Pdl

Question 1

Names of pdl

Answer 1

Other terms previously used for PDL are “Desmodont, Gomphosis, Pericementum, Dental periosteum, Alveolo dental ligament & periodontal membrane

Question 2

Dimensions of pdl

Answer 2

The PDL space ranges in width from 0.15 to 0.38 mm (in humans), with its thinnest portion around the middle third of the root; its thickness varies from tooth to tooth and shows a progressive decrease with age. The PDL of primary teeth is wider than those found in permanent teeth. The PDL appears on radiographs as a radiolucent area between the radiopaque lamina dura of the alveolar bone proper and the radiopaque cementum

Question 3

Notes on development of pdl

Answer 3

• tissue around follicle is called perifollicular mesenchyme
• stem cells of follicle give rise t to osteoblast cementoblast and fibroblast

-After tooth eruption these fibers become oriented in a characteristic fashion and gradually thickened as the tooth comes to function (

Question 4

Chch of any formative cell

Answer 4

by having an open faced or vesicular nucleus with prominent nucleoli, well developed rough endopla

Question 5

Fibroblast of pdl

Answer 5

1. They are the principal cells of the PDL. They constitute about 65% of total cell population.
2. They are large stellate shaped cells with an extensive cytoplasm containing most of the organelles associated with protein synthesis and secretion (Fig. 5).
3. They have a well-developed cytoskeleton with a prominent actin network indicating its functional demands requiring change in shape and migration.
4. They show cell to cell contacts (adherens and gap junction type).
5. The fibroblast produces collagen, reticulin and oxytalan fibers (collagen synthesis produced when the tropocollagen molecule released by fibroblasts as three polypeptide chains intertwined to form helix. Then, tropocollagen molecules are aggregated longitudinally to form microfibrils, which are subsequently arranged laterally to form collagen fibrils (Fig. 6).
   Figure 6: Diagram showing synthesis of collagen fibers.
6. Also, they are found to synthesize higher quantities of chondroitin sulphate.
7. They are aligned along the general direction of the fiber bundles with processes wrap around the fiber bundles.
8. They are capable of synthesizing and degrading collagen (dual function), because of the high rate of turnover of collagen in the ligament, any interference with fibroblast function by disease produces a loss of the supporting tissue of a tooth.
9. The renewal capability is an important characteristic of PDL (The damaged periodontal fibers are replaced and remodeled by newly formed fibers).
10. Fibroblasts are morphologically heterogeneous with diverse appearances depending on their location and activity.

Question 6

The coverage of the pdl side of alveolar bone is periosteum or endosteum

Answer 6

3. The osteoblasts cover the periodontal surface of alveolar bone. As the alveolar bone constitute a
   6PERIODONTAL LIGAMENT
   modified endosteum and not a periosteum (a periosteum comprises at least two distinct layers: inner cellular layer and outer fibrous layer), a cellular, but not an outer fibrous layer is present on the periodontal surface of alveolar bone.

Question 7

Osteoclast origin

Answer 7

Osteoclasts derived from circulating monocytes in the blood. These in turn are derived from the bone marrow.

Question 8

Osteoclast is not only in a lacunae how?

Answer 8

In the LM, the cells appear to occupy bays in bone (Howship’s lacunae) or surround the end of bone spicule.

Question 9

Organelles of osteoclast

Answer 9

In the EM, they exhibit numerous mitochondria, lysosomes, abundant Golgi saccules, free ribosomes and little rough endoplasmic reticulum.

