Development of Normal Occlusion

DEVELOPMENT OF
NORMAL OCCLUSION
Dr.Kapil Saroha
BDS, MDS
Orthodontics and dentofacial orthopedics
Monday, July 31, 2017
Dr.Dentiste's Dental Academy
WWW.DRDENTISTE.COM

INTRODUCTION
Angle defined occlusion as normal relation of
occlusal inclined planes of teeth when jaws are
closed.
Orthodontically normal occlusion is Angle’s
Class I occlusion. The key teeth are the first
molars.
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Centric occlusion:Centric occlusion: The position of maximumThe position of maximum
intercuspation of the teeth.intercuspation of the teeth.
Centric relation:Centric relation: It is the relationship ofIt is the relationship of
mandible to maxilla where the head of themandible to maxilla where the head of the
condyle is in the most retruded unstrainedcondyle is in the most retruded unstrained
position in the glenoid fossa.position in the glenoid fossa.
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FACTORS AFFECTING OCCLUSION
I) GENETIC FACTORS
* TEETH CAN VARY IN SIZE EG’S-
MICRODONTIA(VERY SMALL TEETH) &
MACRODONTIA(VERY LARGE TEETH)
* THE SHAPE OF INDIVIDUAL TEETH MAY
VARY(SUCH AS THIRD MOLARS & UPPER
LATERAL INCISORS.
TEETH CAN BE CONGENITALLY MISSING OR
THERE CAN BE EXTRA TEETH.
* THE SKELETAL SUPPORT(MAXILLA/
MANDIBLE) & HOW THEY ARE RELATED TO
EACH OTHER CAN VARY.
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II) ENVIRONMENTAL FACTORS
HABITS, SERIOUS ILLNESS, NUTRITIONAL
DEPRIVATION ETC CAN HAVE AN AFFECT.
ORTHODONTIC APPLIANCES, ORTHODONTIC
RETAINERS HAVE AN INFLUENCE ON THE
OCCLUSION.
III) MUSCULAR PRESSURE
ONCE THE TEETH ERUPT INTO THE ORAL
CAVITY, THE POSITION OF THE TEETH ARE
AFFECTED BY MUSCULAR PRESSURE ON
THE FACIAL SIDE BY CHEEKS & LIPS & ON
LINGUAL SIDE BY TONGUE.
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FACTORS & FORCES THAT
DETERMINE TOOTH POSITION
The alignment of the dentition in the dental
arches occurs as a result of complex multi
directional forces acting on the teeth during &
after eruption. When teeth erupt they are
directed into a position where opposing forces
are in equilibrium.
The major opposing forces that influence tooth
position originate from the surrounding
musculature.
There is a tooth position in the oral cavity where
the labiolingual & buccolingual forces are
equal. This is called neutral position.
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THE MOUTH OF THE NEONATE
The Gum Pads
At birth the alveolar process are covered by gum
pads, which soon are segmented to indicate the
sites of the developing teeth.
The size of the gum pads at birth might be
determined by any one of the following factors
according to Leighton
The state of maturity of the infant at birth.
The size at birth as expressed by birth weight.
The size of the developing primary teeth.
Purely genetic factors.
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NEONATAL JAW RELATIONSHIPS
Although the upper & lower gum pads touch
throughout much of the arch circumference
there is no precise bite or jaw relationships.
Simpson & Cheung found that only 2% of all
neonates have an anterior open bite..
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PRIMARY TEETH & OCCLUSION
Development of primary teeth
Calcification: The sequence of initial calcification of primary teeth is:
Central incisors - 14 weeks
First molars - 15½ weeks
Lateral incisors - 16 weeks
Canines - 17 weeks
Second molars - 18 weeks
Eruption: Is movement of the tooth toward occlusion.
Sequence of eruption
upper lower
Central incisors 7½ months 6months
Lateral incisors 9 “ 7 ”
Canine 18 “ 16 “
First molar 14 “ 12 “
Second molar 24 “ 20 “
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DEVELOPMENT OF THE PRIMARY
OCCLUSION
NEURO MUSCULAR CONSIDERATIONS:
NEURO MUSCULAR REGULATION OF JAW
RELATIONSHIP IS IMPORTANT TO THE DEVELOPMENT
OF PRIMARY OCCLUSION.
THE TEETH ARE GUIDED INTO THEIR OCCLUSAL
POSITION BY THE FUNCTIONAL MATRIX OF MUSCLES
DURING VERY ACTIVE GROWTH OF THE FACIAL
SKELETON.
