December, 2004
Bracket Head Micro Implant for Orthodontic Anchorage
A. Korrodi Ritto, DDS, PhD and H. M. Kyung DDS, MSD, PhD
Introduction
Endosseous implants have been suggested and used for orthodontic anchorage. Due to the limited implantation space, high cost and long waiting period of osteointegration other solutions appeared in the market.
Non-osteointegrated micro implants, and recently micro osteointegrated implant appeared to overcome the drawback of prosthetic endosseous implants. Skeletal Anchorage System (SAS) includes all the devices fixed to the bone with the goal of increase the anchorage for orthodontic purposes.
The term temporary anchorage device (TAD) refers to all variations of implants, screws, pins and onplants placed specifically for the purpose of providing orthodontic anchorage that are removed upon completion of biomechanical therapy.
Micro implants have some advantages comparing to endosseous implants. The low cost, simple procedures for insertion and removal, immediate loading, and ability to be placed between roots contribute for enhancement of this method by orthodontists.
The following terms can be found in literature: mini implant, mini screw, micro screw, micro implant. Although “MICRO” is connoted with 106 this term is used widely in medical & dental fields academically – “Micro-gnathia”, “Micro-dontia”, “Micro-glossia”…, and should be used to emphasize the small size.
The shape and design indicate that “screw” is more appropriate (all the orthodontic implant has screw type), however to avoid negative connotations this term is not the best reference.
The term “IMPLANT” is used for any material retained more than one month in the body according to CE/MDD norms. So, Microscrew implant is the proper term however the abbreviation Micro-implant is commonly used.
Recently different designs of micro implants appeared in the market for different purposes. Almost all of them have a hole in the head to attach accessories, and others have different kinds of slots or round heads (Fig 1).
Figure 1. Different types of micro implants
This article will describe clinical applications with different designs of micro implants, and will describe the advantages of bracket head micro implant.
CLINICAL APPLICATION
Micro implants are the best and easy way to get absolute anchorage for orthodontic treatment. Different types of head and designs are available now in the market, and their use depends on the particular situation (Fig 2).
Figure 2. A coil spring is inserted into the small head micro implant. On the other end is attached to another micro implant, which has a bigger head.
For example, small head and long head differ on the implantation site. If a depression or bone defect is present, it is recommended to use a long head to avoid mucous impingement when the spring coil or elastomeric is attached to it (Fig 3).
Figure 3. Long head implant is useful in posterior areas, or when there are bone depressions.
Some micro implants have a double slot to permit the use of segmented wires. However, due to the round head, it is difficult to attach a metallic ligature (Fig 4-6).
Bracket head micro implant has two tie wing and one slot which give the same performance as a bracket. It is easy to place the ligature and the wire (Fig 7). In Bracket Head type two kinds of screws were developed depending on the driving directions. Left Handed Screw should turn counterclockwise direction during driving.
This new design makes orthodontic treatment easy, and gives many possibilities for treatment without full fixed appliances.
Figure 4-5. Different slot head micro implants 1- Spider Screw (HDC – Italy); 2- Dual Top Anchor (Jeil Medical Co – Korea); 3 – Aarhus Anchorage System (Medicon & G – Germany).
Figure 6. Using a slot head micro implant and a segmented wire to make canine traction. It is very difficult to fit the ligature wire when the implant has a round head.
Figure 7. Bracket Head micro implant. There are many possibilities for application. BH type has two different threads: clockwise and counter clockwise. The moment of force created after fitting the wire in the slot tends to unscrew or driving more the micro implant. To avoid unscrew the correct type of thread (CW or CCW) should be chosen.
Upper molar intrusion
Molars extrusion causes many difficulties when it is planed rehabilitation with prosthesis or implants, or even when opponent teeth need to be aligned.
The orthodontist can prepare the necessary space for prosthesis or implant by molar intrusion. Upper molar intrusion is one of the most difficult movements to achieve with conventional orthodontics, particularly when there is no tooth distal to the molar.
Intruding force can be achieved by one or two implants in the palatal area, implant in the vestibular area or a combination between fixed appliances and micro implants. Skeletal anchorage is now an easy way to intrude molars.
This case (Fig 8-12) presented a Class I malocclusion with bilateral cross bite, and crowding. Due to an absence of #37 the tooth #27 extruded and was blocked between #36 and #38.
It was planed to expand the maxilla, mesialize and intrude tooth #27. Vestibular force was applied with the fixed appliance (#28 bonded).
An elastic force applied to a micro implant made the palatal intrusion. After 6 months the #27 was in place.
With only a micro implant the therapeutic is easy and comfortable for the patient compared to conventional treatment.
Figure 8. Patient before treatment. Tooth #27 extruded and blocked between #36 and #38.
Figure 9. Occlusal view.
Figure 10. Vestibular intrusion of #27 with conventional mechanics. Lower micro implant to distalize lower molar and premolars.
Figure 11. Sequence of treatment with a micro implant on the palatal area to intrude #27.
Figure 12. End of intrusion and micro implant removed.
Premolar distalization
Elastics, headgear or palatal acrylic buttons are required to increase anchorage when teeth distalization is planed with conventional orthodontics.
Skeletal cortical anchorage using micro implants is a simple approach for any kind of tooth distalization. Just a connection with a spring coil or elastic chain between the micro implant and the tooth is needed. However it is imperative to decide the site for placement to avoid a root contact with the micro implant during the distalization.
