Comportamiento Mecánico de un Premolar Humano Sano Sometido a Fuerzas Funcionales y Disfuncionales en un MEF / Mechanical Behavior of a Healthy Human Premolar Subjected to Functional and Dysfunctional Forces in a FEM

El propósito de este estudio fue analizar el comportamiento mecánico de la estructura dental sana de un primer premolar inferior humano sometido a fuerzas funcionales y disfuncionales en diferentes direcciones. Se buscó comprender, bajo las variables contempladas, las zonas de concentración de esfuerzos que conllevan al daño estructural de sus constituyentes y tejidos adyacentes. Se realizó el modelo 3D de la reconstrucción de un archivo TAC de un primer premolar inferior, que incluyó esmalte, dentina, ligamento periodontal y hueso alveolar considerando tres variables: dirección, magnitud y área de la fuerza aplicada. La dirección fue dirigida en tres vectores (vertical, tangencial y horizontal) bajo cuatro magnitudes, una funcional de 35 N y tres disfuncionales de 170, 310 y 445 N, aplicadas sobre un área de la cara oclusal y/o vestibular del premolar que involucró tres contactos estabilizadores (A, B y C) y dos paradores de cierre. Los resultados obtenidos explican el fenómeno de combinar tres vectores, cuatro magnitudes y un área de aplicación de la fuerza, donde los valores de esfuerzo efectivo equivalente Von Mises muestran valores máximos a partir de los 60 MPa. Los valores de tensión máximos se localizan, bajo la carga horizontal a 170 N y en el proceso masticatorio en la zona cervical, cuando la fuerza pasa del 60 %. Sobre la base de los hallazgos de este estudio, se puede concluir que la reacción de los tejidos a fuerzas funcionales y disfuncionales varía de acuerdo con la magnitud, dirección y área de aplicación de la fuerza. Los valores de tensión resultan ser más altos bajo la aplicación de fuerzas disfuncionales tanto en magnitud como en dirección, produciendo esfuerzos tensiles significativos para la estructura dental y periodontal cervical, mientras que, bajo las cargas funcionales aplicadas en cualquier dirección, no se generan esfuerzos lesivos. Esto supone el reconocimiento del poder de detrimento estructural del diente y periodonto frente al bruxismo céntrico y excéntrico.

SUMMARY: The purpose of this study was to analyze the mechanical behavior of the healthy dental structure of a human mandibular first premolar subjected to functional and dysfunctional forces in different directions. It was sought to understand, under the contemplated variables, the areas of stress concentration that lead to structural damage of its constituents and adjacent tissues. The 3D model of the reconstruction of a CT file of a lower first premolar was made, which included enamel, dentin, periodontal ligament and alveolar bone considering three variables: direction, magnitude and area of the applied force. The direction was directed in three vectors (vertical, tangential and horizontal) under four magnitudes, one functional of 35 N and three dysfunctional of 170, 310 and 445 N, applied to an area of the occlusal and/or buccal face of the premolar that involved three stabilizing contacts (A, B and C) and two closing stops. The results obtained explain the phenomenon of combining three vectors, four magnitudes and an area of force application, where the values of effective equivalent Von Mises stress show maximum values from 60 MPa. The maximum tension values are located under the horizontal load at 170 N and in the masticatory process in the cervical area, when the force exceeds 60%. Based on the findings of this study, it can be concluded that the reaction of tissues to functional and dysfunctional forces varies according to the magnitude, direction, and area of application of the force. The stress values turn out to be higher under the application of dysfunctional forces both in magnitude and in direction, producing significant tensile stresses for the dental and cervical periodontal structure, while under functional loads applied in any direction, no damaging stresses are generated. This supposes the recognition of the power of structural detriment of the tooth and periodontium against centric and eccentric bruxism.

