Genetic Considerations of Diseases and Disorders that Affect the Oral Cavity

Part I. Overview, Dental Decay, Periodontal Disease, Diabetes

S. Michele Robichaux, D.D.S.

Almost every disease and disorder that affects the oral cavity (the mouth) has a genetic component. Even the most common oral diseases - tooth decay and gum disease - have hereditary influences. Both tooth decay (dental caries) and gum disease (periodontal disease) show various clinical symptoms and seriousness among individuals who otherwise practice similar oral hygiene habits. One reason why symptoms are so variable is that individuals inherit different degrees of genetic susceptibility or resistance to germs (bacteria) found in the mouth. Other diseases and disorders that can directly or indirectly affect oral tissues include metabolic diseases (such as diabetes), cancers of the head and neck, and developmental defects (like cleft lip and cleft palate).

ANATOMY OF THE ORAL CAVITY
The mouth is that part of the body bounded by the cheeks, lips, palate, and the floor of the mouth (the area beneath the tongue). The nasal cavity is located above the mouth and is separated from the mouth by the hard and soft palate. Within the oral cavity is the tongue, teeth, tissue supporting the teeth (gums and bone), and salivary glands. The pharynx, or throat, is the region located behind the oral cavity.

IMPORTANCE OF THE DENTAL EXAMINATION
The dentist is many times the first healthcare provider with the opportunity to take thorough health histories and perform an examination of the mouth and associated tissues. Examination of the dental patient is not limited to the oral cavity. Much information is obtained from inspection of exposed body parts and the general appearance of the individual. Techniques used by dental healthcare providers include X-rays, observation and probing of the teeth and gums, observation and palpation of soft tissues, and laboratory studies, all designed to aid in diagnosis of disease processes.

WHAT IS THE DENTIST LOOKING FOR WHEN PERFORMING AN EXAM OF THE ORAL CAVITY?
When a dentist performs an oral examination, he or she is looking for changes from the normal appearance of healthy tissue. Diseased teeth may have areas of stain and decay that can involve any surface of the affected tooth. Stain and decay both cause tooth discoloration, and tooth decay also causes breakdown of tooth structure. Diseased teeth may also involve the tissue supporting them. Infected gum and bone tissue may appear swollen and reddened and may bleed easily when brushing or flossing. Teeth losing adequate tissue support may become loose and change their position within the mouth.

Disease processes of the soft tissue of the cheek, lips, palate and tongue may also show surface changes when compared to healthy tissue. Surface changes may include ulcerations or erosion of tissue, tissue growth or swelling, changes in tissue color, and changes in tissue texture.

DENTAL CARIES
Dental caries, or tooth decay, is the rotting of teeth due to bacterial infection. Bacteria normally grow in the mouth of all individuals. Bacteria colonize and adhere to tooth surfaces within a gelatinous material called dental plaque. These bacteria ferment sugars as their normal way feeding and form acids as a by-product. Repeated cycles of acid production, however, result in the breakdown of minerals in tooth enamel, which is the cause of tooth rotting. If the infection in enamel goes untreated, the disease can spread and include internal components of a tooth, such as dentin and pulp tissue (components rich in blood and nerve supply). Pulp infection can lead to a dental abscess and spread of the infection into nearby tissue, such as the supporting bone.

Why some individuals are more susceptible to dental decay than others is unclear. The structure of enamel proteins, the quality and quantity of saliva, and immune defense mechanisms against bacteria are all possible causes of susceptibility, and each has a genetic component. It is well understood, however, that prevention of dental decay is dependent on good oral hygiene, use of fluorides, and frequent professional health care.

IMPORTANCE OF SALIVA
Saliva supports good tooth health in three ways: (1) Saliva contains enzymes and antibodies that can directly attack the bacteria of dental plaque. (2) Saliva neutralizes acids released by decay-causing bacteria. (3) Saliva contains minerals (including calcium, phosphate and fluoride) needed to replace lost minerals from tooth surfaces. Therefore, good saliva production is important for dental health, and factors that compromise good saliva production contribute to dental decay.

Many medications compromise good saliva production by causing "dry mouth." Some of the 400 or so medications that cause the dry mouth side-effect are antihistamines and decongestants (taken for cold and allergy symptoms), antihypertensive medications (taken for blood pressure regulation), and medications taken for depression. One of the unfortunate side effects of radiation therapy for cancers of the head and neck is destruction of salivary gland tissue, which results in dry mouth and subsequent dental decay.

PERIODONTAL DISEASE
Periodontal disease, like dental caries, is a disease caused by bacteria found in dental plaque. While dental caries involves the teeth, periodontal disease infects the tissues that support the teeth, namely the gums and bone. Periodontal disease more often affects adults, with the majority of adults experiencing signs and symptoms by their mid-thirties.

