Human dentition Dr. Hazem Al Ajrami First Year in Dentistry First Semester Al-Azhar University - Gaza Lama El Banna

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College of DentistryCollege of Dentistry
Human DentitionHuman Dentition
Primary Teeth and OcclusionPrimary Teeth and Occlusion
Dr. Hazem Al AjramiDr. Hazem Al Ajrami

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The Primary TeethThe Primary Teeth

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The deciduous teeth or primary, milk, babyThe deciduous teeth or primary, milk, baby
and temporary teeth are twenty in number, 10and temporary teeth are twenty in number, 10
in each jaw (4 incisors, 2 canines and 4in each jaw (4 incisors, 2 canines and 4
molars).molars).
They start to erupt at the age of six months byThey start to erupt at the age of six months by
the appearance of the primary mandibularthe appearance of the primary mandibular
central incisors in the oral cavity.central incisors in the oral cavity.
At about 2 years old, the last deciduous toothAt about 2 years old, the last deciduous tooth
which is the second molar starts to appear.which is the second molar starts to appear.
At three year of age all the deciduous teeth areAt three year of age all the deciduous teeth are
erupted and are in function.erupted and are in function.

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As the term "deciduous" implies, teeth areAs the term "deciduous" implies, teeth are
shed in order to make way for their permanentshed in order to make way for their permanent
successors. The process of exfoliation takessuccessors. The process of exfoliation takes
place between the 6 and 12 years. One to twoplace between the 6 and 12 years. One to two
years after complete root formation resorptionyears after complete root formation resorption
begins at the root apex of the deciduous teethbegins at the root apex of the deciduous teeth
and continues cervically until resorption of theand continues cervically until resorption of the
entire root has taken place and the crown isentire root has taken place and the crown is
lost from lack of support.lost from lack of support.
The anterior deciduous teeth are replaced byThe anterior deciduous teeth are replaced by
the anterior permanent teeth, while thethe anterior permanent teeth, while the
deciduous molars are replaced by thedeciduous molars are replaced by the
permanent premolars.permanent premolars.

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Extraction of the deciduous molar when theExtraction of the deciduous molar when the
roots are completed and before their resorptionroots are completed and before their resorption
may cause the tooth germ of its successor to bemay cause the tooth germ of its successor to be
removed with the deciduous tooth. As theremoved with the deciduous tooth. As the
developing permanent tooth germ is founddeveloping permanent tooth germ is found
between the divergent roots of the deciduousbetween the divergent roots of the deciduous
molar.molar.
From 6 months to 6 years the oral cavityFrom 6 months to 6 years the oral cavity
contains only deciduous teeth.contains only deciduous teeth.

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From 6 - 12 years, the oral cavity containsFrom 6 - 12 years, the oral cavity contains
mixed dentition (deciduous and permanent).mixed dentition (deciduous and permanent).
From 12 years on, the oral cavity contains onlyFrom 12 years on, the oral cavity contains only
permanent teeth.permanent teeth.
At the age of 4 years the root of the primaryAt the age of 4 years the root of the primary
central incisor starts resorption, while thecentral incisor starts resorption, while the
primary upper second molar is the last toothprimary upper second molar is the last tooth
exhibit root resorption at 7 years.exhibit root resorption at 7 years.
Any deciduous tooth remains in the oral cavityAny deciduous tooth remains in the oral cavity
after the age of 12 years is considered as aafter the age of 12 years is considered as a
pathological condition and is termed retainedpathological condition and is termed retained
deciduous tooth.deciduous tooth.

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The Major Differences BetweenThe Major Differences Between
Primary and Permanent TeethPrimary and Permanent Teeth

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The primary teeth are smaller in size than theThe primary teeth are smaller in size than the
permanent teeth.permanent teeth.
The crowns of the primary teeth are lighter inThe crowns of the primary teeth are lighter in
color (whiter in appearance) than are thecolor (whiter in appearance) than are the
permanent teeth.permanent teeth. The color of primary teeth isThe color of primary teeth is
bluish white, while that of permanent teethbluish white, while that of permanent teeth
ranges from grayish white to yellowish white.ranges from grayish white to yellowish white.
The crowns of the primary teeth are moreThe crowns of the primary teeth are more
bulbous.bulbous.
The crowns of primary anterior teeth are widerThe crowns of primary anterior teeth are wider
mesiodistally in comparison with their crownmesiodistally in comparison with their crown
length (Incisocervical) than are the permanentlength (Incisocervical) than are the permanent
teeth.teeth.

