A temporary anchorage device (TAD) is a device that is temporarily fixed to 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), and which is subsequently removed after use. They can be located transosteally, subperiosteally or endosteally; and they can be fixed to bone either mechanically (cortically stabilized) or biochemecially (osseointegrated). It should also be pointed out that dental implants placed for the ultimate purpose of supporting a prosthesis, regardless of the fact that they may be used for orthodontic anchorage, are not considered temporary anchorage devices since they are not removed and discarded after orthodontic treatment. By using dental implants and temporary anchorage devices for orthodontic purposes we are able to obtain zero anchorage loss. Currently, several terms are used to refer to skeletal anchorage devices, the most inclusive being temporary anchorage devices. Other names include implants, mini-implants, miniscrews, micro-screws, screws, mini-plates, and plates. Implants and mini-implants usually necessitate osseointegration for stability, whereas screws, miniscrews and micro-screws are generally loaded immediately after placement and receive their stability from mechanical retention in the bone Plates are attached to bone through a surgical procedure necessitating the elevation of a flap. A portion is left emerging in the oral cavity to serve as appoint of application of the force system

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Tanta university
Faculty of dentistry
Orthodontic department
A seminar on
Orthodontic mini-implant materials
Collected by
Safa Basiouny Mahmoud Alawy
MSc, PhD Orthodontics
Lecturer of Orthodontics, Faculty of Dentistry,
Tanta University

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Contents
Definition
Types
Materials
• Ideal Requirements Of Mini- Implant Materials
• Parts of an orthodontic miniscrew implant
• Specific Mini-Implant Materials

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Definition: A temporary anchorage device (TAD) is a device that is
temporarily fixed to 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), and which is subsequently removed after use.
They can be located transosteally, subperiosteally or endosteally; and
they can be fixed to bone either mechanically (cortically stabilized) or
biochemecially (osseointegrated). It should also be pointed out that dental
implants placed for the ultimate purpose of supporting a prosthesis,
regardless of the fact that they may be used for orthodontic anchorage,
are not considered temporary anchorage devices since they are not
removed and discarded after orthodontic treatment. By using dental
implants and temporary anchorage devices for orthodontic purposes we
are able to obtain zero anchorage loss.
Currently, several terms are used to refer to skeletal anchorage devices,
the most inclusive being temporary anchorage devices. Other names
include implants, mini-implants, miniscrews, micro-screws, screws, mini-
plates, and plates.
Implants and mini-implants usually necessitate osseointegration for
stability, whereas screws, miniscrews and micro-screws are generally
loaded immediately after placement and receive their stability from
mechanical retention in the bone
Plates are attached to bone through a surgical procedure necessitating the
elevation of a flap. A portion is left emerging in the oral cavity to serve as
appoint of application of the force system
Types:
Three types of temporary anchorage devices are currently in use.
1- Endosseous implants
Def: They are osseointegrated implants which are modified forms of
conventional dental implants.

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Site & indic: They are placed in palate, retromolar area and in the area of
absent or missing teeth.
Adv: Osseointegrated implants can withstand more force than
mechanically retentive implants
Disadv:
a. waiting period before loading,
b. limitation in area of placement because of their size
c. cost
d. extensive surgical procedure
e. difficulty in removal.
2- Surgical miniplates
Def: Modified or even conventional L or T-shaped surgical titanium
miniplates are used with an intraoral extension to anchor the orthodontic
force.
Site: They are placed in the areas of thick cortex like the zygomatic
region, and the buccal cortex of the mandible.
Adv& Indic : Skeletal anchorage system has been successfully used for
en mass distalization of the lower arch in class III cases, intrusion of
posterior segment in open bite cases and for molar distalization.
Surgical miniplates offer absolute anchorage,
Disadv :
1. involve much more extensive surgical procedure,
2. presence of considerable postoperative swelling,
3. discomfort to the patient
4. require surgical removal.

