BIOLOGY OF THE HUMAN
DENTITION
Dr. Samir M. Ziara
B.D.S. (Alexandria Univ.) 
D. D. P. H. Royal Collage of Surgeon 
(London)
M. Sc. P. H. Al-Quds Univ. 
Diploma of H. Administration 
GENERAL CONSIDERATIONS
IN
THE PHYSIOLOGY OF THE
PERMANENT DENTITION
FORM AND FUNCTION
The relationship between the form of the teeth and
function well be discussed in terms of : Type of food in the diet of humans. •
jaw movements. •
Protection of the periodontium. •
Stimulation of the gingiva. •
It is also recognized that the teeth not only •
contribute to the digestion of food but also are
important in speech and personal appearance.
The primary function of the teeth is to prepare food •
for swallowing and to facilitate digestion.
The teeth have their respective forms to facilitate •
prehension, incision, and trituration of food.
The dentition, joints, and muscles in humans have •
the form and alignment to enable the mastication of
both animal and vegetable foods.
This type of dentition is referred to as omnivorous
omnivore
herbivore
vs. Carnivore
The shapes of incisal and occlusal
surfaces of the teeth are related not
only to the function they perform but
also to the movements of the
mandible required to carry out
chewing of a variety of foods.
In order to understand more
completely the form and function of
teeth, the protective aspects of form
will be considered
ALIGNMENT, CONTACTS,
AND OCCLUSION
When the teeth in the mandibular arch come into •
contact with those in the maxillary arch in any
functional relation, they are said to be in
occlusion.
Occlusion is also used to designate the anatomic •
alignment of the teeth and their relationship to
the rest of the masticatory system.
Malocclusion is a term usually used to describe •
deviations in intramaxillary and / or intermaxillary
relations of the teeth and/or jaws.
In proper alignment the teeth are : -
Arranged in arches in each jaw and placed •
in strong contact with their neighbors.
Each tooth in the arch is placed at its most •
advantageous angle to withstand forces
brought to bear upon it.
Each tooth is more efficient, –
The arches are stabilized by the collective action of –
the teeth in supporting each other.
OF THE FIRST MOLARS.
THE LINE OF FORCE EXERTED WHEN THE
TEETH COME INTO CONTACT SHOULD BE
PARALLEL TO THE LONG AXIS OF THE
TEETH.
Present evidence suggests that tangential •
loading results in reduced chewing forces
and that negative feedback from receptors
in the periodontium mediate chewing
forces.
Receptor thresholds for axially directed •
forces appear to be higher than those for
tangentially directed forces and suggest a
positive feedback control on axially
directed tooth forces.
Contact of each tooth with its fellows in the •
arch protects the gingiva between them in
the interproximal spaces
The gingiva is the soft tissue in the mouth that covers
the alveolar bone and surrounds the teeth.
The
mandibular •
centrals and laterals
contact each other at
the incisal third
The form of each •
tooth,
plus
the
location
of
the
contact
areas
creates
narrow
pointed
spaces
between the teeth
that differ from other
interproximal spaces
in other segments of
the arches.
GL
CL
The buccal and lingual contours of the teeth have an
influence on the way in which food is directed to and
away from the gingival tissues.
When a tooth is normally positioned, the gingival margin
and sulcus will have a physiologic relationship to the
tooth in function.
Food impaction. impinging trauma from tough foods,
accumulation of dental plaque may be the consequence
of malposed teeth or over- or under-contouring of
restorations involving bucco-lingual surfaces.
Plaque control by tooth-brushing is important, However,
over- and under-contoured restorations should be
avoided.
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Interproximal Form
The interproximal space between the teeth
is a triangular region. normally filled with
gingival tissue, which is bounded by the
two proximal surfaces of contacting teeth
and the alveolar bone between the teeth,
which acts as the base of the triangle.
