Dental offices are known to be one of the largest users of inorganic mercury(71 b,etc.). It is well documented that dentists and dental personnel who work with amalgam are chronically exposed to mercury vapor, which accumulates in their bodies to much higher levels than for most nonoccupationally exposed. Adverse health effects of this exposure including subtle neurological effects have also been well documented that affect most dentists and dental assistants, with measurable effects among those in the lowest levels of exposure. Mercury levels of dental personnel average at least 2 times that of controls for hair(397-40 I), urine (25d,57,64,69,99,123,124,138,17 I, 173,222,249, 290,362,397-399) and for blood (124,195,253,249,397).
Sweden, which has banned use of mercury in fillings, is the country with the most exposure and health effects studies regarding amalgam, and urine levels in dental professionals from Swedish and European studies ranged from 0.8 to 30.1 ug/L with study averages from 3.7 to 6.2 ug/L (124,172,253,64,68). The Swedish safety guideline for mercury in urine is 5.6 nmol Hg/nmoI(l 1.6 q/L).
Study averages for other countries ranged from 3.3 to 36 microgram/liter(ug/L)(69,70,17 1,290,397). A large survey of dentists at the Norwegian Dental Assoc. meeting( 171) found that the mean mercury level in 1986 was 7.8 q/L with approx. 16% above 13.6ug/L, and for 1987 found an average of 8.6 q/L with approx. 15% above 15.8 ug/L, with women having higher levels than men in general.
A U.S. national sample of dentists provided by the American Dental Association had an average of 5.2 ug/L (70,290). In that large sample of dentists, 10% of dentists had urine mercury levels over 10.4 q/L and 1% had levels over 33.4ug/L(290,25c), indicating daily exposure levels of over 100 ug/day.
Mercury excretion levels were found to have a positive correlation with the number of amalgams placed or replaced per week, the number of amalgams polished each week, and with the number of fillings in the dentist(l71,172,173). In one study, each filling was found to increase mercury in the urine approx. 3%, though the relationship was nonlinear and increased more with larger number of fiIlings(124). Much higher accumulated body burden levels in dental personnel were found based on challenge tests than for controls(303), with excretion levels after a dose of a chelator as high as 10 times the corresponding levels for controls(57,69,290,303). Autopsy studies have found similar high body accumulation in dental workers, with levels in pituitary gland and thyroid over 10 times controls and levels in renal cortex 7 times controls(99,363,38). Autopsies of former dental staff found levels of mercury in the pituitary gland averaged as high as 4,040 ppb. They also found much higher levels in the brain occipital cortex(as high as 300 ppb), renal cortex(as high as 2110 ppb) and thyroid(as high as 28,000 ppb.
In general dental assistants and women dental workers showed higher levels of mercury than male dentists (171,172,173,253,303,362).
Mercury levels in blood of dental professionals ranged from 0.6 to 57 ugL, with study averages ranging from 1.34 to 9.8 q/L (124,195,253,249). A review of several studies of mercury level in hair or nails of dentists and dental workers found median levels were 50 to 300% more than those of controls(38, p287-288,& 10,16,178).
A group of dental students taking a course involving work with amalgam had their urine tested before and after the course was over. The average urine level increased by 500% during the course(63). Allergy tests given to another group of dental students found 44% of them were allergic to mercury( 156). Studies have found that the longer time exposed, the more likely to be allergic and the more effects(6b,154c,l56,503a) . One study found that over a 4 year period of dental school, the sensitivity rate increased 5 fold to over 10%( 154~). Another group of dental students had similar results(362), while another group of dental student showed compromised immune systems compared to medical students. The total lymphocyte count, total T cell numbers(CD3), T helper/ inducer(CD4+CDS-), and T suppressor/cytotoxic(CD4-CD8+) numbers were significantly elevated in the dental students compared to the matched control group(408). Similar results have been seen in other studies as well(408).
Urinary porphyrin profiles were found to be an excellent biomarker of level of body mercury level and mercury damage neurological effects, with coproporphyrin significantly higher in those with higher mercury exposure and urine levels(70,260). Coproporphyrin levels have a higher correlation with symptoms and body mercury levels as tested by challenge test(69,303), but care should be taken regarding challenge tests as the high levels of mercury released can cause serious health effects in some, especially those who still have amalgam fillings or high accumulations of mercury.