Question 10

Origin and nuclei of cementoclast

Answer 10

They are mononuclear or multinucleated giant cells that are derived from monocytes,

Question 11

Em of epi rests of malasez

Answer 11

In EM, they exhibit tonofilaments, they are attached to each other by desmosome and they are isolated from the connective tissue cells by a basal lamina (Fig

Question 12

Ground substance of pdl

Answer 12

Ground substance i. The space between cells, fibers, blood vessels, and nerves in the PDL is occupied by ground substance.

ii. It is an amorphous background material that binds tissue and fluids.
iii. It is made up of two major groups of substances, proteoglycans and glycoproteins (fibronectin, tenascin). Both are composed of proteins and polysaccharides but of different type and arrangement.
iv. The proteoglycans are compounds containing anionic polysaccharides (glycosaminoglycans) covalently attached to a protein core.
v. The PDL ground substance has been estimated to be 70% water and is thought to have a significant effect on the ability of the tooth to withstand stresses.
vi. All the anabolic and catabolic substances pass through the ground substance.
vii. Proteoglycans and glycoproteins are demonstrated histochemically by a dye or as electron dense material under electron microscope.

Question 13

EM vs LM of collagen

Answer 13

The collagen fibrils of PDL when examined by EM are seen to be gathered together to form fibers and when examined in LM many of the collagen fibers are found to be gathered into bundles and these are termed principal fibers.

Question 14

Is collagen attached to any molecules?

Answer 14

to which is attached some sugars and glycoprotein.

Question 15

Interdental ligament

Answer 15

Formed of the trans septal fibers

Question 16

After pdl disease what happens to trans septal fibers

Answer 16

This group reconstructed even after destruction of the alveolar bone has occurred in periodontal disease.

Question 17

Type of pdl fibers that don’t occur in incompletely formed root

Answer 17

Apical group

Question 18

Dentogingival fibers

Answer 18

These fibers extend from the cervical cementum to the lamina propria of both free and attached gingiva.

Question 19

Circular fibers

Answer 19

This small group of fibers form a band around the neck of the tooth interlacing with other groups of fibers in the free gingiva helping to bind it to the tooth.

Question 20

Dentoperiosteal group

Answer 20

Run apically from the cementum over the periosteum of the outer cortical plate of the alveolar process and insert into the alveolar process or the vestibular muscle and floor of the mouth.

Question 21

Accessory fibers

Answer 21

They are collagenous in nature. They run from the cementum in different planes more tangentially to prevent rotation of the tooth and they are found in the horizontal group region.

Question 22

Functions of each fiber group

Answer 22

• accessory— prevent rot
• alv crest — extrusion and lat.
• horizontal— lat mov
• oblique — apical
• apical — protect bv and prevent tipping and lux
• inter radicular— prevent v and horizontal movement

Question 23

2. Oxytalan fibers

Answer 23

a. They are considered as a type of elastic fibers, only Oxytalan fibers are present within the PDL while the mature elastic fibers are not found in PDL and found in the wall of the blood vessels only.
b. These fibers run vertically from the cementum of the root apically forming a meshwork that surround the root and terminates in the wall of blood vessels.
c. They are numerous and dense in the cervical region of the ligament where they run parallel to the gingival fibers.
d. There function is to regulate vascular flow in relation to tooth function and prevent the sudden closure of the blood vessels under masticatory forces.

Question 24

Blood vessels of pdl

Answer 24

• gingival vessels
• apical vessels
• intra alveolar vessels

Question 25

The arterioles and capillaries of the PDL form a network which is more evident at …

Answer 25

the apex and in the cervical part of the ligament.

Question 26

Veins of pdl

Answer 26

The venous vessels tend to run axially to drain to the apex.

Question 27

mechanoreceptors

Answer 27

mechanoreceptors such as knoblike, spindle-like and meissner-like.

Question 28

Pdl n direction

Answer 28

Nerves which are usually associated with blood vessels pass through the apical foramen to enter the PDL space, while running toward the cervix they branch and run both apically and coronally.

Question 29

Pdl n diameter and function

Answer 29

The nerve fibers are either of large diameter and myelinated or of small diameter which may or may not be myelinated.
19PERIODONTAL LIGAMENT
c. The small diameter fibers are concerned with pain and end in fine branches while large diameter fibers are concerned with touch and pressure and terminate in a variety ending known as mechanoreceptors such as knoblike, spindle-like and meissner-like.

Question 30

3. Lymphatics of pdl

Answer 30

a. A network of lymphatic vessels following the path of the blood vessels provides the lymph drainage of the PDL.
b. The flow is from the ligament toward and into the adjacent alveolar bone.