Effect of temperature and time on rheological properties of Daphnes Giraldii Cortex post-crosslinking gel plaster / 中草药

Objective: To provide scientific basis for the temperature condition of Daphnes Giraldii Cortex (DGC) post-cross-linked gel plaster during storage and transportation. Methods: Taking linear viscoelastic region, modulus, yield stress, phase angle, composite viscosity and creep compliance as evaluation indexes, amplitude scanning, frequency scanning, temperature scanning and creep testing were carried out on the cross-linked gel plaster matrix after DGC by an advanced rotary rheometer, and relevant data of elastic modulus, viscosity modulus, phase angle, composite viscosity, creep compliance and yield stress of the samples which were stored at room temperature, -20 ℃ and -50 ℃ for 1, 3, 8, and 13 d were respectively obtained. Results: All samples of DGC post-crosslinking gel plaster showed elastic characteristics and stable state. After storage under different conditions, the state is still stable and the dispersibility is better. The peel strength of samples stored for 8 d and 13 d was decreased. The retention of samples stored at -50 ℃ for 13 d was decreased. Conclusion: DGC plaster containing post-crosslinked gel matrix had stable state, good dispersibility, initial adhesion, peel strength and shape retention when samples were stored below 0 ℃ for 3 d.

Research advances in biodegradable intervertebral fusion cage for spine / 局解手术学杂志

Objective At present, the mainstream surgical mode and the gold standard for the treatment of spine related diseases are still the intervertebral fusion with the intervertebral implantation of the intervertebral fusion device.The intervertebral fusion device routinely used in clinical practice cannot degrade in vivo after implantation, resulting in lifelong foreign body.High elastic modulus also leads to osteoporosis in adjacent vertebral bodies, which leads to implant sinking, stress shielding and'pseudomorphism'of fusion.The ideal biodegradable synthetic intervertebral fusion cage can be progressively degraded and eventually replaced by new bone, which has the advantages of elastic modulus close to cortical bone, good biocompatibility, X-ray permeability and good initial mechanical strength.In this paper, animal analysis of biodegradable intervertebral fusion cage, clinical effect analysis, current shortcomings and future trends were reviewed.

Differential in vitro force degradation of intermaxillary latex and non-latex elastics / Degradación diferencial de fuerza in vitro entre elásticos intermaxilares látex y no látex

ABSTRACT Introduction: Various in vitro studies report that latex and non-latex elastics lose some of their initial force after they have been placed in the oral cavity. However, several differences occur within one single manufacturer, which could be of importance in selecting elastics. The aim of the present study was to conduct an in vitro evaluation of force loss in latex and non-latex elastics of a same manufacturer, activated in conditions simulating the oral cavity. Methods: we used 40 intermaxillary latex (n = 20) and non-latex (n = 20) »" 6 oz (170.10 g) elastics, stretched to 18 mm and immersed in artificial saliva for 24 hours. Force-displacement was measured using a test dynamometer, calculating the percentage of force relaxation (%R) at 0, 6, 12, 18, and 24 hours. The Kruskal-Wallis test was used to compare the groups. Results: latex elastics significantly offered greater force than non-latex elastics during all evaluations (p < 0.05). The %R in latex elastics at 24 hours was 8.7% and 9.2% in non-latex elastics. The largest force loss in both materials occurred during the first six hours. The difference in %R between the two materials was statistically significant between 0 and 6 hours. Conclusions: the latex and non-latex elastics used in this study can be equally used in clinical practice. However, the use of both elastics must be kept under strict control to achieve efficient orthodontic mechanics, since the period of greatest instability occurred between 0 and 6 hours.

