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DEVELOPMENT OF OCCLUSION

DR SHAMNA K T

SENIOR LECTURER

MES DENTAL COLLEGE

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Specific learning objectives

To know the different stages of development of occlusion
To know the development of occlusion in pre dentate stage
To know the development of occlusion in primary dentition
To know the development of occlusion in mixed dentition
To know the development of occlusion in permanent dention
To know the eruption status in both primary and permanent dentition.

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Introduction
Periods of occlusal development

Neo-natal period.
Primary dentition period.
Mixed dentition period.
Permanent dentition period

References

CONTENTS

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INTRODUCTION

Term occlusion is derived from the Latin word, “occlusio” ; defined as the relationship between all the components of the masticatory system in normal function, dysfunction and parafunction.

An ideal occlusion is the perfect interdigitation of the upper and lower teeth, which is a result of developmental process consisting of the three main events, jaw growth, tooth formation and eruption

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Periods of tooth development�

Pre-dental Stage (0-6months)

Deciduous dentition (6 months-6 years)

Mixed dentition (6-12 years)

Permanent dentition

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NEONATAL PERIOD�(lasts upto 6 months after birth)

GUM PADS

Alveolar processes at the time of birth- gum pads.
Pink in colour, firm and are covered by a dense layer of fibrous periosteum.
Each gum pads having transverse groove,dental groove and lateral sulcus.

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Gum Pads

The upper gum pad is horse shoe shaped & shows:

Gingival groove: separates gum pad from the palate.
Dental groove: starts at the incisive papilla, extends backward to touch the gingival groove in the canine region & then moves laterally to end in the molar region.
Lateral sulcus

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The lower gum pad is ‘U’ shaped and rectangular, characterized by:

Gingival groove: lingual extension of the gum pads.
Dental groove.
Lateral sulcus.

Gum Pads

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(From around the 6^th month to 6 years)

Primary Dentition Period

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Sequence of Eruption

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FEATURES OF PRIMARY DENTITION

Spacing- 2 types of dentition are seen:

1)Spaced dentition - usually seen in the deciduous dentition to accommodate the larger permanent teeth in the jaws.

More prominent in the anterior region, and are called ‘physiological spacing’ or ‘developmental spacing’.
Absence of spaces in the primary dentition is an indication that crowding of teeth may occur when the larger permanent teeth erupt.

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2)Non- spaced dentition

Teeth are present without any spaces in between the teeth
Due to narrow dental arches or if teeth are wider than usual
Usually indicates in developing permanent dentition but it is not always the case

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MOLAR RELATIONSHIP

The molar relationship in the primary dentition can be classified into 3 types:

Straight/flush terminal plane.
Mesial step.
Distal step.

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Flush Terminal Plane

If the distal surface of maxillary and mandibular deciduous second molars are in the same vertical plane; then it is called a flush terminal plane

Normal molar relationship in the primary dentition, because the mesiodistal width of the mandibular molar is greater than the mesiodistal width of the maxillary molar.

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Mesial Step

Distal surface of mandibular deciduous second molar is mesial to the distal surface of maxillary deciduous second molar.

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Distal Step

Distal surface of mandibular second deciduous molar is more distal to the distal surface of the maxillary second deciduous molar

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Canine relationship

Relationship of maxillary & mandibular deciduous canines is one of the most stable in primary dentition

Classified as:
Class 1
Class 2
Class 3

Class 1

Class 2

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MIXED DENTITION PERIOD

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MIXED DENTITION PERIOD�(Around 6 years- 12 years)

The mixed dentition period can be divided into three phases:

First transitional period.
Inter-transitional period.
Second transitional period.

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First Transitional Period

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Eruption of 1^st Permanent Molar

The location & relation of the 1^st permanent molar depends much upon the distal surface of the upper & lower 2^nd deciduous molar.

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Transition to Class I Molar Relation

The shift in lower molar from a flush terminal plane to a class I relation can occur in two ways:

Early shift.
Late shift.

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EARLY SHIFT

Early shift occurs during the early mixed dentition period.
Since this occurs early in the mixed dentition, it is called early shift.

LATE SHIFT

This occurs in the late mixed dentition period and is thus called late shift

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Leeway Space of Nance

Described by Nance in 1947

Maxilla: 0.9 mm/segment = 1.8 mm. Mandible: 1.7 mm/segment = 3.4mm.

Although the deciduous posterior segment of teeth is larger than the permanent segment, converse is true of the anterior segments

Nance did not consider large difference in mesiodistal size between the deciduous incisor teeth & their permanent successors– arch needs to be looked in its totality

Maxillary incisors, as a group in one quadrant– 3.2to 3.5 mm larger

Mandibular incisors, as a group in one quadrant – 2.4 to 2.5 mm larger

The latter figures balance out or cancel the 1.7 mm of so called leeway space

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Distal Step

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

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Mesial Step

Primary second molars in mesial step relationship lead to a class I molar relation in mixed dentition. This may remain or progress to a half or full cusp class III with continued mandibular growth.

