The evaluation of microleakage and bond strength of a silicone-based resilient liner following denture base surface pretreatment

STATEMENT OF PROBLEM: The failure of adhesion between a silicone-based resilient liner and a denture base is a significant clinical problem. PURPOSE: The purpose of this study was to examine the effects of denture base resin surface pretreatments with different chemical etchants preceding the silicone-based resilient liner application on microleakage and bond strength. The initial effects of chemical etchants on the denture base resin in terms of microstructural changes and flexural strength were also examined. MATERIAL AND METHODS: Forty-two polymethyl methacrylate (PMMA) denture base resin (Meliodent) specimens consisting of 2 plates measuring 30 x 30 x 2 mm were prepared and divided into 7 groups (n = 6). Specimen groups were treated by immersion in acetone for 30 (A30) or 45 (A45) seconds, methyl methacrylate monomer for 180 (M180) seconds, and methylene chloride for 5 (MC5), 15 (MC15) or 30 (MC30) seconds. Group C had no surface treatment and served as the control. Subsequently, an adhesive (Mollosil) and a silicone-based resilient denture liner (Mollosil) were applied to the treated surfaces, and all specimens were immersed in the radiotracer solution (thalium-201 chloride) for 24 hours. Tracer activity (x-ray counts), as a parameter of microleakage, was measured using a gamma camera. For bond-strength measurement, 84 rectangular PMMA specimens (10 x 10 x 40 mm) were surface-smoothed for bonding and treated with the different chemical etchants using the same previously described group configurations. The adhesive and the silicone-based denture liner were applied to the treated surfaces. Tensile bond-strength (MPa) was measured in a universal testing machine. Flexural strength measurement was performed with 49 PMMA specimens (65 x 10 x 3.3 mm according to ISO standard 1567) in 7 groups (n = 7), with 1 flat surface of each treated with 1 of the chemical etchants preceding adhesive application. The flexural strength (MPa) was measured using a 3-point bending test in a universal testing machine. The data were analyzed by 1-way analysis of variance and the Tukey HSD test (alpha = .05). RESULTS: Significant differences were found between the groups in terms of microleakage (P < .0001). The lowest microleakage was observed in group M180 (30,000 x-ray counts) and the highest in the control group (44,000 x-ray counts). The mean bond strength to PMMA resin ranged from 1.44 to 2.22 MPa. All treated specimens showed significantly higher bond strength than controls (P < .01). The flexural strength values all significantly differed (P < .05). All experimental specimens that had chemical surface treatments showed lower flexural strength than controls (P < .05). CONCLUSION: Treating the denture base resin surface with chemical etchants increased the bond strength of silicone-based resilient denture liner to denture base and decreased the microleakage between the 2 materials. Considering the results of both tests together, the use of methyl methacrylate monomer for 180 seconds was found to be the most effective chemical treatment.     

Economics methods in the Clinical Outcomes Utilizing percutaneous coronary Revascularization and Aggressive Guideline-driven drug Evaluation (COURAGE) trial

Percutaneous coronary intervention (PCI) remains a major therapeutic option for the treatment of chronic coronary artery disease. In the COURAGE trial, 2287 patients with chronic coronary disease were randomized between PCI with medical management and medical management alone. Embedded within the COURAGE trial is a detailed economic analysis being conducted in three health care systems: the US Veterans Administration (VA), Canada, and the US non-VA. Resource use and costs are being collected for each system and overall. Survival is assessed internally in the trial with mean follow-up of 4.5 years. Long-term mean survival will be estimated by projecting survival beyond the trial period by extrapolating the in-trial hazard rates. Utility is being assessed at baseline and at 1, 3, and 6 months and annually thereafter, using a computer-administered standard gamble. Quality-adjusted life years are calculated by multiplying survival by utility. The incremental cost-effectiveness ratio of PCI will be defined as the additional cost of PCI divided by the gain in life years and quality-adjusted life years. The 95% confidence regions of efficacy and costs will be determined by bootstrap over a range of acceptability thresholds, which will then be displayed in the cost-effectiveness plane and as a cost-effectiveness acceptability curve. A multilevel regression model will assess cost-effectiveness from a net benefit perspective. These approaches should provide the most detailed assessment available of the cost-effectiveness of PCI for coronary artery disease.     

