Chronology of deciduous & permanent
Condition of teeth at different ages
Mandible at different ages
Significance of geometric outline form of
the crowns of teeth
The role of physiologic tooth form in
Calcification of deciduous teeth begins before birth & only first permanent
molar begin calcification at birth.
Eruption of the tooth means that: a- developing tooth move from the bony
crypt to appear in the oral cavity. b- crown and cervical third of the tooth
Sequence of eruption of deciduous teeth A,B,D,C,E, mandibular tooth
precedes the maxillary one of the same type. So by the age of two years all
the deciduous teeth are erupted and the root completed at three years.
Root formation of deciduous teeth = eruption+ 1or1.5 years.
Shedding means: resorption of the root of the deciduous teeth due to the
pressure produced from its successor.
Shedding of the deciduous teeth begins at 6 years A and ended at 10 years
E. Date of shedding = Date of eruption of permanent.
Beginning of root resorption of deciduous teeth = shedding – 3years except
lower canine – 1year.
Sequence of eruption of permanent teeth
In the mandible 6-1-2-3-4-5-7-8.
In the maxilla 6-1-2-4-3-5-7-8.
Root formation date fore permanent teeth= date of eruption+
Crown completed for permanent teeth =date of eruption-3years.
The equation used to determine the formed
hard part of each tooth at a specific date
Upper A beginning of calcification
5m until birth + 7m=12m ( crown& 1/3 of root )
Every three month: 1/3 of the tooth is formed.
At birth 5m from the beginning of calcification about ½ of the crown
beginning of calcification--- eruption
8M=12.5M each 1/3 need 3.1M to
formed at birth less than ½ crown formed.
C beg. Of calcification ---------- eruption
4M+18M= 22M SO crown + 1/3 of root formed at 22M. Each 1/3 need 5.5 m to formed
At birth ( about 4m only from the beg. Of calcification) at birth cusp tip formed.
D beg. Of calcification --------eruption
4M+14M= 18M for formation of crown and 1/3 of root So each third need 4.5 M to
At birth occlusal surface only formed .
E beg. Of calcification ------------------eruption
3M+24M=27M each third =6.5m separate cusps of the occlusal surface is formed.
The mesiolingual cusp of lower 6.
Beginning of calcification -----crown completed
Each third formed in15M So at one
year less than 1/3 of crown formed
Beginning of calcification -------crown completed
Each third formed in 12M
So at one year 1/3 of crown formed
start to eruption
part of crowns formed
separate cusps of 6
Incisal 1/3 of 1&2
The deciduous teeth
Incisors , canines and the first deciduous molars are present in the oral
Incisors are in occlusion and their roots completed.
Two third of the canines and first molars roots are formed.
E beg. Of calcification ------------------eruption
3M+24M=27M each third =6.5m **So at one and half year the
second deciduous molar is not yet erupted however the crown is completed
and less than third of the root formed.
The permanent teeth :
Upper central permanent incisor:
Beginning of calcification -----crown completed
Each third formed in15M So at one& half year less than 1/2
of crown formed, nearly incisal third is formed.
Less than half of the crown of maxillary and
mandibular central incisors.
One third of the crown of the mandibular lateral
Less than third of the upper lateral incisor.
More than half of the crown of first molar.
Less than half of the canine is formed.
More than ½ crown
of 1&2 formed
cusps of 7
teeth erupted with
fully formed teeth
crown of 6
½ crown 3
6 is erupted
less than 1/3 of the
Root of lower A
crown of 7 not
E no resorption
8 Calcified separate
cusps are formed
3&4&5 not yet erupted &less
than 1/3 of root formed
C&D&E most of
7 crown& less than
1/3 root formed
root of 6
1&2 is erupted their
All permanent teeth
erupted except 8 .
All roots are completed
Facial and lingual aspects
of all teeth is Trapezoid
To accommodate interproximal gingiva.
Spacing between roots allow sufficient alveolar bone,
periodontal ligament, blood vessels and nerves.
Provide contact between teeth which support & stabilization of
the dental arch.
Contact between upper & lower teeth which prevent over
eruption and elongation on tooth loss.
The proximal aspect is
the base is toward the
cervix & apex is toward the
Wide base cervically provides ----- more strength for
the teeth & increases their stability in the jaw, this is
important for the reduction of forces transmitted to
Tapered labial & lingual surfaces which facilitate
pearcing of food.
Upper teeth trapezoid
Lower teeth rhomboid
* Constricted occlusal surface lead to early penetration of the food.
* Decrease forces on base of the tooth.
* Self cleaning.
* Lingual inclination of the crown of lower molar prevent traumatic
& periodontium degeneration & give proper inter
cuspation and occlusion.
* Keeps the axis of maxillary and mandibular teeth parallel .
* Permits the prominence of cervical ridge so protect the gingival
anterior part of
(Symphysis of mandibule
+mental ossicals) 2parts fuse at 1 year
Condyle process at the level of the upper border of mandible.
Coronoid process at higher level than condyloid.
Mental foramen near the lower border under the crypt of D
Mandibular canal near lower border
Sigmoid notch is shallow
Mandible two half till the end of the first year.
