ANCHORAGE

Presented by : Satyam mehta

BDS IV yr

DefinitionFactors affecting anchorageClassification Implants as Anchorage Units

The term anchorage , in its orthodontics application defined as “Resistance to unwanted tooth movement.

The tooth movement during orthodontic therapy is brought about by force generated by the active components of an orthodontics appliance. The force used to move teeth is derived from certain anatomic areas which acts as Anchors.

GRABER has defined Anchorage as “the nature and degree of resistance to displacement offered by anatomic unit for the purpose of effecting tooth movement”.

Factors affecting anchorage :-•TEETH :- Whenever some teeth are moved orthodontically, the remaining teeth of the oralcavity can acts as anchorage or resistance units. The anchorage potential of teeth depends on a number of factors such as :Root form. Size and Number of roots.Root surface area.Inclination of root.Ankylosed teeth .

•Root form :- The anchorage potential of a tooth depends largely on its root form . Round roots such as in bicuspids can resist horizontally directed forces in any direction .

Flat roots like in mandibular incisors can resist movements in the mesio-distal direction . The triangular roots like canine offers the maximum resistance to displacement compared to round or flat roots .

•Size and number of roots :- Multirooted teeth with large roots have a greater ability to withstand stress than single rooted teeth.

•Root length:- The root length indicates the depth to which the tooth is embedded in bone and the greater is its resistance to displacement.

Root surface area:The root surface of the tooth

that is very important factor determining the anchorage value of the tooth . The root surface area of the tooth that is used as anchorage should greater than the root surface area or the anchorage value of the tooth that has to be moved .

•Inclination of tooth :- The axial inclination of the tooth is important in assessing its value as a source of anchorage . A greater resistance to displacement is offered when the force exerted to move teeth is opposite to that of their axial inclination .

•Ankylosed teeth :- Ankylosed teeth are directly fixed to the alveolar bone and hence lack a periodontal ligament .Orthodontic movements of such teeth is not possible and they can therefore severe as excellent anchores whenever possible .

•ALVEOLAR BONE:- The alveolar bone that surround s a tooth offers resistance to tooth movement up to a certain amount of force and thus provide anchorage .

•BASAL BONE :- Certain areas of the basal jawbone are available intraorally as source of anchorage .These areas include the hard palate and the lingual surface of the mandible in the region of the roots. These intraoral hard areas of basal bone.

CLASSIFICATION OF ANCHORAGE (MOYERS)

According to the nature of force application: • Simple anchorage • Stationary anchorage •Reciprocal anchorage

According to the jaw involved:• Intramaxillary • Intermaxillary

According to the site of anchorage :• Intraoral

• Extraoral• Cervical • Occipital• Cranial• Facial

•Muscular

According to the number of anchorage units:

• Single or Primary anchorage .

• Compound anchorage.

• Multiple or reinforced anchorage.

1. Simple Anchorage: It is defined as dental

anchorage in which the manner & application of force is such that it tends to change the axial inclination of the tooth or teeth that form the anchorage unit in the plane of space in which the force is being applied .Thus the resistance of the anchorage unit to tipping is utilized tomove another tooth or teeth .

ACCORDING TO THE NATURE OF FORCE APPLICATION

Simple anchorage is obtained by engaging with the appliance a greater number of teeth than are to be moved with in the same dental arch. The combined root surface area of the teeth forming the anchorage unit must be double that of the teeth to be moved.

2.Stationary anchorage : It is defined as dental anchorage in which the manner & application of force tends to displace the anchorage unit bodily in the plane of space in which the force is being applied.

Example of a premolar extraction site ,if the appliance were arranged so that the anterior teeth could tip lingually while the posterior teeth could only move bodily.

3.Reciprocal anchorage: In reciprocal situation ,the force applied to teeth and to arch segments are equal ,and so is the force distribution in the PDL. The term generally refers to the resistance offered by two malposed unit when the dissipation of equal and opposite forces tends to move each unit towards a more normal occlusion .

Example :The two teeth or group of teeth of equal anchorage value are made to move in opposite directions. Example of reciprocal anchorage include closure of a midline diastema by moving the two central incisor toward each other .

1. Intramaxillary anchorage : When all the units offering are situated within the same jaw the anchorage is describe as intramaxillary . In this type of anchorage the teeth to be moved and the anchorage units are all situated either entirely in the maxillary or the mandibular arches.

ACCORDING TO THE JAW INVOLVED

2.Intermaxillary anchorage(Baker’s anchorage): Anchorage in which the resistance units situated in one jaw are used to effect tooth movement in the opposing jaw is called intermaxillary anchorage .

1.Intraoral Anchorage : Anchorage in which all the resistance units are situated within the oral cavity . Various intraoral anatomic units that maybe employed are the teeth ,palate and lingual alveolar bone of mandible.

According to the site of anchorage :

2.Extraoral Anchorage ; Anchorage in which the resistance units are situated outside the oral cavity is termed extraoral anchorage . Various extraoral anatomic units as sites of resistance are occipital, back of the neck , cranium and face.A. Cervical anchorage B. Occipital anchorage C. Facial anchorage

A. Cervical anchorage : Extraoral anchorage can alternatively be obtained from the neck or cervical region . Such a type of headgear is called cervical headgear.

B. Occipital anchorage : Extraoral anchorage can be obtained by using headgear that derived anchorage from the occipital or parietal region of the cranium . these devices are used along with a face bow to restrict maxillary growth or to move the dentition or maxillary bone distally .

C. Facial anchorage : The frontal bone and the mandibular symphysis offers anchorage during facemask therapy in order to protract the maxilla.

A)Single or primary anchorage : Anchorage were the resistance provide by a single tooth with greater alveolar support is used to move another tooth with lesser support .

B)Compound Anchorage : Anchorage where the resistance provided by more than one tooth with greater support is used to move teeth with lesser support .

ACCORDING TO THE NUMBER OF ANCHORAGE UNITS :

Implants as Anchorage Units /Absolute Anchorage ,Temporary Anchorage Devices(TAD):A orthodontics have used teeth,intraoral appliances and extraoral appliances to control anchorage minimizing the movements of certain teeth ,while completely the desire movements of the others.There are limitation in ability to completely control all aspects of tooth movement.

A temporary anchorage devices is that which is temporary fixed to the bone for the purpose of enhancing orthodontics anchorage either by supporting the teeth of the reactive unit alltogether and which is subsequently removed after use. They can be located transosteally

subperiosteally endosteally.

They can be fixed to bone ;Mechanically (Cortically stabilized )

Biochemically (osseointergrated

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