Statement - ZZI 01/2011

The use of implants for skeletal anchorage in orthodontics
Recommendations for: Anchorage in orthodontics

F. P. Strietzel1, H. Wehrbein2

Introduction

Endosseous implants for orthodontic anchorage are used more and more frequently in orthodontic treatment for movement of larger groups of teeth or single teeth without loading other teeth. Also, in situations with no or only very limited existing conventional anchorage options in the case of hypodontia, after tooth loss or in patients with periodontally compromised teeth, implants for orthodontic anchorage provide an alternative to extraoral anchorage.

The procedure as well as the application and choice of implants always depend on the long-term treatment aims. On the one hand, there is the option of placing conventional implants in the position of one (or more) abutments for the subsequent prosthetic restoration and then move the teeth or tooth groups into the planned position using orthodontic anchorage and retain the restoration on these implants at a later stage. These implants are intended to remain in the alveolar ridge. On the other hand, orthodontic forces can be applied to teeth or groups of teeth using special implants. Subsequent to completion of orthodontic treatment these implants, which are only intended for orthodontic anchorage, are removed again.

These basic considerations regarding the type and functional life of the implants to be placed also include the special demands on the implants, the range of pre-implantological diagnoses as well as the risks and possible complications to be taken into account during treatment planning, which should be assessed to avoid forensic complications. The patient should also be informed of these prior to treatment.

The complexity of the planning and implementation when using implants for orthodontic anchorage and possible integration in the prosthetic restoration later often requires the interdisciplinary teamwork of colleagues in different specialist fields.

The scientific literature available on the clinical use of implants for orthodontic anchorage consists of case reports and also prospective studies [15, 34].

 

Indication

Defining the indication on the use of implants for orthodontic anchorage requires orthodontists during treatment planning to assess the advantages and disadvantages of alternative treatment procedures and to take into consideration the individual characteristics of the patient (e. g. general medical history, characteristics of the disorder that requires orthodontic treatment, anatomical characteristics at the planned insertion site, age, oral hygiene behaviour, compliance of the patient, support of the therapeutic procedure by the parents or guardians in the case of minor patients). Implants are used as anchorage elements in the following indications in particular: tooth intrusion and extrusion, treatment of teeth misalignment, asymmetrical tooth movement in all planes, increase of anchorage, especially where there is insufficient conventional anchorage, orthodontic space closure, correction of malocclusion, in general for anchorage in orthodontic tooth movement to avoid undesired reactive forces as well as to provide an alternative to orthodontic surgery [14, 17, 25, 26].

Detailed consultation is required with all colleagues involved in the treatment with regard to age and growth phase of the jaw and facial skeleton and the resulting characteristics in relation to the timing of the implant-supported therapy in the overall treatment process. In addition to the growth phases of the jaw and facial skeleton, when planning placement of an implant consideration should also be given to the development of the alveolar process, which accompanies the vertical development of the teeth. When choosing the time of implant placement, there should be a discussion of the comparative advantages and disadvantages of implant treatment, which could result from a subsequent tooth-borne prosthetic restoration and suspension of the jaw growth at the implant site [3].

 

Selection of the implant systems

Selection of the implant systems depends on the treatment plan and the anatomical conditions. While conventional implant systems provide options for prosthetic treatment they do not always also have the means of anchorage for orthodontic force application that are coordinated to the respective implant system, however, these features are incorporated in implants which are used exclusively for orthodontic purposes.

Conventional implants are used in different diameters and lengths, depending on the region of implant placement and the planned dental restoration to be fitted on the implant. Selection of the implants with regard to the implant system, dimensions and positioning requires interdisciplinary consultation. The load-free healing periods should follow the previously existing recommendations regarding the respective implant systems and take into consideration the primary stability and dimensions of the implant as well as the bone quality.

