MAHATMA GANDHI DENTAL COLLEGEAND HOSPITAL

DEPARTMENT OF ORTHODONTICS AND DENTOFACIAL ORTHOPAEDICS ANCHORAGE Guided by-Submitted by-Dr.MRIDULA TREHAN(MDS)ANKITA GUPTAH.O.DBDS FINAL YEARDEPARTMENT OF ORTHODONTICSBATCH 2008-09 AND DENTOFACIAL ORTHOPAEDICS CONTENTS-Introduction-General principles of tooth movementAnchorageSources of anchorage-Intra-oral sources -Extra-oral sourcesClassification of anchorageAnchorage planningAnchorage lossClassification of anchorage demandReferences

INTRODUCTIONGeneral principles of tooth movement-Tooth movement during orthodontic therapy is brought about by forces generated by the active components of an orthodontic appliance.The force used to move teeth is derived from certain anatomic areas, which act as anchors.According to Newtons third law of motion, for every action there is an equal and opposite reaction. In accordance with this low, the forces used to move teeth may induce an equal and opposite force on the anchorage units tending to cause their movement which is not desirable.The resistance that the anchorage areas offer to these unwanted tooth movements is called anchorage.

ANCHORAGE DEFINITION - Graber has defined anchorage in orthodontics as the nature and degree of resistance to displacement offered by an anatomic unit when used for the purpose of effecting tooth movement.

Proffit-the term anchorage, in its orthodontic application, is defined in an unusual way: the definition as resistance to unwanted tooth movement includes a statement of what the dentist desires.

White and Gardiner-anchorage is the site of delivery from which a force is exerted.

Anchor-the force used to move teeth is derived from certain anatomic area, which act as anchors.

SOURCES OF ANCHORAGE-Anchorage during orthodontic therapy is mainly obtained from two sources-1)Intra-oral sources--The teeth-alveolar bone-basal bone-musculature

2)Extra-oral sources--cranium-back of the neck-facial bones

INTRA ORAL SOURCES THE TEETH-Whenever some teeth are moved orthodontically, the remaining teeth of the oral cavity can act as anchorage or resistance units.The anchorage potential of teeth depends on a number of factors such as-1.Root form-Round roots-seen in bicuspids and palatal root of maxillary molars-can resist horizontally directed forces in any direction.Flat roots-seen in mandibular incisors and molars and buccal roots of maxillary molars-can resist movement in mesio distal direction.Triangular roots-seen in canines and maxillary central and lateral incisors-offer the maximum resistance to displacement.2.Size and number of roots-Multirooted teeth with large roots have a greater ability to withstand stress than single rooted teeth.

3.Root length-The longer the root, the deeper it is embedded in bone and the greater is its resistance to displacement.4.Inclination of tooth-A greater resistance to displacement is offered when the forces exerted to move teeth is opposite to that of their axial inclination.5.Ankylosed teeth-Ankylosed teeth can serve as excellent anchors whenever possible.ALVEOLAR BONE-The alveolar bone that surrounds a tooth offers resistance to tooth movement upto a certain amount of force. when the force applied exceeds a certain limit ,the alveolar bone permits tooth movement by bone remodeling.BASAL BONE-Intraoral hard areas of basal bone include the hard palate and the lingual surface of the mandible in the region of the roots, can be used to augment intramaxillary or inter-maxillary anchorage.

MUSCULATURE-The normal tonus of facial and masticatory muscles plays an important role in the normal development of dental arches.Dental anchorage may be increased by making use of hypertonic labial musculature as in the case of lip bumper.

EXTRA ORAL SOURCES1.CRANIUM(OCCIPITAL AND PARIETAL ANCHORAGE)- Extra oral anchorage can be obtained by using headgears that derive anchorage from the occipital and parietal region of the cranium.These device are used along with a facebow to restrict maxillary growth or to move the dentition or maxillary bone distally.2.BACK OF THE NECK(CERVICAL REGION)-Extraoral anchorage can alternatively be obtained from the neck or cervical region.Such a type of headgear is called cervical headgear.3.FACIAL BONES-The frontal bone and the mandibular symphysis offer anchorage during facemask therapy in order to protect the maxilla.Headgears that make use of anchorage from the forehead and chin are called reverse headgear.

