Research progress on the mechanical compatibility of restorative materials with dental tissue / 口腔疾病防治

@#As the main means of mastication, teeth can withstand countless functional contacts. The mechanical properties of teeth are closely related to their tissue structure. Enamel and dentin have a high hardness and modulus of elasticity, and their graded structure allows them to withstand bite forces without being susceptible to fracture. When tooth tissue is defective, full crown restoration is often needed to restore the normal shape and function of the tooth. Metal materials, ceramic materials, and polyetheretherketone (PEEK) materials are commonly used for crown restoration. Metal materials have certain disadvantages in terms of aesthetics and are relatively rarely used in clinical practice. Ceramic materials with different compositions exhibit differences in performance and aesthetics, but their elastic modulus and hardness are much higher than those of dental tissue, resulting in mismatching mechanical properties. In contrast, the elastic modulus of PEEK is lower than that of tooth tissue and similar to that of bone tissue, but its properties can be improved by fiber reinforcement. Notably, when the mechanical properties of a restoration material and tooth tissue are not fully matched, the interface between them often forms a potential weak link, which ultimately affects the stability and long-term effect of the restoration. This article introduces the mechanical properties and corresponding structural characteristics of enamel and dentin. On this basis, the advantages and limitations of existing restoration materials are analyzed, and the possibility of biomimetic design of full crowns is further explored.

Study of occupational and recreational therapy on symptom distress and mental toughness in perioperative period for lung neoplasms patients / 中国实用护理杂志

Objective:To explore the effects of occupational and recreational therapy on symptom distress and mental toughness in perioperative period for lung neoplasms patients.Methods:By adopt convenient sampling method, a total of 92 cases of lung tumor patients were collected the lung cancer department in Tianjin Medical University Cancer Institute & Hospital from December 2019 to September 2020 in pulmonary oncology department. They were divided into observation group and control group according to the order of admission, with 46 cases in each group. The patients in the control group received routine care, the observation group implemented occupational and recreational therapy based on the routine care. At enrollment and 1 month after discharge, the effects were assessed by Chinese Version of the MD Anderson Symptom Inventory (MDASI-C) and Connor-Davidson Resilience scale (CD-RISC), respectively.Results:After intervention, the symptom distress scores and life influence scores in MDASI-C were (4.45 ± 1.09) points and (5.24 ± 1.78) points in the observation group, significantly lower than in the control group (5.84 ± 1.67) points and (6.11 ± 1.32) points, the differences were statistically significant ( t=4.59, 2.59, both P<0.05); the scores of tenacity, power, optimism and total scores of CD-RISC in the observation group were (28.12 ± 4.39) points, (21.07 ± 5.57) points, (10.67 ± 3.03) points and (59.86 ± 8.29) points, significantly higher than in the control group (24.54 ± 4.16) points, (18.23 ± 4.21) points, (9.16 ± 2.47) points and (51.93 ± 5.99) points, the differences were statistically significant ( t values were 2.53-5.10, all P<0.05). Conclusions:Occupational and recreational therapy can effectively alleviate symptom distress and promote mental toughness of lung cancer patients in perioperative period.

Mental toughness of resident physicians in a private tertiary hospital in Davao City, Philippines using the mental toughness index

Background@#Mental toughness is believed to be one of the key factors that may help resident physicians endure their training. Objective: Determine the mental toughness of resident physicians in a private tertiary hospital in Davao City, Philippines using the Mental Toughness Index.@*Methods@#The researchers utilized the MTI and added open ended questions to identify positive and negative factors for the Resident’s MTI scores. The questionnaires were distributed to the residents using the online platform. The responses were recorded using the Likert scales and the short answers given were categorized as nominal data.@*Results@#The study had 37 respondents out of 42 total residents with an over-all response rate of 88.09%. The survey showed that female residents have a significantly higher scores. Resident with the age of 31 years and above have greater scores than younger co-residents. The Departments of Surgery and Obstetrics and Gynecology (OB-GYNE) had the highest scores (50.4, SD, +/- 4.04 vs 50.4, SD, +/- 2.79) among all the clinical departments. The Department of Pediatrics had the lowest mean score of 43.67 (SD, +/- 4.39). The study showed that junior residents have the highest MTI mean scores (49, +/- 3.47) and the mid-level of trainees had the lowest mean MTI scores (46.10, SD +/- 3.51). Residents with previous residency training experience have higher mean scores (50.67, SD +/- 4.37). Support Group was the most cited positive factor identified by the trainees. On the other hand, Personal Reasons were the most frequent negative factor that affect their mental toughness.@*Conclusion@#The study showed female residents, residents aged greater than 31 years, Surgical and OB GYNE residents, Junior Residents and Residents with previous residency training have better MTI scores. Social support groups and personal reasons could positively and negatively impact in their mental toughness, respectively.

