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1.
Korean J Parasitol ; 59(1): 55-59, 2021 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-33684987

RESUMO

We intended to describe a case of cerebral coenurosis in a long-tailed goral, Naemorhedus caudatus, from Hwacheon-gun, Gangwon-do (Province), in the Korea. The goral, a 10-year-old male, was suffering from neurological symptoms, such as turning the circle to one side without lifting the head straight, and died at 30 days after admission to the wildlife medical rescue center in Chuncheon-si, Gangwon-do. A fluid-filled cyst was detected in the left cerebral hemisphere by computed tomography and magnetic resonance imaging. The cyst removed from the deceased goral was transparent, about 3×3 cm in size, contained a clear fluid and approximately 320 protoscolices invaginating from the internal germinal layer. The protoscolex had 4 suckers and a rostellum with 28 hooklets arranged in 2 rows. By the present study, a case of cerebral coenurosis was first confirmed in a long-tailed goral, N. caudatus, from Gangwon-do, in Korea. The residents frequently exposed in the sylvatic environment should be careful the accidental infections of zoonotic metacestode of Taenia multiceps, Coenurus cerebralis, in Korea.

2.
Nat Immunol ; 22(3): 336-346, 2021 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-33574616

RESUMO

The anatomic location and immunologic characteristics of brain tumors result in strong lymphocyte suppression. Consequently, conventional immunotherapies targeting CD8 T cells are ineffective against brain tumors. Tumor cells escape immunosurveillance by various mechanisms and tumor cell metabolism can affect the metabolic states and functions of tumor-infiltrating lymphocytes. Here, we discovered that brain tumor cells had a particularly high demand for oxygen, which affected γδ T cell-mediated antitumor immune responses but not those of conventional T cells. Specifically, tumor hypoxia activated the γδ T cell protein kinase A pathway at a transcriptional level, resulting in repression of the activatory receptor NKG2D. Alleviating tumor hypoxia reinvigorated NKG2D expression and the antitumor function of γδ T cells. These results reveal a hypoxia-mediated mechanism through which brain tumors and γδ T cells interact and emphasize the importance of γδ T cells for antitumor immunity against brain tumors.

3.
Artigo em Inglês | MEDLINE | ID: mdl-33478177

RESUMO

This research developed a sturdy theoretical framework that offers a better comprehension regarding customer approach intentions for eco-friendly museum products. Using a quantitative process, the apparent role of ecological value, connectedness to nature, social pressure, pro-environmental reputation was explored. Data quality testing demonstrated the validity of the construct measures. The critical mediating nature of customer-product relationship quality and feeling of pride was unveiled by conducting a structural analysis. In addition, the feeling of pride was a prominent factor determining sacrifice, visit, pay, and word of mouth (WOM) intentions. Social pressure played a major role in building relationship quality, whereas pro-environmental reputation was a key contributor to increase the feeling of pride. The model contained a strong prediction power for intentions. Results of this study contribute to enriching the extant knowledge regarding customer pro-environmental decision-making process, which is helpful for an eco-friendly museum and its success.


Assuntos
Intenção , Museus , Conhecimento
4.
Materials (Basel) ; 13(22)2020 Nov 20.
Artigo em Inglês | MEDLINE | ID: mdl-33233623

RESUMO

Nickel-titanium (NiTi) endodontic rotary instruments are used extensively in root canal procedures by both general dentists and specialists. However, their vulnerability to fracture is the major reason for clinicians' concern regarding their use. The objective of this study was to investigate the potential effects of spring machining of the file shaft on the fatigue and torsional resistances of NiTi rotary instruments. Three types of NiTi rotary systems with (S) and without (NS) spring machining were used in this study (n = 15 each): a spring file (SPR; #25/.06, SPR-S, SPR-NS), a ProTaper Next X2 (PTN; #25/variable taper, PTN-S, PTN-NS), and a ProTaper Gold F2 (PTG; #25/variable taper, PTG-S, PTG-NS). Spring machining was adjusted on the 6 mm of each file system's shaft via a laser cutting process. The number of rotation cycles until fracture (i.e., cyclic fatigue resistance), ultimate torsional strength, the distortion angle, and the toughness of each subgroup were estimated with specially designed devices. The results were analyzed using a paired t-test at a significance level of 95%. NiTi rotary instruments with spring machining exhibited a higher cyclic fatigue resistance than instruments without spring machining. The groups with spring machining exhibited a higher toughness and larger distortion angle than the groups without it (p < 0.05). In conclusion, spring machining on the shank of NiTi instruments may provide a stress-bearing area and attenuate the torsional and cyclic fatigue of NiTi rotary instruments.

