Temporary AnchorageDevices in Orthodontics

By – Dr. Parag S. Deshmukh

Contents

• Defination of implant.

• Introduction.

• Historical background.

• Parts of implants.

• Types of implants.

• Bone physiology.

• Indications and contraindications.

• Treatment planning.

• Clinical application (miniimplant as absolute anchorage)

• conclusion

Introduction

• Traditionally, orthodontists have used teeth, intraoral appliances, and extraoral appliances, to control anchorage—minimizing the movement of certain teeth, while completing the desired movement of other teeth.

• However, because of Newton’s third law, i.e., for every action there is an equal and opposite reaction, there are limitations in our ability to completely control all aspects of tooth movement.

• The success of orthodontic treatment hinges on theanchorage protocol planned for a particular case.

• Use of extraoral anchorage devices such as headgears requires full patient cooperation, which is sometimes not possible and is unpredictable.

• Introduction of implants in orthodontics have solved this problem.

• Implants have become one of the best sources of reliable anchorage.

• Mini implants have revolutionized the field of anchorage in orthodontics.

IMPLANT TERMINOLOGY :

Implant:

As defined by Boucher Implants are

alloplastic devices which are surgically

inserted into or onto jaw bone.

Osseointegration: BRANEMARK

An intimate structural contact at the

implant surface and adjacent vital bone, devoid

of any intervening fibrous tissue -

Branemark(1983).

TAD• A TAD can be defined as a device that is

temporarily fixed to the bone for the purpose of 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.

HISTORY OF IMPLANTS

GAINFORTH AND HIGLEY(1945) first published the use of

subperiostel vitallium implant to retract maxillary canines in dogs

LINKOW (1969) described endosseous blade implants with

perforation for orthodontic anchorage.

KAWAHARA( 1975) developed Bioglass coated ceramic implant

for orthodontic anchorage.

THE BRANE MARK ( 1964,1969, 1977) MENTOR OF MODERN

IMPLANT SURGERY described the high compatibility and strong

anchorage of titanium in human tissue.

Various bioactive ceramics such as glass ceramic (BROMER ET AL

1977,HENCH ET AL 1973) ,

CREEKMORE(1983) reported the possibility of skeletal anchorage in orthodontics

ROBERTS(1984) used conventional two stage implant in the retromolar region to help reinforce anchorage successfully closing first molar extraction site in the mandible .

After completion of the orthodontic treatment the implant were removed and histologically analysed . They found a high level of osseo integration had been maintained despite the orthodontic loading.

Turley et al ( 1988) used endo-osseous implants in dogs as anchorage for the application of variety of orthodontic and orthopaedic forces

Weherbein and colleagues (1990’s) developed palatal implants called “Straumnn orthosystem” which was specially designed for orthodontics anchorage

Kanomi (1997) first reported the clinical use of mini implants for orthodontic anchorage. He implanted mini bone screw of 1.2 mm diameter and 6 mm length in the alveolar bone between root apices of mandibular incisors and did intrusion of mandibular incisors

PARTS OF IMPLANT The commonly used implant screw/plate has

two parts

a) Implant head

b) Implant body

Head

The head must be of sufficient dimension to accept and hold any coupling elements selected for a particular application.

Different head designs also require different dimensions.

A small diameter and lower profile of the miniscrew head are important for oral hygiene and patient comfort (Lee et al., 2009)

• Bracket like head design, on the other hand, offers theadvantage of three dimensional control and allows thescrew to be consolidated with a tooth to serve asindirect anchorage.

• Examples of this type include Aarhus Mini Implant,Dual Top Anchor System and Temporary MiniOrthodontic Anchorage System.

Neck

• Transmucosal portion that passes through the mucosa.

• Different neck lengths are available for variable mucosal thickness by some manufacturers

• It should be smooth and well polished to facilitate contact with mucosa and discourage plaque accumulation around the neck.

• Most miniscrew failure begins with peri-implant inflammation at this site.

Screw

• It embeds into cortical and medullary bone to provide retention.

• Cutting edge facilitates insertion.

• Screws are either cylindrical or tapered.

• Screws are designed as self drilling and self tapping types.

Miniscrew length and diameter

• Size ranges in –

Length : 4-12 mm

Diameter : 1.2- 2.7 mm

Thread design

• Self Drilling:

It does not require a pilot hole.

