Primary Dentition and Eruption

Primary Dentition: Primary Dentition: Anterior and PosteriorAnterior and PosteriorPrimary Dentition: Primary Dentition:

Anterior and PosteriorAnterior and Posterior

Howard Chi, D.M.D.Howard Chi, D.M.D.

Learning Objectives• Generals of primary dentition• Anatomy of primary anteriors• Anatomy of primary posteriors• Eruption patterns of primary

dentition and permanent dentition

Generals of Primary Dentition

Primary Dentition

* Primary teeth emerge in children between the ages of 6 months and 2 years

* Beginning at age 6 these teeth are gradually replaced by the permanent teeth

Primary Dentition

* Primary teeth are often called deciduous teeth

* From the Latin to fall off* Common nicknames are “milk teeth” or

“temporary teeth”

Primary Dentition

* The teeth function an average of 8 years for maxillary teeth

* The teeth function an average of 7.6 years for mandibular teeth

* Hold an important role in reserving space for permanent teeth

Important Functions Of Sound Primary Teeth

1) Efficient mastication of food2) Maintenance of a normal facial

appearance3) Formulation of clear speech4) Maintenance of proper diet5) Avoidance of infection and pain6) Maintenance of space and arch

continuity

Eruption Time Of Primary Dentition

* First primary teeth to erupt are usually mandibular central incisors at about 6 months

* Last teeth to erupt are the maxillary second molars around 24 months

Mixed Dentition

* First permanent teeth to erupt are the mandibular first molars and then maxillary first molars

* They appear distal to the primary second molars

* With their eruption commences the mixed dentition period

Mixed Dentition

* The roots of primary teeth are completely formed 1 year after emergence of the crown into the mouth

* The roots are short lived beginning to resorb in just three years

* After exfoliation, the permanent teeth emerge within a few months

General Characteristics Of

Primary Teeth1) Primary teeth are smaller in size than

permanent teeth2) They are whiter in color than the

analogous permanent teeth3) They are less mineralized than

permanent teeth

General Characteristics Of

Primary Teeth4) They have shorter crowns with respect to

their roots5) Crowns have a marked constriction at the

cervix6) The enamel seems to bulge close to the

cervical line, rather than gradually tapering

General Characteristics Of

Primary Teeth7) The layers of enamel and dentin are

thinner than on permanent teeth8) The pulp cavities are proportionally larger9) Primary teeth exhibit fewer anomalies10) The crowns appear bulbous, often with

labial or buccal cingula

Primary Anterior Dentition

General Characteristics

Of The Anterior Teeth

1) Usually no depressions on the labial surface of the crowns of incisors

2) There are no mamelons on the incisal edges

3) Facial cervical ridges are prominent

General Characteristics

Of The Anterior Teeth

4) Cingula are prominent and occupy 1/3 cervicoincisal length

5) The roots are long in proportion to the crown length, and narrow mesiodistally

6) The roots bend labially in their apical 1/3 to 1/2 as much as 10 degrees

Proximal Aspect Of Primary Incisors

Root Shape* The roots of maxillary incisors are S-shaped,

bending toward the lingual in the cervical third to half and then bend labially in the apical half

* The roots of mandibular incisors are straight in the cervical half and bend labially in their apical half

* This bend help provide space for the developing teeth

Primary Canines

Uniqueness of Contact Areas:* Mesial and distal contacts are in the middle

third of the crowns, with the mesial being located more cervical than the distal (a condition unique to the tooth and one other, which tooth?)

