RESUMO
In this study, an acrylamide-based adhesive was combined with a thiourethane-based composite to improve bond stability and reduce polymerization stress, respectively, of simulated composite restorations. The stability testing was conducted under physiologic conditions, combining mechanical and bacterial challenges. Urethane dimethacrylate was combined with a newly synthesized triacrylamide (TMAAEA) or HEMA (2-hydroxyethyl-methacrylate; control) to produce a 2-step total-etch adhesive system. Methacrylate-based composites (70 wt% silanized filler) were formulated, containing thiourethane oligomers at 0 (control) or 20 wt%. Standardized preparations in human third molars were restored; then, epoxy replicas were obtained from the occlusal surfaces before and after 7-d storage in water or with Streptococcus mutans biofilm, which was tested after storage in an incubator (static) or the bioreactor (mechanical challenge). Images were obtained from the replicas (scanning electron microscopy) and cross sections of the samples (confocal laser scanning microscopy) and then analyzed to obtain measurements of gap, bacterial infiltration, and demineralization. Microtensile bond strength of specimens stored in water or biofilm was assessed in 1-mm2 stick specimens. Data were analyzed with analysis of variance and Tukey's test (α = 0.05). HEMA-based materials had greater initial gap measurements, indicating more efficient bonding for the acrylamide materials. When tested in water, the triacrylamide-based adhesive had smaller gaps in the incubator or bioreactor. In the presence of biofilm, there was less difference among materials, but the acrylamide/thiourethane combination led to statistically lower gap formation in the bioreactor. HEMA and TMAAEA-based adhesives produced statistically similar microtensile bond strengths after being stored in water for 7 d, but after the same period with biofilm-challenged specimens, the TMAAEA-based adhesives were the only ones to retain the initial bond strength values. The use of a stable multiacrylamide-based adhesive led to the preservation of the resin-dentin bonded interface after a physiologically relevant challenge. Future studies will include a multispecies biofilm model.
Assuntos
Colagem Dentária , Adesivos Dentinários , Acrilamidas , Resinas Compostas/química , Cimentos Dentários/química , Dentina , Adesivos Dentinários/química , Humanos , Teste de Materiais , Metacrilatos/química , Cimentos de Resina/química , Resistência à Tração , ÁguaRESUMO
OBJECTIVES: The aim of this study was to modify the surface of fillers used in dental composites by the synthesis of two novel thiourethane oligomeric silanes, used to functionalize the silica-containing inorganic particles. Several thiourethane silane concentrations were tested during the silanization process to systematically assess the effect of silane coverage on experimental composite conversion, polymerization stress and fracture toughness. MATERIALS AND METHODS: Two different thiourethane silanes were synthesized based either on 1,6-hexanediol-diissocynate (HDDI), or 1,3-bis(1-isocyanato-1-methylethyl) benzene (BDI). Conventional 3-(Trimethoxysilyl)propyl methacrylate was used as the control. Glass fillers were silanized with 1, 2 or 4 wt% of each thiourethane silane, then evaluated by thermogravimetrical analysis. Photopolymerizable resin composites were prepared with Bis-GMA/UDMA/TEGDMA and 50 wt% silanized glass filler. Polymerization kinetics and degree of conversion were tested using Near-IR. Bioman was used to test polymerization stress. Data were analyzed with two-way ANOVA/Tukey's test (α = 5%). RESULTS: The mass of silane coupled to the filler increased with the concentrations of thiourethane in the silanizing solution, as expected. Thiourethane-containing groups exhibited significantly higher degree of conversion compared to control groups, except for BDI 4%. HDDI 4%, BDI 2% and BDI 4% showed significantly lower polymerization stress than control groups. HDDI 4% exhibited significantly higher fracture toughness. CONCLUSIONS AND CLINICAL SIGNIFICANCE: Novel filler functionalization with thiourethane silanes may be a promising alternative for improving dental composites properties by significantly increasing the degree of conversion, fracture toughness and reducing the polymerization stress.