It has either a sharp or a tapered apex to allow placement or a notch in the tip to drill through the cortex.

• Self tapping:

These screws are unable to create their own thread as the advance in the bone

Two designs are available that are-

Thread cutting

Thread forming

Mini-implant design factors

1. Diameter

• A diameter less than 1.1 mm is associated with a higher failure rate(Miyawaki et al., 2003, Park et al., 2006).

• A diameter greater than about 1.6 mm seems to confer no advantageand clearly wider screws run an extra risk of contact with tooth roots.This consideration is now largely of historic interest because almost allscrews are currently between 1.4 and 1.8 mm in maximum diameter

(Park et al., 2006).

• 2.0 mm screws are suitable for sites such as the zygomatic ridge orretromolar pad, where avoidance of roots is not an issue (Park et al.,2006)

2. Length

• This usually refers to the intraosseous threaded part of the screw.

• The range of available body lengths is typically 6 - 12 mm.

• This length does NOT seem to be a factor in stability if the screwis more than 5 mm long (intraosseous length) (Miyawaki et al.,2003, Park et al., 2006).

• All manufacturers produce screws of different lengths

• Longer screws may be advocated if the mucosal thickness is greater e.g. in the palate for alveolar placement.

Materials used

• The material must be nontoxic and biocompatible,

have favorable mechanical properties, and be able to

resist stress and strain with proven effectiveness in

clinical and experimental studies.

• The materials commonly used for implants can be

divided into 3 categories:

– Biotolerant - stainless steel, chromium-cobalt alloy.

– Bioinert - titanium, carbon

– Bioactive - vetroceramic apatite hydroxide,

ceramic oxidized aluminum.

• Conventional implants are made up of pure titanium or titanium alloy or titanium coated stainless steel.

• Grade V medical titanium which is an alloy of titanium, aluminium and vanadium; Ti6Al4V is the material of choice.

• High strength of miniscrew is desired so that it can withstand insertion torque and stresses of orthodontic loading.

CLASSIFICATION OF IMPLANT

• Based on the location

Subperiosteal : In this design, the implant body lies

over the bony ridge.

The subperiosteal design currently in use for orthodontic

purposes is the 'Onplant‘

(Block and Hofman, 1995)

Transosseous ; In this particular variety,

the implant body penetrates the bone completely.

• DISADVANTAGE:

Damage to the intrabony soft tissue structures like

the nerves and vessels .

Endosseous :• These are partially submerged and anchored

within bone. These have been the most popular

and the widely used ones.

• The endosseous implants are most commonly

employed types for orthodontic purposes.

Surgical miniplates:

Modified or conventional L or T shaped surgical titanium miniplates are used with an intraoral extension.

These are placed in the areas of thick cortex similar to zygomatic region and the buccal cortex of the mandible.

Skeletal anchorage system has been successfully used for enmass distalization of lower arch in Class III cases, in maxilla for intrusion of buccal segments in open bite cases, for en mass molar distalization.

These offers absolute anchorage but involves extensive surgical procedure.

based on the composition:

Biotolerent:

Stainless steel

Cobalt chromium alloys

Bioinert:

Titanium

Carbon

Bioactive:

Vetaroceramic

Apatite hydroxide

Ceramic oxidized aluminium

Bioresorbable:

Polylactide.

based on the site of placement:Buccal Palatal

Based on technique of placement: Self drilling Tapping

Based on shape: Cylindrical Tapered Combinition

based on the size: Length 4-12 mm (small, medium, large) Diameter 1.15 – 2.5 mm (small, medium, large)

based on head type: Small LongCircle FixationBracketHook

Since 1995 over 10 new systems of implant have been

introduced Based on the implant morphology:

a) Implant discs

i. Onplant

b) Screw designs - These include:

i. Mini-Implant

ii. Orthosystem implant system

iii. Aarhus implant

iv. Micro-implant

v. Newer systems such as the Spider screw.

They can also be classified depending on the area of

placement as:

a) Subperiosteal Implants

b) Osseous implants

c) Inter-dental implants

Characteristics of an ideal anchorage device include

• Simple to use• Inexpensive• Immediately loadable• Small dimensions, can withstand orthodontic

forces• Immobile• Biocompatible• Provides clinically equivalent or superior results

when compared with traditional anchorage systems.

