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May 12, 2008

By Nanci Oliveira De Felippe, DDS, MS, and Maria Therese Galang, DMD, MS

General dentists and specialized clinicians are familiar with both intraoral and extraoral orthodontic appliances utilized to achieve dental and skeletal movement. However, they are not used to seeing "screws" on the patients' oral mucosa. What is going on in the orthodontic world?

What are TADs?

Temporary Anchorage Devices (TADs), or "miniscrews" as they are commonly referred to, are supplemental sources of anchorage during orthodontic tooth movement. Temporary refers to the normal duration of a miniscrew in a patient's oral cavity. It does not have to remain during the entire length of orthodontic treatment, only during the time necessary to reinforce anchorage. Anchorage is defined as the resistance to unwanted tooth movement. Orthodontists have used various devices in the past to try to avoid anchorage loss but none of them were truly absolute sources of anchorage. Clinicians even resorted to using extraoral anchorage appliances such as headgear and facemasks, but today this innovation marks a new era in orthodontics — the era of skeletal anchorage. We are not relying solely on teeth anymore, nor are we relying on patient compliance; this time we are using a "screw" that is anchored on bone.

Contrary to popular belief, skeletal anchorage is not a novel idea. This was published as early as the 1980s by Creekmore and Elklund(1); however, the difference today lies in the design of the devices themselves. TADs have been manufactured so that they are very small, easy to place, relatively easy to use, and minimally invasive.

TAD basics

TADs are essentially miniature versions of dental implants. They have the exact same parts — the implant head, collar, and body — only in a smaller scale. The average length of a TAD is 8-10 mm while the average diameter is 1.6-2.0 mm. The main difference between implants, mini-plates, and TADs is that the former rely on osseointegration, whereas the temporary anchorage device relies on mechanical retention. Osseointegration is not necessary, thus there is no need to wait for three to six months while the bone heals around the implant. In the case of TADs, they can be loaded immediately — at the same appointment as placement!

These devices are mostly Asian or German made. In the United States, 19 companies offer these types of devices. Rocky Mountain Orthodontics (RMO Dual-Top Anchor system), 3M Unitek (Imtec® Ortho Implant), and Dentaurum Inc. (TOMAS), are some examples. These TADs are made of surgical-grade biocompatible titanium. TADs are classified according to size, method of placement, and method of use.(2) As far as size is concerned, they come in different lengths and diameters depending on the manufacturer. For method of placement, there are self-tapping and self-drilling screws. Self-tapping screws are equipped with screws that interlock in the bone usually after a pilot hole is drilled. Self-drilling screws, on the other hand, have self-cutting flutes that drill into bone, thus eliminating the need for predrilling a pilot hole with the use of a handpiece. There are also TADs that are both self-tapping and self-drilling.(3) Finally, they can be categorized in two methods of utilization: direct or indirect anchorage.

Technique

Ideally, the person utilizing the device should be the one placing it for ease of patient management should there be an emergency or any need to reposition, reactivate, or remove the device. Nonetheless, often orthodontists refer their patients to oral surgeons, periodontists, or general dentists for placement of the TADs due to their minimally invasive nature. The advantage of referring is that the nonorthodontist clinician has the proper in-office equipment, especially in cases where a surgical flap is necessary for hard-to-access areas such as the zygomatic ridge or the retromolar pad area.(4) The disadvantage is the extra cost to the patient. Orthodontists who place the TADs themselves usually incorporate the cost of the miniscrew in the patient's total fee thus minimizing any additional financial burden on the patients. Also good to note is that orthodontic malpractice insurance now includes utilization of TADs in their coverage.

With placement of the TAD, sufficient knowledge of anatomy is key. There are areas to avoid depending on the density or quality of bone. Studies by Poggio et al(5) made use of Cone Beam CT scans to determine bone densities in different areas of the oral cavity. Areas to be avoided due to lack of density include the tuberosity area in the maxilla and the canine-first premolar region in the mandible.

Applications

TADs have several clinical applications and have become an important part of the clinical management of orthodontic patients. Most frequently, they are used in molar uprighting, en masse retraction, or to aid in molar distalization. Another application growing in popularity is achieving profile change via orthodontic treatment to avoid orthognathic surgery.

Orthodontic anchorage

Newton's third law states that "every action has an equal and opposite reaction." It is difficult to avoid the reactive force in orthodontic biomechanics. "Absolute anchorage" is only possible by means of miniscrews and osseointegrated implants. Figure 1 illustrates a case where the lower dentition was distalized without any anterior movement of the lower right second molar (Tooth No. 31).

Figure 1 — TADs used in the distalization of the lower dentition.