Question 31

Cementicles

Answer 31

• multiple or single
• may fuse to cementum causing excementosis or may be free
• free attached or embedded
• same mineralisation as cementum
• nidus is degenerated epi or rests or haemorrhage
• due to aging or at area of trauma

Question 32

Supportive function of pdl

Answer 32

In the pressure side, the alveolar bone will be resorbed while in tension side the alveolar bone will be deposited allowing physiologic tooth movement.
b. PDL permit the tooth to withstand forces of mastication, as the wavy course of the collagen fibers gradually straighten out acting as inelastic string transmitting tension to the wall of the alveolus.
c. PDL fibers being non elastic prevent the tooth from being moved too far.
2.
d. The collagen fibers and the ground substances act as a cushion, also blood vessels and all other components act together as a hydraulic damper or shock absorber.

Question 33

Sensory function of pdl

Answer 33

a. The PDL acts as sensory receptor which is necessary for proper positioning of the jaws during normal function.
b. Its mechanoreceptors which are sensitive to touch and pressure are involved in the neurological control of mastication.
c. It protects both the supportive structure of the tooth and the
substances of the crown from sudden overload by the proprioceptive reflex as it inhibits the activity of the masticatory muscles opening the mouth at once to relive the pressure.

Question 34

Nutritive function of pdl

Answer 34

a. The blood vessels of the PDL provide nutrition to the cells of peridontium and also remove the waste product.

Question 35

Formative function of pdl

Answer 35

a. The fibroblasts are responsible for the formation of new PDL fibers and dissolution of the old fibers.
b. The PDL cells produce the cementoblast forming the new cementum and osteoblast forming the bone.

Question 36

Protective function of pdl

Answer 36

a. Principle fibers: they are arranged in different direction to counteract any force applied to the tooth and convert it into tension to prevent bone resorption.
b. Blood capillaries: they have a specific arrangement in the form of coils attached to the cementum via Oxytalan fibers, this arrangement prevent the blood from being escaped immediately from the capillaries when pressure is exerted on the tooth.
c. The nerves: their protective function is attained by its mechanoreceptors.

Question 37

Homeostatic function of pdl

Answer 37

a. The cells of PDL synthesize and resorb extracellular substances of connective tissue of ligament, alveolar bone, and cementum.
b. There is continuous remodeling of alveolar bone as well as PDL. c. The collagen of the PDL is turned over at a rate faster than any other connective tissue in the body, the cells in the bone half of the PDL may be more active than those on cementum side.

Question 38

The PDL through aging shows

Answer 38

1.
Decrease in vascularity, mitotic activity and number of its cells. 2.
3. 4.
Decrease in number of collagen fibers and increase in arteriosclerotic changes.
Decrease in width due to its orientation to compensate mesial drift. May contain Cementicles.

Question 39

Clinical considerations of pdl

Answer 39

Clinical considerations

1. The primary role of the PDL is to support the tooth in the bony socket; the thickness of PDL varies in different individuals, in different teeth in the same person and in different locations on the same tooth. The thickness of the PDL is maintained by the functional movements of the tooth.
2. For practice of restorative dentistry, the supporting tissues of a tooth out of function can’t withstand the load suddenly placed on it by a restoration indicating the inability of patient to use the restoration immediately.
3. Acute trauma to the PDL may produce pathologic changes such as fractures or resorption of cementum, tear of fibers, haemorrhage, necrosis, resorption of the adjacent alveolar bone, widening of the ligaments and the tooth become loose.
4. Orthodontic tooth movement depends on resorption and formation of both bone and PDL, when the tooth move within its physiologic limit initial compression of PDL is compensated by bone resorption while on the tension side bone apposition occur.
5. Inflammatory diseases of the pulp progress to the apical PDL and replace its fibers with granulation tissue this lesion is called dental granuloma which may contain epithelial cells that undergo proliferation and produce a cyst.
6. Gingivitis if not controlled periodontitis may develop and the destruction may extend to PDL and bone which are very difficult to regenerate.