UNIVERSITY OF GLASGOW

Orthodontic Anchorage

Mohammed Almuzian

Personal note

1/1/2013

Table of Contents Definition................................................................................................................................. 2

Early and modern understanding of OA ..................................................................................... 2

Optimal force level in orthodontics ............................................................................................ 2

Assessment of the anchorage demand or factors that can contribute to OA loss............................. 4

A. Depending on how far the OA unit can move in response to the reactionary force (OA

burn) Nanda, 2009. ................................................................................................................... 5

B. According to the position or the source of the OA (Moyer, 1988) ........................................... 6

1. Extraoral OA ................................................................................................................... 6

2. Intraoral OA .................................................................................................................... 6

I. Intramaxillary (originates from the same arch) can be subdivided into: ................................ 6

A. Originating from teeth ...................................................................................................... 6

B. Originating from soft tissue .............................................................................................. 6

C. Originating from bone ...................................................................................................... 7

II. Intermaxillary (from the opposing arch) like ...................................................................... 7

Evidence for the differential force theory ................................................................................... 7

Methods to reinforce OA........................................................................................................... 7

Measuring OA:........................................................................................................................15

A. Cephalometric measures of OA........................................................................................15

B. Study model measurement ...............................................................................................16

OA in three Planes ...................................................................................................................16

1). Vertical Anchorage. ............................................................................................................16

2). Lateral anchorage ...............................................................................................................16

Orthodontic bone anchorage .....................................................................................................17

Anchorage control during tooth levelling and aligning .....................Error! Bookmark not defined.

How to control anchorage in the leveling stage ................................Error! Bookmark not defined.

Orthodontic Anchorage

Definition

The word Anchorage means the northernmost city in Alaska in the

United States (officially called the Municipality of Anchorage) or it can

be defined at that portion of a harbour or area outside a harbour suitable

for anchoring or in which ships are permitted to anchor (Wikipedia

2013).

So it is better always to use the word orthodontic anchorage (OA) to

refer to the resistance to unwanted tooth movement (Profit, 2000) or

those sites that provide resistance to the reactive forces generated on

activation of any orthodontic appliance to control unwanted tooth

movement. (Mitchell, 2001)

OA loss or burn is associated with undesirable movement of the anchor

units during orthodontic treatment.

Early and modern understanding of OA

Early studies suggested that the rate of tooth movement was associated

with the magnitude of the force applied and the surface area of the root

of the tooth. Partly as a result of this philosophy, clinicians have

undertaken various steps in order to prevent the anchor teeth from

moving, also known as conserving anchorage. These include:

1. Light force: Using a light force sufficient to move the tooth, but not

large enough to move the anchor unit.

2. Root surface area of anchored teeth: Utilize teeth with maximum

root surface area as an anchor unites.

3. Number of anchored teeth: Involving as many teeth in the OA unit

as possible to distribute the force over a larger root surface area

4. Number of teeth to be moved: Only moving one tooth at a time per

quadrant

Optimal force level in orthodontics

Optimal force level in orthodontics defined as a mechanical input that

leads to maximum rate of tooth movement with minimal irreversible

damage to the root, periodontal ligament and alveolar bone. The theory

of optimum forces was proposed by Storcy and Smith in 1952.

Force threshold is defined as the minimum force to produce

movements. Classically, ideal forces in orthodontic tooth movement are

those that just overcome capillary blood pressure 20-25gm/cm3 as per

Schwartz (1932).

Quinn & Yoshikawa, 1985 mentioned four theories regarding force

magnitude:

1. Hypothesis 1 shows a constant

relationship between rate of

movement and stress. The rate of

movement does not increase as the

stress level is increased. However no

studies support this theory.

2. Hypothesis 2 is more complex.

The relationship here calls for a

linear increase in the rate of tooth

movement as the stress increases.

Hypothesis 2 is difficult to disprove

because most studies used only two

force magnitudes and were unable to

describe the behaviour of the curve as the stress reached higher levels

(Johnston 1967).

