Influence of simulated gastric juice on surface characteristics of CAD-CAM monolithic materials.

STATEMENT OF PROBLEM: How the surfaces of monolithic esthetic restorations behave in the presence of acidic substances is unclear. PURPOSE: The purpose of this in vitro study was to evaluate the effect of simulated gastric juice on roughness, morphology, microhardness, substance loss, and color change of computer-aided design and computer-aided manufacturing (CAD-CAM) monolithic materials. MATERIAL AND METHODS: Disks from Lava Ultimate, VITA ENAMIC, IPS e.max CAD, and VITA SUPRINITY were analyzed for roughness, morphology, and microhardness by using a confocal microscope, scanning electron microscope (SEM), and Vickers hardness tester. Substance loss was determined by weighing the specimens on an analytical balance, and color change (ΔE) was assessed by using a spectrophotometer based on the CIELab parameters. All analyses were carried out before and after acid exposure. RESULTS: Acid exposure significantly decreased the roughness, having a very high effect size on this property. The material was highly decisive in determining the microhardness, presenting the following order: VITA SUPRINITY>IPS e.max CAD>VITA ENAMIC>Lava Ultimate. The mass was not significantly affected by the acidic challenge. No significant difference in ΔE was found between Lava Ultimate and VITA ENAMIC and between IPS e.max CAD and VITA SUPRINITY. Lava Ultimate showed a higher ΔE than IPS e.max CAD and VITA SUPRINITY, whereas VITA ENAMIC exhibited higher ΔE only when compared with VITA SUPRINITY. All materials presented ΔE<1. CONCLUSIONS: The simulated gastric juice significantly influenced the roughness of all the evaluated materials and promoted a color change classified as clinically undetectable in all materials.

Zirconia-porcelain bonding: effect of multiple firings on microtensile bond strength.

PURPOSE: To determine the bond strength between zirconia and porcelain with varying numbers of veneer firing cycles. MATERIALS AND METHODS: Fifty specimens of zirconia veneered with feldspathic ceramic were submitted to one (1-firing), two (2-firings), three (3-firings), four (4-firings), or five (5-firings) firing cycles to sinter the porcelain. After the respective number of firings, the specimens were embedded into acrylic resin and sectioned into bars with a 1-mm2 cross-sectional area. The microbars were bonded to a special device and attached to a universal testing machine (Emic DL 1000). Microtensile bond strength testing (MTBS) was performed at 0.5 mm/min. The maximum load for fracture was recorded (N) and the microtensile bond strength was calculated in MPa. Data were analyzed using one-way ANOVA and Tukey's test (α = 0.05). The Weibull modulus and characteristic strength was also calculated for each experimental group. RESULTS: Specimens submitted to a single firing cycle presented the lowest bond strength values (14.1 MPa), two firing cycles provided intermediate bond strength values (15 MPa) and the other groups presented equivalently high values (18.1 - 18.4 MPa). The Weibull modulus did not change between the groups. CONCLUSION: More than three firing cycles of a veneer ceramic provided higher bond strengths between zirconia and the veneering ceramic.

Chemiluminescence as a PDT light source for microbial control.

The photodynamic therapy (PDT) is a combination of using a photosensitizer agent, light and oxygen that can cause oxidative cellular damage. This technique is applied in several cases, including for microbial control. The most extensively studied light sources for this purpose are lasers and LED-based systems. Few studies treat alternative light sources based PDT. Sources which present flexibility, portability and economic advantages are of great interest. In this study, we evaluated the in vitro feasibility for the use of chemiluminescence as a PDT light source to induce Staphylococcus aureus reduction. The Photogem® concentration varied from 0 to 75 µg/ml and the illumination time varied from 60 min to 240 min.The long exposure time was necessary due to the low irradiance achieved with chemiluminescence reaction at µW/cm² level. The results demonstrated an effective microbial reduction of around 98% for the highest photosensitizer concentration and light dose. These data suggest the potential use of chemiluminescence as a light source for PDT microbial control, with advantages in terms of flexibility, when compared with conventional sources.

Efeito citotóxico de agentes clareadores a base de peróxido de hidrogênio a 20% e 38% sobre células odontoblastóides / Cytotoxic effect of a 20% and a 38% hydrogen peroxide bleaching agents on odontoblast-like cells

O objetivo deste estudo foi avaliar a citotoxicidade de diferentes técnicas de clareamento dentário, utilizando agentes clareadores com 20% e 38% de peróxido de hidrogênio (H2O2) sobre células odontoblastóides MDPC-23. Sessenta discos de esmalte/dentina foram adaptados em câmaras pulpares artificiais e divididos em seis grupos de acordo com o tratamento realizado sobre a superfície do esmalte: G1- 20% H2O2 (1 aplicação); G2- 20% H2O2 (2 aplicações); G3- 38% H2O2 (1 aplicação); G4- 38% H2O2 (2 aplicações); G5- 38% H2O2 (3 aplicações) e G6- controle. Em cada aplicação, os agentes clareadores com 20% ou 38% de H2O2 permaneceram sobre o esmalte por 45 ou 10 minutos, respectivamente. Após a última aplicação do gel, o meio de cultura em contato com a dentina foi obtido (extrato) e aplicado sobre as células previamente cultivadas (30.000 células/cm2). Foram realizadas avaliações do metabolismo (Teste de MTT) e da morfologia celular (MEV). A redução do metabolismo celular foi de 96,29%; 96,11%; 96,42%; 95,62% e 97,18% para G1, G2, G3, G4 e G5, respectivamente. Houve diferença estatisticamente significante apenas quando se comparou os grupos tratados com o grupo controle (G6) (Mann Whitney, p<0,05). Nestes grupos tratados, as poucas célulasque sobreviveram aos extratos apresentavam notáveis alterações morfológicas. Concluiu-se que ambas as técnicas de clareamento avaliadas resultaram em intenso efeito citotóxico trans-amelodentinário para ascélulas MDPC-23.

The aim of this in vitro study was to evaluate the trans-enamel and transdentinal cytotoxic effects of two in-office tooth bleaching techniques that employ bleaching gels containing 20% and 38% of H2O2 on cultured odontoblast-like cell line (MDPC-23). Sixty enamel/dentin discs were obtained from bovine central incisors and placed individually in artificial pulp chambers. Six groups were formed according to the following enamel treatments: G1- 20% H2O2 (1 application); G2- 20% H2O2 (2 applications); G3- 38% H2O2 (1 application); G4- 38% H2O2 (2 applications); G5- 38% H2O2 (3 applications); and G6- control (no treatment). In G1 and G2, the bleaching gel was left in contact with the enamel surface for 45 min in each application. However, in G3, G4, and G5 the bleaching gel was applied for only 10 min per application. After the last application, the extracts were collected and applied on previously cultured cells (30.000 cells/cm2) for 24 h. Cell metabolism was evaluated by the MTT assay and cell morphology was analysed by scanning electron microscopy. Cell metabolism decreased by 96.29%; 96.11%; 96.42%; 95.62%; and 97.18% in G1, G2, G3, G4, and G5, respectively. All treated groups differed significantly from non-treated control group (G6) (p < 0.05). However, the difference in cell metabolism among treated groups was not significant statistically. In addition, significant morphological cell alterations were observed in all treated groups. Under the tested experimental conditions, the extracts collected after both tooth bleaching techniques evaluated in this study caused severe toxic effects on cultured odontoblast-like cell MDPC-23.