Indications for implant in orthodontics

1. Provision of anchorage

A. Moderate to maximum anchorage need eg. Fullcusp Class II relationship or adults and older

adolescents (where functional appliances cannot be

used to gain anchorage).

B. Mild to moderate anchorage need when the anchor

unit is limited by an inadequate number of anchor

teeth (e.g early tooth loss or hypodontia) or

periodontal support.

2. Specific teeth movement

• En mass retraction especially in high angle class IImalocclusion where the extrusive tooth movementswould be unfavorable which contraindicates the useof intermaxillary traction to achieve the desired toothmovement.(Park et al., 2005)

• Canine retraction: Sharma et al. compared theanchorage loss with the use of TPAs or TADs and found2.5 mm of mesial movement of the U6s with theformer while the latter provided absolute anchorage(Sharma et al., 2012).

• Bimaxillary protrusion: Liu et al concluded that a better dental,skeletal and soft tissue effects of the TADs in treating these groups.For this reason, they recommended the TADs as routine anchoragedevice in patients with bialveolar dental protrusion (Liu et al.,2009).

• Molar distalization (Sugawara et al., 2006, Sugawara et al., 2004)

• For intrusion of anterior teeth (Lee et al., 2009)

• For intrusion of posterior teeth (Cousley, 2010). Regarding stabilityof molar intrusion by TADs. It was 83% stable (Lee 2008), Minimum3 months retainer after molar intrusion.

• For unilateral intrusion to correct cant of occlusion(Lee et al., 2009)

• Adjunctive treatment when full orthodontic appliance is notrequired and the aim is corrects the position of single tooth.

• Skeletal orthopaedic correction of class III (Ballard technique) (De Clerck et al., 2009)

• Miscellaneous

Provide attachment for artificial teeth in hypodontia cases.

To provide IMF during orthognathic surgery (Harris and Reynolds, 1991)

Contraindication for implant therapy:

Absolute contraindication:

Bleeding Disorders

Bone Metabolism Disorders

Immuno-compromised

Diabetes Mellitus

Anti-coagulant treatment

Pregnancy

Xerostomia

Titanium allergy

Relative contraindications:

When other conventional methods of anchorage are adequate.

Poor Oral hygieneSmoking Local Bone pathologyInadequate bone depth and qualityLocal factors like bone amount and local

infection

Limitations:

• Patients younger than 12 years who have not yet completed skeletal growth should have palatal miniscrews placed away from the midline suture in the paramedian region.

• Thin cortical bone limits the use of mini 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 density of trabecular bone is low.

• Cinician’s skill.

• Ethical issues: Enthusiastic use of an invasive and costly procedure like miniscrewanchorage in all patient is not recommended. There must be a definite indication and should have low risk- benefit ratio.

Bone physiology

IMPLANT-BONE INTERFACE

The relationship between endosseous implants and bone consists of one of two mechanisms :

Osseointegration:

• Acid etched ti screws routinely achieved osseointegration.

• Post operative healing of cortical bone supporting a miniscrewimplant involves the formation of endosteal callus and an intense remodeling response, deemed a regional accelatoryphenomena.

Bone Tissue

Three distinct types of bone (woven, lamellar, and composite) are involved in postoperative healing and maturation of the osseous tissue supporting an implant .

Woven bone :

• It has high cellularity, a rapid formation rate (30 µ/day or more), relatively low mineral density, high random fiber orientation an poor strength.

• It serves an important stabilization role in postoperative healing of endosseous implants .

• During the initial healing process woven bone fills all spaces at the bone-implant interface.

Lamellar bone:• It is the principal load-bearing tissue of the adult skeleton.

• It is the predominant component of a mature bone- implant interface.

• Lamellar bone is formed relatively slowly (less than 1.0 µ/day),has a highly organized matrix, and is densely mineralized.

Composite bone:• It is a combination of paravascular lamellar bone deposited on a

woven bone matrix.

• Formation of composite bone is an important step in achieving stabilization of an implant during the rigid integration process

The healing potential for an implant is determined by three factors:

(1)quality of bone at the site of implantation,

(2) postoperative stability of the implant,

(3) degree of integration of the interface.

