Avaliação da superfície de materiais resinosos expostos ao óxido de alumínio / Evaluation of resinous material surfaces exposed to aluminum oxide powder

O objetivo deste estudo foi avaliar o efeito da deposição de óxido de alumínio sobre restaurações resinosas adjacentes a área tratada pelo sistema de abrasão a ar. Foram utilizados 10 terceiros molares devidamente seccionados e incluído sem cera utilidade deixando exposta a face vestibular. Em cada espécime confeccionou-se com a caneta de alta rotação,4 preparos cavitários de aproximadamente 2mm de diâmetro, eqüidistantes de uma linha central demarcada na cera. As 40 cavidades foram restauradas aleatoriamente com resina composta (Silux-3M) e selante resinoso (Fluoroshield-Dentsply). Em seguida, réplicas de cada espécime foram obtidas pela moldagem com silicone (Imprint II-3M) e modeloem resina epóxi (Stycast 1266- Emerson & Cummings). Na seqüência, foram feitas 2 aplicações de 15s do jato abrasivona parte central dos espécimes, utilizando-se o aparelho PrepStar® regulado a 80 psi, com ponta ativa de 45º e 0,48mmde diâmetro interno posicionada a 5mm da superfície. Ao final de cada aplicação, as superfícies foram lavadas, seca se moldadas novamente. Todas as réplicas foram avaliadas em MEV por 2 examinadores calibrados que fizeram uma avaliação cega quanto ao tipo de restauração. Os dados tabulados em escores foram analisados estatisticamente por análise de variância de Friedman. Os resultados evidenciaram que não houve diferença estatística significativa entre as superfícies das restaurações analisadas antes e após a utilização do jato abrasivo (p>0,05). Uma vez que o jato de óxidode alumínio não foi aplicado diretamente sobre as restaurações, provavelmente a baixa energia cinética das partículas periféricas não foi capaz de produzir alterações em suas superfícies.

Comparison of the flexural strength of five adhesive resin cements.

STATEMENT OF PROBLEM: The increased use of adhesive resin cements in bonded prosthetic restorations has led to restorations debonding under function. PURPOSE: This investigation evaluated the differences in the flexural strength of new adhesive resin cements as a function of specimen age and storage condition. MATERIALS AND METHODS: Four new dual-cure cements were compared to C/B Metabond. Twenty specimens of each of the five cements were prepared in a rectangular glass mold (25 x 2 x 2 mm). The new cements were light-activated with a 550 mW/cm(2) lamp for 80 seconds on both the top and bottom surfaces. The auto-cured cement was allowed to set according to manufacturer's directions. Half the specimens were tested immediately after curing while the other half were stored in distilled water at 37 degrees C for 30 days. A three-point bending test was performed using an Instron at a crosshead speed of 1 mm/min. The results were analyzed by analysis of variance and Scheffé tests ( p < 0.05) to examine the effect of specimen age and storage condition. RESULTS: RelyX ARC exhibited a significantly higher flexural strength compared with Calibra and Panavia F when tested immediately. The standard cement, C/B Metabond, deformed and did not fracture at the immediate test time. After storage, the flexural strength had significantly improved from the immediate test time for Calibra, Cement-It, Panavia F, and C/B Metabond. However, there were no significant differences in the flexural strength among the cements when tested after 30 days in water at 37 degrees C. CONCLUSION: Immediately after curing, these new adhesive resin cements are not equivalent, as evidenced by the significant variability in the measured flexural strength. The distinctions among the cements diminish after aging in water, which may be due to residual polymerization or a plasticizing effect from water absorption. CLINICAL SIGNIFICANCE: When light-cured, all the new adhesive resin cements have greater early strengths than the auto-cured cement; however, the wide variation in immediate bending strength suggests that some cements may be more appropriate for use in high-stress clinical situations such as resin-bonded fixed partial dentures.

Effect of recombinant human bone morphogenetic protein-2 on the osseointegration of dental implants: a biomechanics study.

BACKGROUND: Bone augmentation procedures in combination with dental implants enhance osseointegration in areas that demonstrate localized bone deficit. Clinical confirmation of a biomechanically stable interface is essential for functional implant loading. PURPOSE: The aim of this study was to evaluate biomechanically the effect of recombinant human bone morphogenetic protein (rhBMP)-2 on implant osseointegration and correlate it with periotest and radiographic measurements. MATERIALS AND METHODS: Hollow cylinder implants were filled with absorbable collagen sponge soaked with rhBMP-2 or left empty and implanted in dog mandibles. The animals were followed for 4, 8, and 12 weeks, periotest assessment was performed at the end of each time interval, and specimens were collected for pullout biomechanical testing and radiographic evaluation of bone-implant contact levels. RESULTS: Periotest assessment did not provide evidence of statistically significant differences between the two groups and correlated well with the radiographic bone-implant contact levels. The pullout test revealed a higher correlation between force/displacement and displacement/energy for the experimental group, suggesting that the addition of rhBMP-2 did influence the rate of osseointegration. CONCLUSION: The results from the pullout test support the potential role of rhBMP-2 in clinical applications by promoting a biomechanically mature interface at 12 weeks. However, radiographic and periotest assessment of the bone-implant interface did not provide evidence of the differences observed with biomechanical testing.

