm). The digital-impression performances were not influenced by the operator skill; this is probably due to error compensations made by the intraoral-scanner-software
Clinical outcomes and success rates of quartz fiber post restorations: A retrospective study
No full textStatement of problem
Cast metal posts and dowels are inherently dark and, when metal-free restorations are used, could impair the definitive esthetic appearance. Quartz fiber posts could represent a reliable choice for restoring abutment teeth.
Purpose
The purpose of this study was to evaluate the long-term success rate of teeth restored with quartz fiber posts and fixed dental prostheses (FDPs).
Material and methods
Ninety-nine teeth restored with 114 quartz fiber posts and FDPs were evaluated. The evaluation time ranged from 7 months to 9.25 years. The Kaplan-Meier method was used to obtain success curves. The influence of the tooth location, definitive restoration, and failure pattern upon the success function was analyzed with the log-rank test. The Cox regression test was used to evaluate possible predictors among the interactions of the observed parameters.
Results
The success rate of the restorations was 85.86% in a mean period of 5.88 ±1.37 years, with an estimated success probability of 85% at 6.17 years. The statistical analysis identified the factors related to the arch (P=.045) and type of definitive restoration (P=.021) as significantly associated with success. Post debonding was the most frequent failure mode, followed by endodontic failure, with the latter not necessarily being related to the post itself. No root fractures were recorded. Twelve teeth out of the 14 that failed were restored again, bringing the overall survival rate of the teeth to 98%.
Conclusions
The rehabilitation of abutment teeth with quartz fiber posts can be considered a reliable procedure; however, adhesive techniques and luting materials require improvement.Statement of problem Cast metal posts and dowels are inherently dark and, when metal-free restorations are used, could impair the definitive esthetic appearance. Quartz fiber posts could represent a reliable choice for restoring abutment teeth. Purpose The purpose of this study was to evaluate the long-term success rate of teeth restored with quartz fiber posts and fixed dental prostheses (FDPs). Material and methods Ninety-nine teeth restored with 114 quartz fiber posts and FDPs were evaluated. The evaluation time ranged from 7 months to 9.25 years. The Kaplan-Meier method was used to obtain success curves. The influence of the tooth location, definitive restoration, and failure pattern upon the success function was analyzed with the log-rank test. The Cox regression test was used to evaluate possible predictors among the interactions of the observed parameters. Results The success rate of the restorations was 85.86% in a mean period of 5.88 ±1.37 years, with an estimated success probability of 85% at 6.17 years. The statistical analysis identified the factors related to the arch (P=.045) and type of definitive restoration (P=.021) as significantly associated with success. Post debonding was the most frequent failure mode, followed by endodontic failure, with the latter not necessarily being related to the post itself. No root fractures were recorded. Twelve teeth out of the 14 that failed were restored again, bringing the overall survival rate of the teeth to 98%. Conclusions The rehabilitation of abutment teeth with quartz fiber posts can be considered a reliable procedure; however, adhesive techniques and luting materials require improvement
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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