Effects of thermal cycling on bonding properties of novel low-shrinkage resin adhesive / 华西口腔医学杂志

OBJECTIVES@#The current study aimed to investigate the bonding properties of a novel low-shrinkage resin adhesive containing expanding monomer and epoxy resin monomer after thermal cycling aging treatment.@*METHODS@#Expanding monomer of 3,9-diethyl-3,9-dimethylol-1,5,7,11-tetraoxaspiro-[5,5] undecane (DDTU) as an anti-shrinkage additive and unsaturated epoxy monomer of diallyl bisphenol A diglycidyl ether (DBDE) as a coupling agent were synthesized. A blend of DDTU and DBDE at a mass ratio of 1∶1, referred to as "UE", was added into the resin matrix at the mass fraction of 20% to prepare a novel low-shrinkage resin adhesive.Then, the methacrylate resin adhesive without UE was used as the blank control group, and a commercial resin adhesive system was selected as the commercial control group. Moreover, the resin-dentin bonding and micro-leakage testing specimens were prepared for the thermal cycling aging treatment. The bonding strength was tested, the fracture modes were calculated, the bonding fracture surface was observed by scanning electron microscope (SEM), and the dye penetration was used to evaluate the tooth-restoration marginal interface micro-leakage. All the data were analyzed statistically.@*RESULTS@#After aging, the dentin bonding strength of the experimental group was (19.20±1.03) MPa without a significant decrease (P>0.05), that of the blank control group was (11.22±1.48) MPa with a significant decrease (P<0.05) and that of the commercial control group was (19.16±1.68) MPa without a significant decrease (P>0.05). The interface fracture was observed as the main fracture mode in each group after thermal cycling by SEM. The fractured bonding surfaces of the experimental group often occurred on the top of the hybrid layer, whereas those of the blank and commercial control groups mostly occurred on the bottom of the hybrid layer. Micro-leakage rating counts of specimens before and after thermal cycling were as follows: the experimental group was primarily 0 grade, thereby indicating that a relatively ideal marginal sealing effect could be achieved (P>0.05); meanwhile, the blank control group was primarily 1 grade, and the penetration depth of dye significantly increased after thermal cycling (P<0.05); the commercial control group was primarily 0 grade without statistical difference before and after thermal cycling (P>0.05), while a significant difference was observed between the commercial control group and experimental group after thermal cycling (P<0.05).@*CONCLUSIONS@#The novel low-shrinkage resin adhesive containing 20%UE exhibited excellent bonding properties even after thermal cycling aging treatment, thereby showing a promising prospect for dental application.

A comparative evaluation of gingival microleakage and internal voids in Class II composite restoration with two different lining techniques An in vitro study

Aim: The aim of this study was to evaluate the gingival microleakage and internal voids in Class II composite restoration restored with precure and co-cure lining techniques using stereomicroscopic method. Materials and Methods: Forty-five freshly extracted permanent multirooted human molar teeth were collected and used in the study. After surface debridement and scaling of all teeth, standard Class II mesio-occlusal cavities were prepared. Forty-five samples were randomly divided into three experimental groups (n = 15), and filled according to manufacturer's instructions. Group I was precure group, Group II was co-cure group, and Group III was only bulk fill. The finishing and polishing of the restorations was done after 24 h. Then, all the specimens were subjected to thermocycling for 500 cycles. The gingival microleakage and internal voids of all the groups were evaluated using dye penetration method. Samples were then sectioned and examined under the stereomicroscope at ×40. Readings obtained were subjected to statistical analysis using SPSS ver 20.0 (IBM Corp, ARMONK USA) and Chi-square test. Results: The statistical analysis revealed that extent of microleakage was maximum in Group II (co-cure), followed by Group III (only bulk fill) and Group I (precure). The gingival voids were maximum in Group III (only bulk fill), minimum in Group II (co-cure), and least in Group I (precure). The cervical voids were maximum in Group II (co-cure) and Group III (only bulk fill), followed by Group I (precure). The occlusal voids were maximum in Group II (co-cure) and similar in Group I (precure) and Group III (only bulk fill). Conclusion: The precure lining technique was better than co-cure lining technique in terms of both microleakage and internal voids.

