Oral Health Research - From Tooth Decay to Dental Implants

Oral disorders encompass a wide spectrum of conditions from tooth decay, gum disease and chronic pain to congenital deformities and cancers. Poor general health often leads to poor oral health, and quite possibly the reverse is also true. People with chronic diseases, such as diabetes and AIDS, are more prone to developing persistent gum infections, and there's mounting evidence that extensive gum infection correlates with an increased risk of heart disease or premature labour and low birth-weight babies.

One doesn't have to travel too far back in the last century to find a time when people in mid-life often lost most, or all, of their adult teeth as a result of advanced tooth decay and chronic gum infection (periodontitis). In fact, an epidemic of dental caries (cavities) that continued into the 1970s is responsible for millions of today's elderly Canadians having lost all their teeth. Edentulism (the clinical term for widespread tooth loss) fits the World Health Organization's criteria for chronic disability since it drastically affects how a person speaks and eats - and thus their quality of life, nutrition and general health.

Recent research has shown that traditional dentures do not allow people to eat properly, and things get worse as people age - the bone and mucosa under the dentures just gets thinner and thinner, and eating becomes more and more difficult and painful. To find a solution for the millions of edentulous Canadians, the Canadian Institutes of Health Research (CIHR) has been funding new clinical trials in partnership with manufacturers to see if the insertion of small metal implants into the lower jaw will allow people to eat and speak more easily. Early results suggest that these implants are actually allowing people who lost all their teeth in the caries epidemic to change their diet and improve their nutrition and health.

One of the biggest differences between then and now is fluoride. Most experts agree that water fluoridation is one of the most effective public-health measures ever undertaken. During the last 30 years or so, dental caries in children has decreased significantly throughout the industrialized world - the visible benefit of improved prevention programs - especially fluoridation of municipal water. Despite much controversy at the outset of the practice, retrospective studies comparing municipalities with and without fluoridated water have demonstrated conclusively that fluoridation programs have noticeably lowered rates of dental cavities. (In trace amounts, fluoride impedes bacteria in plaque from releasing cavity-causing acids, and it can also remineralize enamel that has been softened by those acids.) Fluoride is also a common ingredient in many toothpastes and mouthwashes.

In light of fluoride, daily oral hygiene and regular access to professional care, tooth decay is now considered to be a preventable illness. Even so, virtually everyone has dental caries, and about 60 per cent of people also experience localized infection (gingivitis). In most cases, it's limited to reddening of gum tissues. For a significant minority, however, gingivitis can lead to periodontal disease and eventual tooth loss.

Unraveling the Mysteries of Oral Health

Although few in number, Canada's oral-health scientists are regarded as international leaders in such areas as oral infectious diseases, the biology of connective and mineralized tissues, biomaterials, neuroscience and pain. This diversity of expertise reflects the fact that many of the basic tissues (mucosa, bones, joints) and biological processes in the oral cavity - including cell signaling, inflammation, repair and immune response to infection - resemble those in other body sites, such as the skin, lungs, digestive tract and limbs. Thus, the mouth becomes a valuable research model for understanding biological activity in other less accessible organs.

Some 500 species of bacteria populate the oral cavity, and usually a single milliliter of human saliva contains more than 100 million bacteria. While scientists know a great deal about the organisms that create caries, less well understood is how certain groups of bacteria cause periodontal disease - particularly the thrust and parry between microscopic parasite and host cells. Since these microbes are endemic to the oral cavity, how is it that only some people develop periodontitis? And what are the more global implications of periodontal infection on the heart and the unborn? Are the bacteria spreading to other organ systems, or are they releasing toxins that circulate in the blood? These outstanding questions about the mouth's microbiology are well nigh infinite, and many of them useful for elucidating mysteries that affect other body sites.

How teeth, bone and connective tissue are formed is another important area of research. How does the body regulate precursor cells to become calcified tissues? It's a question that has broad application; since mineralization (or demineralization) of tissues is involved in dental cavities, fracture healing, arthritis, hardening of the arteries, osteoporosis and kidney stones. And these are only a few of the more common conditions. The tantalizing prospect of re-growing gum tissues or tooth enamel in a lab dish or, better yet, in an individual's mouth isn't as farfetched as it might initially appear. Indeed, a group in Boston has just succeeded in growing a tooth from cultured cells!

As unpleasant as dental pain can be, there are other types of oral pain that are even more excruciating and much more difficult to treat. Out of necessity, some oral researchers have specialized in the biology of pain signaling and processing. Trigeminal neuralgia, also called tic douleureux, is usually perceived as a severe shooting pain running from the cheek to the middle of the face, upper lip, lower lip and chin on one side. Eating and talking can be very painful. The causes are uncertain, and there's no observable damage to the trigeminal nerve, one of the largest in the face. Somehow the nerve becomes hypersensitive, discharging at the slightest stimulus. Amputees complain of ghostly pain where a limb once was, and so do some individuals who have "phantom tooth-ache" originating from an empty socket left by an extracted tooth.

Temporomandibular Disorders (TMD) group together a series of conditions that cause jaw and muscle pain. Sometimes the pain comes from arthritis, but many of these conditions have no known cause. "Burning mouth syndrome," is another baffling condition that makes people feel as if their tongue and mouth's mucosa had been scorched. Much needs to be learned about all these syndromes, especially as they seem to co-exist with other painful conditions including fibromyalgia, myofascial pain syndrome and irritable bowel syndrome. For the moment, their causes remain unknown, and no truly effective medication exists.

Over the last decades, surgical reconstruction of cleft lips and palettes has also been perfected, often making these congenital deformities nearly invisible. Unfortunately, the same cannot be said for throat and mouth cancer, which is the sixth most prevalent cancer in men. Most commonly linked to tobacco use (especially chewing tobacco or snuff) and alcohol abuse, oral cancer tends to be highly disfiguring, since treatment consists of removing the tumor as well as a surrounding zone of healthy tissue. Typically, individuals who undergo such radical surgery cannot afford to have reconstructive facial surgery afterward and are left with half a jaw or face. In this regard, social policy rather than medical technology limits treatment, and data once again needs to be collected to evaluate what steps can be taken to effectively address this issue.

Setting the Oral-Health Research Agenda

In Canada, 60 to 80 per cent of dental caries and virtually all cases of periodontal disease are experienced by disadvantaged and remote populations including aboriginal peoples, the elderly and people who are cognitively and/or physically disabled. Although there is still much to learned about the basic science of dental cavities and gum infections, there is clearly a sound base of knowledge that needs to be translated into progressive social policies.

One of the crucial thrusts on IMHA's oral-health research agenda is the accumulation of socio-economic data upon which to build public-health strategies that will address the oral-health needs of vulnerable populations. At present, only about 40 per cent of Canadians have access to fluoridated water. And people with low or fixed incomes and no insurance often can't afford basic care, let alone costly restorative treatment.

First Nations peoples, on the other hand, must undergo lengthy pre-approvals from distant federal administrators to receive dental surgery and orthodontics. And in Canada's inner cities, there are hundreds of children whose dental caries is so advanced that they must be treated under a general anesthetic. Many more endure chronic dental pain while waiting for treatment in children's hospitals. In short, the very people who could benefit most from advances in dental care have poor access to treatment or can't afford it.

To address these, and a variety of other issues, IMHA organized the first Oral Health Research Planning Workshop in June 2002. The workshop drew together a broad range of stakeholders to begin laying the groundwork for a national oral health research strategy that will include both research priorities and training programs for oral health research.