• If there is good postoperative stability of the implant in cortical bone, the healing response involves six physiological stages:

1. Callus formation (0.5 month)- initial,

2. Callus maturation (0.5 to 1.5 months),

3. Regional acceleratory phenomenon (RAP) - (1.5 to 12 months) remodeling of the non vital interface and supporting bone ,

4. Osseous integration of the interface (1.5 to 12months)completion of the RAP, increased directcontact of living bone at the interface,

5. Maturation of supporting bone (4 to12months)completion of the RAP, secondarymineralization of new bone and increased direct

contact of living bone at the interface,

6. Long-term maintenance of osseointegration .

• Cutting /filling cones remodeling interface bone in vertical direction emanate from the endosseous surface.

• If the interface is biocompatible implants usually osseointegratebecause of progressive remodeling to replace the nonvital bone interface.

• In the presence of micromotion postoperative remodeling response may fail to osseointegrate the implant.

• The interface of nonintegrated miniscrews are responsible for mobility and movement of loaded TAD’s within bone.

TREAMENT CONSIDERATIONS

Suitability for implants

• Quantity and quality of the bone

• Age of the patient

• Reason behind their seeking implant placement.

Bone:

• Bone quantity and extent of ridge resorption are important factors to assess.

Age of the patient:

• Age of the patient is an important consideration, as implants are problematic if inserted in growing children for the following reasons

1. The use of palatal implants in anterior maxilla contraindicated because of midpalatal suture being open.

2. Resorption from the posterior part of the maxilla resulting from growth changes, could lead to exposure of implant into sinus.

3. Posterior part of the mandible continues to undergo growthchanges in all the planes of space ,and such as definitiveimplant placement in these area difficult to estimate.

4. Even when growth is complete and teeth appear fully erupted,infraocclusion of Implants supported crowns may occur. This isresult of minimal continued eruption of adjacent teeth, postadolescence, and is most frequently seen with upper lateralincisors.

Teeth Number & Existing Conditions

1.Size shape & diameter of existing dentition.

2.Tooth & root angulation.

3.More than 1.5 mm space between implant and naturalteeth.

Periodontium

Bone support :

1. Quality – Best is the thick compact cortical bone with core of dens trabacular cancellous bone .

2. Quantity – 6mm bucco – lingual width with sufficient tissue volume.

Sites of the implants

Implant as a absolute anchorage

Absolute anchorage

1.microimplants

2.miniplates

3.zygomatic ligatures

4.conventional implants

5.ankolysed teeth

6.palatine implants

7.onplants.

There are two basic forms of absolute anchorage

Direct anchorage :

When active segment is pulled directly from microimplant.

Indirect anchorage :

When active segment is pulled from the reactive segment, and this segment is fixed to microimplant to incraseanchorage.

Methods of anchorage control

Problem with Conventional anchors

Head gears require patient compliance so as to be an effective source of anchorage. If the patient is not co-operative enough with the treatment, anchorage preservation becomes a difficult issue to tackle.

There are also many reported cases of Head gear injuries.

• While problems with dental anchors are that, the anchor units experience a reciprocal effect of the forces applied to move the remaining teeth to their optimal positions – thereby tending to move towards the direction of the force applied.

• Therefore skeletal anchorage through implants is chosen to limit the extent of detrimental, unwanted tooth movement.

• The paradigm shift is the usage of implant as skeletal anchors to overcome the problems of conventional anchors.

Difference between conventional

and implant anchorage

APPLICATION OF IMPLANT IN

ORTHODONTICS

ORTHOPEDIC CORRECTION WITH IMPLANTS

Maxillary Protraction :

Smalley et al in 1988 used Branemark implants into the maxilla, zygoma, orbital and occipital bones of monkeys.

A force of 600 gm was delivered to maxillary and zygomatic bones.

A 12mm widening at the zygomaticomaxillary suture was seen and 16mm widening at zygomaticotemporal suture was observed.

The dental changes seen were a 5-7mm change in overjet .

However dental tipping also occurred along with skeletal protraction.

Implants for skeletal expansion

In 1995 - Movassaghi et al tested fronto nasal suture expansion in rabbits from an implanted titanium screw device. The plates were placed in frontal and nasal bones. After 4 weeks of healing, 55 gm force was applied . Force was applied for 5 weeks and a significant increase in growth to the tune of 6 mm across frontonasal suture was seen.

