1,720,958 research outputs found
Effect of root canal preparation, type of endodontic post and mechanical cycling on root fracture strength.
No full textOBJECTIVE:
To evaluate the impact of the type of root canal preparation, intraradicular post and mechanical cycling on the fracture strength of roots.
MATERIAL AND METHODS:
eighty human single rooted teeth were divided into 8 groups according to the instruments used for root canal preparation (manual or rotary instruments), the type of intraradicular post (fiber posts- FRC and cast post and core- CPC) and the use of mechanical cycling (MC) as follows: Manual and FRC; Manual, FRC and MC; Manual and CPC; Manual, CPC and MC; Rotary and FRC; Rotary, FRC and MC; Rotary and CPC; Rotary, CPC and MC. The filling was performed by lateral compactation. All root canals were prepared for a post with a 10 mm length, using the custom #2 bur of the glass fiber post system. For mechanical cycling, the protocol was applied as follows: an angle of incidence of 45°, 37°C, 88 N, 4 Hz, 2 million pulses. All groups were submitted to fracture strength test in a 45° device with 1 mm/ min cross-head speed until failure occurred.
RESULTS:
The 3-way ANOVA showed that the root canal preparation strategy (p<0.03) and post type (p<0.0001) affected the fracture strength results, while mechanical cycling (p=0.29) did not.
CONCLUSION:
The root canal preparation strategy only influenced the root fracture strength when restoring with a fiber post and mechanical cycling, so it does not seem to be an important factor in this scenario
Multi-step adhesive cementation versus one-step adhesive cementation: push-out bond strength between fiber post and root dentin before and after mechanical cycling.
No full textAbstract: This study evaluated the effects of mechanical cycling on resin push-out bond strength to root dentin, using two strategies for fiber post cementation. Forty bovine roots were embedded in acrylic resin after root canal preparation using a custom drill of the fiber post system. The fiber posts were cemented into root canals using two different strategies (N = 20): a conventional adhesive approach using a three-step etch-and-rinse adhesive system combined with a conventional resin cement (ScotchBond Multi Purpose Plus + RelyX ARC ), or a simplified adhesive approach using a self-adhesive resin cement (RelyX U100). The core was built up with composite resin and half of the specimens from each cementation strategy were submitted to mechanical cycling (45 degree angle; 37 degrees C; 88 N; 4 Hz; 700,000 cycles). Each specimen was cross-sectioned and the disk specimens were pushed-out. The means from every group (n = 10) were statistically analyzed using a two-way ANOVA and a Tukey test (P = 0.05). The cementation strategy affected the push-out results (P < 0.001), while mechanical cycling did not (P = 0.3716). The simplified approach (a self-adhesive resin cement) had better bond performance despite the conditioning. The self-adhesive resin cement appears to be a good option for post cementation. Further trials are needed to confirm these results
Different Methods for Inlay Production: Effect on Internal and Marginal Adaptation, Adjustment Time, and Contact Point
No full textThe aim of this study was to evaluate the effect of different production methods of resin and ceramic inlays on marginal and internal adaptation, adjustment time, and proximal contacts. Forty premolars were selected, embedded (their roots), and prepared to receive
inlays that were made as follows (n=10): LaRe—digital impression with a Lava C.O.S. scanner, followed by milling of Lava Ultimate block (composite resin) in a milling center; CeRe—digital impression with a Cerec 3D Bluecam scanner, followed by milling of Lava Ultimate block in Cerec; CeDis—digital impression with a Cerec 3D Bluecam scanner, followed by milling of IPS e.max CAD block (lithium disilicate) in Cerec; and PresDis—impression with polyvinyl siloxane, inlay made using the lost wax technique and IPS e.max Press pressed ceramic (lithium disilicate). Marginal and internal adaptations were
measured using the replica technique. The
inlay adjustments were performed using diamond
burs in a contra-angle hand piece, and
the time for adjustment was recorded using a
timer, in seconds. The tightness of the proximal contact was measured using standardized
metal blades. The statistical analyses for marginal
fit data showed that at the cervical edge,
CeDis (177.8 lm) had greater misfit than CeRe
(116.7 lm), while all the groups had similar
adaptation at the occlusal edge. The groups
had similar internal fit at the pulpal wall,
while LaRe (104.7 lm) . CeDis (66.7 lm) = CeRe
(76.7 lm) at the axial wall. The groups restored
with lithium disilicate ceramic took more time
for adjustment when compared to the resin
restorative material. The lowest proximal contact,
in micrometers, was seen in the CeRe
group (8.8 lm)
Effect of the frequency of mechanical pulses for fatigue aging testing on push-out bond strength between glass fiber posts and root dentin
No full textThe aim of this study was to evaluate the influence of the frequency of mechanical pulses during mechanical fatigue aging on bond strength between glass fiber posts and root dentin. Fiber posts were adhesively cemented in 30 bovine roots and the core was built up with composite. All specimens were subjected to mechanical cycling (45 degrees angle; 37 degrees C; 50N; 2x10(6) pulses) at different frequencies: 2, 4, and 8Hz. After the fatigue, each specimen was submitted to push out test. The bond strength was calculated for data analysis (one-way ANOVA, p=0.05). The frequency did not affect the push-out (p=0.7). The main failure mode was between dentin and cement in all groups. The mechanical pulses were not influenced by the bond strength between root dentin and fiber posts. Thus, it is possible to decrease the time-consuming in vitro tests involving posts without damaging the reliability of the test
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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