The protective functional forms of the tooth crowns includes direct factors and indirect factors :

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.

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. Facial and lingual contours of the crowns.

In the lower second premolar the height of contour lingually is located in the occlusal third.

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.

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.

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:

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

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

5. Curvatures of the cervical lines.General rules:

Cervical line convex

Lingual aspectLabial aspect

Cervical line

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:

Gingival Sulcus & Dentogingival Junction

Stages of passive eruption

II. The indirect factors are:1-Crown form: Which includes:a)Proximal maximal contourb)Facial and lingual maximal contour.c)Crown outline2- 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.

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 Factors1. Crown form:

a-Proximal maximal contour:

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????.……

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

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

B- Facial , lingual maximal contour:

It is discussed before in direct factors

C - crown out line: It is discussed before

C - crown outline1- Facial , lingual crown outline of all teeth

May be represented by trapezoids of various dimensions

2- Proximal crown outline of anterior teethThe schematic outline of the crown from the

proximal aspect can be triangular in form.

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).

4- Proximal crown outline of mandibular posterior teeth

Are rhomboidal in outline.

*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

DistributionRoot outline

***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.

*** Root distribution

Three roots in upper

molar teeth

Two roots in lower molar teeth

Facially ( labially& buccaly), It is cone shape

Root outline:

This cone shaped root provide the interdental space for bone

The wider dimension of the root proximally is to

compensate for its narrow dimensions facially.

Proximally it is almost quadrant

Root outline:

Buccal

Mesial

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.

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 ..

4. The self cleaning ability of the tooth:

5- Cusp form and angles at which teeth are 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 flow pattern during mastication.8- Facial line angles has a direct effect on the symmetry of embrasure.

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