The length and diameter of implants intended exclusively for orthodontic anchorage should be as small as possible to allow them also to be used in the interdental region and to keep the size of the defect as small as possible after their removal; the implant body and orthodontic anchorage device should, however, also be able to withstand the applied forces.

Orthodontic implants are mainly used in the palate or the alveolar process. Palatal implants are intended for placement in the median line or paramedian region. Their diameter is comparable to that of standard implants, their endosseous surface design has a rough texture, their intraosseous length, however, is reduced to correspond with the limited vertical bone availability of the palatal process of the maxilla [39]. Placement of these implants is generally minimally invasive (Fig. 1). The aim is to achieve osseointegration with these implants and therefore a load-free healing phase of between two and three months is required [2, 19, 24, 39, 40, 41]. However, shortening of the healing phase is discussed in favour of immediate orthodontic anchorage if constant forces are used [9]. As these implants have been osseointegrated they generally have to be explanted following completion of orthodontic treatment using a surgical procedure that is as minimally invasive and structure conserving as possible. This may be regarded as a disadvantage in comparison with mini-screw or microscrew implants.

Titanium mini-screw or microscrew implants inserted in the alveolar process are used with both relatively smooth (machined) and also rough-textured surfaces (Fig. 2). They are immediately loaded in contrast to implants inserted in the palate [5, 6, 18, 22, 37, 42]. Osseointegration is not an aim of these implants. These implants can usually be removed after completion of the orthodontic treatment by gently unscrewing them.

The decision about when to start orthodontic loading of these implants should not only take into account their micro or macro texture but also their primary stability as well as the bone quality.

 

Pre-implantological diagnosis

Pre-implantological diagnosis in orthodontics is usually preceded by clinical and radiological examination and assessment of findings, the results of which lead to considerations in an implant-supported treatment strategy.

If conventional implants are intended to be used initially for anchoring appliances for orthodontic force application and subsequently for retaining a dental restoration following completion of orthodontic treatment, the planning requires close cooperation between all those involved in the treatment with regard to optimal implant positioning, anticipated time required and course of treatment and ideal positioning of the natural teeth while taking into account the positioning of the implant prosthetic rehabilitation [29, 43]. The scope of the pre-implantological diagnosis hereby complies with the recommendations of the DGZMK (German Society of Dentistry and Oral Medicine): the panoramic radiograph with radiopaque measurement reference is used as a basis [30]. Additional imaging techniques are used for detailed illustration and assessment of the bony implant site, determination of the distance between the planned implant position and adjacent anatomical structure and to exclude pathological findings at the implant site as well as its surroundings. The range and type of other imaging examinations depend on the individual requirements in each case taking into account the radiation exposure and cost-benefit ratio of the respec-tive technique and must be completed in context with the clinical findings of the justifying indications for the imaging technique [32].

The bony palate and thickness of the palatal vault in the median plane can be displayed using a lateral cephalometric radiograph prior to the use of palatal implants for orthodontic force application. In this case, as with imaging using the panoramic radiograph, it is practical to transfer the implant position from the model analysis using the X-ray to the clinical situation by means of surgical stents [9, 10, 20]. This is because it is difficult to maintain the planned implant axis due to the palatal arch, especially when using palatal implants. It is also important to avoid incorrectly placed implants damaging the anterior teeth, which are sometimes very angled with their root apices highly inclined towards the palatal-dorsal aspect. The use of stents for more accurate transfer of the planned implant position to the clinical situation also has advantages when inserting implants in the alveolar process [35]. The aim should also be to position the implant in the region of the keratinised gingiva. It is important to evaluate the interradicular space availability and distance between the planned implant site and adjacent teeth before inserting miniscrew implant systems in the alveolar process vertically or at an angle. If movement of teeth is planned immediately adjacent to the implant, their change in position should be taken into account when determining the implant position to avoid the implant interfering with tooth movement [44].

The use of computed tomography and cone beam computed tomography enable precise metric evaluation of the vertical bone thickness and volume with a lower tolerance before the placement of palatal implants. However, it is important to note the higher radiation exposure of this examination technique in the context of the higher risk factor for stochastic radiation effects in the case of children and adolescents.