RESUMEN Introducción: diversos estudios in vitro reportan que los elásticos látex y no látex pierden parte de su fuerza inicial después de su colocación intraoral. Sin embargo, en un solo fabricante existen diferencias internas que pueden ser importantes durante la selección de los elásticos. El objetivo de esta investigación consistió en evaluar in vitro la pérdida de fuerza en elásticos látex y no látex de un mismo fabricante, activados en condiciones similares a la cavidad oral. Métodos: se utilizaron 40 elásticos intermaxilares látex (n = 20) y no látex (n = 20) de »" 6 oz (170,10 g), extendidos a 18 mm y sumergidos en saliva artificial por 24 horas. Se obtuvo la medición de fuerza-desplazamiento utilizando un dinamómetro de prueba y se calculó el porcentaje de relajación de la fuerza (%R) a las 0, 6, 12, 18 y 24 horas. Se utilizó la prueba de Kruskal-Wallis para hacer la comparación entre los grupos. Resultados: los elásticos látex ofrecieron una fuerza significativamente mayor que los no látex durante todas las evaluaciones (p < 0,05). El %R para los elásticos látex a las 24 horas fue de 8,7% y de 9,2% para los no látex. La mayor pérdida de fuerza en ambos materiales se produjo durante las primeras seis horas. La diferencia en %R entre los dos materiales fue estadísticamente significativa entre las 0 y 6 horas. Conclusiones: los elásticos no látex utilizados en este estudio pueden ser aplicados en clínica al igual que los de látex. Sin embargo, el uso de ambos elásticos debe mantenerse bajo estricto control para obtener una mecánica ortodóncica eficiente, ya que el periodo de mayor inestabilidad se produjo entre las 0 y 6 horas.

The preliminary study on biomechanical properties of four synthetic implants for reconstructive surgery of pelvic floor dysfunction / 生物医学工程学杂志

This study aimed to investigate biomechanical properties of synthetic implants for reconstructive surgery of pelvic floor dysfunction. In this dissertation, we chose four synthetic implants, i.e. total pelvic floor repair system (PROLIFT), gynecone TVT obtutator system (TVT-O), intra-vaginal sling placement device (IVS) and acellular dermal matrix (Renov), for tensile test respectively. The biomechanical properties of four synthetic implants were measured and analyzed using a material testing machine (Instron 4302 versatile material testing machine). The biomechanical parameters included ultimate stress strength, modulus of elasticity, maximum load and maximum elongation. The results showed that the maximum load of the four symthetic implants was TVT-O > IVS > PROLIFT > Renov, and the maximum load of TVT-O was significantly higher than PROLIFT and Renov ( < 0.05). The ultimate stress strength was TVT-O > IVS > PROLIFT > Renov, with no significant differences among them ( > 0.05). The maximum elongation of the four implants was TVT-O > PROLIFT > IVS > Renov, and the maximum elongation of TVT-O and PROLIFT were both significantly higher than Renov ( < 0.05). The modulus of elasticity was IVS > Renov > TVT-O > PROLIFT, with no significant differences among them ( > 0.05). Taken together, the present study demonstrates that the modulus of elasticity of IVS was the highest in the four synthetic implants; TVT-O had the highest mechanical strength; The maximum load, ultimate stress strength and maximum elongation of Renov were all the lowest; The mechanical properties of PROLIFT was the most stable, and its modulus of elasticity was the lowest in the four synthetic implants, which had good extensibility and elasticity. Therefore, it is necessary to pay attention to the biomechanical properties of new pelvic reconstructive materials for the clinical pelvic reconstructive surgery.

Comparison of flexural strength and modulus of elasticity in several resinous teeth splinting materials

PURPOSE: Direct splinting material should have high flexural strength to withstand force during mastication and low modulus of elasticity to provide some movement while force applied for relief of stress. The purpose of this study was to compare flexural strength and modulus of elasticity of several resinous splinting materials. MATERIALS AND METHODS: Four materials; Super-Bond C&B, G-FIX, G-aenial Universal Flo, FiltekTM Z350 XT; were used in this study. Fifteen rectangular bar specimens of each material were prepared. Three-point bending test were performed to determine physical properties. Maximum load at fracture was recorded and flexural strength and modulus of elasticity were calculated. One-way analysis of variance (ANOVA) and Scheffe's tests at a 0.05 level of significance were conducted on all test results. RESULTS: Statistical analysis reveals that Super-Bond C&B had significant low mean value for flexible strength and the other three materials showed no significant difference. For modulus of elasticity, Super-Bond C&B exhibited statistically lower modulus of elasticity. G-FIX presented intermediate result, showing statistically higher modulus of elasticity than Super-Bond C&B but lower than G-aenial Universal Flo and FiltekTM Z350 XT. There was no significant difference on modulus of elasticity between G-aenial Universal Flo and FiltekTM Z350 XT. CONCLUSION: Using a G-FIX, the newly commercially available splinting material, which shows higher fracture resistance properties comparable to flowable and restorative composite resin and a relatively flexible nature might be a beneficial for stabilizing teeth mobility.

