Development of occlusion

Development of Occlusion

Index

• Introduction• Periods of occlusal development Neo-natal period. Primary dentition period. Mixed dentition period. Permanent dentition period• References

IntroductionTerm 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

Periods of tooth development

Pre-dental Stage (0-6months)

Deciduous dentition (6

months-6 years)

Mixed dentition (6-12 years)

Permanent dentition

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. •The gum pad soon gets segmented by a groove called transverse groove, & each segment is a developing tooth site.

•The pads get divided into ‘labio-buccal’ & ‘lingual portion’, by a dental groove.

• The groove between the canine and the 1st molar region is called the lateral sulcus, useful for judging the inter arch relationship at a very early stage.

Gum Pads contd…The upper gum pad is horse shoe

shaped & shows:o Gingival groove: separates

gum pad from the palate.o 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.o Lateral sulcus.

Gum Pads contd…

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

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

Relationship of Gum Padso Anterior open bite is seen at rest with contact only at the molar region.

o Complete overjet.

o Class II pattern with maxillary gum pad being more prominent.

o Mandible is distal to the maxilla of 2.7 mm- male and 2.5- female. ( Sillman JH 1938)

oThe range of variation of this distal relationship is from 0 to 7 mm. . ( Sillman JH 1938)

Relationship of Gum Pads

o Mandibular lateral sulci lies posterior to maxillary lateral sulci.

o Mandibular functional movements are mainly vertical, and to a little extent antero-posterior. Lateral movements are absent.

Neonatal Jaw RelationshipA ‘precise bite’ or jaw

relationship is not yet seen. Therefore, neonatal jaw

relationship cannot be used as a diagnostic criterion for

reliable prediction of subsequent occlusion in the

primary dentition.

Primary Dentition Period(From around the 6th month to 6 years)

Sequence of Eruption

Features Of Primary Dentition

• Spacing- 2 types of dentition are seen:•A) 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.

Features Of Primary Dentition contd…

• Most subhuman primates have it through out life and use it for interdigitation of the opposing canines. This space is used for early mesial shift.

primate spaces’, ‘simian spaces’ or ‘anthropoid spaces’.


• 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


Shallow overjet & overbite. Initially a deep bite may occur due to the fact that the deciduous incisors are more upright than their successors. The lower incisal edges

often contact the cingulum area of the maxillary incisors. This deep bite is later reduced by:

oEruption of deciduous molars.oAttrition of incisors.oForward movement of the mandible due to growth.


Almost vertical inclination of anteriors.

Molar RelationshipThe molar relationship in the primary dentition can be classified

into 3 types:oStraight/flush terminal plane.oMesial step.oDistal step.

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.

Mesial Step

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

Distal Step

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

Canine relationship

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

• Classified as: Class 1 Class 2 Class 3

Class 1

Class 2

Mixed Dentition

Period

Mixed Dentition Period(Around 6 years- 12 years)

The mixed dentition period can be divided into three

phases:

o First transitional period.

o Inter-transitional period.

o Second transitional period.

First Transitional Period

Eruption of 1st Permanent MolarThe location & relation of the 1st permanent molar depends much upon the

distal surface of the upper & lower 2nd deciduous molar.

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:

oEarly shift.

oLate shift.

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.

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

Secondary spacing

• Term was coined by Baume

• Observed in closed primary dentition

• Secondary spacing can also occur during the eruption of permanent central incisors

Distal StepWhen 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.

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.

Influence of terminal plane on the position of 1st 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%

Exchange of IncisorsDuring 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).

Transition of IncisorsThe 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)

Transition of Incisors contd…

Increase in inter-canine arch width: Significant amount of growth occurs with the eruption of

incisors and canines.

Transition of Incisors contd…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.

Transition of Incisors contd…

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.

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:o Any asymmetry in emergence and corresponding

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

Inter-Transitional Period contd…

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

•Resorption of roots of deciduous canines and molars.

Second Transitional PeriodThe 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.

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:oFlaring of the lateral incisors.oMaxillary 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.o The roots of the central incisors are also forced together, thus causing a maxillary midline diastema.

Ugly Duckling Stage contd…

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.

Ugly Duckling Stage contd…Hence this unaesthetic metamorphosis, eventually leads to an

aesthetic result.

Sequence of EruptionThe 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.

Second Transitional Period contd…Favorable occlusion in this area is largely dependent

on:o Favorable eruption sequence.

o Satisfactory tooth size to available space ratio.

o Attainment of normal molar relation with minimum diminution of

space available for the bicuspids.

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

The Permanent Dentition Period

The Permanent Dentition

Calcification begins at birth with the calcification of the cusps of the first permanent molar and extends as late as

the 25th 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.

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.

The Permanent Dentition contd…

At approximately 13 years of age all

permanent teeth except third molars are

fully erupted.

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.

Andrews keys to normal occlusion

• Key I – Molar relationship MB cusp of the max 1st molar falls

into the mesiobuccal groove of the mand 1st molar and that the distal surface of the DB cusp of the upper first permanent molar should make contact and occlude with mesial surface of the MB cusp of the lower second molar.


Key II Crown angulation (Tip)

• The angulation of the facial axis of every clinical crown should be positive

• The gingival portion of the long axis of the all crowns must be distal than the incisal portion.


Key III Crown inclination

• In upper incisors, the gingival portion of the crown’s labial surface is lingual to the incisal portion.

• In all other crowns, including lower incisors, the gingival portion of the labial or buccal surface is labial or buccal to the incisal or occlusal portion.


Key IV – Rotations

• The fourth key to normal occlusion is that the teeth should be free of undesirable rotations.


Key V – Tight contacts • contact points should be

tight (no spaces).

• In absence of abnormalities such as genuine tooth size discrepancies, contact point should be tight.


Key VI – Occlusal plane or curve of spee

• The curve of Spee should have no more than a slight arch.

• Intercuspation of teeth is best when the plane of occlusion is relatively flat.

• A deep curve of spee results in a more contained area for the upper teeth, making normal occlusion impossible.


Key VII – Correct tooth size or the bolton’s ratio

• Bennett and McLaughlin in 1993 gave seventh key to normal occlusion. i.e. the upper and lower tooth size should be correct.

REFERENCES

• Shobha tandon •Nikhil marwah• Basavaraj subhashchandra phulari• S.I .Bhalajhi

Thank You.

Health & Medicine

Development of occlusion