Carl W. Svare

The Effect of Dental Amalgam Restorations on Blood Mercury Levels

Mercury levels in blood and in mouth air before and after chewing were measured in 47 persons with ana 14 persons without dental amalgam restorations. Questionnaires relating to exogenous sources of mercury exposure were administered to both groups. Differences in the mouth air mercury levels before and after chewing were statistically significant in the group with amalgams, but not in the group without amalgams. Analysis of the data from the questionnaires indicated that little or no exogenous exposure to mercury occurred among the two groups. Blood mercury concentrations were positively correlated with the number and surface area of amalgam restorations and were significantly lower in the group without dental amalgams.

The Effect of Dental Amalgams on Mercury Levels in Expired Air

The expired air of a group of 48 persons, 40 with and eight without dental amalgam restorations, was analyzed for its mercury content before and after chewing. Expired air samples were collected in polyethylene bags, and a known quantity of each was pumped into the mercury detector for measurement. The results showed that examined subjects with dental amalgams had higher pre-chewing mercury levels in their expired air than those without amalgams. After chewing, these levels were increased an average of 15.6-fold in the former and remained unchanged in the latter group. It was concluded that in situ dental amalgams can increase the level of mercury in expired air.

The Contribution of Dental Amalgam to Mercury in Blood

We determined the exposure to mercury from dental amalgam by comparison of blood levels of mercury before and after removal of all amalgams from ten subjects. Baseline concentrations of mercury in whole blood were measured weekly for four to 18 weeks (median = 6.6 weeks) prior to removal. All amalgams were removed in a single appointment. The subjects had an average of 14 surfaces of amalgam, seven of which were occlusal surfaces. Weekly blood sampling was continued for five to 18 weeks (median=7.6 weeks) after the amalgams were removed. The mean baseline concentration of total mercury in whole blood of the ten subjects was 2.18 (SD = 0.90) ng Hgl mL before the amalgams were removed. The baseline mercury levels were related to the number of amalgam surfaces. The linear correlation coefficient was 0.724 with number of occlusal surfaces, and 0.433 with total number of surfaces. After removal of the amalgams, nine of the ten subjects exhibited a statistically significant decrease in blood mercury at the 95% level of confidence. The mean decrease in mercury was 1.13 (SD = 0.60) ng Hg/mL. The half-time for elimination of mercury from blood after amalgam removal was 30.2 (SD = 5.8) days. Removal of the amalgams provided an additional exposure of 1. 46 (SD = 1.17) ng HglmL that was rapidly cleared from the blood with a half-time of 2.9 days. The daily intake of mercury from amalgam in the subjects was estimated to be at least 1.3 μg.

An evaluation of post length within the elastic limits of dentin

Posted teeth were evaluated to determine the reinforcement capabilities of various post lengths. The results suggest that as internal tooth structure is removed from the tooth the tooth becomes weaker, that teeth with posts do show more reinforcement than nonposted teeth with the same manipulation characteristics, and that some load transfer appears to exist with cemented posts.

Exhaled mercury following removal and insertion of amalgam restorations

P atient exposure to mercury from dental amalgam and restorative procedures has not been studied as extensively as mercury exposure to dental personnel. One. study found that in a group of 114 adults not undergoing dental treatment, only six had measurable mercury in the urine, and one of those persons was using a mercurial diuretic.’ This was compared to a group of 24 persons currently undergoing dental treatment. Of that group five showed mercury in the urine before and after treatment. The possibility of mercury absorption from sources other than dental amalgam, such as mercurial antiseptics and germicides, was discussed. The study concluded that dental amalgams do not appear to be an important source of mercury absorption and excretion. In another study Frykholm2 used a radioisotope of mercury in placing four or five amalgam restorations in each of five patients. The urinary excretion of radioactive mercury gradually increased for each individual and reached an average peak of 2.5 pg/liter on the fifth day following treatment. In each case the level then dropped to zero by the seventh or eighth day, at which time the radioactive amalgams were removed to avoid further exposure. On the day following removal, urinary levels of mercury rose to 5 pg/liter and then dropped to zero in 2 days. Some investigators have found urinary excretion of mercury to be quite irregular and therefore an unreliable measure of quantity absorbed. Following exposure there is an early rapid phase of urinary excretion followed by a slower phase that may account for more

