Occurrence of cognitive symptoms in dental assistants with previous occupational exposure to metallic mercury.

Previous investigations have presented evidence for an increased prevalence of late cognitive effects in dental personnel exposed to metallic mercury. We wanted to examine if there was a correlation between mercury exposure and cognitive effects in a Norwegian population of dental workers, and if so, to quantify the occurrence. The study group consisted of 608 female dental assistants from central Norway and 425 female controls from the general population, all under the age of 70. They had responded to a standardized postal questionnaire (Euroquest) inquiring about seven symptoms in regard to neurology, psychosomatics, memory, concentration, mood, sleep disturbances, and fatigue. A score was calculated for each symptom based on 4-15 single questions graded on a scale from 1 (seldom or never) to 4 (very often). Dental assistants and controls had a participation rate of 56.4% and 42.9% respectively. Dental assistants reported more cognitive symptoms than the controls, but on average they reported having each of the symptoms "now and then" or less frequently. There were 4.4% of the dental assistants and 2.8% of the controls who reported having three or more of the seven symptoms "often" or more frequently. The corresponding figures for five or more of the seven symptoms were 1.0% and 0.5% respectively. The occurrence of cognitive malfunction may be moderately increased in dental assistants. For dental assistants there was a relative risk of 1.6 of having three or more symptoms "often" or more frequently, and a relative risk of 2.0 of having five or more symptoms as frequently. It can be assumed from our results that the prevalence of possibly work-related cognitive malfunction in dental assistants is between 0.4% and 2.8%, dependent on the applied severity.