5.
Artigo em Inglês | MEDLINE | ID: mdl-33003521

RESUMO

This study aimed to investigate the effect of social network services (SNS) on hotel chef job satisfaction, and to provide an effective strategy to reduce chef turnover and maintain sustainable economic development in hospitality. The intention was to empirically test and analyze the effect of SNS on hotel chef job satisfaction by applying the social capital theory. The social capital theory was explored and the effect of chefs' social capital on their social presence and job satisfaction was demonstrated. Furthermore, this study aimed to determine the moderation effect of customer orientation. A total of 130 surveys were collected from chefs working at Michelin-starred restaurants in Seoul, Korea. SPSS and AMOS were used to conduct statistical analyses. The outputs included exploratory factor analysis, confirmatory factor analysis, convergent analysis, discriminant analysis, path analysis, mediation effect analysis, and moderation effect analysis. The results illustrated that bridging social capital significantly impacts chef social presence, while bonding social capital does not significantly influence their presence. In addition, both bonding and bridging social capital positively relate to chef job satisfaction. Significant mediation and moderation effects were demonstrated on the path taken by chefs. The results of this study offer theoretical and managerial implications for hotel human resources managers to enhance chef job satisfaction.

6.
J Endod ; 2020 Oct 19.
Artigo em Inglês | MEDLINE | ID: mdl-33091452

RESUMO

INTRODUCTION: The purpose of this study was to investigate if machined springs in nickel-titanium (NiTi) rotary instruments can improve their mechanical properties. The bending and torsion properties were assessed using finite element (FE) model analysis. METHODS: A basic 3-dimensional file model without a spring was created with apical size #25, 25-mm full length, and 16-mm cutting flutes. Three other models were created with a spring machined into their shaft portion with different numbers of spring coils: standard (STspr), 10% more (INspr), and 10% less (DEspr). To compare the mechanical responses among the 4 FE models, file bending and torsion were simulated using FE analysis. RESULTS: Spring machined NiTi rotary instruments showed higher torsional resistance and less bending stiffness than the same instrument without. The spring machined models required more torque to bend or rotate the DEspr model than was required for the STspr and INspr models; however, the STSpr and INSpr models were similar. CONCLUSIONS: Within the limitations of this study, the FE analysis indicated that machining a spring into the shaft of NiTi rotary instruments improved torsional resistance and bending flexibility. Therefore, spring machining has the potential to increase the durability of the NiTi rotary instruments.

7.
Artigo em Inglês | MEDLINE | ID: mdl-33081340

RESUMO

In this study, we aim to propose motives that can help increase the creative activities of Korean performing artists and discuss the policy implications for the sustainable management of Korean performing arts. First, we investigate the characteristics of Korean artists that receive subsidies as a form of government support for undertaking artistic activities. Second, we examine whether receipt of such grants influences the artists' job and life satisfaction. Through a logistics model, we reconstructed the "2015 Survey Report on Artists & Activities" and validated the research hypothesis. We first considered subsidies that could directly impact artists' income and activities and then verified whether subsidies influence artists' job and life satisfaction. As a result of the research, first, art grants should be supported in order to help artists produce creative and experimental works. Second, we showed that artists' subsidies should be expanded in order to enhance artists' quality of life and the sustainability of artistic activities. Above all, subsidy support for artists showed that art can be legitimate as a public good, which is a common asset in society.

8.
J Endod ; 2020 Sep 19.
Artigo em Inglês | MEDLINE | ID: mdl-32961213

RESUMO

INTRODUCTION: This study aimed to compare the torsional resistances and fracture modes of WaveOne Gold and Reciproc Blue using the repetitive torsional loading (RTL) method and conventional single rotation (STL) method. METHODS: A 3-mm file tip was fixed with a brass plate and a torsional load was applied using a custom device. In the RTL method, the file was driven counter-clockwise at 50 rpm until it achieved the pre-set torque of 0.5 N·cm; thereafter, it was returned to its original position. This recovery of the file to its original position was defined as one torsional loading cycle; the number of repetitive load cycles until fracture (NRCF) was counted. In the STL method, the files were rotated at a constant rate of 2 rpm in a counter-clockwise direction until file fracture. The fragments fractured by the two methods were compared under a scanning electron microscope (SEM) to examine the topographic features of the fractured surfaces and longitudinal aspects. RESULTS: With the RTL method, the Reciproc Blue showed a higher NRCF than WaveOne Gold (P < .05). With the STL method, the Reciproc Blue also had a higher ultimate strength than WaveOne Gold (P < .05). SEM findings of the fractured specimens from the two test methods showed different features of torsional failure. CONCLUSIONS: Within the study limitations, both the RTL and STL methods conferred similar torsional resistance. Therefore, the clinically relevant RTL method with repetitive and reciprocation motion can be utilized for testing torsional resistance.

