Effects of exposure to mercury on health of dentists - Sunil Nair Health Informatics Dalhousie University
A PILOT STUDY TO DETERMINE THE EFFECTS OF EXPOSURE TO
MERCURY ON THE HEALTH OF DENTISTS
HINF6030 – RESEARCH METHODS – FINAL
Master of Health Informatics
Sunil Nair Page 1 14/04/2008
The effects of mercury poisoning on adverse human behavior is legendary and is said to be
responsible for the origin of the phrase “mad as a hatter” [1, 11]. Occupational and environmental
hazards of exposure to mercury are well documented [2, 3, 4, 5]. The presence of metallic mercury
in amalgam, used as a tooth restorative material, exposes dental personnel to the dangers of
mercury poisoning . A simple search on PubMed with key words “mercury poisoning” dental
profession” resulted in more than 500 results . Dental Amalgam has been used as a tooth filling
restorative for over 100 years . It is an alloy made by combining mercury with amalgam powder
which contains silver, tin, copper and zinc in specific proportions. This mixing procedure is done in
the dental office in room temperature and is handled by dental personnel including dentists.
Although studies have proved that the end product of this mixture is proven to be a stable and safe
material for teeth restoration [9, 10], minute amounts of mercury vapors are released while the
dental amalgam is being prepared. Mercury is understood to be the most potent non-radioactive
heavy metal toxin to humans . Long-term exposure to mercury may lead to several medical
conditions including renal damage, behavioral changes, Alzheimer’s disease, sexual dysfunction,
autism in children, stress and cognitive dysfunctions to name a few [12, 13, 14].
There have been a number studies done in the recent past that tries to link health and behavioral
problems with the higher suicide rates among dentists [15, 16]. Stress, burnout, substance abuse are
thought to be precursors to the increased number of suicides among dentists . Is this
phenomenon related to long-term exposure to toxic mercury? Although the adverse health effects
of using dental amalgam in dental procedures is well researched and evaluated in much of Europe
and North America, conclusive studies have not been done in populous developing countries like
India. Due to high costs of alternative tooth restorative choices, a large number of dental amalgam
fillings are being done in dental practices in most parts of India. Increasing awareness about the
toxic effects of dental amalgam may have reduced the number of amalgam fillings in India.
In this pilot study, I will be studying the adverse health effects of prolonged exposure to
mercury vapors among dental practitioners in India.
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Null hypothesis, Ho: There is no significant in change in health status to practicing dentists due
to prolonged exposure to mercury.
Alternate hypothesis, Ha: There is a significant change in health status to practicing dentist due
to prolonged exposure to mercury.
It is possible to study the threshold effects of mercury in a Dentist population because they are
more homogenous than other groups in relation to education level, skill of work and ability to take
part in testing. Therefore it is possible to detect any effect of mercury poisoning on long-term
exposure in a specific occupational group.
Independent variable is the effect of mercury exposure to health status.
Dependent variables are the level of mercury in urine, the behavior test score and the cognitive
function test score.
This experiment will use a cross-sectional sample of dentists with over 10 years of practice in a
particular state or province in India.
3.1 The Study population and test procedure
A contact list of registered practicing dentists can be availed from the Indian Dental Association
(IDA). It would be important to pre-select the subjects who are having more than 10 years of
practice as the goal of the experiment is to establish the effects of prolonged mercury poisoning in
causing deterioration of health status among dentists most likely the presence of a chronic
condition. We would consider health status as deteriorated if there are significant behavioural
changes and cognitive dysfunction issues. Both of which can result in cases of increased stress
levels and likelihood of practitioner burnout. In the event of mercury poisoning, the element lodges
itself in brain and attacks the Central Nervous System. Mercury is excreted via the urine.
Therefore, we can evaluate the mental attributes by measuring the behavioural changes and
cognitive function in the subjects and also measure the level of mercury in their urine sample.
Provided we establish proper control we would be able to draw a direct correlation between the
higher levels of mercury in the body and a declining health status.
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The experiment package, preferably online, can be sent to the dentists registered with IDA on or
before January 1998. The package would contain
• A consent form
• Medical Questionnaire
• Dental practice Questionnaire
The questionnaires would be some close-ended and mostly open-ended questions. The close-ended
questions would have modified Likert scale of rating.
3.1.2 Medical questionnaire
A medical questionnaire to evaluate the medical condition of the participants is essential to control
any factors that may influence the test performance or results. Questions would be focused on
variables like age, race, and gender, history of any neurological disorder and medication history.
The questionnaire would also be lifestyle or habits related which would include history of any
alcohol abuse, substance abuse and any other addictions. Lifestyle questions could include dietary
information for example the amount of fish or seafood intake because excessive sea food in the diet
could have increased levels of mercury in the urine sample.
3.1.3 Dental practice questionnaire
This questionnaire would help in controlling some factors like the years of practice. Questions
would be to find out the type of practice setting, urban or rural, whether they use amalgam in
regular practice or not and so on. A sample of the questionnaire is listed in Appendix 4.1.
Using the above pre-test questionnaires, we should be able to control for the following:
• The years of practice, minimum 10 years
• The type of practice
o Urban or rural
o High-tech or not automated
o Amalgam free practice or not
• Confounding factors like
o Sea food intake
o Living/working near a mine or polluted area which are Environmental factors.
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o Pre-existing medical condition
o Number of dental amalgam fillings in the mouth.
