The MIA (Microscrew Implants Anchorage) for lingual orthodontic treatment

Park, Hyo-sang
Associate Professor
Dept. of Orthodontics and Dentistry
Keimyung Uni. Taegu, Korea

www.lingualnews.com  Volume 1, Number 1 - November 2002

Endoseous dental implants have used as orthodontic anchorage for several decades. However their use has not been widely accepted because of several limitations including anatomic, financial and an extended treatment time. Anatomic limitations present the greatest challenge to the clinician due to rigorous requirements such as their need for an adequate edentulous ridge, retromolar area,(1) or palatal area(2).
However, microscrew implants for the purpose of orthodontic anchorage present the clinician with a more versatile option. This device can be placed in areas which would not accept an endoseous implant. For example, interradicular alveolar bone, palatal shelves, the retromolar region, the inferior aspect of the zygomatic arch, and anterior nasal spine.(3). In addition, micoscrew implants are less expensive, and early loading following placement reduces treatment time as compared to the endoseous option.

The sliding mechanics of the MIA technique and it's application to treatment of skeletal Class I and II malocclusions have been previously described.(3-6) However, its application in lingual orthodontics has not been widely discussed in particularly with regard to non-extraction treatment. The following is a case report highlighting the use of microscrew implants as an anchorage aid in lingual orthodontics.

Case
Patient LW is a 28-year-old female which presented for orthodontic treatment with the chief complaint of "crooked front teeth". Her medical history was not remarkable, and she was referred by her dentist of care.
Upon examining her clinically, she was found to have TMJ function within normal limits without pathology. Her facial form was ovoid and symmetric, with an orthognathic harmonious profile. Intraorally she presented with an Angle's Class I malocclusion, 2 mm overjet and 1 mm overbite, and arch length discrepancy in maxillary and mandibular arches were 4mm and 5.5mm respectively. No pathology was noted on her intraoral radiographs. (Fig 1)

Fig 1: Initial photographs and x-rays

Treatment
Due to LW's pleasing soft tissue relationships together with the moderate nature and location of her dental crowding, a "non-extraction" treatment was planned. The patient provided informed consent to undergo extraction of her right maxillary and mandibular third molars, and submit to the placement of microscrew implants to the palatal alveolar bone between first and second molars in maxillary arch and alveolar bone distobuccal to second molars in mandibular arch. .(Fig 2)

Fig 2: Placement of microscrew implants ⇒

After bonding lingual brackets, elastomeric thread was placed from the microscrew implants to the first premolars in the maxillary arch, and to a lingual button on the second premolars in the mandibular arch. (Fig 3)


« Fig 3: Activation of distalizing force by connecting elastic thread between microscrew implants and first premolars in the maxillary arch, and second premolars in the mandibular arch

Aligning of the anterior teeth was carried out tooth by tooth after creating space by moving posterior teeth backward. (Fig 4).

Fig 4: Finishing stage

With achievement of the orthodontic treatment goals, removal of the microscrew implants was carried out under local anesthesia by twisting it in opposite direction of its placement. (Fig 5)

Fig 5: Removal of microscrew implants ⇒

Treatment time was 10 months, and the case was finished with well-aligned dentition, Class I canine and molar relationships, and no deterioration of facial profile. (Fig 6)

Fig 6: Posttreatment intraoral photos and x-rays

   The cephalometric results are described in Table 1                   
                    
 

Before          After

SNA 81.5 81 SNB 78 78 ANB 3.5 3 FMA 33 34.5 PFH/AFH 0.64(49/77) 0.63(48.5/77.5) FH to Occ P 11.5 13.5 Ui to FH 111.5 107 IMPA 96 97 Z angle 67 68

Table 1: Cephalometric pre- and post-treatment analysis

Discussion
The effectiveness and clinical application of microscrew implants has been discussed previously.(3-6) In addition, their use as part of an extraction-based orthodontic treatment plan has also received sparse attention.(7)

The use of microscrew implants along as part of a non-extraction treatment enables retraction of teeth against the device en mass rather than individual molar/premolar distalization, as would be a limitation with common orthodontic biomechanics. Following distalization of posterior teeth and the creation of space to resolve anterior crowding, overjet etc., alignment of anterior teeth becomes a simplified procedure which can now be performed without discernable forward movement of anterior teeth and possible deleterious effects on the facial profile.

