GOOD MORNING

Applied anatomy of maxilla and mandible

Contents

• Introduction• Anatomy of maxilla• Anatomy of Mandible• Applied aspects• Skeletal malocclusion• Anchorage • Cleft plate• Oral asymmetry

Introduction

• As orthodontist are heavily involved in the treating abnormalities in the development of not just the dentition but the entire dentofacial complex, should be able to manipulate facial growth for the benefit of the patient.

• Bones of head and neck include somatic bones, the skull, seven cervical vertebrae and the hyoid developed from the second and third brachial arches.

• The skull cap is formed by frontal , parietal, squamous temporal and a part of occipital bones, develop by intramembranous ossification being a quicker one stage process.

• The base of the skull in contrast ossifies by intracartilaginous ossification which is a two stage process (membrane-cartilage-bone)

• The skeleton of the head is called as skull. It consists of

several bones that are joined together to form the cranium. The

term skull also include mandible (the lower jaw).

• Skull can be divided into two main parts

a) The calvaria or brain box

b) The facial skeleton constitutes the rest of the skull and

includes the mandible.

Bones of the skull

• Skull consist of 22 bones

The calvaria or brain case is composed of 8 bones

2 PAIRED 4 UNPAIRED

1) Parietal 1) Frontal

2) Temporal 2) occipital

3) Sphenoid

4) Ethmoid

• The facial skeleton is composed of 14 bones• 6 paired and 2 unpaired

Maxilla Mandible

Zygomatic bone Vomer bone

Nasal bone

Lacrimal bone

Palatine bone

Inferior nasal concha

• Norma Frontalis

• Norma lateralis

• Norma occipitalis

• Norma verticalis

• Norma basalis

anterior

middle

posterior

• Anterior part of norma basalis:-

1) Alveolar arch:-bears socket of the roots of the upper teeth

2) Hard palate:- formation anterior two third by the palatine

process of the maxillae and posterior one third by the

horizontal plates of the palatine bone.

Sutures :- cruciform sutures made up of intermaxillary

interpalatine and palatomaxillary sutures.

• Greater palatine foramen:- One on each side is situtated just below the lateral part of the palatomaxillary sutures.

• The lesser palatine formamina:- Two or three in number on each side is situated behind the greater palatine foramen.

• Posterior border of the hard palate is free and presents the posterior nasal spine in the median plane.

• The palatine crest is a curved ridge near the posterior border. It begins behind the greater palatine foramen and runs medially.

• Middle part of norma basalis:- The middle part extends from

the posterior border of hard palate to the arbitary transverse

line passing through the anterior margin of the foramen

magnum

Maxilla

• The term maxilla was derived from a Latin word “Mala”

which means cheeks

• It’s the second largest bone of the face

• The two maxillae form the whole of the upper jaw, and each

maxilla enter into the formation of face, nose mouth orbit the

infratemporal and pterygopalatine fossae

Features

• Each maxilla has a body and four process

Body of maxilla:- The body of maxilla is pyramidal in shape with its base

directed medially at nasal surfaces and the apex directed laterally at the

zygomatic process. It has four surface and encloses a large cavity the

maxillary sinus. The surfaces are

1) Anterior or facial

2) Posterior or infratemporal

3) Superior or orbital

4) Medial or nasal

• Maxilla contributes a large share in the formation of facial

skeleton. The anterior surface of the body of the maxilla

presents

a) nasal notch medially

b) the anterior nasal spine

c) Infraorbital foramen

d)Incisive fossa

e)The canine fossa lateral to the canine eminence

• The frontal process articulates anteriorly with the nasal bone, posteriorly with the lacrimal bone and superiorly with the frontal bone.

• The zygomatic process of the maxilla is short and articulates with zygomatic bone

• The alveolar process of maxilla bears sockets.• The palatine process

Anterior or facial surface:-

• Anterior or facial surface:- Directed forward and laterally

• Above the incisor teeth there is a slight depression the incisive

fossa which gives orgin to depressor septi.

• Lateral to the canine eminence there is a larger and deeper

depression, the canine fossa which gives orgin to anguli oris

• Above the canine fossa there is infra orbital foramen which transmits infraorbital nerve and vessels.