An investigation of the microstructure and mechanical properties of dental zirconia manufactured by digital light processing 3D printing / 华西口腔医学杂志

OBJECTIVES@#This study was performed to investigate the microstructure and mechanical properties of dental zirconia manufactured by digital light processing (DLP) 3D printing and the clinical application prospects of this material.@*METHODS@#The experiment (DLP) group was zirconia manufactured by DLP 3D printing, and the control (MILL) group was milled zirconia. The density, grain size, and phase composition were measured to study the microstructure. Flexural strength was measured by using three-point bending tests, while Vickers hardness was determined through a Vickers hardness tester. Fracture toughness was tested using the single-edge V-notched beam method.@*RESULTS@#Zirconia density of the DLP group was (6.019 8±0.021 3) g·cm@*CONCLUSIONS@#Zirconia manufactured by DLP 3D printing had microstructure and mechanical properties similar to those of the milled zirconia. Only the flexural strength and the Vickers hardness of the experimental zirconia were slightly lower than those of the milled zirconia. Therefore, DLP-manufactured zirconia has a promising future for clinical use.

Preferencias alimentarias de Phylloicus sp. (Trichoptera: Calamoceratidae) en un río Neotropical de la Sierra Nevada de Santa Marta, Colombia

Introducción: En los sistemas fluviales colombianos ha sido poco estudiada la fragmentación del material alóctono por parte de los insectos acuáticos. Uno de los organismos trituradores más abundantes en las corrientes tropicales de América es el tricóptero del género Phylloicus (Calamoceratidae). Objetivo: El presente estudio tuvo como objetivo evaluar el efecto de los atributos químicos (nitrógeno, fósforo y lignina) y físicos (dureza) de las hojas de tres especies ribereñas (Ficus tonduzii, Zygia longifolia y Clusia multiflora) dominantes en la parte media del río Gaira, sobre la preferencia de hojas y el crecimiento de larvas de Phylloicus sp. Métodos: Se realizaron experimentos de multiselección de alimento en campo, en los que se ubicaron cámaras experimentales dentro del río por 21 días. Para la valoración de la calidad foliar se recolectaron hojas del río, las cuales se secaron y se pulverizaron para realizar los análisis químicos. Resultados: No se presentaron diferencias significativas en los porcentajes de lignina y fósforo entre las hojas de las tres especies de árboles, pero si en su dureza y en el contenido de nitrógeno. Las hojas de C. multiflora fueron más suaves (180.1± 53.9 g) que las de F. tonduzii (285.3 ± 88.4 g) y Z. longifolia (232.3 ± 60.8 g), pero sin diferencias entre las dos últimas especies. Las hojas de Z. longifolia también tuvieron más nitrógeno (1.9 ± 0.0%) que las de hojas de las otras especies (1 ± 0.0 %). En cuanto a la preferencia de hojas, las larvas de Phylloicus sp. utilizaron en mayor proporción las hojas de C. multiflora. Aunque las hojas de C. multiflora no tuvieron diferencias significativas en el contenido de lignina y fósforo, presentaron valores menores de dureza, lo que podría hacerlas más palatables para Phylloicus sp. Por otra parte, el crecimiento específico diario de las larvas fue mayor cuando usaron hojas de F. tonduzii. Conclusiones: Nuestros resultados parecen indicar que las hojas más preferidas no son necesariamente las de mejor calidad nutricional y sugieren que la dureza de las hojas es la variable más importante en la selección de la hojarasca por parte de las larvas de Phylloicus sp.

Introduction: Fragmentation of allochthonous material by aquatic insects is a functional process that has been little studied in Colombian rivers. One of the most abundant shredder genus in American tropical stream ecosystems is the caddisfly genus Phylloicus (Calamoceratidae). Objective: In this study we evaluate the effect of chemical (nitrogen, phosphorus and lignin) and physical (toughness) attributes of leaves of three dominant tree species (Ficus tonduzii, Zygia longifolia and Clusia multiflora) in the riverine area of the middle section of the Gaira river, on leaf preferences and larval growth of a species of Phylloicus. Methods: Multiple food selection field experiments were performed, in which experimental chambers were located in the river for twenty-one days. For the assessment of leaf quality, leaves were collected in the river, dried and pulverized to perform chemical analyzes. Results: There were no significant differences in lignin and phosphorous percentages between the leaves of the three species, but nitrogen content and leaf toughness differed among them. The leaves of C. multiflora were softer (180.1± 53.9 g) than those of F. tonduzii (285.3 ± 88.4 g) and Z. longifolia (232.3 ± 60.8 g), but without differences between the last two species. The Z. longifolia leaves also had more nitrogen (1.9 ± 0.0 %) than those of the other species (1 ± 0.0 %). Regarding leaf selection, Phylloicus sp. larvae used in greater proportion the leaves of C. multiflora. Although lignin and phosphorous differences were not significant, the leaves of C. multiflora had lower toughness, which could make them more palatable for Phylloicus sp. On the other hand, the daily specific growth of the larvae was higher when they used leaves of F. tonduzii. Conclusions: Our findings seem to indicate that the most preferred leaves were not necessarily those of better nutritional quality and suggest that leaf toughness was the most important variable in the selection of leaf litter by the larvae of Phylloicus sp.

