Dental health in workers previously exposed to mercury vapour at a chloralkali plant.

OBJECTIVES: The dental health of 73 workers previously exposed to mercury vapour at a chloralkali plant was studied and compared with that of 51 non-exposed referents. METHODS: A record of oral, periodontal, gingival and mucosal conditions, including teeth, restorations, prostheses, and oral hygiene, was established during a 30 min examination. The participants' periodontal conditions were assessed according to the community periodontal index of treatment needs (CPITN). The results with the CPITN index were also compared with previously published data for another similar population. RESULTS: There was no significant difference between the exposed workers and the referents with respect to the number of remaining teeth, amount of amalgam restorations, crowns, bridges, or endodontically treated teeth. The oral hygiene among the exposed workers was significantly better than among the referents, but the periodontal health conditions did not significantly differ between the two groups, nor from those of another Norwegian population. DISCUSSION: The present results seem to contradict previous reports claiming tooth loss as a possible result of exposure to mercury vapour.

In vitro abrasion of two acrylic veneers.

OBJECTIVES: The purpose of this investigation was to compare the degree of abrasion in vitro of two acrylic veneers and dental enamel using a dentifrice with and without fluoride. METHODS: Ten specimens of each of the two acrylics and enamel were embedded in resin, and eventually polished to 1 micron with diamond paste. Specimens were brushed in a brushing machine with 10,000 double strokes using a dentifrice (Solidox, A/S Denofa) with and without fluoride. The abrasion was evaluated by the naked eye, by photographs and measured by means of profilometer. RESULTS: One of the polymer materials (Dentacolor, Kulzer) showed a significantly higher resistance to abrasion than the other (Biodent, DeTrey), irrespective of fluoride treatment. Brushing with or without fluoride revealed no significant difference in degree of abrasion between the two acrylic materials. Dentacolor showed significantly higher abrasion resistance than enamel, whereas Biodent did not. There was no significant difference in the degree of abrasion of enamel using dentifrice with or without fluoride. SIGNIFICANCE: Abrasion of acrylic veneering material differed greatly between brands, but did not seem to be influenced by the fluoride in toothpaste.

Mercury and selenium in workers previously exposed to mercury vapour at a chloralkali plant.

The concentrations of total mercury (B-Hg), inorganic mercury (B-IHg), and methyl mercury (B-MeHg) in whole blood, urinary mercury (U-Hg), and selenium in urine (U-Se) and whole blood (B-Se) were determined in 74 chloralkali workers previously exposed to Hg vapour, and compared with 51 age matched referents. Dental amalgam state, fish consumption, and exposure related indices were studied with regard to the determined elements. A significant relation between the surface of dental amalgam and U-Hg (Pearson's r = 0.63, p < 0.001) was found among the referents. Mean U-Se was significantly lower (p < 0.001) among the subjects previously exposed to Hg (34.1 nmol/mmol creatinine) compared with that for the referents (42.6 nmol/mmol creatinine). A significant negative relation between the cumulative Hg dose and U-Se was also found. The mechanisms and the clinical significance of these findings are not clear. No relation between current U-Hg and previous occupational exposure to Hg was found among subjects in whom exposure had ceased more than one year before the study.

Release of mercury vapor from corroding amalgam in vitro.

The release of mercury vapor was determined from eleven different amalgams exposed to externally induced corrosion by galvanic contact with a dental casting gold alloy. The electrolyte was an artificial saliva solution at 37 degrees C. The corrosion rates of the amalgams could be divided into two groups corresponding to the grouping into conventional and high-copper materials. The mercury release rate decreased during the 24 h test period for all the amalgams except one containing indium. There was no significant difference in the total mercury release between the conventional and high-copper amalgams as groups. The same applied for the individual products, except the one containing indium, which released significantly more mercury vapor than the two products with the lowest release.

Corrosion testing by potentiodynamic polarization in various electrolytes.

The effect of different electrolytes on the results from potentiodynamic polarization corrosion testing was studied for nine different dental alloys. In general, the difference in the results was greater between certain alloys using the same electrolyte than between the electrolytes with the same alloy. However, there were some differences between the electrolytes, most pronounced when testing dental amalgams. The electrolyte consisting of 1% NaCl seemed to offer the most corrosive environment. Darvell's and Fusayama's solutions were much less corrosive, at least for dental amalgam specimens. With regard to the ranking by corrosion sensitivity of the amalgams, only the results obtained by using Fusayama's solution were consistent with the clinical experience of the materials.

Use of potentiodynamic polarization technique for corrosion testing of dental alloys.

The number and in particular the diversity in types and composition of alloys used in dentistry are increasing, thus enhancing the need for predictive corrosion testing. No corrosion test is generally accepted as being both applicable to and relevant for all dental alloys. However, some methods have gained a certain recognition, and among these are the potentiodynamic polarization techniques. The purpose of the present work was to study the application, the reproducibility and the influence of some methodological variables on the results of potentiodynamic polarization corrosion testing. Embedded specimens of 18 different dental alloys, representing all major types, were subjected to anodic polarization scan within the potential range of -700 mV to 1000 mV (SCE). Artificial saliva, with and without organic compounds, and sodium sulfide solution were used as electrolytes. The results were processed on a microcomputer using locally developed software. The curves of current density versus potential showed fair reproducibility, with great differences between some of the alloys, showing a clear relationship to nobility or passivity of the alloy. There were marked differences between the results obtained in artificial saliva and in sodium sulfide solution, while addition of organic components to the artificial saliva only had a minor effect. The potentiodynamic polarization corrosion test supplies detailed information such as anodic charge, and open circuit, rupture, and passivation potential. Furthermore, it indicates the passive range and sensitivity to pitting corrosion. These are all useful when evaluating the corrosion properties of a dental alloy. An analysis of variance of the results in this study showed that possible differences between the alloys were clearly detectable with this method. However, for alloys releasing non-ionic products during corrosion/degradation, the method may be inappropriate. It is thus concluded that the method appears applicable as an in vitro corrosion test for most dental alloys, with the possible exception of amalgams.

