The mandible at different ages and importance of proximal spaces
Descriptive dental anatomy
Mandible at different ages
Mandible at different ages
The Mandible at birth:
I. The Mandible at birth is made up of two separate halves, they are united later on
by fibrous tissue at the midline. The two halves of the Mandible joint at an area
called symphysis menti.
II. At birth there are no teeth, the size of the Mandible bone is too small to carry any
teeth but it carries the tooth germ of both the decidious and permanent teeth in
its bony crypts.
III. The mandibular canal runs near the lower border of the mandible while the
mental foramen opens below the crypt of the lower D.
IV. There is no mental protuberance present at that age.
V. The sigmoid notch is very shallow, the ramus bone is small and makes an angle of
170 degrees with the body of the mandible this angle is called the mandibular
VI. The coronoid process is higher than the condyle. The condyle is present at the
same line with the upper border of the mandible.
The Mandible at age of 3 years:
I. The two halves of the mandible joint together at the end of the first year
or beginning of the second year of children.
II. The body of the mandible bone starts growing to be able to occupy the
decidious and after that the permanent teeth, also the body increases in
height by the growth of the alveolar bony socket and the growth of the
first decidious teeth
III. The mandibular angle becomes smaller than at birth and closer to the
adult mandibular angle as it changes from 170 degrees to 140 degrees
The Mandible at the age of six years:
I. The mixed dentition starts by the eruption of the first permanent molar.
II. The mandibular canal is placed above the mylohyoid line.
III. The opening of the mental foramen lies midway between the upper and
lower border of the body of the mandible.
IV. The mandibular angle more closer to the adult mandibular angle.
V. The growth of the mandibular bone causes bone remodeling, the
remodeling of the bone means resorption in certain regions
accompanied with apossition in other regions.
• The Mandible at Adult age:
I. The height and length of the mandible increase by the increase of size of
the alveolar bone and the eruption of the permanent teeth.
II. The mandibular canal is in a parallel position to the mylohyoid line.
III. The mandibular canal and mental foramen are both positioned midway
to the upper and lower borders of the mandible, usually the mental
foramen lies below the sockets lower 5 or lower 4 but in some rare
cases it lies between both sockets.
IV. The appearance of mental protuberance gives the chin appearance in
V. The coronoid is at a lower level than the condyle.
VI. The sigmoid notch becomes deeper
VII. The mandibular angle becomes from 110-120 degrees.
Mandible at old age:
I. There is a decrease in the size of the mandible due to lose of permanent
teeth and the resorption of the alveolar process.
II. The loss of the permanent teeth and decrease in size of the mandible
cause the mental foramen and mandibular canal to become positioned
near the upper border of the mandible.
III. The mandibular angle becomes bigger than at adult age because due to
the loss of teeth the person tries to bring the lower and upper jaws near
each other for mastication, also the ramus becomes oblique for the
IV. The mandibular angle becomes 140 degrees.
V. the condyle bends backward and become in lower level than the
VI. The sigmoid notch is shallower than adult.
The Physiologic Tooth Form Protecting
What is the Peridontium?
The peridontium is the supporting system of the tooth the peridontium is
Alveolar bone proper
The teeth have certain outline and curvatures
that serve in supporting the teeth and that
curvature is so finely drawn that any changes in
these dimensions may seriously injure the tooth
in the future. There are certain factors that may
affect the periodontum:
I. Direct factors
II. Indirect factors
1. The direct factors consist of:
• The proximal contact area
• The interproximal spaces
• Embrasures or spillway
• Facial and lingual contours of the crown
• Curvature of the cervical line mesially and distally
2. The indirect factors consist of:
• Cusp forms
• Root forms
• Root/Crown ratio
• Angle of the tooth axis in the jaw bone
• Self cleansing ability of the tooth which consists of:
1. The smooth rounded surface of tooth and brushing activity of tongue and
2. The flushing activity of saliva.
3. The friction of food material during mastication.
4. The efficient use of tooth brush during home care of teeth.
1.The proximal contact area:
