Temporary Anchorage DevicesDavid R. Telles, DDSDiplomate of the American Board of Oral and Maxillofacial Surgery

Introduction

•Overview•Orthodontics•History•Conventional Mechanics•Anchorage types•Clinical Indications•Surgical Techniques•Outcomes / Complications

Overview• Orthodontists have always tried to develop ways

to move teeth while minimizing the unwanted reciprocal movement of the teeth they pull or push against

• Best situation when ideal anchorage is in place to move teeth in an efficient manner

• History: ▫Use of dental implants▫Unpopular due to

Time for osteointegration Use for restoration purposes Cost

Orthodontics• Goals of therapy

▫Optimization of occlusion▫Aesthestics▫Facial Balance

• Traditional ortho can accomplish which require mild to moderate compensation▫More significant discrepancies require more robust

anchorage E.g. pts with moderate to severe skeletal discrepencies –

may requiring growth modifcation or orthognatic Sx▫May benefit from skeletal anchorage – I.e. cases to

which conventional orthodontics cannot correct severe malocclusions

History• Concept for using implantable devices for skeletal anchorage has

been present for that last ½ century• 1940: Gainsforth and Higley experimented with vitallium screws and

wires in a dog ramus for anchorage• Linkow used blade implants to provide class II elastics • Sherman et. al. used dental implants in dogs for anchorage with

limited success• 1979: Smith noted implants could act as ankylosed teeth for

orthodontic movements• 1988: Shapiro et. al. established the use of dental implants for

orthodontic anchorage • 1995: Block et. al. used HA coated onplant placed in the midline

palatal tissue for use with orthodontics for anchorage• 1999: Umemori et. Al described techniques for using a modified

rigid fixation plate for use with orthodontics – important leap forward since force could be applied without loosening the plates

Orthodontics mechanics and skeletal anchorage• Planning requires a team approach• Anchorage: resistance to unwanted tooth movement• forces involved• In orthodontic tooth movement – it obeys Newton’s third law

▫ for every action, there is an equal and opposite reaction -- every movement of a tooth in the desired direction, the force is distributed to the anchorage segment, potentially affecting the position of those teeth within the anchorage segment

• Example▫ To move a canine posterior (distally) and if only one molar is

present, then the molar has a tendency to drift toward the mesial if the molar is used as an anchor for that movement

▫ If more anchorage is provided to that area then the movement can occur with less of the unwanted mesial movement of the molar

Using Conventional Mechanics• anchorage can be increased by using intraoral or extraoral

techniques• Intraoral techniques commonly use tooth-borne appliances to

improve anchorage.▫ increasing the number of teeth in the anchorage unit

E.g. teeth can be tied together with ligature wire to resist unwanted tooth movement in another area

▫ Another way of increasing teeth in the anchorage segment is to use a transpalatal arch. distributes the force to another segment of teeth across the arch.

▫ elastic bands can be used between the opposing arches to provide additional anchorage used to close space after maxillary premolar extraction by retracting the

anterior dentition of the maxilla with elastic bands bilaterally and attaching the elastic to the

mandibular posterior teeth AKA class II elastics help to minimize the unwanted mesial movement of

the maxillary posterior anchorage segments.

Using Conventional Mechanics• Nance button appliance that holds the posterior

molars in position with an acrylic button on the anterior palate▫Force can be applied to the posterior teeth to close

premolar space▫Helps to offset the tendency for the molar teeth to

move mesial is resisted by the acrylic button on the palate near the incisive foramen

• Extraoral Appliances▫Significantly dependent on compliance of the pt▫Rarely provide force > 6-10 hrs/day▫E.g. Head Gear

Skeletal Appliances• Provide anchorage not tooth-borne• Unwanted reciprocal tooth movement avoided • Other adv:

▫ No or minimal reliance on existing dentition▫ Less dependent on patient compliance▫ Continuous rather than intermittent force may be applied▫ Surgical procedures are necessary, but they are simple in

most instances▫ May be significantly less expensive than other surgical

options, such as orthognathic surgery▫ Force may be applied very soon or immediately after

placement of the device; devices require mechanical stability rather than osteointegration