The first stage of periodontal disease is called gingivitis, or inflammation of the gums. Gingivitis is characterized by redness, bleeding, and swelling of gum tissue (gingiva). Without good oral hygiene, gingivitis can become a chronic infection that may progress into the more severe form of periodontal disease known as periodontitis. Periodontitis is a disease that involves both the gum tissue and supporting bone. The destruction of bone results in the formation of a pocket or space between the tooth and adjacent tissue. Such pockets contain bacteria that can continue and worsen the disease process. Destruction of supporting tooth tissues can lead to tooth loss.

Dental research shows a genetic component in periodontal disease. The inflammation process that accompanies bacterial infection involves the release of powerful molecules, called prostaglandins, from cells of the immune system. Prostaglandins are produced by cells through the work of several enzymes, each of which derives from one or more genes. One type of prostaglandin, prostaglandin E2 (PGE2), may play a key role in the tissue destruction that occurs in periodontal disease. In healthy individuals, PGE2 levels are very low. Levels of PGE2 increase in gingivitis and rise significantly in periodontitis.

Factors such as smoking, age, level of oral hygiene, level of patient education, and level of professional dental care influence the severity of periodontal disease. Certain metabolic diseases, such as diabetes mellitus, also increase the risk of periodontal disease.

DIABETES
Diabetes is a complex disease of carbohydrate (or sugar) metabolism involving the effectiveness of insulin. Insulin is an important hormone produced by the body that helps lower blood sugar levels. Because diabetes is a disease that involves the entire body, signs and symptoms of diabetes can occur in the oral cavity. Dental healthcare professionals have the opportunity to promote health and be involved in prevention, diagnosis, and treatment of diabetes. Some dental consequences of diabetes are described below.

Periodontal disease. Patients with diabetes are at greater risk for periodontal disease. Diabetes causes blood vessel thickening, which slows down the flow of blood to body tissues, including the gums and dental bones. Blood flow is crucial in providing important nutrients and eliminating harmful wastes from body tissues. As a result lowered blood flow, the gum and bone tissue supporting the teeth become less healthy and less resistant to infection from bacteria found in dental plaque.

Studies show that patients with poorly controlled diabetes have periodontal disease more often and more severely than those with good control of diabetes. Also, patients with poorly controlled diabetes have more incidence of tooth loss. Studies have also linked an increased risk for gum disease among diabetics who smoke. Smokers with diabetes, age 45 or older, are twenty times more likely to develop severe periodontal disease compared to individuals who do not smoke and do not have diabetes.

Thrush. Thrush (oral candidiasis) is another complication of diabetes. Thrush is an oral infection caused by fungus that grows in the mouth. The fungus that causes thrush thrives on increased levels of blood glucose found in the saliva of individuals with diabetes. Smoking, poor oral hygiene, and denture-wearers are at greater risk for developing this complication.

Dry Mouth. Dry mouth (xerostomia) is another complication of diabetes. Dry mouth is the result of the decrease in production of saliva by salivary glands. As a result, dry mouth can lead to mouth soreness, tooth decay, increased risk of soft tissue infections, and ulcers.

Tooth Decay. Children with diabetes do not show incidence of increased tooth decay. In fact, studies indicate that tooth decay actually occurs less in children with diabetes due to the children's low sugar diets.

Wound Healing. Diabetes causes an increase in the time for wounds to heal following surgeries or injuries. Dentists observe precautions and work closely with the patient's physician when dental invasive treatment is needed.

REFERENCES
Mealey, B. 2000. Diabetes and periodontal disease. Journal of Periodontology 71(4):664-678.

Offenbacher, S., P.A. Heasman, J.G. Collins. 1993. Modulation of host PGE2 secretion as a determinant of periodontal disease expression. Journal of Periodontology 64:432-434.

Page, R.C. 1995. Critical issues in periodontal research. Journal of Dental Research 74:1118-1128.

Slavkin, H. 1988. Gene regulation in the development of the oral tissues. Journal of Dental Research 1988;67:1142-1149.

Sreebny, L.M., A. Yu, A. Green, A. Valdini. 1992. Xerostomia in diabetes mellitus. Diabetes Care 15(7):900-904.

HOW TO LEARN MORE
www.ADA.org. This is the American Dental Association website. It provides access to news and publications related to dental health.

www.diabetes.org. This is the American Diabetes Association website, a resource center for diabetes information.

www.perio.org. This is the American Academy of Periodontology website, which offers information on gum disease and treatment.

ABOUT THE AUTHOR
S. Michele Robichaux, D.D.S is an assistant professor of biology at Nicholls State University in Thibodaux, Louisiana. She teaches Human Anatomy, Physiology and Histology. Her research interests include the genetics and microbiology of periodontal disease. Dr. Robichaux also practices General Dentistry in Thibodaux, LA.

CONTACT THE AUTHOR
Dr. S. Michele Robichaux
Department of Biological Sciences
Nicholls State University
Thibodaux, LA 70310
(985) 448-4721
biol-smr@nicholls.edu