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Chewing Tobacco Use Linked to Dental Caries

By Mary Daum

If you think a "chaw" of tobacco won't hurt you, chew on this: Chewing tobacco users are more likely to develop dental caries, particularly on the root surfaces of their teeth, than those who don't use tobacco, say scientists at NIDCR and the Centers for Disease Control and Prevention.

"The results of this study give tobacco chewers yet one more reason to quit," said lead author Dr. Scott Tomar of the National Center for Chronic Disease Prevention and Health Promotion, CDC. "We already know that chewing tobacco use is a risk factor for gingival (gum) recession and oral cancer. The damage that it can do to teeth is another item we can add to the list of health consequences."

The CDC-NIH study of dental caries and chewing tobacco use in the United States is the first large-scale, detailed analysis of the relationship between dental decay and the leafy form of tobacco. The study results appeared in the November issue of the Journal of the American Dental Association.

The researchers analyzed dental caries and tobacco use data from more than 14,000 adults age 18 and over. The data were collected by the National Center for Health Statistics between 1988-1994 as part of the Third National Health and Nutrition Examination Survey.

The researchers distinguished between the two types of spit tobacco, also called smokeless tobacco, and other types of tobacco such as cigarettes, pipes and cigars. Spit tobacco comes in two forms, chew and snuff. Chewing tobacco is a bulky, leafy form of tobacco that is packaged as loose leaf, plugs, or twists, and snuff is a finely ground or shredded tobacco.

The survey data revealed that 6 percent of men age 18 and older use some form of spit tobacco, a figure that is consistent with other recent studies on tobacco use. (The researchers limited their data analysis to men since the vast majority of spit tobacco users are men.) Of the men who use spit tobacco, 59 percent use the chewing tobacco form. Almost half of those who use chewing tobacco also use one or more other types of tobacco.

The study showed that men who use chewing tobacco exclusively were four times more likely than those who had never used tobacco to have one or more decayed or filled root surface. Men who currently use only chewing tobacco also were more likely than former tobacco users or those who currently used only snuff to have root caries. On average, the men who used chewing tobacco exclusively had 3.84 decayed or filled root surfaces (out of 112 possible surfaces), more than any other tobacco-use group and those who had never used tobacco.

The researchers also found a dose-dependent relationship between chewing tobacco use and the likelihood of having root caries. The more packages of chew a man used each week, the more likely he was to have a decayed or filled root surface. Additionally, the more years a man had used chewing tobacco, the more likely he was to have a decayed or filled root surface.

The researchers speculate that the high sugar content in chewing tobacco is one reason the product is associated with an increased risk of dental caries on tooth roots and crowns. Additionally, the way chewing tobacco is used might also help promote tooth decay, the scientists say. A typical user holds a wad of chew in his cheek for 30 minutes at a time and uses the product in this manner throughout the day, exposing the teeth to the tobacco for several hours. Moreover, both chew and snuff can contribute to gingival recession and therefore make tooth roots more vulnerable to decay.

"This study shouldn't give chewers the idea they can switch to snuff," said study author Dr. Deborah Winn of NIDCR. "Spit tobacco users should be aware that both chew and snuff are addictive and can cause oral disease." According to Winn, earlier studies have linked spit tobacco in various forms to gingival recession, oral lesions and oral cancer.

Mice Missing Enzyme Suffer Dwarfism, Thin Bones, Arthritis

By Wayne Little

The saying about "not missing something until it's gone" is especially true when referring to a body component, no matter how obscure its function may appear on the surface. An international team of scientists has demonstrated in a mouse model that the absence of an enzyme often linked to disease has devastating effects on skeletal development and is inevitably fatal. A detailed look at the abnormalities provides valuable clues about the role of this enzyme in normal skeletal development, and raises a cautionary flag regarding the use of certain enzyme inhibitors for treating arthritis.

Dr. Kenn Holmbeck from the National Institute of Dental and Craniofacial Research and Dr. Paolo Bianco from Italy led a research effort to produce mice missing an enzyme called MT1-MMP (membrane-type 1 matrix metalloproteinase). The deficient animals appeared essentially normal at birth, but their bones, including those that make up the skull, failed to develop properly. The end result was thin bones, dwarfism and severe arthritis. The study appeared in the October issue of Cell.

The range of effects astounded even the investigators familiar with related enzymes. "We were profoundly surprised by the extent of effects resulting from the absence of MT1-MMP," said Holmbeck. "In other knockout models where closely related enzymes were eliminated, the effects were minimal. The development of arthritis was an especially interesting finding because this disorder has been linked to excess MMP activity in the joints. Broad-spectrum therapies aimed at inhibiting MMPs in arthritic joints should take into account that eliminating MT1-MMP activity could actually exacerbate the problem."

MT1-MMP is one of about 20 MMPs that have been identified in mammals. The existence of so many MMPs is one reason scientists have thought there may be some redundancy of function, so that the absence of any one enzyme would be compensated for by other family members.

To single out the role of a particular MMP, Holmbeck, Bianco and colleagues turned to the "knock-out" mouse. Using a technique known as targeted gene disruption, the investigators created mice that had the MT1-MMP gene obliterated so that it could not code for a functioning enzyme.

The wide range of effects observed in the knockout mice was found to be due to the inability of the mutant mice to cleave collagen, one of the most abundant building materials in cartilage and bone.

Although the link between MT1-MMP and arthritis remains to be determined, the study provides strong evidence that the enzyme is necessary for maintaining healthy joints.

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