Cementum and PDL Flashcards
Features of cementum
- calcified tissue covering root dentine
- thickest at apex and interradicular dentine, thinnest at cervical area
- continual deposition
- avascular
- no innervation
- continuous with PDL on outer surface
Acellular vs cellular cementum
Acellular cementum is first formed while cellular cementum is secondary cementum .
Acellular cementum is in cervical half while cellular cementum is in apical one third
Acellular cementum no cells, cellular cementum contain lacunae and canaliculi which contain cementocytes
Acellular cementum slow rate of development, incremental lines close together. Cellular cementum fast rate of development
Cellular cementum has clearly demarcated border with dentine
Cellular cementum less calcified
Acellular cementum Sharpey’s fibres main component inserted perpendicular to tooth surface. Cellular cementum Sharpey’s fibres of smaller proportion parallel to root surface
Formation of cementum
Dental follicle cells exposed and adhere to hyaline layer of hopewell smith, follicular cells differentiate to form cementoblasts which produce cementum. Continuous deposition throughout life fro continual reattachment of PDL fibres
Function of cementum
Tooth attachment to PDL fibres
Support tooth
Maintain tooth height via deposition of cementum at apices to compensate for tooth attrition
Hold tooth in functional position
Repair and regeneration
Maintain integrity of root, prevent dentine resorption and strengthen root bifurcation
Different nature and origins of organic matrix in cementum
Organic matrix is derived from extrinsic and intrinsic fibres
Extrinsic fibres are sharpey fibres from the PDL, insert into cementum and continue in same direction as principal fibres, insert into acellular cementum
Intrinsic fibres derived from cementoblasts, parallel to root surface, perpendicular to extrinsic fibres. Cementoblasts in cellular cementum
Mixed fibre cementum: both present
What happens to cementum when it ages
Resorption bays due to cementum resorption, increase surface irregularity
Cementum becomes wider due to continual deposition
Clinical observation of cementum
Cementicles: small globular masses of cementum due to micro trauma
Ankylosis: fusion of alveolar bone to cementum with obliteration of PDL
Enamel pearls: small isolated enamel spheres due to stellate reticulum and stratum intermedium during HERS proliferation
Features of periodontal ligament
- richly vascular
- hourglass shaped
- reduced in non-functional or unerupted teeth
- soft
Functions of periodontal ligament
- tooth attachment: attach cementum with lamina dura
- tooth support: prevent loosening
- shock absorber: mild force force interstitial fluid out of blood vessels, moderate force absorbed by extravascular tissue fluid forced out of PDL space, heavy force absorbed by principal fibres,
- sensory: rich with nerve endings, receptors
- maintenance, repair, regeneration: undifferentiated ectomesenchymal cells
- nutritive: well vascularised to maintain cell vitality
Roles of extracellular matrix
- support and provide anchorage for cells
- regulate intercellular adhesion molecules
- regulate migration and attachment and shape
- transport nutrients and waste products
- organise cells into tissue
- production and reservoir of growth factors and hormones
Components of PDL
- collagen: highest turnover rate
- reticular fibres: type 3 collagen, form lattice
- elastic fibres: blood vessel walls
- oxytalan fibres: immature elastic fibres in PDL attached to cementum
- GAGs
- immunocompetent cells
Blood supply of periodontal ligament
Derived from superior and inferior alveolar arteries, lingual and palatine arteries from gingiva
Presence of large numbers of fewest rated capillaries
Vessels anastomose to form capillary plexus
Innervation of pdl
Sensory (nociception, pain and pressure, mechanoreceptor)
Autonomic which control blood vessel diameter
Enter root apex and move up through pdl or through misleading and cervical portion of pdl and branch through walls of alveolar bone
Pulp ages
Fewer fibroblasts
Hypofunction due to decreased width
More oxytalan
Decreased organic matrix production
Describe the 5 types of principal fibres of periodontal ligament
Alveolar crest:
Resist vertical and intrusive forces
Extend outward and apically from cementum to bone from EDJ
Oblique:
Resist vertical and intrusive forces
Extend coronally and outward from cementum to alveolar bone
Main support against masticatory forces
Horizontal:
Resist horizontal and tipping forces
Apical to alveolar crest fibres. Perpendicular to long fibres
Apical:
Resist vertical forces
Cementum at root apex to alveolar bone
Interradicular:
Resist vertical and lateral forces
Cementum to crest of interradicular bone
What happens to PDL principal fibres when they enter occlusion
As tooth erupts, oblique fibres become more obvious. Once in occlusion, cervical fibres more organised than apical portion. After some time in function, fibres follow classic orientation
What are the types of cementum (Classification)(7)
Acellular extrinsic fibre Cellular intrinsic fibre Cellular mixed stratified Acellular intrinsic fibre Mixed fibre acellular Mixed fibre cellular Afibrillar
