The International Journal of Prosthodontics, 02/1991

This in vitro study compared the shear bond strengths of current dentin adhesives. Freshly extracted human molars were prepared to a flat surface and treated with dentin adhesives and composite resin light polymerized in a plastic matrix. Completed samples were stored in 37 degrees C water and thermocycled 1,500 times. Samples were sheared at the tooth/composite resin interface using a wire loop. The reliability index varied significantly between materials. Large coefficients of variation were found for all dentin adhesives. One dentin adhesive was able to achieve a bond strength to dentin that was 47% of the control bond strength of enamel.

This in vivo study recorded the microleakage and marginal discrepancies of cast glass-ceramic cemented crowns compared to gold onlays and a metal ceramic restoration. Within the limits of the small number of samples and the variables inherent in an in vivo study, it was found that (1) dentin bonding agents are not strong enough to produce a gap-free cementation, (2) the marginal adaptation of beveled metal restorations is better than that of glass-ceramic crowns, and (3) the marginal adaptation of cast glass-ceramic crowns is clinically acceptable.

The effect of a commercial ion exchange paste on the tensile strength of high- and low-expansion dental porcelains was investigated. Strength measurements were correlated with changes in surface chemistry. The paste was found to be more effective for aluminous porcelains than for an inlay ceramic, although only when applied to the surface placed in tension. Surface finish also influenced the effectiveness of the paste. The depth of ion exchange was assessed by energy dispersive x-ray analysis and was found to extend to at least 100 microns, although the most marked change occurred within a 10-microns layer below the surface.

The dimensional change of a new castable ceramic material (CD-200) was measured after casting, ceramming, and surface coloring. The marginal and internal adaptations of single crowns were evaluated, as was the fracture strength of single crowns and fixed partial dentures. The material expanded 0.57% after casting, ceramming, and application of surface colorant. Marginal openings ranged between 2.8 and 11.2 microns. Single crowns exhibited fracture strengths lower than or comparable to Dicor single crowns, and fixed partial dentures made from CD-200 were weaker than those fabricated with Dicor.

One advantage cited for the use of Dicor over other ceramic materials is a reported Knoop hardness comparable to human enamel. However, when fabricating dental restorations, a Dicor glass-ceramic casting generally is subjected to several different surface treatments because of processing, esthetic, and functional requirements. Therefore, this study compared the Knoop hardness of Dicor specimens under three conditions: (1) cerammed, (2) cerammed and shaded, and (3) sectioned to reveal internal material. Knoop hardness differences between groups were significant (P less than or equal to .05). The cerammed surface was the hardest; it was harder than human enamel. Shaded specimens had a surface hardness comparable to dental porcelain. However, the internal glass-ceramic material, located beneath the shading porcelain and cerammed surface, had a Knoop hardness slightly higher than that of human enamel.

The substance loss from four commercially available Ni-Cr-Mo and four Co-Cr-Mo alloys was examined using a solution of 0.1 mol/L lactic acid and 0.1 mol/L sodium chloride. Dissolved ions were analyzed over a 5-week period using atomic absorption spectroscopy. The results revealed a considerable range of corrosion rates among the Ni-Cr-Mo alloys, with average values after 35 days between 0.54 and 3,261 micrograms/cm2, while the distribution of values for the Co-Cr-Mo alloys was not as wide - between 0.43 and 34.9 micrograms/cm2.

Proper shaping of the polished surface of a denture is important to facilitate the intraoral manipulation and control of the prosthesis by the patient. A method for the assessment of the polished surface form and tooth position in processed dentures is described. Low-viscosity silicone impression material is placed on the dentures, and the patient's chewing movements are used to define those areas requiring modification.

The potential correlation of the force versus time behavior of four resilient lining materials and their acceptance by patients was investigated. Two modified acrylic resins and two silicone denture lining materials were tested. The response of the soft lining materials to a programmed indentation test was used to define a parameter for each denture liner product. A parameter defined as the Rebound Index, using force-time data obtained from the indentation measurements, was significantly different for the modified acrylic resins compared to the silicone materials. Improved patient acceptance was correlated with higher values of this index.

This study determined the dimensional accuracy of dies made using a combination of four impression materials and three Type IV die stones. A metal die was prepared for a molar complete cast crown, and 10 stone replicas were made using 12 different combinations of impression materials and die stones. The distances between reference points on the metal and stone dies were measured in three directions with a traveling microscope. Analysis of variance and Duncan's MR comparisons (P less than or equal to .05) showed that all of the stone dies were larger than the metal die. Although there were significant differences between some of the impression material/die stone combinations, all of the stone dies were measured to be within 9 microns of each other. No one impression material/die stone combination consistently produced the smallest or largest die in the three measured directions.

This study measured the retention profiles of 11 commercially available stud-type attachment systems suitable for use with overdentures. The vertical distance over which resistance to separation existed was recorded and related to the configuration of the attachments. In many of the systems tested, only a small portion of the vertical length of the attachment contributed to the retention of the unit.

Five microorganisms - Escherichia coli, Streptococcus mutans, Staphylococcus aureus, Serratia marcescens, and Bacillus subtilis - were placed into the canine, first premolar, first molar, and second molar of sterilized quadrant addition-reaction silicone impressions. Four disinfectant solutions - iodophor, neutral glutaraldehyde, phenol, and sodium hypochlorite - were spatulated with sterilized Type IV stone and vibrated into the intentionally contaminated impressions. The casts were removed at 1 and 24 hours, and the surfaces were swabbed, plated on BHI agar, and incubated at 37 degrees C for 3 days. Colony forming units were counted. At 1 hour, only sodium hypochlorite and glutaraldehyde effectively reduced the number of bacteria to the negative control. Incorporation of sodium hypochlorite, glutaraldehyde, and iodophor into gypsum casts reduced viable bacteria to a level equal to the negative controls at 24 hours.