Mercury vaporization during amalgam removal

Effects of Removal Conditions on Mercury Amount Remaining in the Oral Cavity and inside Drainage System after Removing Dental Amalgams

Mercury is produced and drained into the environment by removing dental amalgams, which may cause mercury pollution. This study aimed to clarify the mercury amount remaining in the oral cavity and inside the drain system after removal. The effects of the removal conditions and differences in drainage systems were also investigated. Dental amalgams filled in the tooth and placed in a phantom head were removed using an air turbine under several conditions (two removal methods, absence of cooling water, and intraoral suction). Then, the oral cavity was rinsed with 100 mL of water (oral rinse water), and 500 mL of water was suctioned to wash the inside of the drainage system (system rinse water). Both water samples were collected in two ways (amalgam separator and gas-liquid separator), and their mercury amounts were measured. It was found that the amount of mercury left in the oral cavity and drainage system after dental amalgams removal could be reduced when the amalgams were removed by being cut into fragments as well as using cooling water and intraoral suction. In addition, using amalgam separators can significantly reduce the amount of mercury in the discharge water and prevent the draining of mercury into the environment.

Mercury vapor volatilization from particulate generated from dental amalgam removal with a high-speed dental drill - a significant source of exposure

Background

The ubiquitous use of dental amalgam for over 180 years has resulted in the exposure of millions of dental workers to mercury. Dental amalgam contains approximately 50% mercury. Dental workers, including dentists, dental assistants, and dental hygienists, have been shown to have increased levels of mercury and suffer more from health issues related to mercury exposure than the general public. Mercury is known to be absorbed via inhalation or through the skin. There are many routine dental procedures that require the removal of dental amalgam by using the dental high-speed drill, which we suspected generates an occupational mercury exposure that is not sufficiently recognized.

Results

We showed that drilling dental amalgam generates particulate that volatilizes significant amounts of mercury vapor generally for more than an hour after removal. The levels of mercury vapor created by this procedure frequently exceed the safety thresholds of several jurisdictions and agencies.

Conclusions

A significant, underrecognized source of localized exposure to mercury vapor was identified in this study. The vapor was created by microgram levels of particulate generated from dental amalgam removal with a high-speed dental drill, even when all feasible engineering controls were used to reduce mercury exposure. This exposure may explain why dental workers incur health effects when safety thresholds are not breached. The dispersion patterns for the particulate are not known, so the use of effective skin barriers and inhalation protection are required during amalgam removal to protect the dental worker from this form of occupational mercury exposure. Standard methodologies for occupational mercury exposure assessment appear to be inadequate when assessing mercury exposure during amalgam removal.

Seal, replacement or monitoring amalgam restorations with occlusal marginal defects? Results of a 10-year clinical trial

The aim of this prospective and blind clinical trial was to assess the effectiveness of sealing localized marginal defects of amalgam restoration that were initially scheduled to be replaced. A cohort of twenty six patients with 60 amalgam restorations (n=44Class I and n=16Class II), that presented marginal defects deviating from ideal (Bravo) according to USPHS criteria, were assigned to either sealing or replacement groups: A: sealing n=20, Replacement n=20, and no treatment (n=20). Two blind examiners evaluated the restorations at baseline (K=0.74) and after ten years (K=0.84) according with USPHS criteria, in four parameters: marginal adaptation (MA), secondary caries (SC), marginal staining (MS) and teeth sensitivity (TS). Multiple comparison of restorations degradation/upgrade was analyzed by Friedman test and the comparisons within groups were performed by Wilcoxon test. After 10 years, 44 restorations were assessed (73.3%), Group A: n=14 and Group B: n=16; and Group C: n=14 sealing and replacement amalgam restorations presented similar level of quality in MA (p=0.76), SC (p=0.25) and TS (p=0.52), while in MS (p=0.007) presented better performance in replacement group after 10-years. Most of the occlusal amalgam restorations with marginal gaps showed similar long term outcomes than the restorations were sealed, replaced, or not treated over a 10-year period. Most of the restorations of the three groups were clinically acceptable, under the studied parameters. All restorations had the tendency to present downgrade/deterioration over time.

Mercury vapour release from a dental aspirator

OBJECTIVE

To investigate the release of mercury vapour from a dental aspirator which vented its waste air through its base directly into the surgery environment.

METHODOLOGY

Mercury vapour in air concentrations were measured at the breathing zone of the dentist during continuous operation of the aspirator. Further series of mercury vapour measurements taken at the aspirator exhaust vent were carried out to determine the sources of mercury vapour from this particular device.

RESULTS

At the dentist's breathing zone, mercury vapour concentrations of ten times the current occupational exposure limit of 25 micrograms/m3 were recorded after 20 minutes of continuous aspirator operation. A build up of amalgam contamination within the internal corrugated tubing of the aspirator was found to be the main source of mercury vapour emissions followed by particulate amalgam trapped within the vacuum motor. As the vacuum motor heated up with run time, mercury vapour emissions increased. It was found that the bacterial air exhaust filter (designed to clean the contaminated waste air entering the surgery) offered no protection to mercury vapour. In this case the filter trapped particulate amalgam which contributed to further mercury vapour contamination as high volume air was vented through it.