3. Hypothesis 3 depicts a relationship in which increasing stress

causes the rate of movement to increase to a maximum. Once this

optimal level is reached, additional stress causes the rate of movement to

decline. This hypothesis was originally proposed by Smith and Storey

1952. The available literature suggests that hypothesis 3 may not be an

accurate representation of the data. This had been supported later by Lee

1995.

4. Hypothesis 4 is a composite of some of the foregoing concepts.

Here the relationship of rate of movement and stress magnitude is linear

up to a point; after this point an increase in stress causes no appreciable

increase in tooth movement. This had been supported later by Owman-

Moll 1996 and King 1991. From the study of Samuel 1998 that

compared in his RCT between 100gm and 200gm NiTi spring and also

used the historical data from his previous study in 1993. Samuel in 1998

found that there is no difference between 150gm and 200gm but a

significant difference between the last two forces and 100gm. The

existing clinical data may best support the interpretation provided in

hypothesis 4.

However,

Pilon (1996), working on Beagle dogs, showed that the rate of tooth

movement and amount of OA loss were not significantly different for

forces from 50g to 200g. In some dogs, teeth moved quickly while in

others, teeth moved slowly, regardless of the forces used. The rate of

movement was highly correlated between right and left sides in each

dog, suggesting that inherent metabolic factors may be much more

important than force level in determining the rate of movement of the

teeth (including those in the OA unit). However, Pilon (1996) found that

rate of tooth movement was still related to root surface area, as the OA

units moved less than the teeth being moved. Therefore, there is some

scientific support for the differential force theory, but the exact extent of

its influence is unknown. Other studies have shown that similar

individual variation in orthodontic response to applied force also appears

to occur in humans (Hixon 1969, Hixon 1970).

Ren et al. 2004 systematic review showed insufficient data to determine

whether there is a threshold of force below which tooth movement does

not occur. They also identified a wide range of forces (104–454 gm) over

which the maximum rate of movement could be achieved.

Assessment of the anchorage demand

A. General factors

1. Age

2. Medical condition

3. Medication

4. Individual variation

5. Patient compliances

B. Treatment plan factors

1. Treatment aims: correction of molar relationship after extraction

require little anchorage than correction of sever OJ or crowding

2. Type of movement required, bodily movement require higher

anchorage demand than tipping movement.

3. Extraction pattern, the more posterior teeth extracted the more

anchorage demand will be.

C. Treatment mechanics factors

1. Appliance prescription: MBT less anchorage demand than Roth

and Andrews prescription

2. Appliance type, tip edge appliance required less anchorage

demand than SWA. URA is less anchorage demanding than FA.

3. Mechanotherapy: heavy force need more anchorage.

D. Intra-arch relationship

1. Involved arch: The maxillary arch is particularly susceptible to OA

loss. This is probably due to a combination of factors:

Maxillary anterior teeth are bigger and wider.

The upper anterior brackets have more tipping built into than the lower

anterior brackets.

The upper incisors require more torque control and bodily movement

than the lower incisors, which only require distal tipping or uprighling.

Mandibular bone is harder than cancelous maxillary bone. So that the

upper molars move mesially more easily than the lower molars.

2. Amount of crowding: sever crowding requires more anchorage

3. Location of crowding, the more distance between anchor unit from

the irregular teeth to be align or retracted, the more anchorage demand.

4. Angulation of the teeth, distally angulated canines required higher

anchorage to align and retract them than upright or mesially inclined

canines.

5. Inclination of the teeth, palatally tipped upper incisor require

more anchorage to retract them than proclined one

E. Inter-arch relationship

1. Amount of OB

2. Amount of OJ

3. Amount of centreline problem

4. Skeletal relationship AP: camouflaging moderate to severe skeletal

relationship is more anchorage demanding than mild cases

5. Skeletal relationship vertically, high angle cases require higher

anchorage demand because:

Bone is less dense than bone of low angle case which favour teeth

movement and anchorage loss

The direction of the occlusal plane favour the mesial movement of the

anchor teeth

A weaker muscle fibres associated with high angle case produce less

occlusal interlocking than normal.

