The International Journal of Prosthodontics, 01/1994

The combination of Etch-Free Primer and C&B Metabond has been reported to produce high resin composite to feldspathic porcelain bond strengths without hydrofluoric acid etching. This study compared the shear bond strength of resin composite to a castable glass ceramic that was treated with either Etch-Free Primer and C&B Metabond or ammonium bifluoride (NH5F2) etch/silane under various surface treatment and thermal stress variables. Bond strengths after Etch-Free Primer/C&B Metabond treatment were significantly lower than those for NH5F2/silane treatment. Thermocycling was the most important variable in reducing Etch-Free Primer/C&B Metabond bond strengths.

Three glass-ionomer cements, mixed at room temperature and cold mixed, were evaluated for film thickness at different powder to liquid ratios. Film thickness was measured at 1, 2, and 3 minutes after mixing was initiated. The relative accuracy of the manufacturer's volumetric dispensing systems was also measured. For two of the three cements tested, cold mixing significantly reduced film thickness at extended working times and increased powder/liquid ratios. The results suggest that the appearance of the cement surface indicates setting in advance of film thickness and that cold mixing should be routinely employed.

This study investigated the development of a computer-aided system for designing and fabricating removable complete dentures. The anatomical and morphological information of edentulous residual ridges and surrounding tissues were obtained from maxillomandibular double impressions mounted on a high-speed, three-dimensional laser scanner. Artificial tooth arrangements, occlusion, the outline of polished surface, and denture border location were developed on a work station using a knowledge data base. Established three-dimensional data were transferred into a three-dimensional, laser lithography machine, and a complete denture was fabricated from photopolymerized resin composite material.

The purpose of this study was to compare the relative affinity of bacterial lipopolysaccharide for two casting alloys with varied surface finishes by measuring lipopolysaccharide adherence and elution. Air borne particle abraded and polished Rexillium III and Harmony Hard alloy discs were exposed to 600,000 endotoxin units/mL E. coli lipopolysaccharide in water for 24 hours, whereas control discs were placed in 37 degrees C, lipopolysaccharide-free water. Lipopolysaccharide-exposed and control discs were then transferred every 24 hours to fresh, lipopolysaccharide-free water for up to 96 hours, and previously incubated eluates were tested for the presence of lipopolysaccharide. Initial lipopolysaccharide adherence to abraded Rexillium III discs was significantly greater than lipopolysaccharide adherence to the other groups (P .05). Polished and abraded Rexillium III also exhibited significantly greater lipopolysaccharide elution (P = .0001). However, after 96 hours, more than 99% of the initially adhering lipopolysaccharide remained on both Rexillium III and Harmony Hard discs, regardless of surface treatment.

The security of mandibular dentures for edentulous patients has been quantified using a visual analogue scale. Relining loose dentures was shown to produce an increase in the patients' assessments of denture security for 21 out of 23 patients. The security of a denture after relining was found to correlate with the form of the residual mandibular ridge as measured by the mean anterior ridge height.

The effect of five dental investing techniques, three angles formed between adjoining internal pattern surfaces, and the use of a surface tension-reducing agent on air-bubble entrapment during investing were assessed. One investing technique, which mechanically mixed the investment under vacuum, invested the pattern without vacuum, then subjected the setting investment to .275 mPa of air pressure, was found to produce significantly fewer air bubbles than the other four techniques (P = 0.0096, Student's t test). The volume of the air bubbles was not found to be significantly affected by the different investing techniques, but the angle between adjoining internal pattern surfaces indicated that the more acute the angle, the larger the volume of the trapped air bubbles. When a surface tension reducer was used on the surface of patterns, pattern angles of 90 degrees had fewer trapped air bubbles than those produced with more acute tooth preparation angles, but the surface tension reducer agent had no significant effect on bubble volume. The use of a surface tension-reducing agent on the pattern surface prior to investing significantly reduced air bubble numbers (P = .054).

