Impact of shelf-life simulation on bonding performance of universal adhesive systems.

OBJECTIVES: To evaluate the micro-tensile bond strength to dentin (µTBS), the degree of conversion (DC) and nanoleakage expression (NL) of eight dental adhesives considering their expiry date (as-received, half-life and or end of shelf-life) after shelf-life simulation. METHODS: Five universal adhesives (Single Bond Universal, SBU; Tetric Bond Universal, TBU; OneCoat Universal, OCU; OptiBond Universal, OBU; and Prime&Bond Elect, P&B), two two-step self-etch adhesives (Clearfil SE, CSE; and AdheSE, ASE) and one two-step etch-and-rinse adhesive (Adper Singlebond 2, ASB) were evaluated. Shelf-life was simulated by storing the materials in an acclimatization chamber for different periods of time. The µTBS was tested in accordance with ISO/TS 11,405. DC was evaluated by means of FTIR spectroscopy. NL was evaluated after ammoniacal silver challenge. The significance level of α=0.05 was used for all statistical analyses. RESULTS: The µTBS to dentin of TBU, P&B, ASE, and ASB adhesive systems remained stable throughout the shelf-life periods evaluated, while for SBU, OCU, OBU, and CSE, decreased significantly after evaluation in the 'half-life' or 'end of shelf-life' condition (p<0.05). Except for P&B, ASE and OBU, the degree of conversion significantly decreased after the shelf-life simulation (p<0.05). OCU, ASE, and CSE showed significantly increased percentage of silver deposition within the adhesive layer (p<0.05). SIGNIFICANCE: Storing conditions and progressively longer storage time affect the performance of universal adhesives systems.

Effect of acidic solutions on the surface degradation of a micro-hybrid composite resin.

Composite resins may undergo wear by the action of chemical substances (e.g., saliva, alcohol, bacterial acids) of the oral environment, which may affect the material's structure and surface properties. This study evaluated the effect of acidic substances on the surface properties of a micro-hybrid composite resin (Filtek Z-250). Eighty specimens were prepared, and baseline hardness and surface roughness (KMN0 and Ra0, respectively) were measured. The specimens were subjected to sorption (SO) and solubility (SL) tests according to ISO 4049:2009, but using different storage solutions: deionized water; 75/25 vol% ethanol/water solution; lactic acid; propionic acid; and acetic acid. The acids were used in two concentrations: PA and 0.02 N. pH was measured for all solutions and final hardness (KMN1) and surface roughness (Ra1) were measured. Data were analyzed with paired t-tests and one-way ANOVA and Tukey's test (a=5%). All solutions decreased hardness and increased the Ra values, except for the specimens stored in water and 0.02 N lactic acid, which maintained the hardness. All solutions produced similar SO and SL phenomena, except for the 0.02 N lactic acid, which caused lower solubility than the other solutions. Ethanol showed the highest pH (6.6) and the 0.02 N lactic acid the lowest one (2.5). The solutions affected negatively the surface properties of the composite resin; in addition, an acidic pH did not seem to be a significant factor that intensifies the surface degradation phenomena.

Effect of Acidic Solutions on the Surface Degradation of a Micro-Hybrid Composite Resin

Composite resins may undergo wear by the action of chemical substances (e.g., saliva, alcohol, bacterial acids) of the oral environment, which may affect the material's structure and surface properties. This study evaluated the effect of acidic substances on the surface properties of a micro-hybrid composite resin (Filtek Z-250). Eighty specimens were prepared, and baseline hardness and surface roughness (KMN0 and Ra0, respectively) were measured. The specimens were subjected to sorption (SO) and solubility (SL) tests according to ISO 4049:2009, but using different storage solutions: deionized water; 75/25 vol% ethanol/water solution; lactic acid; propionic acid; and acetic acid. The acids were used in two concentrations: PA and 0.02 N. pH was measured for all solutions and final hardness (KMN1) and surface roughness (Ra1) were measured. Data were analyzed with paired t-tests and one-way ANOVA and Tukey's test (a=5%). All solutions decreased hardness and increased the Ra values, except for the specimens stored in water and 0.02 N lactic acid, which maintained the hardness. All solutions produced similar SO and SL phenomena, except for the 0.02 N lactic acid, which caused lower solubility than the other solutions. Ethanol showed the highest pH (6.6) and the 0.02 N lactic acid the lowest one (2.5). The solutions affected negatively the surface properties of the composite resin; in addition, an acidic pH did not seem to be a significant factor that intensifies the surface degradation phenomena.

