Amelogenesis imperfecta

Definition

Dental anomalies are craniofacial abnormalities of form, function, or position of the teeth, bones, and tissues of the jaw and mouth.

Description

Dental anomalies can range from missing or stained teeth to cleft palates. Many are expressions of other, more complex disorders. The National Institute of Dental and Craniofacial Research (NIDCR) estimates that in the United States a baby is born every hour with a craniofacial defect.

Causes and symptoms

Many dental anomalies are caused by inherited genetic defects or result from spontaneous genetic mutations. The Center for Biotechnology Information recognizes 1,250 gene loci for craniofacial diseases and disorders. Dental deformities may also have environmental, traumatic, or nutritional causes; these may develop or become clinically apparent at any time during an individual's life.

Genetic defects

The most common genetic craniofacial deformity is clefting of the lip and/or palate, a defect estimated by the NIDCR to occur once in every 500 births. A family history of clefting increases the chances of inheriting the disorder. Seen more often in boys than in girls, cleft lip is usually unilateral, appearing three times more frequently on the left side than on the right. Less common is a bilateral cleft, a condition formerly known as "harelip." An incomplete cleft stops short of the nostril; a complete cleft extends into the nostril. Both types frequently involve the palate as well. The typical patient with cleft palate and cleft ridge exhibits large defects in the roof of the palate with a direct opening into the nasal cavity.

Dentinogenesis imperfecta type II (DGI-II), another genetic defect, causes severely discolored teeth that break easily. Amelogenesis imperfecta produces only a soft, thin layer of tooth enamel. This lets the dentin show through, making teeth look yellow, and leaves them weak, easily damaged, and susceptible to decay.

Other genetic anomalies are less debilitating. Malocclusion, meaning bad or misaligned bite, is caused by crowding teeth, extra teeth, missing teeth, or jaws that are out of alignment. Most malocclusions are inherited genetically, although some can be caused by accidents, early or late loss of baby teeth, or prolonged thumb sucking. Orthodontia usually corrects this problem.

Relative microdontia is an inherited condition that produces smaller-than-normal teeth, usually in the upper jaw. To correct this condition crowns or veneers are applied to make the teeth the same size as the others. Microdontia is neither painful nor harmful; treatment is intended to improve the patient's bite and appearance.

Partial anodontia, or congenitally missing teeth, is a condition in which one or more permanent teeth fail to appear, although primary (baby) teeth usually erupt. Third molars are absent in as many as 35 percent of all subjects examined. Maxillary lateral incisors and maxillary and mandibular second premolars (bicuspids) also frequently fail to appear. When this happens, many dentists choose to leave the primary tooth in place to prevent the malocclusion that might otherwise occur. If this is not feasible, a dentist may extract the tooth and close the space with braces or cover it with a bridge.

Idiopathic anomalies

Stafne's bone cavity, also called static bone cyst or lingual mandibular bone concavity, is an anomaly of unknown etiology. A painless condition, it is an indentation of the jawbone that may contain muscle or salivary tissue. The skin covering this area is soft to the touch and feels concave. No treatment is required, although biopsies are often performed to rule out the presence of a malignant tumor.

Condylar hyperplasia, another idiopathic anomaly, affects the temporomandibular joint and surrounding tissues. The condition is characterized by unrestrained growth of the condyle, which deforms the face, jaw, and bite. Surgery is usually required to restore order, although once growth has stopped orthodontics are often helpful. Condylar hypoplasia occurs when one condyle is markedly shorter than the other, a condition that also causes facial and dental deformities. Surgery can restore balance, and orthodontics are indicated as well.

Environmental causes

Environmental anomalies are caused by external agents, including diet, that affect the teeth and gums. Extended use of the antibiotic tetracycline in young children, for example, can cause dark brown discoloration of the teeth. Fluorosis, an overabundance of fluorine in the diet, can create white or mottled spots on the teeth. This is most commonly seen in children who ingest greater-than-recommended amounts of fluoride by swallowing large quantities of fluoridated toothpaste. Teeth naturally darken with age, as the enamel thins and the dentin shows through. Coffee, tea, and red wine can also stain the teeth. Even children who swim an average of six hours or more a week in a pool may develop brown stains on their teeth.

Bulimia can cause severe decalcification of the teeth. Acid from constant regurgitation eats away at the enamel, especially in the molar region. This weakens the teeth, making them both susceptible to decay and highly sensitive. Unless the bulimia is arrested, sensitivity increases until the nerve is exposed and root canal therapy is needed or extraction is required.