• Lecator labi superioris arises between the infraorbital margins and infra orbital foramen.

• Medially the anterior surface ends in a deep concave border, the nasal notch which terminates below into process with the corresponding process of maxilla forms the anterior nasal spine. Anterior surface bordering the nasal notch gives orgin to nasal depressor septi

Infratemporal surface

• Convex and directed backwards and laterally .

• Forms anterior wall of infratemporal fossa

• separated from anterior surface by zygomatic process .

• Near the centre of surface open two or three alveolar canals

for posterior superior alveloar nerve and vessels.

• Posterioinferiorly there is a rounded eminence the maxillary

tuberosity which articulates superiomedially with pyramidal process

of palatine bone and gives origin laterally to superficial head of

medial pterygoid muscle.

• Above the maxillary tuberosity the smooth surface form the anterior

wall of pterygopalatine fossa and is grooved by maxillary nerve.

Superior or orbital surface

• It is smooth ,triangular , and slightly concave and forms the greater part of the floor of orbit.

• Anterior border forms a part of the infraorbital margin.

• Medially it is continuous with the lacrimal crest of frontal

process.

• Posterior border forms anterior margin of the inferior orbital fissure,in the middle it is notched by infraorbital groove.

• Medial border presents anteriorly the lacrimal notch which is converted into nasolacrimal canal by decending process of lacrimal bone.

• Behind the notch,the border articulates from before backwards with the lacrimal ,ethmoid, and the orbital process of palatine bone.

• Surface presents infraorbital groove leading forwards to infraorbital canal which opens on anterior surface as infraorbital foramen.

• Inferior oblique muscle of eyeball arises from depression ;lateral to lacrimal notch at the anteromedial angle to the surface.

MEDIAL OR NASAL SURFACE

• Forms a part of lateral part of nose.

• Posterosuperiorly displays large irregular opening of maxillary sinus.

• Above sinus, there are parts of air sinuses which are completed by ethmoid and lacrimal bones.

• Below hiatus ,smooth concave surface forms a part of inferior meatus of nose.

• Behind hiatus ,surface articulates with perpendicular plate of palatine bone.

• Front of hiatus; nasolacrimal groove which is converted into nasolacrimal .

MAXILLARY PROCESSES

• ZYGOMATIC PROCESS• FRONTAL PROCESS• ALVEOLAR PROCESS• PALATINE PROCESS

ZYGOMATIC PROCESS

• Is a pyramidal lateral projection on which the anterior , posterior, and superior surfaces of maxilla converge.

• In front and behind it is continuous with the corresponding surfaces of the body, but superiorly it is rough for articulation with the zygomatic bone.

FRONTAL PROCESS

• Projects upwards and backwards to articulate above with nasal

margin of frontal bone ,in front with nasal bone and behind

with lacrimal bone.

• Lateral surface is divided by a vertical ridge ,the anterior

lacrimal crest , into smooth anterior part and a grooved

posterior part.

• Medial surface forms part of lateral wall of nose.

a) Uppermost area is rough for articulation with ethmoid to close the anterior ethmoidal sinuses.

b) Ethmoidal crest is a horizontal ridge about the middle of the process. Posterior part of crest articulates with middle nasal concha ,and anterior part lies beneath the agger nasi.

.

• The anterior smooth area gives origin to the orbital part of

orbicularis oculi and levator labii superioris. Posterior grooved

area forms anterior half of floor of lacrimal groove.

• The area below the ethmoidal crest is hollowed out to form the

atrium of middle meatus.

• Below the atrium is the conchal crest which articulates with

inferior nasal concha.

ALVEOLAR PROCESS

• Forms half of the alveolar arch, and bears sockets for the roots

of upper teeth.

• Buccinator arises from posterior part of its outer surface up to

the first molar tooth.

• A rough ridge ,the maxillary torus ,is sometimes present on

inner surface opposite the molar sockets.

PALATINE PROCESS

• Is a thick horizontal plate projecting medially from the lowest

part of the nasal surface.

• Inferior surface is concave and the two palatine processes

form anterior three-fourth of bony palate. It presents numerous

vascular foramina and pits for palatine glands.

