Key points
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Skeletal anchorage devices enhance the versatility and expand the range of traditional orthodontic therapy.
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Rapid and reliable movement of teeth can correct some deformities that were previously only possible with invasive orthognathic surgery.
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Proper placement of devices and communication with the orthodontist are crucial to successful treatment with anchorage devices.
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Devices can be placed in the office setting in a matter of minutes without the added time, expense, and risk of treating patients in the operating room.
The placement of temporary skeletal anchorage devices is becoming increasingly common for surgeons in the office. These devices provide advantages for orthodontists and surgeons as well as patients. There are several types of skeletal anchorage device that all attempt to enhance the capabilities of traditional orthodontics.
Skeletal anchorage can provide results where traditional methods fall short. Traditional techniques involve moving a small number of teeth using a greater number of other teeth for anchorage. For difficult orthodontic movements such as distalization of molars or closure of an anterior open bite, these traditional methods provided little, if any, chance of long-term success. Other methods rely heavily on patient compliance for maintenance of elastics or headgear to provide appropriate vectors of force. Often these are unable to produce the desired movements.
Many patients and providers have opted for orthodontic camouflage of malocclusions with suboptimal results. Those who desire an optimal final result may require orthognathic surgery to correct skeletal discrepancies. However, orthognathic procedures are costly with lengthy recovery periods. They also carry considerable surgical risks of anesthesia, bleeding, nerve damage, necrosis of maxillary segments, and bad splits of the mandible. Several methods of skeletal anchorage have been developed to overcome these challenges and provide an expanded range of capabilities for the orthodontist.
Advantages of skeletal anchorage
Through the use of skeletal anchorage devices, some significant orthodontic changes can be made. Intrusion of teeth (even multiple teeth) can be accomplished quickly and easily without extruding the anchoring segment. With the intrusion of posterior teeth, the occlusal plane can be changed, leading to autorotation of the mandible, changes in lower facial height, and closure of anterior apertognathia. The procedures are simple to perform and can be done in the office with local anesthesia alone or in combination with intravenous (IV) sedation. The risks are minimal and, after a short healing time, the orthodontist can rapidly move teeth and decrease the overall orthodontic treatment time while avoiding problems with patient compliance.
Advantages of skeletal anchorage
Through the use of skeletal anchorage devices, some significant orthodontic changes can be made. Intrusion of teeth (even multiple teeth) can be accomplished quickly and easily without extruding the anchoring segment. With the intrusion of posterior teeth, the occlusal plane can be changed, leading to autorotation of the mandible, changes in lower facial height, and closure of anterior apertognathia. The procedures are simple to perform and can be done in the office with local anesthesia alone or in combination with intravenous (IV) sedation. The risks are minimal and, after a short healing time, the orthodontist can rapidly move teeth and decrease the overall orthodontic treatment time while avoiding problems with patient compliance.
Methods of skeletal anchorage
Three main devices have been used to provide anchorage. Endosseous dental implants were first used as a means of providing an immobile device for the application of force. Although dental implants can be simple to place, they are permanent and have several drawbacks compared with newer temporary devices. Dental implants are costly and require a substantial amount of bone for placement, which limits the options for appropriate placement location, and may require placement in edentulous spaces, palatal bone, or in the retromolar areas. Following placement, a delay of several weeks or months to allow for osseointegration is indicated. These drawbacks have largely been eliminated by newer temporary miniscrews and miniplates.
Placement of miniscrews
A miniscrew is a pure titanium or titanium alloy screw that is placed through mucosa directly into bone ( Fig. 1 ) using a hand driver ( Fig. 2 ). They are essentially a simple bone screw and can be placed in a matter of seconds by orthodontists or surgeons. Caution is needed to avoid placing screws into tooth roots, especially when placed through keratinized tissue. Placement in keratinized tissue can also limit the amount of tooth movement because of interference by the screw. This risk can be reduced by placing the miniscrews in a more apical position through nonkeratinized tissue. However, this location caries a higher risk of loosening and failure in these positions according to Cheng and colleagues. Orthodontists must also use caution to avoid placing any angular moment on miniscrews to prevent turning and loosening of the screw ( Fig. 3 ).
Placement of miniplates
Miniplates require more time and skill for placement but carry several advantages compared with miniscrews. They are often used in cases of miniscrew failure and provide a more rigid means of anchorage that can tolerate large forces. The surgeon or orthodontist can choose from a variety of designs but each plate contains a polished isthmus that extends through the mucosa to connect to the intraoral hardware. Self-drilling screws are used to secure the plate directly to bone in a variety of locations without damaging the roots of nearby teeth. The plates allow improved direct and indirect leverage and rapid movement of teeth.
Miniplate placement in the maxilla and mandible follow a few simple rules. Plates are placed apical to the tooth roots, and therefore do not interfere with tooth movement. In the maxilla, plates are placed in areas of thicker cortical bone at the buttresses of the piriform rim or zygomaticomaxillary buttress ( Fig. 4 ). The isthmus travels through the mucosa with the attachment device positioned near or slightly apical to the dental segment and adjacent to the keratinized mucosa. The plates are malleable and easily bent to fit the bony contours.
It is not advisable to place miniplates along the anterior wall of the maxillary sinus. The bone is thin in this area and could lead to loosening of screws and loss of anchorage over time.
The mandible provides sufficient cortical bone thickness for placement of stable plates and screws in nearly any location. However, the mental nerve must be considered when planning incision design and plate placement. In the posterior regions, an incision is typically made similarly to incisions used for third molar removal or sagittal split operations for advancement or setback of the mandible. Plate placement here is far away from mandibular tooth roots and does not endanger the inferior alveolar nerve ( Fig. 5 ). The position allows intrusion of the posterior segment, distalization of molar teeth, and uprighting of mesioangular teeth.