• In 1997 Andrew Parr et al conducted experiments on Mid nasal expansion using endosseous titanium screws.

• They divided the sample into 3 groups- 1 control and 2 experimental groups.

• 1 N and 3N loading forces were applied in the two experimental groups.

• Their results showed a 92% stability of implants.

• Sutural expansion of 5.2mm and 6.8 mm respectively was seen in the 1N and 3N load categories.

• Mineral apposition and bone formation rates were significantly higher in the experimental group.

• The 3N group showed more expansion but this did not affect the rate of bone formation across the suture.

ENDOSSEOUS IMPLANT:

Implants for dental anchorage a) Implants for intrusion of teeth Creekmore in 1983 published a case report of usage of a vitallium implant for anchorage, while intruding the upper anterior teeth. The vitallium screw was inserted just below the anterior nasal spine . After an unloading period of 10 days, an elastic thread was tied from head of the screw to the arch wire. Within one year, 6mm intrusion was demonstrated along with lingual torque .

• Another study by Southard in 1995 compared the intrusion potential of implants with that of teeth (dental anchors). Titanium implants were placed in extracted 4th premolar area in dogs, followed by an unloading period of three months. Then, an intrusive force of 50-60 gm via 'V' bend was effected. This was compared with intrusive potential of teeth on the other side using the same mechanics. No movement of implant was seen at the end of the experiment whereas, on the other side, the tooth acting as the anchor units tipped severely. Therefore, implants are definitely superior to the teeth acting as anchor units.

b) Implants for space closure

• Extensive research relating to usage of retromolar implants for orthodontic anchorage has been done by Eugene Roberts. The first clinical trial was on an adult wherein an atrophic extraction site had to be closed. A special implant was developed of size 3.8mm width and 6.9 mm length, which was placed in the retromolar area. A 0.021" X .025" SS wire was used for used for anchorage from the screw around the premolar bracket . The extraction spaces were closed using forces from buccal as well as the lingual sides by activating the lingual arch. The premolar was prevented from moving distally with the help of 0.021 X .025" wire acting as an anchorage. The modification in this technique as suggested by him in 1994 includes the usage of a .019" X.025" TMAwire ---This wire is termed as the anchorage wire.

A. Patient before treatment, showing missing mandibular first molarwith mesial tipping of second and third molars into extractionsite.

B. Beginning of active treatment, with anchorage wire In place. C. Molars translated mesially with no appreciable distal movement of

premolars. D. Five months after active treatment, 9 mm of mesial translation of

mandibular molar root apices.

• Although the retromolar implants popularised by Eugene Roberts are very efficient in preserving anchorage, they suffer from certain drawbacks, which in turn has hindered their acceptance in routine clinical practice.

DISADVANTAGE OF RETROMOLAR (ENDOSSEOUS) IMPLANT:

o The important limitations are :

A) Bulkiness of the implant and therefore the non suitability ofplacement in the inter-dental areas.

b) It involves a two stage procedure and therefore a long waitingtime before loading the implant.

c) Anatomical limitations - such as erupting teeth, nerve canal etc.also add to their minimal usage.

d) Cost of the implants - These are the root form implants used fortooth replacement and therefore, very expensive.

SUBPERIOSTEL IMPLANT

THE ONPLANT

• This is a classic example of a sub periosteal implant in Orthodontics , Developed by Block and Hoffman in 1995, this system consists of a circular disc 8-10 mm in diameter with a provision for abutments in the center of the superficial surface . These abutments would enable the Orthodontist to carry out tooth movement against the Onplant. The undersurface of this Titanium disc is textured and coated with Hydroxyapatite (HA). The Hydroxyapetite,being bioactive helps in stabilisation of the implant by improving integration with bone. The average thickness (height) of the implant is 3 mm . Lateral view Different shapes Internal surface

Method of Placement:

• The onplant is placed by a surgeon through a specialised procedure known as Tunneling. After making an incision in the posterior region of the palate, a sub- periosteal tunnel flap is created extending till the desired location, using an elevator. Care is taken to position the onplant as close to the midline as possible. The onplant is not disturbed for a period of 3-4 months to allow bio-integration. Later, the superficial surface of the onplant is exposed using a trephine and the desired abutment is then threaded on. Various head designs

Studies on Onplants:

• Extensive animal studies have been carried out on onplants. They point out to the fact that onplants bio-integrate and can tolerate a maximum force of 16 Ibs (1 pound = 450 grams).

