Compatibility of Type IV dental stone with polysulfide impression materials.

PURPOSE: In the American National Standards Institute/American Dental Association specification no. 19, compatibility of impression materials with dental stones is assessed by the presence of a 20-microns-wide line reproduced on an unmodified calcium sulfate dihydrate cast. In actual dental practice, modified type IV dental stones are used, although little is known of their compatibility with polysulfide impression materials. This study evaluated the compatibility of 6 polysulfide impression materials and 11 modified type IV dental stones. MATERIALS AND METHODS: A line 20 microns wide was etched on four glass dies. Four samples of each combination of impression material and dental stone were prepared according to the manufacturer's directions with an additional 3 minutes for the final setting time. Compatibility was determined by the presence of the reproduced line on the dental stones, as observed under low angle 10 x magnification by four rater groups. RESULTS: The line was reproduced on all of the impression specimens, and the examiners recorded 66 positive identifications of the line on the stone casts out of a possible 1,056 ratings for a total of 6.25% of the specimens. Out of a possible 66 impression-stone combinations, only 18 reproduced the 20-microns line. The combinations reproducing the lines most frequently (75%) were Neoplex with Blue Die Stone (Columbus Dental, St Louis, MO) and Coeflex with Indic Die Stone (Coe Lab Inc, Chicago, IL). CONCLUSIONS: The study showed that many combinations of polysulfide impression materials and modified type IV dental stones did not reproduce the 20-microns line; therefore, not every polysulfide is compatible with every type IV dental stone.

The reporting of statistical inferences in selected prosthodontic journals.

Dental periodicals are the fundamental source of prosthodontic research. The ability to understand and contribute to dental literature is basic to the prosthodontic profession. The purpose of this study is to tally relative frequency with which various descriptive (n = 18), graphical (n = 7), and inferential statistical procedures (n = 68) are used in the prosthodontic literature. Our method consists of four procedures: journal selection, choice of 1987 through 1988 articles with inferential statistical content, tally of the statistical procedures in those articles, and quality control procedures used in obtaining these data. At least 50% of 10 prosthodontists selected 17 of 100 journals most likely to be read by prosthodontists. In the 17 journals, 1,320 articles were screened of which 406 were selected and evaluated for their statistical procedures. The bar and line plots were the most common graphical procedures occurring in over one fourth of the 406 articles. Percentages, means, and standard deviations occurred in more than 40%. Although 58% used the .05 significance level, only 0.3% mentioned power. Analysis of variance was used more often than the t tests (42% v 29%), whereas correlation/regression (21%) and chi-square tests (14%) were used less often. The t tests, analysis of variance (Duncan, Tukey, and Student-Newman-Keuls multiple comparison procedures), chi-square tests, correlation and regression, and the Wilcoxon tests occurred in at least 5% of the 406 articles.

Surface detail reproduction of Type IV dental stones with selected polyvinyl siloxane impression materials.

Four polyvinyl siloxane impression materials and 14 modified Type IV dental stones were evaluated for their abilities to reproduce surface detail. Each combination of impression material and dental stone was used to duplicate a 20-microns-wide line. Surface detail reproduction was observed by two paired-rater groups. The line was reproduced in all impression material specimens, but in only 32% of the stone cast specimens. Some combinations of impression material/dental stone reproduced the line all or most of the time, but 12 combinations did not reproduce the line at all.

Torch versus oven preceramic soldering of a nickel-chromium alloy.

Base metal preceramic solder joints have been described as unpredictable and inconsistent in tensile strength. Compared to base metal postoldered joints, presoldering with a gas-oxygen torch produces weaker joints that have increased porosity and voids. This investigation compared the tensile strength of base metal solder joints presoldered with a gas-oxygen torch to that of joints presoldered in a porcelain oven under vacuum. The mean (+/- SD) solder joint tensile strength was 460.0 (+/- 99.4) MPa for the oven-soldered and 520.2 (+/- 37.8) MPa for the torch-soldered specimens. A strong, consistent, void-free preceramic solder joint was produced between a nickel-chromium base and gold solder by both torch- and oven-presoldering techniques; however, preceramic soldering with a torch tended to result in a stronger bond.

Compatibility of a new epoxy resin with impression materials.

This study evaluated the compatibility of five polyvinyl siloxanes (Reflect, Exaflex, President, Permagum, and Extrude), one polysulfide (Permalastic) and one polyether (Polygel) impression materials with the new epoxy resin, AlphaDie 87. Only the polysulfide and the polyether were prepared with the "super separator". A line 20 microns wide was scribed into three glass dies (plates). Each nonaqueous elastomeric was used to make an impression of the line in each of the three glass dies. Each of the impressions was allowed to set in a water bath (36 degrees C). The epoxy die material was introduced onto the line surface of the impression to create a copy of the line. The epoxy was allowed to set against the impression. Detail reproduction of the line, or compatibility, was determined by the presence of the reproduced line on the epoxy specimen by three raters. There was unanimous agreement among the 63 independent homogenous ratings of line presence on impression specimens. The line was reproduced on all of the impression specimens but only in 71.4% (5/7) of the epoxy specimens. The epoxy specimens reproduced the line in all the polyvinyl siloxane specimens (5/5).

Dimensional stability of a mark made in a photoplastic wafer as a function of time.

This study investigates in vitro the dimensional stability of the Vishay's mark as a function of time. The Vishay was placed between a hardened, 1/2 inch diameter steel ball and a flat tungsten carbide cutting tool blank in an Instron testing machine. A compressive force of 10 pounds applied, and three separate marks made within the photoplastic wafer. The mark was displayed as a 10x image on the Vishay analyzer's monitor. The image was photographed, along with a standard, using a 35 mm camera tripod setup. To evaluate stability of the marks, photographs were taken at 1 hour, 1 day, 3 weeks, and 2.25 years after indentation. Each mark's image was measured three times with a Sigma-Scan digitizing software and reduced to real dimensions. The three marks were treated as a block and time as four repeated measures. An ANOVA was used to compare the mark sizes at these times. The four means across time were not significantly different (P = 0.34). Both Greenhouse-Geisser, and Huynh-Feldt epsilon correction factors for repeated measures were 0.34 which resulted in an adjusted significance level of 0.36. This indicates unequal correlations from one time to another, but does not affect the insignificant differences of these means. The Vishay photoplastic wafer can store mark size for at least 2.25 years in vitro.

Using a syringe to make void-free casts from elastomeric impressions.

A syringe can be used to place dental stone into the deepest part of an impression, filling it from the bottom up, expressing air as the impression fills.

Panoramic radiographic examination of edentulous patients.

A study of panoramic radiographs made on 114 edentulous patients was described. Six radiographic entities were identified: root fragments, retained teeth, radiolucencies, radiopacities, foreign bodies, and mental foramina at or near the crest of the residual ridge. The percent of positive findings in this study and those of previous studies support the fact that one of three edentulous patients has a potentially complicating condition within the denture base foundation. These investigations stress the necessity of radiographic examination of all edentulous patients prior to treatment with complete dentures. The high incidence of positive findings suggests not only the need for radiographic examinations of all patients, but also the frequency with which the dentist is faced with the necessity of modifying the treatment plan.