CONCLUSION

It is not known how many dental aspirators are in use that vent their waste air directly into the surgery or if this aspirator is representative of others in existence. The safety of dental aspirating systems with regard to mercury vapour exposure requires further investigation.

Current materials and techniques for direct restorations in posterior teeth. Part 1: Silver amalgam

This paper, the first of two reviewing materials and techniques for direct intracoronal restorations in posterior teeth, deals with the use of silver amalgam. Based on a consensus view on appropriate applications and contraindications for silver amalgam, the toxicity of amalgam and competing materials, financial implications and international legislation, consideration is given to the continued use of this material. It is concluded that silver amalgam still has a place in everyday practice, albeit restricted in comparison to its former use. Amalgam should only be used where it offers clear advantages over other materials. This requirement for use of silver amalgam will continue until true substitutes are developed and evaluated, alternative materials are optimised and dentists are fully trained in the use of adhesive techniques.

Dental amalgam and cognitive function in older women: findings from the Nun Study

The authors determined the number and surface area of occlusal dental amalgams in a group of 129 Roman Catholic sisters who were 75 to 102 years of age. Findings from this study of women with relatively homogeneous adult lifestyles and environments suggest that existing amalgams are not associated with lower performance on eight different tests of cognitive function.

The dentist's exposure to elemental mercury vapor during clinical work with amalgam

Continuous measurements of mercury vapor in the breathing zone of the dentist were made under ordinary clinical conditions. Fifty old amalgam fillings were removed and replaced by new ones. The mercury vapor measurements were performed by means of atomic absorption spectrophotometry. On the basis of the type of suction device used, the measurements were divided into seven groups, each of which consisted of a series of measurements. During the cutting, filling, and polishing operations the mean mercury vapor levels in the breathing zone of the dentist were in the range of 1-2 micrograms Hg m-3 air when proper mercury hygiene measures were taken. This is far below the currently valid threshold limit value (30 micrograms Hg m-3 air) in Sweden. The saliva extractor and the dental mirror-evacuator did not influence the mercury vapor levels when used together with the high-volume evacuator. However, when only a saliva extractor was used, the cutting of amalgam fillings caused highly fluctuating mercury vapor levels, which were 2-15 times higher than the threshold limit value.

Mercury vapour suppression by various liquid media

Fresh and used photographic fixer, Merconvap and water were evaluated for their ability to suppress the vapourization of mercury. Mercury vapour concentration above the four test storage liquids was measured at various times between 10 min and 335 days, using a mercury vapour measuring instrument. The data were analysed using a Student-Newman-Keuls multiple comparison test (P = 0.05). The results showed that fresh and used fixer and Merconvap suppressed the vapourization of mercury to below the detection limit of the measuring instrument (0.01 mg/m3). Water was much less effective compared with the other liquids and showed an increase in mercury vapour concentration with log t.

Dental mercury--a public health hazard

The aim of this review is to point out the health hazards of the uncontrolled global use of implanted mercury-leaking dental amalgam fillings. In spite of the pandemic use of amalgam, most dentists and doctors are still ignorant about the levels of mercury exposure and its health implications. This review discusses the following chronically neglected aspects in clinical practice: The use of materials science in calculating the mercury exposure levels, which may exceed the TLVs by an order of magnitude; Microbial dissolution and methylation of mercury from amalgam by oral and intestinal bacteria; Diagnostic problems and effects of chronic mercury exposure with emphasis on intestinal, cardiovascular, mental and neurologic symptoms and disorders; Diagnostic value of faeces--instead of urine examination--as the main indicator of Hg exposure; Lack of control groups unexposed to Hg (amalgam free) for epidemiologic investigations of health problems; Contribution of dental mercury to environmental pollution. In conclusion, a lack of interdisciplinary research and of a critical approach to established clinical routine appears to be the reason for the failure of the dental profession to protect the patient from Hg exposure when saving the tooth.

Quantitation of total mercury vapor released during dental procedures

An in vitro method is described in which measurements were made of the total amount of mercury vapor released from three types of amalgam during routine dental procedures. It was found that the greatest amount of mercury was released during dry polishing of one amalgam (44 micrograms). Removal of amalgam from a Class I cavity under water spray and high volume evacuation also generated large amounts of mercury as expected (15-20 micrograms). However, under the more clinically relevant conditions of extending evacuation for one minute to remove residual amalgam and mercury after cutting, this value was reduced by approximately 90%. The total amount of mercury generated during placement (6-8 micrograms), wet polishing (2-4 micrograms) and trituration (1-2 micrograms) were also measured. The study showed that dental procedures associated with amalgam do potentially expose the patient and operator to mercury vapor. However, the total amount of mercury released during any procedure was far below the total exposure level calculated from the daily threshold limits established by regulatory agencies for occupational exposure.

