Orthodontic anchorage provided by teeth and conventional methods is often insufficient in managing severe and complex malocclusion. Alternate anchorage systems are required to enhance the quality of treatment outcomes and induce tooth movements, such as the intrusion of the molars and vertical control of the buccal segments. Dental implants are considered immobile in bone and could be a source of absolute anchorage. The dental implants, although proved to be excellent anchorage sources, could not gain popularity among orthodontists for their very properties and quality of osseointegration, making their removal difficult, if not impossible, after they have served their purpose.

The invention of non-osseointegrated, temporary anchorage devices (TADs), a relatively new armamentarium, is considered a game changer in the clinical practice of orthodontics. TADs have become popular in a fleeting time, and this subject is now the latest clinical and research fad in orthodontics. Researchers and clinicians are excited about the possibilities of new inventions in temporary anchorage devices and the clinical potential they have to offer.

TADs include mini screw implants (MSI), skeletal anchorage systems (SAS) and bone plates on the zygoma and mandible that are inserted to achieve anchorage and later removed on completion of their utility or after the completion of orthodontic treatment. Temporary anchorage devices (TADs) and temporary skeletal anchorage devices (TSADs) are often used interchangeably. However, we typically refer to mini screw implants as TADs and reserve the term TSAD for more advanced anchorage devices, such as extra alveolar mini screws, infrazygomatic crest screws (IZC), buccal shelf screws, bone pates and and similar devices.

The first attempt to utilise an implant as a stable device for orthodontic anchorage was conducted by Gainsforth and Higley in 1945. They implanted Vitallium screws into a dog’s ramus to distalise maxillary canines.

Per Ingvar Branemark introduced the concept of osseointegration and titanium implants for replacing teeth in the mid-1960s. ^,

Creekmore and Eklund inserted a surgical Vitallium bone screw just below the anterior nasal spine for deep bite correction. Maxillary central incisors were intruded 6 mm in 1 year of treatment by this method. Similar outcome was achieved for the intrusion of lower incisor teeth by Kanomi by using surgical titanium bone screw in 4 months of treatment. He implanted a MSI of 1.2 mm diameter and 6 mm long in the alveolar bone between the root apices of mandibular incisors and did intrusion of the mandibular incisors. Over the past few years, success with several types of implants has been reported; presently, these devices are termed TADs ( Table 72.1 ).

TAD is a device that is temporarily fixed to the bone for enhancing orthodontic anchorage either by supporting the teeth of the reactive unit (indirect anchorage) or by obviating the need for the reactive unit altogether (direct anchorage), which is subsequently removed after use.

The implantable anchorage devices can be grouped as osseointegrated or mechanical/non-osseointegrated.

These can also be grouped based on the types of anchorage devices used on the following basis:

• 1.

  Endosseous implants

  • These osseointegrated implants are modified forms of conventional dental implants. These are placed in the palate, retromolar area and the area of absent or missing teeth. Osseointegrated implants can withstand more force than mechanically retentive implants (TAD), but they have drawbacks like a waiting period before loading, limitation of placement because of their relatively large size, cost, the extensive surgical procedure required in the placement and difficulty in removal. Such implants were earlier used in the palate for intraoral molar distalisation.

• 2.

  Surgical miniplates ^,

  • Modified or conventional L- or T-shaped surgical titanium miniplates are used with an intraoral extension to anchor the orthodontic force. These are placed in the region of a thick cortex similar to the zygomatic region and the buccal cortex of the mandible. A skeletal anchorage system has been successfully used for en masse distalisation of the lower arch in class III cases. In maxillary dentition, these have been used to intrude the buccal segment in open bite cases and en masse molar distalisation.

  • Surgical miniplates offer perfect anchorage but involve more extensive surgical procedures, the presence of considerable post-operative swelling, and discomfort to the patient, and thus require surgical removal again.

• 3.

  Mini screw implants (MSIs) ( Fig. 72.1 )

  • Mechanically retentive MSIs can provide anchorage in orthodontics for a short duration. MSIs are commercially available in the screw diameter range of 1.2–2.7 mm and lengths varying from 4 to 12 mm. Because of their tiny diameter, these are highly versatile in their placement sites. The most common site for their placement is the inter-radicular bone between the teeth. MSIs are grouped as absolute anchorage units, although they might slightly tilt or move after loading.