 

Surgical procedure

The surgical procedure during implant placement follows the principles of implantological surgical techniques taking into consideration the anatomical characteristics of the implant site while ensuring the vitality of the adjacent bone tissue as well as achieving adequate primary stability of the implant [33]. Using implants that are solely intended for orthodontic force application generally requires only a minimal incision or gaining access using a mucosal punch (particularly suitable when using palatal implants). Sometimes only transgingival access and minimally invasive implant site preparation aimed at preserving the vitality of the bone adjacent to the implant is required.

Implants for placing vertically or angled in the alveolar process, crista zygomaticoalveolaris, spina nasalis anterior, mandibular retromolar triangle or the mandibular symphysis are generally self-tapping or self-drilling screw implants with a reduced diameter (1.8 to 2 mm) and with lengths that allow intraosseous anchorage to a depth of 5 to 14 mm. As with palatal implants, they are mainly one-piece implants and their section for orthodontic anchorage is primarily exposed transmucosally to the oral cavity [1, 8, 21, 27, 28, 31, 38, 44, 45]. Osseointegration is not an aim of these implants. They can be loaded immediately after they have achieved primary stability [12, 13].

Orthodontic implants are usually intended for use throughout the entire period of orthodontic treatment. Explantation instruments that are specially tailored to the implant system should be used for removal – provided that they are contained in the surgical instrumentarium for that purpose [40]. It should also be ensured that during explantation immediate adjacent structures (e. g. the bony palatal vault, nasal floor, adjacent tooth roots or mandibular canal), which already had to be protected during implant placement, are not damaged during exposure and removal of the implant. Miniscrew system implants can normally be gently removed by simply unscrewing them and using very minimal osteotomy. During removal, however, the proximity to the adjacent teeth must also be taken into account, as their distance to the implant could quite easily have been reduced during orthodontic treatment. If implants are left load-free for a long period after completion of orthodontic loading, it results in an increase in the amount of torque required to unscrew them [16].

Apart from the instrument, appliance, diagnostic and spatial prerequisites, placement of implants for orthodontic use assumes basic proficiency and skills with regard to the surgical procedure as well as the ability to deal with possible complications. This therefore highlights the advantages of interdisciplinary teamwork during planning and implementation of an implant-supported orthodontic treatment and, if necessary, interim and final prosthetic treatment [23].

 

Risks and possible complications

The risks and possible complications to be considered during treatment planning when using orthodontic anchorage depend on the respective individual characteristics of the general medical history and anatomy, planned implant site as well as unusual features during the course of treatment. These risks should be explained to patients and they should also be informed about any conditions or complications that may arise, which may make it necessary to change the course of treatment.

In addition to the basic general risks of the surgical procedure of implant placement in the case of conventional implants that are planned to be used initially for orthodontic treatment and subsequently for a permanent prosthetic restoration, there are specific risks with regard to the planned insertion site (e. g. in the mandibular posterior region there is the general possibility of postoperative sensitivity disorders in the innervation area of the alveolar nerve and mental nerve of the affected quadrant; in the maxilla there is the possibility of accidental opening of the floor of the maxillary sinus or nasal cavity) which should be taken into consideration with surgically related postoperative restrictions of the patient. These include the necessity to observe recall appointments for follow-up, necessity of a correct technique and monitoring for effective oral hygiene and also alternative treatment options without the use of implants. If implants are placed shortly before completion of jaw growth, the anticipated suspension of further jaw growth as well as the necessary corrective measures that arise as a result should be taken into consideration. [36].

There have only been few reports in the literature to date about the risks and possible complications during or after insertion of orthodontic implants for exclusive orthodontic anchorage.

