The effect of different adhesives on vinyl polysiloxane bond strength to two tray materials.

STATEMENT OF PROBLEM: Although stock trays often provide mechanical retention for elastomeric impression materials, manufacturers typically recommend the use of an adhesive, whether a stock or custom tray is used. Universal adhesives for vinyl polysiloxane (VPS) are used in practice, but comparative bond strengths have not been reported. PURPOSE: The aim of this study was to evaluate the bond of 3 VPS materials with a methylmethacrylate autopolymerizing and a light-polymerizing tray material, using the adhesive recommended by the manufacturer of the impression material, and 2 universal adhesives (paint-on and spray-on). MATERIAL AND METHODS: Ten specimens per group, for a total of 180 flat 15 x 15 x 20-mm specimens, were made from the 2 tray materials and finished to 320 grit with silicon carbide paper. Four paint-on adhesives (Coltene, Caulk, Kerr VPS, or universal VPS) and 1 spray-on adhesive (Sili Spray) were applied and dried following manufacturers' instructions or for 10 minutes. Three impression materials, Affinis, Aquasil, and Take I, were automixed and injected into a perforated cylinder positioned in a universal testing machine. Tray specimens were positioned against the open cylinder end in contact with the VPS material. Tensile tests (cross-head speed 5 mm/min) were conducted until adhesive separation failure. Mean values and standard errors of the adhesive strength were recorded in MPa for each material combination. Data were first analyzed with Welch analysis of variance (ANOVA) to determine overall significance, and then with a 3-way ANOVA and the Tukey HSD test to make pairwise comparisons, with alpha=.05 for all testing. RESULTS: For all impression materials tested, the universal spray-on adhesive consistently demonstrated significantly lower bond strengths than all other adhesives (P<.05). Equivalent or significantly (P<.05) higher bond strength values were found for the universal paint-on adhesive for the 3 impression materials tested. CONCLUSION: The use of GC paint-on universal adhesive provided significantly higher adhesive values than those obtained with the adhesives supplied by the manufacturers of the impression materials tested, with the exception of the Kerr impression and adhesive material combination where no significant differences were found.

CYP2C19- and CYP3A4-dependent omeprazole metabolism in West Mexicans.

Omeprazole has been used as a drug probe for CYP2C19, but no systematic data are available for Mexican populations. The aim of this study was to evaluate the phenotype frequencies of the CYP2C19 polymorphism in West Mexicans. Besides omeprazole, sulfone was measured to evaluate CYP3A4 after administration of the 20-mg dose to 127 healthy volunteers. Logarithms of metabolic indexes of omeprazole/hydroxyomeprazole for CYP2C19 and omeprazole/omeprazole sulfone for CYP3A4 had trimodal distributions. Five subjects (4%) had a log CYP2C19 metabolic index below -0.9, suggesting an ultra-extensive phenotype. Poor metabolizers (log metabolic index > 0.6) were 6%. For CYP3A4, 11 subjects (9%) were below -0.3 of the log metabolic index. The log metabolic index of omeprazole/omeprazole sulfone was above the antimode of 0.6 for 11% of this population. The mean log metabolic index of CYP3A4 extensive metabolizers (80%) was 0.166, which seems to be higher than the data described for Caucasians and lower than that for Asians.

Phenotype of CYP2C19 and CYP3A4 by determination of omeprazole and its two main metabolites in plasma using liquid chromatography with liquid-liquid extraction.

We present a new simple and reliable HPLC method for measuring omeprazole and its two main metabolites in plasma. This can be used for studying CYP2C19 and CYP3A4 genetic polymorphisms using omeprazole as the probe drug. Omeprazole, hydroxyomeprazole and omeprazole sulfone were extracted from plasma samples with phosphate buffer and dichloromethane-ether (95:5). HPLC separation was achieved using an Ultrasphere ODS C(18) (Beckman) column. The mobile phase was acetonitrile-phosphate buffer (24:76, pH 8), containing nonylamine at 0.015%. Retention times were 9.5 min for omeprazole, 3.25 min for hydroxyomeprazole, 7.4 min for omeprazole sulfone and 6.27 min for internal standard (phenacetine). Detection (UV at 302 nm) of analytes was linear in the range from 96 to 864 ng/ml. This is useful for calculating metabolic index for CYP2C19 and CYP3A4 in adults and children. This method is stable, reproducible, improves resolution and has practical advantages such as low cost.

The influence of coffee with milk and tea with milk on the bioavailability of tetracycline.

