1,720,968 research outputs found
Deformations and cyclic fatigue resistance of nickel-titanium instruments inside a sequence
Full text linkTo compare the effect of brushing motion on torsional and cyclic fatigue resistance of TF Adaptive instruments after clinical use. 20 packs of TFA small sequence (SybronEndo, Orange, CA, USA) were used for this study and divided into two groups. Each instrument prepared one resin tooth, consisting in 4 canals with a complex anatomy. In group A, no brushing motion was performed. In group B, after the green instrument reached the working length, brushing motion with circumferential filing was performed for 15 seconds in each canal (overall 1 minute). All the instruments were then subjected to cyclic fatigue test and mean values and standard deviation for time to fracture were evaluated. Data were subjected to one-way analysis of variance and Bonferroni t-test procedure with a significance set at P < 0.05. No instruments were broken during preparation of root canals. Two TF Adaptive
green and 5 yellow showed unwinding after intra-canal clinical use. No statistically significant differences were found between green instruments of both groups (P > 0.05), while a statistically significant difference was found between the Yellow instruments (P < 0.05), with group B showing an higher resistance to cyclic fatigue. A prolonged passive brushing motion did not adversely affected mechanical resistance of the instrument used for this purpose. Resistance to both deformations and cyclic fatigue
of the second instrument within the TFA small sequence was enhanced by the coronal flaring provided by the brushing action of the first instrument used
Cone-beam computed tomographic analysis on root and canal morphology of mandibular first permanent molar among multiracial population in Western European population
Full text linkObjectives: In the present study, confluent canals in the mandibular first molar's mesial root were investigated in an Italian population by means of cone-beam computed tomography (CBCT). Materials and Methods: A total of 200 molars, selected from the CBCT examinations of 130 patients who required this type of X-ray study as part of their dental treatment, were examined. The evaluated parameters were number of canals, root canal system configuration, presence of apical confluences, distance between confluences and apical foramina, which canal had a higher degree of curvature, and symmetry between left and right elements in the same individual. Statistical Analysis Used: Percentages of the cases were reported. Results: All the examined roots presented two canals. In 59% of cases, a Vertucci Type IV canal configuration was observed, while in 41% of cases, a Type II configuration was observed. Apical confluences were present in 41% of cases. The average distance between confluences and apical foramina was 2.85 mm. When confluences were present, the mesiobuccal canal showed a higher degree of curvature in 78% of cases. Symmetry in Vertucci configuration was seen in 88% of cases. Conclusions: Apical confluences in the mesial roots of mandibular molar can be present in a significantly high number of cases, and their recognition is essential to prevent the iatrogenic errors during canal instrumentation
In vitro evaluation of carrier based obturation technique: a CBCT study
Full text linkAIM:
The goal of the study was to compare the ability of two different carrier based obturation (CBO) techniques to reach working length and fill in three-dimensions root canal systems, by using CBCT.
MATERIALS AND METHODS:
Twenty-six extracted molars were scanned with CBCT and 40 curved canals were selected (between 30° and 90°) and divided in two similar groups (n=20). All canals were prepared up to size 25 taper .06 using nickel-titanium instrumentation. The canals in the Group SC were obturated using Soft-Core obturators (Kerr, Romulus, Mi, USA), while Group TH canals (n= 20) were obturated using Thermafil Endodontic Obturators (Tulsa Dental Products, Tulsa, OK, USA), strictly following manufacturers' instructions for use. The obturations were analyzed by means of CBCT to measure the distance from the apical limit of obturation to the apical foramen and the presence of voids inside root canals.
RESULTS:
There was no significant difference between the two groups in the mean distance of the apical extent of the obturation (t test, p>0.05). Overfilling occurred in only 3 cases (2 in Group TH and 1 in Group SC). The percentages of voids in both groups were very low with no significant difference (Z test, p>0.05).
