16th Lec 08 Landmarks of the Skull

8/3/2019 16th Lec 08 Landmarks of the Skull

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LANDMARKS OF THE

SKULL


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Skull is composed of 22 bones. Some of these aresingle and some are paired

Group into two categories: one group surroundsthe brain and one group forms the face

The following eight bones make up theneurocranium, the bones surrounding the brain:

Frontal brain (single) Sphenoid bone (single)

Ethmoid bone (single)

Occipital bone (single)

Temporal bone paired)

Parietal bone (paired)


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Neurocranium bones

Frontal brain (single)

Parietal bone(paired)

Occipital bone(single)

Sphenoid bone(single)

Ethmoid bone

(single) Temporal bone

(paired)


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PAIRED BONES SINGLE/UNPAIRED

-maxillae -mandible-palatines -vomer

-inferior nasal conchae -ethmoid

-nasals -frontal

-lacrimals -sphenoid

-zygomatics -occipital

-temporals

-parietals


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MAXILLAE

Entire upper jaw

Contributes to the formation of the upperportion of the face, nose, orbits and hardpalate


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PALATAL BONE

Makes up the floor of the nose


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Muscles of mastication


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Muscle of mastication move the mandible

They include four pairs of muscles:

masseter, temporalis, medial pterygoid andlateral pterygoid muscles

There are five different ways the mandible

moves: elevate, depress, retrude, protrudeand lateral excursions


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Temporalis Muscle Fan-shaped, large but flat muscle

with both vertical anterior (andmiddle) fibers and more horizontalposterior fibers.

Innervation: temporal branchesof the mandibular division of the5th nerve

Origin: arises from the entire

temporal fossa which comprisedof the squamous part of temporalbones and the greater wing of thesphenoid bones and the adjacentportions of the frontal and parietalbones

Insertion: Inserts on the coronoid

process of the mandible Action:

Anterior & middle vertical fiberselevation of the mandible

Posterior fibers retraction of themandible


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Medial Pterygoid Muscle Located on the medial surface

of the ramus

It is active during protrusion

Innervations: nerve vagus

Origin: arises mainly from themedial surface of the lateralpterygoid plate and the

pterygoid fossa between themedial and lateral pterygoidplates of the sphenoid bone.

Insertion: inserts on the medialsurface of the mandible in atriangular region at the angleand on the superior adjacentportions of the ramus just abovethe angle

Action: elevates the mandibleand for lateral positioning of the

mandible


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Masseter Muscle Largest, most superficial, bulky

and powerful of the muscles of

mastication Origin: arises from the inferior

and medial surfaces of thezygomatic bone, the zygomaticprocess of the maxillae, and thetemporal process of zygomatic

bone. From here it extendsinferiorly and posteriorly towardsits insertion

Insertion: inserts on the inferiorlateral surface of the ramus andangle of the mandible

Action: elevates the mandibleand applies great power incrushing food.


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Lateral pterygoid muscle Has the fibers aligned most

horizontally

Short, thick, somewhat conicalmuscle located deep in theinfratemporal fossa and is theprime mover of the mandible

Origin: arise from two heads,

both located on the sphenoidbone Superior head smaller,

attached to the infratemporalsurface of the greater wing of thesphenoid bone. Active duringvarious jaw-closing movements

only, such as chewing Inferior head larger, attached to

the adjacent lateral surface of thelateral pterygoid plate on thesphenoid bone. Active during thejaw-closing movements andprotrusion only.


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Insertion: inserts on the depression on thefront neck of the condyloid process called

the pterygoid fovea, and into the anteriormargin of the articular disc.

Actions: to protrude the mandible

To depress the mandible

Contralateral abduction. When only one lateralpterygoid contracts, it pulls the condyle on that sidemedialward and anteriorly, moving the body of the

mandible and its teeth toward the opposite side.


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SUPRAHYOID INFRAHYOID

-geniohyoid - sternohyoid

-mylohyoid - thyrohyoid-stylohyoid - sternothyroid

-digastric - omohyoid


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Temporomandibular Joint


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Temporomandibular Joint

Joint or articulation is the connection betweentwo separate parts of the skeleton.