Screening test that are less burdensome and less expensive are now available as first morning void urine samples have been found to be highly correlations to 24 hour urine test for mercury level or porphyrins(73). 2. The average dental office exposure affects the body mercury level at least as much as the workers on fillings(57,64,69,123,138,171,173,3O3), with several studies finding levels approximately the same as having 19 amalgam fillings( 123,124,173).
Dental Office Exposure
Many surveys have been made of office exposure levels( I ,6,7,10, etc.) The level of mercury at breathing point in offices measured ranged form 0.7 to over 300 micrograms per cubic meter(ugIM3) (120,172,253,249). The average levels in offices with reasonable controls ranged from 1.5 to 3.6 ug/M3, but even in Sweden which has had more office environmental controls than others spot levels of over 150 ug/M3 were found in 8 offrces(l72). Another study found spot readings as high as 200 ug/M3 in offices with few controls that only used saliva extractor( 120).
OSHA surveys find 6-16% of U.S. dental offices exceed the OSHA dental office standard of 50 ug/M3, and residual levels in equipment sterilizers often exceed this level(454).
The U.S. ATSDR mercury vapor exposure MRL for chronic exposure is much lower, 0.2 ug/M3 (217) (giving approx. 4 ug/day exposure), similar to U.S. EPA and Health Canada guidelines(2,209). Thus most offrce mercury levels were found to far exceed the U.S. guidelines for chronic mercury exposure.
Use of high speed drill in removal or replacement has been found to create high volume of mercury vapor and respirable particles, and dental masks to only filter out about 40 % of such particles (2 19,247). Amalgam dust generated by high speed drilling is absorbed rapidly into the blood through the lungs and major organs such as the heart receive a high dose within minutes(2 19a,395c,503c). This produces high levels of exposure to patient and dental staff. Use of water spray, high velocity evacuation and rubber dam reduce exposure to patient and dentai staff significantly, as seen in previous discussion. In addition to these measures researchers also advise all dental staff should wear face masks and patients be supplied with outside air( 120,153).
Some studies note that carpeting and rugs in dental offices should be avoided as it is a major repository of mercury(6,7,2 1 d,71 b,l88,395c,503) For offrice’s using an aspirator, at the dentist’s breathing zone, mercury vapour concentrations of ten times the current occupational exposure limit of 25 microg/m3 were recorded after 20 minutes of continuous aspirator operation(219). 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 vacuummotor. 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. Use of such measures along with a Clean-Up aspirator tip was found to reduce exposure to patient and staff approximately 90%(397).
Dentists were found to score significantly worse than a comparable control group on neurobehavioral tests of motor speed, visual scanning, and visuomotor coordination(69,70,123,249,290,395,1b), concentration verbal memory, visual memory(68,69,70,249,290,395,1 b), and emotional/mood tests(70:249,290,395,1 b). Test performance was found to be proportional to exposure/body levels of mercury(68,70,249,290,395,1 b).
Significant adverse neurobehavioral effects were found even for dental personnel receiving low exposure levels(less than 4 ug/l Hg in urine)(290). This study was for dental personnel having mercury excretion levels below the 10th percentile of the overall dental population. Such levels are also common among the general population of non- dental personnel with several fillings. This study used a new methodology which used standard urine mercury levels as a measure of recent exposure, and urine levels after chelation with a chemical, DMPS, to measure body burden mercury levels. Thirty percent of dentists with more than average exposure were found to have neuropathies and visuographic dysfunction(395). Mercury exposure has been found to often cause disability in dental workers(230b,395c,503,504a,etc.)
Chelators like DMPS have been found after a fast to release mercury from cells in tissue to be available for excretion. This method was found to give enhanced precision and power to the results of the tests and correlations. Even at the low levels of exposure of the subjects of this study, there were clear demonstrated differences in test scores involving memory, mood, and motor skills related to the level of exposure pre and post chelation(290). Those with higher levels of mercury had deficits in both memory, mood, and motor function compared to those with lower exposure levels. And the plotted test results gave no indication of there existing a threshold below effects were not measurable.
