A possible case of mercury-related toxicity resulting from the grinding of old amalgam restorations.

A possible case of mercury-related toxicity resulting from the grinding of old amalgam restorations. Scand 1989;15:302-304. The poten tial hazards of metallic mercury in dentistry are well recognized. The present report concerns a patient who experienced an uncommonly high mercury exposure and, possibly, mercury-related toxicity from va por released during extensive grinding of old amalgam fillings.

The potential hazards of amalgam in denti stry have received considerable attention in recent times. In dental offices and elsewhere cases have been reported of poisoning by metallic mercury due to the careless handling and spillage of the metal (l , 2). In this paper we present a patient who had experienced uncommonly high mercury exposure and, possibly, mercury-related toxicity from vapor released during the extensive grinding of old amalgam fillings. We did not see the patient until one year after the treatment. The anamnestic information was gathered from the patient and from the notes of the physicians who had treated her.

Case report
A 60-year-old woman was treated by a dentist during 12 visits over a period of 2.5 months (from 8 November 1985 through 22 January 1986). During the first two sessions two teeth earlier filled with amalgam were ground to the form of a bar to support a dental bridge. To improve occlusion, about I mm (measured from the occlusion models) was ground from the surface of II more amalgam-filled teeth, and three broken fillings were replaced during the following sessions. The dentist used a high-speed drill, water cooling , and aspiration .
One week after the beginning of the treatment the patient developed symptoms of stomatitis. Her lips and the mucous membranes of her oral cavity smarted, her tongue felt swollen, and salivation was strongly increased.
During the next week her throat became sore and did not improve with penicillin treatment. She felt an odd taste of rancid lard in her mouth, and her sense of smell weakened. She later suffered from dizziness and headache in the morning. Two months after the beginning of the treatment (6 January 1986) she felt sharp pains in her thorax and had a temperature (38.9°C) for a few days but no other symptoms of respiratory infection. The erythrocyte sedimentation rate (ESR) was 28 mm /h, but there were no actual abnormalities in her chest radiograph. The symptoms did not clearl y respond to doxycycline treatment, and the woman's temperature remained slightly increased (37.7°C) for three weeks. After one week the ESR was 26 mm /h and remained unchanged for two months .
During the last month of the dental treatment the woman's sense of touch in her left hand and fingers weakened, her fingers became sensitive to cold, and her hand grip weakened. The toes of her left foot ached and had a tendency to cramp, and later the sense of touch became weaker in her foot. She had muscular twitchings of the upper lip and difficulties to remember things. Her general condition deteriorated, she felt unwell , and she lost 9 kg over the next few months. She also became anxious and depressed.
The patient was examined at the Institute of Occupational Health in December 1986, one year after the treatment. In the neurological examinations her tendon reflexes were weak, but symmetrical all over. Her senses of touch and pain were weakened in her fourth and fifth fingers and on the dorsum of the left hand and in the third, fourth and fifth toes of her left foot. The grip force of her left hand was also decreased .
In a repeated neurological examination by one of us (EK) in March 1987 the tendon reflexes of the woman's extremities were normal, as well as her senses of pain and vibration and her posture. Her sense of touch was weakened only in her left hand, but the motor function of her left ulnar nerve appeared normal. The patient responded to the scent of coffee but could not identify it. She could not recognize a salty or sweet taste .
Both in October 1986 and in March 1987 the electroneuromyographic findings of the upper and lower extremities were normal, as were the electroencephalograms made in May 1986 and March 1987. According to the neuropsychological examinations her cognitive This level per se would not normally be regarded as high enough, among long-term expo sed workers , to imply a significant risk of symptomatic mercury to xicity. Ho wever , th e dent al treatment in this case constituted a pattern of repeated intensive acute exposures which may have enhanced local effects and the distribution of mercur y in the brain. A high-speed wat ercooled drill was used , and aspira tion was app lied. The grinding process was, however, exceptionally extensive, and, as a result of repetiti ve procedures, mercury may have accumulated to toxic levels. In the occupationally unexposed Finnish population the average urinary mercur y level is less than IO ug/I with an average of 3-5 ug/I (7).
The early effects of long-term exposure to mercury vapor are non specifi c. A sympto m complex encompassing fatigue, general weakness, anorexia, diarrhea , and loss of weight is called asthenic vegeta tive syndrom e or " micromercurialism" (8). Early subjective symptoms, performance changes on behavioral tests, and a change in spontaneous tr emor frequency appear at an increasing rat e when the concentration o f mercury in urine reaches 50-100 ug /l (6). Higher levels of mercury cause behavioral and psychological changes such as irrit abilit y, memory disturbances, insomn ia, excessive shyness, depression, and, in extreme cases, even delirium and hallu cinat ions (9). Th is syndrome is called erethismus mercuriali s. Typical neurological symptoms of mercury toxicity are intention tremor of the hands and muscular twitchin gs of the eyelids and lips. Very high concentrations of inhaled mercury have caused chemica l pneumonitis (9).
Nov. Jan. capa city was good, but there was some impairm ent in motor per formance. Especiall y the result s of the " Mira" drawing test (3) were abnormal. In the 1950s the pati ent had had severe lung tub erculosis, which was treated with induced left-sided pneumothorax. A curr ent chest radio graph showed pleural thickening and fibrotic pulm on ary changes, but no signs of congestive heart disease. The pat ient had received Digoxin'? (125 ug/d) and Furosemide") (40 mg/d) since September 1985 becau se of mild dyspnea at that time. She had not earlier experienced chest pain s similar to tho se that occurred aft er the dental treatment.
An analysis for ur inar y mercur y was performed three months after the cessation of the dental treatment and was repeated during a follow-up period of almos t a year (figure I). The specimens were incorporated into routine sample series and analyzed with coldvapor atom ic absorption spectrophoto metry, which is regularly monitored by internal and extern al qu ality contro l procedure s. Afte r the second measurement , in May 1986, all the amalgam fillings were removed and replaced with gold fillings. Th is treatment was performed with extreme caution , with the aid of water cooling, aspiration, and protection of the oral mucosa .