Craniomandibular joint/temporomamdibulararticulation between the mandible and twotemporal bones

Three articulating parts of temporomandibularjoint:

1. mandibular condyle2. articular fossa and articular eminence (tubercle) ofthe temporal bone

3. articular disc


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Articulating parts of the condyle


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condyle

fossa

meniscus


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Articular eminence

Articulardisc

Retrodiscal pad

condyle

Lateralpterygoidmuscle


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Articular Disc

0val fibrous plate foundbetween the condyle headand the mandibular fossa.

It is avascular, semi-rigid,biconcave disc whichserves to adopt the bonysurface of the joint duringfunctional activity.1. inferior synovial cavity

(condylo-discal) is thelower cavity between thecondylar head and thedisc.2. superior synovial cavity(temporo-discal) is the

upper cavity between thetemporal bone and thedisc.


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The meniscus has three parts:

1. anterior band is the thinner anterior

segment which is continuous with theligament fibers of lateral pterygoid muscles.

2. Intermediate band is the connecting part ofanterior and posterior bands.

3. Posterior band is the thickened posteriorpart (bilaminar area) consisting of upperstratum which is attached to the temporal

bone and the lower stratum which isattached to the condyle on its medial andlateral borders.


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Fibrous capsule/articular capsule (sometimes

referred to as capsular ligament)

Is a sheet, sac, or tube of tissue that enclosesthe joint like a tube.

The fibrous capsule is composed of two layers:

a. Inner layer (synovial membrane) lines the fibrouscapsule. This is a thin layer of tissue that secretes afluid, synovia, that lubricates the joint. The synovialfluid is a dialysate of blood plasma containingglobulin and mucin and is clear, yellowish andviscous fluid.

b. Outer layer is thickened on its lateral border toform the temporomandibular ligament.


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Ligaments that support the joint

Ligaments are slightly elastic bands oftissue. They support and confine themovement of the mandible to protectmuscle from being stretched beyond

their capabilities.a. Capsular ligament

b. Temporomandibular ligament

c. Stylomandibular ligamentd. Spenoidmandibular ligament

TMJanatomy
http://../TMJanatomy2004Jan.ziphttp://../TMJanatomy2004Jan.zip


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Temporomandibular joint is described as ginglymo-arthrodial joint.

Ginglymus(hinge joint) the manner of movement

takes place on one plane.

Arthrodial is one in which the principal movement isgliding.

Two types of movements:

1. Gliding type occurs between the articular discand the articular surface of the temporal bone.

2. Hinge type occurs between the inferior surface ofthe anterior disc and the head of the condyle.

TMJmove
http://../TMJmove2004Jan.ziphttp://../TMJmove2004Jan.zip


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Dynamics & Components of occlusion

OCCLUSION

refers to the contactrelationships of theteeth resulting fromneuromascularcontrol of themasticatory system.It is when the teethin the mandibulararch come into

contact with theteeth in the maxillaryarch in a functionalrelationship.

K t O l i


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Molar Relationshipa. The distal surface of the

distal marginal ridge ofthe maxillary 1stpermanent molarcontacts and occludeswith the mesial surface ofthe mesial marginal ridgeof the mandibular 2nd

molarb. The mesiobuccal cusp of

the maxillary 1st molarfalls within the groovebetween the mesial andmiddle cusps of the

mandibular 1

st

permanent molars.c. The mesiolingual cusp of

the maxillary 1st molarseats in the central fossaof the mandibular 1stmolar.

Keys to Occlusion

Mesiobuccal

cusp


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- ROTATIONS

Teeth should be free of undesirablerotations.

TIGHT CONTACTS In the absence of such abnormalities as

genuine tooth size discrepancies, contactpoints should be tight.


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CURVE OF SPEE

A flat occlusal planeshould be atreatment goal.

Measured from themost prominent ofthe mandibular 2ndmolar to the

mandibular centralincisor.

Dental Arch Formation


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Dental Arch Formation

In both dental arches the

alignment of teethfollows a paraboliccurve.