6. Occlusal interlock

F. Factors relate to the anchorage unites

1. Root surface area of the anchor units, incisors especially lower

incisors require less anchorage demand than canines and premolar.

2. Teeth condition& PD support, heavy restored, PD compromise

teeth or short rooted teeth provide less anchorage support than normal

teeth.

Classification of OA

A. Depending on how far the OA unit can move in response to the

reactionary force (OA burn) Nanda, 2009.

1. Minimum 75% OA burn

2. Moderate 50% OA burn.

3. Maximum 25% OA burn or if no movement of the OA unit is

permissible

B. According to the position or the source of the OA (Moyer,

1988)

1. Extraoral OA

Like HG or facemask EOA.

2. Intraoral OA

I. Intramaxillary (originates from the same arch) can be subdivided

into:

A. Originating from teeth

1. Simple OA (one tooth providing OA to other tooth)

2. Compound OA (group of teeth providing OA to one tooth or

smaller number of teeth). This theory is not fully proven, but indirect

evidence strongly suggests that the theory has substance. For example,

Saelens & DeSmit (1998) showed that greater mesial movement of the

molars and less resolution of anterior crowding occurred when second

premolars rather than first premolars are extracted. However, the

available data on the relationship between the applied force and the tooth

movement achieved has not yet confirm a clearer picture (Hixon 1969,

Hixon 1970, Quinn & Yoshikawa 1985).

3. Stationary OA (refers to the advantage that can be obtained by

putting bodily movement of one group of teeth against tipping of

another).

4. Differential anchorage: mean moving the teeth by tipping them

first then upright them to reduce the stress on the anchor teeth

5. Reciprocal It may be that equal movement of both the active and

reactive units is desirable, such as expansion or closing a midline

diastema, when OA is described as reciprocal. (Hixon, 1969)

6. Differential force theory: is a combination of Stationary and

Differential anchorage.

The active units are allowed to tip by relying on the anchor units which

are hold by the effect of their bodily reaction.

Then the active units are uprighted.

B. Originating from soft tissue

1. Lip bumper

2. Bone palatal vault like Nance and URA

C. Originating from bone

1. Skeletal or bone OA (implants/miniscrews/plates)

2. Cortical Anchorage

II. Intermaxillary (from the opposing arch) like

1. Myofunctional appliance

2. Intermaxillary elastic. the disadvantages of this are

Need patient compliance

Molar extrusion

Proclination of anterior segment

Difficulty with URA

Evidence for the differential force theory

A study by Pilon et al (1996) in beagle dogs showed that the rate of

tooth movement and the amount of anchorage loss were not significantly

different for forces ranging from 50 g to 200 g. Some dogs had teeth that

moved quickly and others moved slowly regardless of the force level.

The rate of movement was highly correlated between the left and right

sides for any dog and this suggests that inherent metabolic factors may

be much more important than force level in determining the rate of

movement of teeth including those in an anchorage unit. Anecdotal

clinical observation certainly suggests that human patients show similar

variation in orthodontic response to applied force (Hixon, 1969 & 1970).

A Meta review by Ren et al (2003) referred to over 400 studies of

relevance and it is clear that the details of the relationship between force

applied and tooth movement remain insufficiently understood or

documented.

More recent study by Yee et al (2009) who measured canine retraction

and anchorage loss with a light (50 gm) and heavy (300 gm) forces over

a 12 week period. The 300 gm force produced significantly more

movement of both the canine and the anchorage unit and the percentage

of anchorage loss was significantly higher (62%) with the heavy force

than with the light force (55%). The size of that difference is certainly

not dramatic but does support the differential force theory.

