Alternatives of Skeletal Anchorage in Orthodontics - Principles and applications

 

Daniel Koo, DDS

Julio Pedra e Cal-Neto, DDS

Mariana de Pinho Noronha, DDS

Graduate Students, Department of Orthodontics, School of Dentistry, State University of Rio de Janeiro, RJ, Brazil

Alvaro Francisco Carriello Fernandes, DDS, MSc

Assistant Professor, Department of Orthodontics, School of Dentistry, State University of Rio de Janeiro, RJ, Brazil

Jonas Capelli Junior, DDS

Professor, Department of Orthodontics, School of Dentistry, State University of Rio de Janeiro, RJ, Brazil

 

Corresponding Author

Daniel Koo

Boulevard 28 de Setembro 157 - 2 Andar - Vila Isabel

CEP – Rio de Janeiro – RJ

e-mail: dankoo97@hotmail.com

Alternatives of Skeletal Anchorage in Orthodontics - Principles and applications

 

Abstract

One of the most challenging problems in orthodontics is anchorage.  According to Newton's Third Law, for every action there is a reaction that can cause unwanted movements of the achorage teeth.  The ideal intraoral anchorage would not displace and would not require patient's compliance (like headgears).  So, to that end clinicians have used different kinds of stable anchorage such as prosthetic osseointedgrated implants, bone screws along with bone plates (miniplates), onplants, zygoma wires and miniscrews which is a small diameter titanium microimplant specially designed for orthodontic use.

 

Key-Words

Implants, Miniscrews, Orthodontics, Skeletal Anchorage

 

INTRODUCTION

 

Anchorage in orthodontics has been defined as the nature and degree of resistance to displacement offered by an anatomic unit when used for the purpose of performing tooth movement.1 The teeth are the most frequent anatomic units used for anchorage in order to move other teeth into a more desirable position.

In simple anchorage the resistance of the anchoring teeth unit to tipping is needed to move another tooth or teeth.  The number, the shape, size and length of each root must be considered, because different teeth have different resistance values to tooth movement.  This situation may cause undesired movements of the anchorage teeth.12

Other kinds of traditional anchorage systems use extra-oral elements such as: headgears, or intraoral appliances like Nance buttons or other types of appliance designs.  But some of them need patient cooperation and others cannot be considered stable anchorage. 

To no longer depend on patients' compliance, several devices and techniques have been introduced as alternative means of skeletal anchorage: conventional dental implants28,30, special intraoral implants, onplants, zygoma wires22, intentionally ankylosed teeth18, miniscrews, miniplates17,19,21.

This paper will attempt to review the literature of alternative skeletal anchorage used in the orthodontics.

 

CONVENTIONAL IMPLANTS

 

The first attempt to implant a stable device to be used for orthodontic anchorage was made by Gainsforth and Higley10 (1945) by inserting vitallium screws into a dog’s ramus to distalize a maxillary canine. Linkow20 (1970) presented several cases associating endosseous implants in orthodontics. In one of the cases, the author used a blade vent implant as a posterior mandibular anchorage for intermaxillary elastics.

Sherman30 (1978) studied bone reaction to orthodontic forces on vitreous carbon dental implants in dogs. The wrought ticonium implants were also tested in rats with low rate of success.7  Nowadays it is known from the early studies of Branemark et al. 3 (1977) that the osseointegrated titanium implants offer more predictable results. Many studies have been carried out on dogs using osseointegrated titanium implants and the results showed stability of these implants as anchorage for orthodontics. 6, 28, 32

The conventional implants have been useful aids as anchorage in orthodontic treatment, especially in cases with a large number of missing teeth. Conventional dental implants are inserted in the edentulous areas. After the healing period it can be used as an orthodontic anchorage for retraction of anterior teeth,9 mesial movement of posterior teeth,14 extrusion of the impacted teeth,23 lingual movement of a mandibular canine,35 crossbites and anterior open bite.25 At the end of orthodontic treatment, the abutment is used to support a fixed prosthesis as part of the comprehensive treatment plan.15, 16  The osseointegrated implants could be also used for distraction osteogenesis,1 midface sutural expansion24 and maxillofacial protraction.31

