Effect of hydrogen peroxide application on color and surface roughness of two restorative materials

Aim: This study investigated the effect of an in-office bleaching technique on lightness, color and surface roughness of two commercially available materials: a resin-modified glass-ionomer cement and a nanohybrid resin composite. Methods: Twelve disk-shaped specimens were prepared with both materials. The samples were bleached with 35% hydrogen peroxide. Bleaching was tested initially onto a smooth surface and later onto a polished one of the same specimens. The effect of the treatments on lightness and color was verified with a spectrophotometer. Surface roughness was measured with a digital surface roughness tester. The data were statistically analyzed by repeated measures ANOVA and post hoc Tukey's test (alpha = 0.05). Results: Significant variation in lightness and color was observed on the resin-modified glass-ionomer cement after the first bleaching procedure. Roughness increased significantly only after polishing the resin-modified glass-ionomer cement surface. Composite color variation was evident in the last observation period, but roughness and lightness variation due to bleaching and polishing was not significant. Conclusion: The bleaching treatment caused significant color alterations on the materials tested. This study observed that the application of in-office bleaching onto the glass-ionomer cement promoted clinically observable color alteration, and polishing after bleaching is contraindicated for this material. (AU)

Influence of curing protocols on water sorption and solubility of a self-adhesive resin-cement

Aim: To evaluate the effect of different activation protocols on the polymerization of a self-adhesive dual cured resin-based cement. Methods: Thirty disc-shaped specimens were prepared with the resin cement RelyX U200 (3M ESPE) and divided according to three protocols: immediate light-activation for 40 s, delayed light-activation (10 min after manipulation, for 40 s) or self-curing without light-activation. The specimens were desiccated, kept in water at 37 °C for 7 days and desiccated again to calculate water sorption, solubility and mass variation. Data were analyzed by Shapiro-Wilk Test and Wilcoxon tests (α=0.05). Images after the specimens' final desiccation were also made. Results: The Wilcoxon test revealed a significant difference for sorption and mass variation (p<0.05) and the highest value was observed in self-curing or chemical activation group (CA), followed by delayed light-activation (DL) and immediate light-activation (IL). Besides the water sorption parameters, there were also microvoids on the discs from the delayed and no light-activation groups. Conclusions: The light-activation immediately after manipulation is recommended for the evaluated resin cement (Au)

Repair on silorane-based composite

Introduction: Silorane-based composites have low polymerization shrinkage and good color stability. However, the effectiveness and the best surface treatment to carry out repairs to this type of restoration is unclear. Objective: To evaluate the effect of different types of repair made on a silorane-based composite. Material and methods: 80 disks of silorane-based composite were prepared (Filtek P90, 3M ESPE) and divided into eight groups (n = 10), according to the surface treatment being carried out before repairs of either the same silorane composite or a dimethacrylate material (Filtek Z350, 3M ESPE) were conducted. In two groups the immediate adhesion without repair (positive control) was evaluated. In other two groups repairs without any surface treatment (negative control) were evaluated. Surface treatments before the repair of the four remaining groups included the application of adhesive systems specific to silorane (Silorane System Adhesive, 3M ESPE) or to dimethacrylate (Adper Single Bond 2, 3M ESPE) and roughening followed by application of adhesive system. All groups were stored into distilled water at 37°C for 1 week prior to the microshear bond strength evaluation. Results: The group immediate adhesion silorane-dimethacrylate and group repair silorane-dimethacrylate without surface treatment showed lower microshear bond strength values and were statistically different from groups with surface treatment and immediate adhesion silorane-silorane (p < 0.05). Conclusion: Surface treatments with application of adhesive systems compatible with the repair material or roughening prior to the application of these adhesive systems are suitable for repairing silorane-based composites.

Influence of different surface treatments on the shear bond strength of a methacrylate resin composite repaired with silorane-based resin

Introduction: When repairs are needed in restorations made with methacrylate-based resin composites, the clinician still has doubts whether it is possible to use a silorane-based material and which is the best procedure. Objective: To evaluate the shear bond strength between a methacrylate-based resin composite and a silorane-based material using different surface treatments. Material and methods: Eighty flat bases made with methacrylate resin composite (Filtek Z350 XT) were prepared (n = 8). The bases were stored into water at 37°C for one week. Ten groups were evaluated: G1 (control - no repair); G2 (surface grinding, washing, drying, adhesive and repair with Filtek Z350 XT); G3 (surface grinding, washing, drying, adhesive and repair with silorane - Filtek P90); G4 (surface grinding, washing, drying, adhesive, silane and repair with Filtek Z350 XT); G5 (surface grinding, washing, drying, application of silane, adhesive and repair with silorane - Filtek P90). All groups were kept at 37°C for 24 h in either water (G1 to G5) or ethanol (G6 to G10). The results were analyzed with one-way ANOVA and Tukey test (α = 0.05). Results: There were significant differences between groups (p < 0.001). Only repairs made with silane and Z350 XT (G4 = 46.2 ± 12.9; G9 = 48.1 ± 16.3) resulted in values similar to controls (G1 = 59.2 ± 15.8; G6 = 62.3 ± 15.9) (p = 0.33). The smallest value occured when the repair was performed with silane and silorane-based based and stored into ethanol (G10 = 29.9 ± 12.4). The storage media had little influence on the results. Conclusion: The silorane-based resin composite was not effective for repair of the methacrylate-based material.