Monobloque aspecto funcional: postes de fibra de vidrio / Monoblocks and functionality: the case for fiberglass posts

Durante muchos años se han utilizado los postes colados, considerados como un estándar en la odontología protésica, pero presentan limitantes técnicas y mecánicas, ya que exhiben altos módulos de elasticidad y, por lo mismo, imposibilitan la capacidad de disipar las fuerzas con efectividad, lo que significa concentrar tensiones dentro del conducto radicular. Literatura basada en evidencia científica describe a los postes de fibra de vidrio con módulos de elasticidad semejantes o próximos a la dentina, presentando propiedades anisotrópicas, en comparación con los postes tradicionales, que presentan propiedades isotrópicas. Se propone un concepto restaurador que involucra el poste, el cemento y la dentina, constituyendo un complejo homogéneo denominado ®monobloque¼ que permite un mejor comportamiento mecánico benéfico para el remanente dentario

For many years now, cast posts have been regarded as standard in prosthetics despite the technical and mechanical limitations caused by their high moduli of elasticity, which prevent the forces involved from being effectively dissipated and, therefore, concentrate stress within the root canal. Scientifi c evidence-based literature describes fi berglass posts with moduli of elasticity similar to or approaching that of dentin as having anisotropic properties, as opposed to the isotropic properties of traditional posts. We propose a restorative approach that involves the post, the cement, and the dentin, forming a homogeneous complex known as a ®monobloc¼ that enables enhanced mechanical behavior that benefits the remaining tooth structure.

Right wire in orthodontics: a review

Quality of orthodontic wire such as stiffness, hardness, resiliency, elasticity and working range are important determinants of the effectivenes of tooth movement. Commonly used types of orthodontic arch wire:1) stainless steel(ss) wire, 2) conventional nickel- titanium (NiTi)alloy wire,3) improved super elastic NiTi- alloy wire( also called low hysteresis(LH)wire), and titanium molybdenum alloy(TMA) wire.

Analysis of flexural strength of composite resins polymerized by 2nd and 3rd generation leds / Análise da resistência flexural de resinas compostas polimerizadas por led 2a e 3a geração

Este estudo teve o propósito de investigar as propriedades mecânicas de 3 resinas compostas, utilizando dois fotopolimerizadores à luz de LED com diferentes densidades de potência. Material e Métodos: Sessenta espécimes (2x2x12 mm) de 3 marcas comerciais de resina composta (n = 20): Grupo Z350 - resina composta nanoparticulada Filtek Z350(3M ESPE), Grupo AP - resina composta microhíbrida Amelogen Plus (Ultradent), Grupo DF - resina composta microparticulada Durafil (Heraeus Kulzer). Em seguida, os grupos foram divididos em 2 subgrupos de acordo com LED utilizado para fotopolimerização, variando a densidade de potência: Subgrupo 500 - 500 mw/cm2 (2ª geração); Subgrupo 1100 - 1100 mw/cm2 (2ª geração). Os espécimes foram armazenados em recipiente escuro e seco à 37 ºC em estufa por 24 h e submetidos ao ensaio de mini-flexão na máquina de Ensaio Universal EMIC para determinar o módulo de elasticidade e resistência à flexão 3 pontos. Os dados foram submetidos aos testes ANOVA dois fatores (Resina composta X LED) e Tukey (5%). Resultados: Para a resistência flexural, ANOVA mostrou diferenças significantes para a interação entre os fatores: Grupo Z350/1100 (em Mpa) - 105,36a; Grupo AP/1100 - 81,49ab; Grupo DF/1100 - 66,43bc; Grupo AP/500 - 66,13bc; Grupo DF/500: 60,61bc; Grupo Z350/500: 47,19c. Para o módulo de elasticidade, ANOVA mostrou diferenças significantes para o fator Resina composta: Grupo Z350 (em GPa): 8,85a; Grupo AP: 7,61b; Grupo DF: 1,94c; e para o fator LED: Subgrupo 1100: 7,13a; Subgrupo 500:5,14b. Conclusão: O LED de 3ª geração (1100 mw/cm2 ) demonstrou aumentar significantemente as propriedades flexurais das resinas compostas, e o tipo de partícula de carga da resina composta parece influenciar diretamente nas propriedades flexurais das resinas compostas...

