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Biomedical subjects

C W Fairhurst

Publications and source records attributed to C W Fairhurst.

At least 37 records · Page 2Linked to original sources
PubMed1986

Arresting caries by sealants: results of a clinical study.

In each of 14 patients, one bilateral occlusal carious lesion was sealed and the other lesion was left open as a control. The control lesions showed patterns of sudden increases in cavity depth, as well as evidence of being active bacteriologically; whereas, with one exception, the sealed lesions were inactive bacteriologically. The residual carious material in the sealed lesions suggested a complete cessation of the carious process. No clinical or radiologic signs were seen to suggest that the health of the sealed tooth had been compromised.

Adolescent↗
PubMed1984

Measurement of oxide adherence to PFM alloys.

A method has been reported for evaluating adherence of an oxide to its substrate metal to a maximum value of about 40 MPa. Oxidized alloy plates were cemented between two aluminum cylinders with a high-strength cyanoacrylate cement and loaded in tension until failure occurred either at the oxide/metal interface, within the oxide layer, or in the cement itself. Significant differences were found among the oxide adherence values obtained from different PFM alloys. The oxides formed on five of the alloys exhibited adherence strengths in excess of the published value for cohesive strength of dental opaque porcelain, indicating that they possess sufficient adherence to act as the transition zone between the porcelain and the alloy. In addition, a correspondence was found between the quality of porcelain bond for a given alloy and its oxide adherence strength. These results remove the principal objection to the oxide-layer theory of porcelain bonding in dental alloy systems and emphasize the importance of oxide adherence in the establishment of a bond. It is therefore suggested that future work devoted to porcelain-metal bonding should seek to elucidate the mechanism of oxide adherence to PFM alloys and explore the development of new alloys which form adherent oxides.

Adhesiveness↗
PubMed1984

A comparative clinical study of two pit and fissure sealants: 7-year results in Augusta, GA.

This 7-year evaluation of the Augusta study reinforces earlier conclusions regarding the long-term retention of sealants and their efficacy in caries protection. Although more time will be required to answer all the questions about sealants, sufficient data are now available to document their efficacy as caries-preventive agents. It is imperative that the dental profession provide this safe and effective preventive technique for the public so that dental disease can either be reduced or further postponed.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1983

Corrosion of the eta'(Cu-Sn) phase in dental amalgam.

Previous studies have shown preferential corrosion of the eta'(Cu-Sn) phase in high-copper dental amalgam both in vitro and in vivo, while samples of pure eta' have shown high corrosion resistance. To clarify this contradiction, samples of pure eta' crystals mixed with other phases were prepared and tested. Evaluation of the corrosion resistance was based on the results of coulometry at constant potential and potentiodynamic polarization. The corrosion susceptibility of eta' in the matrix of gamma 1(Ag-Hg) was considerably higher than the susceptibility of isolated eta'. The susceptibility of pure eta' also could be increased by plating it will small amounts of Hg. It was concluded that in dental amalgam, the presence of mercury in the phases surrounding eta' reduces its resistance to corrosion. Although eta' is more resistant to corrosion than gamma 2(Sn-Hg) which appears in low-copper amalgams, it is the least corrosion resistant major phase in high-copper amalgams and can suffer deterioration.

Copper↗
PubMed1983

An x-ray spectrometric technique for measuring porcelain-metal adherence.

This study demonstrated a correlation between silicon x-ray counts and area fractions of adherent porcelain as determined by point-counting. This correlation has allowed a method to be devised for measuring area fractions of porcelain adherent to porcelain-fused-to-metal (PFM) fracture surfaces. The described method, after controlled destruction of the porcelain mass, uses silicon x-rays excited by the electron beam in a scanning electron microscope. Under the conditions employed in these studies, the x-ray technique has shown that this gold alloy retains more porcelain than does either of two particular nickel-chromium alloys.

Chromium Alloys↗
PubMed1983

High-temperature behavior of a Pd-Ag alloy for porcelain.