Research progress on the antibacterial properties of dental resin materials / 口腔疾病防治

@#Dental resin materials have been widely used in the treatment of dental defects. However, the polymerization shrinkage of the resin materials tends to cause microleakage and accumulation of bacterial plaque, which leads to secondary dental caries. Endowing dental resin with antibacterial properties is an important way to solve this problem. Adding antibacterial agents to dental resin is the main method to give it antibacterial properties. Antimicrobial agents are mainly divided into three types: release type, non-release type and mixed type. In terms of antibacterial effects, the selection and addition of antibacterial agents will affect the antibacterial and mechanical properties of dental resin materials; and the long-term antibacterial effect of antimicrobial agents in the oral cavity remains to be verified; as antimicrobial agents or other environmental factors can lead to drug resistance and even dormant persistent bacteria. In recent years, researchers have been committed to improving the antibacterial effect by modifying antibacterial agents. The sustained release of antimicrobial agents via carriers is also the main research direction. This paper reviews the research progress on the antibacterial properties of dental resin materials.

Knowledge about composite restorations repair vs replacement- a survey among a subpopulation of saudi dental students / Conhecimento sobre reparo e substituição de restaurações de resina - uma pesquisa entre uma subpopulação de estudantes sauditas de odontologia

Objective: The purpose of this study was to evaluate the knowledge among dental students at King Khalid University, Jazan University, and Najran University in the kingdom of Saudi Arabia about when to repair or replace defective direct composite restoration. Materials and Methods: A questionnaire-based survey was formulated, pursuing the information about management (repair/replacement) of defective composite restorations and distributed among 200 dental students of three universities in the southern region of the kingdom of Saudi Arabia. The data were collected with the help of an online questionnaire. Data entry and the analysis were done using the statistical software package SPSS version 20.0. It was presented using descriptive statistics in the form of frequencies and percentages for qualitative variables, and range means and standard deviations for age, quantitative variable. Analytic statistics were done using Chi-Square tests (χ2) to test the significant difference between categorical variables. The level of significance, the p-value was 0.01(p<0.01). Results: The decision to choose between composite repair or replacement was influenced by whether this topic was taught to them at various undergraduate levels during Bachelor of Dental Surgery. The reason associated with the decision to repair defective composite restorations, 76% reported as cost-effective followed by Increased longevity (71%), the permanent filling (70%), patient's preference for repair (65%), and least time consuming (50%). 67% participants preferred significantly (p<0.001) repair due to secondary caries in the previously restored tooth with composite, followed by the small surface defect in a composite restoration (65%), risk of pulpal damage significantly (p<0.001) in a defective composite restoration (62.5%) and more invasive and destructive treatment option (35%). More than half of respondents 123 (61.5%) reported that they were not taught about composite repair during the Bachelor of Dental Surgery. Conclusion: It is suggested with the help of our study that didactic and clinical training components regarding composite repair should be seriously included in the teaching curriculum of dental institutions as it is in the best interest of the patient. Dental students should be provided with clinical training on this topic so that they can follow proper decision-making protocols available during repair or replacement of defective resin composite restorations. Other researches in the future can be carried out for refining the guidelines and techniques utilized for composite repair. (AU)

Objetivo: O objetivo deste estudo foi avaliar o conhecimento entre estudantes de odontologia da King Khalid University, Jazan University e Najran University, no reino da Arábia Saudita, sobre quando reparar ou substituir restaurações de resina composta direta defeituosas. Material e Métodos: Foi formulada uma pesquisa baseada em questionário, buscando informações sobre o manejo (reparo / substituição) de restaurações de resina composta e distribuída entre 200 estudantes de odontologia de três universidades da região sul do reino da Arábia Saudita. Os dados foram coletados com o auxílio de um questionário online. A entrada e análise dos dados foram feitas com o software estatístico SPSS versão 20.0. Foi apresentado por meio de estatística descritiva na forma de frequências e percentuais para as variáveis qualitativas, e amplitude de médias e desvios-padrão para a idade, variável quantitativa. A estatística analítica foi feita usando testes de qui-quadrado (χ2) para testar a diferença significativa entre as variáveis categóricas. Ao nível de significância, o valor de p foi de 0,01 (p <0,01). Resultados: A decisão de escolher entre o reparo ou substituição do compósito foi influenciada pelo fato de este tópico ter sido ensinado a eles em vários níveis de graduação durante o Bacharelado em Odontologia. O motivo associado à decisão de reparar restaurações de resina composta defeituosas, 76% relataram como custo-benefício seguido por maior longevidade (71%), restauração definitva (70%), preferência do paciente para reparo (65%) e menos demorado ( 50%). Sessenta e sete por cento dos participantes preferiram o reparo significativamente (p <0,001) devido a cárie secundária no dente previamente restaurado com resina composta, seguido pelo pequeno defeito de superfície em uma restauração composta (65%), risco de dano pulpar significativamente (p <0,001) em um restauração de resina composta com defeito (62,5%) e opção de tratamento mais invasiva e destrutiva (35%). Mais da metade dos entrevistados, 123 (61,5%) relataram que não foram ensinados sobre reparo de resina composta durante o Bacharelado em Odonotlogia. Conclusão: É sugerido com a ajuda de nosso estudo que os componentes do treinamento didático e clínico sobre reparo de resina composta devem ser seriamente incluídos no currículo de ensino de instituições odontológicas, pois é do interesse do paciente. Os estudantes de odontologia devem receber treinamento clínico sobre este tópico para que possam seguir os protocolos de tomada de decisão adequados disponíveis durante o reparo ou substituição de restaurações de resina composta com defeito. Outras pesquisas no futuro podem ser realizadas para refinar as diretrizes e técnicas utilizadas para reparo de resina (AU)