Abrasive effect of a rotating electrical toothbrush on dentin.

The Rota-dent brush has been compared to conventional manual toothbrushes as to the abrasive effect on the dentin. Thirty-two teeth were embedded in epoxyresin. The test blocks were ground and polished, thereafter brushed with Jordan Soft, Jordan Blå Kjerne, Wisdom Plaque Master (hard) and three different Rota-dent brushes, Standardpoint, Hollow-cup and Longpoint. The brushing experiment was made in a test chamber filled with distilled water. After the brushing, the profiles of the brushtracks on the blocks were measured. On all the blocks, small tracks appeared which were not measurable. Conventional toothbrushes and Rota-Dent brushes used without dentifrice gave minimal abrasion on the dentin.

Effect of placement of amalgam restorations on urinary mercury concentration.

Dental amalgam emits mercury, especially during setting. In addition, the preparation of the amalgam and its compaction into the cavity involve unbound metallic mercury or create a waste product with free metallic mercury. The present study was performed to explore whether emission of mercury in these situations would measurably influence the individual urinary mercury concentration of dental patients as a result of a single-session treatment with dental amalgam restorations. Informed consent was obtained from the patients of nine children about to be treated with amalgam restorations as part of their regular dental care. The children delivered a total of five morning urine samples before, during, and after the treatment period. No effect on the urine mercury concentration was found during the treatment period. Conclusively, one single session of amalgam treatment did not per se represent a mercury exposure of sufficient quantity to be detectable in a longitudinal, individual study.

Studies in oral galvanism: mercury and copper levels in urine, blood and saliva in submerged electrically cutting divers.

The aim of the study was to analyse the concentration levels of mercury and copper in urine, blood/blood plasma and saliva in relation to intra-oral electrical activity. Five Swedish Navy divers took part in the study in order to determine whether working submerged with electrical cutting equipment produced changes in the presence and level of oral galvanism and whether this posed a serious occupational health risk. The investigation concluded that the risk of seriously increased intra-oral electrical activity during welding or cutting activities was small. Development of the study is suggested, with long-term sampling of urine and blood samples of divers supported.

Electrical activity in dental amalgam of submerged divers during welding.

Divers performing underwater manual metal arc welding/cutting (UMMA) have complained about a metallic taste phenomenon. In several dives with voluntary leakage in their diving suits, potential alterations in dental amalgam were registered when they performed UMMA. Polarization resistance values were obtained for the test amalgam cylinders used and the diver's dental restorations. These values, along with the recorded potential values of the amalgam test cylinders and of the diver's dental restorations, enabled us to calculate the depolarizing current, using the law of Ohm. The current depolarizing the amalgam test cylinder did not differ significantly from the mean intermetallic currents between the dental restorations. The clinical effect of intraoral currents when performing UMMA welding should be regarded as small, whereas considerably higher currents should not be ruled out in an intense cutting situation.

Correlation between amalgam restorations and mercury concentrations in urine.

The creatinine-adjusted urinary concentration of mercury in 73 schoolchildren with a mean age of 12 years was determined. In addition, the number of amalgam restorations and their size, prevalence of allergy, and days absent from school due to illness were recorded for each individual. A significant positive correlation (r = 0.55) was found between urine Hg and extent of amalgam restorations, but no correlation existed between urine Hg and allergy or between urine Hg and absence from school due to illness. Neither could any correlation be found between extent of amalgam restorations and either allergy or absence from school.

Influence of submerged electrical welding/cutting on dental amalgam in Swedish divers.

Professional commercial divers working with electrical cutting and welding sometimes experience a metallic taste phenomenon. An enquéte study among divers showed no influence of different equipment on the occurrence of such metallic taste, but it seems to occur less frequently in low salinity water. It has been suggested that this metallic taste phenomenon is due to increased corrosion rate of dental restorations, especially of amalgam. Experimental results recording the potential of amalgam specimens placed in the oral cavity of divers during welding, showed influence on the potential, and thus probably on the corrosion rate, during welding only when the diver came into direct contact with the water, e.g. through leakage in the suit.

Porosity in posterior composite resins.

The percent pore area and the mean pore size were measured in specimens made of nine brands of composite resin restorative materials. The overall percent porosity ranged from 0.01 to 4.5%. The specimens for the study were prepared in two ways; by condensation or by pressure. Most of the materials, including all those chemically activated, showed more porosity in the condensed than in the pressure specimens. Reversed results emerged for two of the materials, and for another two, the specimens were similar in this respect. The mean pore sizes were smaller in the condensed than in the pressure specimens. Neither mean pore size nor total amount of porosities could be correlated to the curing method of the materials.