|Year : 2015 | Volume
| Issue : 1 | Page : 87-89
Microimplant assisted extraction space closure: Biomechanical considerations
Nishant Negi1, Pravesh Jhingta2, Deepak Sharma2, Mohinder Chandel3
1 Department of Orthodontics and Dentofacial Orthopedics, H. P. Government Dental College and Hospital, Shimla, Himachal Pradesh, India
2 Department of Periodontics, H. P. Government Dental College and Hospital, Shimla, Himachal Pradesh, India
3 Department of Oral Surgery, H. P. Government Dental College and Hospital, Shimla, Himachal Pradesh, India
|Date of Web Publication||2-Apr-2015|
Department of Orthodontics and Dentofacial Orthopedics, H. P. Government Dental College and Hospital, Shimla - 171 001, Himachal Pradesh
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Implants have revolutionized the field of orthodontics by providing infinite or absolute anchorage. This new treatment approach has widened the therapeutic possibilities of orthodontic treatment. The science of biomechanics remains a mainstay of clinical orthodontics. The biomechanical variations with force application are significant when comparing conventional and mini-implant orthodontics. In order to fully exploit the potential of mini-implants, adequate knowledge of biomechanical principles and their modification in relation to mini-implants is imperative. This case report presents extraction space closure with temporary anchorage devices and describes biomechanical variations required in different clinical scenarios.
Keywords: Biomechanics, microimplants, retraction
|How to cite this article:|
Negi N, Jhingta P, Sharma D, Chandel M. Microimplant assisted extraction space closure: Biomechanical considerations. J Dent Implant 2015;5:87-9
|How to cite this URL:|
Negi N, Jhingta P, Sharma D, Chandel M. Microimplant assisted extraction space closure: Biomechanical considerations. J Dent Implant [serial online] 2015 [cited 2019 Sep 22];5:87-9. Available from: http://www.jdionline.org/text.asp?2015/5/1/87/154457
| Introduction|| |
Anchorage control is one of the most challenging aspects of orthodontic treatment. Newton's third law states that, for every action there is equal and opposite reaction. During conventional orthodontic treatment, it is virtually impossible to achieve absolute anchorage without some movement of anchor teeth. Therefore, even a small reactive force can produce undesirable orthodontic tooth movements thus compromising treatment objectives. To reinforce anchorage various auxiliaries like lingual arches, holding arches, elastics and headgears are used. However, these appliances require full cooperation of the patient to be effective.
Nowadays absolute anchorage can be obtained without patient cooperation using dental implants, screws, and miniplates. ,, These are used as temporary anchorage devices (TAD's) which are removed after use. Microimplants are most popular TAD'S having numerous advantages like ease of implantation and removal, low cost, possible immediate loading, and possible placement in most areas of alveolar bone.  TAD's can provide infinite anchorage that has been defined in terms of implants as showing no movement (zero anchorage loss) as a consequence of reaction forces.  The reactionary forces are applied to cortical skeleton and are distributed and dissipated there.
The use of microimplants for anchorage reinforcement produces somewhat different mechanics. This case report presents extraction space closure with TAD's and describes biomechanical variations required in different clinical scenarios.
| Case report|| |
A 13-year-old male patient reported to our clinic with a complaint of forwardly positioned upper front teeth [Figure 1]. On examination, he had Angles's class II molar relationship with increased overjet and overbite of 7 mm and 4 mm respectively. Skeletally he had average growth pattern. Our treatment plan included extraction of upper first premolars and lower second premolars. As this case warranted maximum anchorage in the upper arch, we decided to use skeletal anchors in the form of microimplants. One microimplant on each side was inserted into attached gingiva between maxillary second premolars and maxillary first molars, at a height of about 6-8 mm from the main archwire [Figure 2]. Anterior hooks were soldered on the archwire between maxillary laterals and canines. Niti coil spring was used to retract maxillary teeth with force of about 150-200 g on each side [Figure 2]. After 6 months of retraction, complete closure of the extraction space was achieved [Figure 3].
| Discussion|| |
Anchorage reinforcement is most critical in cases requiring premolar extraction for the correction of proclined maxillary anterior teeth. Anchorage loss of 3.6-3.8 mm has been reported in such cases treated with conventional orthodontic treatment.  Microimplants can be used in such critical anchorage cases. Mechanics with microimplants is considerably different from conventional orthodontics because the forces used during retraction are not reciprocal. Microimplants can be placed in many different areas of the mouth and at different heights on the gingiva relative to the occlusal plane, creating several biomechanical orientations, e.g., low, medium and high. Thus, various types of tooth movements can be produced depending on the position of microimplant, the height of elastomeric attachment, and magnitude of force applied. 
Retraction with microimplants is accomplished by placing E-chin or coil springs between microimplants and anterior hooks soldered on the archwire. In average growers microimplants should be placed 8-10 mm above main archwire as force system during retraction will help in maintaining overbite relationship. In cases with deep bite, microimplants should be placed at height >8 mm from main archwire as the force system produced during retraction will rotate occlusal plane counterclockwise and will open the bite. On the other hand, in patients with open bite malocclusion, microimplants should be placed nearer to the main archwire as force system thus produced will rotate the occlusal plane in clockwise direction and will deepen the bite. 
In many instances, it is difficult to place microimplants high enough due to reduced sulcus depth and danger of inducing inflammation in the mobile mucosa. Melsen et al.,  recommended that the archwire hook extend 10 mm from the main archwire, but anatomic limitations usually make this impractical. E chain or coil spring positioned above the bracket level may impinge on the soft tissue. Therefore, it may not be possible to use a retraction force that passes through the Center of Rotation, and other methods like use of inter maxillary elastics, bite planes and additional microimplants can be employed to overcome adverse effects.  In horizontal and transverse plane, care should be taken to prevent the development of buccal crossbites. 
Incorporation of skeletal anchorage into orthodontic treatment has opened several therapeutic possibilities that until recently were considered impossible without the use of orthognathic surgical procedures.
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[Figure 1], [Figure 2], [Figure 3]