Factors influencing clinical application of bulk-fill composite resin / 华西口腔医学杂志

Bulk-fill composite resin are simple to operate, and they reduce polymerization shrinkage and microleakage compare to traditional resin-based composites. However, their clinical application could be affected by numerous factors, such as the material itself, light curing, placement techniques, storage condition, and preheating. This review aimed to summarize the definitions, classifications, indications, clinical properties, and influencing factors of the clinical application of bulk-fill resin-based composites and discuss the ways to improve their clinical effectiveness.

Comparison of the Polymerization Shrinkage of Eclipse Resin for Prostheses with Conventional Acrylic Resins / Comparación de la Contracción de Polimerización de la Resina Eclipse para Prótesis con Resinas Acrílicas Convencionales

ABSTRACT: The objective of this study was to compare the polymerization shrinkage of Eclipse photopolymerization resin for prosthesis based on urethane dimethacrylate (UDMA) with that of three heat-cured acrylic resins based on polymethyl methacrylate (PMMA) after the polymerization process and immersion in water. A total of 40 prostheses were fabricated on a standard metallic upper edentulous model: group 1, Eclipse; group 2, Triplex hot; group 3, Veracril; and group 4, Lucitone 199. Subsequently, the polymerization contraction was tested using a microscope in which measurements were made in micrometres at 3 points located in the middle parts of the right and left sides and the middle part of the palate at three time points once the prosthesis was completed, after 30 days of immersion in water for 8 hours a day at a temperature of 37 °C, and after cutting the prosthesis at the level of the second premolar. ANOVA revealed that the contraction of the polymerization no statistically significant differences between the groups, (P> 0.05). The type of resin and its interaction with the processing method behaves similarly for all test resins. The Veracril heat-cured resin obtained the lowest contraction value in the three measurements (mm) and the highest value was obtained with the Eclipse photopolymerization resin. The Eclipse resin exhibited no lower polymerization shrinkage compared to conventional acrylic resins based on polymethyl methacrylate (PMMA), however it was not significantly affected by immersion in water.

RESUMEN: El objetivo de este estudio fue comparar la contracción de polimerización de la resina de fotopolimerización Eclipse para prótesis basadas en dimetacrilato de uretano (UDMA) con la de tres resinas acrílicas curadas con calor a base de polimetacrilato de metilo (PMMA) después del proceso de polimerización e inmersión en agua. Se fabricaron un total de 40 prótesis en un modelo edéntulo superior metálico estándar: grupo 1, Eclipse; grupo 2, triplex caliente; grupo 3, veracril; y grupo 4, Lucitone 199. Posteriormente, la contracción de la polimerización se probó utilizando un microscopio en el que se realizaron mediciones en micrometros en 3 puntos ubicados en las partes medias de los lados derecho e izquierdo y la parte media del paladar en tres puntos de tiempo una vez la prótesis se completó, después de 30 días de inmersión en agua durante 8 horas al día a una temperatura de 37 °C, y después de cortar la prótesis a nivel del segundo premolar. ANOVA reveló que la contracción de la polimerización no presenta diferencias estadísticamente significativas entre los grupos, (P> 0,05). El tipo de resina y su interacción con el método de procesamiento se comportan de manera similar para todas las resinas de prueba. La resina curada con calor Veracril obtuvo el valor de contracción más bajo en las tres mediciones (mm) y el valor más alto se obtuvo con la resina de fotopolimerización Eclipse. La resina Eclipse no mostró una contracción de polimerización menor en comparación con las resinas acrílicas convencionales basadas en polimetilmetacrilato (PMMA), sin embargo, no se vio afectada significativamente por la inmersión en agua.

