Temporary anchorage devices (TADs) in orthodontics

Introduction:• Anchorage control is one of the most

important aspects of orthodontic treatment. The success of orthodontic treatment depends on the anchorage protocol planned for a particular case .(1)The current perspective of implants in orthodontics is mainly being investigated with the use of TAD which are relatively new arnamentarium in clinical practice.(2)

History

• Gainforth and Higly(1945)-studied effectiveness of vitallium screws and stainless steel wires in the mandibles of dogs to retract the maxillary canine.

• Branemark and coworkers (1964,1969)-worked on concept of Osseo integration and use of titanium implants to replace missing tooth.

Cont.

• Linkow(1969)-First reported a patient treatment with the use of Osseo integration implant for both restorative and orthodontic purpose.

• Creekmore and Eklund (1983)- used surgical vitallium bone screw just bellow the anterior nasal spine to treat deep overbite and it was 1st clinical report on the use of TAD.

Cont.

• Kanomi (1997)-first reported the clinical use of mini-implants for orthodontic anchorage. He implanted in the alveolar bone between the root apices of mandibular incisors and did intrusion of mandibular incisors.(2)

Classification1. According to the shape and size: I) Conical (Cylindrical) a) Miniscrew Implants b) Palatal Implants c) Prosthodontic Implants II) Mini plate Implants III) Disc Implants (Onplants)2. According to Implant bone contact: I) Osteointegrated II) Non-osteointegrated3. According to the application: I ) Used only for orthodontic purposes. (Orthodontic Implants) or TAD (temporary anchorage devices) I I ) Used for prosthodontic and orthodontic purposes.(1)

Cont.

• TADs can also be grouped based on types of anchorage device used on the following basis-

1.Endosseous implants2.Surgical miniplates3.Miniscrew implants(2)

Endosseous:

-These Osseo integrated are modified form of conventional dental implants.

-Placed in palate,retromolar area,area of absent or missing teeth.

-can withstand more force than mechanically retentive implants.

-Drawback-limitation in the area of placement,

Cont.

Because of large size-extensive surgical procedure-difficulty in removal-costly

Surgical miniplates

1.Modified or even conventional L or T shaped surgical titanium mini plates

2.Placed in thick cortex similar to -zygomatic region -buccal cortex of mandible.

3.Use-en mass distalization of lower arch in class-3,maxillary intrution of buccal segment in openbite,en-mass maxillary molar distalization

Miniscrew implants

1.Mechanically retentive miniscrew implants used for short period.

2.The tiny size( diameter 1.2-1.7mm and length 4 to 12mm) screws are versatile in site of placement most commonly inter –radicular bone between teeth.

Classification of miniscrew of implants

1.Based on composition Biotorant Stainless steel Chromium-cobalt alloy Bioinert Titanium Carbon Bioactive Vetaroceramic Apatite hydrxi Ceramic oxidised aluminium Bioresorbable polyactide

Cont.2.Based on the site of placement Buccal Palatal3.Based on technique of placement Self-drilling Tapping4.Based on shape Cylindrical Tapered Combination

Cont.5.Based on size Lenth4-12mm(small,medium,large) length1.15-2.5mm(small,medium,large)6.Based on head type Small Long Circle Fixation Bracket Hook

Design and parts

Conventional orthodontic miniscrew implants are made of bioinert pure titanium or titanium alloy or titanium coated stainless steel. Among these titanium alloy (Ti6Al4V) is the most commonly used materials for its biocompatibility and high strength property that it can withstand torque insertion and stresses of orthodontic loading. screws are designed to withstand up to 500g force.

Cont.

Mini screws are designed to be mechanically retained in the bone because they should not Osseo integrate for the ease of subsequent removal following completion of their use. They should be preferably self drilling to placement.(2)

Parts

1.Head: It is the portion exposed in oral cavity.It

provides attachments for spring and elastics.It has a screw driver slot or a specific shape to engage the miniscrew driver for implant placement. Solid head with a screw driver slot is recommended for easy insertion and removal.

Cont.

2.Neck: Screw neck or Transmucosal portion that

passes through the mucosa. The neck connect the main screw with the head remains in contact with mucosa. The neck should be smooth and well polished to facilitate contact with mucosa and discourage plaque accumulation arround the neck.

Cont.

3.Screw: It embeds into the cortical and medulary

bone to provide retention.The screws are designed self drilling and self tapping. self drilling is one that does not require a pilot hole and has either a sharp tapered apex to allow placement or a notch in the tip to drill through the cortex.