Discussion
Three different rou tes for the uptake of mercury from amalgam have been proposed (4). A corrosion pro cess liberates mercury ions which may reach the central nervous system from the dental pulp either along a venou s or neur al rout e. Ho wever , the content of mercury in trigeminal nerves has varied in different studies, and the significance of retrograde axon al transpo rt so far seems obscure. Ingested mercur y will be partl y absorbed in the intestine. The most impor tan t rout e for the uptak e of mercur y fro m ama lgam is the inh alation of mercury vapor released during dental filling pro cedures or the remo val of old amalgam resto ration s. High mercury levels, up to about I mg/m' , have been measured in the breathing zone of a dent ist , especially if water coolin g and aspiration have been neglected (5). With adequate water cooling and aspiration the mercury concentrati on in the dent ist's breathing zone was O. I I mg/rn' (5). In the oral cavity of the pat ient the concentra tion may be considerab ly higher. By way of compa rison, the hygienic standa rd (time-weighted average fo r 8 h) for mercur y in workroom air is 0.0 5 mg/m ' in man y countries, including Finland (6).
Three mon ths after the dent al treatment our pat ient still had an abnormally high mercury concentration in her urine. The level of urinar y mercur y decreased during th e ob servation period by a rate corresponding to a half-time of about two months, which is a value consistent with the recognized elimination rate of mercury from the bod y (6). Thu s we ca n speculate that the mercur y level in the pati ent' s urine during treatm ent may have been somewhere in the ran ge of 50-80 ug/l.
In the behavioral tests our patient showed impairment of certain qualities of motor performance reminiscent of changes found among mercury-exposed workers. Her symptoms seemed more severe than what could be expected from the measured urinary mercury levels. The effects of a series of high acute exposures may be different from those of the long-term exposure. On the other hand it needs to be stressed that many of the symptoms and signs of mercury poisoning are subjective and nonspecific, and thus the diagnosis in single cases is circumstantial. It is possible that some parts of the symptom complex of our patient were due to other causes .
The patient had earlier experienced transient numbness in her upper extremities. The neurological symptoms and signs of her left hand might also be explained by degenerative changes in the cervical spine. The patient's thoracic symptoms and high temperature are also somewhat puzzling as no certain clinical diagnosis could be reached at the time. It is known that exposure to mercury vapor can cause acute bronchitis, bronchiolitis, pneumonia, and fever (6).
The symptoms of our patient correspond to those described in the literature under the clinical syndrome micromercuralism caused by mercury exposure (8). The changes in the senses of smell and taste, which in this case appeared to be particularly vulnerable to mercury toxicity, would suggest a mechanism of axonal flow of mercury through the olfactory nerve from the nasal cavity (10).
Our case indicates a potential risk of mercury vapor exposure both for patients and dentists during extensive grinding of amalgam restorations. Such operations need to be carefully planned from the work hygiene point of view to guarantee the safety of both the patient and the dentist. High-volume aspiration is essential, in addition to effective water-cooling of the drill. If excessive exposure is nevertheless anticipated, 304 it can be assessed by urinary mercury measurements. Multiple nonspecific symptoms and minor objective signs may cause great difficulties in the differential diagnostics, and therefore an objective verification of potentially hazardous exposure is an important criterion.