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In the primary teeth: the enamel seems to beIn the primary teeth: the enamel seems to be
bulge close to the cervical line as enamel endbulge close to the cervical line as enamel end
abruptly at the neck, in the permanent teeth:abruptly at the neck, in the permanent teeth:
enamel tapers gradually toward the neck.enamel tapers gradually toward the neck.
The cervical ridge of enamel is quiteThe cervical ridge of enamel is quite
prominent on the facial aspects of the primaryprominent on the facial aspects of the primary
teeth.teeth.
The crown dimension at the neck is moreThe crown dimension at the neck is more
constricted.constricted.
The roots of the primary anterior teeth areThe roots of the primary anterior teeth are
narrower and longer in comparison withnarrower and longer in comparison with
crown length, as well as tooth length andcrown length, as well as tooth length and
width, than are the permanent teeth roots.width, than are the permanent teeth roots.

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Absence (decrease) of root trunk in primaryAbsence (decrease) of root trunk in primary
molars.molars.
The roots of the primary molars are relativelyThe roots of the primary molars are relatively
longer and more slender than the roots of thelonger and more slender than the roots of the
permanent teeth (for the permanent teeth thepermanent teeth (for the permanent teeth the
roots are thicker).roots are thicker).
The roots of the primary molars are moreThe roots of the primary molars are more
divergent and flare more extending outdivergent and flare more extending out
beyond projected outlines of the crown. Thisbeyond projected outlines of the crown. This
flare allows more room between the roots forflare allows more room between the roots for
the development of permanent tooth crowns.the development of permanent tooth crowns.

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The roots thin out rapidly as the apices areThe roots thin out rapidly as the apices are
approached.approached.
The roots of the primary teeth showThe roots of the primary teeth show
physiological root resorption and shedding,physiological root resorption and shedding,
in the permanent teeth if the root is resorpedin the permanent teeth if the root is resorped
it consider a pathological condition.it consider a pathological condition.

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Pulp Chambers and Pulp CanalsPulp Chambers and Pulp Canals

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A comparison of sections of primary andA comparison of sections of primary and
permanent teeth demonstrates the shape andpermanent teeth demonstrates the shape and
relative size of pulp chambers and canals:relative size of pulp chambers and canals:
 Crown widths in all directions are large inCrown widths in all directions are large in
comparison with root trunks and cervices.comparison with root trunks and cervices.

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 The enamel and dentine thickness are less:The enamel and dentine thickness are less:
 The enamel is relatively thin and has aThe enamel is relatively thin and has a
consistent depth.consistent depth.
 The dentin thickness between the pulp chamberThe dentin thickness between the pulp chamber
and the enamel is much less than in theand the enamel is much less than in the
permanent teeth.permanent teeth.
 The thickness of enamel and dentine in primaryThe thickness of enamel and dentine in primary
teeth is approximately half its thickness inteeth is approximately half its thickness in
permanent teeth, therefore a cavity must bepermanent teeth, therefore a cavity must be
shallower than in permanent teeth to avoid pulpshallower than in permanent teeth to avoid pulp
exposures.exposures.

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 The pulp chambers are relatively large, and theThe pulp chambers are relatively large, and the
pulp horns are high occlusally placing thempulp horns are high occlusally placing them
much closer to enamel than the permanentmuch closer to enamel than the permanent
teeth.teeth.
 Primary roots are narrow and long whenPrimary roots are narrow and long when
compared with crown width and length.compared with crown width and length.

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OcclusionOcclusion

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Definition:Definition:
Occlusion may be defined as that situationOcclusion may be defined as that situation
which is created when the mandibular teethwhich is created when the mandibular teeth
come into contact with the maxillary teeth in acome into contact with the maxillary teeth in a
functional relations.functional relations.

