Abstract
The incorporation of miniscrews into orthodontic treatment planning has allowed for predictable control of anchorage and has increased the ability to correct severe skeletal discrepancy with nonsurgical orthodontics. It is the goal of this article to review the terminology, design, placement, and activation of miniscrews, as well as the advantages and complications associated with their use so that the multidisciplinary team will become familiar and comfortable with this novel treatment modality.

The aims of orthodontic treatment include providing the patient with a stable and functional occlusion that provides dental and facial esthetics while promoting the long-term health of the periodontium and temporomandibular joints. These aims have been traditionally achieved with orthodontic bands and brackets, orthopedic appliances, extraction of teeth, and orthognathic surgery.

Recently, a new anchorage device has been added to the orthodontic armamentarium that allows for more predictable achievement of these goals, the orthodontic miniscrew. Miniscrew use is arguably the most frequently discussed topic in orthodontics today and is becoming a topic of discussion in periodontics as orthodontists are seeking the services of periodontists for this technique-sensitive procedure. General dentists should be familiar with orthodontic miniscrews because patients who receive this treatment can achieve a higher quality result and will inevitably be co-treated in general and specialty dental offices.

Design and Placement

Orthodontic miniscrews, often referred to as microscrews, temporary anchorage devices (TADs), orthodontic implants, or mini implants, are small, machined titanium screws placed in the alveolar or basal bone of the maxilla or mandible to provide an anchor for orthodontic tooth movement. Unlike endosseous dental implants that rely on osseointegration for ultimate stability, these screws rely on cortical bone for mechanical stability immediately at placement. Cortical bone at the neck of the miniscrew is the basis of orthodontic miniscrew retention, and this osseous interface is critical for stability without any expectation of osseointegration.

Figure 1—A majority of miniscrews marketed today are self-drilling with a tapered core and dual thread, making them easy to place. Jeil Medical Corporation, #702, Kolon Science Valley II, 822, Guro-ku, Guro-dong, Seoul 152-050, Korea; www.jeilmed.co.kr. Distributed by RMO, Inc., P.O. Box 17085, Denver, CO 80217; www.rmortho.com.	Figure 2—Miniscrews are available in various head designs, with variations of the button (left) and bracket design (right) shown here in the RMO Dual-Top Anchor System, which is the most common and versatile. Jeil Medical Corporation, #702, Kolon Science Valley II, 822, Guro-ku, Guro-dong, Seoul 152-050, Korea; www.jeilmed.co.kr. Distributed by RMO, Inc., P.O. Box 17085, Denver, CO 80217; www.rmortho.com.
Figure 3—En masse retraction of the upper right sextant via direct anchorage. A Ni-Ti coil is tied directly from the button head of the miniscrew to the upper right canine, resulting in a distalization force to correct the class II canine and molar relationship.	Figure 4—Molar uprighting via indirect anchorage. A 0.019 in x 0.025 in stainless steel wire is bonded to the lower right first premolar and tied into the bracket head of the miniscrew with a stainless steel ligature. A 0.020 inch round stainless steel wire with a composite stop and an open-coil spring provide the distalization and intrusion forces on the lower right second molar, using the first premolar as the anchor.

Titanium miniscrews can be classified according to external diameter, intraosseous design/shape (straight and tapered), and insertion method (predrilling and self-drilling). In general, these screws range in diameter from 1.4 mm to 2.3 mm and in length from 5 mm to 12 mm. Most of these screws have a self-drilling tip (Figure 1), allowing for placement with a manual hand screwdriver or reduction handpiece, such as those used in endosseous implant placement, at 1 rotation every 5 to 10 seconds without the need for a pilot drill osteotomy. In situations where cortical bone is dense, such as in the anterior mandible or palate, a pilot drill can be used to create an entry point for the miniscrew.

In arriving at a patient's orthodontic diagnosis indicating benefit from miniscrew-aided treatment, the orthodontist prepares the patient for miniscrew placement by providing adequate interradicular space through proper root positioning. Periapical or vertical bitewing radiographs are used, often with radiographic markers, to assure sufficient interradicular distance of no less than 2 mm. The patient is then referred to the periodontist or oral surgeon, topical or local anesthesia is used to anesthetize the location of screw placement, and the screw is placed so that the head of the screw protrudes minimally from the soft tissue, minimizing patient discomfort and soft-tissue irritation.