Bond strength for orthodontic brackets contaminated by blood: composite versus resin-modified glass ionomer cements.

PURPOSE: The purpose of this study was to evaluate and compare the shear bond strengths of a self-cured glass ionomer versus composite cement for bonding of stainless steel buttons with various enamel surface and setting conditions. MATERIALS AND METHODS: Stainless steel orthodontic buttons were bonded using composite material under 3 different enamel and setting conditions: 1) conditioned and dry enamel surface, 2) conditioned and precontamination of the enamel surface with blood before bonding, 3) conditioned and immediate blood contamination postbonding and were compared with 3 different enamel conditions and setting for bonding with the glass ionomer cement: 1) nonconditioned and wet enamel surfaces, 2) nonconditioned and blood contamination of enamel before bonding, and 3) nonconditioned and immediate blood contamination postbonding. The brackets were bonded to 109 recently extracted teeth and allowed to set in a moist plastic container for 24 hours. They were subsequently tested in shear mode with a universal testing machine. The maximum bond strength and the site of bond failure were recorded. In addition, the location of the bond failure was studied. RESULTS: Composite was capable of sustaining greater forces than the resin-modified glass ionomer materials. Hence, it took more force to debond a bracket cemented with composite than with resin-modified glass ionomer. The effect of contamination was similar in both of the materials, and the magnitude of the decrease in bond strength was nearly of the same proportion. The postcontamination values were not significantly different from the uncontaminated bond strength for either material. The type of bond failure was significantly different for the different materials, and there were significant differences among the treatment conditions. CONCLUSION: Composite resin had significantly greater shear strength than resin-reinforced glass ionomer cement. Both materials showed a significant decrease in bond strength when precontaminated with blood. The postcontamination values were not significantly different from the uncontaminated bond strength for either material.

Quality of removable partial dentures worn by the adult U.S. population.

STATEMENT OF PROBLEMS: Research-based assessments of the quality of removable partial dentures (RPDs), especially within a large patient population, are lacking. PURPOSE: This study evaluated the prevalence and quality of RPDs by use of the National Health and Nutrition Survey (NHANES III) data set. MATERIAL AND METHODS: Estimates of the health and nutritional status of the American population were obtained from the NHANES III data set (1988-1994). Calibrated dentists performed dental examinations on 17,884 adults. If the subject wore an RPD, its quality was assessed with 5 criteria: integrity, tooth wear, the presence of temporary reline material or adhesive, stability, and retention. In this study, the data on RPD defects were used to assess the prevalence of problems. The original population was divided into 4 subgroups: paired RPD data = subjects wearing both maxillary and mandibular RPDs (n = 600 prostheses, 300 maxillary and 300 mandibular); single RPD data = subjects with only one RPD (n = 1003 prostheses, 511 maxillary and 492 mandibular); maxillary versus mandibular RPD data = all subjects with all RPDs (n = 1603 prostheses, 811 maxillary and 792 mandibular); and pooled RPD data = all subjects with a single RPD plus subjects with 2 RPDs, counting only the RPD with the most defects (n = 1303 prostheses, 674 maxillary and 629 mandibular). The subjects were analyzed with descriptive statistics. The distribution of defects in the RPDs was examined for possible associations with chi(2) tests. The paired data for patients with both maxillary and mandibular RPDs were analyzed with Wilcoxon signed rank tests. The prevalence of RPDs as a function of patient age and the association between RPD defects and patient age were analyzed with chi(2) tests. The results were considered highly significant at P<.0001 and significant at P<.05. RESULTS: Of the 17,884 adults who underwent a dental examination, 1306 had RPDs. Three patients were excluded because their records were incomplete, leaving 1303 patients available for analysis. Most of the prostheses examined (65%) had at least 1 defect. Lack of stability was the most prevalent single defect. Distinctions in the type and prevalence of defects were observed between mandibular and maxillary RPDs. Mandibular RPDs had significantly more problems related to retention, whereas maxillary RPDs had significantly more problems related to the presence of reline material and to integrity defects. Tooth wear defects were significantly associated with patient age (P<.0001). Only one third of the RPDs were considered satisfactory according to NHANES III criteria. CONCLUSION: A review of the database used in this study indicated that, in spite of a decline in tooth loss, RPDs are still used in all age cohorts, including young adults. A large number of RPDs were found to have defects.