 

SPECIAL IMPLANTS

 The use of conventional implants for orthodontic anchorage is limited when treating purely orthodontic patients with full dentition or where extraction sites are to be closed. For these patients alternative sites have been used: namely the retromolar areas and the palate.27, 39

Roberts et al.27(1990) placed a specially designed implant in the retromolar area as an anchorage device to intrude and mesially translate second and third molars into an atrophic first molar extraction site.

The small palatal implant is temporarily inserted in the median palate when maximal anchorage is required in the maxilla associated with complete dentition19 (Figure 1). The mid-sagittal area of the palate lends sufficient bony support for the small implant insertion.40 The requirements for the palatal implants are: small dimension especially in lengths, positional stability and reliability throughout treatment, reliable fixation of orthodontic wires, patient tolerance, and ease of clinical application38, 39.

Figure 1 - Palatal Implant used as skeletal anchorage during overjet reduction.

 

The Orthosystem (Institut Straumann, Waldenburg, Switzerland) is one example of palatal implants for orthodontic purposes. This system consists of a titanium endosseous implant body (self-tapping thread with a sandblasted, large grit, acid-etched surface) with 3.3mm in diameter and 4.0 or 6.0mm in length, transmucosal neck section (4.1mm in diameter) and 1.5, 2.5 or 4.5 mm in height, abutment, clamp cap (5mm in diameter and 2.65mm in height) providing attachment for square wires, screw, and wire ( 0.8 X 0.8mm or 1.2 X 1.2mm)39.

Clinical studies have reported retraction of upper anterior teeth in 8mm after 9 months of treatment with 0.5mm mesial movement of anchored teeth,19 canine teeth showed an average retraction of 6.7mm in 11 months with 0.9mm of anchorage loss.39 All of the implants were immobile at the end of treatment. Wehrbein and co-workers investigated the stability of short implants subjected to horizontal loading in humans38 and in a long-term basis in dogs41 and the results showed the maintenance of stability and osseointegration of these implants.

Implant removal is performed using a 5.0mm standardized trephine. After a 2 month healing period the mucosa presented recovering of normal aspects.39 This system presents several advantages: shorter treatment time, superior esthetics, easy placement and removal, compliance-free nature, maximum anchorage, relatively predictable outcomes and reduction of orthodontic appliances.39 However, another surgical procedure is necessary for implant removal and this treatment requires higher cost and presents a risk of perforation of the nasal cavity.

Recently a biodegradable implant has been developed.8, 11 It is designed to provide orthodontic anchoring functions and then to be resorbed without foreign body reactions or signs of clinical inflammation. The implant, which is made from a biodegradable polylactide, showed adequate loading capacity for clinical application in orthodontics.11

 

ONPLANTS

 

Block and Hoffman2 (1995) have designed a thin titanium alloy disk called 'onplant' as a skeletal anchorage device for orthodontics. It is textured and coated with hydroxyapatite (75¼m) on one surface and a threaded hole on the opposite side for abutment. The onplants are disks with tappered shape periphery with 2mm in thickness and 10mm in diameter. The onplant is placed in the middle of the palate in the same way as a palatal implant. After a healing period of approximately 12 weeks orthodontic forces are loaded on the abutment

Since it does not have to be inserted into bone, it can be placed in patients with various stages of dental eruption. This type of device may reduce treatment time and does not depend on patient compliance. However, it presents extra cost and more clinical studies must be developed to offer more predictable results.

 

ZYGOMA WIRES

 

In a partially edentulous patient, the best bone quality is found in the region of the zygomatic arch and the infrazygomatic crest. In extreme cases where no other solutions could be found, Melsen et al. 22 (1998) have tried zygoma ligatures as a form of maxillary anchorage.