• Posterolaterally it is marked by two antero-posterior grooves

for greater palatine vessels and anterior palatine nerves.

• Superior surface is concave from side to side, and forms

greater part of floor of nasal cavity.

• Medial border is thicker in front than behind. It is raised

superiorly into nasal crest.

• Posterior border articulates with horizontal plate of palatine

bone.

• Lateral border is continuous with alveolar process.

ARTICULATIONS• Superiorly articulates with

1) nasal

2) frontal

3) lacrimal bones.• Medially, with

1) Ethmoid

2) inferior nasal concha,

3) vomer,

4) palatine

5) opposite maxilla.• Laterally,

1) zygomatic bone

Growth

• The attachment of facial skeleton anterioinferiorly to the

calvarial bone determines the chondracranial influence of

facial growth.

• The site of attachment are clearly defined by the

pterygomaxillary fissure and the pterygopalatine fossa

between the sphenoid bone of the clavarial bone and the

maxillary and palatine bone of the posterior aspect of the face.

• The nasal cavity and the nasal septum have considerable influences in determining facial form.

Zygomatic bone is attached to the calvarial skeleton at the temporozygomatic and frontozygomatic sutures. The maxillary and nasal bones of the anterior aspects are attached to calvaria at the fronto maxillary and frontonasal sutures

Direction of growth and resoption of facial bone at various sites.The overall effect if the combination of these growth sites is a downward and forward displacement of face and vice versa for the cranial base

• The frontomaxillary, frontozygomatic, frontonasal, ethmoidomaxillary, and frontoethmoidal sutures are the sites of bone growth in a largely vertical direction as a result of eyeball and nasal septal expansion.

• If the nasal septum is defective, the height of the middle third of the face is less affected than its anteroposterior dimension resulting in concavity of the face.

• Sutures function mainly as sites of fibrous union of the skull bones, allowing for adjustments brought by surface apposition and remodeling.

GROWTH FIELDS

All surfaces, inside and outside, of every bone are covered by an irregular pattern of

“growth fields” comprised of various soft tissue osteogenic membranes or cartilages.

The genetic component for bone growth resides in the bone’s investing soft tissues –

muscles, integument, mucosa, blood vessels, nerve, connective tissue, the brain, etc.

• The growth fields have either depository or

resorptive activity.

• The varying activities and rates of growth of

these fields are the basis for the differential

growth processes that produce bone of

irregular shapes.

• The soft tissue acts as a functional matrix to

control bone growth whereas the bone itself

only reports – via a feedback mechanism which

is connected to the connective tissues – when the

shape, size and biomechanical aspects coincide

with the functional requirements.

Mandible

• The word mandible came from the latin word mandibula meaning chew.

• The mandible ,or the lower jaw, is the largest and the strongest bone of the face. It develops from the first pharyngeal arch. It has a horseshoe-shaped body which lodges the teeth, and a pair of rami which project upwards from the posterior ends of the body. The rami provide attachment to the muscles of mastication.

• BODY• Each half of the body has outer and inner surfaces, and upper

and lower borders.• The outer surface presents the following features.

1. symphysis menti

2. mental protuberance and mental tubercles.

3. mental foramen.

4. oblique line

5. incisive fossa.

Inner surface

1) Mylohyoid line2) Submandibular fossa3) Sublingual fossa4) Posterior surface of

symphysis menti5) The mylohyoid groove

RAMUS

• The ramus is quadrilateral in shape and has two surfaces,

lateral and medial, four borders, upper, lower, anterior and

posterior, and the coronoid and condyloid processes.

The medial surface presents the following:• Mandibular foramen and mandibular canal.• Lingula• The mylohyoid groove• Mandibular notch.• Coronoid process• Condyloid process

• The lower border is the backward continuation of the base of the mandible. Posteriorly, it ends by becoming continuous with the posterior border at the angle of the mandible.

• The anterior border is thin, while the posterior border is thick.