▫ Devices are easily removed

Anchorage types• Direct –

▫ Apply force directly from the anchor to the segment or tooth that is being moved

▫ E.g. maxillary plates placed in the zygomatic butress may be designed to provide intrusion force to maxillary molars to close anterior open bites

• Indirect▫ Tie the anchor device to the segment of teeth that requires additional

anchorage such that more traditional mechanics can be used in the area▫ Involves an inelastic or even rigid connection between the anchor and the

orthodontic appliances▫ E.g. maxillary anchor tied by steel ligature to the anterior teeth to provide more

anchorage – then a coil spring could be used on the archwire to distalize the molar teeth Indirect due to the force used is along the archwire by the coil spring

▫ ADV: Most orthodontists already design their movements of teeth based on traditional

mechanics• Either technique can accomplish similar outcomes – help to allow

orthodontic movements which once were deemed difficult or impossible

Take note

•Skeletal anchorage devices do not allow faster movement of teeth, or the ability to overcome exceptionally large discrepancies

•the devices have limitations•Provide absolute anchorage for

orthodontic movement

Devices for skeletal anchorage• Dental Implants

▫Costly, Reqs OI▫Requires aggressive Sx for removal

• Mini dental implants• Onplant

▫Placed in midpalatal region▫Long-term studies not documented

• Bone screws▫Self-tapping and self-drilling systems available▫Bicortical screws 8-12 mm in length▫Stability determined by thread pitch based on bone

type – typically 0.6 mm

Devices for skeletal anchorage• Devices should –

▫ Be designed for the purpose of skeletal orthodontic anchorage

▫ Have a very high quality of manufacturing with standardized quality control

▫ Have an appropriate pitch thread to ideally engage bone▫ Have the appropriate core and external diameter to

withstand orthodontic forces in maxillary and mandibular bone

▫ Be designed well at the runout and shafthead interface to avoid fracture

• Screws smaller than 1.5 mm tend to fail and not recommended

• Bracket head screws offer little adv

Devices for skeletal anchorage

•Skeletal anchorage plates▫Adv: incresed stability, 3D support▫Are modified leforte osteotomy plates▫Do no require osteointegration▫May be immediately loaded▫Allow placement of multiple screws away

from vital anatomical structures

Clinical Indications

•Mesial or distal Movement of Teeth with maximum anchorage

•Uprighting or intruding molar teeth•Closure of anterior open bite•Orthopedic growth modification

Clinical Indications• Mesial or distal Movement of

Teeth with maximum anchorage▫e.g. loss of 1st molar – moving

teeth anteriorly – to prevent movement of anterior teeth distally a skeletal anchor can be |used Can prevent inadvertent movement canine relationship to

class II Helps maintain overbite-overjet relationship

▫E.g. Class III pt can have posterior mandibular teeth stabilized and compensate mand ant teeth and hold posterior teeth to prevent mesial tipping of molars OR to provide anchorage to distalize molar teeth

Clinical Indications

•Mesial or distal Movement of Teeth with maximum anchorage

Clinical Indications

•Uprighting or intruding molar teeth▫Considered one of the more difficult

movements in ortho e.g. molar moving mesially post-extration

▫Use of a skeletal anchor can help uprighten without extrusion which results typically with conventional orthodontics

▫Intrusion also can be accomplished with skel anchorage

Clinical Indications•Closure of anterior open bite

▫Accomplished via placement of orthodontic screws or plates in the posterior maxilla, apical to the dentition

▫Force is generated to intrude the posterior molars and premolars to close the anterior openbite Numerous case reports show success No long term data on stability compared to

orthognathic surgery Should be reserved to pts not willing to undergo

orthognathic Sx

Clinical Indications• Orthopedic growth modification

▫Can be used in a manner similar to headgear▫Considered to be used in phase I of orthodontic Tx▫For pts with Class III