Methods to reinforce OA

1. Compound OA: Include more teeth in the anchor unit.

2. Anchor bends (stationary anchorage): Bends made in the

archwire between the molar and premolar teeth at an angle of 30 to the

occlusal plane can prevent the molar tipping in reaction to a mesially

directed force thus increasing its OA potential. In the SWA it is called

The Tweed-Merrifield philosophy or bio-progressive theory. Tweed

described tipping the molars distally like a ‘’tent stakes’’.

3. Tipping and uprighting (Differential force theory):

TipEdge or Begg principle where the upper anterior teeth are allowed to

tip distally using the force of the intermaxillary class II elastic, but the

molar is prevented from moving forward by a ‘tipback bend’.

Additionally, the tipback bend helps to overcome the vertical extrusive

effect of the elastic on the anterior teeth.

However, it is not clear whether tipping and subsequently uprighting a

tooth consumes less OA than achieving the same result with bodily

movement. More recently, a good study by Shpack et al (2008), found

that bodily retraction of a canine consumes the same anchorage as

tipping followed by uprighting and incidentally, bodily retraction was

more rapid by an average of 38 days.

4. Extraoral orthodontic anchorage support (See the HG note):

Example HG or PHG which get its support from a very stable skeletal

structure outside the mouth like cranium, occipital area and the chin.

Feldmann, 2009, RCT to measure the anchorage loss with Onplant (1),

TAD (2), EOT (3) & TPA (4). They found that after levelling/aligning

phase: the anchorage was stable in the group 1, 2 & 3 while group 4

showed 1.0 mm. But after space closure phase, the anchorage was stable

in the group 1 & 2 but group 3 & 4 showed 1.6 and 1.0 mm of mesial

drift of molars respectively. Feldmann, 2012, measured the patients’

perceptions in term of pain, discomfort, and jaw dysfunction with

Onplant (1), TAD (2), EOT (3) & TPA (4). The results confirm that

there were very few significant differences between patients’ perceptions

of skeletal and conventional anchorage systems during orthodontic

treatment

TADs or HG. Junqing in 2008 showed again a better result by TADs in

comparison with HG.

5. Musculature forces: for example

Functional appliance: It must be remembered that a reactionary

mesially directed force occurs in the mandible and the reactionary

distally directed force occurs in the maxilla during the use of the

functional appliance. This could lead to upper teeth distalization and

lower teeth mesialization. See the functional appliance note

The lip pumper: It mainly consists of a thick round stainless steel wire

that fit in the headgear tube of the molar band and stays away from the

labial surface of the incisor by the effect of the loop mesial to the

entrance to the molar tube. The acrylic pad is embedded in the anterior

part of the wire and act to actively displace the lip forward. The

reciprocal force of the displaced lip will be transferred to the molars via

the heavy wire and result in molar uprighting and distalisation. As a

consequence of the change in the soft tissue equilibrium by the lip

pumper, there is a proclination in the incisors under the effect of tongue

as well as increase in the intercanine width (Cetlin & Ten Hoeve, 1983).

The forces are originated from the deliberately displaced lower lip by the

acrylic lip pad. However, the effects of lip bumper were described by

O'Donnell 1998, Bjeregaard 1990 & Nevant 1991 & include:

i. Molar distalization and tipping

ii. Reduce anterior crowding

iii. Incisor proclination and protrusion

iv. Increase intercanine and intermolar width and perimeter

6. Intermaxillary elastics:

This relies on using the opposing arch to provide OA to the other arch.

Care must be taken to realise that intermaxillary traction is an inefficient

method of space closure and if prolonged can lead to excessive extrusion

and tipping of the anchor teeth.

Sometime elastic can be used in conjunction with sliding jigs . This

was a mainstay of the original Tweed technique in which the force from

Class II elastics aid in pushing the upper molars distally via a sliding jig.