Assuntos
Resinas Compostas , Ácidos Polimetacrílicos , Bis-Fenol A-Glicidil Metacrilato , Teste de Materiais , Metacrilatos , Polietilenoglicóis , Silanos , Propriedades de SuperfícieRESUMO
OBJECTIVE: The aim of this study was to investigate the influence of the photoinitiator system on the polymerization kinetics of methacrylamide-based monomers as alternatives to methacrylates in adhesives dental-based materials. METHODS: In total, 16 groups were tested. Monofunctional monomers (2-hydroxyethyl methacrylate) - HEMA; (2-hydroxy-1-ethyl methacrylate) -2EMATE, (2-hydroxyethyl methacrylamide) - HEMAM; and (N-(1-hydroxybutan-2-yl) methacrylamide) -2EM; were combined with bifunctional monomers containing the same polymerizing moieties as the monofunctional counterparts (HEMA-BDI; 2EMATE-BDI; HEMAM-BDI; and 2EM-BDI) at 50/50 M ratios. BHT was used as inhibitor (0.1 wt%) and the photoinitiators used were: CQ + EDMAB (0.2/0.8), BAPO (0.2), IVOCERIN (0.2), and DMPA (0.2), in wt%. The polymerization kinetics were monitored using Near-IR spectroscopy (â¼6165 cm-1) in real-time while the specimens were photoactivated with a mercury arc lamp (Acticure 2; 320-500 nm, 300 mW/cm2) for 5 min, and maximum rate of polymerization (Rpmax, in %.s-Ì1), degree of conversion at Rpmax (DC@Rpmax, in %), and the final degree of conversion (Final DC, in %) were calculated (n = 3). Initial viscosity was measured with an oscillating rheometer (n = 3). Data were analyzed using Two-way ANOVA for the polymerization kinetics and one-way ANOVA for the viscosity. Multiple comparisons were made using the Tukey's test (â = 0.05). RESULTS: There was statistically significant interaction between monomer and photoinitiator (p < 0.001). For the methacrylates groups, the highest Rpmax was observed for HEMA + DMPA and 2EMATE + BAPO. For methacrylamides groups, the highest Rpmax were observed for HEMAM and 2EM, both with DMPA. Final DC was higher for the methacrylate groups, in comparison with methacrylamide groups, independent of the photoinitiators. However, for the methacrylamide groups, the association with BAPO led to the lowest values of DC. In terms of DC@Rpmax, methacrylate-based systems showed significantly higher values than methacrylamide formulations. DMPA and Ivocerin led to higher values than CQ/EDMAB and BAPO in methacrylamide-based compounds. BAPO systems showed de lowest values for both HEMA and HEMAM formulations. For the viscosity (Pa.s), only 2EM had higher values (1.60 ± 0.15) in comparison with all monomers. In conclusion, polymerization kinetics was affected by the photoinitiators for both monomers. Viscosity was significantly increased with the use of secondary methacrylamide. SIGNIFICANCE: this work demonstrated the feasibility of using newly-synthesized methacrylamide monomers in conjunction with a series of initiator systems already used in commercial materials.