Effect of zirconia substructure thickness on the mechanical properties and adhesion of veneering porcelain

Aim: This study investigated the influence of yttrium-stabilized tetragonal zirconia polycrystals (Y-TZP) thickness on fracture load of porcelain-veneered crowns (FL), fracture toughness of porcelain (FT), and the shear bond strength zirconia/porcelain (SBS). Methods: Artificial first molar was prepared for full crown (N=45) with different occlusal reduction. Y-TZP cores were made with different thickness at the occlusal face (1mm, 2mm and 3mm) (n=15). The cores were veneered with VM9 ­ Vita porcelain with 1.0 mm layer. For FL testing, axial load was applied to the mesiolingual cusp of the crowns. For FT testing, flat Y-TZP plates (5X5 mm) with 1, 2 or 3 mm thickness were veneered with 1.0 mm porcelain layer (n=10). FT by indentation fracture technique was measured close to the interface and at the top surface. For SBS by knife-edge shearing rod, cylindrical porcelain with 5 mm in diameter and 3 mm was applied on flat Y-TZP plates (1, 2 and 3 mm thickness) (n = 10). Results: Data analyzed by 1-Way ANOVA for FL of crowns and SBS between Y-TZP and porcelain were not significant. Two-way ANOVA for FT was significant for zirconia thickness and measurement area. The post-hoc test showed higher values for the groups with 2 and 3mm, and higher values at the interface, irrespectively of Y-TZP thickness. Conclusion: The zirconia thickness did not affect the FL of veneered crowns and the SBS between the ceramics, but FT of porcelain was lower in thinner zirconia substructure and close to the interface Y-TZP/Porcelain

Effect of Surface Roughness on the Mechanical Properties of Ceramic-Polymer Blocks for CAD/CAM Dental Restoration / 대한치과재료학회지

The effect of surface roughness of ceramic-polymer CAD/CAM blocks on the mechanical properties was investigated in this study. Commercially available Polyglass (Vericom, Korea) and Enamic (Vita, Germany) were selected for this purpose. They were cut into either (4.0×2.1×17.0) mm and (3.0×4.0×17.0) mm, followed by grinding, and polished sequentially with 6 µm and 1 µm diamond paste. Flexural strength, fracture toughness, and Weibull analysis were determined according to ISO 6872 Dentistry-Ceramic materials. The elastic moduli were calculated from a stress-strain curves under flexural loading. The statistical significances of the mechanical properties between the products and surface roughness were analyzed with ANOVA and pared t-test at a significance level of 0.05. After grinding with 6 µm diamond paste after cutting by observing with an atomic force microscope, the arithmetic average roughness decreased to 47~49% and the maximum roughness decreased to 68~69%. When polishing with 1 µm diamond paste, The average roughness decreased to 13~22% and the maximum roughness decreased to 16~19%. When the flexural load was applied, stress increased linearly and fractured without plastic deformation both Polyglass and Enamic. As the surface roughness decreased, the mechanical properties were increased both Polyglass and Enamic. However, the mechanical properties of Polyglass increased up to P3, while Enamic showed almost maximal values at E2, after that there was no significant differences between E2 and E3. It could be due to the different microstructure between two blocks used in this experiment.

Mechanical Properties and Microstructure of the Leucite-Reinforced Glass-Ceramics for Dental CAD/CAM / 치위생과학회지

The computer-aided design/computer-aided manufacturing (CAD/CAM) system was introduced to shorten the production time of all-ceramic restorations and the number of patient visits. Among these types of ceramic for dental CAD/CAM, they have been processed into inlay, onlay, and crown shapes using leucite-reinforced glass-ceramics to improve strength. The purpose of this study was to observe the mechanical properties and microstructure of leucite-reinforced glass-ceramics for dental CAD/CAM. Two types of leucite-reinforced glass-ceramic blocks (IPS Empress CAD, Rosetta BM) were prepared with diameter of 13 mm and thickness of 1 mm. Biaxial flexural testing was conducted using a piston-on-three-ball method at a crosshead speed of 0.5 mm/min. Weibull statistics were used for the analysis of biaxial flexural strength. Fracture toughness was obtained using an indentation fracture method. Specimens were observed by field emission scanning electron microscopy to examine the microstructure of the leucite crystalline phase after acid etching with 0.5% hydrofluoric acid aqueous solution for 1 minute. The results of strength testing showed that IPS Empress CAD had a mean value of 158.1±8.6 MPa and Rosetta BM of 172.3±8.3 MPa. The fracture toughness results showed that IPS Empress CAD had a mean value of 1.28±0.19 MPa·m(1/2) and Rosetta BM of 1.38±0.12 MPa·m(1/2). The Rosetta BM sample exhibited higher strength and fracture toughness. Moreover, the crystalline phase size and ratio were increased in the Rosetta BM sample. The above results are expected to elucidate the basic mechanical properties and crystal structure characteristics of IPS Empress CAD and Rosetta BM. Additionally, they will help develop leucite-reinforced glass-ceramic materials for CAD/CAM.