This case (Fig 13-16) presents a Class II div.1 malocclusion with a severe crowding and upper midline shift to the left. Due to big restorations on upper first molars, it was planed to extract #16, #26#, and #38 and #48 at the end of the treatment.
Figure 13. Patient before treatment. Upper mid line shifted to the left. Full Class II malocclusion
The right upper premolars and canine were distalized using a micro implant as anchorage unit.
Figure 14. Teeth #16 and #26 extracted and micro implant placed between #17 and #15. Premolar distalization sequence with coil spring.
Figure 15. Canine retraction and spaces closed. Correcting upper midline
After the distalization the overjet and midline were corrected.
With this approach no elastics or headgear was placed during treatment. The case was finished in 19 months with a nice intercuspation.
Figure 16. End of treatment.
Lower molars mesialization
Stability of the lower front teeth is required for lower molar mesialization. With conventional anchorage reverse curve arches and heavy forces are applied on the lower incisors to prevent overjet increase due to lingual tipping. Root resorption can therefore appear in these cases.
Micro implant anchorage eliminates the need of heavy forces and reverse curve arches, preventing root resorption. Root parallelism is achieved during mesialization due to a segmented arch placed near the centre of resistance. A spring coil is fitted between the segmented arch and the micro implant.
In this case (Fig 17-20), the #37 moved to the #36 position with a good parallelism. However, on the other side a conventional technique was used and more time was needed to mesialize the #47. The difficulty is bigger to get the same result, and sometimes parallelism is difficult to achieve.
Figure 17. Patient before treatment. Class I malocclusion with first molars extraction.
Lower incisors intrusion can be done by several ways with skeletal anchorage. Force can be applied directly from the lower arch or teeth to the micro implant (Fig 21) or by using an utility arch from the micro implant to the lower incisors. A composite build-up was required to bond a bracket (Fig 22). The introduction of bracket head micro implants simplified this method. The arch is fitted into the slot
Figure 18. Closing spaces. Right side with conventional mechanics and left side with micro implant anchorage.
Figure 19. Space closed.
of the micro implant. Depending on the moment of force, a BH CW or CCW is placed.
For patients with need of minor treatments as the case showed bellow, the BH implant is the best choice. A colleague who wants to place an implant for the #24 sent this patient because the space was too big. It was decided to distalize #23 and correct the midline deviation with teeth drift. At the same time the #36 will be corrected. Small loops are attached to the BH implant and to the brackets (Fig 23).
Figure 20. End of treatment. Good parallelism on the left side. Difficulties to achieve the same result with traditional mechanics on the right side for the same time of treatment.
Figure 21. Lower incisors intrusion. Lower arch attached to micro implants
Figure 22. Lower incisor intrusion with an utility arch in an adult patient with osteoporotic condition. Utility arch was attached to micro implants. A build up in composite and a bracket was constructed for support.
Figure 23. Distalizing the canine and aligning #36. Two months after the midline was corrected.
Figure 24. BH implant used for upper molar distalization. The direction of the implant head is dependent of the movement intended to do.
Figure 25 a-c. The BH implant was placed between #26 and #27 and a segmented wire was used to correct the cross bite of #27.
Figure 25d. Using a transpalatal arch attached to a BH mini implant.
Other possibilities with the BH implant include distalizing molars (Fig 24) or cross bite treatment (Fig 25a-d).
Treatment can also be carried out without full fixed appliances. BH implant can be the skeletal anchorage for all the treatment (Fig 26, 27). This is very useful for adult patients with osteoporotic condition or molars mobility when en mass retraction and levelling is required.
Figure 26. A case treated with 4 premolars extractions. Alignment and retraction is achieved with BH implant anchorage.
Figure 27. Biprotrusion case with crowding treated with 4 premolars extractions and BH implant for en mass retraction and levelling.
Discussion and Conclusion
Many times orthodontists encounter problems concerning lack of anchorage. Although extra oral appliances can be used to provide anchorage, they depend on patient’s cooperation.
Anchorage plays an important role in orthodontic treatment. Endosseous implants were used for absolute anchorage however they have limitations.
Skeletal cortical anchorage using micro implants start to be used as a routine for absolute anchorage. With this approach, the treatment is faster and don’t need patient’s cooperation.
Bracket head type is a revolutionary system to help orthodontic treatment. Minor corrections can be made without the need of full fixed appliance. Segmented wires can be attached to the micro implant to move teeth.
References
1. Ritto A.K., Kyung H.M. Solutions with Micro Implants. Ortodontia Journal 8:6-13; 2004.
2. Ritto A.K., Kyung H.M. Soluções com micro implantes. Orthodontic Cyberjournal www.oc-j.com 2004
3. Ritto A.K. Micro Implants in Orthodontics. Int. Journal Of Orthod. 15 (3): 22-24;2004
4. Ritto A.K. Easy movements with mini implants. Thai Jornal Orthod. (in press).
Contributed by:
A. Korrodi Ritto DDS, PhD
ESpecialist in orthodontics
Hee-moon Kyung DDS, MSD, PhD
Hee-moon Kyung is Professor Department of Orthodontics, School of Dentistry, Kyung-pook National University, Taegu Korea.