Often, in severely crowded cases, space gain with tooth extraction is barely enough to align the dentition. This is a typical situation where the orthodontist cannot "afford" to have any anchorage loss or anterior movement of the posterior teeth while aligning the anterior dentition.

Correction of dento-alveolar saggital dysplasia; i.e., when upper and lower arches are either in Class II or III relationship, may be achieved by running interarch elastics to the miniscrew. Again, the miniscrews are used as anchorage, therefore unwanted extrusion of the posterior teeth or proclination of the anterior teeth is avoided.

Profile change

At times, patients are not happy with their profile and lip appearance. Orthognathic surgery is an effective way to correct the skeletal relationship needed for a straight and harmonious profile. Nonetheless not every patient agrees to have a surgical procedure.

The literature supports(6,7) the use of miniscrews to reinforce anchorage while retracting the anterior dentition or advancing teeth. Figure 2 illustrates a case that was treated in 23 months. Four miniscrews were placed — two mesial to the lower first molars (Teeth Nos. 19 and 30) and two buccal and mesial to the upper first molars (Teeth Nos. 3 and 14).

Figure 2 — Treatment rendered orthodontically to avoid orthognathic surgery. Note profile change after 23 months in treatment.

Preprosthodontics

Since it is difficult to predict final tooth position in patients with missing teeth, miniscrews come in handy to reinforce the anchorage needed to move teeth through edentulous space. Figure 3 illustrates a case that was treated with limited (upper arch only) fixed appliances in 18 months. Two miniscrews were placed on the edentulous ridge on the lower left first molar (Tooth No. 19) area to achieve positive overjet/correct the unilateral posterior crossbite and align the dentition prior to implant restoration of the tooth.

Figure 3 — Tooth movement in preparation for prosthesis (premolar alignment to the edentulous alveolar ridge).

The biomechanics to upright a molar may be complex not only because molars are multirooted teeth and therefore offer more resistance to movement, but also because of side effects such as extrusion, which may not be desired. The molar shown on Figure 4 was completely uprighted in eight months.

Figure 4 — Molar uprighting using miniscrews.

In addition, intrusion of antagonist teeth that have supraerupted into an edentulous area may be easily achieved with miniscrews. The molar shown on Figure 5 was intruded enough to accommodate for the height of a new crown on the opposing arch (intrusion time of six months).

Figure 5 — TADs and molar intrusion, preprosthetic.

Molar distalization and protraction

Most adult patients understandably decline to wear a headgear. Several growing patients are also demonstrating poor compliance toward the utilization of extraoral devices. A well-accepted application of TADs is to distalize upper molars in order to correct Class II malocclusions or to protract lower second molars to close edentulous space. Figure 6 illustrates a case that had the lower right second molar protracted 4.5 millimeters in eight months. One miniscrew was placed between the first premolar and canine (Teeth Nos. 29 and 28) on the same side and the molar (Tooth No. 31) to be mesialized was directed connected to it via power chain.

Figure 6 — Lower molar protraction; TAD being used to reinforce anchorage.

Intrusion and extrusion

Facial asymmetry is not only a major complaint for patients with craniofacial anomalies but also for our everyday growing and nongrowing patients. Often severe cases are treated via orthognathic procedures, but mild cases are now being effectively treated with miniscrews. By leveling the occlusal plane via skeletal anchorage, the orthodontist is able to improve facial symmetry. The case illustrated on Figure 7 had the correction of occlusal cant obtained in nine months. Two miniscrews were placed (one buccal and one palatal) mesial to the upper first molar on the right side (Tooth No. 3) to obtain intrusion of the upper right posterior segment.

Figure 7 — Correction of occlusal cant.

Opening and closing the bite may also be accomplished with similar methodology; however, the long-term stability is still questionable.

Contraindications

Patient selection is definitely one of the most important considerations when incorporating TADs in the treatment plan. The most common contraindications include patients taking intravenous bisphosphonates due to impaired bone physiology (although this is still subject to further research) and those with extremely poor oral hygiene.

Risks and complications

Like most novel therapeutic methods, there are risks and complications associated with TADs as well. These are summarized in Tables I and II below.

A common risk, if not the most popular risk during placement, would be root approximation. Experimental studies have shown that the damage to a root even upon intentionally hitting it with a miniscrew will not be enough to devitalize the tooth. Another common complication encountered by clinicians during placement is the bunching up of the soft tissue around the hand driver. Often this is due to a low frenum attachment. It is recommended to place TADs in attached gingiva to avoid this problem. Fracture is also a common complication associated with miniscrews both during placement and during removal. The main cause of fracture is bending or changing the direction of the screw while inserting or removing it. Use of a mouth mirror is convenient to double check that the vector remains constant during placement. A rare, but serious, complication is miniscrew slippage. This may occur in areas with very thin bone where the screw slips along its ridge instead of engaging in proper bone. Thorough knowledge of anatomy is essential in order to avoid these critical areas.