Assuntos
Cimentos Dentários , Metacrilatos , Acrilamidas , Bis-Fenol A-Glicidil Metacrilato , Resinas Compostas , Teste de Materiais , Fotoiniciadores Dentários , PolimerizaçãoRESUMO
This study aims at modifying dual-cure composite cements by adding thio-urethane oligomers to improve mechanical properties, especially fracture toughness, and reduce polymerization stress. Thiol-functionalized oligomers were synthesized by combining 1,3-bis(1-isocyanato-1-methylethyl)benzene with trimethylol-tris-3-mercaptopropionate, at 1:2 isocyanate:thiol. Oligomer was added at 0, 10 or 20 wt% to BisGMA-UDMA-TEGDMA (5:3:2, with 25 wt% silanated inorganic fillers) or to one commercial composite cement (Relyx Ultimate, 3M Espe). Near-IR was used to measure methacrylate conversion after photoactivation (700 mW/cm(2) × 60s) and after 72 h. Flexural strength and modulus, toughness, and fracture toughness were evaluated in three-point bending. Polymerization stress was measured with the Bioman. The microtensile bond strength of an indirect composite and a glass ceramic to dentin was also evaluated. Results were analyzed with analysis of variance and Tukey's test (α = 0.05). For BisGMA-UDMA-TEGDMA cements, conversion values were not affected by the addition of thio-urethanes. Flexural strength/modulus increased significantly for both oligomer concentrations, with a 3-fold increase in toughness at 20 wt%. Fracture toughness increased over 2-fold for the thio-urethane modified groups. Contraction stress was reduced by 40% to 50% with the addition of thio-urethanes. The addition of thio-urethane to the commercial cement led to similar flexural strength, toughness, and conversion at 72h compared to the control. Flexural modulus decreased for the 20 wt% group, due to the dilution of the overall filler volume, which also led to decreased stress. However, fracture toughness increased by up to 50%. The microtensile bond strength increased for the experimental composite cement with 20 wt% thio-urethane bonding for both an indirect composite and a glass ceramic. Novel dual-cured composite cements containing thio-urethanes showed increased toughness, fracture toughness and bond strength to dentin while demonstrating reduced contraction stress. All of these benefits are derived without compromising the methacrylate conversion of the resin component. The modification does not require changing the operatory technique.
Assuntos
Resinas Compostas/química , Cimentos de Resina/química , Compostos de Enxofre/química , Uretana/química , Ácido 3-Mercaptopropiônico/química , Peróxido de Benzoíla/química , Bis-Fenol A-Glicidil Metacrilato/química , Cerâmica/química , Colagem Dentária , Dentina/ultraestrutura , Módulo de Elasticidade , Humanos , Isocianatos/química , Cura Luminosa de Adesivos Dentários/métodos , Teste de Materiais , Metacrilatos/química , Maleabilidade , Polietilenoglicóis/química , Polimerização , Ácidos Polimetacrílicos/química , Poliuretanos/química , Autocura de Resinas Dentárias/métodos , Silanos/química , Estresse Mecânico , Propriedades de Superfície , Resistência à Tração , para-Aminobenzoatos/químicaRESUMO
OBJECTIVES: To evaluate conversion, bulk mechanical properties and camphorquinone (CQ) consumption in methacrylate resins, comprising a range of overall initiator concentrations and CQ/amine ratios. METHODS: BisGMA (Bisphenol-A glycidyl dimethacrylate), TEGDMA (triethyleneglycol dimethacrylate) and UDMA (urethane dimethacrylate) were mixed at a 1:1:1 molar ratio. CQ was used as the visible light photosensitizer, in combination with EDMAB (Ethyl p-dimethylamino benzoate), at 3:1, 2:1, 1:1, 1:2 and 1:3 weight ratios, at 0.5, 1.0, 1.5, 2.0 and 3.0 wt% overall initiator concentration. Butylhydroxytoluene was added at 0.05 wt% as an inhibitor. Unfilled resins were photoactivated with a dental light source (VIP Jr, Bisco) for 60 s at 600 mW/cm(2). Flexural strength/modulus were assessed in 2×1×10 mm bars, tested in three-point bending. Degree of conversion was assessed at the bottom of the same specimens using FT-RAMAN. CQ consumption was measured using a UV-vis spectrometer. Data were analyzed with two-way ANOVA/Tukey test (α=5%). RESULTS: Lower conversion and inferior mechanical properties were observed with lower overall initiator concentrations and higher amine/CQ ratios. The lowest overall initiator concentration (0.5%) presented the statistically lowest conversion/properties results, except for the 1:3 amine/CQ ratio. For overall concentrations equal or greater to 1.5%, the amine/CQ ratio did not influence conversion or mechanical properties. CQ consumption was less efficient for the highest overall initiator concentrations and lower amine/CQ ratios. CLINICAL RELEVANCE: Above 1.5 wt% overall initiator concentration, the conversion and general mechanical properties were independent of the initiator concentration. Therefore, there seems to be no benefit to increasing the initiator concentration above that level. At higher camphorquinone concentrations, light transmission and photosensitizer consumption becomes impaired, which could lead to decreased depth of cure and yellowing of the restoration.