9.
Korean J Parasitol ; 58(4): 403-411, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32871634

RESUMO

Adult ascarid worms from the field mice, Apodemus agrarius, were observed with a light and scanning electron microscope, and molecularly analized with 18S rRNA gene. In the scanning electron microscope, 3 prominent labia were present in the anterior end of male and female worms, but the interlabia and gubernaculum were absent. Scanning electron micrographs showed cervical alae as vestigial organs that looked like a slightly uplifted superficial sewing stitch. Total 6 pairs of post-cloacal papillae were observed on the tail of the male worms. The tail of female worms was blunt and conical shape with a spine-like structure, mucron. The eggs were sub-globular, coated with the albuminous layer and 73 by 82 µm in average size. The superficial pits of T. apodemi egg (mean 8.6×6.7 µm) are obviously bigger than those of Toxocara spp. The partial sequence of 18S rRNA showed the sequence homology of Toxocara canis (99.6%), Toxocara cati (99.4%), Toxascaris leonina (99.4%), and Toxocara vitulorum (99.2%). Conclusively, it was confirmed that ascarid nematodes, Toxocara apodemi, recovered from striped field mice in Korea are taxonomically conspecific relationship with genus Toxocara and genetic divergence from other Toxocara species.


Assuntos
Murinae/parasitologia , Toxocara/genética , Toxocara/ultraestrutura , Animais , Feminino , Humanos , Masculino , Microscopia Eletrônica de Varredura , RNA de Helmintos/genética , RNA Ribossômico 18S/genética , República da Coreia , Toxocara/classificação , Toxocara/isolamento & purificação
10.
J Endod ; 2020 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-32640266

RESUMO

INTRODUCTION: This study aimed to compare the biomechanical properties of a mandibular first molar with different endodontic cavity designs and increasing sizes of root canal preparations using finite element analysis (FEA). METHODS: The experimental finite element models were designed with 3 different endodontic access cavities and 2 sizes of canal preparations: traditional access cavity, conservative access cavity, and truss access cavity and #30/.04 and #40/.04 of root canal preparations. Vertical and oblique loads were applied with a 250-N static force to simulate masticatory forces. Mathematical analysis was performed to evaluate the stress distribution patterns. Maximum von Mises (VM) stresses were assessed at the occlusal surface; cervical line; and 1 , 3, 5, and 7 mm from the root apices. RESULTS: Decreasing the size of the access cavity was associated with a higher magnitude of cervical stresses. The magnitude of VM stresses was maximum at the 7-mm level and was minimum at the 1-mm level from the root apex. Increasing the size of the access cavity was associated with the transmission of stresses to a further apical direction regardless of the extent of root canal enlargement. The root canal enlargement from #30 to #40 increased radicular VM stresses within all models. CONCLUSIONS: Within the limitations of this study, conservative and truss access designs preserved a significant volume of tooth structure. The extent of root canal enlargement should be as small as practical without jeopardizing the biologic objectives of root canal treatment.

11.
Vaccines (Basel) ; 8(3)2020 Jul 27.
Artigo em Inglês | MEDLINE | ID: mdl-32727077

RESUMO

Genital herpes is a venereal disease caused by herpes simplex virus (HSV). Although HSV symptoms can be reduced with antiviral drugs, there is no cure. Moreover, because HSV infected individuals are often unaware of their infection, it is highly likely that they will transmit HSV to their sexual partner. Once infected, an individual has to live with HSV for their entire life, and HSV infection can lead to meningitis, encephalitis, and neonatal herpes as a result of vertical transmission. In addition, HSV infection increases the rates of human immunodeficiency virus (HIV) infection and transmission. Because of the high burden of genital herpes, HSV vaccines have been developed, but none have been very successful. In this review, we discuss the current status of genital herpes vaccine development.