Activation

Most of these screws have button or bracket head designs (Figure 2) to which various orthodontic auxiliaries can be attached, including elastic chain or thread, nickel titanium or stainless steel springs, steel ligatures, orthodontic wire, or composite-bonded wire. Using mini-screws as direct anchorage means the auxiliaries are directly attached from the screw to the tooth, teeth, or archwire that is to be moved (Figure 3). Indirect anchorage means using the auxiliaries to attach to a tooth, teeth, or appliance, which can then be used as an anchor to move adjacent teeth (Figure 4). Regardless of activation type, the goal of miniscrew use is absolute control of tooth movement, without movement of teeth that are not to be moved, using as few orthodontic brackets and appliances as needed to achieve different types of tooth movement.

Figure 5—This patient presented with an upper left canine that had erupted into the congenitally missing lateral position. As a result, the upper left primary canine was retained. The patient and parents chose to have the canine distalized and the lateral replaced as opposed to canine substitution.	Figure 6—Miniscrew-aided orthodontics was chosen because the posterior occlusion at initial presentation was class I and the upper midline was coincident with both the lower dentition and the face. The upper left primary canine was extracted and the crown reduced in width and placed on the 0.020 stainless steel wire for esthetics.
Figure 7—The lever arm, bent from 0.019 in x 0.025 in stainless steel wire, activated with power thread provides a distalization force close to the center of resistance of the canine, minimizing tipping of the tooth distally and assuring proper final root position.	Figure 8—At the completion of canine distalization, which took approximately 7 months, a prosthetic lateral incisor was placed on the orthodontic arch wire. Despite mild tissue overgrowth around the head of the miniscrew, removal was performed with only topical anesthesia and minimal patient discomfort.

Advantages

Traditional orthodontic mechanics are plagued with the inability to provide ideal tooth position without at least a minimal effect on surrounding teeth and soft and hard tissues. A prime example is closure of premolar extraction spaces in the maxilla in which only movement of the anterior teeth distally is desired, which is called maximum anchorage. Traditionally, a variety of modalities including transpalatal bars, headgear, a Nance button, tipback bends or stops in the archwire, or class II elastics have been used to achieve this result. Despite these attempts at anchorage preservation, even the most adept orthodontist will admit to minimal movement of the posterior teeth anteriorly (losing anchorage) in some, if not all, of these cases. Maximum anchorage is, therefore, not absolute anchorage. The introduction of miniscrews into the orthodontic armamentarium allows for mechanics that essentially assure no loss of anchorage (ie, absolute anchorage).

Figure 9—The postdistalization radiograph indicates bodily movement of the canine with acceptable root positioning for continuation of the remaining 8 months of orthodontic treatment.

In addition to providing absolute anchorage, miniscrews allow for tooth movement that was essentially impossible before. Significant intrusion or distalization of teeth, in which both the crown and root(s) of groups of teeth are ideally positioned ("en masse" movement), is extremely difficult with traditional orthodontic biomechanics (Figures 5-9). It would be a gross overstatement to say that these movements cannot be achieved with traditional orthodontic mechanics; however, the side effects of these movements, including proclination of incisors and extrusion of posterior teeth with resultant opening of the bite, are often undesirable and counterproductive. Miniscrews allow for greater predictability and reliability in these movements with minimal or no side effects and with less need for patient cooperation.

Last, implementing miniscrews into orthodontic treatment planning has allowed the orthodontist to expand the "envelope" or treatment potential of nonsurgical orthodontics. When traditionally treatment planned, many orthodontic patients are candidates for surgical correction of their malocclusions. These procedures are, however, often unrealistic from a cost-to-benefit standpoint, and an alternative in treatment is sought. A typical example is a patient with a mild anterior open bite in which the anterior teeth of both the maxilla and mandible are ideally positioned within alveolar bone and the posterior teeth are normally positioned or slightly extruded (Figures 10-13). An attempt at closing the anterior open bite by extruding anterior teeth may not be desirable from an esthetic standpoint and may compromise the patient's periodontal health. These cases may be amenable to intrusion of posterior teeth to close the bite and provide a periodontally stable, functional occlusion that is also esthetically acceptable.

Although miniscrews will never completely eliminate the need for surgical orthodontic treatment, there is a place for miniscrew use as an alternative in many borderline surgical cases for excess vertical dimension (open bite) and retraction of teeth for profile change. In addition, the miniscrew is extremely helpful with the treatment of complex interdisciplinary cases, which can be simplified with fewer orthodontic brackets and appliances to achieve better tooth position for periodontal and restorative reasons.