• Block and Hoffman further suggest that these onplants could be used not only for dental anchorage; for e.g.: retraction of anteriors or distalising posteriors, but also for orthopedic traction. Human trials are however, limited.

Disadvantages of Onplants:

a) A long waiting period prior to orthodontic force application.(3months – osseointegration)

b) Excessive surgical intervention - Two surgeries are necessaryafter onplant placement; one to uncover the onplant coverscrew and the other to remove the onplant itself followingOrthodontic treatment.

c) Cost factor.

OSSEOUS IMPLANT

• Osseous implants are those that are placed in dense bone such as the zygoma ,the body and ramus area or the mid-palatal areas.

• The implant systems under this category are the

1. Skeletal Anchorage system,

2. Graz implant supported system ,

3. Zygoma anchorage system .

SKELETAL ANCHORAGE SYSTEM

• The skeletal anchorage system was developed by Umemori and Sugawara.

• Appliance design: It essentially consists of titanium miniplates, which are stabilised in the maxilla or the mandible using screws.

• The earlier of these miniplates were the conventional surgical mini plates, which are used by Oral Surgeons for rigid fixation.

• The recent versions of these miniplates have been modified for attaching orthodontic elastomeric or coil springs.

• Different designs of miniplates are available and this fact offers some versatility in placing the implants in different sites.

• The 'L' shaped miniplates have been the most commonly used ones, while the 'T' shaped ones have been proposed for usage while intruding anterior teeth .

• The screws used for fixing the miniplate are usually 2-2.5mm in diameter

Method of Placement :

• Titanium miniplates were implanted after a local anesthesia with intravenous sedation.

• First, a mucoperiosteal incision was made at the buccal vestibule directly under the first or second lower molars.

• The mucoperiosteal flap was then elevated, and the surface of the cortical bone at the apical region of the molar was exposed.

• An L-shaped miniplate was adjusted to fit the contour of each cortical bone surface and was fixed by bone screws (length, 5 mm or 7 mm) with the long arm exposed to the oral cavity from the incised wound (there are two holes in the long arm of the miniplate; the exposed hole will be used to directly receive the intrusive force).

• The implant was placed such that it did not interfer with mandibular movement.

• All of the miniplates were transfixed at the region of the buccal vestibule.

• Loading was done after wound is healed.

Advantage of Miniplates:

• The shape of the miniplate can be adjusted to the type of tooth movement: i.e, intrusion of molars, intrusion of incisors, distalization or protraction of teeth, etc., and the thickness of the patient’s bone.

• Position of the plate can be adjusted during the treatment .

• It can be placed without destroying the teeth or bone The anchor plates are monocortically placed at the piriform opening rim, the zygomatic buttresses, and any regions of the mandibular cortical bone.

• The anchor plates work as the onplant and the screws function as the implant, SAS enables the rigid anchorage that results from the osseointegration effects in both the anchor plates and screws All portions of the anchor plates and screws are placed outside the maxillary and mandibular dentition, so the SAS does not interfere with tooth movement

Distalization of molars:

• It is possible to distalize the mandibular molars with anchor plates placed at the anterior border of the mandibular ramus or mandibular body.

• Distalization of the mandibular molars enables the clinician to correct anterior crossbites, mandibular incisor crowding, and mandibular dental asymmetry without extracting premolars.

Single molar distalization

• Extraction of the third molars is done to create the space for the molar distalization.

• After the buccal segments are leveled and aligned, stiff archwires .

• L-shaped anchor plates are placed at the anterior border of the mandibular ramus.

• Then the bands or brackets of the first molars are taken off, and a retractiveforce is applied to the second molars with an open coil spring.

• To avoid the side effects of the reciprocal coil spring, the first premolars must be firmly ligated with anchor plates.

• After the distalization of the second molars, distalization of the first molars is done with the same procedure.

