Development of The Dentition
Prof. Nadia el Harouni
By the end of this lecture you should be able to:
1- Recognize the normal features of the mouth of the neonate
2- Discuss features of normal occlusion of the primary dentition
3- Understand normal development of the primary to permanent dentition.
4- Recognize the normal pattern of eruption of the permanent dentition.
Humans have two dentitions, the deciduous (primary) and permanent
Dental arches constantly change from birth to adulthood, these changes can
be divided into four stages:
1. Gum pad stage
2. Deciduous dentition stage
3. Mixed dentition stage
4. Permanent dentition stage
A) The Mouth of the Neonate
1. The Gum Pads
The maxillary arch is horseshoe shaped, and the gum pads extend buccally
beyond those in the mandible (wider in every way)
At birth the alveolar processes are covered with gum pads , soon
segmented by transverse grooves into 20 sites of developing teeth
At birth the gum pads are not wide enough to accommodate the
developing incisors which are rotated and crowded in their crypts but
during the first year of life the jaws grow rapidly in width. This allows
the incisors to erupt in good alignment guided by the pressure of the
tongue and lip.
The lateral sulcus is the groove marking the distal of the canine
The gingival groove is the horizontal groove separating the max.
gum pads from the palate.
The dental groove extends from the incisive papilla to meet the
gingival groove at the canine region then lateral to the molar region
The lower arch is U shaped and the lower gum pad is slightly
everted labially it shows:
The lateral sulcus
The gingival groove: the lingual extension of the gum pads
The dental groove: joins the gingival groove at the canine
2. Neonatal Jaw Relationships.
No precise relationship is seen
Anterior open bite is normal. The tongue fills the space between the gum
pads and rests on the lower lip
3-Precociously erupted primary teeth Natal teeth:A child may be born with teeth already present in the Oral
Neonatal teeth erupt within the first month of life
Pre-erupted teeth appear within the second and third months of life
85% are deciduous (estimated) (management ?)
Mand. centrals 7 months
Max. centrals 9 months
Max. laterals 11 months
Mand. laterals 11 months
Max. & mand. Ds 18 months
Max. & mand. Cs 2 Years
Mand. Es 2 years
Max. Es 2 years
B) The Primary Teeth and Occlusion.
1. Development of the primary teeth
At the fourth month IU
At birth - of the crowns are formed
Always a range
c) Teething Only trivial symptoms
d) Size and shape of primary teeth. not much variability as in
e) Ankylosis of primary teeth:
More common than permanent, Lower more than upper not truly submerged
2- Development of the primary occlusion
a) Primary dental arches.
Slight increase anteriorly from birth till 12 months
Posteriorly more increase
b) Occlusal relations.
No 3 dimensional reln until the eruption of the first molars ,
The normal signs of normal deciduous occlusion include
-Primate spaces; The deciduous teeth are usually spaced as they erupt.
The spaces mesial to the maxillary canines and distal to the mandibular
canines are slightly wider and known as primate spaces. The spaces that
exist between the deciduous molars usually close by the time of eruption of
the 1st permanent molars, whereas the spaces between the deciduous
incisors remain till these teeth are replaced by their successors.
-Shallow overbite and overjet
-Almost vertical anteriors
-Ovoid arch form
-CLASS I molar and cuspid relation
-Straight /flush terminal plane which changes into a mesial step by
the age of 6 due to
a) cuspal attrition so the mandible moves forward
b) greater spacing in the mandible than the maxilla
d) Disorders of the primary occlusion.
Variable according to ethnic group and culture
Class III and anterior crossbite
Bruxism: a functional malocclusion.
The mixed Dentition stage
Transition from deciduous to permanent dentition
It is the period from 6 to about 12 years of age .During this
period both the deciduous and the permanent teeth are
The permanent teeth which follow the deciduous teeth are called
successional teeth ( incisors, canines and premolars) while the
permanent molars are called accessional teeth.
Calcification of the permanent dentition All start after birth except 6s (might)
As the permanent teeth are calcified after birth, they are susceptible to local
and general environmental changes
a) Interrelationships between calcification and eruption.
Eruption is a developmental process that moves the tooth
from its crypt position through the alveolar process into the
During eruption, the root elongates, the primary root resorbs,
the permanent tooth moves occlusaly and the alveolar
Permanent teeth begin their eruptive movement when their
crown is completed.
It takes 2 to 5 years for the posterior teeth to reach the
alveolar crest following completion of their crowns and from
12 to 20 months to reach occlusion after reaching the alveolar
margin. Roots are completed a few months after occlusion is
It may appear that the incisor erupts first, whereas, in truth, the
molar has preceded it in starting eruption, but is moving so slowly
that the incisor passes by it
b) Factors regulating and affecting eruption.
4- Nutritional (to a lesser extent).
5- Gender differences; Girls usually ahead
c) Timing and variability of eruption
Very variable, no set rules.
N.B. Recently It has been observed that eruption occurs only from 8 pm till
midnight or 1 am (growth hormone release?!) stops during the day or the
d) Sequence of eruption.
Also variable but most common;
maxilla: 6,1, 2, 4, 5, 3, 7, 8
6,1, 2, 4, 3, 5, 7, 8
mandible: 6, 1, 2, 3, 4, 5, 7,8
6, 1, 2, 4, 3, 5, 7, 8
Unfavorable where 7 erupts before 5
First molars 6 years
rs 16-25 y
Mandibular teeth erupt ahead of maxillary teeth except the maxillary
e) ectopic eruption: The eruption of a tooth in an abnormal position in the
permanent dentition, usually upper 6 or lower 1,2,3
NB impaction :Failure of a tooth to emerge usually due to insufficient
space ,or supernumerary tooth blocking its path or for no local reasons as
f) Factors Determining the tooths position during eruption.
2-presence of adjacent teeth
3-early loss of deciduous
4-pattern of resorption
5-local pathological conditions
6-general pathology affecting growth.
7-mesial drifting tendency.
II- Pre-occlusion stage
1-lips, cheeks, muscles.
2-objects brought in the mouth.
3-caries and extractions of adjacent Teeth
III- Occlusal stage
All previous in addition to muscles of mastication through forces of
occlusion and the anterior component of force
Uses of the dental arch perimeter
A) Alignment of the permanent incisors
b) space for the cuspids and premolars
c) adjustment of the molar occlusion.
First permanent molar:
1st permanent molars are the keys of the dental arches.
The upper molar is located at the base of the key ridge that descends from
the zygomatic arch.
It is guided into place through
1. the position of the second deciduou