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3- Miniscrew implants
• Mechanically, retentive miniscrew implants can provide absolute
anchorage in orthodontics for short duration.
• Mini-implants are commercially available in the screw diameter
range of 1.2-2 mm and length varying from 6-10 mm. Because of
their tiny screw size they are highly versatile in their site of
placement.
• The most common site for their placement is the inter-radicular
bone between
• teeth. Miniscrew implants are now popular as absolute anchorage
units.
• Advantages
1. No extensive surgical procedure for placement
2. Rapid healing and can be immediately loaded since we do not need
osseointegration.
3. Can be placed in various locations due to small size.
4. Low cost
5. Can be used for a variety of tooth movements like, en mass
retraction, en mass distalization, intrusion, molar distalization
6. Easy removal because they are mechanically retentive.
Materials
Ideal Requirements Of Mini- Implant Materials
The material must be:
• nontoxic and biocompatible
• posses’ excellent mechanical properties
• provide resistance to stress and strain, resistance to corrosion.
The materials used for implants can be broadly divided into 4 categories

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1. Biotolerant: - Material that is not necessarily rejected but are
surrounded by fibrous layer in the form of a capsule.
Eg. Stainless Steel, Chromium-Cobalt Alloy
2. Bioinert: - Material that allows close apposition of bone on their
surface, leading to contact osteogenesis.
Eg. Titanium, Carbon
2. Bioactive: - Materials that allow formation of new bone onto their
surface, but ion exchange with host tissue leads to formation of a
chemical bond along the interface (bonding osteogenesis).
Eg. Vetro ceramic apatite hydroxide, Ceramic oxidized aluminum.
4. Bioresorbable: (polylactide).
Bioinert pure titanium is the material most often used and it is the
successful one. Orthodontic implants are usually marketed as titanium or
titanium coated stainless steel.
Grade V medical titanium which is an alloy of titanium, aluminum and
vanadium; Ti6A14V is commonly used.
Parts of an orthodontic miniscrew implant
Important factors in orthodontic mini-implant design are:
• They should be mechanically retained and require no
osseointegration.
• Stresses on implant should be multi-directional and more of one
sided lateral stress.
• Design should provide provision for attachment of orthodontic
springs or auxiliaries.
• Should be a self-drilling, to make the procedure simple.

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Parts include head, neck and screw.
Head. It is the portion exposed in the oral cavity. It provides attachments
for springs and elastics. It has a screw driver slot or a specific design
shape to engage the implant driver for implant placement.
• Solid head with a screw driver slot is recommended for
easy insertion and removal.
• For attachments, hole through head and button head are provided, but
hollow neck for attachments weakens implant.
• Bracket head designs with slots are also recommended since they
provide 3-D control and better indirect anchorage.
• Two component implant provides separate screw and head portion with
different neck lengths which are screwed together after placement and it
reduces the risk of fracture.
fixation head

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bracket head
hook head
double head
Neck. Neck is the portion that passes through the mucosa.
• Transmucosal portion should be smooth to avoid tissue irritation.
• Different neck lengths should be available for different mucosal
thickness.
Screw. It embeds into the cortical and medullary bone to provide
retention. Screw portion can be of different types:
• Cylindrical and tapered cylindrical screw portions: We prefer tapered
cylindrical because of better retentive properties.

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• Self-drilling and self-tapping screws: Self-drilling implants have sharp
apex and cutting edges and they do not require pilot drill for insertion.
Tapered screw cylindrical screw
Length
-Screw length refers to the body part of the mini screw
-Length differs by manufacturers and range from 4-12mm
-Selection depends on :
1-bone depth at the planned implant sit
2-location of adjacent anatomically vital structures (roots, blood vs,
nerves)….should be evaluated by radiographs
Diameter
-refers to the widest part of the mini screw body which is the
distance between 2 thread tips
- differs by manufacturers and range from 1-2.3mm

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-Selection depends on :
1-bone width of the implant site which is confirmed with radiographs
2-mini screw with smaller diameter should be used in tooth bearing
area to avoid hitting dental roots while mini screw with larger
diameter should be used in non-tooth bearing area to achieve larger
scale of tooth movement
Specific Mini-Implant Materials
1- Stainless Steel
-The primary stainless steel alloy presently recommended for device
manufacture is the American Iron and Steel Institute (AISI) type 316L.
Type 316L (low Carbon) Austenitic Stainless Steels contains: 10-14%
of Nickel, 2-3% of Molybdenum, 16-18% of Chromium and a maximum
of 0.03% of carbon.
-ASTM recommends type 316L for implant fabrications for the obvious
reason that:
1- presence of less carbon decreases the chance of forming chromium
carbide that generally results in intergranular corrosion.
2- Lowering of the carbon content also makes this type of stainless
steel more corrosion-resistant to chlorine-bearing solutions such as
physiological saline in the human body.
3- To maintain the specified austenitic microstructure, the normal
hardening and tempering heat treatments of carbon-and low-alloy
steels cannot be performed.
4- Indeed, within the composition and phase specifications of 316L,
hardening can be achieved only by a process known as cold-working.
Cold-working can produce a twofold to threefold increase in yield
strength, a 40% increase in ultimate strength, but a corresponding 80%
decrease in ductility, thus making the material far more brittle.
2- Cobalt- chromium alloys.
-Two main types of cobalt-based alloys are used for surgical implant
purposes; a cast alloy and a wrought alloy, which vary significantly in
composition.