Effects of incorporation of 2.5 and 5 wt% TiO₂ nanotubes on fracture toughness, flexural strength, and microhardness of denture base poly methyl methacrylate (PMMA)

PURPOSE: The aim of this preliminary study was to investigate, for the first time, the effects of addition of titania nanotubes (n-TiO2) to poly methyl methacrylate (PMMA) on mechanical properties of PMMA denture base. MATERIALS AND METHODS: TiO2 nanotubes were prepared using alkaline hydrothermal process. Obtained nanotubes were assessed using FESEM-EDX, XRD, and FT-IR. For 3 experiments of this study (fracture toughness, three-point bending flexural strength, and Vickers microhardness), 135 specimens were prepared according to ISO 20795-1:2013 (n of each experiment=45). For each experiment, PMMA was mixed with 0% (control), 2.5 wt%, and 5 wt% nanotubes. From each TiO2:PMMA ratio, 15 specimens were fabricated for each experiment. Effects of n-TiO2 addition on 3 mechanical properties were assessed using Pearson, ANOVA, and Tukey tests. RESULTS: SEM images of n-TiO2 exhibited the presence of elongated tubular structures. The XRD pattern of synthesized n-TiO2 represented the anatase crystal phase of TiO2. Moderate to very strong significant positive correlations were observed between the concentration of n-TiO2 and each of the 3 physicomechanical properties of PMMA (Pearson's P value ≤.001, correlation coefficient ranging between 0.5 and 0.9). Flexural strength and hardness values of specimens modified with both 2.5 and 5 wt% n-TiO2 were significantly higher than those of control (P≤.001). Fracture toughness of samples reinforced with 5 wt% n-TiO2 (but not those of 2.5% n-TiO2) was higher than control (P=.002). CONCLUSION: Titania nanotubes were successfully introduced for the first time as a means of enhancing the hardness, flexural strength, and fracture toughness of denture base PMMA.

Raloxifene neutralizes bone brittleness induced by anti-remodeling treatment and increases fatigue life through non-cell mediated mechanisms / El raloxifeno invierte fragilidad ósea inducida por el tratamiento anti-remodelación y aumenta la resistencia a la fatiga a través de mecanismos mediados no celulares

Pre-clinical data have shown that tissue level effects stemming from bisphosphonateinduced suppression of bone remodeling can result in bone that is stronger yet more brittle. Raloxifene has been shown to reduce bone brittleness through non-cellular mechanisms. The goal of this work was to test the hypothesis that raloxifene can reverse the bone brittleness resulting from bisphosphonate treatment. Dog and mouse bone from multiple bisphosphonate dosing experiments were soaked in raloxifene and then assessed for mechanical properties. Mice treated with zoledronate in vivo had lower post-yield mechanical properties compared to controls. Raloxifene soaking had significant positive effects on select mechanical properties of bones from both vehicle and zoledronate treated mice. Although the effects were blunted in zoledronate bones relative to vehicle, the soaking was sufficient to normalize properties to control levels. Additional studies showed that raloxifene-soaked bones had a significant positive effect on cycles to failure (+114%) compared to control-soaked mouse bone. Finally, raloxifene soaking significantly improved select properties of ribs from dogs treated for 3 years with alendronate. These data show that ex vivo soaking in raloxifene can act through non-cellular mechanisms to enhance mechanical properties of bone previously treated with bisphosphonate. We also document that the positive effects of raloxifene soaking extend to enhancing fatigue properties of bone. (AU)

Los datos preclínicos han demostrado que los efectos a nivel de tejido que se derivan de la supresión del remodelado óseo inducida por bifosfonatos puede dar como resultado un hueso que es más fuerte pero más frágil. Está comprobado que el raloxifeno reduce la fragilidad ósea a través de mecanismos no celulares. El objetivo de este trabajo fue probar la hipótesis de que el raloxifeno puede revertir la fragilidad ósea resultante del tratamiento con bifosfonatos. Se emplearon huesos de perro y ratón de múltiples experimentos con diferentes dosis de bifosfonatos los cuales fueron sumergidos en raloxifeno y luego se evaluaron sus propiedades mecánicas. Ratones tratados con zoledronato in vivo mostraron propiedades mecánicas post-rendimiento más bajas en comparación con los controles. Luego de sumergirlos en raloxifeno se observaron efectos positivos significativos en algunas propiedades biomecánicas tanto en los huesos de ratones tratados con vehículo como con zoledronato. Aunque los efectos se atenuaron en los huesos tratados con zoledronato en relación con los tratados con vehículo, el raloxifeno fue suficiente para normalizar las propiedades a niveles basales. Estudios adicionales mostraron que los huesos sumergidos en raloxifeno tuvieron un efecto positivo significativo en los ciclos de fractura (+ 114%) en comparación con los huesos de ratón sumergido en vehículo. Finalmente, el raloxifeno mejoró significativamente las propiedades de costillas de perros tratados durante 3 años con alendronato. Estos datos muestran que la inclusión ex vivo en raloxifeno puede actuar a través de mecanismos no celulares para mejorar las propiedades mecánicas de huesos previamente tratado con bifosfonatos. También documentamos que los efectos positivos del raloxifeno mejoran las propiedades de fatiga del hueso. (AU)

