histology and physiology of teeth

Periodontium and factors related to it

indirect factors Protects The Periodontium

Periodontium and factors related to it

  • Generally There are direct and indirect Factors that protecting
    periodontium .

Indirect Factors Protect The Periodontium

1-Crown Form

it involve

A-proximal maximal contour

usual it located at incisal third of anterior teeth due to reduction MD diameter in middle and cervical third , and in middle third of posterior teeth .

It is important to have a prominent contour on teeth crowns (on mesial,
distal, surfaces), Essential in that it protects gingival tissue from food
bruising and trauma , It also stops the food from getting into gingival sulcus
, and it is responsible for the development many feature on teeth such as embrasure ,inter proximal space and proximal contact of contacted teeth(6) .

B-facial and lingual maximal contour

it explained before in direct factors

C-crown out line

All parts of each tooth crown, with the exception of the incisal or occlusal elements, may be depicted schematically within one of three geometric figures;

a triangle, a trapezoid or a rhomboid.

Facial And Lingual Aspects Of All Teeth : a trapezoid of various dimensions may outline the outline of these surfaces.

The shorter of the trapezoid’s rough sides reflect the crown’s bases at the cervices. While the longest of the rough side reflects the incisal or occlusal surfaces and forms the approximate point when the jaws are closed at which the opposing teeth meet.
This structure and design defines the following basics of form:

  • Create interproximal spaces to fit the gingival interproximal.

Develop a gap between the roots of the adjacent teeth that allows adequate
room for the bone and supporting structures required to hold the gingival
tissue to a normal level to provide adequate blood circulation to the area,
-Provides an area of contact between adjacent teeth helping to protect the
interproximal gingiva.

  • The arrangement of the teeth tends to prevent elongation of the antagonists,

since each tooth has two antagonists in the opposing arch except for the
lower central and upper third molars,
Mesial And Distal Surfaces Of All Teeth:

A-anterior teeth Such aspects can
be included inside a triangle, the basis of which is defined by the crown’s
cervical portion and the incisal ridge’s apex , This architecture makes
provision for:

  •  a broad base to the crown for maximum strength
  • labially and lingually tapering outline, narrowing to a relatively thin ridge
    (incisal ridge) which makes cutting easier and penetration through food

B- The posterior maxillary teeth It is possible to provide the outline of these
features within a trapezoid with the longest imperfect side representing the
cervical portion of the crown ,Theconcept lays the following basics:

  •  Since the occlusal surface is narrowed, the tooth can more easily be pushed
    into food material,
  •  If the occlusal surfaces were as wide as the bases of the crowns would
    transmit excessive masticatory forces to the roots.
  • The design makes teeth self-clean.


C- Posterior mandibular teeth:

The contours of such surfaces are somewhat rhomboidal , Compared to the bases the occlusal surfaces are constricted, The rhomboidal architecture sets out the following basics:

  •  The crown is lingually inclined that allows for proper intercuspin ,
  • Maintain the crown point and the base of both jaw teeth together,
  • Prevent competing cusps from clashing with each other(7) .

2-Root Form :

The width, shape, length, curvature, and number of roots,
concavities and direction of the periodontal fibers all affect the amount and
direction of resistance a tooth can offer to withstand the forces exerted on
it,and transmitting the occlusal forces into wide area so protect

3-Angulation Of Root And Crown: –

Lingual Inclination Of Crown Of
Lower Posterior Teeth:

Especially in premolars and molars this anatomical property is seen from the proximal aspect , The crown is angulated not only lingually to the root of the same tooth, but also to the crown of the opposing maxillary tooth as seen in the central occlusion , At the same time, parallel or even continuous are holding the axes of the teeth roots in both arches.

The porpose of this arrangement is to establish the intercusp relationship between the posterior maxillary and mandibular teeth as they are brought into centric occlusion, When the crown disturbs that relationship The axis of the cusps of both dental arches would clash , This not only loses the teeth’ smasticatory function but also disturbs the periodontium because of the cusp to cusp relationship’s elaborate traumatic occlusion(9).

Distal angulation of crown and root of permanent molars:

Those angulations
are seen from the buccal side , The distal angulation of the crown is due to or
the product of:

(I)the inclination of the occlusal surface in a mesiodistal

direction toward the cervix,

(ii) the distal length of the crown is less than that
found mesially ,The roots also tend distally in relation to the cervix of the
tooth, and thereafter such inclination is increased. Thus, the roots of the
second molars have a distal extra inclination than those of the first molars,
and the third molars have a more distal inclination than the second molars ,
The importance of distal roots and crowns inclination may be fostering
mesial teeth drift as the lower molars strike the upper molars during
functional mandibular movements.

The persistent mesial drift enters and
retains the proximal contact relationship, otherwise the teeth are separated leading to the sequelae of proximal contact loss(10).

4-Self Cleansing Ability :

It is accomplished through proper teeth form with smooth rounded surfaces , proper teeth alignment in the dental arches ,regular gingival attachments.
In addition to the tongue , lips and cheeks brushing activity, the saliva
washing effect and the fluid intake, Both of these are responsible for the best
oral and dental hygiene combined with the main influences(11).



Since once shaped teeth do not change their shape and should remain for
life, their static shape and supporting periodontium should be stable and
self-protective for them ,The physiological tooth type conforms to the
basic physical design laws in order to be functionally more effective, The
effective design for thorough function, however, should in turn secure the
maintenance of teeth in the jaw further, The periodontium includes the
investing and supporting tissues of the teeth and it consists of the
attachment apparatus and the dentogingival unit , The degeneration of the periodontium is likely to accelerate in the presence of specific intrinsic
biologic factors .


6-Garg N, Garg A. Textbook of endodontics. New Delhi: Jaypee Bros.Medical Publishers; 2010.

7-mahmod3mmar. geometric outline [Internet]. Slideshare.net. 2020[cited 14 May 2020]. Available from:

8-Chandra S. Textbook of dental and oral anatomy, physiology and occlusion with multiple choice questions. New Delhi: Jaypee Brothers Medical Publishers; 2004.


10- Berkovitz B, Moxham B, Linden R, Sloan A. Master Dentistry Volume 3 Oral Biology E-Book.

11- Walsh M, Darby M. Dental Hygiene – E-Book.