  • MSIs can be broadly grouped based on their material composition, shape, head type, placement technique and site ( Table 72.2 ).

    TABLE 72.2

    Classification of intra alveolar MSIs

    1. Based on composition a. Biotolerant • Stainless steel • Chromium cobalt alloy b. Bioinert • Titanium • Carbon c. Bioactive • Vitroceramic • Apatite hydroxide • Ceramic-oxidised aluminium d. Bioresorbable • Polylactide 2. Based on the site of placement a. Buccal b. Palatal 3. Based on the technique of placement a. Drilling b. Tapping 4. Based on shape a. Cylindrical b. Tapered c. Combination 5. Based on size a. Length 4–12 mm (small, medium, large) b. Diameter 1.15–2.5 mm (small, medium, large) 6. Based on head type a. Small head type b. Long head type c. Circle head type d. Fixation head type e. Bracket head type f. Hook head type g. Combination of tube slot and hook h. Interchangeable head type 7. Recent modifications a. Zinc oxide coated b. Silver coated

  

  Miniscrew implant (MSI).

  Most MSIs are 4–12 mm long and 1.2–2.7 mm in diameter. Kind courtesy: Prof. Hee-Moon Kyung, Kyungpook National University, Daegu, Korea.

  Source: https://dentos.co.kr/2010/products/microimplants/

Materials

The materials used for implants can be grouped into four categories:

• (i)

  Biotolerant: Stainless steel, chromium-cobalt alloy

• (ii)

  Bioinert: Titanium and carbon

• (iii)

  Bioactive: Vitroceramic, apatite hydroxide and ceramic-oxidised aluminium

• (iv)

  Bioresorbable: Polylactide

Conventional MSIs are typically made of bioinert medical-grade titanium alloy or titanium-coated stainless steel. The most commonly used material is a medical-grade titanium alloy known for its biocompatibility. Grade V medical titanium, also known as Ti6Al4V, is an alloy of titanium, aluminium and vanadium, and is the preferred material due to its combination of biocompatibility and high strength, which is greater than that of commercially pure titanium. The high strength of MSIs is important for withstanding insertion torque and orthodontic loading stresses. Although orthodontic mechanisms usually apply forces of no more than 300 g, MSIs are designed to withstand load up to 500 g.

MSIs are designed to be mechanically retained in the bone because they should not osseointegrate for the ease of subsequent removal following completion of their use.

They should preferably be self-drilling to make the MSI placement procedure simple. The head of the MSI is designed with a provision for the attachment of an orthodontic spring or auxiliary or bracket head to receive an arch wire.

A conventional MSI has the following parts:

• Head : It is the portion exposed in the oral cavity. It provides attachments for springs and elastics. It has a screwdriver slot or a particular design/shape to engage the miniscrew driver for implant placement. A solid head with a screwdriver slot is recommended for easy insertion and removal.

  • For orthodontic attachments, a hole through the head and button is suitable. Many orthodontists prefer a bracket head MSI for the versatility of attachment these provide.

  • Bracket head designs with slots are also used in some cases for direct wire engagement or indirect anchorage.

  • A two-component MSI provides a separate screw and a head portion with different neck lengths, which are screwed together after placement in the bone. Such a design offers the flexibility of interchangeable heads with distinctive designs to fulfil the needs of biomechanics. This model has been suggested to have reduced the risk of fracture at the neck.

• Neck: The screw neck/trans-mucosal portion is the portion that passes through the mucosa. The neck connects the intra-bony portion of the MSI to the head. The neck remains in contact with oral mucosa or gingival attachment. The emergence profile from bone to mucosa is often equal to the maximum outer diameter of the screw. Different neck lengths are available for variable mucosal thickness by some manufacturers, while most of the others offer a uniform length. The surface of the neck portion should be smooth and well-polished to facilitate contact with mucosa and discourage plaque accumulation around the neck. The junction of MSI with mucosa is critical since most MSI failures begin with peri-implant inflammation at this site.