FACIAL MUSCLES

1) Muscle of the scalp 1) occipitofrontalis 2) Muscle of auricle 1) auricularis anterior 2) auricularis superior 3) auricularis posterior3) Muscles of the eyelids 1) orbicularis occuli 2)Corrugator supercilii 3)Levator palpebrae superioris

4 ) Muscles of the nose

1) procerus

2) compressor naris

3)dilator naris

4)depressor septi

5) Muscle around the mouth

1) Orbicularis oris

2) Zygomatic major

3) Levator labii superioris

4) Levator angli oris

5) Zygomatic minor

6) Depressor anguli oris

7) Mentalis

8) Risoris

9) buccinaor

MUSCLES OF MASTICATION

MUSCLES OF MASTICATION

• Masseter muscle• Temporalis muscle• Medial pterygoid muscle• Lateral pterygoid muscle

• COMMON CHARACTERISITICS:

1. All are inserted to the mandible

2. All are innervated by the mandibular division of the trigeminal nerve

3. All are concerned with biting and chewing• FUNCTIONS:

1. To move the mandible

2. To secure then stabilize the mandibular positions

3. To determine the direction of mandibular movements

Masseter muscle

• It is a flat quadrangular muscle, partly tendinous, partly fleshy. • It overlies the lateral surface of the mandibular ramus.

• ACTION: elevate the jaw,

with the superficial fibers

causing protraction

Deep part

Superficial part

TEMPORALIS MUSCLE

• It is a large, fan-shaped muscle at the sides of the head.

ACTION: anterior fibers elevate the mandible, while the posterior fibers retract the mandible

Blood supply: Deep temporal branches of maxillary artery.

LATERAL (or EXTERNAL) PTERGOID MUSCLE

• It is a thick and triangular muscle with two heads.

• It is the muscle of mastication that occupy primarily a horizontal position.

Action: acting together they

protrude and depress the mandible; acting alone and alternatively they produce side to side movements of the mandible.

Medial pterygoid muscle • It is almost a mirror-like image of the masseter muscle.• It is rhomboidal and runs practically in the same

direction on the inner surface of the mandible

Action: assets in elevating and protrusion of the mandibleacts together with lat. Pterygoid of the same side in rotating the mandible

Temporomandibular joint

• The temporomandibular joint is an example of ginglymo-arthrodial articulation and its movements are combination of gliding movements and loose hinge movements.

• GINGLYMOARTHROIDAL: The TMJ offers hinging movements in one plane, therefore it is considered as ‘ginglymoid’. It also provides for gliding movement, hence ‘arthroidal’.

The temporomandibular joint is made up of the following -

A. BONY COMPONENTS

1. Condylar head

2. Glenoid fossa

3. Articular eminence

B. SOFT-TISSUECOMPONENTS

1. Joint capsule

2. Articular disk

3. Ligaments

C. MUSCLES ASSOCIATED WITH THE TMJ– Muscles of mastication– Muscles attached to the joint– Muscles of facial expression– Muscles of the neck

MAXILLARY ARTERY

• The larger terminal branch of the external carotid artery given off behind the neck of the mandible.

• It has a wide territory of distribution and supplies1) the external and middle ears and the auditory tube2) the dura mater 3) The upper and lower jaws4) The muscles of the termporal and infra temporal regions5) The nose and paranasal air sinuses6) The palate7) The root of the pharynx

Branches

• Applied aspects of maxilla and mandible

ROTATION OF JAWS

• Studies of growth were carried out in the 1960s primarily by Bjork and coworkers in Copenhagen, the extent to which both the maxilla and mandible rotate during growth.

Forward rotation of the mandible with the center (type I) at the joints (a)With the center at the incisal edges of the lower incisors (type II) (b)With the center at the premolars (type III) (c)

Backward rotation of the mandible with the center at the joints (a) and with the center at the last occluding molarsType I:- Bite is raised increased Anterior facial heightFlattening of cranial baseMiddle cranial fossa is raised in relation to anteriorIncomplete development of middle cranial fossaeType II-Occurs in relation with growth in the saggital direction at the mandibular condylesBecause of position of the center of rotation at the molar the symphysis swung backward and the chin may not follow this movement and a characteristic double chin can occur

