Temporary Anchorage Devices in Orthodontics- Review

INTRODUCTION
Traditionally, orthodontists have used teeth, intraoral appliances, and extraoral appliances, to control anchorage— minimizing the movement of certain teeth, while completing the desired movement of other teeth. However, because of Newton’s third law, ie, for every action there is an equal and opposite reaction, there are limitations in our ability to completely control all aspects of tooth movement. For example, we often have inadequate mechanical systems with which to control anchorage, which leads to anchorage loss of reactive units and often incomplete correction of intra- and interarch alignment problems. Moreover, in an attempt to overcome these limitations, clinicians often incorporate bulky acrylic appliances or extraoral appliances that, when combined with the ever challenging problem of uncooperative patients, are often a futile attempt at best.1
The use of implant anchorage simplifies orthodontic treatment by sparing us the need for patient compliance and the complexity of treatment. Among different type of anchor implants, the bone screws seemed to be more popular and widely accepted by orthodontists, because they offer several advantages over the other systems: smaller fixture, easier surgical procedures and less trauma, lower cost and risk, more clinical indications
IMPLANT TERMINOLOGY
Implant: As defined by Boucher Implants are alloplastic devices which are surgically inserted into or onto jaw bone. Osseointegration: An intimate structural contact at the implant surface and adjacent vital bone, devoid of any intervening fibrous tissue.
PARTS OF IMPLANT
The commonly used implant screw/plate has two parts -
a) Implant head, which serves as the abutment and in the case of an Orthodontic implant, could be the source of attachment for elastics/ coil-springs
b) Implant body, which is the part embedded inside bone. This may be a screw type or a plate type -which is flatter and can be used in resorbed and knife edged ridges. The plate design that has been used in Orthodontics as the skeletal anchorage system varies from these conventional plate implants. (Fig.1)

CLASSIFICATION OF IMPLANT
Implants can be broadly classified under the following headings:
Based on the location
Subperiosteal ; In this design, the implant body lies over the bony ridge. This type has had the longest history of clinical trials but a decreased long-term success rate; probably due to the fact that the chances of getting it dislodged are high. Also, the complexity of their designs requires a precise casting procedure. The subperiosteal design currently in use for orthodontic purposes is the 'Onplant'.
Transosseous ; In this particular variety, the implant body penetrates the mandible completely. These have enjoyed good success rate in the past. However they are not widely used because of the possible damage to the intrabony soft tissue structures like the nerves and vessels. Even in the field of Orthodontics, transosseous implants have not been used Endosseous ; These are partially submerged and anchored within bone. These have been the most popular and the widely used ones. Various designs and composition are available for usage in specific conditions. The endosseous implants are also the most commonly employed types for orthodontic purposes.
Based on the configuration design .
Root form implants: These are the screw type endosseous implants and the name has been derived due to their cylindrical structure Blade / Plate implants: According to the composition
Stainless steel, Cobalt-Chromium-Molybdenum (Co-Cr-Mo), Titaniu, Ceramic Implants, Miscellaneous such as Vitreouscarbon and composites
According to the surface structure Threaded or Non-threaded: The root form implants are generally threaded as this provides for a greater surface area and stability of the implant.
Porous or Non Porous: The screw type implants are usually non porous, whereas the plate or blade implants (non threaded) have vents in the implant body to aid in growth of bone and thus a better interlocking between the metal structure and the surrounding bone.

ANCHORAGE PURPOSE

Orthopedic – Maxillary expansion, Maxillary Protraction.

Orthodontic – Intrusion, space closure, Distalization.

PLACEMENT OF TEMPORARY ANCHORAGE DEVICES

Insertion technique Proper angle of insertion is important for cortical anchorage, the patient’s safety and biomechanical control. In the posterior maxilla, the angle of insertion should be 30 to 45 degrees to the occlusal plane.2 Steeper angulation (< 30 degrees) minimizes the risk of root perforation but may increase the risk of miniscrew slippage. In the anterior maxilla and posterior edentulous maxilla, the angle of insertion should approximate 90 degrees to the occlusal plane (parallel to the paranasal sinus floor) to minimize perforation of the sinus. 3 This allows for a more gingival position of the TAD head, which is biomechanically advantageous during molar intrusion. In the mandible, the angle of insertion should be 30 to 45 degrees to the occlusal plane to increase the surface area contact between the miniscrew and the thicker cortical bone.2 A surgical stent made of orthodontic wire can be used to guide insertion.(Fig.2)

A recommended sequence of procedures for inserting miniscrews (modified Cope Placement Protocol™)4,5  include the following:

In many instances, the tissue punch and predrilling may be omitted (such as when a self-drilling screw is placed within the attached gingiva of the maxilla).