Microleakage in posterior teeth with different materials and different types of cavities

Background: The purpose of this study was to investigate the behavior of a resin-based 2,2-bis (p-[2′-hydroxy-3′-methacryloxypropoxy] phenylene) propane and a composite resin modified with oxirane, regarding the ability of marginal sealing, both with direct restorations and indirect restorations. Materials and Methods: To achieve this, mesio- and disto-occlusal cavities were made on the same tooth, totalling 100 cavities. These cavities were restored with two materials, Filtek P90 (3M ESPE) and Opallis (FGM). Then, they were divided into two groups: Fifty direct restorations, each sample restored with the two materials, following the manufacturer's protocol and fifty indirect restorations, and then cemented with a paste obtained by diluting the resin in its adhesive. The templates were thermally cycled, 30 s at 5°C and 30 s at 55°C for 500 cycles and then were immersed in methylene blue for 24 h. Afterward, they were trimmed using a plaster trimmer from occlusal toward a gingival direction. These samples were analyzed with stereomicroscope (×3) by two blinded observers. Then, a system which considers the average number of surrounding walls that have suffered infiltration on a scale of 0–3 was used. Results: Data were subjected to statistical analysis (Mann–Whitney and Kruskal–Wallis tests) with a significance level of 5% maximum. Conclusion: It was concluded that the indirect restorations showed the greatest number of restorations with score 0 and 1 (34) and lowest score 2 and 3 (16). This suggests that indirect restorations regardless of the material used behaved more effectively regarding the marginal sealing of restorations.

Comparative evaluation of microleakage around Class V cavities restored with alkasite restorative material with and without bonding agent and flowable composite resin: An in vitro study

Background: Marginal adaptability of restorative material is one of the prime factors for success of a restoration. Aim: To evaluate microleakage at enamel restoration and dentin restoration interface of Class V cavities restored with new alkasite restorative material Cention-N, with and without using bonding agent and flowable composite resin. Materials and Methods: Thirty Class V tooth preparations were divided into three groups (n = 10): Group-I restored with Cention-N (Ivoclar Vivadent) without adhesive, Group-II was restored with Cention-N after application of eighth-generation bonding agent (3M ESPE, Single Bond Universal Adhesive), and Group-III was restored with flowable composite resin (Tetric-N-Flow, Ivoclar Vivadent). All samples were subjected to 200 thermocycles between temperature baths at 5°C and 55°C. All samples were cut longitudinally through the center of the restorations with the help of isomet diamond saw. The sections were then observed under binocular stereomicroscope at 20×. Two evaluators scored the depth of dye penetration independently at enamel and dentin margins. Statistical Analysis: Kruskal–Wallis nonparametric analysis followed by Dunn's multiple comparison tests were done to evaluate differences among the experimental groups. Mann–Whitney test was used to compare the difference between occlusal and gingival scores within each restoration. Results: Microleakage seen in decreasing order: Cention-N without adhesive >Flowable composite >Cention-N with adhesive. Conclusion: Microleakage at enamel restoration interface was less than microleakage at dentin restoration interface of each group, but the difference was not statistically significant. Least microleakage was seen with Cention-N with adhesive followed by flowable composite. More microleakage was seen with Cention-N without adhesive.

Degree of Conversion and Polymerization Shrinkage of Low and High Viscosity Bulk-Fill Giomer-based and Resin-based composites / 대한소아치과학회지