Other relevant risks with implants for orthodontic anchorage, apart from the above-mentioned risks and complications, include implant failure and undesired incidents with impairment of the patient’s wellbeing, jaw and residual dentition: implant failure can cause the course of orthodontic treatment to be interrupted and its success put into question; mechanical irritation of the oral mucosa due to unfavourably positioned implants and anchorage superstructure can cause pain and result in lack of compliance by the patient; incorrect positioning of implants can either render them unusable for adequate force application or result in oral mucosa inflammation and local infections and consequently implant failure; defects after implant failure due to inflammation can in certain circumstances delay renewed implant placement or make it impossible; with incorrect implant positioning and too close contact between the implant and adjacent tooth (which occurs occasionally during the course of implant treatment) it is possible to damage the immediately adjacent teeth – also during explantation.

Assessment of the success of implants for orthodontic force application focuses primarily on the stability and functionality of the anchorage throughout the entire period of dental treatment. However, assessment also includes the lack of signs of infection and inflammation, mobility, inadequate loading capacity and pain as well as damage to adjacent roots or other adjacent structures [15]. In a review study success rates were given for osseointegrated palatal implants of 85–100 % and 75–100 % for non-osseointegrated implants (mini-plates 85–100 %, miniscrews 75–100 %) [15].

To date the data derived from the literature on implant failures and associated factors provide only little information. The cumulative time-in-situ rates of implants after use in the alveolar process exclusively for orthodontic force application throughout the course of orthodontic treatment were given in clinical prospect studies between 86 % [22] and 89 % [7] and in retrospective studies between 85 % [6] and 91 % [37]. Palatally placed implants for orthodontic force application achieved a time in situ of 90 % [11].

Significant risk factors for implant failure were established as use in the posterior mandible [6, 7, 37], use of implants in the zone of non-keratinised gingiva [7], use of short implants [6] as well as excessive (> 10 Ncm) or inadequate (< 5 Ncm) insertion torque [22]. The primary stability after placing the implants also appears to be an important prognostic factor with orthodontic implants and in particular if the intention is to load the implants immediately. Occasionally an unfavourable position of the implant and associated chronic mechanical damage to the mucosa can make it necessary to remove the implant [13].

Conclusions

The use of implants for orthodontic anchorage places high demands on determining the indication and detailed treatment planning. Depending on the complexity of the treatment aim, it is of particular advantage to have interdisciplinary teamwork by specialists in different fields. In addition to precise agreement on the timing of treatment procedures, the interdisciplinary procedure requires consideration of the current growth and development status of patients as well as their biological, general medical and anatomical conditions, their compliance and, if necessary, the final planned prosthetic restoration in adulthood.

It is necessary to provide the patient with detailed information before treatment regarding the timing of procedures, individual treatment stages and their aims and also the restrictions, risks and possible complications involved. They complement the basic consultation required in the planning of orthodontic treatment with their key points and must also take into account the main characteristic involved in orthodontic treatment, namely the minor age of many patients, who nevertheless have a considerable joint responsibility for the success of treatment [4].

Implants for orthodontic force application provide the possibility of reliable anchorage without the risk of reactive, undesired tooth movements and numerous application options with regard to objectives and sites. With correct preparation the implants can generally be placed and removed without extensive surgery or complications. The requirements for high compliance of the patients in orthodontic treatment are the same as those for patients in orthodontic treatment. Good oral hygiene and strict adherence of recall appointments are essential. The costs are relatively low compared with conventional anchorage techniques.

Footnote

1 Charité – Medical University Berlin, Germany, Charité Centre 3 for Dental and Maxillary Medicine, Department of Oral Medicine, Dental Radiology and Oral Surgery (Director: Univ.-Prof. Dr. A.-M. Schmidt-Westhausen)

2 University Medical Center of the Johannes-Gutenberg University, Mainz, Germany, Department of Oral and Maxillofacial Diseases, Department of Orthodontics (Director: Univ.-Prof. Dr. Dr. H. Wehrbein)

Übersetzung: LinguaDent

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