Biomecánica de las fracturas por stress / Biomechanical features of stress fractures

Se define como estrés (stress) tanto la fuerza que una carga externa ejerce sobre un cuerpo sólido como la fuerza reactiva que acompaña a la primera (Ley de Newton), por unidad de área imaginaria transversal a su dirección. Las cargas internas reactivas inducen deformaciones proporcionales del cuerpo. La resistencia del cuerpo a deformarse se llama rigidez. La deformación puede resquebrajar el cuerpo y, eventualmente, producir una fractura por confluencia de trazos. La resistencia del cuerpo a separarse en fragmentos por esa causa se llama tenacidad. La resistencia del cuerpo a la fractura es proporcional al stress que puede soportar sin separarse en fragmentos por deformación (no hay fractura sin deformación y sin stress previo). El stress máximo que un cuerpo puede soportar sin fracturarse resulta de una combinación de ambas propiedades: rigidez y tenacidad, cada una con distintos determinantes biológicos. Una o varias deformaciones del cuerpo pueden provocarle resquebrajaduras sin fracturarlo. La acumulación de resquebrajaduras determina la "fatiga" del material constitutivo del cuerpo, que reduce su rigidez, tenacidad y resistencia a la fractura para la próxima ocasión ("fragilidad por fatiga"). En el caso de los huesos, en general, los términos stress y fatiga tienen las connotaciones amplias referidas, respecto de todas las fracturas posibles. La fatiga predispone a fracturas a cargas bajas, que se denominan (correctamente) "fracturas por fatiga" y también (incorrectamente) "fracturas por stress", para distinguirlas de las que ocurren corrientemente, sin resquebrajaduras previas al trauma, que se denominan (incorrectamente) "fracturas por fragilidad, o por insuficiencia". En realidad, todas las fracturas se producen por stress y por fragilidad o insuficiencia (en conjunto); pero la distinción grosera entre fracturas "por fatiga, o por stress", por un lado, y "por fragilidad" o "por insuficiencia", por otro, aceptando las amplias connotaciones referidas antes, tiene valor en la práctica clínica. Este artículo intenta explicar esas particularidades biomecánicas y describir las distintas condiciones que predisponen a las fracturas "por fatiga o por stress" en la clínica, distinguiéndolas de las fracturas "por fragilidad o por insuficiencia" (manteniendo estas denominaciones) y detallando las características de interés directo para su diagnóstico y tratamiento. (AU)

The term "stress" expresses the force exerted by an external load on a solid body and the accompanying, opposed force (Newton's Law), expressed per unit of an imaginary area perpendicular to the loading direction. The internal loads generated this way deform (strain) proportionally the body's structure. The resistance of the body to strain expresses its stiffness. Critical strain magnitudes may induce micro-fractures (microdamage), the confluence of which may fracture the body. The body's resistance to separation into fragments determines its toughness. Hence, the body's resistance to fracture is proportional to the stress the body can support (or give back) while it is not fractured by the loadinduced strain (no stress, no strain -> no fracture). Therefore, the maximal stress the body can stand prior to fracture is determined by a combination of both, its stiffness and its toughness; and each of those properties is differently determined biologically. One or more deformations of the body may induce some microdamage but not a fracture. Microdamage accumulation determines the fatigue of the material constitutive of the body and reduces body's toughness, leading to a "fatigue-induced fragility". In case of bones, in general, both stress and fatigue have the referred, wide connotations, regarding any kind of fractures. In particular, bone fatigue predisposes to low-stress fractures, which are named (correctly) "fatigue fractures" and also misnamed "stress fractures", to distinguish them from the current fractures that occur without any excess of microdamage, that are named (wrongly) "fragility" or "insufficiency" fractures. In fact, all fractures result from all stress and fragility or insufficiency as a whole; however, the gross distinction between "fatigue or stress fractures", on one side, and "fragility or insufficiency fractures", on the other, accepting the wide connotations of the corresponding terminology, is relevant to clinical practice. This article aims to explain the above biomechanical features and describe the different instances that predispose to "fatigue or stress fractures" in clinical practice, as a different entity from "insufficiency or fragility fractures" (maintaining this nomenclature), and describe their relevant features to their diagnosis and therapy. (AU)