Schudy’s concept of growth rotation

Schudy’s concept of growth rotation

Cockwise rotation

Jaw bones or mandible grows downwards and

backwards

Conterclockwise rotation

Bone grows upward and

forwards

More posterior gorwth and less anterior growth

More anterior growth and less

posterior growth

Results in long face called as high

angle cases

Results in short face called as low

angle cases

Proffit’s description of rotation

Rotation depending upon the location of growth

Internal rotation (IR) rotation occurs in the core of the jaw bone

Core is the portion that covers the inferior

alveolar nerve

Two types of internal rotation

Rotation around condyle or matrix rotation

Rotation centered within mandible or intramatric

rotation

External rotation (ER)Rotation due to

surface changes)

Remaining parts of mandible like alveolar process the

muscular processes condylar process

11-12degree external rotation

15 degree of internal

rotationaTotal rotation

• Bjork and Skieller distinguished two contributions to internal rotation (which they called total rotation) of the mandible:

• (l) matrix rotation, or rotation around the condyle• (2) intramatrix rotation, or rotation centered within the body of

the mandible

• Bjork also named 7 structural signs of extreme growth

rotations.

•1. Inclination of the condylar head.

•2. Curvature of the mandibular canal.

•3. Shape of the lower border of the mandible

•4. Inclination of the symphysis.

•5. Inter Incisal Angle.

•6. Inter premolar, Inter molar Angle.

•7. Anterior lower Facial height.

FACIAL DEFORMITIES RELATED TO MAXILLA

• Facial Clefts: are among the most common congenital malformation in humans.

• Fetal Alcohol Syndrome: caused by very high blood alcohol levels during the first trimester of pregnancy.

• Hemifacial Microsomia: is a microstomia is a congenital defect characterized by a lack of tissue on the affected side of the face.

FACIAL DEFORMITIES RELATED TO MANDIBLE

• Agnathia: mandible may be grossly deficient or

absent. Occurs due to deficiency of neural crest

tissue in the lower part of the face.

• Micrognathia: characteristic for many

syndromes like Pierre Robin Syndrome, Down’s

Syndrome.

• Macrognathia: causes prognathism

• Hemifacial hypertrophy: evident at birth tends to be prominent at puberty. Unilateral enlargement of the mandible, the mandibular fossa and the teeth.

• Bifid or Double Condyle: results from the persistence of the septa dividing the fetal condylar cartilage.

Skeletal malocclusion

CLASS II MALOCCLUSION

Components of class II malocclusion:-

Maxilla

Maxillary skeletal position

Maxillary dentoalveolar

position

mandible

Dental position

Skeletal position

mandible

Normal mandible Retrognatic mandible

maxilla

Normal maxilla

Prognatic maxilla

• Deficient in mandibular size

• Mandible well defined but still class II due to posterior

positioning of glenoid fossa

• A deficiency in the anteroposterior position of the mandible is

a common finding in class II

• A decrease in vertical dimension cause the mandible to rotate

upward and forward

• These patients have a low mandibular plane angle deep bite

with a strong chin point or flared maxillary incisors

Increased vertical dimension

• A patient with increased lower anterior facial height often is characterized by

Retruded mandible Poorly defined chin point with a hyperactive mentalis

muscle. Anterior open bite The ratio between anterior to posterior facial height is

increased Maximum advancement of chin point is desired as the goal

of treatment increase in the vertical dimension of patient during treatment should be minimized

Treatment

• Once the component has been identified one or more specific

treatment protocols can be used. MAXILLA :-

1) Maxillary skeletal position

Protrusion Retrusion

Protrusion

• The most common treatment for true maxillary skeletal protrusion is extraoral traction.

• Extraoral traction appliances are divided arbitrarily into two types

1) Face-bow

2) Head gear

Retrusion

• There are a significant number of class II patients whose malocclusions are characterized in the part, by maxillary skeletal retrusion

.• This condition tends to be found in patients who have a long

lower face height, a steep mandibular plane angle and a retruded position of the chin point.

• Maxillary skeletal retrusion is extremely difficult to treat directly.

• Occasionally retrusion may be treated indirectly by using such appliances as posterior bite block or the veritcal-pull chin cup that may produce a slight upward and forward movement of the maxilla and a counterclockwise rotation of the mandible

MANDIBLE

mandible

Mandibular skeletal position

Mandibular dentoalveolar

position

Mandibular dentoalveolar position

• Many of the techniques described in the treatment of tooth size/ arch length.

