Biomedical subjects
Publications and source records attributed to C W Fairhurst.
Eleven porcelain-fused-to-metal bond tests were analyzed for interfacial shear stress distribution using finite-element stress analysis. Stress concentration effects are significant in ten of the 11 tests. A high probability of tensile failure within porcelain or the interfacial region was found in eight of the 11 tests analyzed.
The ESCA technique provides a useful approach to identifying probable sites of fracture initiation in ceramic-fused-to-metal systems in which the analyzed fracture area is 1 mm2 or larger. The primary disadvantages of this technique include high equipment cost, the need for meticulous removal of superficial oxide layers formed at room temperature, and susceptibility to surface contamination by carbon, nitrogen, and oxygen. From this study the following may be concluded: 1. Judgment of the composition of any fracture surface (except that which occurs exclusively in porcelain) by naked-eye examination or optical microscopic inspection may be erroneous. 2. Generalizations on the nature of adherence zone failures for nonprecious allow-ceramic systems should not be made in the absence of fracture surface or adherence zone composition data determined by means of an acceptable analytical technique. 3. It appears unlikely that fractures originating in one of the regions of the adherence zone will have a composition analysis identical to that of metal, metal oxide, or bonding agent standards, since considerable interdiffusion or chemical interaction between these regions will have altered the original chemical compositions.
Based on the present measurements on working time, setting time, and compression set of polyether and polysulfide materials, the following observations were made: 1. The manufacturer recommends a working time for polyether that is approximately 40 seconds more than that indicated by the clinical or ADA test. 2. Clinically, if more working time is desired, polysulfide impression material should be used. 3. Polysulfide material is more sensitive to temperature change than the polyether material. 4. If the material is allowed to set longer, the percentage change in compression set decreases. 5. For polyether, an increase in setting time of 2 minutes will significantly reduce the distortion of the impression upon removal.
At the present time, a trend has been shown that the progress of sealed caries is markedly slowed by sealant therapy as compared to open lesions. This fact has been substantiated by depth measurements, viable bacterial counts, standardized radiographs, and clinical observations. The radiographic and clinical observations agreed with the previously reported two parameters in confirming that (1) sealed cavities showed little or no change in depth and (2) open lesions showed a significant increase in depth as compared to sealed lesions.
1. A method for measuring depth changes in carious lesions has been developed. 2. A method for estimating bacterial viability in the study lesions has been developed. 3. Sealed cavities showed little or no change in depth over a 1-year period. 4. Open lesions showed a significant increase in depth as compared to sealed lesions. 5. Elimination or marked decrease in viable organisms under the sealant occurred.
In an HCD amalgam, eta Cu-Sn crystals were found dispersed within gamma1 matrix areas. Previously, eta Cu-Sn phase was thought to form only as part of a reaction zone surrounding Ag-Cu dispersant particles. The eta Cu-Sn crystals found in matrix areas of this HCD amalgam are smaller and more widely scattered than eta Cu-Sn crystals dispersed in the gamma1 matrix of HCSC amalgams.
The chemistry of microstructures near the interfacial reaction zones of four non-precious alloys and two different brands of dental porcelain has been analyzed. It was found that most non-precious dental alloys contain second phases which can alter elemental concentration profiles. Recommendations for assessing interfacial reaction zone chemistry in dental non-precious alloys are offered.
Two pit and fissure sealants, an autopolymerized unfilled resin, and an ultraviolet-light-curing unfilled resin, applied to the permanent first molars of children are compared in terms of retention and efficacy.
A total of 254 children were examined 36 months after a single application of sealant. In 128 children, 201 permanent first molars were treated with Delton, and, in 126 children, 205 permanent first molars were treated with Nuva-Seal. Delton was completely retained on 80% of all paired permanent first molars, partially retained on 10%, and completely lost on 10% of the study teeth. Nuva-Seal was completely retained on 60% of all paired permanent molars, partially retained on 21%, and completely lost on 19% of the study teeth. Delton was 69% effective in preventing occlusal caries on permanent first molars three years after a single application. Nuva-Seal was 39% effective in preventing occlusal caries on permanent first molars three years after a single application. Both sealants have been shown to prevent dental caries on permanent first molars of children three years after a single application.