During treatment, certain complications may also arise. Nonetheless, most of them may be minimized or avoided with proper patient instruction and good oral hygiene.

Future research

Long-term studies are still needed to evaluate the clinical stability of the treatment modalities that include miniscrews. The most debatable long-term results involve vertical changes such as intrusion, extrusion, and occlusal plane change. Furthermore, researchers are still testing whether TADs really provide absolute anchorage; i.e. no movement of the anchor unit — in this case the miniscrew — or if there is bone remodeling around the area of placement.(10)

Another area of research is osteoporosis and the prolonged use of bisphosphonates, which may interfere with the placement and success rate of TADs. Bisphosphonates do not allow osteoclastic activity to take place, thus interfering with normal bone biology.

Finally, orthodontists and general practitioners would benefit a great deal from clinical trials involving a large population in order to elucidate issues regarding TADs and orthodontic tooth movement.

Acknowledgements

The authors thank Dr. Budi Kusnoto and the orthodontic residents at the University of Illinois at Chicago (Drs. Silvana Gonzalez-Manzur, Zuhair Bakhsh, Carrie Hedin, Hala Taha, Clara Chow, and Lihong Lin) for the clinical illustrations.

Nanci De Felippe, DDS, MS, is chief of orthodontics at The Craniofacial Center and assistant professor in the Department of Orthodontics at the University of Illinois at Chicago. She has received several scholarships and awards including the "Orthodontic Resident/Student Scholar Award" — First Place — for best clinical research of 2004. She has presented nationally and internationally. Currently, she has 10 articles published in renowned journals such as The American Journal of Orthodontics and Dentofacial Orthopedics and Journal of Craniofacial Surgery. You may contact her by e-mail at nolive2@uic.edu.

Maria Therese S. Galang, DMD, MS, is an assistant professor of orthodontics at the University of Illinois at Chicago College of Dentistry. She obtained her dental degree (DMD) from the University of the Philippines Manila in 2000. She then obtained her MS in oral sciences in 2004 and her certificate in orthodontics in 2007, both from the University of Illinois at Chicago. Dr. Galang is the predoctoral orthodontics course director at the University of Illinois at Chicago College of Dentistry and co-teaches the orthodontic technique course at the graduate level for the orthodontic residents. She is a Diplomate of the American Board of Orthodontics, and serves as a reviewer for the World Journal of Orthodontics. Dr. Galang has given lectures on temporary anchorage devices both locally and abroad. You may contact her by e-mail at mgalang@uic.edu.

References

1. Creekmore TD, Elklund MK. The possibility of skeletal anchorage.
J Clin Orthod 1983; 17(4):266-269.

2. Lin JC, Liou EJ, Yeh CL, Evans CA. A comparative evaluation of current orthodontic miniscrew systems. World J Orthod 2007; 8(2):136-144.

3. Schnelle MA, Beck FM, Jaynes RM, Huja SS. A radiographic evaluation of the availability of bone for placement of miniscrews. Angle Orthod 2004; 74(6):832-837.

4. Mah J, Bergstrand F. Temporary anchorage devices: a status report. J Clin Orthod 2005; 39(3):132-136.

5. Poggio PM, Incorvati C, Velo S, Carano A. "Safe zones": a guide for miniscrew positioning in the maxillary and mandibular arch. Angle Orthod 2006; 76(2):191-197.

6. Paik CH, Nagasaka S, Hirashita A. Class III nonextraction treatment with miniscrew anchorage. J Clin Orthod 2006; 40(8):480-484.

7. Carano A, Velo S, Leone P, Siciliani G. Clinical applications of the Miniscrew Anchorage System. J Clin Orthod 2005; 39(1):9-24.

8. Kravitz ND, Kusnoto B. Risks and complications of orthodontic miniscrews. Am J Orthod Dentofacial Orthop 2007; 131(4 Suppl):S43-51.

9. Cheng SJ, Tseng IY, Lee JJ, Kok SH. A prospective study of the risk factors associated with failure of mini-implants used for orthodontic anchorage. Int J Oral Maxillofac Implants 2004; 19(1):100-106.

10. Liou EJ, Pai BC, Lin JC. Do miniscrews remain stationary under orthodontic forces? Am J Orthod Dentofacial Orthop 2004; 126(1):42-47.

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