PDL Flashcards
where is the PDL
- is a layer of connective tissue
- surrounds root of the tooth (occupying space between cementum and bone)
what is the PDL
- 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
what is the origin of the periodontal ligament
- ectoderm - mesenchyme - dental sac
what are some physical characteristics of the PDL
- .12 - .33 mm in thickness
- fibrous makeup
- non elastic
what is the organic matrix of the PDL
- main constituent -> fibers
- ground substance
- tissue fluid
what is the formation of the PDL like
- 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
when do the fibres take their final position
- 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
what other components are forming at the same time as the PDL
- 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
what is the nerve supply for the PDL
- sensory nerves of the 5th cranial nerve
- from 2nd division for maxilla
- from 3rd division for mandible
- provide a sense of touch and pressure
what are rests of malassez
- 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
what are cementicles
- calcified, very small bodies cementum in the PDL
- no clinical significance
what are osteoblasts and osteoclasts
- osteoblasts: bone forming cells
- osteoclasts: break down bone
- both located near bone
- cementoblasts and cementoclasts = same idea
what are the principle fibers of the PDL
- 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
what are the 7 groups of principle fibers
- free gingival fibers
- transseptal fibers
- alveolar crest fibers
- horizontal fibers
- oblique fibers
- apical fibers
- interradicular fibers
what are free gingival fibers
- 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
what are transseptal fibers
- 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
what are alveolar crest fibers
- located at level of alveolar crest of bone to cementum
- resist horizontal movement of the tooth
- bone to cementum
what are horizontal fibers
- below alveolar crest
- resist horizontal pressure applied to crown of tooth
- cementum to bone in a horizontal manner
what are oblique fibers
- 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
what are apical fibers
- radiate around apex of tooth
- resist forces from lifting tooth out of socket
- also prevent tilting
what are interradicular fibers
- in root furcation
- only on multirooted teeth
- stabilizes the tooth
what is the clinical importance of the PDL (functions)
- supportive: primary function is to attach tooth to bone
- formative
- resorptive
- sensory
- nutritive
why is arrangement of PDL fibers important
- 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
what do fibroblasts do in the PDL
- maintain/repair PDL
what do cementoblasts do
- produce cementum during tooth development and throughout life
- produce secondary cementum in adult tooth
what do osteoblasts do
- proceeds or builds bone especially during orthodontics
what is the purpose of resorption regarding the PDL
- normal occlusal pressure -> pull tension PDL
- tends to stimulate formation c and b
what does excessive pressure on the PDL cause
- creates pressure tension
- may cause resorption of bone (osteoclasts)
- may destroy ares of the PDL and cementum (cementoclasts)
- important in orthodontics
what is the sensory function of the PDL
- determines pressure and touch
- pain determined from tooth pulp
what is the nutritive function of the PDL
- blood vessels present providing essential nutrients