Mood scores including anger were found to correlate more strongly with pre chelation urine mercury levels; while toxicity symptoms, concentration, memory(vocabulary,word), and motor function correlated more strongly with post-chelation mercury levels. Another study using DMPS challenge test found over 20 times higher mercury excretion in dentists than in controls, indicating high body burden of mercury compared to controls(491).
Dentists and adverse health
Many dentists have been documented to suffer from mercury poisoning(6f,71,72,74,193,246,247,248,369), other than the documented neurological effects such as chronic fatigue, muscle pains, stomach problems, tremors, motor effects, immune reactivity, etc.
One of the common effects of chronic mercury exposure is chronic fatigue due to immune system overload and activation. Many studies have found this occurs frequently in dentists and dental staff along with other related symptoms- lack of ability to concentrate, chronic muscular pain, burnout, etc.(249,369,377,378,490,b1) . In a group of dentists and dental workers suffering from extreme fatigue and tested by the immune test MELISA, 50% had autoimmune reaction to inorganic mercury and immune reactions to other metals used in dentistry were also common(369). Tests of controls did not find such immune reactions common. In another study nearly 50 % of dental staff in a group tested had positive autoimmune ANA titers compared to less than 1 % of the general population(35).
One dentist with severe symptoms similar to ALS improved after treatment for mercury poisoning(246), and another with Parkinson’s disease recovered after reduction of exposure and chelation(248). Similar cases among those with other occupational exposure have been seen. A survey of over 60,000 U.S. dentists and dental assistants with chronic exposure to mercury vapor and anesthetics found increased health problems compared to controls, including significantly higher liver, kidney, and neurological diseases(99,193). Other studies reviewed found increased rates of brain cancer and aIlergies(99,193).
Swedish male dentists were found to have an elevated standardized mortality ratio compared to other male academic groups(284). Dental workers and other workers exposed to mercury vapor were found to have a shortening of visual evoked potential latency and a decrease in amplitude, with magnitudes correlated with urine excretion levels( 190). Dentists were also found to have a high incidence of radicular muscular neuralgia and peripheral sensory degradation( 190,395,490).
In one study of dentists and dental assistants, 50% reported significant irritability, 46% arthritic pains, and 45% headaches(490a), while another study found selective atrophy of muscle fibre in women dental workers(490b). In a study in Brazi1(492), 62% of dental workers had urine mercury levels over 10 mg/L, and indications of mild to moderate mercury poisoning in 62% of workers. The most common problems were related to the central nervous system.
Both dental hygienists and patients get high doses of mercury vapor when dental hygienists polish or use ultrasonic scalers on amalgam surfaces(240,400,503c). Pregnant women or pregnant hygienist especially should avoid these practices during pregnancy or while nursing since maternal mercury exposure has been shown to affect the fetus and to be related to birth defects, SIDS, etc.( 10,23,3 I c,37,38, I 10,142,146,401,19,3 1,50). Amalgam has been shown to be the main source of mercury in most infants and breast milk, which often contain higher mercury levels than in the mother’s blood (20,61 ,112,186,287). Because of high documented exposure levels when amalgam fillings are brushed( 182,222,348) dental hygienist are advised not to polish dental amalgams when cleaning teeth. Face masks worn by dental workers filter out only about 40% of small dislodged amalgam particles from drilling or polishing, and very little mercury vapor(247). Dental staff have been found to have significantly higher prevalence of eye problems, conjunctivitis, atopic dermatitis, and contact urticaria(247,156,74).
An epidemiological survey conducted in Lithuania on women working in dental offices(where Hg concentrations were < 80 ug/M3) had increased incidence of spontaneous abortions and breast pathologies that were directly related to the length of time on the job(277a). A large U.S. survey also found higher spontaneous abortion rate among dental assistants and wives of dentists( 193), and another study found an increased risk of spontaneous abortions and other pregnancy complications among women working in dental surgeries(277b). A study of dentist and dental assistants in the Netherlands found 50% higher rates of spontaneous abortions, stillbirths, and congenital defects than for the control group(394), with unusually high occurrence of spina bifida.
A study in Poland also found a significant positive association between mercury levels and occurrence of reproductive failures and menstrual cycle disorders, and concluded dental work to be an occupational hazard with respect to reproductive processes(40 1).