In the name of GOD

Anchorage and its control Presented by: Dr Somayeh Heidari Orthodontist

Reference: Chapter 8 Contemporary Orthodontics William R. Proffit, Henry W. Fields, David M.Sarver. 2013. Mosby

Anchorage : resistance to unwanted tooth movement

Reaction forces can move other teeth as well if the appliance contact them. Anchorage is the resistance to reaction forces that is provided (usually) by other teeth, (some times) by the palate, head or neck (via extraoral force) and (less frequently) by anchors screwed to the jaws. An important aspect of treatment is maximizing the tooth movement that is desired, while minimizing undesirable side effects.

Keeping the pressure in the PDL of anchor teeth as low as possible. Strategy for anchorage control Concentrate the force needed to produce tooth movement where it was desired, and then to dissipate the reaction force over as many other teeth as possible. Keeping the pressure in the PDL of anchor teeth as low as possible. It would only be necessary to be certain that the threshold for tooth movement was not reached for teeth in the anchorage unit.

Greater forces, though equally effective in producing tooth movement, would be unnecessarily traumatic and unnecessarily stressful to anchorage.

Anchorage situations

Reciprocal tooth movement forces applied to teeth and to arch segments are equal, and so is the force distribution in the PDL.

> The anchorage value of a tooth, is its resistance to movement, this is as a function of its root surface area, which is the same as its PDL area. The larger the root, the greater area for the force distribution. >

The movement would not be truly reciprocal but would be close to it.

Reinforced anchorage Reinforcing anchorage by adding more resistance units is effective. With more teeth (or extraoral sutures) in the anchorage, the force is distributed over a larger area. This reduces the pressure on the anchor units.

More pressure in the PDL of the anterior teeth differentially anterior teeth retraction

Pressure – Response curve

Pressure – Response curve

Slipped, burned or blown anchorage Keeping the force light has two virtues: Minimize trauma and pain Makes it possible to create anchorage Too much force: Destroy the effectiveness of reinforced anchorage by pulling the anchor teeth up onto the flatter portion of the pressure response curve. Slipped, burned or blown anchorage

Stationary anchorage pitting bodily movement of one group of teeth against tipping of another

this would have the effect of doubling the amount of anterior retraction compared with posterior forward movement. the successful implementation of this strategy requires light force. if the force were large enough to bring the posterior teeth into their optimum movement range, it would no longer matter whether the anterior segment tipped or was moved bodily.

Cortical anchorage the consideration is the different response of cortical compared with medullary bone. cortical bone is more resistance to resorption, and tooth movement is slowed when a root contact it. torquing the roots of posterior teeth outward against the cortical plate to inhibit their mesial movement.

it is doubtful that this technique greatly augments anchorage. it has the potential to create root resorption. dense cortical bone that formed within the alveolar process (old extraction site) affect tooth movement.

torquing movements are limited by the facial and lingual cortical plates. if a root persistently forced against to cortical plate, tooth movement is greatly slowed and root resorption is likely, but penetration of the cortical bone may occur. although torquing the root out of the bone is possible, fortunately, it is difficult.

Skeletal (Absolute) anchorage if structures other than the teeth used as an anchor unit, tooth movement or growth modification may be produced without unwanted side effects. until recently, extra-oral force (headgear) was the only way to obtain anchorage that was not from the teeth.

Two problems of headgear: 1- impossible for the patient to wear headgear all the time 2- the force against the teeth is larger than optimal The force system is far from ideal

with successful bone implant techniques, the potential existed for “no tooth movement except what was desired” that could be described as absolute anchorage. osseointegration is not necessary, and perhaps no desired for temporary attachments to provide orthodontic anchorage.

Temporary Anchorage Device (TAD)

Thanks for your attention