Staphylococcus aureus endocarditis: The Grady Memorial Hospital Experience

BACKGROUND: Staphylococcus aureus is a common cause of endocarditis. Previous studies have shown that the mortality rate associated with S aureus endocarditis remains high, and methicillin resistance is becoming more prevalent. METHODS: Over the past 4 years, 283 patients with suspected endocarditis were referred to the cardiology department of Grady Memorial Hospital for echocardiography. Their clinical course and demographic information was entered into a database. Among these patients, 87 (30.6%) were confirmed to have endocarditis, with 41 (47.1%) of them culture positive for either methicillin-resistant (MRSA) or methicillin-sensitive S aureus (MSSA). Of these patients, 14 were MRSA culture positive, and 27 were MSSA culture positive. These two groups were compared with respect to demographic information and morbidity and mortality outcomes. RESULTS: The MRSA and MSSA groups were found to be similar upon analysis in all baseline characteristics. There was a non-statistical trend among the two groups in origin of infection, as the MRSA group tended toward nosocomial infection more often. Outcomes, including surgery, death, and complications were also found to be similar between the two groups. CONCLUSIONS: There does not seem to be difference in the outcome of MRSA versus MSSA endocarditis. Nosocomial infection may predispose patients to MRSA endocarditis, but a larger study with a greater sample size is necessary to evaluate these questions more accurately.     

S-phase fraction combined with other patient and tumor characteristics for the prognosis of node-negative, estrogen- receptor-positive breast cancer

Women with estrogen-receptor (ER)-positive breast cancer and no axillary lymph-node involvement are considered to have excellent overall prognosis. However, this population is not homogeneous with regard to risk of recurrence; in fact, some of these patients have a prognosis no better than that of many women with ER-negative tumors or positive axillary nodes. Consequently, better tumor markers and better use of those currently available are needed to distinguish patients who would benefit from more aggressive therapy from those for whom such therapy is unnecessary.A well-defined cohort of over 4000 breast cancer patients from National Surgical Adjuvant Breast and Bowel Project (NSABP) Protocol B-14 who had ER-positive tumors and no axillary lymph-node involvement was analyzed to ascertain the usefulness of tumor cell S- phase fraction for prognosis. The significance of clinical tumor size, patient age at surgery, ER and progesterone receptor (PgR) expression, and nuclear grade was also explored. Statistical methods based on smoothing splines were used to relate treatment failure and mortality rates to patient and tumor characteristics. Models for 5- and 10-year disease-free survival (DFS) and overall survival were developed and summarized. The attenuation of the prognostic importance of covariates over time was investigated.After other characteristics were accounted for, a strong association was found between S-phase fraction and DFS, as well as survival. Tumor size, patient age at surgery, and PgR status were also significantly associated with outcome. The diversity of risk in the B-14 population was more extreme than is generally recognized. The prognostic capabilities of S-phase, tumor size, and PgR status were sharply attenuated as the time from surgery increased.     

Dual modulation of calcium channel current via recombinant α2-adrenoceptors in pheochromocytoma (PC-12) cells

 The ability of recombinant rat α_2D-and α_2B-adrenoceptors expressed in nerve-growth-factor-differentiated pheochromocytoma PC-12 cells to modulate Ca²⁺ currents, recorded by the whole-cell patch-clamp technique, has been studied. Ca²⁺ currents in different cells were either reversibly reduced or increased by dexmedetomidine, an α₂-adrenergic agonist, in a concentration-dependent manner. Pertussis toxin pretreatment reduced the number of cells that showed an inhibitory response and reduced the magnitude of inhibition. In cells expressing the α_2B-adrenoceptor, pertussis toxin increased the proportion of cells from which a stimulatory effect on Ca²⁺ currents could be recorded. The magnitude of the inhibitory responses was unaffected but the stimulatory responses were considerably reduced by the dihydropyridine Ca²⁺ channel blocker nifedipine (5 μM). All effects of dexmedetomidine were reversible upon wash-out and inhibited by the antagonist rauwolscine. The results support the idea that modulation of voltage-dependent Ca²⁺ channels in transfected PC-12 cells is mediated by activation of recombinant α_2D- and α_2B-adrenoceptors. This receptor activation predominantly causes inhibition of dihydropyridine-insensitive Ca²⁺ channels via pertussis-toxin-sensitive G proteins. Additionally receptor activation can also lead to stimulation of dihydropyridine-sensitive Ca²⁺ channels via pertussis-toxin-insensitive mechanisms. Received: 25 March 1997 / Received after revision: 27 August 1997 / Accepted: 12 September 1997