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Good occlusion contributes for theGood occlusion contributes for the
following;following;
1.1. Important for mastication.Important for mastication.
2.2. Helps to bring about symmetry and goodHelps to bring about symmetry and good
appearance.appearance.
3.3. Promotes good pronunciation in speech.Promotes good pronunciation in speech.
4.4. It helps in the stability of the jaw relations.It helps in the stability of the jaw relations.

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There are groups of functional relationsThere are groups of functional relations
presented by the mandibular movements:presented by the mandibular movements:
 Centric occlusion.Centric occlusion.
 Protrusive occlusal relation.Protrusive occlusal relation.
 Retrusive occlusal relation.Retrusive occlusal relation.
 Lateral occlusal relation (Right and left).Lateral occlusal relation (Right and left).

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Centric OcclusionCentric Occlusion

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Definition:Definition:
It is the relation of the upper and lowerIt is the relation of the upper and lower
teeth when they are in maximumteeth when they are in maximum
intercuspation and the condyles are resting inintercuspation and the condyles are resting in
the most retrusive unstrained position in thethe most retrusive unstrained position in the
glenoid fossa.glenoid fossa.
In the centric occlusal relation each toothIn the centric occlusal relation each tooth
in one jaw contact two teeth in the opposingin one jaw contact two teeth in the opposing
jaw except for the mandibular central incisorjaw except for the mandibular central incisor
and maxillary third molars.and maxillary third molars.

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This serves to:This serves to:
 Equalize the forces of contact in occlusion,Equalize the forces of contact in occlusion,
thereby distributing the work.thereby distributing the work.
 It preserves the integrity of the dental arch inIt preserves the integrity of the dental arch in
case of loosing a tooth, since the secondcase of loosing a tooth, since the second
antagonist prevents the elongation andantagonist prevents the elongation and
displacement of the opposing tooth.displacement of the opposing tooth.

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With the jaw closed in centric occlusion, theWith the jaw closed in centric occlusion, the
following observations are noted:following observations are noted:
 The occlusal surfaces of the maxillary teethThe occlusal surfaces of the maxillary teeth
touch the occusal surfaces of the mandibulartouch the occusal surfaces of the mandibular
teeth.teeth.
 The palatal cusps of the maxillary premolarsThe palatal cusps of the maxillary premolars
and molars rest in the deepest parts of theand molars rest in the deepest parts of the
occlusal sulci of the mandibular premolars andocclusal sulci of the mandibular premolars and
molars.molars.

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 The buccal cusps of the mandibular premolarsThe buccal cusps of the mandibular premolars
and molars rest in the deepest parts of the sulciand molars rest in the deepest parts of the sulci
of the maxillary premolars and molars.of the maxillary premolars and molars.
 The cusps of the maxillary teeth overlap theThe cusps of the maxillary teeth overlap the
cusps of the mandibular teeth, so that thecusps of the mandibular teeth, so that the
maxillary teeth are facial to the mandibularmaxillary teeth are facial to the mandibular
teeth.teeth.

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 The amount of facial horizontal overlap of theThe amount of facial horizontal overlap of the
maxillary teeth is called an Overjet.maxillary teeth is called an Overjet.
 The maxillary incisors are facial to theThe maxillary incisors are facial to the
mandibular incisors.mandibular incisors.
 The maxillary incisors also vertically overlapThe maxillary incisors also vertically overlap
the mandibular incisors. The vertical overlap isthe mandibular incisors. The vertical overlap is
called Overbite.called Overbite.

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Protrusive Occlusal RelationProtrusive Occlusal Relation

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When the mandible moves forward fromWhen the mandible moves forward from
centric occlusion, the only teeth that shouldcentric occlusion, the only teeth that should
touch are the anterior. The mandibular fourtouch are the anterior. The mandibular four
incisors should glide across the maxillary fourincisors should glide across the maxillary four
incisors. The canine may touch slightly, but noincisors. The canine may touch slightly, but no
posterior teeth should touch in a mandibularposterior teeth should touch in a mandibular
protrusive movement.protrusive movement.