This study aimed to investigate the mechanical properties of three composite resins using 2nd and 3rd generation LED-based light-curing devices. Material and Methods: Sixty specimens distributed according to the type of resin (Group Z350 - nanoparticle composite resin [Filtek Z350 / 3M ESPE]; Group AP - microhybrid composite Amelogen Plus/Ultradent; Group DF - Group composite resin Durafil l/Heraeus Kulzer), and the light-curing device (Group 2ndG - 2nd generation LEDbased curing unit at power density of 500 mW/cm2 ; Group 3rdG - 3rd generation LED-based curing unit at power density of 1100 MW/cm2 ). The specimens were stored in a dark, dry container at 37 °C in an incubator for 24 h and submitted to the mini-flexural test on universal test machine (EMIC) to determine the elastic modulus and flexural strength using a three-point test. The data were submitted to twoway ANOVA (Resin Composite X LED) and Tukey test (5%). Results: Concerning to flexural strength (in MPa), ANOVA showed significant in Tukey test for the interaction between the factors: Group Z350/3rdG - 105.36a; Group AP/3rdG – 81.49ab; Group DF/3rdG – 66.43bc; Group AP/2ndG – 66.13bc; Group DF/2ndG: 60.61bc; Group Z350/2ndG: 47,19c. With regard to the modulus of elasticity (in GPa), the results obtained were: Factor resin composite - Group Z350 (8.85a) > Group AP (7.61b) > Group DF (1.94c); Factor LED - Group 3rdG (7.13a) > Group 2ndG (5.14b). Conclusion: It was concluded that the 3rd generation LED (1100 mw/cm2 ) significant increased the means of the flexural properties of composites. It was also concluded that the result of flexural properties of composites depends on the resin material tested...

Metodologia para o cálculo dos módulos de elasticidade longitudinal e transversal em vigas de madeira de dimensões estruturais / Methodology used to determine the shear and longitudinal modulus of elasticity in timber beams

Este trabalhou objetiva apresentar uma metodologia analítica para o cálculo dos módulos de elasticidade longitudinal (E) e transversal (G) em vigas de madeira de dimensões estruturais, segundo o emprego das teorias de vigas de Euler Bernoulli e Timoshenko, sendo utilizado o ensaio de flexão estática a três pontos. As madeiras testadas foram o Pinus elliottii e a Corymbia citriodora. Os resultados encontrados relevaram ser o módulo de elasticidade longitudinal 18,70 vezes superior ao módulo transversal do Pinus elliottii e 21,2 superior ao módulo transversal do Corymbia citriodora, sendo estes compatíveis quando comparada a relação entre E e G estabelecida pela norma Brasileira ABNT NBR 7190:1997 (Projeto de Estruturas de Madeira), que define ser o módulo de elasticidade longitudinal vinte vezes superior ao transversal.

This paper proposed a test method to obtain the shear (G) and longitudinal (E) modulus of elasticity in timber beams with structural dimensions, based on the static three-points bending tests and the Euler Bernoulli and Timoshenko beams theories. The woods tested were the Corymbia citriodora and Pinus elliottii. The results revealed that the longitudinal modulus of elasticity of Pinus elliottii is 18.70 greater than the shear modulus, and 21.16 greater than the shear modulus of Corymbia citriodora, being consistent this results when compared to the proposed by the Brazilian standard ABNT NBR 7190:1997 (Design of Wood Structures), being the longitudinal modulus of elasticity twenty times greater than the shear modulus.

