Orthodontic Treatment in the Primary Dentition
The goals of orthodontic care in the primary dentition should be either intervention for conditions that predispose one to develop a malocclusion in the permanent dentition or monitoring of conditions that are best treated later.1 Some conditions can be effectively managed, and the result provides a long-term benefit. With other conditions, treatment should be deferred.
The clinician needs to differentiate skeletal problems from dental problems in order to fulfill these goals. Treatment of skeletal malocclusions in this age group is ordinarily deferred until a later age; the delay is generally for more practical reasons, not because of an inability to alter skeletal structure at this age. Three general reasons are offered for delaying treatment. First, the diagnosis of skeletal malocclusion is difficult in this age group. Subtle gradations of skeletal problems and immature soft tissue development make clinical diagnosis of all but the most obvious cases difficult. Second, although the child is growing at this stage, the amount of facial growth remaining when the child enters the mixed dentition years is sufficient to aid in the correction of most skeletal malocclusions. Third, any skeletal treatment at this age requires prolonged retention (really active treatment over a sustained period of years to maintain the correction) because the initial growth pattern tends to reestablish itself when treatment is discontinued.
Skeletal problems are addressed only if there is progressive asymmetry as a result of a functional disturbance.2 The reason for treating these patients early is that treatment at a later time may be more difficult and complex if the child continues to grow asymmetrically and if dental compensation increases. The goal of early treatment is to prevent the asymmetry from becoming worse or to alter growth so that the asymmetry improves. The majority of progressive asymmetry patients are treated first with removable functional appliances that are designed to alter growth by manipulating skeletal and soft tissue relationships and allowing differential eruption of teeth. Orthognathic surgery is a second treatment for progressive asymmetry but is reserved for patients with the most severe asymmetry or those whose condition does not respond to functional appliance therapy. It may be necessary to operate a second time when the child is older because growth often tends to remain asymmetric even after surgical correction. Because diagnosis and treatment of progressive asymmetry are difficult, it is recommended that these cases be referred to a specialist for evaluation and treatment.
Early evaluation of patients with dentofacial anomalies is also advocated. Dentofacial anomalies include a number of environmentally and genetically induced conditions that alter the relationship of the facial structures. Examples of such anomalies include cleft lip and palate, hemifacial microsomia, Crouzon and Apert syndromes, and mandibulofacial dysostosis (Treacher Collins syndrome). A specialist or specialty team works to minimize the facial disfigurement through early surgical and orthodontic intervention.
Selected dental malocclusion in the primary dentition is readily managed by the practitioner who has knowledge of fixed and removable appliances. The key to successful orthodontic management is careful diagnosis and treatment planning, which depend on the database obtained at the initial examination. In this age group, tooth movement usually is restricted to tipping teeth into the proper position, such as anterior crossbite correction. Rarely are orthodontic appliances designed to move teeth bodily indicated, but posterior crossbite correction is one of those.
Before specific treatment problems are discussed, the biology of tooth movement should be reviewed briefly. A force applied to a tooth causes alterations in the periodontal ligament and surrounding alveolar bone. Recent reviews of bone cell biology show that the osteoblast plays a significant role in tooth movement. Studies have indicated that the osteoblast dictates both the resorptive and formative phases of bone remodeling. In addition, the osteoblast is a receptor for many of the resorptive agents in bone. Prostaglandin production and cyclic adenosine monophosphate elevation are thought to be the primary mediators associated with tooth movement and bone remodeling. These messengers interact with the cell membranes. Change in shape of individual cells through mechanical stress in the biological system may also have a role in initiating metabolic activity.3
After the bone remodeling process begins, the tooth starts to move. When the tooth has moved a certain distance, the force exerted by the orthodontic appliance diminishes to an amount below that necessary for tooth movement. During this time, remodeling is completed and the periodontal ligament and alveolar bone cells begin to return to their normal state. This reorganization period is necessary to prevent injury to the tooth and supporting structures. The clinical implication of cellular change, tooth movement, and cellular reorganization is that orthodontic appliances should be reactivated only at 4- to 6-week intervals with a light, continuous force to avoid injury to the periodontium. Therefore there is some biological basis for the recommendation of monthly visits during orthodontic treatment. After tooth movement is complete, the patient enters the retention phase of treatment. Retention is the period of time that the teeth are held in their new position. Retention is necessary because teeth that have been moved orthodontically tend to move back or relapse into their original position after the appliance has been removed. Relapse may be due to many factors; however, gingival changes are a factor. The gingival tissue does not regain its pretreatment shape like bone and periodontal ligament. The gingiva contains a network of gingival fibers that are compressed or stretched during tooth movement. The genes of both collagen and elastin are activated, and tissue collagenase is inhibited. This causes the extracellular matrix of the gingiva to become more elastic and at greater risk for relapse. Reorganization of the gingival tissues most likely requires a full year. Surgical treatment such as a gingival fibrotomy has been shown to overcome instability, indicating the role of gingival fibers in relapse.4 This type of procedure would not be performed in the primary dentition, but could be required in the mixed or permanent dentitions. If surgical treatment is not performed, long-term retention is indicated to prevent relapse.5
The most common arch length problem in the primary dentition is tooth loss. This is managed as outlined in Chapter 25 with space maintenance if the space is adequate. If space has been lost, which can occur in the posterior sextants because of the tooth loss, space regaining can be instituted. A notable situation in which to use space regaining is when the primary first molar is lost prematurely. If the second primary molar is lost, timely placement of the distal shoe is required, to prevent space loss with the eruption of the permanent first molar. Thus the only realistic space regaining in the pri/>