The force level is 250 gm per side is needed. In addition the class II

elastic help in correction of class II malocclusion by clockwise rotation

of the occlusal plane which can be compensated in growing patient. This

is why it should not be used for more than 6 months in adult patient

(Tweed, 1967)

7. Intraoral skeletal system: like the TADs, miniplates, implant &

Onplant. See the TADs note. By the way TADs considered type of

cortical bone anchorage

Feldmann and Bondemark 2008 in their RCT measured the anchorage

loss with Onplant (gp1), TADs (gp2), HG (gp3) & TPA (gp4). They

found anchorage loss only in gp4 after levelling/aligning phase

(approximately 1mm) but this had been increased to reach 2mm.

additionally, gp3 showed 1.6 mm of anchorage loss while the anchorage

was stable in the gp 1 & 2 from the start until the end of treatment.

Three years later, the same authors measured the difference patient

perception in the four groups in term of pain, discomfort, and jaw

dysfunction. They concluded a very few significant differences between

skeletal and conventional anchorage systems in term of patient

perceptions.

Sharma et al 2012. compared the anchorage loss with the use of TPAs

or TADs and found 2.5 mm of mesial movement of the U6s with the

former while the latter provided absolute anchorage

Junqing in 2008 showed again a better result by TADs in comparison

with HG for treatment of bialveolar dental protrusion.

Liu 2009 compared the use of TPA and TADs in he found that

better dental, skeletal and soft tissue changes could be achieved

by minicrew implants especially in hyperdivergent patients. Skeletal

anchorage should be routinely recommended in patients with bialveolar

dental protrusion.

Salma and Hajeer 2014 TAD better than TPA

8. Palatal vault: Example URA & Nance appliance which relies on

the bone and soft tissue anchorage

9. Cortical anchorage:

By the way TADs considered type of cortical bone anchorage

Rickets technique by intentionally bringing the buccal roots of the

anchor teeth into contact with the cortical plates of bone thus increasing

the OA value of such teeth. It should be appreciated that this process

should be carried out with great care and precision since overzealous

torque can produce root resorption or in extreme cases cortical

perforation. (Brezniak & Wasserstein, 2008)

The transpalatal arch, qaudrihleix & the lingual arch. It also depends on

the idea of compound-cortical anchorage by increasing the number of

teeth in the OA system as well as cortical bone anchorage theory.

However there is a risk of root resorption (Brezniak & Wasserstein,

2008) See the TPA note.

Transpalatal arches uses to provide anchorage

Provision of transverse

anchorage

TPAs can be used to improve arch width

stability when aligning palatally impacted

maxillary canine (Fleming, Sharma et al.

2010)

In cleft palate, TPA has its application to

maintain the form of the expanded arch just

before alveolar bone grafting. (Harris and

Reynolds 1991)

For almost the same application, TPAs act as

a retainer after RME

after surgical expansion of the palate in order

to hold the osteotomies part together during

healing period. (Harris and Reynolds 1991).

TPAs are used to counteract the buccal

tipping of the crown of the molars during

intrusion of the anterior teeth using

Segmented Burstone Arch Wires mechanics.

(Burstone 1966)

For the same reason TPA is combined with

Class II bite correctors to counteract the

buccal forces applied by the (TFBC) Twin

Force Bite Corrector. (Rothenberg, Campbell

et al. 2004)

As an adjunct to headgear (HG), TPAs are

used to reduce buccal tipping of the molar

and palatal cusp hanging the molar

distalization. (Baldini and Luder 1982)

However, a study by Wise et al. showed no

difference between the use of HG with or

without a TPA during molar distalization.

(Wise & Magness et al. 1994).

Lastly, TPAs were used with palatally or

buccally placed TAD to control molar tipping

when posterior teeth are intruded to treat

anterior open bites. (Cousley 2010)

Provision of vertical

anchorage

It had been showed that placing the TPA

4mm away from the palate might introduce

some intrusive effect by the tongue on the

molars which can help in correcting or

controlling the over eruption of maxillary

molars.(Goshgarian 1974).