A horizontal canal is drilled approximately 1cm lateral to the alveolar process, with entrance and exit holes in the superior portion of the infrazygomatic crest. A 0.12 inch stainless steel is pulled through this canal and the anchorage can be used immediately after insertion. Treatment time varies from three to six months. At the end of the treatment, wires are removed under local anesthesia by pulling at one end without requiring a surgical reopening. For this technique no special equipment is required, materials are inexpensive, anchorage can be used immediately after insertion and the treatment time  is short.

 

ANKYLOSED TEETH

 

The intentionally ankylosed teeth may be used as anchorage for protraction of the maxilla. Kokich et al. 18 (1985) used this technique to treat a five-year-old boy presenting Apert syndrome with premature synostosis of both coronal sutures and concomitant cranial base anomalies. Alternative treatments such as surgical repositioning and extraoral traction using deciduous teeth were rejected.

Ankylosis was intentionally done by extraction of deciduous canines, followed by the endodontic treatment, removal of remaining periodontal fibers and teeth were kept out of socket for 45 minutes before the reimplantation. A 2mm hole was made through the crown to pass a 0.040-inch wire. A period of 8 weeks was allowed for ankylosis and subsequently the protractor appliance was loaded. After 12 months of treatment a 4mm protraction was achieved and the intentionally ankylosed teeth became mobile at the end of treatment with signs of radiographic root resorption on radiograph. Ankylosed teeth have also been successfully used as anchors for palatal expansion 13.

 

MINISCREWS

 

Miniscrews have been used by several authors to overcome several of the disadvantages presented by conventional implant anchorage such as limited space (insertion in edentulous areas only), limited direction of force application (dental implant is placed on the alveolar ridge and is too large for horizontal orthodontic traction), severity of surgery, discomfort of initial healing and difficulty in oral hygiene.17 Creekmore and Eklund5 (1983) inserted surgical vitallium bone screw just below the anterior nasal spine for deep bite correction. Maxillary central incisors were elevated 6mm in one year of treatment by this method. Similar outcome was achieved for the intrusion of lower incisors by Kanomi17 (1997) using surgical titanium bone screw (Micro Plus Titanium Plating System, Leibinger, Freiburg, Germany) in 4 months of treatment. The use of miniscrews for molar and anterior teeth intrusion, horizontal traction, molar distalization and distraction osteogenesis depending on the location of miniscrew insertion are also suggested17,38 (Figure 2).

Figure 2 - Miniscrews used to retract incisors.

Costa et al. 4 (1998) have developed miniscrews especially for the orthodontic therapy. This titanium miniscrew has a 2mm diameter and a 9mm length. Two different size caps can be adapted to the head of the miniscrews. This system does not require flap dissection, allows for the immediate loading thus shortening the treatment time, and the removal procedure is simple using same screw-driver used for insertion.

 

MINIPLATES

Titanium miniplates may be temporarily implanted in the maxilla and mandible as an immobile anchorage (Figure 3). Umemori et al. 34 (1999) fixated the miniplates using bone screws on the buccal cortical bone around the apical regions of the lower first and second molars and elastic threads were used to intrude the lower molars in open-bite malocclusion. After 5 months of treatment, 3.5 to 5 mm of intrusion was achieved. This system presents several advantages: no preparation is necessary to obtain a location for implantation, a stable rigid anchorage is ensured, tooth movement is possible shortly after placement (approximately 1 month), simplified treatment mechanics, and shortened orthodontic treatment period.

Figure 3 - Intrusion of molar using miniplate associated with a palatal miniscrew.

 

CONCLUSION

Several alternative skeletal anchorage systems for orthodontic therapy were reviewed. Most of these devices and techniques are new with the published studies being low in sample size and lacking of long-term clinical follow-ups. However, the viability of these skeletal anchorage systems is an important adjunct to orthodontics.

 

REFERENCES

 

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