Mercury and selenium concentrations and their interrelations in organs from dental staff and the general population

Mercury (Hg) and selenium (Se) concentrations were determined by radiochemical neutron activation analysis in samples from the pituitary glands, occipital cortices, renal cortices, abdominal muscles, and thyroid glands of cadavers. Samples were retrieved from dental staff occupationally exposed to Hg and from the general population. Increased concentrations of both Hg and Se in samples from dental staff showed that Se accumulated together with Hg. Regression analysis of data from the pituitary glands and occipital cortices of dental staff indicated the accumulation of Se at a rough stoichiometric ratio of 1:1 with Hg. The same stoichiometric ratio between the elements was seen in the renal cortices from the general population. The regression analysis showed that a substantial fraction of Se was not associated with Hg; it is assumed that this corresponds to biologically available Se. Concentrations of biologically available Se decreased with advancing age in the pituitary gland, but not in other organs, and varied appreciably between organs.

Thermal effect on the dissolution of mercury from two dental amalgams

Various factors affect dissolution of mercury from dental amalgams. In this study we examined the effect of temperature on the release of mercury from two dental amalgams, namely an admixed high-copper amalgam (Contour) and a new tin- and copper-free amalgam (Composil). Ten cylindrically-shaped specimens of each type of amalgam were used in this investigation, and were divided into two equal groups. The five specimens in each group were each incubated in 10 ml purified water at either 37 degrees C or 60 degrees C, with a change of water every 24 h over an 8-day period. The quantity of mercury released from each amalgam specimen during each incubation period was expressed as micrograms cm-2 24 h-1. The amount of mercury released was estimated by cold-vapour atomic spectrometry. The results demonstrate that specimens incubated at 60 degrees C released significantly larger amounts of mercury than specimens incubated at 37 degrees C for both types of amalgam. The release of mercury by Composil was significantly greater than that by Contour (P less than or equal to 0.0001) for both temperatures studied. Raising the incubation temperature caused a disproportionate increase in mercury release from Composil compared to Contour.

Exposure to mercury vapor during setting, removing, and polishing amalgam restorations

The level of mercury vapors in the oral cavity was determined by analyzing 242 samples of intra-oral air before and after removing, setting, and polishing dental amalgam. The analysis was effected using atomic absorption spectrometry in cold vapors with the detection limit of 6 micrograms/m3. A score of 1 to 3 was assigned to each restoration to adjust the differences of the amalgam sizes. The present study showed that the vapor was released during any procedure: removing, setting, and polishing amalgam. The mean levels were between 85 and 326 micrograms/m3. However, before the restorative procedures, no mercury vapors had been detected in the oral cavity. This investigation has also demonstrated a significant direct correlation between Hg vapor concentrations in intra-oral air and the sizes of amalgam restorations during each procedure: removing, setting, and polishing. The statistic analysis showed no significant difference of mercury vapors in the oral cavity between the use or nonuse of water coolant during the amalgam polishing.

Particulate inhalation during the removal of amalgam restorations

An aerosol that contains amalgam particles is created when a high-speed hand-piece is used to remove an existing amalgam restoration. Those particles smaller than 10 microns are considered to be fully respirable. This means that a significant percentage of the particles have the potential to travel to the terminal alveoli, where they may become lodged. Long-term exposure to fully respirable particles may compromise a person's respiratory function. Amalgam restorations were placed in the typodont teeth of a mannequin designed to simulate the head and the respiratory tract of a patient. The amalgam restorations were removed under three experimental conditions: dry cut (control), wet cut (water spray) with high-velocity evacuation, and wet cut with high-velocity evacuation and a rubber dam. Particulate exposure was evaluated in the simulated respiratory tracts of the patient and the dentist that were equipped with ambient particle sizing samplers. Use of water spray and high-velocity evacuation significantly reduced patient exposure to particles. The use of a rubber dam, together with water spray and high-velocity evacuation, was responsible for a further significant reduction of exposure to particles when compared with water spray and high-velocity evacuation alone. The dentist, however, was exposed to moderate levels of fully respirable particles for all conditions tested. It is therefore recommended that all dental personnel wear face masks while removing existing amalgam restorations.

Effect of admixed indium on mercury vapor release from dental amalgam

The purpose of this study was to evaluate the effect of admixed indium on the amount of mercury vapor released from dental amalgam. We made amalgam specimens according to ADA Specification Number 1. We added various amounts (0-14% by weight) of indium to the alloy powder. We also tested the commercial amalgams Dispersalloy, Valiant, and Indiloy. Specimens were held at 37 degrees C and 100% humidity. We used a Jerome Mercury Vapor Analyzer (model 411) to measure the mercury vapor released. We analyzed the data by means of ANOVA and Student-Newman-Keuls procedures. Admixed indium significantly decreased the amount of mercury vapor released from dental amalgams; the period of the greatest effect on mercury vapor released was during the setting phase of amalgam; and dental amalgams with greater than or equal to 8% admixed indium released the least amount of mercury vapor.