Angle of the mandible 170 degree.
cartilage 14WIUL20Y give condyle+
posterior part of
Increase in length by bone
remodeling make room for
Increase in height by
eruption of teeth +alveolar
bone formation+ bone
deposition at lower border
of the mandible
in height in length
Coronoid process higher than condyloid process.
Mental foramen midway between upper& lower border.
Mandibular canal slightly above mylohyoid line.
Sigmoid notch more deeper.
Angle of the mandible 140 degree.
Chin is poorly developed.
Condyle process at a higher level than coronoid process.
Sigmoid notch deepest.
Mental foramen mid way between upper & lower border under the
socket of lower 5.
Angle of the mandible 110-120 degree.
Chin is significantly prominent ----- mental protuberance.
Condyloid process at a lower level than coronoid process
Sigmoid notch is shallower.
Mental foramen near the upper border of the mandibule.
Mandibular canal near the upper border.
Angle of the mandible 140 and the ramus inclined posterior.
Body of the mandible has reduction in height due to loss of teeth
and alveolar process.
At adult period
At old age
It is the system of attachment and
investing tissues surrounding the tooth
that serve to attach the tooth in its socket.
This includes, the gingiva, periodontal
ligament cementum and the alveolar
form physiologically may affect
the periodontium by. Direct factors &
1- Proximal contact area.
2- Inter proximal spaces.
3- Embrasures or spill ways.
4-Facial and lingual contours of the
5- Curvature of the cervical line.
1- Cusp, crown and root form:
Crown (proximal maximal contour, Facial & lingual
maximal contour and geometric outline) & root form
(length, number& distribution and root outline (cone
shape) ) .
2- Proportion between size of crown and root.
3-Angulation of teeth in jaw.
4-Self cleaning ability of the teeth which is achieved
A- Proper alignment of teeth in the dental arch.
B- Normal gingival attachment.
C- Brushing action of the tongue, lips & cheek.
D- Washing effect of saliva & fluid intake.
E- Friction of food during mastication.
F- Home care of teeth as teeth brushing.
Each tooth has a mesial and distal contact areas
except lower& upper 8 ( has no distal contact area).
Contact areas are small in anterior teeth and
increase in size in posterior teeth.
The mesial contact area is located more incisally,
while the distal one is more cervically.
Generally in anterior teeth the contact areas are
near the incisal ridge and become more cervically
as we go to posterior teeth.
However these relations are greatly
1- length & width of the crown.
2- Level & height of proximal
The contact area in
anterior teeth is
3- proximal wear.
5- disproportional growth
between teeth & jaw.
6- developmental anomalies.
developmental missing or unerupted
In posterior teeth
the contact area
is more buccally
1- Stability of the dental arch by combined anchorage of all the teeth
in each arch by positive contact .
2- Protects the inter dental gingiva.
3- Prevents food impaction between teeth.
4- distribution of masticatory force among the adjacent teeth in the
individual dental arch.
If proper contact is lost:
1- Food impaction between teeth.
2- Dental caries and gingival inflammation.
3-Disturbance of proper alignment of teeth
change in angulations of teeth
Destruction of periodontium and loss of teeth.
Embrasure is an open space between adjacent teeth in the same dental
arch, formed by the curved smooth surfaces of teeth. They diverge from
the contact area incisally, occlusally or cervically, labially, buccally or
Cervical embrasures are filled with the inter dental papilla.
The size of the embrasure depend on the position of the contact area:
Occlusal embrasure in posterior teeth larger than incisal embrasure of
1- Makes a spill way for escapement of food during
mastication which lead to reduce forces on the
teeth and periodontium.
2-Proper embrasure and contact prevent food from
being forced between teeth & so protect the inter
3- Embrasure allow proper degree of frictional
massage during mastication
4-Embrasure and rounded surfaces of teeth
ensures self cleaning ability of teeth. If there was
no embrasure and teeth surfaces were not
stagnation of food and poor oral
Triangular spaces filled with inter dental papilla
at the alveolar process.
proximal surfaces of teeth.
at the contact area.
The form of the inter proximal space depend on the tooth form
& position of the contact area:
*Wide cervix of the tooth
narrow inter proximal space.
* Narrow cervix
wide inter proximal
* Wide inter proximal space give considerable space between
roots of teeth for bone & investing tissues including B. Vs.,
The height of contour of the
labial and buccal surfaces of all
teeth is at the cervical third.
The height of curvature lingually
- At the cervical third in
- At the middle third in
The physiologic importance of the labial,
buccal& lingual contours of the crowns
1- Hold the gingiva under definite tension.
2- Protect the gingival margin by deflecting
the food away during mastication which
allow proper degree of gingival massage.
3- If these curvatures are absent or under
* the gingiva will be pushed apically
4- If the curvature is over developed this
* over protection to the gingiva & prevent
* allow food accumulation which lead to
In individual tooth the curvature of
the cervical line mesially greater
Generally the curvature of the
cervical line in anterior teeth
greater than in posterior teeth.
In molars, it is nearly straight
mesially and straighter distally .