Usually the maxillary

arch is larger thanmandibular archresulting in the maxillarycusps overlapping the

mandibular cusps whenthe arches are inmaximal occlusal

contact.

CentralFossa

line

FacialOcclusal

line

Lingual

Occlusalline

Central

Fossaline


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Purposes of contact relation between teethof the same dental arch:

A. It protect the gingival papilla in theinterproximal spaces, thereby avoidingperiodontal involvement which could be

destructive.B. The collective activity of all teeth in

contact shoulder to shoulder stabilizes

each tooth in the dental arch.

Th t f t th li t i th h


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Three segments of tooth alignment in the arches:

1. anterior segment acurve line including theanterior teeth ending atthe labial ridge of thecanine

2. middle segment astraight line including thedistal portion of the

canines, the premolars &the buccal ridge of themesiobuccal cusp of the1st molar

3. posterior segment - astraight line from the

buccal cusp of the 1st

molar, the line remainingin contact with buccalsurfaces of the 2nd & 3rdmolars.

Ph i th d l t f


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Phases in the development ofdental arches:

Phase 1 the 1stpermanentmolars

(cornerstones)take their placesimmediatelyposterior to the

deciduous 2ndmolars.

Phase ll central incisors & lateral incisors develop


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Phase ll - central incisors & lateral incisors develop

lingually to deciduous anterior roots.

Ph lll th l i t i t


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Phase lll the premolars come in anterior tothe 1st permanent molars, taking the place of

deciduous molars.


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Phase lV the canines or keystones takethe place of the deciduous canine.


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Phase V the jaws develop sufficientlyas the individual approaches maturity

to accommodate the 3rd

molars distalto the 2nd molars.


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Compensating Curvatures of the DentalArches

1. BonwillEquilateralTriangle

- the angles of the

triangle areplaced at thecenter of eachcondyle and at

the mesial contactareas of themandibularcentral incisors.


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2. Curve of Speea curvealignment

observed at thecusps & incisalridges of theteeth as seen

from the pointopposite the 1stmolars. Antero-posterior relationof the teeth

viewed from thelateral aspect.


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Curve of Wilson it is thecurvature

established bythe tilting of themandibularposteriors

making themaxillary archconvex and themandibulararch concaveas one viewsthe arches fromthe front.


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Curve of Monsoon the

mandibular archadapts itsocclusalsurfaces to the

curved surfaceof a segment ofa sphere of a 4inch radius.

All teeth away from the perpendicular to occlusal plane


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All teeth away from the perpendicular to occlusal plane,have various degrees of inclinations. There are two types

of tilt to be considered.

A. FACIO-LINGUAL TILT the tooth with the greatest inclinationtilting facially is the maxillary central incisors followed nextby the mandibular lateral incisors. All teeth tilt faciallyexcept the 2nd premolar and the mandibular molar whichhave lingual inclinations. The straightest teeth (perpendicular to

the occlusal plane) having the least tilt are the premolars.B. MESIO-DISTAL TILT except for the maxillary central incisors

and the mandibular central and lateral incisors which may haveslight distal tilt, all teeth tilt mesially. The greatest degree of mesialtilt is found in the maxillary canine and the least and slighttilt is that of the premolars.


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MORTAR AND PESTLE DESIGN of some of the occlusalcontacts of teeth clearly explains the functional form of the

teeth. A good direct example would be the buccal cusps ofthe mandibular molars in contact with the central sulci ofthe maxillary molars.

The Facial and Lingual Relations of Each Tooth in


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gOne Arch to its antagonist in the Opposing Arch in

Centric occlusion

Each tooth has two antagonist except the mandibular centralincisors and the maxillary 3rd molars


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DEVP OF DENTITION FROM

BIRTH TO COMPLETE DEC. DENT.MOUTH OF THE NEONATE 0 TO 6 MONTHS

The Gum PadsThe alveolar arches of an infant at the time of birth

are called Gum Pads. These are nothing but greatlythickened oral mucous membrane of the gums,

which soon become segmented, and each segmentis developing tooth site. They are pink in color and

firm in consistency.