The mechanism of formation of nodular material on the surface of a Pd-Ag-based alloy for porcelain during pre-porcelainization heat treatment was investigated using scanning electron microscopy, x-ray diffraction, quantitative metallography, and Auger electron spectroscopy. The nodules were found to form by a Nabarro-Herring creep mechanism driven by the internal oxidation of tin and indium. Implications of this process with regard to porcelain bonding and discoloration are discussed.

Chemical Phenomena↗
PubMed1982

Slots vs pins: a comparison of retention under simulated chewing stresses.

The specimens of composite resin retained by pins exhibited significantly lower cycle life than did all other groups. At low loads, the pins and slots are comparable (when composite resin is used), but there is a dramatic decrease in the life of restorations retained with pins as the load is increased. At the 30-micrometer end point, the composite restorations retained with pins failed at a mean of 250 cycles, whereas the composite restorations retained with a slot failed at 250,000 cycles - a 1000X increase in cycle life. In general, cycle life of composite resin retained with a slot is comparable to or greater than that of amalgam retained with a slot or pins. Whether the life difference between the pin- and slot- retained amalgam restoration is clinically significant is not known; however, the baseline for a clinical study of the two types of retention for definitive amalgam restorations has been completed and will be reported in the future.

Composite Resins↗
PubMed1982

Correlation of thermal shock resistance with thermal compatibility dat for porcelain-metal systems.

On the basis of this study the following conclusions may be made: (1) A strong linear relationship exists between the thermal shock resistance and compatibility index values of the systems studied. (2) Compatibility index analysis and thermal shock testing are promising approaches for evaluation of porcelain-metal compatibility. (3) Further refinements of the model are necessary to account for the effects of stress relaxation, thermal diffusivity, thermal history, elastic modulus, porcelain tensile strength, and geometry on the predicted stress state of porcelain-metal systems.

Dental Alloys↗
PubMed1981

A thermal shock test for porcelain-metal systems.

Certain conclusions may be made on the basis of this study. 1) The effects of alloy, porcelain, and alloy-porcelain interaction on the temperature differential required to induce porcelain crazing are significant. 2) The effect of porcelain is the most significant determinant of delta T values. 3) Under thermal shock conditions, the crazing resistance of porcelains decreases in the order: V less than [C, N, W] greater than B, where C greater than W. 4) For the conditions used, the thermal shock test is a sensitive discriminator of the crazing resistance of porcelain-metal systems.

Dental Alloys↗
PubMed1981

A comparative study of two pit and fissure sealants: results after 4 1/2 years in Augusta, Ga.

A total of 220 children were examined at 4 1/2 years (54 months) after a single application of a pit and fissure sealant. In 110 children, 177 permanent first molars were treated with Nuva-Seal; and in 110 children, 168 permanent first molars were treated with Delton. Nuva-Seal was completely retained on 35% of all paired permanent molars, partially retained on 21%, and completely lost on 44% of the study teeth. Delton was completely retained on 72% of all paired permanent molars, partially retained on 14%, and completely lost on 14% of the study teeth. These data indicate that occlusal caries protection on permanent molars is assured if the sealant is completely retained on the tooth. Delton was four times more effective in providing protection against pit and fissure caries than Nuva-Seal.

Acrylates↗
PubMed1980

Thermal expansion of dental alloys and porcelains.

The effect of thermal coefficient of expansion (alpha) mismatch on porcelain-metal bonding is frequently referred to in the dental literature. Thermally induced stresses may develop at metal-porcelain system interfaces due to differences in the coefficients of thermal expansion of the porcelains, metals, and metal oxides. The objective of this research is to characterize alloy and porcelain expansion behavior as a first step in developing a more specific definition of thermal compatibility. It is clear from comparisons of porcelain data and alloy data that the porcelain has expansion characteristics which are quite different from those of the alloys. The overall differences in values between these alloys and porcelains constitute a mismatch. First run dilatometric heating measurements for porcelain yield large differences between delta L/L and alpha values as compared to cooling measurements. For a comparison of alloy and porcelain expansion characteristics, data should be obtained at several temperatures up to the glass transition temperature (Tg) of the porcelain.

Chromium↗