• En masse distalization of the entire buccal segments:

Direct retractive force is applied from the anchor plates to the first premolars to perform en masse distalization of the buccal segments. Elastic chains or nickeltitanium closed coil springs usually provide the retractive orthodontic force.

• Intusion of lower molar for correction of open bite. Intrusion of the lower molars was achieved with the application of elastic orthodontic force on the SAS , Lingual crown torque was applied to the lower molars with Burstone’s precision lingual arch to avoid buccal flaring during intrusion .

A) L-shaped miniplate for intrusion of molars B) L-shaped for distal movement of molars C) Y-shaped intrusion and distalizaton of maxillary molars D) Straight miniplate for intrusion of molars

ADVANTAGE OF SAS

• The SAS enables tooth movement to be controlled 3-dimensionally, so that treatment goals can be accomplished, even when the amount of tooth movement required is more than the mesiodistalwidth of the premolars.

• SAS, it is not always necessary to extract the mandibular first or second premolars, even in patients with moderate to severe crowding.

• The molar relationship in patients with symmetric or asymmetric Class III molar relationships can be corrected without having to extract mandibular premolars

ZYGOMA ANCHORAGE SYSTEM( ZAS )

(Hugo De Clerck and Geerinckx of Belgium introduced this system in 2002.)

• Appliance design The upper part of the Zygoma Anchor is a titanium miniplate with three holes, slightly curved to fit against the inferior edge of the zygomaticomaxillarybuttress . A round bar, 1.5mm in diameter, connects the miniplate and the fixation unit. A cylinder at the end of the bar has a vertical slot, where an auxiliary wire with a maximum size of .020 can be fixed with a locking screw. The plate is attached above the molar roots by three self-tapping titanium miniscrews, each with a diameter of 2.3mm and a length of 5mm or 7mm. The miniscrews do not need to be sandblasted, etched, or coated. Square holes in the center of the screw heads accommodate a screw-driver for initial placement, while pentagonal outer holes are used to remove the screws at the end of treatment

ADVANTAGE

1. Miniscrews are small enough to be placed between the roots of the teeth in the alveolar bone.By connecting two or more miniscrews, the orthodontic reaction forces can be neutralized.

2. The surgical procedure is uncomplicated because the screws are placeddirectly through the gingiva, without a mucoperiosteal flap, and can beloaded immediately after insertion.

3. Miniscrews can be used in the anterior or posterior region and attached withelastics or coil springs to the fixed appliance for direct anchorage.

4. Anchorage can be adapted to changing treatment needs in different parts ofthe dental arches.

DISADVANTAGE

• The main disadvantage of these screws is their proximity to the roots, which may be damaged during placement of the screws or when the adjacent teeth are displaced.

5. The ZAS uses three miniscrews, increasing total anchorage over othertypes of implants.

6. The point of application of the orthodontic forces is brought down to thelevel of the furcation of the upper first molar roots.

7. The vertical slot with the locking screw makes it possible to attach anauxiliary wire, which can move the point of force application somedistance from the anchor.

ORTHOSYSTEM IMPLANT

• Developed by Wehrbein, this is a titanium screw implant with a diameter of 3.3 mm inserted into the median palate or the retromolar regions of the mandible or the maxilla . The implants are surface treated with sand blasting and acid etching for reducing to improve integration. They are available in two sizes of 4 mm and 6 mm length. An 8 week waiting period has been suggested before applying forces onto this implant.

RESORBABLE SCREWS FOR

ORTHODONTIC ANCHORAGE

A CORRODI RITTO, DDS, Phd

• The risks associated with metallic microfixation devices used in paediatric craniofacial surgery and the need of a subsequent removal operation has given a rise to the development of biodegradable- mini osteosynthesis devices.

• Devices made of poly lactic acid (pLA) and polyglycolic acid (pGA) and their copolymers have been used in the internal fixation of fractures and osteotomies in orthopaedic. surgery since 1980's after extensive experimental studies.

Common related problems associated with

metallic fixtures

• Restriction of growth

• Passive translocation of metallic Implants (device transposition).

• Metallic fixation devices may also cause a distinct cosmetic deformity.

