Dental Amalgams
The accepted practice of most American dentists for several generations has been to treat tooth decay by "drilling and filling" using silver fillings.  Silver fillings are actually a mixture of silver, copper, tine and zinc amalgamated (dissolved) with mercury.  The amount of mercury in these composites is approximately 50%.  Older fillings may have an even greater percentage of mercury.
Mercury is more poisonous than any other metal except plutonium.  Although the safety of dental filling material containing mercury has been debated in dental circles since the 1800's, the official opinion of the American Dental Association is that when mercury is combined with other metals and used in dental amalgam fillings, the toxic properties of mercury are rendered harmless.  There exists a growing awareness among health care practitioners and researchers that this is not the case and that a significant amount of mercury is released by these fillings to cause health problems, especially in susceptible individuals. 
Research has demonstrated that mercury vapor is continuously released from amalgam fillings in measurable quantities from the moment fillings are inserted into teeth.  There has been found to be a direct correlation between the amount of mercury released and the number of amalgams.  Mercury is inhaled, swallowed and absorbed directly in the mouth.  In his book "It's all in your head - Diseases Caused by Silver-Mercury fillings", Hal Huggins, D.D.S. described his breakthrough work establishing that mercury is released from compounds that are toxic and that these compounds can cause illness.  Sequential removal can result in remission of the illness.
The mercury present in the fillings is not the only problem with dental filings.  A phenomenon called "electrogalvanism", or electricity in the mouth is also a problem.  The phenomenon is created when dissimilar metals are present in the mouth, such as mercury amalgam mixtures and gold, resulting in an electric current being established in the mouth.  as you know food can get trapped between the teeth and can be used by bacteria as a food source.  One of the products of the bacteria is acid, which can directly affect the teeth as well as contribute to the electrochemical reaction of the fillings. The result is a "battery-like" effect, which can release mercury from the fillings and potentially, cause a direct electrical stimulus to the pituitary and hypothalamus glands.

Mercury and Illness
Studies have linked mercury exposure with a number and variety of illnesses including allergies, chronic fatigue, depression, GI disorders, neurological problems, reproductive disorders, birth defects, kidney disease, heart problems, hypertension, respiratory disorders and skin disease.
Mercury can interfere with any process or organ in the body since it is poisonous to all cells, but it has a marked effect on the immune system.  This has been shown by research indicating the presence of mercury amalgam fillings in the mouth reducing the immune system efficiency by 1/3 to 1/2.
Over a long period, small amounts of mercury exposure can produce the same devastating effects as a large dose in a short time.  Insidious long term exposure to mercury can produce damage after many years with no trace of the etiology of the problem.  If a person has a chronic health problem for which a cause has not been found and mercury fillings are present in the mouth, mercury toxicity may be the contributing factor.

Mercury Poisoning and Psychological Disorders
Evidence linking mercury exposure to psychological disorders has been assimilating over the past 60 years.  Psychological symptoms of mercury poisoning are erethism (irritability, excitability, outburst of temper and quarreling), extreme shyness and avoidance of strangers, anxiety, hallucinations, suicidal tendencies, melancholia and manic depressive psychosis may occur.
Mercury poisoning disrupts the emotional sphere and produces psychological disorders as a result of mercury's strong affinity for brain tissue.  During the last century, felt hat makers were regularly exposed to mercuric nitrate.  they became known as "Mad Hatters" because of the emotional problems they developed, including sudden anger, drowsiness, depression, loss of memory, timidity, insomnia, hallucinations, delusions and mania.  In 1941, brain damage due to mercury poisoning was identified as the cause of the Mad Hatter syndrome.
Of 53 Iraqi patients hospitalized for exposure to mercury pesticide, 26 revealed psychological disorders.  Mercury poisoning at Minimata Bay in Japan (now called Minimata Disease) resulted in an increase in the number of babies who developed cerebral palsy and mental retardation.  Mercury passes easily through the placenta and accumulates in the fetus.  A Russian study of prenatal mercury poisoning found that 7 out of 10 new babies exposed to mercury in utero were mentally retarded, while a report from Sweden identified a mother who had eaten seed treated with alkyl mercury and was unaffected but her child was born with severe retardation.
Several dentists who were exposed to mercury in their practices developed symptoms of irritability. excitability, fearfulness, restlessness, melancholy, depression, timidity, fatigue, weakness, indecisiveness, headaches and hopelessness.   These symptoms disappeared after their mercury levels were reduced by medication.  Rats exposed to mercury vapor were found to increase their spontaneous aggressive behavior, anger is a common symptom of mercury toxicity.