Robert D. Ringle

The Effects of Acetone, Ethanol, HEMA, and Air on the Stiffness of Human Decalcified Dentin Matrix

During resin-bonding procedures, dentin surfaces are treated with acidic conditioners to remove the smear layer and decalcify the surface to expose the collagen fibrils of the underlying matrix. These decalcified surfaces are then either air-dried or treated with dehydrating solvents, procedures which may modify the physical properties of the dentin matrix. The purpose of this study was to evaluate the effects of dehydration on the stiffness of the decalcified dentin matrix. Small (8 x 1.7 x 0.9 mm) beams of dentin were prepared from mid-coronal dentin of extracted human molars. The ends were covered with varnish for protection, and the specimens were placed in 0.5 M EDTA for 5 days to decalcify. The stiffness was measured by both the cantilever technique and by conventional stress-strain testing. Specimens tested by the cantilever technique were sequentially exposed to water, acetone, alcohol, HEMA, and glutaraldehyde. Specimens tested by conventional stress-strain testing were exposed either to water, acetone, or HEMA, or were allowed to air-dry. The results indicate that the stiffness of decalcified human dentin matrix is very low (ca. 7 MPa), if the specimens are wet with water. As they are dehydrated, either chemically in water-miscible organic solvents or physically in air, the stiffness increases 20- to 38-fold at low strains or three- to six-fold at high strains. These increases in modulus were rapidly reversed by rehydration in water. Exposure to glutaraldehyde also produced an increase in stiffness that was not reversible when the specimens were placed back in water.

The effect of glaze on porcelain strength

The self-glazing technique provides an esthetic and hygienic surface for crowns and fixed partial dentures that use porcelain veneers. A study of the biaxial flexure strengths of polished vs. glazed specimens is needed to verify that current laboratory methods are appropriate for planned fatigue studies. Four groups of 50 porcelain disk specimens each were subjected to the following polishing and firing procedures: group one was fired, glazed-no hold, and polished; group two was fired, polished, and glazed-no hold; group three was fired, polished and glazed-1 min. hold; group four was fired, polished, and not glazed. The piston-on-three-ball method was used for testing biaxial flexure strengths. Significantly lower differences in biaxial flexure strengths were noted when group two values were compared with values from groups one, three and four. The results show that the Weibull distribution is an appropriate model for our studies. Differences in glaze thickness among the groups were noted in SEM examination; however, bulk (interior) microcrack density differences were absent. The specimens that were fired, polished to a 1 micron surface finish, and not glazed (group four) were significantly higher in flexure strength than groups one and three at the p less than 0.001 level. The hypothesis that glazing of porcelain surfaces improves the biaxial flexure strength of test specimens was rejected.

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.

Adherence Controlling Elements in Ceramic-Metal Systems. II. Nonprecious Alloys

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, Cr2O 3, or more complex forms such as TiO · Cr2O3 and NiCr2O4 may play a prominent role in controlling ceramic-metal adherence.

The Relationship Between Oxide Adherence and Porcelain-Metal Bonding:

The lack of a reliable bond test has hindered the elucidation of the mechanism for porcelain-metal bonding in dental systems, because a test capable of detecting differences among porcelain-metal bonds of various qualities is required before the reasons for these differences may be ascertained. A method was developed in the present study whereby specimens of alloys with differing physical properties may be deformed to a constant strain to yield a fracture surface suitable for measurement of the area fraction of retained porcelain by an x-ray spectrometric technique described previously. The method proved sufficiently discriminating that significant differences could be found in 48 of the possible 66 comparisons among alloys and treatments. Linear regression analysis revealed a strong correlation (r 2 = 0.947) between the area fractions of retained porcelain measured in the present study and the oxide adherence strength values measured previously. This strong correlation, when considered in light of the literature evidence for the presence of an oxide layer at the porcelain-metal interface, provides compelling support for the oxide layer theory of porcelain-metal bonding in dental alloy systems.

Porcelain-Metal Thermal Compatibility

The effect of thermal expansion coefficient (a) mismatch on porcelain-metal bonding has been frequently discussed in the dental literature.1-5 Only recently6 have comprehensive studies of several porcelains and metals been completed. With these data available, an analysis of the thermal compatibility of various porcelain-metal combinations has become feasible. The concept of the compatibility index Ci was presented in 1978.7 This concept is based upon the classical bimetal thermostat equation of Timoshenko:8

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.

Cyclic fatigue of a model feldspathic porcelain

OBJECTIVES This study was conducted to evaluate the fatigue parameters of a model porcelain based on the Weinstein patent using cyclic fatigue and to compare the parametric values obtained from cyclic fatigue tests with those from dynamic fatigue tests previously reported by Fairhurst et al. (1993). METHODS Cyclical biaxial flexure of 1 mm thick and 12 mm diameter disks was performed at 37 degrees C in distilled water at a frequency of 4 Hz with constant stressing rates between a minimum and maximum stress. Three groups of samples (50, 40, 40) were tested with a maximum stress of 51, 47, and 43 MPa, respectively. The crack growth exponent, n, and the scaling constant, sigma fo, were derived from the regression constants obtained from a linear regression of the logarithm of the median time to failure with the logarithm of the maximum stress. RESULTS No significant differences were found between the cyclic fatigue parameters, n and sigma fo, derived from the median time to failure and those obtained from dynamic fatigue data. SIGNIFICANCE Within the limits of error in this determination, the median cyclic fatigue life can be estimated by the use of fatigue parameters obtained from dynamic fatigue testing.

Microstructures in Non-precious Alloys Near the Porcelain-Metal Interaction Zone

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.

A Thermal Shock Test for Porcelain-Metal Systems

A thermal shock test was employed to evaluate the crazing resistance of 55 porcelain-metal systems. The effect of the porcelain brand used was the most significant determinant of porcelain crazing. The effects of the alloys and alloy-porcelain combinations, although also significant, were second order effects.