PRIMARY DENTAL ARCHES :
USUALLY THERE IS GENERALISED INTERDENTAL
SPACING IN THE ANTERIOR REGION.
WIDER SPACES USUALLY FOUND MESIAL TO ALL
MAXILLARY CUSPIDS & DISTAL TO THE MANDIBULAR
CUSPIDS ARE TERMED “PRIMATE SPACES”.
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THE ANTERIOR PART OF THE DENTAL
ARCHES INCREASES SLIGHTLY FROM
BIRTH TO 12 MONTHS & CHANGES VERY
LITTLE THERE AFTER.
POSTERIOR DIAMETER INCREASES MORE
MARKEDLY THAN THOSE IN THE ANTERIOR
PART OF THE ARCH.
PALATAL VAULT WIDTH INCREASES FROM
BIRTH TO 12 MONTHS & REMAINS
CONSTANT THROUGH OUT THE FIRST 2
YEARS.
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OCCLUSAL RELATIONS
WITH THE ERUPTION OF PRIMARY FIRST
MOLAR THE
FIRST 3 DIMENSIONAL OCCLUSAL
RELATIONSHIP IS ESTABLISHED.
THE PRIMARY POSTERIOR TEETH OCCLUDE
SO THAT MANDIBULAR CUSP ARTICULATES
JUST AHEAD OF ITS CORRESPONDING
MAXILLARY CUSP.
THE MANDIBULAR SECOND PRIMARY
MOLAR IS SOME WHAT WIDER MESIO
DISTALLY THAN THE MAXILLARY GIVING
RISE TO A FLUSH TERMINAL PLANE .
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THE FOLLOWING ARE NORMAL SIGNS OF
PRIMARY DENTITION
I) SPACED ANTERIORS
II) PRIMATE SPACES
III) SHALLOW OVERBITE & OVERJET
IV) STRAIGHT TERMINAL PLANE
V) CLASS I MOLAR & CUSPID RELATIONSHIP
VI) ALMOST VERTICAL INCLINATION OF
ANTERIOR TEETH.
VII) OVOID ARCH FORM
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MIXED DENTITION PERIOD(6 TO 12 YEARS)
i: The period during which both primary &
permanent teeth are in the mouth together is
known as the mixed dentition.
ii: Those permanent teeth that follow into a
place in the arch once held by a primary teeth
are called “successional teeth” eg: incisors,
cuspids & bicuspids.
iii: Those permanent teeth that erupt
posteriorly to the primary teeth are termed
“accessional” .
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AVERAGE AGE OF ERUPTION OF
PERMANENT TEETH.
ToothTooth MaxillaMaxilla MandibleMandible
Central incisorCentral incisor 7-87-8 6-76-7
Lateral incisorLateral incisor 8-98-9 7-87-8
CanineCanine 11-1211-12 9-109-10
Ist premolarIst premolar 10-1110-11 10-1210-12
IInd premolarIInd premolar 10-1210-12 11-1211-12
Ist molarIst molar 6-76-7 6-76-7
IInd molarIInd molar 12-1312-13 11-1311-13
IIIrd molarIIIrd molar 19-2119-21 19-2119-21
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ERUPTION OF INCISORS
1: INCISOR LIABILITY
2: UGLY DUCKLING STAGE
1: INCISOR LIABILITY
- WHEN CENTRAL INCISOR ERUPT THEY USES ALL
EXCESS SPACE FOUND IN NORMAL PRIMARY
DENTITION.
- THE MAXILLARY ARCH ON AVERAGE HAVE JUST
ENOUGH SPACE TO ACCOMMODATE THE PERMANENT
LATERAL INCISORS.
- IN MANDIBULAR ARCH WHEN LATERAL INCISOR ERUPT
THERE IS ON AVERAGE 1.6MM LESS SPACE AVAILABLE
FOR 4 MANDIBULAR INCISORS. THIS DIFFERENCE
BETWEEN AMOUNT OF SPACE NEEDED FOR INCISORS &
THE AMOUNT AVAILABLE FOR THEM IS CALLED
“INCISOR LIABILITY”.