• Intra bony screw: It is the part of the MSI that embeds into the cortical and medullary bone to provide retention. The thread of the screw around the shank or main body of the MSI has a cutting edge that facilitates insertion. The depth of the cutting blade and its angle considerably influence the stresses generated during insertion and, hence, the amount of insertion torque required to insert the MSI. The MSIs are either cylindrical or tapered in shape. MSIs are designed as self-drilling and self-tapping implantable devices. Self-drilling implants have a sharp apex and cutting edges and do not require a pilot drill for insertion.

Miniscrew length and diameter

Commercially available MSI size ranges in length of 4–12 mm and diameter of 1.2–2.7 mm. The length of an MSI is defined as the length of the threaded body and not the length of the entire screw. The total MSI length value is determined by the screw part, neck, and head length.

The major diameter of the MSI is the maximum diameter determined by the outer diameter of the threads and is referred as diameter in day-to-day clinical practice. The minor diameter relates to the inner (core or shaft) diameter, which usually ranges from 0.2 to 1.6 mm ( Fig. 72.2 ).

MSI parts.

(A) MSI length. (B) Outer and inner diameters and pitch. (C) Symmetric thread design. (D) Asymmetric thread design.

Primary considerations in choosing the site of the MSI include the desired biomechanical advantage required, cortical bone thickness, inter-radicular bone volume and proximity of vital structures, such as neurovascular bundle, inferior alveolar canal, mental foramen, palatine foramen, and vessels in the palate to the implant site ( Fig. 72.3 ).

Safe zones for miniscrews.

(A) Safe and danger zones are determined by the mesiodistal lengths in the maxilla and mandible. (B) Safe and dangerous zones are also determined by the buccopalatal distance in the maxilla and the buccolingual distance in the mandible. The red areas indicate danger zones, and the green, blue, yellow and orange areas indicate the safe zones..

Source: From Purmal K, Alam MK, Pohchi A, Abdul Razak NH. 3D mapping of safe and danger zones in the maxilla and mandible for the placement of intermaxillary fixation screws. PLoS One. 2013 Dec 19;8(12):e84202

Posterior region ^, : Most frequently used MSI sites are buccal inter-radicular bone in the maxilla and mandible in the molar-premolar area. In the maxilla and mandible, the MSI can be safely placed between the roots of the second premolar and first molar and between the first molar and second molar through the buccal cortical plate.

In the palate, the optimal site is the inter-radicular space between the first and the second premolars, the second premolar and first molar, and the first and second molars. The more apical the site, the safer the placement.

MSIs inserted in the posterior palatal slope should be placed mesially to the second molar to avoid damage to the greater palatine artery and the palatine nerve exiting at the greater palatine foramen.

Anterior region : The optimal site in the maxillary anterior teeth lies between central and lateral incisors at an approximate distance of 6 mm above the cementoenamel junction (CEJ) on the labial cortical plate. One MSI each can be placed on either side of the centre line between the central and lateral incisors. A single MSI can also be inserted in the maxilla in the midline just below the anterior nasal spine. In the mandible, the excellent anterior site lies at the inter-radicular bone between the lateral incisor and canine.

For the anterior palate, MSI length is determined by the bone depth, which can be assessed on a lateral cephalogram. The anteroposterior location and inclination of the MSI are planned to optimise the available bone. MSIs can also be inserted in para-median positions in the palate, usually 6–9 mm posterior to the incisive foramen and 3–6 mm laterally.

Other locations: These are retromolar, infra-zygomatic, maxillary tuberosity and mandibular symphysis ( Fig. 72.4 ). Also see chapter 73 on extra alveolar mini screw implants.

Various sites for miniscrew placement.

(A) Buccal sites on maxilla. (B) Palatal sites on maxilla. (C) Buccal sites on mandible.

Case selection, informed consent and records: The patient’s medical history and assessment of the suitability of the patient to undergo the additional procedure of miniscrew placement are of great significance. The patient’s oral cavity must be free from gingival inflammation and periodontal disease. He/she should have enough motivation and aptitude to put in the extra effort to maintain a plaque-free mouth, especially around the miniscrew. In addition to routine orthodontic records, intraoral radiographs of the proposed miniscrew site(s) are obtained to assess the inter-radicular bone width, any evidence of crestal bone loss, the length of the roots and their mesio distal angulation . The patient and his/her parents should be well informed and explained the procedure and the course of events, including possible complications associated with this mode of therapy. Informed consent should always be obtained. Any concerns about the quality of bone on routine X-rays, medical history or history of medication that can influence bone metabolism call for an assessment of bone density. Bone density values can be obtained as site specific through CT scan or cone beam computed tomography (CBCT). It has been suggested that D4 and D5 bone types are not good for implants.