Assessment of preload in carbon coated prosthetic screws

Introduction : The mechanical aspects of tightening screws over implants are important to ensure a successful prosthetic rehabilitation. Screw loosening is a common problem that can be avoided with passive adaptation of the components and an increased tensile force developed in the screw, a preload. Objective: This in vitro study evaluated the effect on preload of a carbon lubricant deposited on the surface of titanium alloy prosthetic screws: conventional Ti6Al4V and surface enhanced. Material and methods: Conventional titanium alloy prosthetic (n = 7) and carbon coating surface enhanced screws (n = 7) were compared. Each prosthetic screw supporting a metallic UCLA over an implant was tightened with the manufacturer’s recommended torque of 32 N.cm. The removal torque values, recorded for ten consecutive cycles of tightening and removal, were used to estimate the preload. Implant blocks were then sectioned and the interfaces were observed by light microscopy.Results: The lowest removal torque, and consequently the highest preload values, was achieved for the lubricated group in most cycles. The contacts between threads were located at the coronal aspect of all observed screw mating threads.Conclusion: Data indicate that the lower coefficient of friction of a carbon lubricant can generate higher preload. The machining precision observed produced the adaptation and regular contact interfaces.

Initial endosseous healing response to lactide/glycolide copolymer / Estudo da resposta tecidual inicial em defeitos ósseos enxertados com PLGA

Introduction: The search for less invasive treatments, with fast and effective bone regeneration, has lead to the development of synthetic bioresorbable alternatives for bone graft. The commercial product FisiograftTM gel (Ghimas Spa, Italy), based on lactide-glycolide copolymer, is used as an injectable biocompatible and bioresorbable material for filling bone defects in dental surgery applications. These polymers are also used in the production of suture threads, pins and plates for bone fixation, and barriers for guided tissue regeneration. Objective: The main objective of this pilot study was to observe the initial bone healing response after the application of polylactide-glycolide graft material in adult animals. Material and methods: Bone defects were prepared in right and left femora of 12 month-old male Wistar rats. The defects in one leg received the synthetic graft material and the contra-lateral defects did not receive any treatment. After four days, the animals were subjected to euthanasia, the femora were removed, and tissue blocks were prepared for histological analysis. Results: Blood clot remained in the centre of control defects with initial connective tissue organization on the edges. The graft material was observed in the centre of the treated defects, restricted to the area where it was applied, with neovascularization next to the graft material. The pattern of bone healing did not differ between groups, starting from the margins of the defects and from bone fragments, with neovascularization followed by deposition of non-mineralized bone matrix towards the centre. Conclusion: The results indicate that the lactide-glycolide copolymer gel was effective as a filling and osteoconductive material, allowing tissue healing during its resorption process. Additional studies are necessary to verify its capacity to promote bone regeneration.

Introdução: A busca de tratamentos menos invasivos, com rápida e efetiva regeneração óssea, tem levado ao desenvolvimento de alternativas sintéticas e biorreabsorvíveis para enxertos ósseos. O material sintético à base de copolímeros de ácidos polilático e poliglicólico (PLGA), no produto comercial FisiograftTM gel (Ghimas Spa, Itália), é indicado pelo fabricante como dispositivo biorreabsorvível e biocompatível para preenchimento de defeitos ósseos em periodontia, cirurgia bucomaxilofacial e implantodontia. Esses polímeros são usados também na fabricação de fios de sutura, pinos e placas para fixação óssea em ortopedia e barreiras para regeneração tecidual. Objetivo: Este estudo piloto in vivo teve como objetivo principal observar o período inicial da resposta óssea na aplicação de PLGA em animais adultos. Material e métodos: Foram produzidos defeitos ósseos em cada fêmur de ratos machos Wistar com 12 meses de idade. Metade dos defeitos foi preenchido com FisiograftTM gel, e defeitos contralaterais não receberam material de preenchimento. Os animais foram submetidos a eutanásia após quatro dias do pós-operatório, e os blocos de tecido foram preparados para análise histológica. Resultados: O centro do defeito no grupo controle encontrou-se preenchido com coágulo sanguíneo, enquanto o tecido conjuntivo se organizou próximo às bordas. Nos defeitos enxertados foi verificado que o gel se manteve restrito ao local em que foi aplicado, com neovascularização próxima ao copolímero. O padrão de deposição óssea não diferiu entre os grupos, sempre a partir das margens do defeito e da superfície dos fragmentos ósseos, representado pela deposição de matriz não mineralizada em direção ao centro do defeito. Conclusão: Neste trabalho, a utilização do gel mostrou-se eficaz como material de preenchimento e osteocondutor, possibilitando neovascularização e reparo tecidual inicial durante sua reabsorção. Estudos adicionais são necessários para verificar o efeito desse...