The effect of milk added to coffee or black tea on the bioavailability of tetracycline was evaluated in 12 healthy volunteers according to a crossover design. Results showed that even a small volume of milk containing extremely small amounts of calcium severely impair the absorption of the drug, so that the presence of this metal ion should be carefully controlled in order to avoid decreasing the available tetracycline.

Reproducibility of occlusal contacts relative to mounting cast variables.

This study evaluated the accuracy of occlusal contacts relative to the mode in which casts are mounted. Specifically, the direct effect on occlusal contacts was assessed with respect to: (a) the type of mounting stone used; (b) the amount of material used relative to the distance between the mounting plate and the cast base; and (c) the presence or absence of a restriction of the articulator's vertical opening. A 3 x 2 x 2 factorial analysis of variance and a Dunn's Multiple Comparison Procedure (P < .05) showed that one of the three mounting stones was statistically significantly less accurate in reproducing occlusal contacts when a distance of 19 mm existed between the cast and the articulator, regardless of the existance of articulator restriction.

Alternatives to posterior complete crowns: integrating foundations with cuspal protection.

A common approach for restoring compromised posterior teeth is to reconstruct the missing anatomic crown with a dental restorative material and prepare the remaining tooth structure for an artificial veneer. Because this procedure is also compounded by designing subgingival finish lines for tooth preparations, a conservative approach for the fabrication of one-piece castings is suggested that incorporates both foundations and cuspal protection, with finish lines prepared above the gingival crest. Patient selection, advantages, disadvantages, and armamentarium are discussed.

Measurement of oxide adherence to silver-free high-palladium alloys.

The purpose of this study was to test the adherence strength of oxides to some silver-free high-palladium alloys, and to compare the results to values obtained from Au-Pd and Ni-Cr metals. The results showed that the adherence strengths of the oxides were greater than the reported cohesive strength of opaque porcelain. This would indicate that the oxides formed on the alloys examined in this study are sufficiently adherent to their substrates to produce adequate porcelain bonds.

Comparison of the effects of three sprue designs on the internal porosity in crowns cast with a silver-free high-palladium alloy.

This study tested the effect of bsprue design on internal porosity of a silver-frees high-palladium alloy. The designs evaluated consisted of: (1) a cylindrical sprue, (2) a cylindrical sprue with a reservoir, and (3) cylindrical sprue with a constriction at the point of attachment with the pattern. Ten identical complete crowns were made with each sprue design. The cast crowns were embedded in epoxy resin, sectioned, and polished. A total of six sites for each sample were analyzing computer. The mean amount of internal porosity from all analyzed sites for each sprue design was calculated as a percent site porosity per total site and differences between the experimental sites and groups tested. The analysis of variance found no significant differences among the sprues and no significant interaction, but determined a significant difference (p less than 0.05) among the sites analyzed. Tukey's studentized range test showed that the sprue contained a significantly greater percentage of porosity than any of the other sites analyzed.

Occlusal accuracy of casts made and articulated differently.

This study evaluated the occlusal accuracy of gypsum casts constructed from irreversible hydrocolloid and selected nonaqueous elastomeric materials. Master metal casts were attached to a vertically moving apparatus that allowed their occlusal surfaces to produce repeatable contacts. Impressions were made with irreversible hydrocolloid, polysulfide, and vinylsiloxane. Resulting maxillary casts were mounted with a constant positioning device and mandibular casts were mounted with zinc oxide-eugenol paste records or by maximum intercuspation. Four specific master occlusal contacts were compared with contacts generated from the mounted gypsum casts; a perfect score was 40 (four contacts x 10 casts). A chi-square linear model for category data was used to compare groups. Results indicated that casts made from irreversible hydrocolloid should not be articulated with the use of a zinc oxide-eugenol paste but are best articulated by using maximum intercuspation (32/40 contacts).

Evaluating six sprue designs used in making high-palladium alloy castings.

Six different sprue designs were studied to determine which, if any, could be used to produce more complete castings with a high-palladium alloy. A standardized mesh test pattern was used to ensure objective measurements and accurate evaluations of the spruing techniques. This study of problems usually encountered when casting high-palladium alloys found that: Differing sprue designs effect significant differences in obtaining complete castings (p less than .05) as indicated in the ANOVA. The connection between the casting and the sprue should be constricted to improve castability of high-palladium alloys. Although this spruing technique may be used in different sprue designs to improve the quality of castings, further research seems indicated.