Miniscrew selection: The selection of MSI size and design is governed by the anatomical limits of its placement and intended biomechanics. While the selection of miniscrew diameter depends on the availability of inter-radicular bone, miniscrew length depends on the buccolingual/buccopalatal dimensions of the alveolus or nasopalatal thickness of the palate. Longer implants are used in the retromolar area, while regular sizes suffice for buccal inter-radicular bone in the maxilla and mandible. Implants of smaller length but larger diameter are more suitable for the anterior palate.

We have most often used 1.4–1.5 mm diameter MSI and 7–8 mm length in the maxilla and mandible into the buccal inter-radicular bone of the maxillary second premolar and first molar for en masse retraction of anterior teeth in premolar extraction cases. For intraoral molar distalisation, we found 1.4–1.6 mm diameter screws in the length of 8 mm suitable when between the roots of the first and second premolars. Other important considerations of miniscrew selection are:

A miniscrew intended to be placed between roots should be narrow enough to get accommodated leaving at least 1 mm bone around its maximum diameter.

For insertion into the trabecular bone, such as in the retro-molar area in the mandible, a longer screw is selected. A minimum of 2 mm diameter, 10 mm length or longer MSI is appropriate. Extra alveolar mini screw implants are discussed in chapter 73 .

MSIs of 1.2–1.3 mm diameter can withstand as much as 500 g of force, although most orthodontic applications need forces of less than 300 g. A larger diameter (1.4–1.6 mm) miniscrew can be used if there is enough space between the roots and greater force is needed.

If the inventory permits, the MSI of the proper neck height appropriate to the mucosal thickness at the implant site should be used.

Surgical procedure : MSI placement is a short and simple procedure that must be performed with high diligence. The procedure should strictly adhere to asepsis in the operatory, including the use of all disposables. The armamentarium should be arranged on a sterile tray.

A miniscrew placement guide can be created based on a recent plaster model. Various miniscrew guide devices have been developed to assist in accurate miniscrew placement, although their sensitivity can vary. Recently, clinicians have been using 3D CBCT and custom surgical guides printed using stereolithographic techniques. This method improves the precision of placing orthodontic self-drilling MSIs near dental roots and maxillary sinuses. ^,

Following an accurate clinical assessment and observations on a recently taken intraoral periapical X-ray, the location and angulation of the self-drilling screw is predetermined. The patient is also advised to start with 250 mg amoxicillin or a suitable antibiotic on the night before the surgery, and those who seem to be less tolerant of pain can be given a safe pain killer 1 h before surgery. The mouth is thoroughly cleaned of any material alba or plaque, especially around the miniscrew placement zone.

The patient is asked to rinse with 10 mL of 0.12% chlorhexidine gluconate mouthwash for 1 min. The procedure can be done under 15% topical anaesthesia; however, we have found much comfort with infiltration of 0.5 mL of local anaesthesia. The patient is made to feel relaxed and allayed of anxiety before MSI insertion is initiated. Once the location of the MSI is marked, the process of the MSI insertion is initiated. For self-tapping non-self-drilling types of screw, a dent is made on the cortical bone first with a 0.9 mm round bur at 300–500 rpm under copious saline irrigation. Irrigation helps to dissipate heat generated by drilling, which can be detrimental to the success of the miniscrew.

Using an appropriate driver: Miniscrew is then carefully driven at the pre-determined site at the desired angle. A buccal screw in the premolar-molar area is placed between the roots of teeth at an angulation of 45–60 degrees to the long axes of the teeth in the maxilla. The insertion angulation is lowered to 10–30 degrees in the posterior mandible. The miniscrew location is confirmed on an intraoral periapical (IOPA) radiograph taken immediately upon procedure completion.