FORCE LOAD
In regard to stationary anchorage, numerous articles have recommended loading forces of 300 grams of force or less.6,7,8 Dalstra and colleagues9 suggested loading forces of 50 g in regions of thin cortical bone and fine trabecula. Buchter and colleagues8 reported that TADs inserted into dense mandibular bone remained clinically stable at forces up to 900 g. In regions of poor bone density, simply placing a longer screw or applying lighter force does not ensure stationary anchorage.10 Intrusive force should be light and continuous to produce the appropriate pressure within the periodontal ligament and minimize the risk of root resorption.11 Kalra and collagues12 used 90 g of force to intrude maxillary molars in children; Melsen and Fiorelli13 used 50 g of force to intrude maxillary molars in adults. Park and colleagues14 used 200 g of force for miniscrew-supported maxillary molar intrusion, and Umermori and colleagues15 used 500 g of initial force for miniplate-supported mandibular molar intrusion. The recommended force for miniscrew-supported maxillary molar intrusion is 100 to 200 g. En-masse intrusion of the second premolar and the first and second molar requires greater force, approximately 200 to 400 g per side.16,17

REMOVAL OF THE IMPLANTS
Can be done easily because complete osseointegration does not occur and it is removed by engaging the head of the microimplant. It is very important for a patient to maintain the oral hygiene. While placing the implants we should be careful that we don’t damage the root surface and even after the placement its position should be verified by periapical radiograph.

FUTURE OF IMPLANT
The ideal implant design would be one that would be simple to place as well as remove, causing minimum discomfort to the patient. At the same time, they should be optimum in resisting the conventional Orthodontic forces. One would be looking at newer designs, which could be placed by an Orthodontist himself. Also, since the implants need not last for a very long time, biodegradable implants may be a lucrative option. Biodegradable screws made of L-polylactide have been introduced by Glatzmaier et al and are currently undergoing clinical trials. The system, termed as the BIOS (Bioresorbabale implant for Orthodontic systems) consists of resorbable polylactide with a metal abutment.

CONCLUSION
Implants for the purpose of conserving anchorage are welcome additions to the armamentarium of a clinical Orthodontist. They help the Orthodontist to overcome the challenge of unwanted reciprocal tooth movement. The presently available implant systems are bound to change and evolve into more patient friendly and operator convenient designs. Long-term clinical trials are awaited to establish clinical guidelines in using implants for both orthodontic and orthopedic anchorage.

REFERENCES

1. Jason B. Cope. Temporary Anchorage Devices in Orthodontics: A Paradigm Shift. Semin Orthod 11:3-9 © 2005 Elsevier.
2. Carano A, Velo S, Leone P, Siciliani G. Clinical applications of the Miniscrew Anchorage System. J Clin Orthod 2005;39(1):9–24.
3. Kravitz N, Kusnoto B. Dual-Top Anchor Mini Orthoscrews: seminar manual—UIC Clinical Test Protocol 2005. Denver: Rocky Mountain Orthotics; 2005:17–40.
4. Cope JB, Herman RJ. The ortho implant system. In: Cope JB, ed. OrthoTADs: The Clinical Guide and Atlas. Dallas: Under Dog Media LP; 2006.
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11. Proffit WR. Contemporary orthodontics. 3rd ed. St. Louis: Mosby; 2000.
12. 1Kalra V, Burstone CJ, Nanda R. Effects of a fixed magnetic appliance in the dentofacial complex. Am J Orthod Dentofacial Orthop 1989;95(6):467–78.
13. Melsen B, Fiorelli G. Upper molar intrusion. J Clin Orthod 1996;30(2):91–6.
14. Park YC, Lee SY, Kim DH, Jee SH. Intrusion of posterior teeth using mini-screw implants. Am J Orthod Dentofacial Orthop 2003;123(6):690–4.
15. Umemori M, Sugawara J, Mitani H, Nagasaka H, Kawamura H. Skeletal anchorage system for open-bite correction. Am J Orthod Dentofacial Orthop 1999;115:166–174.
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17. Erverdi N, Keles A, Nanda R. The use of skeletal anchorage in open bite treatment: a cephalometric evaluation. Angle Orthod 2004;74(3):381–90.