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-Despite these differences, however, the trade designation of Vitallium
(or in Britain, "Stellite") is often applied erroneously to both alloys.
-The cobalt-based alloys display a useful balance between mechanical
properties and biocompatibility, both forms being somewhat superior to
stainless steel in strength and corrosion resistance but more
expensive to manufacture.
-Co-Cr alloys are hardly used as mini-implant materials.
3- Titanium and Its Alloys
-American Society for Testing and Materials (ASTM) has classified
commercially pure titanium into different grades. There are five
unalloyed grades of commercially pure Ti grades I, II, III, IV and V,
based on concentration of iron (0.2-0.5 wt %) and oxygen (0.18-0.40 wt
%). Other impurities include nitrogen (N), carbon (C) and hydrogen (H).
-Four possible types of titanium alloys can be produced: alpha, near
alpha, alpha - beta and beta (β) on the basis of their microstructure. Alpha
(α) alloys essentially have an all-alpha microstructure and no α phase on
cooling.
-An alpha alloy will basically comprise of titanium that is commercially
pure titanium with alpha stabilizing elements added such as aluminum,
nitrogen, and oxygen.
-Addition of aluminum to titanium increases the tensile strength, creep
strength and elastics modulus and also will expand the α phase and
increase the strength.
-The mechanical properties of alpha titanium can be altered using
different cooling rates after annealing at temperatures higher than that
required for alpha to beta phase transformation. These cooling rates can
produce structures with varying grain morphologies and therefore
produce titanium with variable strengths. With α phase alloys, the
presence of minimal amounts of interstitial elements such as hydrogen,
nitrogen, oxygen and carbon can affect the mechanical properties in much
more distinct manner. Titanium produces detectable embrittlement due to
precipitation of titanium hydride when the alloy is slow cooled in alpha

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phase region [for ex. 4000C]. The alpha phase alloy most commonly
examined is commercially pure titanium.
-Commercially pure titanium (cp) along with other near alpha alloys
exhibit best corrosion resistance, but it lacks strength.
-A beta-stabilized (β alloy) titanium alloy will have vanadium,
molybdenum, iron, chromium and zirconium added to stabilize the phase.
It has higher yield and ultimate tensile strength than all alpha-alloys.
- Alpha-beta alloys have a composition of a mixture of alpha and beta
phases and 10-50% of β phase at room temperature. One of the most
successful alpha-beta alloys is Ti-6Al-4V, which has an excellent
combination of strength, toughness and corrosion resistance.
Comparison of Mechanical Properties Of Cp Titanium, Titanium
Alloys And Other Alloys
-To determine the optimum factor of safety for mini screw implants, the
variations of mechanical properties and deterioration, such as fatigue by
continuous bending stress during tooth movement and corrosion in oral
environment, should be considered.
-The factor of safety for a mini screw is in inverse proportion to its
diameter.
-The strength of titanium or any other alloys depends on its
microstructure, which is influenced by composition, heat treatment and
machining process of the mini screws implants.
-Elastic modulus, strength and biocompatibility are important
consideration in choosing an orthodontic miniscrew material.
-The material chosen should have sufficient mechanical strength to resist
the torsional stresses developed at the screw threads during clinical
placement and removal without permanent deformation. It should also
have a low modulus for optimum force transfer to bone.
-Commercially pure Ti (cp Ti) is the most used material in implantology
because of its proven biocompatibility with human tissues, high
corrosion resistance in body fluids, lack of allergenicity, high specific

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strength, and low elastic modulus when compared with other metallic
biomaterials.
-Nevertheless, orthodontic mini-implants are smaller than conventional
dental implants and must bear high orthodontic loads. These factors
contribute to the possible fracture of cp Ti mini-implants during
placement and removal. To overcome this disadvantage, Ti alloy
implants, made with aluminum (Al) and vanadium (V), (Ti-6Al-4V) for
greater strength and fatigue resistance than cp Ti, are required.
References
Sana S, Manjunath G. Mini- Implant Materials: An Overview. J Dent and
Med Sci.2013;7:15-20.
James C Y et al. A comparative evaluation of current orthodontic mini
screw systems. World J Orthod. 2007;8:136-44.