Provision of

anterioposterior

anchorage

Nance appliance can be used to provide

anchorage to distalize the molars such as the

Pendulum Appliance (Hilgers 1992), rapid

molar distalization (REF); the distal jet

(Carano, Testa et al. 1996, Carano, Testa et

al. 2002), Jones Jig (Jones and White 1992,

Paul, O'Brien et al. 2002, Patel, Janson et al.

2009) and the Lokar Distalising Appliance

(Lokar 1994, McSherry and Bradley 2000).

In the same field, TPA can be used to

maintain molar position after

distalization.(Prakash, Tandur et al. 2011)

again TPA can be used to provide anchorage

during fixed appliance treatment through

bringing the roots of the upper molars in

contact with cortical bone (Cortical

anchorage).

However, there are many studies that

compare the effectiveness of the TPA with

other methods. Zablocki & McNamara

(Zablocki, McNamara et al. 2008) concluded

that the mean anchor loss of 4.1 mm was seen

in association with the TPA and 4.5 mm in

control group.

Feldmann & Bondemark (Feldmann and

Bondemark 2008) in their RCT measured the

anchorage loss with Onplant (gp1), TADs

(gp2), HG (gp3) & TPA (gp4). They found

anchorage loss only in gp4 after

levelling/aligning phase (approximately

1mm) but this had been increased to reach

2mm. additionally, gp3 showed 1.6 mm of

anchorage loss while the anchorage was

stable in the gp 1 & 2 from the start until the

end of treatment. Three years later, the same

authors measured the difference patient

perception in the four groups in term of pain,

discomfort, and jaw dysfunction. They

concluded a very few significant differences

between skeletal and conventional anchorage

systems in term of patient perceptions.

(Feldmann, List et al. 2012).

A study comparing Nance and TPA

appliances, found that both appliances are

moderately effective in preserving anchorage

(anchorage loss of around 1mm over 6

months) and there is no difference in

anchorage support between them but TPA

well tolerated by the patient. (Stivaros, Lowe

et al. 2010).

Sharma et al. 2012 compared the anchorage

loss with the use of TPAs or TADs and found

2.5 mm of mesial movement of the U6s with

the former while the latter provided absolute

anchorage.

Lastly an interest finite element simulation

study conducted by Kojima et al. (2008)

showed that TPA provides no anterioposterior

anchorage.(Kojima and Fukui 2008)

10. Natural anchorage. Ankylosed teeth possess no periodontal

membrane and as such are not subject to the normal physiologic

response to forces placed on the tooth and movement will be absolutely

resisted. Kokich in 1985 illustrated a case where he utilised two

deciduous canines, which he deliberately ankylosed by extraction

followed by reimplantation

11. Treatment planning steps to reinforce the OA

a. Extraction pattern: extraction of the teeth which close to the reactive

unit will reduce the OA demand.

b. Appliance prescription.

I. Standard edgewise less anchorage demanding.

SWA comparing to standard edgewise. Johnston et al (1988) reported

that the use of the SWA cost 0.8mm more OA (measured by the

Pitchfork method) in the maxilla when compared with Standard

Edgewise treatment. However, this may be explained by the fact that a

preadjusted appliance makes it less likely that a clinician will finish a

case with inadequately torqued upper incisors, and the slightly higher

OA requirement with the SWA therefore reflects the achievement of

more anchorage demanding occlusal goals.

II. Roth incisors are more OA demanding

III. Andrews canines are less OA demanding

IV. MBT less OA demand than Roth and Andrews system because:

The wagon wheel effect: because increasing the incisor torque will cause

the mesial tip of ULS to reduce and this will reduce the anchorage

demands

Reduced canine, premolar and molar tip compared to Roth

Increased molar root torque buccally, increase anchorage by cortical

bone theory

Reduce upper molar mesial tip reduced the OA demand

Upper molar 10 degree offset, counteract the unwanted rotational

movement during space closure in the upper arch and this might

strengthen the anchorage

V. Tip-Edge is less OA demanding than SW because of the relying on the

tip-uprighting principle.