Skeletal anchors can be placed in the maxilla/mandible to provide forward orthopedic force to the maxilla and encourage class I relationship

Vector of force similar to reverse-pull headgear w/o need for external appliance therapy

▫Limited use due to risk of growing/developing dentition and risk of multiple surgical procedures on pediatric pt

Surgical Techniques

•The type of anchor (miniscrew, anchor plate), location, angle of the device is determined by the orthodontic Tx plan

Placement of Skeletal Anchorage plates• devices typically consist of a bone plate with holes for screw

placement and a transmucosal connecting arm that extends from the plate to a specialized working end

• working end -- allows for the attachment of wire, springs, elastics, and other orthodontic constructs

• Placement typically carried out under local anesthesia• Monocortical screws• Maxilla

▫ Typically placed within one of the vertical butresses of the midface (zygomaticomaxillary, piriform rim)

▫ transmucosal position of the connecting bar should be located at approximately

▫ the mucogingival junction▫ Nonkeratinized mucosal tissues should be avoided

NOTE: When the transmucosal location of the connecting bar is within the unattached tissues of the maxillary vestibule, increased irritation, inflammation, infection, and soft tissue overgrowth may result.

Placement of Skeletal Anchorage plates•Mandible

▫Avoid IAN, mental nerve, teeth roots▫Typically placed in the symphysis, ramus,

posterior body of the mandible▫If bone plate positioned directly over

mandibular canal – use of monocortical screws helps avoid injury to the IAN

Placement of miniscrews• Similar to placing IMF screws• Placed near or @ the mucogingival junction• To engage the cortical and cancellous bone• Longest length possible while avoiding vital anatomical

structures• Maxilla

▫ Zygomatic or piriform butress▫ Hard palate▫ Alveolar process between teeth

• Mandible▫ Between teeth▫ Symphysis▫ Retromolar pad

• Does not require elevation of a soft tissue flap

Post-op• Post-op imaging to confirm placement and

proximity to anatomy• Abx x 5-7 days – pen, amox, clinda, etc.• Encourage OH• Prescribe CHG bid x 7 days• Cheek irritation seen peeking @ POD #10• May be immediately used following surgical

placement both miniscrews + plates▫Manipulation with full orthodontic forces typically

delayed 7-10 days post-op to allow for adequate healing @ the Sx site/ soft tissue

Outcomes + Complications• Outcomes vary based on screw or plate systems• A number of reports have listed loosening or outright failure of

orthodontic anchorage screws to be above 15%.• Rate of failure of plates < 5%• Prospective unbias literature still required• Complicaitons

▫ Device failure▫ Loosening associated with design flaw▫ Infection▫ Operator related complications:

Stripping of screws Overworking screw Poor stability due to poor choice of placement Failure to place working attachments through attached mucosa Misplacement for use by orthodontist Root damage to teeth – typically seen with discomfort during mastication

Outcomes + Complications

•Patient related complications▫Poor quality bone▫Reasonable OH▫Systemic disordered affecting bone or

mucosal healing▫Previous Hx of radiation therapy to the H &

N region▫Hx of bisphosphonate use▫Smokers

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of skeletal class I bialveolar protrusion. J Clin Orthod 2001;35:417–22.• Umemori M, Sugawara J, Mitani H, et al. Skeletal anchorage system for

open-bite correction. Am J Orthod Dentofacial Orthop 1999;115:166–74. • Sugawara J. Dr. Junji Sugawara on the skeletal anchorage system. J Clin

Orthod 1999;33:689–96.• Bae SM, Park HS, Kyung HM, et al. Clinical application of micro-implant

anchorage. J Clin Orthod 2002; 36:298–302. • Gainsforth BL, Higley LB. A study of orthodontic anchorage possibilities in

basal bone. Am J Orthod 1945;31:406–17.• Linkow LI. The endosseous blade implant and its use in orthodontics. J

Orthod 1969;18:149–54. • Sherman AJ. Bone reaction to orthodontic forces on vitreous carbon dental

implants. Am J Orthod 1978; 74:79–87.