Biomedical subjects
Publications and source records attributed to J R Mackert.
The claim that mercury from dental amalgam produces "reduced immunocompetence" was examined by measuring the levels of the three major populations of lymphocytes on 37 subjects--21 with amalgam restorations and 16 without. The results of this study show no indication that amalgam restorations affect the human immune system nor do they support the "reduced immunocompetence" claim.
This paper looks at the issues of the current amalgam controversy: the daily dose of mercury from amalgam, hypersensitivity to mercury, claims of adverse effects from amalgam mercury and alleged overnight "cures." In addition, the toxicity and allergenicity of the proposed alternative materials are examined with the same kind of scrutiny applied by the anti-amalgam group to dental amalgam.
The overall objective of this clinical study was to determine the feasibility of using a sealed composite restoration to arrest caries. This objective was to be achieved using minimal tooth preparation for Class I lesions, without the traditional Class I cavity preparation and without the removal of the carious lesion. The minimal tooth preparation consisted of no [corrected] removal of the carious lesion, bevel in enamel only, and usually not requiring any anesthetic injection. These ultra-conservative sealed composite restorations placed over caries (CompS/C) were compared with ultra-conservative sealed amalgam restorations (AGS) and with the traditional (unsealed) amalgam restorations (AGU). This study showed that: 1) caries is arrested under the CompS/C restoration for a period of 4 years; 2) sealant retention is similar in both the CompS/C and the AGS groups; 3) the marginal integrity of the AGS restorations is markedly superior to that of the AGU restorations; and 4) sealant appears to prevent wear of posterior composite restorations.
The effects of Oxy-haemoglobin were investigated in the rat isolated basilar artery and compared to Methylene blue and NG-Nitro-L-Arginine (NOLAG), as these compounds interfere with the relaxation induced by the endothelium-derived relaxing factor. Acetylcholine induced a concentration-related relaxation of serotonin-precontracted arteries which was further enhanced by the application of L-arginine. Similarly, the spasmolytic activity of L-arginine was enhanced by acetylcholine. Oxy-haemoglobin, Methylene blue and NOLAG induced an increase of resting tension and inhibited acetylcholine-induced relaxation. Furthermore, inhibition of acetylcholine-induced relaxation by Oxy-haemoglobin and NOLAG but not that by Methylene blue was partially reversed by L-arginine.
The bonding of an experimental low-fusing porcelain to titanium and Ti-6Al-4V was evaluated by an x-ray spectrometric technique that measures the area that remains covered with porcelain following a controlled deformation of the metallic substrate. Oxide adherence strength values for titanium and Ti-6Al-4V oxidized at 750 degrees and 1000 degrees C were measured in tension with use of high-strength adhesives. The effect of further oxidation that would occur during porcelain firing was evaluated via simulated porcelain firings without actual porcelain application. Interface cross-sections of the titanium-porcelain and Ti-6Al-4V-porcelain bonds were examined in a scanning electron microscope (SEM). The porcelain was found to delaminate completely from the metal substrate, leaving less than 1% of the surface covered with porcelain. The oxide adherence of the specimens oxidized at 750 degrees C was good, but those oxidized at 1000 degrees C exhibited significantly lower oxide adherence (p = 0.001). The simulated porcelain-firing oxidation treatments also produced a significant decrease in oxide adherence (p = 0.004). The 750 degrees C oxidation treatments produced oxide films too thin to be visualized in the SEM, whereas the 1000 degrees C oxidation treatments produced oxide films approximately 1 micron thick. The lower oxide adherence of the 1-micron-thick oxide films is consistent with reports in the titanium literature of oxide delamination when the oxide film reaches 1 micron in thickness.
Dogs were utilized in a study to compare the bond strengths of dentin bonding agents made to dentin in vivo and then again in vitro in the same teeth 30 min, one day, one week, and one month post-extraction. No statistically significant differences were observed between bonds made in vivo and those made in vitro at any time period. Contamination of the dentin surfaces with blood or saliva lowered the bond strengths, but these could be restored to control values by re-surfacing of the dentin with a bur.
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 (r2 = 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.
Several investigators have attempted to assess the extent of mercury exposure from dental amalgam restorations through the use of mercury vapor measurements of intra-oral or expired air. The sampling times and flow rates of the mercury vapor analyzers used in intra-oral measurements are not comparable with physiological inhalation times or flow rates of air through the mouth during inhalation. Analysis of the assumptions and measurement techniques employed in previous attempts to estimate mercury exposure from amalgam restorations shows that adequate compensation had not been made for these measurement parameters. Calculation of the mercury vaporization rates responsible for the mercury vapor concentration values previously reported enabled the daily dose of mercury to be estimated for subjects with various numbers of amalgam restorations. The corrected estimates for daily dose of mercury from amalgam restorations are a factor of sixteen lower than those previously reported.
A study based on the single criterion of resistance to loading forces was conducted to investigate the suitability of lingual composite rest seats for anterior teeth. The minimum acceptable resistance level was chosen from a review of the literature; other basic criteria were described; and the desirability of this technique was discussed.
A study to investigate the suitability of lingual composite rest seats for anterior teeth was based on the single criterion of repetitive load cycling. A 3-year minimum survival was chosen, with load and cycling values based on a review of the literature. An attempt was made to simulate the effect of saliva on composite.
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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.
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.
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.
Porosity and strength of spherical Cu-rich alloy amalgams were analyzed in the under-graduate materials laboratory. The minimum value for porosity was obtained for 46% initial Hg content, whereas the maximum strengths were obtained for 42% initial Hg. This result did not coincide with the data previously obtained for the conventional spherical alloy amalgam, in which the maximum strength and the minimum porosity were strictly associated with the optimum initial Hg content. Although no critical value for porosity could be definitely demonstrated by this effort, this result may be an indirect indication for 4.5 vol% porosity as the critical value.
Dental laboratories need an internal method to detect silver-containing metal ceramic alloys that stain porcelain. A fiberoptic colorimeter, calculations, and data describe Ag-vapor staining in standard CIE (1976) L*a*b* color space. The color difference value (CDV) of delta L*, delta a*, delta b*, and delta E* for porcelain before and after firing with Pd-Ag alloy, Au-Pt-Pd alloy, and control groups were calculated from L*, a*, and b* values. The CDV for all groups showed a more translucent (-delta L*) porcelain after the second firing. The CDV of porcelain disks exposed to Pd-Ag alloy showed an intense yellow (+ delta b*) stain with slight "greening" (-delta a*). The disks exposed to the Au-Pt-Pd group showed a slight yellow (-delta b*) stain. The delta b* values for the Pd-Ag group were significantly different from the other groups. This color shift (+ delta b) was clearly observed with the unaided eye.