12.
J Oral Rehabil ; 47(10): 1247-1253, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32668036

RESUMO

BACKGROUND: The vibrations created by post-space preparation during the first visit for endodontic treatment could have a significant effect on the intensity of post-operative pain than that association with post-space preparation at the second appointment. OBJECTIVE: The aim of this study was to evaluate the effect of vibrations generated during post-installation, on post-operative pain in endodontically treated teeth. METHODS: One hundred patients with asymptomatic teeth requiring primary root canal treatment and post-installation were enrolled in this study. Fifty patients underwent endodontic treatment with post-installation at the first visit (group 1), while the remaining 50 patients underwent post-installation at the second visit (group 2). The intensity of post-operative pain in both groups was evaluated 1, 2, 3 days and 1 week after the first visit using the visual analogue scale. The time required to achieve complete pain relief for each patient was also recorded. The patients' age, sex, tooth type, size of the periapical lesion and time required for complete post-operative pain relief for each tooth were recorded. RESULTS: The pain intensity score was significantly higher in group 1 than group 2 (P < .05). No significant differences were observed in parameters such as sex, tooth type, jaw and size of the periapical lesion (P > .05), whereas age had a significant effect on the post-operative pain scores (P < .05). CONCLUSION: Vibrations occurring during post-installation on the same visit as that of root canal filling may increase the post-operative pain.

13.
Restor Dent Endod ; 45(2): e21, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-32483538

RESUMO

The aim of this article was to review age-dependent clinical recommendations for appropriate root canal instrumentation techniques. A comprehensive narrative review of canal morphology, the structural characteristics of dentin, and endodontic outcomes at different ages was undertaken instead of a systematic review. An electronic literature search was carried out, including the Medline (Ovid), PubMed, and Web of Science databases. The searches used controlled vocabulary and free-text terms, as follows: 'age-related root canal treatment,' 'age-related instrumentation,' 'age-related chemo-mechanical preparation,' 'age-related endodontic clinical recommendations,' 'root canal instrumentation at different ages,' 'geriatric root canal treatment,' and 'pediatric root canal treatment.' Due to the lack of literature with practical age-based clinical recommendations for an appropriate root canal instrumentation technique, a narrative review was conducted to suggest a clinical algorithm for choosing the most appropriate instrumentation technique during root canal treatment. Based on the evidence found through the narrative review, an age-related clinical algorithm for choosing appropriate instrumentation during root canal treatment was proposed. Age affects the morphology of the root canal system and the structural characteristics of dentin. The clinician's awareness of root canal morphology and dentin characteristics can influence the choice of instruments for root canal treatment.

14.
J Endod ; 46(8): 1125-1129, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32497655

RESUMO

INTRODUCTION: The aim of this study was to compare the buckling resistance of nickel-titanium (NiTi) instruments for glide path preparation depending on the test mode (static vs dynamic). METHODS: The conventional PathFile (PF; Dentsply Sirona, Ballaigues, Switzerland) and heat-treated ProGlider (PG, Dentsply Sirona) and WaveOne Gold Glider (WG, Dentsply Sirona) were evaluated. The instrument tips were placed in a small dimple prepared in an aluminum cube in a customized device. The file was then pushed in the axial direction at a 1.0-mm/s crosshead speed with rotation (dynamic mode) or without rotation (static mode). The dynamic mode of WG used its dedicated reciprocating rotation, whereas the others were rotated continuously at 300 rpm. The axial load and lateral buckling displacement were simultaneously measured. Data were analyzed statistically using 2-way analysis of variance (P = .05). RESULTS: The buckling resistance in the dynamic mode was higher than in the static mode for PG and WG (P < .05), whereas PF was not influenced by test modes (P > .05). In the dynamic mode, the PG required the highest buckling load followed by PF and WG (P < .05). In the static mode, the WG showed the lowest load (P < .05). The dynamic mode showed significantly more upper level lateral buckling displacement than in the static mode (P < .05). CONCLUSIONS: When the glide path preparation instruments moved in the dynamic mode as in clinical situations, the buckling resistance of the heat-treated NiTi glide path instruments was higher than in the static condition. The heat-treated instruments may have better buckling resistance than the conventional NiTi instrument in clinical situations.


