geometric outline

dental physiologic form for the best students

1. Lecture 3
from direct factors
 crown form
.) crown outlines (
Dr: 3mmar
Mobile: [phone]
F.B: [email protected]

2. In general all aspects of tooth crown may be described as one of
three geometric figures of different dimensions.
this figures are trapezoid , triangular & rhomboid

Rhomboid
Trapezoid
Triangle
Crown outline
(Geometric Concept of Crowns Outline)
Each tooth has specific form which related to its functions in
mastication , speech & esthetics

3. The Periodontium
Is the investing , supporting , attachment
and covering system of teeth.
It consists of:
Two Soft Tissues Two Hard Tissues
1- Gingiva
2- Periodontal Ligament
1- Cementum
2- Alveolar Bone

4. 1- Facial , lingual crown outline
of all teeth
•May be represented by trapezoids of various dimensions
*The shortest of the uneven sides is toward the tooth
cervix
* The longest of the uneven sides is toward the occlusal or

incisal aspect

5. Significances of the trapezoid outline
form of the crown in protecting the
periodontium
1- Provide contact between the teeth at
certain areas
2- Provide interproximal spaces
which contains inter-proximal tissue
3- Provide spacing between
the roots of neighboring teeth
to allow sufficient supporting alveolar
bone.
4- reduce , distribute the force exerted on
the teeth , those transmitted into peri-odontium
5- allow for off set relation of opposing teeth
which prevent the elongation of antagonist ,stabilize the remaining tooth for longer period.

6.  prevents elongation
of antagonists
if a tooth is missed
 and helps to stabilize
the remaining teeth for
a longer period than if
the tooth has a single antagonist.
This arrangement (offset relation)

7. 2- Proximal crown outline of anterior teeth
•The schematic outline of the crown from the
proximal aspect can be triangular in form.
•The base of this triangle is toward the cervix, while
its apex is toward the incisal ridge

8. Significances of Greater labiolingual measurement
cervically at the base of the triangle than at its apex
**Increases the teeth strength
**Increases the stability of teeth in the jaw
**Increases the efficient resistance against

masticatory forces
*** This is important for the reduction of
forces transmitted to the investing
periodontium

9. Progressive incisal constriction
•Facilitates
penetration and
incising food
without elaborating
excessive trauma to
the marginal gingiva
as food slides over
the cervical tooth
surface

10. 3- Proximal outline of maxillary posterior teeth
They are trapezoidal in outline.

The largest sides is toward the
tooth cervix
while the shortest is toward the
occlusal surface (narrow occlusal
surface).
Significances of of this trapezoid outline:-
** provide narrow occ. Surface which
1- facilitate the initial penetration of food.
2- reduce the masticatory force when transmitted from
narrow occ. surface to wide cervical base & thus to peri-odontium.
** Make the tooth self cleansable by allowing sliding of the food material
along the inclination of facial , lingual surfaces.

11. 4- Proximal crown outline of mandibular posterior
teeth
•Are rhomboidal in outline.
Due to lingual inclination of the long axis of the
crown to the axis of the root of mandibular
posterior teeth ,the acute angles of the rhomboid
forms is pointed out to the occlusolingual and
buccocervical line angles

12. Significance of the rhomboid outline form
of the crown in protecting the periodontium
are
.
1-Allows for establishment of the
intercusp relation between
the opposing teeth when they are
brought into centric occlusal relation.
.
This arrangement prevents traumatic occlusion
and its periodontium degenerative sequlae.
.
2- To keep the axis of roots of the
mand., max. teeth parallel.
If the mandibular crowns and roots
have the same relation as the maxillary ones,
the cusps would hit , clash during function &
would not be in proper intercusp relation.
3-Permits the prominence of the cervical ridge.This physiologic form
permits protection of gingival contour

13. *The individual tooth form can be lost as a result of caries,
attrition, or trauma.

Functional tooth form that has been lost can be
approximated by restorative treatment in many cases.
Restorations, crowns, bridges, partial or complete
dentures or implants may be used.

14. Thanks
Dr: 3mmar
Dr. Mona Hassan Farid