The International Journal of Prosthodontics, 01/1992

The flexural strength of a new heat-pressed ceramic material (IPS-Empress) was measured before and after pressing and/or simulated firing treatments (eg, veneering, surface coloring, glazing). Heat pressing the material significantly improved its flexure strength whereas heat treating the material alone did not. Additional firings (heat treatments) after heat pressing further increased material strength. The final strength values ranged between 160 and 180 MPa and were comparable to some other all-ceramic systems. No clinical implications were drawn from these data.

The rate of alcohol loss from two tissue conditioners was investigated by applying them to complete denture record bases and immersing them in water in a sealed container. Samples were taken regularly and analysed by gas chromatography. The alcohol was found to leach out much more quickly than expected with the greatest loss occurring in the first 12 hours and peaking at approximately 60 hours.

Differential loss of chrome from surface colorants during firing can make the prediction of final porcelain color difficult. This investigation was undertaken to assess the color change of nine extrinsic colorants during firing. Colorants were applied to metal-ceramic substrates, and color was measured both before and after firing using a colorimeter. CIE LAB color coordinates were obtained as a measure of the direction and quantity of color change. Color change for yellow (delta E*ab = 4.00) was significantly greater than that for the other groups (delta E*ab = 0.41-1.25). Changes in L*a*b* values for yellow samples were toward those of the controls.

Partial-coverage porcelain laminate restorations, placed to provide undercut areas for I-bar direct retainers of removable partial dentures, were evaluated over simulated 2- and 5-year periods of placement and removal movements. SEM photomicrographs and computer imaging were used to quantify wear of the I-bar tips and the contacting laminate surfaces. These data were statistically compared to previously collected data of I-bar clasp tip wear against human enamel under the same experimental conditions. None of the laminate restorations debonded during this investigation. I-bars contacting laminates exhibited significantly more wear than I-bars contacting human enamel; however, the combined laminate-I-bar wear compared to the combined enamel-I-bar wear produced no significant difference.

It has been a clinical impression that the retromylohyoid extension in complete mandibular dentures contributes to stability. This hypothesis was tested in six individuals by means of cineradiography and placement of a metal marker in the mandible and dentures during chewing exercises, with and without the relevant denture extension. Analysis of tracings of the movements of the markers revealed that statistically significant differences existed between first and second chewing experiences. Movement in a horizontal plane around a vertical axis, however, was common to all dentures during all chewing. It is concluded that the retromylohyoid extension has a stabilizing effect on complete mandibular dentures.

The pattern and severity of root caries in a selected older population, living in the community and attending a general dental practice in Bexhill, East Sussex, England, is reported. A total of 146 patients were examined to determine the relationship among removable partial dentures, their design, and root caries. Of those patients, 57% wore removable dentures and had a higher prevalence of exposed root surfaces and root caries, particularly on abutment teeth. In addition, root caries lesions on abutment surfaces were found to be larger and more active than those on nonabutment surfaces.

This study evaluated the effectiveness of eight disinfectant sprays on irreversible hydrocolloid impressions contaminated with three microorganisms (Staphylococcus aureus, Mycobacterium phlei, or Bacillus subtilis) or mixed oral flora. Alcide LD, OMC II, Biocide, and Professional Lysol Spray were relatively ineffective under the test conditions. Sporicidin and 0.525% sodium hypochlorite were able to effect a 4-log10 (99.99%) reduction against S aureus only. A 4-log10 reduction in bacterial counts was achieved by 5.25% sodium hypochlorite and Impresept in all tests except against B subtilis. Full-strength sodium hypochlorite (5.25%) was the most effective disinfectant overall and required the shortest contact time.

The bonding of nonaqueous elastomeric impression materials to the impression tray is critical for an accurate impression; mechanical locks and adhesive materials are commonly used to enhance bonding. This study evaluated the bonding of three elastomeric materials to a light-polymerized resin tray. Roughening the tray surface prior to the application of an adhesive enhanced the bond.

Retainers for composite retained prostheses (Maryland bridges) have traditionally relied upon an etched base metal alloy for micromechanical retention. This study compared the tensile bond strength of three resin cements using two alloy surface treatments. Rexillium III and Olympia disks were cast, oxidized, and given simulated porcelain firings. Paired specimens were cemented with Comspan, Panavia EX, or C & B Metabond after air abrasion with aluminum oxide or silicoating. Air-abraded Olympia disks were tin plated prior to luting with Panavia EX. Electrolytically etched Rexillium III specimens luted with Comspan served as controls. Specimens were thermocycled and tested in tension. Highest tensile bond strengths were achieved with: (1) Olympia specimens, where the bonding surface was air abraded but tin plated before cementation with Panavia EX, and (2) Rexillium III specimens, where the bonding surface was air abraded or silicoated and the disks were cemented with C & B Metabond.

Various measurement methods have been described for the determination of dimensional accuracy and stability of denture base materials. This investigation introduces a computerised coordinate measuring machine (CCMM) and compares it with two methods routinely used for assessment of the accuracy of fit of denture base materials. The results demonstrate that the three methods (digital calipers, optical comparator, and CCMM) are acceptable for linear measurement. The CCMM was also used in its scanning mode to define and to quantify the contour changes of the resin bases. The advantages of the CCMM become apparent when two-dimensional changes require assessment.

This study involving 500 edentulous patients (250 males, 250 females) was undertaken to introduce a dimensionless factor termed the palatal height ratio, defined as the ratio of the width of the edentulous maxillary arch to the height of the palate. The authors categorized the height, width, and anteroposterior dimensions of the edentulous maxillae. Measurements were made on diagnostic casts at five defined points. The difference between males and females was statistically analyzed and the variables were categorized. The results of this study may be helpful for a better standardization of the same variables in future studies.

Two methods of removing zinc oxide-eugenol (ZOE) luting cement from amalgam were compared by determining their effect on the tensile bond strength of amalgam cylinders luted together using a 4-META resin cement. The samples were examined using scanning electron microscopy and energy dispersive x-ray analysis. Results showed that mechanical cleansing with pumice leaves ZOE residue mixed with pumice, which inhibits bonding, while the bond strength of samples cleansed with a dental degreasing agent was similar to that of an uncontaminated control group.