CLASSIFICATION OF ANCHORAGE(MOYERS)ACCORDING TO THE MANNER OF FORCE APPLICATION-1.Simple Anchorage2.Stationary Anchorage3.Reciprocal AnchorageACCORDING TO JAW INVOLVED-1.Intramaxillary2.IntermaxillaryACCORDING TO THE SITE OF ANCHORAGE-1.Intraoral2.Extraoral: a.Cervical b.Occipital c.Cranial d.Facial3.Muscular

ACCORDING TO THE NUMBER OF ANCHORAGE UNITS-1.Single or primary anchorage2.Compound anchorage3.Multiple or reinforced anchorage

Simple anchorage- removable appliance incorporating a screw for buccal movement of a palatally placed premolar

SIMPLE ANCHORAGE-It is defined as dental anchorage in which the manner and application of force is such that it tends to change the axial inclination of the tooth or teeth that form the anchorage units in the plane of space in which the force is being applied.Thus the resistance of the anchorage unit to tipping is utilized to move another tooth or teeth.Example-removable appliance incorporating a screw for buccal movement of a palatally placed canine.

STATIONARY ANCHORAGE-It is defined as dental anchorage in which the manner and application of force tends to displace the anchorage unit bodily in the plane of space in which the force is being applied.The anchorage provided by a tooth resisting bodily movement is considerebly greater than one resisting tipping force.

Examples ofreciprocal anchorage-(A)Finger spring used to close a midline (B)Correction of midline diastema using elastic (C)Cross bite elastics for correction of single tooth posterior cross bite (D)Arch expansion using a removable appliance incorporating a coffin spring

RECIPROCAL ANCHORAGE-It refers to resistance offered by two malposed units when the dissipation of equal and opposite forces tends to move each unit towards a more normal occlusion.Here two teeth or two groups of teeth of equal anchorage value are made to move in opposite directions.Examples-closure of a midline diastema by moving the two central incisors towards each other. -The use of crossbite elastics and dental arch expansion .

INTRA ORAL ANCHORAGE-Anchorage in which all the resistance units are situated within the oral cavity is termed intraoral anchorage.The teeth to be moved and the anatomic areas that offer anchorage are all within the oral cavity.Intraoral units are- the teeth,palate and lingual alveolar bone of mandible.

Occipital headgear-anchorage from the cranium(B)face mask for protection of maxilla-anchorage from forehead and chin Examples of extraoral anchorage

EXTRAORAL ANCHORAGE-Anchorage in which the resistance units are situated outside the oral cavity is termed intraoral anchorage.Extraoral units are-occiput,back of the neck,cranium and face.Examples-use of headgear that derive anchorage from the cervical or cranial regions and facemask that derives anchorage from the facial bones.

Lip bumper utilizing muscular anchorage

MUSCULAR ANCHORAGEIn certain cases the perioral musculature is employed as resistance units.Muscular anchorage makes use of forces generated by muscle to aid in the movement of teeth.Example-use of a lip bumper to distalize the molars.

INTRAMAXILLARY ANCHORAGEWhen all the units offering resistance are situated within the same jaw.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.

BAKERS Anchorage-(A)ClassII intermaxillray anchorage (B) ClassIII intermaxillary anchorage

INTERMAXILLARY ANCHORAGEAnchorage in which the resistance units situated in one jaw are used to effect tooth movement in opposing jaw is called intermaxillary anchorage.It is also termed BAKERS ANCHORAGE.Examples-class II elastics traction applied between the lower molar and upper anteriors -class III elastics traction applied between the upper molar and lower anteriors

SINGLE OR PRIMARY ANCHORAGECases wherein the resistance provided by a single tooth with greater alveolar support is used to move another tooth with lesser support is referred to as single or primary anchorage.

COMPOUND ANCHORAGEAnchorage where the resistance provided by more than one tooth with greater support is used to move teeth with lesser support is called compound anchorage.