D

Primary Canines

Primary canine root:* Are bulky in the middle and cervical

thirds, tapering in the apical third where they bend labially

Primary Posterior Dentition

1) The molar crowns are wider mesiodistally, yet shorter cervico-occlusally

2) The second molars are much larger than the first molars3) The molar crowns have a narrow chewing surface4) The molar occlusal anatomy is shallow (cusps are short)5) The buccal cusp tips are not pointed and their slopes

meet at very obtuse angles

General Characteristics

Of The Posterior Teeth

6) There are few grooves or depressions in the crowns7) The root furcations are near the crown, with little or no

root trunk8) The roots are widely spread beyond the outlines of the

crown9) The roots are thin and slender10) The second molar roots are spread more widely than

the first molar roots

General Characteristics

Of The Posterior Teeth

Primary Molars

* Primary first molars are smaller than primary second molars

* Primary first molars are quite unique in their shape

* Primary second molars have considerable likeness to permanent first molars

* Maxillary molars have three roots and mandibular possess two

Primary Maxillary First Molar

Uniqueness for primary maxillary first molar:

1. Resembles a permanent premolar*2. Groove pattern is “H” shape

Primary Mandibular First Molar

Uniqueness for primary mandibular first molar:1. Resembles no other tooth in either primary

or permanent dentition*2. Two roots: Mesial and distal. With the Mesial

root wider and longer than the distal (opposite of permanent mandibular molars (in length))

Eruption Patterns:Eruption Patterns:Primary and Primary and

Permanent DentitionPermanent Dentition

Eruption Patterns:Eruption Patterns:Primary and Primary and

Permanent DentitionPermanent Dentition

Eruption and Resportion

• Eruption: Historically denotes the eruption of tooth through the gingiva

• Resorption: The permanent tooth in its follicleattempts to force its way into the position held by its predecessor

• The pressure brought to bear againstprimary root causes resorption of the rootuntil exfoliated

Dental Age• Has been assessed on the basis of the

number of teeth at each chronological age

• Calcification of the organic matrix, rootformation, and tooth eruption are important indicators of dental age

• Dentition is the single best physiologicalindicator of chronological age in juveniles

Primary Tooth Eruption Sequence

1) Central Incisors2) Lateral Incisors3) First Molars4) Canine5) Second Molars

Primary Mandibular

Incisors

• Centrals erupt at a mean age of 6 months

• Laterals erupt at a mean age of 7 months(occasionally, all lower incisors will eruptbefore the maxillary incisors)

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Primary Maxillary Incisors

• Maxillary central follow mandibularcentral by mean age of 1 months and

erupt at 7 months

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• Laterals erupt at a mean age of 9 months

Primary Maxillary Incisors

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PrimaryFirst

Molars

• First molars erupt at a mean age 12-14 months

• Mandibular usually erupts first

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Primary Canines

• Mandibular canine erupts at a mean age of 16 months

• Maxillary canine erupts at mean age of 18 months

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Primary Second Molars

• Mandibular second molars erupt at a

mean age of 20 months

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• Maxillary second molars erupt at a mean age of 24 months

Primary Second Molars

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Succedaneous Teeth (Teeth that replace a primary

predecessor)

1) Permanent Incisors2) Permanent Canines

3) Permanent Premolars

Permanent First Molar• Begin to calcify at about

the time of birth

• Emerge distal to primary second molar

• First molars are the first to erupt• Occurs at 6 years of age and are occasionally called "6-year molars"

PermanentFirstMolar

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Permanent Mandibular

Central Incisor

Second permanent tooth to

emerge into the oral cavity

•Mandibular central erupt at 6 years

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Permanent MaxillaryCentral Incisor

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• Maxillary central at age 7-8 years

Permanent MandibualrLateral Incisor

• Mandibular lateral at 7-8 years (may erupt along with the maxillary central incisors)

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Permanent MaxillaryLateral Incisor

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• Maxillary lateral at age 8-9 years

Permanent Mandibular

Canine

• Mandibular canines erupt following the lateral incisors between ages of 9-10 years

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Maxillary First

Premolar

• Generally erupts at 10-11 years oldfollowing the mandibular canine

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Maxillary Second And Mandibular First Premolars

• Follow the maxillary first premolars• Generally erupt at 10-12 years old

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Mandibular Second Premolar And Maxillary Canine

• Follow the maxillary second premolars andmandibular first premolars

• Generally erupt at age 11-12 years

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PermanentSecondMolars

• Erupt at 11-13 years of age• Mandibular usually erupts first

called "12-year molar"

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PermanentThird

Molars

• Erupt at age 17 or later• Considerable jaw growth required

to allow room for these teeth

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