The survey questionnaire would have a high inter consistency reliability, as to improve the
reliability all the points on the Likert rating scale and are labelled with words. The questionnaire
would have controls for different response patterns of the respondent, controls for the effects of an
issue’s position in survey, to measure the variability of each question and even able to detect
Threats to Internal validity
o As the questionnaire is administered online there could be a possibility that the respondents
might have difficulty in understanding the questions or they may interpret it differently that
the researcher intended.
o There could be ambiguity in the statements.
o Since there are some close-ended questions the subjects tend to answer the choices offered
in the survey and do not volunteer to give a response.
o Subjects realize that they are chosen for a study and they respond differently than they
would do normally.
o We do not know how many subjects will take the survey seriously.
As the subjects are chosen based on convenience there could be confounding variables in the study
o Some could have more work experience than the others.
o Those who volunteered for the study were different in terms of motivation from those who
did not participate.
o Age– There is possibility that some of the senior dentists have been practicing for many
o Possibility that men are more practicing dentistry than women or vice versa.
o Possibility that the dentists in the urban practice were all young using the latest
technologies and newer restorative materials.
o There could be a possibility that a dentist from a rural practice has decided to shift to the
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Threats to external validity
o Since this study is done only in a particular area we are not sure how the dentists in other
areas are practicing.
o As we are taking only limited number of dentists from each setting we cannot confirm that
it’s a good sample to represent the whole population.
o We are discussing only about dentists and their opinion but do not refer to dental
hygienists, dental nurses (who would maximum utilize/ prepare dental amalgam, as they
have a heavy workload).
o The time of the year could also affect the external validity.
Threats to construct validity
o There could be evaluation apprehension as some may be over anxious (not due to the
survey questions) and this might lead to their poor performance or some subjects may want
to “look good” and might give a good response.
o The researcher can bias the outcome of the study. The survey questions could be
manipulated to encourage the subjects to answer in a desirable manner what we want.
Threat to Statistical Validity
o A possibility that the survey questions used to assess the impact of chronic exposure to
mercury on health and cognitive functioning are undependable.
o We as researchers could make changes to the statistical tests to get desirable results as per
3.3 Experimental design
As this is a pilot study a small number of participants could be chosen for both groups.
o Urine samples could be taken to measure the mercury levels.
o A set of behavioural test covering a broad range of functions could be administered.
o For cognitive function test a Cognitive Drug Research Computerized Assessment system
could be used. 
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This would be a descriptive cross sectional study. There is only one component which is the
assessment of health status by administering validated questionnaires to document demographic
data, medical history and lifestyle and habit information.
A complete medical exam and urine sample can also be collected then measured for mercury
The behavioural and cognitive tests can be administered.
3.4 Comparisons to be made
A cross-sectional analysis can be done with the results.
Comparisons will be made between the mercury levels in dentist practicing in urban and rural
setting, those who do not use amalgam and those who use amalgam in their practice.
4.1 Sample Dental Practice Questionnaire
SAMPLE PRE-TEST DENTAL PRACTICE QUESTIONNAIRE
1. Years in dental practice.
d. More than 30 years.
[With this question we can filter those dentists who have been in practice for more than 10
2. What type of dental practice do you have?
a. General practice, I do all the work.
b. Specialist practice, I do the fillings
c. Consultant, I visit other dentist.
d. General practice for more than 10 years but now specialist practice.
e. Other _______________
[With this question we can determine the financial status of the practice, the stress level of
dentist as well, the dental surgeon at the more than 10 years old general practice where the
dentist does all the work could be more stressed, burnout, than a specialist or consultant
who chooses the time and number of patients to see.]
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3. How would you describe your practice setting?
a. Urban – high-tech [this would mean that the practice is located in an urban setting
and follows all safety standards and infection control, uses modern equipments and
b. Urban [practice is in urban area, safety followed, the clinic is modern, but not
c. Rural – high tech [ rural-safety standards followed-automated]
d. Rural – rural area-no safety standards are followed, not automated]
[With this question, other than separating urban and rural practice setting, we can
differentiate between a clinic where safety standards are maintained and not maintained.
This would mean that in a rural clinic with no safety standards and no automation, every
amalgam filling done would induce more mercury in to the air and in turn increases the
probability of the dentist to be exposed to the vapours.]
4. Do you use dental Amalgam in your practice, if yes, how many fillings per week are done?
a. No, mine is amalgam free clinic
b. Yes, 1-25 fillings per week.
c. Yes, 26-50 fillings per week
d. Yes, 51-100 fillings per week
e. More than hundred fillings per week.
5. Where is your lab located?
a. In the office/clinic premises
b. Within office but separate room
c. Away from main clinic area
d. At a distant location.
e. Not applicable
[This question would help differentiate he level of exposure. Though amalgam is almost
always mixed at chair side, some dentists insist on the trituration process at a distant
location thereby reducing the exposure]
6. What type of flooring do you have in your clinic?
a. Carpet through out
d. Carpet in the lab; ceramic or vinyl in the clinic area
e. Hardwood throughout.
[This question would help assess the kind of cleaning that can be maintained. A carpeted
clinic or lab would lodge spilled mercury and be difficult o clean even with vacuum.]
7. What is your opinion/knowledge about hazards of mercury usage in dental office?
a. Very toxic, will not use.
b. Toxicity depends on safety methods followed.
c. Research is not substantial
d. Don’t care
[An urban practice where amalgam is done and safety is practiced and if the dentist doesn’t
care about the ill effects of mercury, then there are chances of careless handling]
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