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Occurs during the protrusive movement.Occurs during the protrusive movement.
Steps:Steps:
 Starting from centric occlusion the mandibleStarting from centric occlusion the mandible
moves downward to free the cusps.moves downward to free the cusps.
The occlusal cycle of anterior teethThe occlusal cycle of anterior teeth

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 The mandible moves forward for bitting by theThe mandible moves forward for bitting by the
anterior teeth, while the balancing side at theanterior teeth, while the balancing side at the
posterior teeth.posterior teeth.
 Then the mandible moves backward andThen the mandible moves backward and
upward to centric occlusion.upward to centric occlusion.
 This alternating protrusion to working andThis alternating protrusion to working and
back to centric is called occlusal cycle ofback to centric is called occlusal cycle of
anterior teeth.anterior teeth.

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Downward and ForwardBackward and UpwardBackward and Upward

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Retrustive Occlusal RelationRetrustive Occlusal Relation
The mandibular teeth show posterior relationThe mandibular teeth show posterior relation
to centric occlusion with the maxillary arch.to centric occlusion with the maxillary arch.
Actually retrusion is very limited andActually retrusion is very limited and
nonfunctional movement.nonfunctional movement.

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Lateral Occlusal RelationLateral Occlusal Relation

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In lateral occlusal relation, the mandibuleIn lateral occlusal relation, the mandibule
moves toward the right or left side. The side tomoves toward the right or left side. The side to
which the mandible moves is referred to aswhich the mandible moves is referred to as
Working Side.Working Side.
The side away from which the mandible isThe side away from which the mandible is
moving is referred to as Non-Working Side.moving is referred to as Non-Working Side.
On artificial teeth this non working side isOn artificial teeth this non working side is
referred to as Balancing Side.referred to as Balancing Side.

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The occlusal cycle of posterior teethThe occlusal cycle of posterior teeth
Occurs during lateral movements of theOccurs during lateral movements of the
mandible. It starts from centric occlusion andmandible. It starts from centric occlusion and
ends also in centric occlusion.ends also in centric occlusion.
Steps:Steps:
 From centric occlusion the mandible movesFrom centric occlusion the mandible moves
down word to free the cusps.down word to free the cusps.

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 The mandible moves to lateral side (e.g. Right),The mandible moves to lateral side (e.g. Right),
this side is the working side. The other side isthis side is the working side. The other side is
the non working or balancing side.the non working or balancing side.
 In the working side the buccal cusps of theIn the working side the buccal cusps of the
maxillary and mandibular teeth are in contact.maxillary and mandibular teeth are in contact.
 In the non working side, the palatal cusps of theIn the non working side, the palatal cusps of the
maxillary teeth contact with the buccal cusps ofmaxillary teeth contact with the buccal cusps of
the mandibular teeth.the mandibular teeth.

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working sideworking side non working sidenon working sidecentric occlusioncentric occlusion

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 Then the mandible moves to centric occlusion.Then the mandible moves to centric occlusion.
 Alterations from one side to the other wereAlterations from one side to the other were
performed.performed.
 These lateral movements are known as theThese lateral movements are known as the
occlusal cycle of posterior teeth.occlusal cycle of posterior teeth.

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The permanent first molars are consideredThe permanent first molars are considered
the key of occlusion since:the key of occlusion since:
1.1. They are the first permanent teeth to developThey are the first permanent teeth to develop
and erupt in the oral cavity.and erupt in the oral cavity.
2.2. They are guided by the presence of theThey are guided by the presence of the
primary second molars.primary second molars.

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3.3. They are the largest teeth in the dental arch.They are the largest teeth in the dental arch.
4.4. Their eruption is not disturbed since theyTheir eruption is not disturbed since they
have no deciduous predecessors.have no deciduous predecessors.
5.5. The maxillary first molars are preferred asThe maxillary first molars are preferred as
they erupt from the fixed maxilla.they erupt from the fixed maxilla.

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Thank YouThank You