Assuntos
Níquel , Titânio , Ligas Dentárias , Desenho de Equipamento , Teste de Materiais , Preparo de Canal Radicular , Rotação
15.
Materials (Basel) ; 13(8)2020 Apr 17.
Artigo em Inglês | MEDLINE | ID: mdl-32316559

RESUMO

This study aimed to evaluate the effect of adaptive motion applied to conventional nickel-titanium (NiTi) rotary instruments on torsional stress generation during shaping procedure. One hundred and twenty mesio-buccal canals of molars were randomly assigned to two groups according to the kinetics; adaptive motion (AD) and continuous rotation (CR). Each group was divided into four subgroups (n = 15) according to the NiTi instrument systems: HyFlex EDM, One Curve, Twisted File Adaptive, and ProTaper Next. A glide path was established with PathFile #1, for each file group being used with either of the kinetic movements. During the instrumentation with the designated motion and file system, the generated torque was measured via the control unit and acquisition module. Based on the acquired data, the maximum and total torque were calculated. The data were statistically analyzed using Kruskal-Wallis and Mann-Whitney tests at a significance level of 95%. The maximum and total torque generated by all instruments were significantly reduced by the adaptive motion (p < 0.05). In the CR group, HyFlex EDM generated the highest maximum and total stress. In the AD group, HyFlex EDM showed the highest maximum torsional stress, and One Curve showed the highest total torsional stress (p < 0.05). The TF Adaptive instrument with adaptive movement produced the lowest maximum and total torsional stress (p < 0.05). Under the conditions of this study, the use of adaptive motion would be useful to reduce the torsional stress of instrument and root dentin. The reduction of torsional stress through adaptive motion may enhance the durability of instruments and reduce the potential risk of dentinal cracks.

16.
Artigo em Inglês | MEDLINE | ID: mdl-32235632

RESUMO

Having friendships and interpersonal social connections is a normal and expected necessity of life that enhances an individual's well-being. Digital platforms, such as mobile social network applications (MSNA), present a means for people with disabilities to integrate in society. This study combines intrinsic benefits (such as enjoyment experience and information) and extrinsic benefits (such as social networking) to explore the impact of these benefits on online friendships, and the influence of these online friendships on the perceived social connectedness and well-being of people with physical disabilities. The partial least squares methodology was used to conduct statistical analysis on survey data; the outputs were obtained through convergent analysis, discriminant analysis, and bootstrapping. The results showed that enjoyment experience and social network benefits significantly influence online friendships, which influence perceived social connectedness and well-being. In addition, the perceived social exclusion has a significant moderation effect. Our findings are expected to help local disability service organizations develop effective digital disability inclusion strategies to combat widespread social exclusion among people with disabilities.


Assuntos
Pessoas com Deficiência , Aplicativos Móveis , Redes Sociais Online , Apoio Social , China , Humanos , Inquéritos e Questionários
17.
Antiviral Res ; 177: 104755, 2020 05.
Artigo em Inglês | MEDLINE | ID: mdl-32112797

RESUMO

Genital herpes is one of the most common sexually transmitted infections (STIs), and it is mainly caused by the neurotropic herpes simplex virus (HSV-2). Not only does this infection cause ulcers, but HSV-2 can also stay in a latent state in the nervous system of the host throughout their lifespan. As a result, many people do not know that they harbor this infection. Moreover, HSV-2 serves as a major risk factor for human immunodeficiency virus (HIV) infection and can be transmitted to the fetus. Despite the high risk of infection and adverse effects, attempts at development of an effective vaccine for HSV-2 have not yet been successful. In this study, we developed a DNA vaccine for HSV-2 (SL-V20). This multivalent DNA vaccine effectively reduced the pathological symptoms of infection and induced efficient elimination of the virus in a mouse model. Intramuscular injection of SL-V20 led to induction of an HSV-2-specific T-cell response in the vagina, the major infection site, and in draining lymph organs. Dendritic cells (DCs), especially basic leucine zipper ATF-like transcription factor 3 (Baft3)+ DCs and partially interferon regulatory factor 4 (Irf4)+ DCs, were involved in this T-cell-mediated protective response, while B cells were dispensable for these prophylactic effects. This study demonstrates that SL-V20 offers a novel and effective vaccine against vaginal HSV-2 infection and may be applicable to patients, pending validation in clinical studies.

18.
BMC Oral Health ; 20(1): 29, 2020 01 30.
Artigo em Inglês | MEDLINE | ID: mdl-32000767

RESUMO

BACKGROUND: To report a case of type III dens invaginatus associated with peri-invagination periodontitis in an immature permanent mandibular central incisor with open apex, in which only the invagination area was treated and vitality was preserved. CASE PRESENTATION: A 9-year-old boy was referred complaining of pain in the mandibular left central incisor. After radiographic examination, an invagination into the pulp chamber of the tooth associated with periapical radiolucency was detected. Endodontic access was performed and the orifice was identified under a dental operating microscope. The invagination area was chemo-mechanically cleaned. After 1 week, the invagination was obturated with mineral trioxide aggregate. During the 2-year follow up period, the tooth was asymptomatic. Radiographic examination revealed significant progression of periapical healing and root development in the main root canal of the tooth. CONCLUSION: Non-surgical root canal treatment of the invagination may preserve pulp vitality, and continuous root development of the tooth.