Assuntos
Aminas/análise , Cânfora/análogos & derivados , Metacrilatos/química , Cânfora/química , Teste de Materiais , Espectrofotometria UltravioletaRESUMO
Current challenges in adhesive dentistry include over-hydrophilic bonding formulations, which facilitate water percolation through the hybrid layer and result in unreliable bonded interfaces. This study introduces nanogel-modified adhesives as a way to control the material's hydrophobic character without changing the basic monomer formulation (keeping water-chasing capacity and operatory techniques unaltered). Nanogel additives of varied hydrophobicity were synthesized in solution, rendering 10- to 100-nm-sized particles. A model BisGMA/HEMA solvated adhesive was prepared (control), to which reactive nanogels were added. The increase in adhesive viscosity did not impair solvent removal by air-thinning. The degree of conversion in the adhesive was similar between control and nanogel-modified materials, while the bulk dry and, particularly, the wet mechanical properties were significantly improved through nanogel-based network reinforcement and reduced water solubility. As preliminary validation of this approach, short-term micro-tensile bond strengths to acid-etched and primed dentin were significantly enhanced by nanogel inclusion in the adhesive resins.
Assuntos
Nanopartículas/química , Cimentos de Resina/química , Condicionamento Ácido do Dente/métodos , Bis-Fenol A-Glicidil Metacrilato/química , Canfanos/química , Química Farmacêutica , Resinas Compostas/química , Colagem Dentária , Dentina/ultraestrutura , Adesivos Dentinários/química , Módulo de Elasticidade , Humanos , Interações Hidrofóbicas e Hidrofílicas , Teste de Materiais , Metacrilatos/química , Maleabilidade , Polimerização , Poliuretanos/química , Solubilidade , Estresse Mecânico , Temperatura , Resistência à Tração , Fatores de Tempo , Temperatura de Transição , Viscosidade , Água/químicaRESUMO
The clinical success of fiber posts has been attributed to their lower elastic modulus. The tested hypothesis was that fiber posts could lead to lower risk of post debonding and lower risk of root fracture, despite an increase in root stresses. Stress analyses were carried out with a 3D finite element model of a premolar restored with a metallic or a fiber post. Bonded and non-bonded post/cement interface conditions were simulated. We calculated risk-of-fracture indices by determining the highest principal stress values divided by the tensile strength. Shear stresses along the post/cement interface were analyzed for the bonded models. Compared with the premolar restored with a metallic post, the fiber post generated lower stresses along the interface and higher stresses in the root. However, with the fiber post, fracture was less likely to occur in the root, since its core and post fracture indices were higher.
Assuntos
Materiais Dentários/química , Planejamento de Prótese Dentária , Vidro/química , Técnica para Retentor Intrarradicular/instrumentação , Fraturas dos Dentes/prevenção & controle , Raiz Dentária/fisiologia , Dente Pré-Molar/patologia , Fenômenos Biomecânicos , Resinas Compostas/química , Simulação por Computador , Ligas Dentárias/química , Colagem Dentária , Análise do Estresse Dentário , Módulo de Elasticidade , Análise de Elementos Finitos , Humanos , Imageamento Tridimensional , Teste de Materiais , Modelos Biológicos , Cimentos de Resina/química , Fatores de Risco , Resistência ao Cisalhamento , Estresse Mecânico , Resistência à Tração , Raiz Dentária/lesões , Dente não Vital/patologiaRESUMO
PURPOSE: To evaluate the effect of light guide distance and the different photoactivation methods on the degree of conversion (DC) and microleakage of a composite. METHODS AND MATERIALS: Three photoactivation protocols (600 mW/cm2 x 40 seconds; 400 mW/cm2 x 60 seconds or 200 mW/cm2 x 20 seconds, followed by 500 mW/cm2 x 40 seconds) and three distances from the light source (0, 3 or 7 mm) were tested. Cylindrical specimens (5 mm diameter; 2 mm tall; n=3) were prepared for the DC test (FT-Raman). Class V cavities were made in 90 bovine incisors to conduct the microleakage test. The specimens were conditioned for 15 seconds with phosphoric acid (37%), followed by application of the adhesive system Prime & Bond NT (Dentsply/Caulk). The preparations were restored in bulk. The specimens were stored for 24 hours in distilled water (37 degrees C) before being submitted to the silver-nitrate microleakage protocol. The restorations were sectioned and analyzed under 25x magnification. RESULTS: Statistical analyses (two-way ANOVAs and Tukey test, alpha=0.05) found significance only for the factor distance (p=0.015) at the top of the composite for the DC test. Conversion was statistically lower for the 7 mm groups compared to the 0 and 3 mm groups, which were equivalent to each other. At the bottom of the specimens, none of the factors or interactions was significant (p<0.05). The Kruskal-Wallis test showed that, in general, the soft-start method led to lower microleakage scores when compared to the continuous modes, mainly when associated with a distancing of 7 mm (p<0.01). With the exception of specimens irradiated with 400 mW/cm2 that did not demonstrate variations on scores for the distances tested, higher microleakage was observed for shorter distances from the light source. CONCLUSIONS: Soft-start methods may reduce microleakage when the light guide distancing provides a low level of irradiance, which also causes a discrete reduction in the DC.