Modification study of cyanoacrylate medical adhesive / 医疗卫生装备

Objective To perform modification study of cyanoacrylate (CA) medical adhesive and to select the optimal mo-difying material and the best ratio.Methods Carboxylic multi-walled carbon nanotubes (MWCNTs-COOH), multi-walled carbon nanotubes (MWCNTs), hydrophobic nano-silica, nitrile rubber, epoxy resin and polymethyl methacrylate (PMMA) were used to modify 5% triclosan/cyanoacrylate antimicrobial adhesive respectively. The bond strength, toughness and viscosity of the modified adhesive were examined in different concentrations.Results 0.064% MWCNTs-COOH, 6% nano-silica, 4% nitrile rubber and 6.4% epoxy resin all had good effects in strength modification. The bond strength were (14.71±1.48)MPa, (14.03±1.92)MPa, (14.6±1.78)MPa and (14.05±1.46)MPa respectively. 8% nano-silica had the lowest Tg of (1.1±0.24)℃ and the strongest viscosity of (15 536.68±28.4)cP. When the nano-silica concentration was 8%, the compound was very viscous and sticky. When the antimicrobial adhesive modified with 6% nano-silica, the bond strength was (14.03±1.92)MPa, the Tg was (3.6±0.68)℃, and the viscosity was (5 278.87±31.68)cP.Conclusion 6% nano-silica is the best modifying material, and has the optimal effect of modification.

Effect of water storage on the fracture toughness of dental resin cement used for zirconia restoration / 대한치과보철학회지

PURPOSE: The aim of this study was to compare the fracture toughness of currently available resin cements for zirconia restorations and evaluate the effect of water storage on fracture toughness of those resin cements. MATERIALS AND METHODS: Single-edge notched specimens (3 mm x 6 mm x 25 mm) were prepared from three currently available dual cure resin cements for zirconia restorations (Panavia F 2.0, Clearfil SA luting and Zirconite). Each resin cement was divided into four groups: immersed in distilled water at 37degrees C for 1 (Control group), 30, 90, or 180 days (n=5). Specimens were loaded in three point bending at a cross-head speed of 0.1 mm/s. The maximum load at specimen failure was recorded and the fracture toughness (K(IC)) was calculated. Data were analyzed using one-way ANOVA and multiple comparison Scheffe test (alpha=.05). RESULTS: In control group, the mean KIC was 3.41 +/- 0.64 MN.m(-1.5) for Panavia F, 2.0, 3.07 +/- 0.41 MN.m(-1.5) for Zirconite, 2.58 +/- 0.30 MN.m(-1.5) for Clearfil SA luting respectively, but statistical analysis revealed no significant difference between them. Although a gradual decrease of K(IC) in Panavia F 2.0 and gradual increases of KIC in Clearfil SA luting and Zirconite were observed with storage time, there were no significant differences between immersion time for each cement. CONCLUSION: The resin cements for zirconia restorations exhibit much higher K(IC) values than conventional resin cements. The fracture toughness of resin cement for zirconia restoration would not be affected by water storage.

The effect of thermocycling on fracture toughness and hardness of different core build up materials.

Introduction: Core build up materials are routinely used to restore grossly decayed teeth and in the oral environment they are subjected to changes in the temperature due to consumption of hot and cold food. Aims: The purpose of this study was to determine the effect of thermocycling on the fracture toughness and hardness of 5 core build up materials. Materials and Methods: Fifteen specimens were prepared for each of the following materials: DPI alloy, Miracle‑mix, Vitremer, Fuji II LC and Photocore. American Standard for Testing Materials guidelines were used for the preparation of single‑edge notch, bar‑shaped specimens. Ten specimens of each material were thermocycled for 2000 cycles and the other 5 specimens were not thermocycled (non‑thermocycled group). All specimens were subjected to 3-point bending in a universal testing machine. The load at fracture was recorded and the fracture toughness (KIC) was calculated. Vickers hardness test was conducted on the thermocycled and non‑thermocycled group specimens. Results: Photocore had the highest mean KIC in both thermocycled and non‑thermocycled groups. Miracle‑mix demonstrated the lowest mean fracture toughness (KIC) for both thermocycled and non‑thermocycled groups. By applying Mann Whitney ‘U’ test the Vickers hardness value in all materials used in the study is highly superior in non‑thermocycled group as compared to thermocycled group (P < 0.01). Non‑thermocycled Photocore showed highest hardness values of 87.93. Vitremer had lowest hardness of 40.48 in thermocycled group. Conclusion: Thermocycling process negatively affected the fracture toughness and hardness of the core build‑up materials.

Influência da composição da matriz orgânica, conteúdo inorgânico e tratamento térmico sobre diferentes propriedades de compósitos experimentais / Influence of composition of the organic matrix, filler content and thermic treatment on different properties of experimental composites

Objetivo: Analisar a influência da matriz orgânica, do conteúdo inorgânico e do tratamento térmico (TT) sobre diferentes propriedades de compósitos experimentais, tais como o grau de conversão (GC), tenacidade à fratura (KIC), resistência à flexão (RF) e módulo de elasticidade (ME). Métodos: Para o experimento foram analisadas seis formulações de compósitos experimentais com proporções molares de Bis-GMA:TEGDMA de 5:5 e 7:3, a carga utilizada foi o vidro de bário, nas concentrações de 30, 50 e 70% em peso, e os fotoiniciadores a amina e canforoquinona. O GC foi analisado através da espectroscopia no infra-vermelho (FTIR) (n=5). A KlC foi avaliada pelo método single-edge notched beam (SENB). As imagens das superfícies de fratura foram capturadas por um estereomicroscópio e a KlC calculada (n=10). A análise da RF e ME foi realizada através do teste dos três pontos (n=10). Para todos os fatores de variação estudados, metade dos espécimes imediatamente após à confecção receberam TT em estufa convencional, a 170º C por 10 minutos e a outra metade não. Após 24 horas, as amostras foram destinadas de acordo com os ensaios realizados...