The aim of this study was to compare the degree of conversion and polymerization shrinkage of low and high viscosity bulk-fill giomer-based and resin-based composites. Two bulk-fill giomer (Beautifil Bulk Restorative (BBR), Beautifil Bulk Flowable (BBF)), two bulk-fill (Tetric N-Ceram Bulk-fill (TBF), SureFil SDR flow (SDR)) and two conventional resin composites (Tetric N-Ceram (TN), Tetric N-flow (TF)) were selected for this study. The degree of conversion was measured by using Fourier transform infrared spectroscopy. Polymerization shrinkage was measured with the linometer. For all depth, BBR had the lowest degree of conversion and SDR had the highest. At 4 mm, the degree of conversion of low and high viscosity bulk-fill giomer resin composites was lower than that of bulk-fill resin composites (p < 0.05). At the depth between 2 mm and 4 mm, there were significant difference with TBF, TN and TF (p < 0.05), while no significant difference in the degree of conversion was measured for BBR, BBF and SDR. Polymerization shrinkage of six resin composites decreased in the following order: TF > SDR > BBF > TBF > TN and BBR (p < 0.05). Polymerization shrinkage of bulk-fill giomer resin composites was lower than that of bulk-fill resin composites (p < 0.05). From this study, it is found that the bulk-fill giomer resin composites and TBF were not sufficiently cured in 4 mm depth. The degree of conversion of low and high viscosity bulk-fill giomer resin composites was significantly lower than bulk-fill resin composites in both 2 mm and 4 mm depths. Therefore, such features of bulk-fill giomer resin composites should be carefully considered in clinical application.

Linear polymerization shrinkage of Bulk Fill resins

Objective: the objective of the present study was to analyzethe polymerization shrinkage gap of different compositeresins. Methods: four commercial brands (n=5)were tested: Z350 (3M/ESPE); Filtek Bulk Fill (3M/ESPE);Surefill (Dentsply); Xtra Base (Voco). Increments of compositeresins were inserted into a circular metal matrixof 7 mm internal diameter and 4 mm high and pressedby two glass plates supported on polyester strips. Afterphotoactivation with a Optilight Plus device (Gnatus),with light intensity of 1000 ± 10mW/cm2, the test sampleswere polished and 24h later, taken to the scanningelectron microscope for analysis of the polymerizationshrinkage gap, measured at 4 points in the sample (3, 6,9, and 12 o'clock). The data were analyzed by analysisof variance (Anova one-way). Results: the highest meanof polymerization shrinkage gap was observed for FiltekZ350 (3M/ESPE), while the lowest mean of gap wasfound for Xtra Base (Voco) brand, with significant differencesbetween the groups. Conclusion: the inorganicfiller content and different associations in the organicmatrices interfered expressively in the polymerizationshrinkage gap.

Clinical application and research progress of bulk-fill resin-based composites / 口腔疾病防治

@#Traditional resin-based composites have been placed in cavities by incremental layering technique. The shrinkage stress may result in microleakage, post-operative sensitivity which lead to the failed restorations. In 2009, bulk-fill resin-based composites were reported to have the capability to be placed and cured in 4-5 mm increments, because of the improved resin matrix, modified nano-hybrid fillers and new photo initiators. This group of materials can simplify operation in clinical application in addition to decrease shrinkage stress and polymerization shrinkage. The aim of this review is to summarize the classification and properties of bulk-fill resin-based composites and to discuss the development of these new materials in the future.

Clinical Evaluation of Class I Restorations Made with Composite with Low Degree of Polymerization Shrinkage.

Aims: The objective of this study was to clinically evaluate the performance of a conventional resin system and one with low polymerization shrinkage. Study Design: A prospective, randomized, blind, split-mouth study. Place and Duration of Study: Dental Clinic, division of Heath Sciencies, State University of West Parana - UNIOESTE/Brazil, between October, 2011 and October, 2012. Methodology: Teeth were restored with one of the two tested materials (n = 10): Conventional composite resin restorations (CCR) and Silorane-based resin composite restorations (SCR). The materials were used according to manufacturer’s instructions. After time intervals of 30 days, 6 months and 1 year, the restorations were assessed using the USPHS criteria. The data obtained were tabulated and evaluated by the Chi-square test for clinical parameters and for the restoration criteria (p< 0.05). Results: No statistically significant differences between the two composite resins were found, with exception of marginal adaptation, in which CCR showed better results than SCR. Conclusion: The silorane-based composite resin showed no advantage over the methacrylate resin.

Effect of the photoinitiator system on the properties of a dental material based on a hybrid polymer / Efeito do sistema fotoiniciador sobre as propriedades de um material dentário baseado em um polímero híbrido