Figure 10—When teeth are acceptably positioned within bone for stability and periodontal health, this patient demonstrates a skeletal openbite. Attempts at closing this openbite orthodontically predisposes this patient to relapse and periodontal problems.	Figure 11—The skeletal openbite can be clearly seen on this lateral cephalometric radiograph, taken with the condyles seated in the mandibular fossa.
Figure 12—Four months after intrusion of both the maxillary and mandibular posterior teeth, the bite has closed, allowing for positive overbite. Orthodontic detailing can now be performed to finalize the occlusion.	Figure 13—The postintrusion lateral cephalometric radiograph, taken with the condyles seated in the mandibular fossa, demonstrates closing of the anterior openbite and a decrease of the mandibular plane angle.

Complications

Potential morbidity is associated with any dental procedure, and a discussion of miniscrew use would be incomplete without outlining possible complications. Miniscrew placement does require an additional periodontal procedure above and beyond the traditional orthodontic treatment plan. This often involves local anesthesia, possible surgical flap, and the technique-sensitive placement of the miniscrew at the exact location needed for proper orthodontic activation. This may involve referral to a periodontist or oral surgeon for a procedure not often covered by insurance. This increases the cost to the patient, not to mention the additional time commitment.

Precise placement of miniscrews should be performed by a dental professional with a thorough understanding of soft- and hard-tissue anatomy, surgical response, and healing. Periodontists and oral surgeons often have the clinical expertise and knowledge base to maximize results with this treatment modality.

It is widely accepted that successful maintenance of the miniscrew is improved when it is placed in keratinized tissue vs oral mucosa, not only from research in this area¹ but from knowledge gained from basic periodontal and endosseous implant technique,² although at least 1 report has suggested no difference in success relative to surrounding tissue type.³ Restriction of tissue movement around the soft-tissue collar of the miniscrew is desirable during the course of activation. Regardless, ideal miniscrew placement for orthodontic activation in a particular situation may be necessary in an area of alveolar mucosa in the buccal vestibule. This may lead to inflammation and an increased failure rate of the mini-screw,^3,4 often manifested by the loosening of the screw to a point at which it can no longer be activated or possible complete loss of mechanical stability within cortical bone.

Even with proper technique and placement in keratinized tissue, miniscrew failure may occur. Additionally, minor errors in placement (wobbling or poor accessibility) may render the miniscrew unusable by the orthodontist or may cause damage to roots of adjacent teeth (with inadequate interradicular space). However, because complications are few, advantages and clinical applications favor the use of the miniscrew for successful treatment.

Completion of Treatment

Upon completion of treatment, miniscrews can be removed with the same handle or screwdriver used to place them, often without the need to anesthetize the patient. If soft-tissue inflammation or overgrowth has occurred around the head of the screw, topical anesthetic is usually adequate for miniscrew removal. Soft-tissue healing is usually uneventful, and any minor complications can be addressed by the periodontist.

Despite the surface of most miniscrews being machined type 5 titanium, the minimal surface area of the screw because of its small diameter and length makes any osseointegration that may have occurred clinically insignificant. Removing the miniscrew yields little resistance to unscrewing, unlike attempts to remove an osseointegrated endosseous implant. If a miniscrew is removed along the same axis as it was placed with little or no torquing of the head, the high-grade titanium with increased tensile strength makes screw fracture at removal extremely rare.

Conclusion

Miniscrews are an enormously helpful adjunct in orthodontic treatment planning. With communication between skilled specialists and proper planning and execution, miniscrew use can both simplify orthodontic treatment and allow for superior treatment not previously possible. The increased cost and time commitment of both the dentist and patient are well worth the added benefits of occlusal and periodontal health afforded by mini-screw use, especially when considered over the long-term. As more dental professionals realize the benefits of miniscrew-aided orthodontics, this treatment modality will become increasingly acceptable to the profession, as well as to patients, and it will dramatically improve orthodontic diagnosis and treatment in the future.

References

1. Cheng SJ, Tseng IY, Lee JJ, et al. A prospective study of the risk factors associated with failure of mini-implants used for orthodontic anchorage. Int J Oral Maxillofac Implants. 2004;19:100-106.
2. Schou S, Holmstrup P, Hjørting-Hansen E, et al. Plaque-induced marginal tissue reactions of osseointegrated oral implants: a review of the literature. Clin Oral Implants Res. 1992;3:149-161.
3. Park HS, Jeong SH, Kwon OW. Factors affecting the clinical success of screw implants used as orthodontic anchorage. Am J Orthod Dentofacial Orthop. 2006;130:18-25.
4. Miyawaki S, Koyama I, Inoue M, et al. Factors associated with the stability of titanium screws placed in the posterior region for orthodontic anchorage. Am J Orthod Dentofacial Orthop. 2003;124:373-378.