The gingiva within this space is called the •
gingival. or interdental papilla
Normally, the gingiva covers part of the •
cervical third of the tooth crowns and fills
The gingival line follows the curvature but not •
necessarily the level of the cervical line.
The cervical line is defined as the "cemento- •
enamel junction of crown and root." The gingival
line and the cervical line must not be thought of
as being identical; although they normally follow
a similar curvature.
they are seldom at the same level on the tooth •
The cervical line is a stable anatomic •
demarcation.
whereas the gingival line merely represents •
the gingival level on the tooth at anyone
period in the individual's life. and this level is
variable.
Malalignment of the teeth will change the •
gingival line-something that may not be
conducive to the health of the tissue
Even though the teeth are in good •
alignment. unless the proper relation is
kept between the width of each tooth at the
cervix and the width at the point of contact
with neighboring teeth. the spacing
interdentally will be changed.
This is an important point to observe in •
clinical examinations.
When considering the tooth form from the •
mesial and distal aspects, it is possible to
observe a curvature on the crowns at the
cervical third above the cervical line.
labially or buccally and lingually. It is called
the cervico-enamel ridge or merely cervical
ridge. with the location added (buccocervical ridge. and so forth).
ROOT FORM
The length and shape of the root (or roots) of each •
tooth must be considered important, the canine, for
instance. because of its position and the work
required of it, would be torn out of its socket, or at
least displaced, by forces brought to bear upon it, if
the root were not of extra size and length.
Fracture would be imminent if the root were not •
larger than that of other single-rooted teeth.
The root form, therefore, is associated with the •
overall form of the tooth and the work it has to do.
The angle at which the incisal and •
occlusal surfaces of the tooth crowns
are placed with respect to the root
bases is also important.
The mesial view of an anterior tooth •
will show that the incisal ridge or cusp
is centered over the root.
The mesial view of an upper first •
molar, which is a muIti-cusped tooth,
demonstrates the same principle.
The points on the occlusal surface that are •
ontacted by opposing teeth will prove to be
well within the confines of the root base of
the crown.
The measurement from cusp tip to cusp tip •
buccolingually is much less than the
buccolingual diameter of the root base
(Fig. 1-16).
Note the flare of roots for stabilization. •
OCCLUSAL CURVATURE
Close observation indicates that the •
occlusal and incisal surfaces of all the
crowns taken together in either arch would
not contact a flat plane.
Looking at the teeth from a point opposite •
the first molars buccally, we see that a line
following the occlusal and incisal surfaces
describes a curve.
This arrangement of natural teeth was described •
originally in the German literature in 890 by F. Graf
von Spee, and it is called the curve of Spee
There is no acceptable scientific evidence that the •
occlusion should be spherical, ie., that each cusp
and incisal edge touch or conform to a segment of
the surface of a sphere. However. it has been
suggested that the composite arrangement of the
occlusal surfaces of all of the teeth in each dental
arch and their approximate conformation to a
segment of a sphere gives the curvature threedimensional quality.
Centric occlusion.
The occlusion of
natural teeth is
seldom if ever
"ideal."
This illustration
shows normal
occlusion.
Note the' 'curve of
Spee." Also note the
margin of the
alveolar
bone in its relation
to the cervical line of
the teeth.
This curvature is reflected in the lingual inclination
of the mandibular molars and is the basis for the
curve of Wilson; i.e., the curvature of the
mandibular teeth is concave and that of the
maxillary teeth convex
The occlusal surface of a maxillary molar makes an
acute angulation mesially with the long axis of its
roots.
The length and shape of the roots. the angle at
which the incisal and occlusal surfaces
are placed with respect to the roots, sufficient
dimensions for strength, and an efficient
design for thorough work with resistance against
lines offorce suggest their importance to
occlusal stability.
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A segment of a
sphere placed
on the
occluding
surfaces of the
mandibular
teeth. showing
their
compensating
occlusal
curvature.
CURVE OF WILSON