Cont.

self tapping mimiscrews are able to create their own threads as they advance.These are two type

thread forming-compress the bone around the thread as the miniscrew advance.

thread cutting- either a notch at the tip parellal to the long axis or a sharpened thread that actually cuts threads into the bone as the miniscrew is inserted.

Indication of TAD

1.As maximum anchorage requirements in retraction such as high angle bimaxillary protrusion.

2.In case of missing teeth eg.1st molar it can provide anchorages well as manage the space.

3.To achieve difficult tooth movements- - anterior and posterior intrusion -en mass desalination of upper and lower

arches.

Cont.

- Molar up righting - Molar distalisation4.In adjunctive adult orthodontics for difficult

tooth movement.5.Implants are even used for attaching

orthopaedic forces to jaws when there is lack of anchorage units.

Limitations:

1.Orthodontic miniscrew implants are not indicated in the patient having systemic problems that affect bone metabolism and major medically compromising condition.

2.Patients younger than 12 years who have not yet completed skeletal growth.

3.In heavy smokers and patient with bone metabolic disorders.

Cont.

4.These should not be placed in the areas of bone remodeling such as a healing socket or near a deciduous tooth.

5.Thin cortical bone limits the use of miniscrew implants. Because miniscrew implants are mechanically retained ,loosening of screw can develop as a result of thin cortical bone, if thinner than 0.5 mm and also if bone density of trabecular bone is low.

Cont.

6.Clinicians skill.7. Ethical issue

Safe zone for miniscrew implants

1.Posterior region: Most common sites are inter radicular bone

between 2nd premolar and 1st molar and between 1st and 2nd molar.In palate inter radicular bone between 2nd premolar and 1st molar and between 1st molar and 2nd molar. In posterior palate should be placed mesially to the 2nd molar to avoid damage of greater palatine artery and the palatine nerve.

Cont.2.Anterior region: In maxilla between central and lateral incisors

at 6 mm above CEJ.A single ms can placed in maxilla in the midline below anterior nasal spine. In mandible between lateral incisor and canine.

For the anterior palate, ms length is determined by the bone depth assessed in cephalogram. The anteroposterior location of ms are planed to optimize the available bone.In paramedian portion of palate ,6-9 mm posterior to the incisive foramen 3-6 mm laterally.

Cont.

3.Other location: mandibular symphysis, retromolar

infrazygomatic and maxillary tuberosity areas.(2)

Miniscrews placement protocols1.Case selection: Routine orthodontic records,intraoral

radiograph of the miniscrew site to asses the bone width. Crestal bone loss,root lenth ,angulation of roots.Assesment of bone density required on if doubt exist on quality of bone on routine X-rays or medical history or history of medication which can alter bone metabolism.Bone density value obtained through CT scan or cone beam computed tomography(CBCT).

Cont.

2. Miniscrew selection: Selection of miniscrew size is governed

by the anatomical limits of its placement.longer implants are used in retromolar area while conventional in inter radicular bone in maxilla and mandible. We have used 1.4-1.5 mm in the length of7-8 mm length inter radicular area of maxilla and mandible.

Cont.

Other considerations: A miniscrew intended to be placed between

roots should be narrow enough to get accommodated and should have at least 1 mm bone around its maximum diameter.

Miniscrew implants having 1.2-1.3 mm diameter can withstand 500g force where orthodontic application need forces of less than 300g.

Surgical procedure:

Following an accurate clinical assessment and observations, the patient is advised to start suitable antibiotic(250 mg amoxicillin) on the night before surgery.The mouth is thoroughly cleaned .

1. patient rinse with 10ml of o.12% chlorhexidine gluconate mouth wash for 1 minute.

2.Local aneasthesia

Cont.

3. Miniscrew is then carefully driven at predetermined site at the desired angle using appropriate driver.(45-50 to long axis in maxilla and 10-30 reduce in posterior mandible).

4. Post operative care. Careful review of unusual signs of inflammation and check on mobility of implant.

Removal:

• Miniscrew can be removed under topical anaesthesia with the instruments used for driving followed by anticlockwise turns by holding with tweesers.

Safe zone

Safe zone

Refference

1.Temporary anchorage device insertion variables: effects on retention

Joseph S. Petreya; Marnie M. Saundersb; G. Thomas Kluemperc;

Larry L. Cunninghamd; Cynthia S. BeemaneABS.Angle orthodontist.vol 80:no 04;20102.Om Prakash Kharbanda .Orthodontics

diagnosis and management of malocclusion.