The immediate post-operative phase would require strict oral hygiene maintenance, restrictions on hard food to avoid damage to miniscrew and a course of antibiotics. The painkillers can be taken as and when needed.

Further follow-up after a week should include a careful review of any unusual signs of inflammation and a clinical review of the mobility of the implant. Miniscrews that are likely to fail would show inflammation around the neck and mobility within the first few days. After every meal, the patient is instructed to brush around MSI with a soft brush. Chlorhexidine mouthwash (0.12%, 10 mL) should be used at least twice daily. The patient should be educated to keep an eye on the MSI that becomes mobile, or if there is pain in and around MSI, he should report it to his orthodontist immediately.

There is a general agreement that Mini-Screw Implants (MSIs) are not meant to achieve osseointegration and rely instead on mechanical locking within the bone for anchorage. Consequently, most clinicians recommend immediate loading of MSIs with light forces. However, in our practice, we prefer to wait for a 2–3 week cooling period before loading an MSI, following Kharbanda’s protocol.

Drilling the MSI (self-tapping or self-drilling) results in bone compression, stresses and microfractures of lamina dura and alveolar bone, resulting in bone trauma, collection of bone debris and release of inflammatory mediators. Studies by our group of researchers have extensively focused on the stability and peri-implant inflammation measured through the peri miniscrew implant crevicular fluid (PMICF). The analyses revealed the presence of inflammatory markers in PMICF within 1 h and 24 h of MSI insertion and loading. The inflammatory markers gradually decrease towards the baseline at 3 weeks. Dr. Kharbanda’s protocol, therefore, follows a delayed loading after 3 weeks to enhance stability of MSI.

We prefer an indirect loading protocol for the treatment of maximum anchorage cases, especially in bimaxillary protrusion and severe class II cases ( Fig. 72.5 ). This protocol necessities the use of a triple buccal tube on maxillary molars and a double tube on mandibular molars. An auxiliary wire framework, ‘K-Connector’, is fabricated on a 0.017 × 0.025-in. stainless steel wire, which connects the molar at its auxiliary tube and the bracket head of the MSI ( Figs 72.6 and 72.7 ). The MSIs are indirectly loaded for en masse retraction of the anterior teeth using a conventional sliding mechanism ( Fig. 72.8 ). The connector is so fabricated that it is passively fitted in slots on the MSI or the connected molar without exerting any force at both ends. The MSI-supported indirect anchorage for en masse retraction is now fully prepared. In all cases involving first premolar extractions, simultaneous en masse retraction of the upper and lower anterior teeth is achieved by activating 200g NiTi springs. Each spring is connected to a molar hook and is activated to attach to a soldered intermaxillary hook. The base wire used is stainless steel (SS), measuring 0.019 × 0.025 in., with a slight torque applied. The patient is followed every 6–8 weeks. Once the extraction spaces are closed, the MSIs, along with the connector, are removed, and finishing is carried out in the usual manner.

A schematic diagram of Kharbanda’s protocol for MSI anchorage.

Steps in the fabrication of K universal connector.

(A) MSI inserted into the buccal inter-radicular bone between the second premolar and first molar. (B) 0.017 × 0.025-in. stainless steel wire is bent gingivally immediately mesial to the molar auxiliary tube so that the free end passes distal to the MSI head, touching it. (C) A point is marked on the wire at the level of the MSI slot. (D) A bend is given in the wire at the marked point so that the wire is now parallel to the MSI slot. (E and F) The torque in the horizontal segments of the wire is adjusted so that the wire framework can be passively seated.

K-connector for indirect MSI anchorage.

(A) Miniscrew placed interdentally to indirectly enhance orthodontic anchorage in an adult male with severe arch length discrepancy. (B) A successful miniscrew is centred in the thin interdental septum bone. (C) A specially designed wire connects the miniscrew head to the maxillary first molar tube. (D) The bracket head is coated with light cure composite to prevent irritation to cheek mucosa.

Indirect anchorage with miniscrews.

En masse retraction using Sentalloy (Dentsply GAC 355 Knickerbocker Avenue Bohemia, NY, USA) closed coil spring attached between gingivally soldered hook on arch wire and miniscrew reinforced molar.

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