• Palpability or wound dehiscence especially if placed under a scarred, tight scalp

• allergic reactions

Material

• Polylactic acid (PLA) and polyglycolic acid(PGA) are derivatives of cyclic diesters of glycolic and lactic acid from which they have been produced by ring opening polymerization, resulting in poly-alpha-hydroxy derivatives of the original acids

Polyglycolic acid:

• It is a brownish, hard crystalline polymer melting at

about 224-228"C, with a glass transition temperature of 36° C.

• It lacks a methyl group, which makes it hydrophilic and thus more susceptible to hydrolysis and faster degradation than polylactide.

• The oldest and best known commercial product made of PGA is DEXON.

• Polylactic acid is a pale-coloured semicrysllllline polymer with a glass transition temperature of 57° C and a melting point of 174-184° C.

• The asymmetric lactic acid molecule has two stereoisomericforms L and D lactide.

• In the human body, the L-isomer exists in carbohydrate metabolism and the D-isomer is found in acidic milk.

• If the polymer consists only of the L isomer, it is called poly-L.lactic acid, PLLA, which has most commonly been used in orthopaedic implants.

• Weakness of these materials was the major limiting factor in the manufacture of mini implants in the 1980’s.

• Bulky, highly crystalline PLLA implant caused foreign body reactions, which cast a shadow on all biodegradable implants.

• Remnants of pure polylactic acid (PLA) implant have been identified up to eight years after implantation, raising the question as to whether PLA is too "biostable" to be used as a bioresorbable material.

• The self-reinforcing technique invented by Rokkanen and Tormala enables the manufacture of extremely strong orthopaedic implants and also thin but strong mini implants.

• The histological demonstration of complete device resorption without adverse local tissue effects is important before clinical application, because incomplete polymer elimination may eventually be associated with chronic inflammatory tissue changes.

BIOCOMPATIBILITY

• Bioabsorbable materials generally undergo two-phase degradation process in the body.

• In the first, mainly physical phase, water molecules hydrolyse the chemical bond of the polymer and cut long polymer chains to short chains.

• During this depolymerization process, the overall molecular weight and strength of the polymer become reduced and the polymer fragments.

• The second phase involves phagocytosis of the fragments by macrophages, and the polymer mal. rapidly disappears.

• PGA is converted hydrolytically into glycolic acid and PLA into lactic acid, which are further metabolized in the citric acid cycle to carbon dioxide and water, and the final products are excreted respiration or urine

• Hydrophilic PGA, although highly crystalline, becomes absorbed very quickly in the body, losing virtually all strength in 6 weeks and all mass within about 3 to 12 months.

• Excellent biocompatibility and slow biodegradation of PLA have been documented , since the first experiments no inflammatory cell infiltrations have been reported, and foreign body reactions have been limited to around the implanted material.

• Complete absorption of PLG A 75/25 has been reported in 220 days.

• PLG A 50/50 in 180 – 140 days, and

• PLG A 82/18 in 180-450 days.

• With PGL A implants no implant related clinical foreign body reactions have been reported.

Clinical example

• Resorbable screws (1.6 mm diameter) composed of a polylactic acidpolyglycolic acid copolymer (PLGL A 75/25) were placed in the area of tooth 16.

• Two screw were placed because the distal screw was not well fixed and it was decided to keep it in place and place another one mesially.

Biomechanics

Entire arch distalization

Molar intrusion

• The extruded molar required pure molar intrusion along the long axis the tooth without extrusion of the adjacent teeth.

• The c-res of the upper molar is expected to be at the center of the occlusal table , close to the palatal root.

• The recommended insertion points are mesial interdental area of the buccal surface and distal interdental area on the palatal side, or viceversa.

Enmass anchorage loss(molar mesialisation)

• To avoid mesioinclination of posterior teeth andretroinclination of anterior teeth during molar mesialisation,mechanics are followed

• A long hook is welded to the first molar band and microimplantis inserted from distal from the canine in the c-res ,in this waymolar can be moved mesially without side effects.

CONCLUSION

• Implants for the purpose of conserving anchorage are welcome additions to the armamentarium of a clinical Orthodontist. They help the Orthodontist to overcome the challenge of unwanted reciprocal tooth movement. The presently available implant systems are bound to change and evolve into more patient friendly and operator convenient designs. Long-term clinical trials are awaited to establish clinical guidelines in using implants for both orthodontic and orthopedic anchorage.

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