Objective: To analyze the influence of organic matrix, the inorganic content and thermic treatment (TT) on different properties of experimental composites, such as the degree of conversion (DC), fracture toughness (KIC), flexural strength (FS) and elastic modulus (EM). Methods: This experiment analyzed six formulations of experimental composites with 5:5 and 7:3 molar proportions of Bis-GMA: TEGDMA. The load used was barium glass at concentrations of 30, 50 and 70% by weight and the photoinitiators, camphorquinone and amine. GC was analyzed by infrared spectroscopy (FTIR) (n=5). The KIC was evaluated by a "single-edge notched beam" (SENB). The images of the fracture surfaces were captured by a stereomicroscope and KIC calculated (n=10). The analysis FS and EM were performed by testing three points (n=10). For all the variation factors studied, half of the specimens immediately after the preparation received TT in conventional oven at 170º C for 10 minutes and the other half not. After 24 hours, the samples were designed according to the tests. Data were analyzed using ANOVA/Tukey the degree of conversion, fracture toughness and flexural strength, and Kruskal-Wallis test for the elastic modulus (=5%). Results: Analysis of GC (%) statistical significance was observed for the three variation factors analyzed individually (monomer, filler and TT), as well as for the interaction monomer x TT (p <0.001). For KIC and FS, significant changes were observed only in the three variation factors (monomer, filler and TT) analyzed individually (p<0.001). For EM, the individual factors (monomer, filler and TT) TT x filler interaction showed statistical significance (p <0.001), as well as the monomer x filler interaction (p = 0.001). Conclusions: The organic matrix and inorganic content of experimental composites influenced the GC, KIC, FS and EM, and the TT caused improvements in the properties studied.

Comparison of two fracture toughness testing methods using a glass-infiltrated and a zirconia dental ceramic

PURPOSE: The objective of this study was to compare the fracture toughness (KIc) obtained from the single edge V-notched beam (SEVNB) and the fractographic analysis (FTA) of a glass-infiltrated and a zirconia ceramic. MATERIALS AND METHODS: For each material, ten bar-shaped specimens were prepared for the SEVNB method (3 mm x 4 mm x 25 mm) and the FTA method (2 mm x 4 mm x 25 mm). The starter V-notch was prepared as the fracture initiating flaw for the SEVNB method. A Vickers indentation load of 49 N was used to create a controlled surface flaw on each FTA specimen. All specimens were loaded to fracture using a universal testing machine at a crosshead speed of 0.5-1 mm/min. The independent-samples t-test was used for the statistical analysis of the KIc values at alpha=0.05. RESULTS: The mean KIc of zirconia ceramic obtained from SEVNB method (5.4 +/- 1.6 MPa.m1/2) was comparable to that obtained from FTA method (6.3 +/- 1.6 MPa.m1/2). The mean KIc of glass-infiltrated ceramic obtained from SEVNB method (4.1 +/- 0.6 MPa.m1/2) was significantly lower than that obtained from FTA method (5.1 +/- 0.7 MPa.m1/2). CONCLUSION: The mean KIc of the glass-infiltrated and zirconia ceramics obtained from the SEVNB method were lower than those obtained from FTA method even they were not significantly different for the zirconia material. The differences in the KIc values could be a result of the differences in the characteristics of fracture initiating flaws of these two methods.

FRAGILIDAD Y COMPORTAMIENTO MECÁNICO DEL ESMALTE DENTAL / BRITLENESS AND MECHANICAL BEHAVIOR OF DENTAL ENAMEL

El esmalte dental es el tejido duro más mineralizado del cuerpo humano. En este trabajo se estudiaron las propiedades mecánicas fundamentales de este tejido para terceros molares de pacientes jóvenes colombianos. Se establecieron la dureza, la tenacidad a la fractura aparente y la fragilidad del esmalte dental en función de la profundidad a partir de la superficie oclusal mediante técnicas de medición de microindentación. Se encontró que las mediciones de dureza son altamente dependientes de la carga utilizada, hallándose que para valores de carga pequeños las huellas alcanzan a representar la dureza de un solo prisma de hidroxiapatita, mientras que para valores altos de carga las huellas abarcan un número de prismas suficientes para estimar la dureza general del esmalte. En términos generales los valores de las propiedades medidas son semejantes a los encontrados en estudios realizados en pacientes jóvenes norteamericanos, evidenciando que estas propiedades del esmalte son independientes de las características raciales o étnicas para pacientes jóvenes, lo cual no es necesariamente extensible al comportamiento de estos tejidos en pacientes mayores.