• Lip bumber can be used effectively for mandibular dentoalveolar retrusion

• Mainly indicated in individuals who have very tight cheek and lip musculature and a defined mentolabial sulcus.

• Mild to moderate deficiency in mandibular arch length a removable mandibular schwarz appliance can be used.

Mandibular skeletal position:-

• Mandibular skeletal retrusion is most common

• Functional jaw orthopedic appliances may be indicated.

• All functional jaw orthopedic appliances have one aspect in

common they induce a forward mandibular posturing as part

of the treatment effect

Treatment options

1) FR-2 of frankel

2) Twin block appliance

3) Herbst appliance

4) Bionator The first two are primarly indicated in mixed dentition. Herbst in early permanent dentition.

Condylar light bulb analogy:

• Condyle acts like a light bulb on a dimmer switch

• Lights up during advancement, dimming back to near normal levels during retention.

• Growth potential diminishes with age while remodeling potential last long into adulthood.

LIGHT BULB ANALOGY

Improved clinical use of Twin-block and Herbst as a result of radiating viscoelastic tissue forces on the condyle and fossa in treatment and long-term retention: Growth relativity AJO DO 2000

• Light bulb analogy of condylar growth and retention. When the growing condyle is continuously advanced, it lights up like a light bulb on a dimmer switch. When the condyle is released from the anterior displacement, the reactivated muscle activity dims the light bulb and returns it close to normal growth activity. In the boxed area, the upper open coil shows the potential of the anterior digastric muscle and other perimandibular connective tissues to reactivate and return the condyle back into the fossa once the advancement is released. The lower coil in the box represents the shortened inferior LPM. The open coil above the yellow condylar light bulb represents the effects of the stretched retrodiskal tissues.

Biodynamic factors involved in condylar-glenoid fossa (C-GF) growth modification duringorthopedic mandibular advancement in treatment and retention. Metabolic action describes the pump-like influx and expulsion of nutrients and other chemicals from the engorged blood vessels of the proliferating retrodiscal tissues (dark blue region) extending between the condyle and the fossa. This biodynamic action (light blue circle) occurs in the retrodiskal tissues and fibrocartilage during condylar displacement. The expulsion of these accumulated metabolites occurs during reseating of the protracted condyle and is clinically evident as relapse of the previously observed condition.

VERTICAL EXCESS

• Skeletal open bite• Long face syndrome• Elongation of maxillary and mandibular

posterior teeth

Long face syndrome

• Low muscle activity Long face syndrome Increased anterior

facial height Decreased posterior

facial height Hight mandibular

plane angle High gonial angle

Low bite forces

Decreased masticatory mucle thickness and

volumeMuscle fiber type slow

Obliquely placed masticatory muscles

Rx OF VERTICAL EXCESS

• HIGHPULL HEADGEAR TO MOLARSMaintain vertical position of maxillaInhibit eruption of maxillary posteriors

Rx OF VERTICAL EXCESS

• HIGHPULL HEADGEAR TO A MAXILLARY OCCLUSAL SPLINT

Gummy smileExcessive incisal show (increased ant. dental

height)Disadvantage: allows mandibular teeth to

erupt freely

TRANSVERSE DIMENSION

The transverse dimension of maxilla can be widen and this temporary defect in the mid palatal suture region remodels with osseous tissue.

• Suture is formed by the junction of the three opposing pairs of bones namely premaxillae,maxillae and the palatines but often for practical purposes they will be treated as single entity called as a Midpalatal suture.

• The suture starts to ossify posteriorly (Davida 1926) and always shows a greater degree of obliteration posteriorly then anteriorly, while ossification comes very late anterior to Incisive foramen.

The simplest definition of a cleft is that “Its an opening in an anatomical part that is normally not open.

Cleft plate

Orthodontist plays a major role in the management of the Cleft patient.

Palatal integrity is essential at birth to enable feeding.The orthodontist helps in designing and fabrication of the following appliances that may be used for the Cleft palate patient management: Feeding plate for the neonate.Orthodontic correction plate for the gum pad.

