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Numerical study on the influence of material characteristics on Ni-Ti endodontic instrument performance.
No full textNi-Ti rotary endodontic instruments (files) are used in dentistry during the endodontic treatment to shape
the root canal of the tooth while removing the pulp when infected. Up to now, the studies for evaluating
their performances and drawbacks were mainly limited to experimental tests on product flexural and
torsional resistance. This work exploits computational analyses for investigating the effects of materials
with different mechanical properties on the behavior of rotary endodontic instruments. The aim is to
understand the appropriate material choice to reduce the criticality of the treatment in particular clinical
conditions. In particular, the interaction between an accurately modeled rotating file and differently shaped
root canals during the clinical procedure was studied performing finite element analyses. Strains induced by
the treatment on a file made of a ‘‘standard’’ Ni-Ti alloy (characterized by average properties of the
pseudoelastic behavior), a ‘‘long’’ Ni-Ti alloy (characterized by wide transformation region), a ‘‘super’’
Ni-Ti alloy (characterized by an extended Hookian behavior without transformation region), and stainless
steel were compared. The results accurately show the advantages of the use of Ni-Ti alloy with respect to
stainless steel and the better performance of the ‘‘long’’ alloy in all the tested case
Mechanical behaviour of Ni-Ti rotary endodontic files in simulated clinical conditions: a computational study.
No full textAIM: To develop an accurate finite element (FE) model for studying rotary endodontic instruments and to demonstrate the usefulness of the FE method in improving the knowledge of the mechanical behaviour of these instruments during root canal preparation. METHODOLOGY: An accurate geometrical model of a Ni-Ti ProTaper F1 instrument was created. The interaction between the rotating instrument and differently shaped root canals during the insertion and removal procedure was studied using FE analyses. The complex thermo-mechanical behaviour of the Ni-Ti alloy was reproduced using an ad hoc computational subroutine. With the aim of demonstrating the enhanced performance of the shape memory alloy employment, the same analysis was performed on a 'virtual' ProTaper F1 made of stainless steel. RESULTS: The Ni-Ti instrument operated in its pseudo-elastic range and was able to recover its original shape and to follow the canal curvature without deviation. The radius and the position of the canal curvature are the most critical parameters that determined the stress in the instrument with higher stress levels being produced by decreasing the radius and moving from the apical to the mid root position. CONCLUSIONS: The most demanding working conditions were observed in canals with sharp curves, especially in areas where the instruments had larger diameters. To prevent possible damage to instruments and fracture, it is advised that the instruments should be discarded following their use in such canals
A Comparative Computational Analysis of the Mechanical Behavior of Two Nickel-Titanium Rotary Endodontic Instruments.
No full textINTRODUCTION: A finite element model of two nickel-titanium (Ni-Ti) rotary endodontic instruments (ProTaper and SystemGT; Dentsply-Maillefer, Ballaigues, Switzerland) was developed to investigate the mechanical behavior of these devices and to identify the benefits/limitations of different geometries during instrumentation in various root canals. METHODS: Instrument shape, curved root canal geometry, and Ni-Ti alloy pseudo-elastic behavior were investigated in this study using computational techniques. Two different operating conditions were simulated: (1) the file insertion-removal cycle which resembles the standard working condition and (2) the file subjected to a torque in the counter-clockwise direction, which mimics the auto-reverse movement of the instrument when the tip is locked in the canal wall. RESULTS: The simulations of standard and auto-reverse conditions produced bending and torsion loading conditions in the files, respectively. In the standard situation in which different canal shapes were considered, the strains in the SystemGT were generally lower than the strains in the ProTaper and always in the pseudo-elastic range; in only 1 case did the ProTaper overcame the pseudo-elastic range limit. In the auto-reverse situation, a better behavior of the ProTaper was detected. CONCLUSIONS: The two simulated conditions highlighted the different mechanical properties of the files; the SystemGT showed slightly better performances under flexural solicitation, whereas the Protaper presented better behavior under torsion solicitations
Performance of Ni-Ti alloys in the teeth root canals shaping: a numerical study on rotary endodontic instruments
No full text
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
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