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Influence of terminal plane on the position of 1^st permanent molar

Distal Step – 23.3% incidence, abnormal, Class II- 38.6%

Straight terminal plane – 49.2% incidence, Class I or II

Mesial Step - <2mm 26.7%, class I 58.9%

>2mm 0.8%. Class III- 2.5%

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Exchange of Incisors

During the first transitional period the deciduous incisors are replaced by the permanent incisors. The mandibular central incisors are usually the first to erupt. The permanent incisors are considerably larger than the deciduous teeth they replace. This difference between the amount of space needed for the accomodation of the incisors and the amount of space available for this, is called ‘Incisal liability’.

The incisal liability is roughly about 7.6 mm in the maxillary arch & about 6 mm in the mandibular arch (Wayne).

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Transition of Incisors

The incisal liability is over come by the following factors:

Interdental physiological spacing in the primary incisor region. (4 mm in maxillary arch & 3 mm in mandibular arch)

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Transition of Incisors

Increase in inter-canine arch width:

Significant amount of growth occurs with the eruption of incisors and canines.

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Transition of Incisors

Increase in anterior length of the dental arches:

Permanent incisors erupt labial to the primary incisors to obtain an added space of around 2-3 mm.

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Transition of Incisors

Change in inclination of permanent incisors:

Primary teeth are upright but permanent teeth incline to the labial surface, thus decreasing the inter-incisal angle from about 150 degrees in the deciduous dentition to 123 degrees in the permanent dentition. This increases the arch parameter.

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Inter-Transitional Period

This is a stable phase where little changes take place in the dentition. The teeth present are the permanent incisors and first molar along with the deciduous canines and molars. This phase prepares for the second transitional phase. Some of the features of this stage are:

Any asymmetry in emergence and corresponding differences in height levels or crown lengths between the right and left side teeth are made up.

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Inter-Transitional Period

Root formation of emerged incisors, and molars continues, along with concomitant increase in alveolar process height.

Resorption of roots of deciduous canines and molars.

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Second Transitional Period

The second transitional period is characterized by the replacement of the deciduous molars and canines by the premolars and permanent canines respectively.

At around 10 years of age the deciduous canines shed, but just before the shedding there is a transient or self correcting malocclusion seen in the maxillary incisor region between the age of 8 – 9 years.

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Ugly Duckling Stage�(Broadbent’s phenomenon)

Around the age of 8 - 9 years, a midline diastema is commonly seen in the upper arch, which is usually misinterpreted by the parents as a malocclusion.

Its typical features are:

Flaring of the lateral incisors.
Maxillary midline diastema. Crowns of canines on young jaws impinge on developing lateral incisor roots, thus driving the roots medially and causing the crowns to flare laterally.
The roots of the central incisors are also forced together, thus causing a maxillary midline diastema.

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Ugly Duckling Stage contd…

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Ugly Duckling Stage contd…

With the eruption of the canines, the impingement from the roots shift incisally thus driving the incisor crowns medially, resulting in closure of the diastema as well as the correction of the flared lateral incisors.

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Ugly Duckling Stage contd…

Hence this unaesthetic metamorphosis, eventually leads to an aesthetic result.

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Sequence of Eruption

The canines in the upper arch erupt only after the premolars have replaced the deciduous molars, whereas the canine erupt before the premolars in the lower arch.

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Second Transitional Period contd…

Favorable occlusion in this area is largely dependent on:

Favorable eruption sequence.
Satisfactory tooth size to available space ratio.
Attainment of normal molar relation with minimum diminution of space available for the bicuspids.

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Second Transitional Period �contd…

Eruption of permanent second molars

Before emergence- second molars, oriented in a mesial & lingual direction

Teeth- formed palatally, guided into occlusion by Cone Funnel mechanism , upper palatal cusps (cone) slides into the lower occlusal fossa (funnel)

Arch length is reduced by mesial eruptive forces

Thereby, crowding if present is accentuated

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The Permanent Dentition

Calcification begins at birth with the calcification of the cusps of the first permanent molar and extends as late as the 25^th year of life. Complete calcification of incisor crowns take place by 4 – 5 years and of the other permanent teeth by 6 – 8 years except for third molars.

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The Permanent Dentition contd…

The permanent incisors develop lingual to the deciduous incisors and move labially as they erupt.

The premolars develop below the diverging roots of the deciduous molars.

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The Permanent Dentition contd…

At approximately 13 years of age all permanent teeth except third molars are fully erupted.

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Features of Permanent Dentition

Vertical overbite of about one third the clinical crown height of the mandibular central incisors. Overjet and over bite decreases throughout the second decade of life due to greater forward growth of the mandible.

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