Objetivo: Nesse estudo, foram avaliados os efeitos de dois diferentes protocolos de cura sobre as propriedades de um compósito usando um polímero híbrido como resina dentária. Material e Métodos: Dois compósitos diferentes foram preparados, um contendo uma mistura de TEGDMA/Bis-GMA (50:50) e, outro contendo uma mistura de TEGDMA/p-MEMO (50:50), [p-MEMO: precursor oligomérico inorgânico]. Ambos compósitos foram reticulados com lucirin e canforoquinona. Os compósitos foram preparados com 70% em massa de carga inorgânica. Resistência flexural foi avaliada com uma máquina de testes universal e o grau de conversão calculado por espectroscopia na região do infravermelho. Um picnômetro a gás hélio foi usado para obter os dados de contração de polimerização. Testes de sorção foram feitos e microscopia eletrônica de varredura foi usada para avaliar efeitos deletérios sobre as superfícies das resinas. Resultados: A amostra constituída com TEGDMA/p-MEMO reticulada com lucirin (L-T/p) apresentou os melhores valores das propriedades monitoradas. Conclusão: Lucirin é o sistema fotoiniciador mais adequado para compostos dentários contendo polímeros híbridos.

Objective: In this study, the effects of two different cure protocols upon the properties of composites using a hybrid-polymer as dental resin were evaluated. Material and Methods: Two distinct dental composites were prepared, one containing a mixture of TEGDMA/bis-GMA (50:50) and, another containing a mixture of TEGDMA/p MEMO (50:50), [p-MEMO: oligomeric inorganic precursor]. Both composites were polymerized with lucirin and canphorquinone as photoinitiators. The composites were made with a 70 % wt of inorganic filler. Flexural strength was evaluated with a universal test machine and the degree of conversion was measured by infrared spectroscopy. A helium pycnometer was used to obtain polymer shrinkage data. Sorption tests were performed and SEM microscopy was used to show deleterious effects upon the resins’ surfaces. Results: The sample based on TEGDMA/p-MEMO polymerized with lucirin (L-T/p) showed the best values of the monitored properties. Conclusion: Lucirin is the most suitable photoinitiator for dental composites containing hybrid polymers.

Analysis of stresses during the polymerization shrinkage of self-curing resin cement in indirect restorations: A finite-element study.

Background: Adhesive cementation is essential for the longevity of indirect esthetic restorations. However, polymerization shrinkage of resin cement generates stress, which may cause failures in the tooth–restoration interface. So, understanding of the biomechanics of resin cement is important for predicting the clinical behavior of an esthetic indirect restoration. Aims: To analyze the stresses generated during polymerization shrinkage of self‑curing resin cement in ceramic and in indirect resin (IR) restorations, using the finite‑element method (FEM). Settings and Design: Numerical study using the finite‑element analysis. Materials and Methods: A three‑dimensional (3D) model of a second molar restored with ceramic or IR onlay restoration was designed. The polymerization shrinkage of self‑curing resin cement was simulated in FEM software using an analogy between the thermal stress and the resulting contraction of the resin cement. The localization and values of tensile stresses in the dental structure, cement, and adhesive layer were identified. Results: The location and value of the tensile stresses were similar for the two restorative materials. High tensile stresses were identified in the axiopulpal wall and angles of the tooth preparation, with the major stresses found in the cement located in the axiopulpal wall. Conclusions: The high stresses values and their concentration in the angles of the prepared tooth emphasize the importance of round angles and the use of cements with lower rates of shrinkage.

Nano Composites.

Nanotechnology was first described in 1959 by physicist Richard P Feynman, who viewed it as an unavoidable development in the progress of science, and has since been part of mainstream scientific theory with potential medical and dental applications since the early 1990s. Nanotechnology’s most tangible contribution to dentistry to date has been the restoration of tooth structure with Nanocomposites. Nanocomposites are characterized by filler-particle sizes of <= 100 nm, which offer these materials aesthetic and strength advantages over conventional microfilled and hybrid resin-based composite (RBC) systems. They offer advantages primarily in terms of the smoothness, polishability and precision of shade characterization, notwithstanding the flexural strength and microhardness they offer similar to those of the better-performing posterior RBCs. The strength and aesthetic properties of the resin based Nanocomposite makes it possible for it to be used for both anterior and posterior restorations. This article aims to address the current major uses of practical nanotechnology in dentistry, mainly the restoration of tooth structure with RBCs that make use of nanoparticles.

Stress analysis of two methods of ceramic inlay preparation by finite element.

