PDL

Question 1

where is the PDL

Answer 1

• is a layer of connective tissue

- surrounds root of the tooth (occupying space between cementum and bone)

Question 2

what is the PDL

Answer 2

• the main suspensory tissue of periodontium
• creates attachment between cementum and bone
• also connection with connective tissue of gingiva, explains how inflammation of gingiva can spread to PDL and destroy attachment - pockets

Question 3

what is the origin of the periodontal ligament

Answer 3

• ectoderm - mesenchyme - dental sac

Question 4

what are some physical characteristics of the PDL

Answer 4

• .12 - .33 mm in thickness
• fibrous makeup
• non elastic

Question 5

what is the organic matrix of the PDL

Answer 5

• main constituent -> fibers
• ground substance
• tissue fluid

Question 6

what is the formation of the PDL like

Answer 6

• begins developing/organizing fibres after cementum has begun
• from mesenchymal cells of the dental sac
• dental sac cells -> fibroblasts -> these cells secrete collagen fibres and eventually become the PDL fibres

Question 7

when do the fibres take their final position

Answer 7

• fibres take final position and orientation as the tooth erupts (initially arranged around tooth and parallel with root surface)
• majority of fibres from bone to cementum
• exception: cervical area – cementum to gingiva and adjacent tooth

Question 8

what other components are forming at the same time as the PDL

Answer 8

• blood vessels -> branches of the superior or inferior alveolar artery and vein - from various locations:
• enter at the bottom of the bone (bottom of the alveolar socket) continuous with blood vessels entering the pulp
• also enter PDL through openings in the bone
• lymphatic vessels follow the path of blood vessels

Question 9

what is the nerve supply for the PDL

Answer 9

• sensory nerves of the 5th cranial nerve
• from 2nd division for maxilla
• from 3rd division for mandible
• provide a sense of touch and pressure

Question 10

what are rests of malassez

Answer 10

• small groups of epithelial cells
• become located in the mature PDL
• remnants of hertwig’s epithelial root sheathe during development
• may have role in formation of cysts/tumors

Question 11

what are cementicles

Answer 11

• calcified, very small bodies cementum in the PDL

- no clinical significance

Question 12

what are osteoblasts and osteoclasts

Answer 12

• osteoblasts: bone forming cells
• osteoclasts: break down bone
• both located near bone
• cementoblasts and cementoclasts = same idea

Question 13

what are the principle fibers of the PDL

Answer 13

• large bundles of fibres
• bundles of collagenous connective tissue fibers
• individual fibers are non elastic (they work as meshwork to absorb shock)
• 7 groups according to location and orientation

Question 14

what are the 7 groups of principle fibers

Answer 14

1. free gingival fibers
2. transseptal fibers
3. alveolar crest fibers
4. horizontal fibers
5. oblique fibers
6. apical fibers
7. interradicular fibers

Question 15

what are free gingival fibers

Answer 15

• located at the cervical part of the root
• embedded at one end of the cementum - extend gingiva
• hold gingiva firmly to tooth surface
• pull taut (tightly drawn) with incisal/occlusal forces
• go around the tooth and the free gingiva
• extend into interdental papilla

Question 16

what are transseptal fibers

Answer 16

• beneath free gingival fibers
• run from cementum on one side of tooth, across alveolar crest of bone to cementum of adjacent tooth
• in between teeth – across top of bone
• only mesial and distal surfaces
• help to maintain teeth in proper relationship to each other

Question 17

what are alveolar crest fibers

Answer 17

• located at level of alveolar crest of bone to cementum
• resist horizontal movement of the tooth
• bone to cementum

Question 18

what are horizontal fibers

Answer 18

• below alveolar crest
• resist horizontal pressure applied to crown of tooth
• cementum to bone in a horizontal manner

Question 19

what are oblique fibers

Answer 19

• located in apical 1/3 of the root
• extends apically (oblique/diagonal manner) into cementum
• help resist occlusal stress
• no jamming of root tip at bottom of socket
• keeps tooth suspended

Question 20

what are apical fibers

Answer 20

• radiate around apex of tooth
• resist forces from lifting tooth out of socket
• also prevent tilting

Question 21

what are interradicular fibers

Answer 21

• in root furcation
• only on multirooted teeth
• stabilizes the tooth

Question 22

what is the clinical importance of the PDL (functions)

Answer 22

1. supportive: primary function is to attach tooth to bone
2. formative
3. resorptive
4. sensory
5. nutritive

Question 23

why is arrangement of PDL fibers important

Answer 23

• arranged so that functional pressure (normal occlusal pressure) from any direction produces a pull tension on most fibers of the PDL
• keeps tooth suspended in alveolar socket
• also creates equal distribution of forces around the tooth
• forces not directed in one area -> spread out
• strong pressure -> accidental blow to tooth
• cause damage to PDL
• stretching
• produce temporary tooth movement
• can repair itself

Question 24

what do fibroblasts do in the PDL

Answer 24

• maintain/repair PDL

Question 25

what do cementoblasts do

Answer 25

• produce cementum during tooth development and throughout life
• produce secondary cementum in adult tooth

Question 26

what do osteoblasts do

Answer 26

• proceeds or builds bone especially during orthodontics

Question 27

what is the purpose of resorption regarding the PDL

Answer 27

• normal occlusal pressure -> pull tension PDL

- tends to stimulate formation c and b

Question 28

what does excessive pressure on the PDL cause

Answer 28

• creates pressure tension
• may cause resorption of bone (osteoclasts)
• may destroy ares of the PDL and cementum (cementoclasts)
• important in orthodontics

Question 29

what is the sensory function of the PDL

Answer 29

• determines pressure and touch

- pain determined from tooth pulp

Question 30

what is the nutritive function of the PDL

Answer 30

• blood vessels present providing essential nutrients