Poor nutrition can also cause dental anomalies. Scurvy, a disease caused by a lack of vitamin C, affects periodontal and other connective tissue, causing purple, swollen, bleeding gums and, if untreated, tooth loss. Anemia, caused by a lack of iron in the diet, causes fiery red gum tissues. Both of these anomalies can be corrected with proper nutrition and routine care.

Other anomalies

Concrescence is the fusion of teeth above and below the gum line, although each tooth has separate roots. The teeth are united by cementum only. It may be caused by crowding or injury. Most commonly it occurs with the second premolars (bicuspids). This is a painless anomaly and treatment is required only for cosmetic reasons.

Supernumerary teeth are extra permanent teeth that may or may not erupt and can be found anywhere in the mouth. The most common is the mesiodens, a small tooth with a cone-shaped crown and a short root situated between the maxillary central incisors. Heredity may play a role in the development of supernumerary teeth, but other factors are thought to contribute as well. Supernumerary teeth can be extracted with no harm to the patient.

Diagnosis

Dental anomalies can be evidence of systemic disease and may have more than one cause. After weighing the patient's symptoms, pain (if any), health risks, family history, aesthetic considerations, treatment costs, and insurance coverage, the dentist will decide whether to treat or simply monitor the condition.

Treatment

Treatment is intended to eliminate or diminish the defect, manage pain, and alleviate the patient's concerns. Treatment may progress in multiple phases, including a program of continuing care that allows the dentist or doctor to evaluate the treatment's effectiveness.

In most cases, surgery can correct the deformity. Cleft lips are usually repaired before the infant is a month or two old, with excellent cosmetic and functional results. Surgical repair of a cleft palate, however, is not usually performed until the patient is approximately eighteen months old, to minimize the risk of damaging important growth centers. Psychological services are often included as part of the treatment along with speech and hearing services.

Depending on the severity of the anomaly, treatment can be expensive, but medical and dental insurance can help limit out-of-pocket expenses for the patient. Sometimes treatment will be covered by medical insurance if procedures are performed by an oral surgeon or medical doctor instead of a dentist.

Prognosis

Although many orofacial anomalies are currently managed, rather than treated, the rapid advance of science-such as the ability to identify mutated genes-promise future cures and treatments that will eliminate or reduce the number of defects currently seen. Gene therapy may also someday be applied to the treatment of many craniofacial anomalies, both to repair congenital defects and to accelerate healing after trauma. Gene mapping may also help doctors know which patients are susceptible to what type of anomalies.

The NIDCR is the primary sponsor of craniofacial research and training in the United States. The institute supports a variety of projects, including basic studies of cell migration and differentiation, cell signaling, patterns of gene expression, growth factor effects, tooth formation and eruption, and bone formation. These studies explore the genetic and molecular mechanisms behind craniofacial abnormalities and are intended to prevent or correct the anomaly or improve the patient's ability to function with it.

Health care team roles

No one specialist can provide the range of treatment that is frequently needed for many dental anomalies. The most effective management is accomplished with a team of professionals who can render a comprehensive diagnosis, determine treatment needs and priorities, and supervise long-term planning. A list of physicians and specialists required to treat a craniofacial deformity might include: plastic surgeon, otolaryngologist (ear, nose, and throat specialist), audiologist, speech-language pathologist, oral/maxillofacial surgeon, orthodontist, pediatric/family dentist, dental hygienist, prosthodontist, and geneticist or genetic counselor.

Prevention

The ADA advises dentists to discourage patients from using tobacco and illicit drugs, and to emphasize sound nutrition to maintain oral health and prevent nutritional anomalies. The NIDCR encourages clinical studies to diagnose genetic anomalies, decrease environmental risks, and improve treatment. Genetic counseling, mapping, and testing can help prevent dental anomalies in the next generation of children.

Key Terms

Anomaly

A deformity or abnormality.

Bridge

A dental prosthesis covering an open space in the mouth.

Cementum

A bony substance that covers the root of the tooth.

Condyle

The uppermost end of the mandible that sits in the zygomatic arch and allows the jaw to move.

Congenital

Present at birth; a nonhereditary condition acquired in utero.

Crown

1. The natural part of the tooth covered by enamel. 2. A restorative, protective shell that fits over a diseased or malformed tooth.

Decalcification

The wearing away of the enamel on the teeth.

Etiology

Cause or origin.

Extraction

Removal of the tooth.

Genetic

Inherited from the parents.

Mandible

Jaw, especially the lower jawbone.

Maxillary

Relating to the upper jaw region.

Maxillary central incisors

The front teeth on the upper jaw.

Maxillary lateral incisors

The teeth on the right and left quadrants of the upper jaw next to the front centrals.

Root canal therapy

Removal of the pulp of a tooth.

Veneer

A thin porcelain overlay that covers only the anterior surface of a tooth.