Assuntos
Dens in Dente/terapia , Incisivo/anormalidades , Periodontite Periapical/terapia , Criança , Cavidade Pulpar/patologia , Necrose da Polpa Dentária/terapia , Humanos , Incisivo/diagnóstico por imagem , Masculino , Radiografia Interproximal , Reprodutibilidade dos Testes , Tratamento do Canal Radicular , Coroa do Dente/anormalidades , Coroa do Dente/diagnóstico por imagem , Raiz Dentária/anormalidades , Raiz Dentária/diagnóstico por imagem
19.
J Endod ; 46(4): 539-544, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-32067720

RESUMO

INTRODUCTION: The aim of this study was to investigate the influence of apical filling material and the modification made to the apical preparation design in surgical endodontics on the areas of stress concentration in the mesial root of a mandibular molar using finite element analysis. METHODS: The filling material was injected under 2 conditions (ie, with or without mineral trioxide aggregate retrograde filling). The apical preparation design was modified by extending the preparation mesially while maintaining a similar prepared area. We contained the displacement of all the nodes at the base of the supporting bone and applied a force of 150 N to the vertical axis. We analyzed stress generation and concentrations numerically for all cavity design groups. RESULTS: In the presence of retrograde filling, the von Mises stress decreased gradually according to the enlargement of the prepared cavity in the subgroups. When the retrograde filling was absent, the von Mises stress increased as the prepared cavity enlarged. The modification of the apical preparation extending in the mesial direction showed a drastic decrease in stress concentration. CONCLUSIONS: Within the limitations of this study, it was advantageous to perform mesial retrograde preparation within the mesial root dentin to maintain a balanced root dentin on both sides of the apical preparation and create a low-stress field. The surgeon should be careful not to wash out or dislodge the retrograde filling material during obturation to avoid failure of surgery.


Assuntos
Endodontia , Dente Molar , Preparo da Cavidade Dentária , Análise de Elementos Finitos , Raiz Dentária
20.
J Endod ; 46(3): 431-436, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-31911005

RESUMO

INTRODUCTION: The aim of this study was to compare the influences from different access angles and curvature radii on cyclic fatigue resistance of nickel-titanium rotary files. METHODS: Two file systems (2Shape [TS; MicroMega, Besançon, France] and HyFlex CM [HCM; Coltène/Whaledent, Allstätten, Switzerland]) were used. A total of 192 instruments of TS #25/.04 (TS1), TS #25/.06 (TS2), HCM #25/.04, and HCM #25/.06 were evaluated at 3 insertion angles (0°, 10°, and 20°) and 2 radii (5 mm and 3 mm) in 16-mm stainless steel artificial canals with a 60° curvature. Cyclic fatigue resistance was determined by the number of cycles to failure (NCF) using a customized testing device. Data were analyzed statistically with the significance level established at 95%. RESULTS: In the 3-mm radius canal, the instruments showed lower cyclic fatigue resistance than in the 5-mm radius canal (P < .05). HCM #25/.06 and all .04 taper instruments had a significant NCF reduction at 20° and 10° in the 3-mm radius canal (P < .05), whereas TS2 showed no significant differences. In the 5-mm radius of curvature, although .06 taper instruments had no significant NCF reduction for each angle tested, .04 taper files exhibited significant NCF reduction when tested at 20° (P < .05). Comparing the same size instruments, HCM had higher NCF than TS (P < .05). Instruments with a .04 taper exhibited higher NCF than the .06 ones with the same heat treatment (P < .05). CONCLUSIONS: An inclined insertion into the canals decreased cyclic fatigue resistance of thermal-treated instruments with a .04 taper at all radii of curvature tested. The synergistic effect of a small radius of curvature and access angulation of heat-treated instruments decreases their fatigue resistance.


Assuntos
Ligas Dentárias , Instrumentos Odontológicos , Falha de Equipamento , Níquel , Titânio , Cavidade Pulpar , Desenho de Equipamento , Teste de Materiais , Rádio (Anatomia) , Preparo de Canal Radicular
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