This procedure can be adapted to non-extraction treatment in using labial or lingual fixed appliances. The ability to produce "absolute" anchorage against which posterior teeth can be retracted as a unit should necessarily shorten treatment time. This type of anchorage also simplifies the application of biomechanics required to affect bodily movement of these teeth. This device makes practical the direction of the line of force through the Center of Resistance, thus facilitating the efficiency of the system. Power-arm extensions from the teeth to be distalized are activated by attachment to the microscrew implants.7 This permits predictable biomechanical control of the movements these teeth will undergo.

In other words, by en masse movement of the posterior teeth, Class II or Class III canine and molar relationships can easily be treated with MIA. In addition, this eliminates the need for intermaxillary elastics to correct Class II or Class III dental relationships. Therefore, there is no need to be concerned with the reactive mechanics, such as loss of anchorage, canting of the occlusal plane, or loss of vertical control, which these can cause.

In lingual orthodontic treatment, the best position for placement of microscrew implants in maxillary arch is the palatal interradicular alveolar bone between the first and second molars. Their vertical positioning is determined by the types of tooth movement required. As has been reported earlier, there is normally an acceptable amount of space between palatal roots of the maxillary first and second molars.3 Therefore, this area should be the primary placement site for this device.

In the mandibular arch, buccally placed microscrew implants are preferable because of ease of access. In this instance the device is recommended to be placed in the interradicular bone between mandibular first and second molars, or distobuccal to the second molars, or in the retromolar area. Again, the choice is dependent on the type and amount of tooth movement required as well as availability of a healthy osseous implant site. This usually indicates that the former location is preferable. It should also be noted that these sites are valid choices for either labial or lingual appliance treatment.

The cephalometric superimpositions of the case report presented above indicate that the maxillary incisors and maxillary and mandibular molars did in fact move distally.(Fig 7)

Summary
The microscrew implant system can provide "absolute" anchorage for en masse distal movement of posterior teeth. By moving posterior teeth in this manner the treatment time can be shortened. The microscrew implants can be adapted in labial treatment as well as lingual treatment. 

Fig 7: Cephalometric superimposition

References
1. Wehrbein, H.; Merz, B.R.; Hammerle. C.H.F.; Lang, N.P.; Bone-to-implant contact of orthodontic implants in humans subjected to horizontal loading, Clin Oral Impl. Res. 9:348-353, 1998.
2. Roberts, W.E.; Nelsen, C.L.; and Goodacre, C.J.: Rigid implant anchorage to close a mandibular first molar extraction site, J. Clin. Orthod. 38(12): 693-704, 1994.
3. Park, H.S.: The use of Micro-implant as orthodontic anchorage. Nare Pub. Co. Seoul 2001.
4. Park, H.S.: The skeletal cortical anchorage using titanium microscrew implants, Kor. J. Orthod. 1999:29:699-706.
5. Park, H.S.: A new protocol of the sliding mechanics with micro-implant anchorage(MIA), Kor. J. Orthod. 2000:30(6):677-85.
6. Park, H.S.; Bae, S.M.; Kyung, H.M.; and Sung, J.H.: Micro-implant anchorage(MIA) for treating skeletal class I bialveolar protrusion, J. Clin. Orthod. 35(7): 417-422, 2001.
7. Lee, J.S., Park H.S., Kyung H.M.: The M.I.A.(Micro-implant Anchorage) in Lingual Orthodontic Treatment for Skeletal Class II Malocclusion J. Clin. Orthod. 2001:35(10):643-647.

Product information: Absoanchor
Contact Fax: 82-53-421-7607

Dr. Park provided, over 20 times, a 2-day-program for MIA, including one-day lecture and a one-day hands-on course in several countries (Korea, Japan, Taiwan, Spain, USA)

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Adult and Lingual Orthodontics
EDITORS:
Dr. Silvia Geron D.M.D., M.Sc
Dr. Rafi Romano D.M.D., M.Sc
Dr. Pablo Echarri D.M.D., M.Sc