lecture 2

2. The direct factors are:
1. Proximal contact areas.
2. Inter proximal spaces.
3. Embrasures ( spillways ).
4. Facial and lingual contours of the
crowns .
5. Curvatures of the cervical lines.

3. 4. Facial and lingual contours of the crowns.
The height of contour=crest of
curvature.
1. The height of contour of facial
aspect of all teeth is located in the
cervical third. Represented by
....................
2. The height of contour of lingual
aspect of all anterior teeth is located
in the cervical third. Represented by
..............
3. The height of contour of lingual
aspect of all posterior teeth is
located in the middle third
Represented by ............except……..

4. 4. Facial and lingual contours of the crowns.
In the lower
second premolar
the height of
contour lingually
is located in the
occlusal third.

5. 1. Hold the gingiva under definite tension.
2. Deflect the food away from the gingival margin to
prevent food impaction and gingival recession.
3. Deflect the food over the gingiva which allows some
massage to it .
These uniform curvatures are of physiological
significance :
4- Facial and lingual contours of the crowns.

6. Too small or absent convexity:
The food will push the gingival
tissue apically leading to gingival
recession.
.
Wrong dental restorations replacing the normal contour of
the teeth may lead to the followings:
4- Facial and lingual contours of the crowns.

7. 4. Facial and lingual contours of the crowns.
There will be too much
protection of the gingiva
from proper massage and
also the gingiva loses its
tone. Food will accumulate
around the gingival region
resulting in its chronic
inflammation.
C. Too great curvature:

8. Too large convexity:
This will provide too much protection to the
gingiva.
Gingiva will lose its tone.
Food will accumulate around the gingival
region (food impaction)
resulting in gingival inflammation.
(Gingivitis) Periodontitis Tooth loss

9. 5-Curvature of the cervical line mesially and distally
(Dentogingival junction).
Cervical line.
Gingival line.
The curvature of the cervical line
depends on:
**Height of contact area.
**Diameter of the crown
buccolingually
Mesial Distal

10. 5. Curvatures of the cervical lines.
General rules:

11. Cervical line convex
Lingual aspectLabial aspect
Cervical
line

12. 5. Curvatures of the cervical lines.
Normal attachment epithelium follows the curvature
of the cervical line. The cervical line is at stable
entity, in contrast to the gingival margin and the
attachment epithelium which recede often a lower
level as the individual becomes older.
Physiologic role:

13. Gingival Sulcus & Dentogingival Junction

14. Stages of passive eruption

15. II. The indirect factors are:
1-Crown form: Which includes:
a)Proximal maximal contour
b)Facial and lingual maximal contour.
c)Crown outline
2- Roof form:
a) Length, number and distribution.
b) Root outline.
3- Angulation of crown and root:
a) Lingual angulations of the crown of lower posterior teeth.
b) Distal angulations of crown and root of permanent molars.
4- The self-cleansing ability of the tooth.
5-Cusp form and angles at which teeth and set in jaws (Occlusal anatomy).
6- Continuity of marginal ridges has a direct effect on embrasures.
7- Continuity of central grooves of post. Teeth provide more efficient food f low
pattern during mastication.
8- Facial line angles have a direct effect on the symmetry of embrasure.

16. It is the crest of curvature of the mesial and distal surfaces of the
crown at the contact area.
***It can be noted from the facial
or lingual aspects.
***Its position differs among the
various teeth.
II. Indirect Factors
1. Crown form:
a-Proximal maximal contour:

17. In anterior teeth
Proximal maximal contour is located in the incisal
third of the crown.
The reduction of mesiodistal
diameter at the cervical and
middle thirds
This is due to
Why…….????

18. The reduction of mesiodistal
diameter at the occlusal and
cervical thirds
In posterior teeth
Proximal maximal contour is located in the middle
third of the crown.
This is due to

19. Significances of the proximal contour of the crown:
it is responsible for the development and governs the design of the
interproximal form including the embrasure, interproximal space
and the proximal contact of the adjacent crowns.
proximal contour of the crown in the size of the embrasure,
and interproximal space
proximal contour of the crown in the size of the contact area

20.  B- Facial , lingual maximal
contour:
It is discussed before in direct factors
 C - crown out line:
It is discussed before

21. C - crown outline
1- Facial , lingual crown outline of all teeth
 May be represented by trapezoids of various dimensions

22. 2- Proximal crown outline of anterior teeth
 The schematic outline of the crown from the proximal
aspect can be triangular in form.

23. 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).

24. 4- Proximal crown outline of mandibular posterior teeth
 Are rhomboidal in outline.

25. *The roots are the tools responsible for the transmission of
occlusal forces to the jaw.
*They must do this with the least injurious to the investing periodontium
2- Root form:
Length
Number
Distribution
Root outline

26. ***Length and number of roots
**Teeth have single root
if they do little work, as
biting of food
**The root remains single
but long in teeth that pierce
and tear elastic or tough
food
**When teeth perform extra
work as food mastication so
more than root is needed as in
incisors
canines .
premolars and
molars.

27. *** Root distribution
Three roots
in upper
molar teeth
Two roots in
lower molar teeth

28. Facially ( labially& buccaly), It is cone shape
Root outline:
This cone shaped root provide the interdental space for bone

29. The wider dimension of the
root proximally is to
compensate for its narrow
dimensions facially.
Proximally it is almost quadrant
Root outline:
Buccal
Mesial

31. 3-Angulation of root and crown:
a - Lingual angulations of crown of lower posterior teeth
From the proximal
aspect of premolars
and molars
**The crown is not only
angulated lingually to the
root of the same tooth, but
also to the crown of the
opposing tooth when both
come into centric
occlusion.
**, The axes of the roots of
teeth in both arches are
kept parallel or continuous.
This arrangement serves in
securing physiologic
occlusion.

33. b. Distal angulation of crown and root
permentant molars
from the buccal aspect.
**The distal angulation of the crown is
due to the progressive tilt of occlusal
surface toward the cervix in a
mesiodistal direction, since the crown
length distally is less than that found
mesially.
**The roots also incline distally in
relation to the tooth cervix, and such
inclination is increased posteriorly
where the roots of second molars have
more extra-distal inclination .
.

35. 4. The self cleaning ability of the tooth:

36. In addition to the direct and indirect factors, There are other
factors that also protect the periodontium: