What are orthodontics?

Science and Profession

The term “orthodontics” comes from the Greek words meaning “straight teeth.” It is practiced by a dental specialist called an orthodontist. Orthodontists graduate from dental school and then specialize in orthodontics. To explore orthodontics as a field, one must first consider teeth and the mouth. Ideally, thirty-two human teeth are arranged in appropriate orientations in the dental arches of each jaw. Four incisors are located in the center of each arch; on either side of them are a cuspid or canine tooth, followed by two bicuspids (premolars) and three molars.

The first molar on the side of each jaw is viewed as particularly important to orthodontics. Appropriate tooth development within the jaw and correct tooth eruption enable proper dental health, which keeps teeth in the mouth for most of an individual’s life. They also ensure appropriate mastication of food and good digestive health, as well as self-confidence with an attractive smile.

Teeth are rarely optimally placed in the jaws. One important reason for this is heredity. This facet of orthodontics relates to the teeth and to jaws. The genes that control the size and shape of human teeth and jaws vary considerably. In addition, the genes for teeth and jaws are highly individualized and often poorly related to one another. Hence, it is likely that orthodontic problems caused by tooth-jaw mismatch will occur.

Other aspects of the development of irregular tooth positioning arise from living. In some cases, teeth are damaged by decay, oral diseases, or injury. In others, poor oral habits such as thumb sucking move them out of appropriate positions. In many cases, minor problems may be handled by restorative dentistry, such as filling dental caries (cavities) or placing crowns. Most treatment of poorly positioned teeth, however, is carried out by orthodontists on nearly 5 million Americans per year. The majority of these patients are children, but many adults are presently undergoing orthodontic treatment.

There are several main goals of orthodontic treatment involving the bones of the jaws and the teeth. First, occlusion is improved so that all teeth engage one another properly for chewing and swallowing. Speech patterns are also improved, because almost twenty letter sounds in the English language involve interactions between tooth, tongue, and jaw movements. Another goal is increased resistance to decay and periodontal disease, which cause havoc in mouths where teeth are too close together or misaligned in other ways. The final orthodontic goal is improved appearance, which is for many individuals the primary reason for undergoing treatment.

Most orthodontic problems are termed malocclusions and are caused by defects of teeth or the jaws. Malocclusions are often classified according to the system developed by Edward H. Angle, the originator of modern orthodontics. He developed three classes of occlusion, defined by relationships between the upper and lower first molars.

In normal occlusion (class I), the lower first molars are seen slightly farther forward than their upper counterparts when the mouth is closed. This relationship positions the rest of the teeth for optimum chewing. When the arch length of either jaw is too small for all the teeth to be in appropriate positions, they become crowded. Also, in some individuals bimaxillary protrusion occurs, in which the front teeth of the jaws flare outward. These occurrences are unattractive and lead both to tooth decay and to periodontal disease.

Classes II and III are malocclusions that can be considered together. They are caused by improper positioning in the closed mouth of the lower first molars, either very far back or very far forward. In the first case (class II), the position of the first molars produces buck teeth because of the protrusion of the upper jaw in the closed mouth. The resulting problems are uncosmetic appearance and the ease with which buck teeth can be knocked out. Class II malocclusion is most often attributable to a hereditary size mismatch of the jawbones. Class III malocclusion is often termed crossbite. It causes the lower jaw to be positioned so that the lower front incisors are in front of the upper ones. In some cases, this problem is treated by orthodontics; in others, surgery is required.

The Angle classification system does not include faulty vertical relationships of the jaws, which produce other problems. Examples are overbite, which hides the lower teeth entirely in the closed jaw, and open bite, which leaves a gap between the upper and lower front teeth in the closed mouth. These situations may be asymmetric and make closures lopsided.

Functional malocclusions are also caused by thumb sucking, chewing of the lower lip, or tongue thrusting. With thumb sucking, class II malocclusion may result or be enhanced, or open bite may occur. Chewing the lower lip will cause the upper front teeth to flare outward, and tongue thrusting (often a consequence of mouth breathing because of asthma) may cause open bite, crossbite, or class II malocclusion.

Defects of the teeth themselves occur as well. They are caused by overretention or underretention of the baby teeth and missing or lost permanent teeth. These conditions cause the remaining teeth to drift in the mouth and should be corrected as soon as possible in order to preclude occlusion problems.

Diagnostic and Treatment Techniques

The first stage of orthodontic treatment is an extensive diagnostic procedure that requires several office visits. First, the orthodontist compiles a complete dental and medical history. Then, the patient’s mouth and teeth are examined thoroughly. This effort, accomplished in one visit, leads to a preliminary treatment plan. During the next visit, complete x-rays of the jaws are taken to show their relationship to each other, dental impressions of the teeth and jaws are made, and color photographs of the face and mouth are taken.

On the third visit, the patient is given a comprehensive diagnosis, and a treatment plan is described. At this point, the patient is informed about the problems to be treated, the probable consequences if they are left untreated, the steps to be used and their duration, the results that are expected, and any possible treatment complications. The overall cost of the treatment is also discussed. After agreement is reached, treatment begins and may require up to several years of visits at varied intervals. The process begins with the use of orthodontic appliances worn to move the teeth to new positions. After this, a simpler appliance called a retainer is worn until the bone of the tooth sockets, remodeled by the earlier treatment, is able to maintain the new dental arrangement.

Patient compliance with treatment instructions is crucial. Short-term noncompliance can lengthen the treatment period greatly; extreme noncompliance may completely destroy the endeavor. Most aspects of modern orthodontic treatment are relatively painless. If soreness occurs, it may usually be relieved quickly by combining saltwater gargles, temporary soft diets, and mild analgesics. Soreness caused by the rubbing of metal appliance parts against the inside of the cheeks or lips may be prevented by application of a wax supplied by the orthodontist. Pain that lasts for more than several days should be reported; it can usually be alleviated by an office visit where the orthodontist adjusts the offending portion of the appliance.

Throughout the course of orthodontic treatment, it is recommended that patients keep careful written records of orthodontic instructions and a complete daily record of use of the orthodontic appliance prescribed. The orthodontic appliances also need to be kept clean, stored carefully if removable, and guarded carefully during sports or other physical activities. The teeth must also be kept clean to prevent tooth decay. In addition, hard or sticky foods must be avoided.

The mechanical devices used by orthodontists vary widely. Their purposes are to direct jaw growth, to move selected teeth, to alter the behavior of the jaw muscles, and to maintain the position of the teeth once they have been moved. These appliances operate on two main principles. First, bone growth slows when pressure is applied against it and accelerates when the bone is kept in traction. This is how desired facial bone growth is attained. Second, when pressure is applied to the bone in tooth sockets, bone growth slows on the side to which the pressure is applied. Conversely, the growth of bone is stimulated on the other side of the tooth. This is the principle that generates tooth movement in the mouth. Applied properly, the combination of jaw and tooth treatment achieves results that can be fine-tuned over the treatment period. A lengthy treatment period ensures the minimum amount of pain while this movement occurs.

There are two main categories among the many orthodontic appliances used: fixed and removable appliances. Each category has numerous subcategories, and there are variants within each subcategory. Fixed appliances are firmly affixed in the mouth for the duration of treatment. They are made of metal cylinders shaped to fit snugly around individual teeth and cemented in position. The main fixed appliance types are bracketed appliances, lingual arch wires, habit control appliances, and space retainers.

Bracketed appliances, usually called braces, move teeth and direct growth of bone in the dental arches. Although braces are often disliked by patients on aesthetic grounds, orthodontists view them as an unrivaled means to cause precise tooth movement and directed bone growth. They are made up of several components. First, bands (metal cylinders) are applied around chosen anchor teeth. Then, metal or sturdy synthetic polymer brackets are cemented to each tooth in positions that determine the direction of the force to be applied to it. Next, arch wires are passed across each bracket to the anchor teeth, where they are attached to the bands. Elastic or wire ligatures keep the arch wires in the brackets at all times.

Much of the pressure that engenders tooth movement comes from the shape of the arch wires and their composition. Elastic bands are also used to provide special treatment to a given tooth or tooth group. These bands must be removed before eating and replaced daily. When necessary, external headgear is used to apply pressure to teeth and/or jaws, either pulling them forward or pushing them backward.

Lingual bracketed appliances, a newer device often called “invisible braces,” are fixed appliances attached to the teeth on the inside of the dental arch. They are not externally visible except for the bands on the anchor teeth. Thus, they are advantageous aesthetically. They do not function as well as standard braces, however, and often interfere with normal speech. Other fixed appliances include lingual arch wires, habit control devices, and space retainers.

A wide variety of removable appliances may also be used. They are either entirely or partly removable by wearers. Removable appliances are most effective when worn constantly, but they can be removed at meals and on special occasions. Their use gives much less precise results than fixed appliances, however, and requires the continuous, unflagging cooperation of patients. Active, partly removable appliances put pressure on teeth and jaws. Functional appliances, which are completely removable, alter the pressure created by the muscles of the mouth and so act on the teeth and bones (for example, lip bumpers, which keep lips away from teeth).

Removable habit control appliances and space retainers are used, respectively, to prevent activities such as thumb sucking and to maintain desired spaces between teeth until the new dental arrangements have stabilized. They are specially designed bands, acrylic plates, or combinations thereof. Space retainers exert enough pressure on teeth to keep them in place but not to move them. Special headgear may also be used as an auxiliary to in-the-mouth appliances. In some cases, diseased or extra teeth must be extracted as part of the treatment regimen.

Perspective and Prospects

Orthodontics has changed markedly since its inception. The changes include efforts at making braces more appealing and a changing clientele, evolving from one in which most patients were children to a population having many adult customers. The new direction in producing more cosmetic bracketed appliances arises from several factors.

First is the development of stronger and better synthetic polymer and ceramic replacements for metals, allowing the creation of materials that are less visible and that still produce the unrivaled therapeutic capabilities of bracketed appliances. A second factor is the interest of adults in orthodontic treatment. This discriminating population wishes to appear as attractive as possible, even in braces, and has both the independence of judgment and the monetary power to drive trends toward the use of such materials.

The adult move toward orthodontics in the United States is founded partly on the funding of orthodontic work by entities as diverse as Medicaid for welfare recipients and third-party group dental insurance plans. In addition, the adult public is being made more aware that it is not necessary to live out life with an unattractive smile simply because orthodontic treatment was not attempted in childhood or adolescence.

Considerable research has been carried out in the treatment of problems associated with orthodontics, including the root tip resorption that often halts such treatment. It is hoped that a combination of these endeavors and factors will continue to improve orthodontics.

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