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THE MOUTH OF THE NEONATE

The maxillary arch is horseshoe-shapeand the gum pads tend to extendbuccally and labially beyond in the

mandible The mandibular arch is posterior to the

maxillary arch when the gum padscontact

The lower gum pad is U-SHAPE andRECTANGULAR


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Relationship of gum padsAnterior open bite is seen at

rest with contact only in themolar region. Tongue

protrudes anteriorly through

the space.


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NEONATAL JAWRELATIONSHIPS A precise bite or jaw

relationship is not yet seen.

Therefore, neonatal jawrelationship cannot be used as a

diagnostic criterion for reliable

prediction of subsequentocclusion in the primary dentition.


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PRECOCIOUSLY ERUPTEDPRIMARY TEETH NATAL TEETH - present at birth

NEONATAL TEETHerupt during

the first month

PRE- ERUPTIVE TEETH- erupt

during the second or third month

1:1000 and 1:30000 incedence ofneo natal and natal teeth


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PRIMARY TEETH & OCCLUSION

1. Important factors in thedevelopment of the primary teeth:

Calcification


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1. Important factors in the developmentof the primary teeth:

Eruption

DEVELOPMENT OF PERMANENT


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DEVELOPMENT OF PERMANENTDENTITION

1. Calcification

The deciduous dentition stage


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The deciduous dentition stagestarts from the eruption of thefirst deciduous tooth, usually thedeciduous mandibular centralincisors and ends with theeruption of the first permanent

molar, i.e. from 6 months to 6years of postnatal life. By 2 years of age, deciduous dentitionis usually complete and in full

function. Root formation of alldeciduous teeth is complete by 3years of age.

NORMAL SIGNS OF PRIMARY


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NORMAL SIGNS OF PRIMARYDENTITION

a. Spaced anteriors: Spacing is usually seen inthe deciduous dentition to accommodatelarger permanent teeth in the jawsb. Primate / simian / anthropoid space: Thisspace is present mesial to the maxillarycanine and distal to the mandibular canine.Most subhuman primates have it throughout life and used it for interdigitation ofopposing canines. This space is used for


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mesial shift

c. Shallow overjet and overbite.

d. Straight / flush terminal plane

relation


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Important factors in the development of theprimary occlusion:

Overbite and Overjet


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Important factors in the development of theprimary occlusion:

Overbite

Vertical measurement a distance in which the

maxillary incisal margin closes vertically pastthe mandibular incisal margin.

Overjet

Horizontal measurement the distance between

the lingual aspect of the max incisors and thelabial surface of the mand. incisors


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Fl h t i l l Wh th di t l f


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Flush terminal plane When the distal surfacesof maxillary and mandibular deciduoussecond molars are in the same vertical plane;

this is the normal molar relationship in theprimary dentition because the mesiodistalwidth of the mandibular molar is greater thanthe mesiodistal width of the maxillary molar.

Mesial step distal surface of mandibulardeciduous second molar is mesial to thedistal surface of maxillary deciduoussecond molar.

Distal step distal surface of mandibulardeciduous second molar is more distal thanthe distal surface of maxillary deciduoussecond molar, i.e. the upper second molaroccludes with two opposite teeth.


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2. Important factors in the development ofthe primary occlusion:

Occlusal relationships

THE MIXED DENTITION STAGE


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THE MIXED DENTITION STAGE

This is the period where teeth of

both deciduous and permanent

dentition are seen. It extendsfrom 6-12 years of age. Most

malocclusions make their

appearance during this stage.

ERUPTION OF PERMANENT


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FIRST MOLARThe first permanent molars erupt at

6 .They play an important role in

the establishing and in the

function of occlusion, in thepermanent dentition.

Anteroposterior positioning of

the permanent molars isinfluenced by:


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Terminal plane relationship

When the deciduous second molars

are in a flush terminal plane, the

permanent first molar erupts

initially into a cusp-to-cusp

relationship, which later transformsinto a class I molar relation using

the primate spaces. This is brought

about by mesial shift of the

permanent first molar followingexfoliation of

- primary molar and thus making use of the leeway


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p y g yspace (late mesial shift).