Objective: Ceramic inlays are bonded to tooth structure with resin cements. During the resin cement setting, shrinkage stress develops at the interfaces. During tooth preparation, the undercut areas formed due to the different patterns of caries progression can either be blocked out before taking impression with suitable cement such as glass ionomer cement, or before making the final restoration in the laboratory. Then, the relieved space will be filled with luting cement in clinic. The aim of this study was to compare these two methods of undercut filling in term of stress distribution in the ceramic inlay. Materials and Methods: An axisymmetric finite element analysis was performed to study the stress distribution during inlay cementing. The solid model was generated from a longitudinal section of maxillary premolar in which a class I cavity with 60 degree undercut at the preparation wall and 20 degree divergence of the vertical walls was prepared. A thermal model was used to simulate the polymerization shrinkage of the resin cement. Finite element analysis was carried out in ANSYS environment. Results: Filling the undercut by glass ionomer cement decreased the stress concentration at the ceramic/cement interface. The dominant normal stress at the tooth cement interface in absence of glass ionomer cement was tensile with maximum of 30 Mpa. Using glass ionomer, cement developed stresses with different compressive and tensile signs. With increasing the thickness of resin cement (100 μm, 150 μm, 200 μm), the stress increased. Conclusion: Cements with minimum shrinkage and as thin layer as possible should be used. Filling the undercut with glass ionomer cement decreases the stress. Other experimental and clinical studies must follow this research.

Síntese e análise de compósitos experimentais para uso odontológico reforçados com nanoargila / Synthesis and analysis of experimental composites for dentistry use reinforced with nanoclay

O objetivo do presente estudo foi de avaliar os efeitos de diferentes frações de partículas de nanoargila modificadas do tipo montmorilonita Cloisite® 20A em propriedades físicas, mecânicas e biológicas de resinas experimentais do tipo nanohíbrida. Compósitos dentais foram preparados através da mistura de 30% de matriz resinosa (BisGMA/TEGDMA) em 70% de partículas de carga (vidro de bário silicato silanizado ­VB, dióxido de silício ­ SD, partículas de nanoargila MMT). Quatro grupos de compósitos experimentais foram formados, variando o percentual de nanoargila empregada (0%, 5%, 7,5%, 10%). O processamento foi realizado em uma máquina de dupla mistura (SpeedMixer DAC, Germany, 3500 rpm). A citotoxicidade in vitro do material foi avaliada baseada nas normas ISO 10993- 5-2009 e comparado com compósito comercial. Ensaios mecânicos para cálculo de Resistência à Flexão e Módulo de Elasticidade foram realizados em máquina de ensaios universal EMIC. O aparelho Acuvol® foi utilizado para o ensaio de contração de polimerização. A sorção e solubilidade dos compósitos foram calculadas baseadas nas normas ISO 4049. Os dados foram analisados estatisticamente, utilizando-se a tabela ANOVA e o Teste de Tukey para comparação dos grupos de dois em dois. O nível de significância utilizado foi de 95% (p< 0,05). Por meio do exame dos resultados, concluiu-se que foi possível esfoliar 5 e 7,5% de partículas de MMT satisfatoriamente na matriz BisGMA/TEGDMA, porém, o inserção de 10% de MMT na matriz orgânica não trouxe vantagens ao compósito, certamente por não permitir a total exfoliação de suas partículas. A inserção de 5 e 7,5% de nanoargila ao compósito dental experimental possibilitou uma diminuição da contração de polimerização do material em 22,13 e 17,4%, respectivamente. Além disso, esses dois grupos permaneceram com suas propriedades mecânicas e de absorção e solubilidade satisfatórias, além de apresentar ausência de citotoxicidade para as células fibroblasticas L929 testadas

The aim of the present study was to evaluate the effect of different weight fractions of modified montmorillonite nanoclay fillers Cloisite ® 20A on mechanical, physical and biological properties of nanohybrid experimental resins. Dental composites were prepared by mixing 30% of resin matrix (BisGMA / TEGDMA) to 70% of particulate fillers (Silanized barium silicate particles - BS, silicone dioxide - SD, montmorillonite nanoclay cloisite 20AMMT). Four groups of experimental composite were formed with various fractions of the nanoclay fillers (0%; 5%; 7,5%; 10% ). Processing was performed using a dual high speed mixing machine (SpeedMixer DAC, Germany, 3500 rpm). In vitro citotoxicity of the material was calculated based on standards ISO 10993-5-2009 and compared to a comercial composite. Tensile strenght and elastic modulus were performed using an universal test machine EMIC. The volumetric shrinkage was calculated by Acuvol® machine. Water sorption and solubility were measured based on International Standard ISO 4049. Data were statistically analyzed by ANOVA and Tukey Test for multiple comparisons. The significance level utilized was 95% (p < 0,05). By the results, it was concluded that it is possible to exfoliate nicely 5 and 7.5% of MMT particles inside Bis-GMA/TEGDMA matrix. However, insertion of 10% of MMT did not improve composite, certainly, because the total exfoliation of particles did not occured. Insertion of 5 and 7.5% of nanoclay in dental composite diminished polymerization shrinkage in 22,13% and 17,4% , respectively. Furthermore, these two groups maintained their mechanical properties, satisfactory sorption and solubility and also presented no citotoxicity for L929 fibroblastic cells