Dentinal smearing: An investigation of the phenomenon

/I I n order to prevent damage to the pulp, it is possible that treatment should-be aimed‘ toward a reduction in the permeability of the dentin rather than toward an attempt to stimulate irregular secondary dentine formation.“’ If dentin can be smeared by instrumentation, and if smearing effectively closes the orifices of dentinal tubules, further investigations into its clinical applications are warranted. If the permeability of dentinal tubules can be reduced by smearing, a modification of current concepts of pulpal protection could result when potentially irritative restorative materials are used. For example, if the deleterious effect of the phosphoric acid in zinc phosphate cement could be mediated by an effective chemical barrier, the need for a cavity varnish could be eliminated.‘-’ Hydration of exposed dentin by fluid flow from capillary forces and differential pressure gradients results in restorative materials potentially resting on a moist surface.x-‘7 Obturation of the external orifices of exposed tubules could obviate the problem of adhesion to moist surfaces. Clinically, it would be advantageous if a biomechanical procedure could decrease or eliminate the permeability and the exudation of the fluid tubular contents onto exposed

Mercury Vapor Emission from Dental Amalgam

The patterns of mercury vapor emission from carved, burnished, and polished surfaces made from four commonly used dental amalgam alloys were determined with the use of a selenium sulfide detection method. Mercury vapor was emitted more intensely from the marginal region; carved and burnished surfaces emitted the same amount. There was a difference in the amounts emitted from the different alloys tested.

Comparison of the Dentinal Crazing Ability of Retention Pins and Machinist's Taps

Retention pins have been shown to produce minute cracks in dentin (crazing), and this may significantly weaken tooth structure (W. E. DILTS, D. A. WELK, H. R. LASWELL, and L. GEORGE, JADA 81:387-391, 1970). The design of a typical retention pin* shown in Figure 1, left, is such that the threads are wedged into the dentin as the pin is inserted. Considerable stress is thereby produced at the pin thread edges. Such stress concentration is known to initiate cracking in brittle materials in general and, thus, crazing might be expected under these conditions in dentin. Machinists tapst (Fig 1, right), however, are designed so that threads are cut, rather than wedged, into the dentin as the tap is inserted. High stress concentration therefore, should not be produced at the tap thread edges. Thus, a machinists tap should be less likely to cause dentinal crazing. The purpose of this study was to make a preliminary investigation of this hypothesis. A retention pin and a tap of similar diameter were screwed into similar sized holes in the dentin of each of 25 freshly extracted teeth. These teeth were embedded in Bioplastict and sectioned longitudinally through both the pin and the tap with a thin sectioning machine. The cut surfaces then were polished and examined microscopically for the presence or absence of crazing. We found that 54% of the retention pins produced dentinal crazing, which corroborates the results of Dilts et al, whereas only 20% of the taps produced crazing. Figure 2, right, is an example of the dentinal

The Effect of Rotary Instrumentation on the Permeability of Dentin

The filtration and diffusion of tritiated water through dentin disks were measured in a split-chamber diffusion cell. The dentin had been cut with a diamond disk and the surfaces modified with a carbide fissure bur or diamond bur. Disks were given a secondary burnishing treatment with a blank bur or a modified blank bur. Burnishing reduced the permeability of dentin cut with a fissure bur.

Effect of Surface Treatment on the Corrodibility of Dental Amalgam

Potentiostatic anodic polarization data for unfinished, burnished, and polished amalgam surfaces were taken. From the standpoint of corrodibility, these tests indicated that physically improved amalgam restorations can be obtained by burnishing rather than by polishing or leaving amalgam carved and unfinished.