When the deciduous second molars are in a distal step,the permanent first molar will erupt into a class IIrelation. This molar configuration is not self correctingand will cause a class II malocclusion despite Leewayspace and differential growth.

Primary second molars are in a mesial step lead to aclass I molar relation in mixed dentition. This may remain

or progress to a half or full cusp class III with continuedmandibular growth.

Early mesial shift in arch with physiologic spacing:

In a spaced arch, eruptive force of the permanent

molars causes closing of any spaces between theprimary molars or primate spaces, thus allowingmolars to shift mesially.


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Leeway space of Nance -

the combined mesiodistal widths of

deciduous canine, first and second

molars is more than that of thecombined mesiodistal width of

permanent canine, first and second

premolar. The difference between

the two is called the leeway space.


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BROADBENTS PHENOENON UGLY

DUCKLING STAGE (7 14 YEARS)


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DUCKLING STAGE (7-14 YEARS)Diastema is commonly seen in the upper arch,which is usually interpreted by the parents as amalocclusion. Crowns of canines in young jawsimpinge on developing lateral inc. roots thusdriving the roots medially and causing thecrowns to flare laterally. The roots of the central

incisors are also forced together thus causing amaxillary midline diastema. The period from theeruption of lateral incisors to canine is termed asthe Ugly Duckling stage. It is an unaestheticmetamorphosis, which eventually leads to an

aesthetic result. With eruption of canines, theimpingement from the roots shifts incisally thusdriving the incisor crowns medially, effectingclosure of diastema


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INCISOR ERUPTION


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INCISOR ERUPTION

INCISOR LIABILITY-for incisor to erupt innormal alignment , there is an obligatespace requirement in the anterior part of

the arches The total sum of the mesio-distal width of

four permanent incisor is larger than that

of primary incisors by 7.6mm in maxillaand 6mm in the mandible

DEVELOPMENT OF PERMANENT


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DENTITION

THE FULL PERMANENT


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DENTITION

Dentition and occlusal adjustment before themiddle teens

During eruption of succedanaeous teeth

many activities occur simultaneously

THE FULL PERMANENT


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DENTITION

Dentition and occlusal adjustment before themiddle teens

During eruption of succedanaeous teeth

many activities occur simultaneously The primary tooth resorbs

The root of the permanent tooth lengthens

The alveolar process increases in height

The permanent tooth moves through the bone

FACTORS REGULATING &


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AFFECTING ERUPTION

If the primary tooth is extracted prior to theonset of permanent eruptive movementsthe permanent tooth is likely to be delayedin its eruption.

FACTORS DETERMINING TOOTH


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POSITION DURING ERUPTION

MANDIBLE


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MANDIBLE

The most favorable eruption sequencein the mandible:

Cuspid

1st Bicuspid 2nd Bicuspid

2nd Molar

MAXILLA


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MAXILLA

The sequence of eruption in the maxilla 1st Bicuspid

2nd Bicuspid

Cuspid 2nd Molar

PERMANENT DENTITION


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PERMANENT DENTITION

Dimensional Changes The dental arch perimeter decreases

during the late adolescent and young

adult periods After 15 years, the dimensional changes

seem to show a continued shortening ofthe perimeter

DENTITIONAL & OCCLUSAL DEVELOPMENT


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IN THE YOUNG ADULT

Phillips, Reitan and Shafer enumerated thevarious major factors causing root resorptionof permanent teeth:

Physiologic tooth movement

Adjacent impacted teeth pressure Periapical or Periodontal inflammation

Tooth implantation or replantation

Contnuous occlusal trauma

Tumor or cyst Metabolic or systemic diseases

Idiopathic factors

PATTERN OF ERUPTION


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PATTERN OF ERUPTION

In Maxilla : 6 1 2 4 5 3 7

In Mandible : 6 1 2 3 4 5 7

Documents

16th Lec 08 Landmarks of the Skull