Primers have been reported to increase adhesion between silicone elastomers and polyurethane liners used for maxillofacial prostheses. This study evaluated two primers, three polymerization methods, and seven primer reaction times to determine the conditions for optimum adhesive bond strength. The T-peel strength of specimens was determined as described in ASTM Standard D 1876-72. Failure modes were evaluated, and two-sample t tests and one-way ANOVA were used to compare means for significant (P .05) differences. Bond strengths were significantly greater for polyurethane treated with primer 1205 rather than S-2260 regardless of the polymerization method or primer reaction time. Neither any single polymerization method nor single primer reaction time consistently yielded greater bond strengths.

This paper reports the development of a newly modified, noncontact spectrophotometer for clinical use. The instrument is capable of accurately measuring the color within small areas (1 x 2 mm) of a tooth. This spectrophotometer used a 45 degree/0 degree geometry, a 150W halogen lamp, and fiberoptics to focus the light, together with a lens having a focal point distance of 85 mm. A movable platform was added to the apparatus to automatically scan and measure the color of specific areas. Short-term repeatability indicated the color difference delta E to be approximately 0.15.

Porcelain restorations have double-layer color effects resulting from the presence of body and opaque layers. The purpose of this study was to quantify the color differences resulting when a defined thickness of body porcelain is fired on an opaque porcelain of the same shade designation and from the same porcelain brand. A color difference coefficient was defined as the color change resulting from a 1-mm-thick layer of body porcelain on an opaque porcelain of the same shade and brand. Six shades and four porcelain brands were evaluated in this study. The range of color difference coefficients for all shades and brands was 6.76 to 14.32. There was no significant difference between shades or between brands. The use of color difference coefficients is a practical method of evaluating porcelain shades and brands and should provide guidance in the choice of porcelains and the fabrication of porcelain restorations to better achieve the desired esthetics.

The T-Scan system was used to evaluate the distribution of time and force in occlusal balance. Sixty normal subjects demonstrated bilateral balance and an anteroposterior center of force in the first molar region. However, patients with craniomandibular disorders demonstrated marked differences from the control group. The T-Scan system was found to be clinically useful as a diagnostic screening method for occlusal stability in intercuspal position.

Distortions of cast removable partial denture frameworks result more from the method of sprue connection than from other variables in the investment and mold preparation. A standard test pattern and optical measuring equipment were used to evaluate residual casting stresses. Based on the data obtained from the initial study, modified removable partial framework patterns were made and cast under varying conditions. The use of a dorsal spruing technique and a box-type casting flask resulted in less distortion than use of the conventional vertical sprue attachment and investing in a ring flask. Dorsal spruing and use of a box-type casting flask reduced the deformation of a cast partial denture framework in the area of the palatal bar and retentive elements up to 0.3 mm. Such a tension-free casting method means a better fit of the partial framework on the master cast and intraorally.

Whereas other radiographs may be adequate for assessment of mandibular anterior implant sites, the use of computerised tomography is recommended for evaluating potential implant sites in the maxillae. A complete denture replica with appropriate radiopaque markers aids in the assessment. Hounsfield densitometric measurements provide additional information on the quality of available bone.

Stainless steel wire 0.036 inch in diameter was compared with Kevlar 49 polyaramid fiber as a means of reinforcing a four-unit posterior provisional fixed restoration with 2 pontics. Three reinforcement patterns for wire and two for Kevlar 49 were evaluated and compared with the control, which was an unreinforced provisional restoration. A central tensile load was placed on the cemented provisional restoration and the variables were measured: (1) the initial stiffness; (2) the load at initial fracture; and (3) the unit toughness, or the energy stored in the beam at a point where the load had undergone a 1.0-mm deflection. Statistical analysis showed (1) the bent wire configuration had a significantly higher initial stiffness (P or = .05), (2) there was no difference between designs for load at initial fracture, and (3) the bent wire had a significantly higher unit toughness value (P or = .05).