Effects of immediate and delayed light activation on the polymerization shrinkage-strain of dual-cure resin cements / 대한치과보철학회지

PURPOSE: This study was designed to compare the amount of polymerization shrinkage of dual-cure resin cements according to different polymerization modes and to determine the effect of light activation on the degree of polymerization. MATERIALS AND METHODS: Four kinds of dual-cure resin cements were investigated: Smartcem 2, Panavia F 2.0, Clearfil SA Luting and Zirconite. Each material was tested in three different polymerization modes: self-polymerization only, immediate light polymerization and 5 minutes-delayed light polymerization. The time-dependent polymerization shrinkage-strain was evaluated for 30 minutes by Bonded-disk method at 37degrees C. Five recordings of each material with three different modes were taken. Data were analyzed using one-way ANOVA and multiple comparison Scheffe'test (alpha=.05). RESULTS: All materials, except Panavia F 2.0, exhibited the highest polymerization shrinkage-strain through delayed light-activated polymerization. No significant difference between light activation modes was found with Panavia F 2.0. All materials exhibited more than 90% of polymerization rate in the immediate or delayed light activated group within 10 minutes. CONCLUSION: As a clinical implication of this study, the application of delayed light activation mode to dual-cure resin cements is advantageous in terms of degree of polymerization.

Microleakage evaluation of Silorane-based composite and Methacrylate-based composite in class II box preparations using two different layering techniques: An in vitro study.

Aim: The aim of this study was to compare the microleakage in Class II box preparations with the gingival margin above and below the cemento-enamel junction (CEJ) restored with Silorane composite and methacrylate composite using two different layering techniques. Materials and Methods: Standardized box preparations (mesial box 1 mm above the CEJ and distal box 1 mm below the CEJ) were prepared in 60 upper premolars. The teeth were randomly divided into four groups containing 15 samples each; Group I: Restored with a Silorane composite using an oblique layering technique, Group II: Restored with Silorane composite using a vertical layering technique, Group III: Restored with methacrylate composite using the oblique layering technique, and Group IV: Restored with methacrylate composite using the vertical layering technique. The samples were stored in distilled water, followed by thermocycling and immersed in 2% methylene blue. The samples were sectioned and evaluated for microleakage at the gingival margin. Statistical Analysis: Kruskal-Wallis, Fischer exact test, Wilicoxon test, and Mann-Whitney U test. Results: Silorane composite had significantly lesser microleakage. No significant difference in microleakage was observed above and below the CEJ for Silorane-based composite. Conclusion: Silorane composite resin showed lesser microleakage compared to methacrylate composite resin. Clinical Significance: The Silorane-based composites improve the marginal adaptation due to their reduced shrinkage, thereby decreasing the residual stress at the adhesive-tooth interface.

Evaluation of polymerization shrinkage stress in silorane-based composites / 대한치과보존학회지

OBJECTIVES: The purpose of this study was to evaluate the polymerization shrinkage stress among conventional methacrylate-based composite resins and a silorane-based composite resin. MATERIALS AND METHODS: The strain gauge method was used for the determination of polymerization shrinkage strain. Specimens were divided by 3 groups according to various composite materials. Filtek Z-250 (3M ESPE) and Filtek P-60 (3M ESPE) were used as a conventional methacrylate-based composites and Filtek P-90 (3M ESPE) was used as a silorane-based composites. Measurements were recorded at each 1 second for the total of 800 seconds including the periods of light application. The results of polymerization shrinkage stress were statistically analyzed using One way ANOVA and Tukey test (p = 0.05). RESULTS: The polymerization shrinkage stress of a silorane-based composite resin was lower than those of conventional methacrylate-based composite resins (p 0.05). CONCLUSIONS: Within the limitation of this study, silorane-based composites showed lower polymerization shrinkage stress than methacrylate-based composites. We need to investigate more into polymerization shrinkage stress with regard to elastic modulus of silorane-based composites for the precise result.