RESUMO
This study investigated the influence of silane concentration and filler size distribution on the chemical-mechanical properties of experimental composites. Experimental composites with silane contents of 0%, 1% and 3% (in relation to filler mass) and composites with mixtures of barium glass particles (median size = 0.4, 1 and 2 μm) and nanometric silica were prepared for silane and filler analyses, respectively. The degree of conversion (DC) was analyzed by FTIR. Biaxial flexural strength (BFS) was tested after 24-h or 90-d storage in water, and fracture toughness, after 24 h. The data were subjected to ANOVA and Tukey’s test (p = 0.05). The DC was not significantly affected by the silane content or filler distribution. The 0% silane group had the lowest immediate BFS, and the 90-d storage time reduced the strength of the 0% and 3% groups. BFS was not affected by filler distribution, and aging decreased the BFS of all the groups. Silanization increased the fracture toughness of both the 1% and 3% groups, similarly. Significantly higher fracture toughness was observed for mixtures with 2 μm glass particles. Based on the results, 3% silane content boosted the initial strength, but was more prone to degradation after water storage. Variations in the filler distribution did not affect BFS, but fracture toughness was significantly improved by increasing the filler size.
RESUMO
OBJECTIVES: This study evaluated the effect of composite pre-polymerization temperature and energy density on the marginal adaptation (MA), degree of conversion (DC), flexural strength (FS), and polymer cross-linking (PCL) of a resin composite (Filtek Z350, 3M/ESPE). METHODS: For MA, class V cavities (4 mm x 2 mm x 2 mm) were prepared in 40 bovine incisors. The adhesive system Adper Single Bond 2 (3M/ESPE) was applied. Before being placed in the cavities, the resin composite was either kept at room-temperature (25 degrees C) or previously pre-heated to 68 degrees C in the Calset device (AdDent Inc., Danbury, CT, USA). The composite was then light polymerized for 20 or 40s at 600 mW/cm(2) (12 or 24 J/cm(2), respectively). The percentage of gaps was analyzed by scanning electron microscopy, after sectioning the restorations and preparing epoxy resin replicas. DC (n=3) was obtained by FT-Raman spectroscopy on irradiated and non-irradiated composite surfaces. FS (n=10) was measured by the three-point-bending test. KHN (n=6) was measured after 24 h dry storage and again after immersion in 100% ethanol solution for 24h, to calculate PCL density. Data were analyzed by appropriate statistical analyses. RESULTS: The pre-heated composite showed better MA than the room-temperature groups. A higher number of gaps were observed in the room-temperature groups, irrespective of the energy density, mainly in the axial wall (p<0.05). Composite pre-heating and energy density did not affect the DC, FS and PCL (p>0.05). SIGNIFICANCE: Pre-heating the composite prior to light polymerization similar in a clinical situation did not alter the mechanical properties and monomer conversion of the composite, but provided enhanced composite adaptation to cavity walls.
Assuntos
Resinas Compostas/química , Adaptação Marginal Dentária , Cura Luminosa de Adesivos Dentários , Análise de Variância , Animais , Bovinos , Análise do Estresse Dentário , Dureza , Temperatura Alta , Teste de Materiais , Maleabilidade , Polimerização , Polímeros/química , Distribuição AleatóriaRESUMO
The aim of this study was to evaluate the influence of light exposure associated with 35% hydrogen peroxide (Pola Office, SDI, Melbourne, Vic., Australia) or 15% hydrogen peroxide (BriteSmile, Discus, Culver City, CA, USA) on the microhardness and color changes of bovine enamel. Experimental groups were Britesmile + Light (BL) (15% hydrogen peroxide + plasm arc; 4 x 20 minutes), Britesmile + No Light (BN) (BL, no light), Pola office + Light (PL) (35% hydrogen peroxide + LED; 4 x 8 minutes), and Pola office + No light (PN) (PL, no light). Color changes (DeltaE) and the CIELAB (Commission Internationale de l' Eclairage, L* a* b* color system) parameters (L*, a*, and b*) were assessed with a spectrophotometer before (B), immediately (A), 1 day and 7 days after bleaching. The microhardness was measured before (B) and after (A), the obtained data were submitted to a two-way analysis of variance, and DeltaE were submitted to t-test for each period. Only Pola Office, in which the peroxide is associated with the light, improved DeltaE when evaluated immediately after bleaching (p < 0.001). Light exposure did not influence DeltaE after 1 day or 7 days for either bleaching system. The enamel microhardness was not altered after bleaching for BriteSmile. However, enamel microhardness was reduced after bleaching for Pola Office, 283 MPa (+/-21) and 265 MPa (+/-27), respectively. It was concluded that these two bleaching systems were efficient regardless of the light systems used. However, the 35% hydrogen peroxide altered the enamel microhardness. CLINICAL SIGNIFICANCE Enamel microhardness was affected by a 35% hydrogen peroxide in-office bleaching therapy. Moreover, the in-office bleaching outcome was not improved by using the light associated with systems tested in this study. (J Esthet Restor Dent 21:387-396, 2009).
Assuntos
Esmalte Dentário/efeitos da radiação , Fototerapia , Clareamento Dental/métodos , Animais , Bovinos , Cor , Esmalte Dentário/anatomia & histologia , Dureza , Peróxido de Hidrogênio/administração & dosagem , Peróxido de Hidrogênio/efeitos da radiação , Oxidantes/administração & dosagem , Oxidantes/efeitos da radiação , Fototerapia/instrumentação , Fototerapia/métodos , Doses de Radiação , Distribuição Aleatória , Espectrofotometria , Temperatura , Fatores de Tempo , Água/químicaRESUMO
Objetivo: avaliar a influência da relação água/pó e do uso de um modificador (NaCl) nas resistências à compressão úmida e seca de gessos tipo IV e V. Material e métodos: os gessos tipo IV e V foram manipulados segundo três proporções água/pó: a fornecida pelo fabricante, com excesso de 10% de água (em peso) e com excesso de 30%. Em relação ao fator modificador, foram testadas duas condições: nenhum aditivo ou com adição de NaCl. Para a confecção das amostras (n = 5) foram utilizadas matrizes cilíndricas com 1,5 cm de diâmetro e 3,0 cm de altura. A variável "resistência à compressão" foi avaliada nas condições úmida (após uma hora da espatulação) e seca (após sete dias), sendo o teste realizado em uma máquina de ensaios universal. Os dados foram analisados segundo o método de análise de variância (ANOVA). Resultados: os três fatores considerados no estudo - tipo de gesso, idade e manipulação - apresentaram diferenças estatisticamente significantes, assim como suas interações, com excessão da interação gesso e idade. A resistência à compressão do gesso tipo IV foi maior do que a do tipo V apenas quando mantida a relação água/pó do fabricante. Houve redução dos valores de resistência à compressão nos grupos com excesso de água e, para o gesso tipo IV, com o uso de aditivo. A resistência a seco foi marcadamente maior do que a úmida para todos os grupos. Conclusões: tanto o excesso de água durante a manipulação como o uso de NaCl podem interferir na resistência à compressão dos gessos tipo IV eV.