SWA comparing to tipe-dgewise. Lotzof (1996) found that the TipEdge

appliance consumed less OA than the SWA during canine retraction

(~0.6mm less, over a 3 week observation period). However, the results

did not reach statistical significance due to the small sample size, and it

should also be noted that the canines retracted with the TipEdge

appliance were not fully uprighted in this study. Shpack, 2008 compare

retraction of the canine using tipedge bracket and regular bracket in split

mouth study found that canine retraction in the first group was longer

and the anchorage loss was same in both groups.

VI. Self-ligating bracket: it is suggested that because there is less friction

in the system, lighter forces can be used and that this will be ‘lighter’ on

anchorage.

12. Biomechanical steps to reinforce OA

a. Using light force that is not overload the OA units.

b. Laceback and bendback which used with SWA

Robinson in 1989, in a prospective study found a 2.47 mm difference

in the lower incisor anteroposterior position between cases treated with

or without lacebacks. In the laceback group there was a mean 1.0 mm

distal movement of the incisors and a mean 1.76 mm mesial movement

of the first molars (so the OA loss is 0.76mm). In contrast the non-

laceback group demonstrated a mean 1.47 mm proclination of the

incisors compared with a mean 1.53 mm forward movement of the

molars (so the OA loss is 3mm).

Usmani 2002, results showed that Lacebacks do not prevent ULS

proclination, they have no effect on molar position, the amount of ULS

proclination depend on the angulation of the canine and the laceback

makes no difference. So there is no benefit from laceback.

Irvin 2004, in first premolar extraction cases, the use of laceback

ligatures conveys no difference in the anteroposterior or vertical

position of the lower labial segment. Furthermore, the use of laceback

ligatures creates a statistically and clinically significant increase in the

loss of posterior anchorage

Sueri et al 2006 applied the MBT technique with extraction of the first

premolars to study the effectiveness of laceback ligatures on maxillary

canine retraction. Canine distalization was successfully achieved with

laceback ligatures. Canine and molar movements were significantly

smaller in laceback cases.

Fleming 2012 in their systematic review found that there is no

evidence to support the use of lacebacks for the control of the sagittal

position of the incisors during initial orthodontic alignment

c. Stopped arch and utilities. (It is a type of compound anchorage theory):

The use of stopped arch wires recruits OA from the posterior and

anterior teeth while sliding individual teeth along the archwire. Rajcich

& Sadowsky (1997) showed that retraction of canines with sliding

mechanics, where the molar is prevented from tipping or sliding mesially

by an auxiliary arch and tip-back bends, incurs very little OA loss.

d. Subdivision of desired movement

Moving a single tooth at a time, rather than dividing the arch into more

equal segments can preserve anchorage. For example, in extraction

cases where OA is not at a premium, canines are usually retracted until

sufficient space exists to align the incisors, and the complete labial

segment is then retracted as a unit. According to the differential

anchorage theory, this would be expected to increase OA demand

compared with fully retracting the canines to a class I relationship and

then retracting the incisors. Therefore, if Enmasse retraction of the 6

anterior teeth is carried out, there must be a good reason to choose this

more OA demanding option. Generally, the advantages of Enmasse

retraction are simplicity, and avoiding the need to repeat stages of

treatment, such as realigning the teeth following sectional mechanics.

Heo in 2007 showed no significant differences existed in the degree of

anchorage loss of the upper posterior teeth and the amount of retraction

of the upper anterior teeth associated with en masse retraction and two

step retraction of the anterior teeth. Again TianMin Xu 2010 fond no

difference between Enmasse and two stage retraction.

Measuring OA:

OA is assessed by comparison over time of tooth position relative to a

non-tooth structure. The data is either

1. Cephalometric using

LLS position in relation to N-Pog or NB or MP

Pitchfork or Pancherz analysis

Superimposition technique

2. Intraoral photograph

3. Study models by superimposing on the rugae area (Sandler 2014)

4. Direct Clinical assessment especially if one arch is left as a base line.

A. Cephalometric measures of OA

1. Lower incisor AP position – a more labial position of the lower

incisors at the end of tooth movement is considered to represent OA loss.