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2: UGLY DUCKLING STAGE
IN THE MAXILLARY ARCH THERE MAY BE SPACE
CALLED A DIASTEMA BETWEEN THE MAXILLARY
CENTRAL INCISORS. THIS TENDS TO CLOSE AS
LATERAL INCISORS ERUPT BUT MAY PERSIST EVEN
AFTER THE LATERAL INCISORS HAVE ERUPTED,
PARTICULARLY IF THE PRIMARY CANINES HAVE BEEN
LOST OR IF THE UPPER INCISORS ARE FLARED TO THE
LABIAL. SINCE THE SPACED UPPER INCISORS ARE NOT
VERY ESTHETIC THIS IS REFERRED TO AS “UGLY
DUCKLING STAGE”. THE SPACES TEND TO CLOSE AS
THE PERMANENT CANINE ERUPT.
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FROM A CLINICAL POINT OF VIEW THERE ARE TWO
VERY IMPORTANT ASPECTS TO THE MIXED
DENTITION PERIOD
A) THE UTILIZATION OF THE ARCH PERIMETER.
B) THE ADAPTIVE CHANGES IN OCCLUSION THAT
OCCUR DURING THE TRANSITION FROM ONE
DENTITION TO ANOTHER.
THE ALVEOLAR PROCESS IS ONE MOST ACTIVELY
ADAPTABLE AREAS OF BONE GROWTH DURING THE
PERIOD OF TRANSITION BETWEEN THE DENTITIONS.
THEREFORE IT IS AN IDEAL TIME FOR MOST MAJOR
ORTHODONTIC INTERVENTIONS.
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USES OF DENTAL ARCH PERIMETER
There are 3 uses:
i) Alignment of the permanent incisors: they
arrive typically crowded.
As the larger permanent incisors erupt they
find space in the arch only because
a) The arch width increases slightly.
b) There was some inter dental spacing in
the primary dentition.
c) The permanent incisors tip labially a bit.
d) The primary cuspids move distally into
primate spaces.
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II) SPACE FOR THE CUSPIDS AND PREMOLARS:
THE CUSPIDS & PREMOLARS ERUPT INTO
NORMALLY EXCESSIVE POSTERIOR LEEWAY
SPACE.
III) ADJUSTMENT OF THE MOLAR OCCLUSION:
A) THE FIRST PERMANENT MOLARS WHICH
TYPICALLY ERUPT END TO END MUST CHANGE TO
A CLASS I RELATIONSHIP IF NORMAL OCCLUSION
IS TO BE OBTAINED.
B) MOLAR ADJUSTMENT TAKES PLACE BY LATE
MESIAL SHIFT OF THE FIRST PERMANENT MOLAR.
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THE LEEWAY SPACE IS THE DIFFERENCE IN SIZE
BETWEEN THE PRIMARY TEETH & THEIR PERMANENT
SUCCESSORS. THE COMBINED MESIODISTAL WIDTH
OF CDE IS LARGER THAN THE COMBINED
MESIODISTAL WIDTH OF UNDERLYING 3 4 5 IS
REFERED TO AS “LEEWAY SPACE”.
THIS IS 1.7MM ON EITHER SIDE OF LOWER ARCHE
TOTALLY 3.4MM WHERE AS IT IS 0.9MM ON EITHER
SIDE OF UPPER ARCH TOTALLY 1.8MM.
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OCCLUSION CHANGES IN THE
MIXED DENTITION
1: The flush terminal plane of the primary
dentition typically provides an end to end
relationship of first permanent molar. This is
achieved by
a) A late mesial shift after the loss of the
second primary molar.
b) Greater forward growth of mandible than
the maxilla.
c) Combination of the above.
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2: DISTAL STEP LEADS TO ANGLE’S CLASS II
MOLAR RELATIONSHIP OR END-END MOLAR
RELATIONSHIP.
3: EARLY MANDIBULAR GROWTH MAY HAVE A
MESIAL STEP RELATIONSHIP IN THE PRIMARY
MOLARS PRODUCING A CLASS I MOLAR
RELATIONSHIP AT EARLY AGE OR CLASS III
RELATIONSHIP WITH CONTINUED MANDIBULAR
GROWTH.
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CONCLUSION
Genetic & environment influences the size of the
teeth, the timing of the development, dentition & its
eruption. Teeth tend to develop along a genetically
predetermined course.
The alignment of the dentition in the dental arches
occurs as a result of complex multidirectional
forces acting on the teeth during & after eruption.
It is important for an orthodontist to understand &
recognize the changes that are normally occuring
in the dentition to be able to diagnose any
abnormal developments & treat them.
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Tby –
dr. Kapil Saroha
BDS, MDS
DENDEN ISTIST
Monday, July 31, 2017 Dr.Dentiste's Dental Academy WWW.DRDENTISTE.COM

Development of Normal Occlusion

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