Twenty-four maxillary anterior composite restorations from a clinical study of resin coating were examined at the time of baseline evaluation and at 23 months; electroplated positive replicas, impression negative replicas, and SEMs were used for evaluation. Coated restorations had smooth surfaces after 23 months, in comparison with rough surfaces of uncoated restorations. Defects in some of the resin coatings were found at the time of baseline evaluation; these included isolated areas of the composite or etched enamel that were not covered by the resin. Later examinations showed cracking of part of the edges of resin coating, development of bare areas, thinning of the coating edges, or generalized loss of the protective coating. The defects seen immediately after placement of the coatings were probably caused by errors in technique that include: application of the resin in a layer that was too thin; surface contaminants in the area of application; moisture on the surface of the composite or enamel; and areas of inadequate enamel etching were adjacent to the cavosurface margin of the composite. The appearance of bare spots or total loss or thinning of the resin coating edges during the later examinations is caused by wearing or abrading of the resin coatings from natural or mechanical causes. This seems to be a function of the initial coating thickness and its location on the tooth.
Bonding between porcelain and dental ceramic alloys is thought to be dependent upon the establishment of a continuous electron structure across the ceramic-metal interface (Pask, Proc. Porcelain Enamel Inst.,33,1,1971). Such a structure most likely results from the compatibility of metal ions at the metal surface saturated in an oxide form with the complex oxide structure of the ceramic matrix. Reaction zone compounds are expected to play a prominent role in the strength of the ceramic-metal bonds but thus far none have been detected or identified. The present study was centered on the determination of possible adherence zone compounds in four composite ceramic-metal couples examined by x-ray energy analysis. Elemental analysis of four couples revealed the presence of a predominant Al-Cr interaction resulting from the formation of an Al-Cr-O compound or mixed complex. The Cr ions were supplied by the Cr2O3 oxide layer at the metal surface and the Al was provided by the initial bonding-agent coating.
Selected area reflection electron diffraction has been used to determine the phases present in the reaction zones surrounding the Ag-Cu eutectic dispersant in Dispersalloy amalgam. The experiments were carried out on two kinds of specimens, (1) Dispersalloy amalgam and (2) Dispersalloy amalgam using 30, 50, 75, and 100% more mercury than found in commercially available capsules. The results show that the reaction zones in the specimens of the present investigation consist of Cu6Sn5 and Ag2Hg3. These diffraction data confirm the presence of the phases in the reaction zone which are suggested by the elemental analysis obtained by Mahler and his associates using an electron probe. Moreover, the strong intensity of the eta-Cu6Sn5 diffraction rings suggests a composition which is predominantly Cu6Sn5, again, in agreement with the electron probe data.
Elemental analysis of two precious alloyceramic systems revealed the accumulation of Sn atoms within the interaction zone of couples subjected to a range of metal oxidation time; and varying total firing times. The source of Sn atoms which accumulated within the interaction zone was the opaque porcelain layer which contained an initially higher Sn concentration than the alloy. It is hypothesized that SnO2 provides continuity of electronic structure between alloy and ceramic structures and is a primary factor in controlling ceramic-metal adherence.
Nickel-chromium alloy-ceramic couples used in this study exhibited Cr, Ni-Cr, and Ti-Cr interactions with bonding agent-ceramic complexes. Bonding agents may broaden or suppress the width of interaction zones. Metal oxides such as NiO, Cr2O3, or more complex forms such as TiO-Cr2O3 and NiCr2O4 may play a prominent role in controlling ceramic-metal adherence.
Composite restorations containing quartz fillers have shown persistent roughness after finishing which contributes to marginal discoloration and staining. Resin finish coatings have been used to attempt to overcome this problem. This study was designed to compare the durability of two resin coating materials used on two brands of composite restorative materials. Results showed that composites glazed with resin coating finishes at placement maintained their luster, color match, and surface smoothness significantly better after one year than composites that were not coated. After a year it was concluded that composites on which the resin coating is intact maintain their color match, luster, and smoothness significantly better than uncoated composite restorations.
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