Resinas compostas podem sofrer desgaste pela ação de substâncias químicas (saliva, álcool, ácidos bacterianos) presentes no ambiente oral, que podem afetar a estrutura e as propriedades superficiais do material. Assim, este estudo avaliou o efeito de substâncias ácidas nas propriedades superficiais de uma resina composta micro-híbrida (Filtek Z-250). Oitenta espécimes foram preparados e mensurados quanto à dureza e rugosidade superficial iniciais (KMN0 e Ra0, respectivamente). Os espécimes foram submetidos a testes de sorção (SO) e solubilidade (SL) de acordo com a ISO 4049:2009, porém usando diferentes soluções de armazenamento: água deionizada, solução etanol/água 75/25% em volume, ácido lático, ácido propiônico e ácido acético. Os ácidos foram utilizados em duas concentrações: PA e 0,02 N. O pH foi mensurado para todas as soluções e a dureza e rugosidade superficial finais (KMN1 e Ra1, respectivamente) foram mensuradas. Os dados foram analisados com testes t-pareado e ANOVA a um fator, e teste de Tukey (p<0,05). Todas as soluções reduziram a dureza e aumentaram os valores de Ra, exceto para os espécimes armazenados em água e ácido lático 0,02 N, que mantiveram a dureza. Todas as soluções produziram fenômenos de SO e SL similares, exceto o ácido lático 0,02 N, que causou menor solubilidade do que as outras soluções. Etanol mostrou o maior pH (6,6) e o ácido lático 0,02 N o menor deles (2,5). As soluções afetaram negativamente as propriedades superficiais da resina composta; além disso, um pH ácido não parece ser um fator significante para intensificar os fenômenos de degradação superficial.

Calcium hydroxide, pH-neutralization and formulation of model self-adhesive resin cements.

OBJECTIVES: This study investigated the incorporation of calcium hydroxide (CH) and its effect on pH-neutralization and fundamental properties of model self-adhesive resin cements (SARCs). METHODS: Two-paste SARCs were obtained. Paste A: UDMA/Bis-GMA/TEGDMA/HEMA co-monomer, 25% phosphate monomer (GDMA-P), and 50% glass fillers; Paste B: UDMA/HEMA co-monomer, water, photoinitiators, and 60% glass fillers. CH was added at final concentrations of 0 (control), 0.25%, 0.5%, 1%, 2%, and 4%. Equal volumes of the pastes were mixed before testing. pH-neutralization of the eluate was followed during 24-h storage in distilled water. Other physico-chemical properties were evaluated only for the control and CH concentrations that neutralized the eluate. These evaluations included degree of CC conversion, film thickness, flexural strength/modulus, work-of-fracture, hardness, depth of cure, water sorption/solubility, and dentin bond strength. Statistical comparisons were conducted at a 5% significance level. RESULTS: All CH concentrations above 0.25% caused pH increase of the eluate at 24h. The only CH concentrations leading to pH-neutralization were 2% and 4%. Compared with the control cement, the addition of 4% CH decreased the flexural strength, flexural modulus, work-of-fracture, CC conversion, and dentin bond strength. The cement with 2% CH had similar properties to the control cement, except for lower work-of-fracture and lower film thickness. Hardness, depth of cure, and water sorption were not affected by CH. The cement with 4% CH had lower solubility and film thickness than the other materials. SIGNIFICANCE: Incorporation of 2% CH to SARCs may lead to pH-neutralization without dramatically affecting other material properties.