• Orthodontic cum prosthetic plate used in deciduous and

permanent dentition.

• Fixed Orthodontic appliance.

• Rapid palatal expansion appliance in the pre-puberty growth

period.

• Headgear for pre-maxillary fragment.

ANCHORAGE:- Orthopeadic correction-

Two methods for obtaining the Skeletal anchorage:-

• Intentionally Ankylosed teeth.

• Endosseous Implants.

Anatomy of Maxilla and TADS

• Knowing the anatomy and density of bone helps in identifying the ideal place to insert the Implants.

• Bone density and Misch classifications

• Stationary anchorage failure often occurs because the TAD was placed in a region of low bone density with inadequate cortical thickness

• D1 (> 1,250 HU) is dense cortical bone• primarily found in the anterior mandible, buccal shelf and

midpalatal region .• D2 (850-1,250 HU) is porous• cortical bone with coarse trabeculae found primarily in the

anterior maxilla, the midpalatal region and the posterior mandible.

• D3 (350-850 HU) is thin (1 mm), porous cortical bone with fine trabeculae,found primarily in the posterior maxilla and mandible.

• D4 (150-350 HU) is fine trabecular bone,

found primarily in the tuberosity region

Orofacial Asymmetry:-

• Stedman’s medical dictionary symmetry may be defined as “equality or correspondence in form of parts distributed around a center or an axis, at the two extremes or poles or on the two opposite sides of the body”

CLASSIFICATION. Asymmetries can be classified according to the structures

involved into dental, skeletal and functional.

Dental asymmetries

Skeletal asymmetries

Muscular asymmetries

Functional asymmetries

• Dental asymmetries: These can be due to local factors such as early loss of deciduous teeth, congenitally missing tooth or, and habits such as thumb sucking. Lack of exactness in genetic expression affects the teeth on the right and left sides causing asymmetries in mesiodistal crown diameters.

• Skeletal asymmetries: The deviation may involve one bone such as the maxilla or mandible, or it may involve a number of skeletal and muscular structures on one side of the face, e.g. hemifacial microsomia

• Muscular asymmetries: Facial disproportions and midline discrepancies could be the result of muscular asymmetry, as might occur with hemifacial atrophy or cerebral palsy. Sometimes muscle size is ill-proportioned as in masseter hypertrophy." Abnormal muscle function often results in skeletal and dental deviations.

• Functional asymmetries: These can result from the mandible being deflected laterally or antero-posteriorly, if occlusal interference’s prevent proper intercuspation in centric relation. These functional deviations may be caused by a constricted maxillary arch (even if the constriction, in itself, is symmetrical), or a more localized factor such as a malposed tooth. The abnormal initial tooth contact in centric relation results in the subsequent mandibular displacement in centric occlusion.

The association of anatomical entities as applied to clinical orthodontics

• Vertical and horizontal growth has an important effect on vertical overbite as were as over jet

• The type of terminal growth will indicate the best retention procedures

• Facial esthetics is significantly affected by the rotation of the mandible and the degree if facial divergence.

Conclusion

• One should have a thorough understanding of the

basic anatomy constitution of the tissue structure and

anatomy of the area before intervening or indulging

in deciding treatment plans.

REFRENCES

• Contemporary Orthodontics – William R Profit.• Text Book of Craniofacial growth – Sridhar

Premkumar• Colour atlas of dental medicine Orthodontic –

diagnosis- Rakosi• Orthodontics and dentofacial orthopedics-

James A McNamara

• Text Book Of Anatomy- Gray’s Anatomy

• Human Anatomy- B.D. Chaurasia

• Facial growth – Geoffrey H. Sperber

• Janusz Skrzat et al., The morphometry of the human palatine sutures(Folia Morphol., 2003, Vol. 62, No. 2)

• Improved clinical use of Twin-block and Herbst as a result of radiating viscoelastic tissue forces on the condyle and fossa in treatment and long-term retention: Growth relativity AJO DO 2000

• Age related differences in mandibular ramus growth: a histologic study- Mark G. Hans, Donald H. Enlow, Regina Noachter

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