Value of the shear wave elasticity in the diagnosis of benign and malignant breast lesions / 中华超声影像学杂志

Objective To evaluate the value of supersonic shear wave elastrography(SWE) in the diagnosis of benign and malignant breast lesions.Methods SWE was performed on 134 breast lesions of 123 female patients and 74 normal breast glands to determine the values of overall elastic modulus and dispersion,and ROC curves were used to assess the diagnosis boundary value of two kinds of data respectively.Results According to the diagnostic gold standard-histopathology,the values of overall elastic modulus and dispersion were statistically significant when comparing benign lesions and malignant lesions with normal glands.ROC curve displayed that,when the Youden index reached to maximum,the diagnosis boundary value of overall elastic modulus was 41.01 kPa,the sensitivity and specificity of the value were 68.5％ and 83.8％ respectively; the diagnosis boundary value of dispersion was 12.25 kPa,the sensitivity and specificity of the value were 87.0％ and 88.7％ respectively.Conclusions The values of overall elastic modulus and dispersion for solid breast lesions can be used to reflect the elastic characteristics of lesions quantificationally,which is useful to diagnose benign and malignant breast lesions in clinical.

Infinite to finite: An overview of finite element analysis.

The method of finite elements was developed at perfectly right times; growing computer capacities, growing human skills and industry demands for ever faster and cost effective product development providing unlimited possibilities for the researching community. This paper reviews the basic concept, current status, advances, advantages, limitations and applications of finite element method (FEM) in restorative dentistry and endodontics. Finite element method is able to reveal the otherwise inaccessible stress distribution within the tooth-restoration complex and it has proven to be a useful tool in the thinking process for the understanding of tooth biomechanics and the biomimetic approach in restorative dentistry. Further improvement of the non-linear FEM solutions should be encouraged to widen the range of applications in dental and oral health science.

Tensile properties of orthodontic elastomeric ligatures.

Context: Tensile properties of elastomeric ligatures become important when efficiency of orthodontic appliances is considered. Aims: The aim of this study was to compare tensile strength, extension to tensile strength, toughness and modulus of elasticity of elastomeric ligatures in both the as-received condition and after 28 days of immersion in the simulated oral environment. Furthermore, the changes that occurred in tensile properties of each brand of ligatures after 28 days were evaluated. Setting and Design : Experimental-laboratory based. Materials and Methods: Elastomeric ligatures were obtained from different companies and their tensile properties were measured using Zwick testing machine in both the as-received condition and after 28 days of immersion in the simulated oral environment. Statistical Analysis Used: The data were analyzed using independent sample t-tests, analysis of variance and Tukey tests. Results: After 28 days, all the ligatures experienced a significant decrease in tensile strength, extension to tensile strength and toughness ( P < 0.05), whereas modulus of elasticity increased in some groups and decreased in others. There were significant differences in tensile properties of different brands of ligatures in both conditions ( P < 0.05), with the exception of modulus of elasticity after 28 days. Conclusions : The decrease in strength properties of elastomeric ligatures shows that they should be replaced at each appointment to reduce the risk of rupture. There are significant differences in tensile properties of different brands of ligatures, which should be considered during selection of these products.

Low modulus titanium alloy plating for femoral shaft fractures: A finite element analysis / 中华创伤骨科杂志

