The continuous application of force by an active plate can be achieved by three mechanisms: (1) orthodontic screws, (2) spring components, or (3) elastics.
The clamping effect holds the active plate in the mouth until the teeth are tipped; once the remodeling processes commence, the clamping effect subsides. Additional retentive components are therefore necessary. Spring components that perform corrective functions cannot be used as retentive components. Because the spring force can only be as great as the normal clamping force of the baseplate, its effect will decline after the appliance has been worn for a short period of time.
Active orthodontic appliances include the removable, self-activating plates with which artificial, continuously applied orthodontic forces bring about changes in tooth or mandibular position by means of springs, screws, or elastics (Fig 10-20).
Forms of dysgnathia can be treated with mechanically or functionally effective, active or passive, rigid or elastic appliances. In the case of extreme malpositions, surgical measures may become necessary prior to orthodontic treatment (eg, extraction to eliminate crowding). A fundamental distinction is made in orthodontic treatment devices between removable and fixed appliances.
When a tooth or group of teeth is moved by springs and bands, the appliance has to be supported on other teeth to exert the movement thrust. In the process, the same movement thrust acts on the abutment, which means the teeth to which the appliance is anchored are loaded and may also be moved. Depending on the nature of the fixation of appliances, the distribution of forces in the masticatory system being treated can vary widely. In relation to distribution of forces for orthodontic tooth movements, a distinction is made between the following types of anchorage:
Forces are transferred to teeth by means of orthodontic appliances, and these forces are evident as tensile and compressive effects in the periodontium and produce the necessary remodeling stimuli. Every tooth movement causes areas of compression and tension in the
periodontal ligament, the extent of which depends on the type of movement. Tipping movements produce neutral areas around the center of rotation in the middle of the root, while the pressure and tension peaks are found at the root apex and the alveolar margin. During a parallel shift of a tooth, the areas of compression and tension arise throughout the length of the root.
With regard to the amount of force applied to achieve orthodontic tooth movements, four levels of biologic intensity are defined (Fig 10-9).
It is possible to carry out orthodontically induced tooth movements because the dental attachment apparatus with all its tissue structures is capable of constantly renewing itself and adapting to functional changes. These tooth movements require accelerated, very active remodeling rates in the periodontal ligament and in the hard tissues, especially in the jawbone. In an analysis of remodeling processes, a distinction is made between physiologic
tooth mobility, physiologic tooth migration, and therapeutic changes of tooth position.
Local occlusal deviations, malpositions of teeth, and anomalies in occlusal position can be identified directly in the patient or through the use of orthodontic models. These models are excellent aids to a thorough analysis of an occlusal anomaly and for planning purposes. As a means of measuring the shape of the dental arches and describing the deformations in the arches, these models are even better suited than examination of the patient.
Orthodontics is the specialty involving the description and treatment of anomalies in the regular development of the masticatory system (Fig 10-1).Treatment relates to anomalies of tooth position, defective jaw development, and malocclusions, as well as abnormalities in the development of tooth germs and jaws. Maldevelopment of the dentition can be measured against statistical normal values of an optimal masticatory system. This normal dentition is a correct dentition in which the parts of the system have developed in a functional equilibrium during a process of differentiation.This process is genetically controlled, but it is supported by functional demands during chewing and altered by other influences. Therefore, the result is not always an optimal regular dentition; faulty development, referred to as dysgnathia, can arise.