Dental enamel is one of the hardest and most mineralized tissues of the human body. This work studied the main mechanical properties of this hard tissue for third molars obtained from young Colombian patients. The hardness, apparent fracture toughness and brittleness of enamel were measured as a function of distance from the occlusal surface to the Dental Enamel Junction (DEJ) by means of microndentation techniques. It was found that the hardness measurements are highly dependent on the indentation load, with high values of hardness found when low loads were used. This behavior is explained by the size of the indentations which approached the size of single hydroxyapatite prisms for low load values, while for high load values the size of the indents covered several prisms. Overall, the mechanical properties measured on the enamel from young Colombians are close to the properties reported in the literature for young North American patients. Whether these similarities among young patients persist for older patients deserves further investigation.

In vitro comparative evaluation of the effect of two different fiber reinforcements on the fracture toughness of provisional restorative resins.

Background: Fracture of provisional fixed partial denture (FPD) may jeopardize the success of provisional prosthodontic treatment phase and cause patient discomfort. Aim: The aim of this study was to compare the fracture toughness of the Polymethyl Methacrylate (PMMA) resin and Bis-Acryl Composite (BAC) resin reinforced with the Polyethylene and Glass fibers. Materials and Methods: Three groups (N=10) of each of the two materials were prepared for the fracture toughness test. Two groups had the different reinforcements and group without reinforcement served as the control. The mean fracture toughness (MPa.m½ ) was compared by One-way ANOVA, followed by the Scheffe analysis. Fracture toughness between fiber-reinforced PMMA and BAC resin was compared by the independent samples t test. Results: For the controls, the fracture toughness for PMMA resin (0.91) was significantly lower than for the BAC resin (1.19). Glass fiber reinforcement produced significantly higher fracture toughness for both, PMMA (1.48) and BAC (1.82) resin, but the Polyethylene fibers did not (0.95 for PMMA and 1.23 for BAC resin). Among the reinforced groups, Silane impregnated Glass fibers showed highest fracture toughness for the BAC resin (1.82). Conclusion: Of two fiber reinforcement methods evaluated, Glass fiber reinforcement for the PMMA and BAC resin produced highest fracture toughness. Clinical Implications: On the basis of this in--vitro study, the use of Glass and Polyethylene fibers tested may be an effective way to reinforce resins used to fabricate fixed provisional restorations.

Effect of mental toughness level on positive and negative emotion and mental health in children with epilepsy / 中华行为医学与脑科学杂志

ObjectiveTo explore the effect of mental toughness level on positive and negative emotion and mental health in children with epilepsy.MethodsIn accordance with the International League against epilepsy and epilepsy syndrome in 1989 International Classification of young children with epilepsy,160 cases were sampled.Based on the Adolescent Resilience Scale ( HKRA ) score,according to the 27％ principles of delimitation,the patients were divided into high HKRA score group and low HKRA score group,43 cases in each group.Then positive emotions and negative affect scale (PANAS),mental health test (MHT) were applied to two groups.Results,Except family support dimension,the others HKRA dimension and total score were higher in female children with epilepsy than those in male patients,there was significant difference (P＜ 0.01 ).The positive affect score were higher in high HKRA score group than that of low HKRA group ; and negative emotion was significantly lower than that in low HKRA group (P＜ 0.01 ).Except physical symptom dimension,other dimensions and total score of HKRA in high HKRA score group were higher than those in low HKRA group,there was significant difference (P＜ 0.01 ).Children with epilepsy HKRA score was positive correlation with positive emotion score but negative correlation with negative affect scores (P ＜ 0.01 ) ; in addition to physical symptom,HKRA score and MHT score,and all the other dimensions were negatively related (P＜0.01 or 0.015).ConclusionThe mental toughness level are significantly related to children's epilepsy patients with positive and negative emotion and mental health status.A high level of mental toughness can increase positive emotional experience,and reduce the negative emotional experience of children with epilepsy.

Effect of aging on rising fracture resistance in human dentin / 医用生物力学

Objective To investigate effects of aging on the fracture mechanical behavior of human dentin with finite element numerical method. Methods The finite element model was established according to the typical compact tension specimen in the experiment. The stable crack growth in human dentin was simulated with the cohesive zone model to compare the crack extensions of the young and aged dentin. Results The growth toughness and plateau toughness of the aged dentin were 0.51 and 1.19 MPa•m1/2, respectively, which were significantly lower than those of the young dentin (7.48, 1.71 MPa•m1/2). However, the initiation toughness of the young and aged dentin showed no significant difference with 0.51 and 0.38 MPa•m1/2, respectively. Conclusions The crack growth resistance of human dentin is decreased significantly with aging. Based on the cohesive zone model, the crack growth behavior of biological hard tissue, whose mechanical properties are related with age (such as the human dentin), can be well predicted by using numerical methods.