A. What is the proximal contact area?
The proximal contact area is the spot on the proximal tooth surface where the
tooth touches the tooth adjacent to it in the same dental arch
The proper location of the contact areas can be observed from:
• The labial or buccal aspect
• The incisal or occlusal aspect
B. The normal location of the contact areas are:
• Every tooth has distal contact area in a more cervical area the the mesial
• The contact area is wider in posterior teeth than in anterior teeth and
more cevically in postion
• The contact area is centered labioligually in anterior teeth while in
posterior teeth it is deviated more bucally
C. What are the importance's of the proximal
• It stabilizes the tooth within the alveolus which thereby stabilizes the
• It helps prevent food impaction which can lead to decay and periodontal
• It protects the interdental papillae of the gingival
2. The interproximal spaces:
A. What is the definition of interproximal spaces?
The interproximal space is a triangular space between adjacent teeth cervical
to their contact, the sides of the triangle are the proximal surfaces of the
adjacent teeth and the apex of the triangle is the area of contact of two teeth.
This space is occupied by the interdental papilla
B. What are the importance’s of the interproximal spaces:
• The healthy interdental papilla is smooth and elastic tissue that prevent
• Interproximal space gives sufficient space for the alveolar bone between
the neighboring teeth to support them in their sockets
3. The embrasure or spillway:
A. What are embrasures?
Embrasures are triangle shaped space or area between two adjacent teeth in
the same dental arch, where their proximating surface diverge from the area
of contact facially, lingually, and oclussaly.
Also there is a good relation between the location of contact areas and the
• The lingual embrasures are larger than the facial ones since most teeth are
narrower on the lingual side than the facial side, the lingual embrasures
also are larger than the buccal embrasures in posterior teeth more than in
• The incisal embrasure is shallow and narrow faciolingually on the anterior
teeth but broad in posterior teeth this is because the contact area is more
cervical in the posterior teeth than in the anterior teeth.
B. The importance of the embrasure’s are as follows:
• They make a spillway for the escape of food during mastication thus
reducing the forces upon the teeth.
• They make the teeth self cleansing because the rounded smooth surface
of the crowns are more exposed to the cleansing action of foods, fluids
and the friction of the tongue, lips, and cheeks. If there was no escape way
for the food the lodgement of food would cause to very poor oral hygiene.
• They allow proper stimulation for the gingival by permitting the proper
degree of frictional massage during mastication.
4. Facial and lingual contours of the crown.
A. The location of the facial and lingual contours:
• The height of contour on both labial and lingual surfaces of all the anterior
teeth is located in the cervical third.
• The height of contour of the buccal surfaces of all posterior teeth is
located in the cervical third.
• The height of contour of the lingual surfaces of all posterior teeth is
located in the middle third except the lower second premolar where it is
located at the oclusal third.
B. The physiological importance of these uniform curvature:
• The curvature holds the gingival under definite tension.
• They protect the gingival margin by deflecting food away from it during
• The proper curvature will deflect food over the gingival margin preventing
unnecessary frictional irritation, but will allow some massage to soft
C. If the proper curvature of teeth was replaced by improper contour by
unsuccessful dental restoration the following will occur:
• If the proper contour are absent or too small the gingival tissue will be
pushed apically and gingival recession will occur.
• If the curvature is too great there will be too much protection of the
gingival from proper massage and also the gingival will lose it’s tone. The
food material will accumulate around the gingival area resulting in chronic
5. Curvature of the cervical line mesially and
A. The curvature of the cervical line from different aspects:
• The curvature of the cervical line mesially and distally differs in different
teeth generally speaking this curvature is greater in the anterior teeth
than in the posterior teeth .
• In individual tooth it’s greater mesially than distally.
• It tends to be straight buccolingually in the distal surface or even the
mesial surfaces of some molars.
B. The importance of the curvature of the cervical line mesially and distally:
• The importance of the curvature of the cervical line is due to the face that
it is the site of attachment of the gingival to the tooth by means of a
structure called the attachment epithelium .
• If the teeth are in normal alignment and contact, the attachment
epithelium follows the curvature of the cervical line but not necessarily at
the same level. Any break in this epithelium will result in major injury to
the periodontium due to the penetration of the bacteria and their toxins
causing damage to the investing tissue of the tooth.