Assuntos
Resinas Acrílicas , Resinas Compostas , Infiltração Dentária , Restauração Dentária Permanente , Cura Luminosa de Adesivos Dentários , Poliuretanos , Resinas Acrílicas/química , Animais , Bovinos , Resinas Compostas/química , Técnicas In Vitro , Incisivo , Poliuretanos/químicaRESUMO
Polymerization stress development results from the complex interplay of volumetric shrinkage, reaction kinetics, and viscoelastic properties. The objective of this study was to examine the relationships among volumetric shrinkage, degree of conversion, rate of polymerization (RP(max)), and stress development for 2 model bis-GMA-based composites. Three irradiances were used--220, 400, or 600 mW/cm(2)--with exposure times adjusted to deliver the same radiant energy. Volumetric shrinkage was determined with a mercury dilatometer, degree of conversion and RP(max) by differential scanning calorimetry (DSC), and polymerization stress with a low-compliance device (Sakaguchi et al., 2004b). Results indicated that polymerization reaction rate and shrinkage were not correlated. Irradiance was directly related to polymerization reaction rate and to stress development. The group with the highest stress/degree of conversion exhibited the lowest RP(max), so it can be assumed, within the limitations of this study, that the conversion was most closely related to stress development.
Assuntos
Bis-Fenol A-Glicidil Metacrilato/efeitos da radiação , Cura Luminosa de Adesivos Dentários , Bis-Fenol A-Glicidil Metacrilato/química , Varredura Diferencial de Calorimetria , Análise do Estresse Dentário , Dureza , Cinética , Metacrilatos/efeitos da radiação , Transição de Fase , Polietilenoglicóis/efeitos da radiação , Ácidos Polimetacrílicos/efeitos da radiação , Poliuretanos/efeitos da radiaçãoRESUMO
The influence of composite organic content on polymerization stress development remains unclear. It was hypothesized that stress was directly related to differences in degree of conversion, volumetric shrinkage, elastic modulus, and maximum rate of polymerization encountered in composites containing different BisGMA (bisphenylglycidyl dimethacrylate) concentrations and TEGDMA (triethylene glycol dimethacrylate) and/or BisEMA (ethoxylated bisphenol-A dimethacrylate) as co-monomers. Stress was determined in a tensilometer. Volumetric shrinkage was measured with a mercury dilatometer. Elastic modulus was obtained by flexural test. We used fragments of flexural specimens to determine degree of conversion by FT-Raman spectroscopy. Reaction rate was determined by differential scanning calorimetry. Composites with lower BisGMA content and those containing TEGDMA showed higher stress, conversion, shrinkage, and elastic modulus. Polymerization rate did not vary significantly, except for the lower value of the 66% TEGDMA composite. We used linear regressions to evaluate the association between polymerization stress and conversion (R(2)=0.905), shrinkage (R(2)=0.825), and modulus (R(2)=0.623).