Objective To investigate the effects of internal plating with high and low moduli of elasticity on the stress and its distribution on the femoral shaft fracture. Methods A femur from a normal Chinese adult male was scanned by 64-detector row helical CT at 0. 5 mm interval. The CT images were used to establish a finite element model of the femur by software. The mid-femoral fracture was simulated in the model and fixated by eight-hole plates of Ti-6Al-4V (high modulus group, E = 110 GPa) and of Ti2448 (low modulus group, E = 30 GPa). When the femur was in axial compression, flexion and torsion loads, the stress and its distribution on the bone fracture site were analyzed to compare the biomechanics of the plates with high and low moduli. Results Under axial compression load, the contact stress between fracture ends in the low modulus group was larger than that in the high modulus group, while the max stress at the hole (11.47MPa) was smaller than that in the high modulus group (13.89 MPa) . Under four-point bending load, the contact stress in the low modulus group was still larger, while the bending movement was smaller. Under the torsion load, stress on the femur was well-distributed in both groups, but the max stress at the hole in the low modulus group (11.47 MPa) was smaller than that in the high modulus group (31.24 MPa). Conclusions Under internal fixation by plates of low modulus, the stress stimulus at the fracture site may be increased,while the stress concentrated at the hole may be decreased. The stress shielding of the low modulus plate may also be modified.

Comparison of the elastic modulus among three dentin adhesives before and after thermocycling / 대한치과보존학회지

The purpose of this study was to determine the effects on the elastic moduli of the adhesive and the hybrid layer from thermocycling. Twenty one human molars were used to create flat dentin surfaces. Each specimen was bonded with a light-cured composite using one of three commercial adhesives (OptiBond FL [OP], Clearfil SE Bond [CL], and Xeno III [XE]). These were sectioned into two halves and subsequently cut to yield 2-mm thickness specimens; one specimen for immediate bonding test without thermocycling and the other subjected to 10,000 times of thermocycling. Nanoindentation test was performed to measure the modulus of elasticity of the adhesive and the hybrid layer, respectively, using an atomic force microscope. After thermocycling, XE showed a significant decrease of the modulus in the adhesive layer (p < 0.05). Adhesives containing hydrophilic monomers are prone to hydrolytic degradation. It may result in the reduced modulus of elasticity, which leads to the mechanically weakened bonding interface.

Cuspal deflection in class V cavities restored with composite resins / 대한치과보존학회지

The purpose of this study was to evaluate the effect of the polymerization shrinkage and modulus of elasticity of composites on the cusp deflection of class V restoration in premolars. The sixteen extracted upper premolars were divided into 2 groups with similar size. The amounts of cuspal deflection were measured in Class V cavities restored with a flowable composite (Filtek flow) or a universal hybrid composite (Z-250). The bonded interfaces of the sectioned specimens were observed using a scanning electron microscopy (SEM). The polymerization shrinkage and modulus of elasticity of the composites were measured to find out the effect of physical properties of composite resins on the cuspal deflection. The results were as follows. 1. The amounts of cuspal deflection restored with Filtek flow or Z-250 were 2.18 +/- 0.92 microm and 2.95 +/- 1.13 microm, respectively. Filtek flow showed less cuspal deflection but there was no statistically significant difference (p > 0.05). 2. The two specimens in each group showed gap at the inner portion of the cavity. 3. The polymerization shrinkages of Filtek flow and Z-250 were 4.41% and 2.23% respectively, and the flexural modulus of elasticity of cured Filtek flow (7.77 GPa) was much lower than that of Z-250 (17.43 GPa). 4. The cuspal deflection depends not only on the polymerization shrinkage but also on the modulus of elasticity of composites.

The mechanical properties of a new Ti-Nb-Zr-Sn alloy with low elastic modulus for dental use / 实用口腔医学杂志

Objective:To study the mechanical properties of a new titanium alloy with lower elastic modulus for prosthodontic use.Methods:Samples of a newly developed Ti-Nb-Zr-Sn alloy with low elastic modulus were prepared.The microstructure,microhardness profile of the specimen cross section were measured by microhardness test meter and metallurgical microscope.Results:The data of the tensile strength(MPa),yield strength(MPa),elongation(%),elastic modulus(GPa) and microhardness(Hv)of Ti-Nb-Zr-Sn alloy were 681.7,410,6,42.1 and 453 respectively.The microstructure was with fine crystal grains.Conclusion: The microstructure and microhardness profile of the Ti-Nb-Zr-Sn alloy may meet the requirement for dental applications.