Measures such as LiNPo or LiMn are used to assess this.

2. Pitchfork Analysis (Johnston 1996). Superimpositions on bony

structures – the reference structures are the maxilla and zygoma. This

analysis is used to measure AP movement of the upper and lower

incisors and molars. It provides a useful summary of the contributors to

AP effects of treatment, but no measurement of changes in incisor

inclination or canine angulation.

3. Pancherz : measure linear changes from perpendicular drawn from

sella to occlusal line (weakness is that it depend on max structure and OP

which is changeable)

4. Subjective analysis using superimposition technique such as

DeCosta’s line in the cranial base and Bjork’s stable structures in the

maxilla and mandible are used. Then the position of the anchor unit is

assessed subjectively. All reference structures have disadvantages, both

in principle and in terms of the practicalities of reliable identification and

measurement of landmarks.

B. Study model measurement

The use of palatal rugae as a reference for OA loss measurements has

been suggested, and is becoming more widely used with developments in

digital imaging, which assist the recording, enhancement and

measurement of study models.

Hoggan & Sadowsky (2001) concluded that rugae landmarks are as

reliable as cephalometric structures for superimposition, but the SD of

repeated measurements was +0.8mm, so changes of less than 1.6mm

using this method are unlikely to be statistically significant.

OA in three Planes

It is important to remember that orthodontic forces may be applied in a

sagittal (anterposterior), coronal (vertical) or lateral (horizontal)

direction. As such, consideration of the OA requirements must be

considered likewise in these directions.

1). Vertical Anchorage.

Consideration of vertical OA is important in the reduction of curve of

Spee (overbite) or in the treatment of anterior open bite.

Reduction of the curve of Spee can involve putting the resistance of

extrusion of the posterior teeth against the resistance of the intrusion of

the anterior teeth. In the clinical situation a degree of both occurs and a

type of reciprocal-compound OA could be said to exist. During the

levelling stage of treatment, extrusion or intrusion forces applied to

individual teeth would be counteracted by the OA values of a greater

number of teeth. To increase the efficiency of this type of tooth

movement it is advisable to band the second permanent molars. This is

classically thought to increase the OA value of the posterior segment

hence encouraging intrusion in the anterior segment. It may be

worthwhile considering in this case that extrusion of the second

permanent molar would have a greater effect on overbite than extrusion

of the first permanent molar as it is positioned more distally in the arch.

Anterior open bite: Intrusion of the posterior teeth can be made more

efficient by utilising intermaxillary traction with “box” elastics in the

anterior segments. This process helps withstand the intrusive effects of

the “reverse curve” imparted in the wire and can be considered a type of

intermaxillary compound anchorage. This process has found favour in

the technique of “Kim” mechanics.

2). Lateral anchorage

Consideration of horizontal OA is important in the treatment of

maxillary constriction resulting in crossbites. Such a case where

equivalent groups of teeth are moved equivalently is a classic case in the

use of reciprocal anchorage. Occasionally the occasion is seen where

there may not be an equivalent number of teeth in crossbite on both sides

of the arch. In such cases it is important to incorporate a greater number

of teeth in the anchor unit than in the unit in which maximum tooth

movement is desired. This is achieved by the inclusion of palatal arms

into the respective side of the quadhelix.

Movement of palatally placed ectopic canines can be quite OA

demanding. OA is usually obtained by applying force to the canine when

the upper arch has been stabilised by a heavy gauge stainless steel

archwire or applying the horizontal force from the two maxillary molars

conjoined by a palatal arch.

Both these methods increase the OA value of the anchor units by

increasing its root surface area and by preventing tipping and rotation

Orthodontic bone anchorage

Please refer to the TAD note.