(A)Upper anterior inclined plane (B)Sved plane Examples of reinforced anchorage

REINFORCED OR MULTIPLE ANCHORAGEAnchorage in which more than one type of resistance unit is utilized is termed reinforced anchorage.Reinforced anchorage refers to the augmentation of anchorage by various means such as extraoral appliance,upper anterior inclined plane or a transpalatal arch connecting the two maxillary molars.Methods of reinforcing anchorage-a.extraoral forces to augment anchorage-Such as cranium,back of neck and face can be used to reinforced anchorage.b.upper anterior inclined plane-A removable appliance incorporating an upper anterior inclined plane results in forward glide of mandible during closure of the jaw.This result in stretching of the retractor muscle of mandible,which subsequently contracts and forces the mandible against the upper inclined plane.Thus a distal force is applied on the maxillary teeth thereby reinforcing maxillary anchorage.A modification of anterior inclined plane is the SVED APPLIANCE that has an additional upper incisal capping.

(A)Transpalatal arch (B)Lingual arch Examples of reinforced anchorage

c.use of transpalatal arch and lingual arches-Transpalatal arch is a wire that spans the palate in a transverse direction connecting the first permanent molars of either side.They are used in fixed mechano therapy to augment anchorage.An arch connecting the contralateral lower molars running along the lingual aspect of the mandibular arch prevents mesial movement of the lower molars.This is called the ligual arch.The lingual arch and transpalatal arch are soldered to the lingual aspect of molar bands that are cemented to these teeth.

d.use of implants-Implants are slowly being introduces as sources of anchorage.They are specially useful in patients who have lost lot of teeth or hypodontia.Intraoral aids may be limited in their anchorage potential,endoosseous implants are a valuable alternative for stable intra oral anchorage.Microimplants as a source of anchorage in orthodontic treatment is relatively new.

ANCHORAGE PLANNINGThe requirement depends on a number of factors,which are listed below-1.Number of teeth being moved-The greater the number of teeth being moved,the greater is the demand on the anchorage.2.Type of teeth being moved-The movement of slender anterior teeth offers lesser strain on the anchorage than robust multirooted teeth.3.Type of tooth movement-Whenever bodily tooth movements is required,there is a greater strain on the anchorage.In contrast,tipping tooth movements offer a relatively lesser strain on the anchorage units.4.Duration of tooth movement-Treatment of a prolonged duration places an undue strain on the anchorage.5.Skeletal pattern-Patients who exhibit vertical skeletal growth pattern show more tendency for mesial tooth movement and anchorage loss.Patients who exhibit a horizontal growth pattern show lesser tendency for the mesial movement of the anchor teeth.This is attributed to the strong facial musculature they exhibit.6.Occlusal interlock-A good buccal occlusion may act to resist tooth movement.

ANCHORAGE LOSS-In spite of the precaution taken in planning anchorage, a certain amount of unwanted movement of the anchor teeth invariably occurs during orthodontic treatment.Such unwanted movement of anchor teeth is called ANCHORAGE LOSS.

CLASSIFICATION OF ANCHORAGE DEMAND-Based on the anchorage loss that is permissible,the anchorage demand of an extraction case can be of three types-a.Maximum anchorage casesb.Moderate anchorage casesc.Minimum anchorage cases

Maximum anchorage

Maximum anchorage cases-In cases where anchorage demand is very high,not more than of the extraction space should be lost by forward movement of the anchor teeth.The anchorage in these patients should be augmented to avoid unwanted movement of the anchor teeth.

Moderate anchorage

Moderate anchorage cases-In these cases, the anchor teeth can be permitted to move forward into 1/4th to of the extraction space.

Minimum anchorage

Minimum anchorage cases-In these cases, the anchorage demand is very low. More than half of the extraction space can be lost by the anchor teeth moving mesially.

References-S.I.Bhalajhi:Orthodontics :The art and science,Fourth editionGraber TM-Orthodontics:Principles and practice,Third editionProfitt WR:Contemporary orthodontics,fourth editionRobert E Moyers:Hand book of orthodontics