CONCLUSIONS:
The two tested CBO techniques showed similar positive results in terms of performance, even if, after checking with verifiers, in most cases the size of the selected Soft-Core obturator was one size smaller than Thermafil
Erratum to: Cutting efficiency of nickel–titanium rotary and reciprocating instruments after prolonged use
Full text linkAbstract The aim of the present study was to compare the cutting efficiency of Twisted File instruments used in continuous rotation or TF Adaptive motion and evaluate if prolonged use significantly affected their cutting ability. 20 new NiTi instruments were used in the present study (TF tip size 35, 0.06 taper; Sybron-Endo, Orange, CA, USA), divided into 2 subgroups of 10 instruments each, depending on which movement was selected on the endodontic motor. Group 1: TF instruments were activated using the program TF continuous rotation at 500 rpm and torque set at 2 N; Group 2: TF instruments were activated using the reciprocating TF Adaptive motion. Cutting efficiency was tested in a device developed to test the cutting ability of endodontic instruments. Each instrument cut 10 plastic blocks (10 uses) and the length of the surface cut in a plastic block after 1 min was measured in a computerized program with a precision of 0.1 mm. Maximum penetration depth was calculated after 1 use and after 10 uses, and mean and standard deviation (SD) of each group was calculated. Data were statistically analyzed with a one-way ANOVA test (P.05). TF instruments used in continuous rotation (Group 1) cut a mean depth of 10.4 mm (SD = 0.6 mm) after the first use and 10.1 mm (SD 1.1 mm) after 10 uses, while TF instruments used with the Adaptive motion cut a mean depth of 9.9 mm (SD = 0.7 mm) after the first use and 9.6 mm (SD = 0.9 mm) after 10 uses. There was no statistically significant difference between the two groups investigated (P[0.05) nor between instruments after 1 or 10 uses. In conclusion, the TFA motion showed a lateral cutting ability similar to continuous rotation and all tested instruments exhibited the same cutting ability after prolonged use
Cone-beam computed tomography in the assessment of periapical lesions in endodontically treated teeth
Full text linkObjective: This study aimed to evaluate the relationship between the quality of the coronal restoration and the root canal filling on the periapical status of endodontically treated teeth using CBCT. Materials and Methods: CBCT data were obtained from the records of patients who deny any dental treatment in the 2 years prior to the CBCT examination. CBCT images (90 kVp and 7 mA, exposure time of 23 s, and a voxel size of 0.2 mm, with a field of view of 13 cm × 13 cm) of 1011 endodontically treated teeth were observed. A score was given to the quality of the root filling and the quality of the coronal restoration. Statistical Analysis Used: Data were statistically analyzed to correlate the periapical status with gender, dental group. and quality of endodontic treatment and restoration (Chi-square test with a significance level of P 0.05). A statistically significant factor (Chi-square test, P < 0.0001) resulted when different qualities of sealing were compared. Conclusions: CBCT showed that high-quality root canal treatments followed by an adequate coronal sealing restoration avoid the presence of periapical periodontitis in time
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
Incidence of deformation and fracture of twisted file adaptive instruments after repeated clinical use
Full text linkObjectives: The aim of the present study was to investigate the incidence of deformation and fracture of twisted file adaptive
nickel-titanium instruments after repeated clinical use and to identify and check whether the three instruments within the
small/medium sequence showed similar or different visible signs of metal fatigue.
Material and Methods: One-hundred twenty twisted file adaptive (TFA) packs were collected after clinically used to prepare
three molars and were inspected for deformations and fracture.
Results: The overall incidence of deformation was 22.2%, which was not evenly distributed within the instruments: 15% for
small/medium (SM)1 (n = 18), 38.33% for SM2 (n = 46) and 13.33% for the SM3 instruments (n = 16). The defect rate of
SM2 instruments was statistically higher than the other two (P < 0.001). The fracture rate was 0.83% (n = 3), being two SM2
instruments and one SM3.
Conclusions: It was observed a very low defect rate after clinical use of twisted file adaptive rotary instruments. The untwisting
of flutes was significantly more frequent than fracture, which might act as prevention for breakage. The results highlight the
fact that clinicians should be aware that instruments within a sequence might be differently subjected to intracanal stres
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