Periodontium Flashcards
What is the role of the periodontium?
- retain tooth in socket
- resist masticatory loads
- defensive barrier, protecting tissues against threats from oral environment
What is the periodontium composed of?
Cementum
Gingiva
Alveolar bone
Periodontal ligament
What is unique about the periodontium?
The only breach in the body’s surface is where the teeth pass through the oral epithelium
What is the junctional epithelium?
A physical barrier separating the body tissues from the oral environment
What are periodontal diseases divided into?
Diseases of the gingiva alone
Diseases of all the periodontal tissues
What are periodontal diseases divided into?
Diseases of the gingiva alone
Diseases of all the periodontal tissues
What are properties of cementum?
Covers root dentine
Similar in structure to bone
-Collagen matrix
-Lamellar arrangement
Provides attachment for some periodontal fibres
Laid down by cementocytes
What are the two types of cementum?
Acellular
Cellular
What are the properties of acellular cementum/extrinsic fibre?
No cells
Usually adjacent to dentine
First formed (primary cementum)
Contain collagen fibres from PDL (sharpeys fibres)
Present on cervical 2/3 of root
What are the properties of cellular cementum/intrinsic fibre?
Contains cementocytes
Later formed (secondary cementum)
Present in the apical part of the root and in furcation regions
Normal collagen fibres present
No role in tooth attachment
May represent a transitional form
What are the properties of the alveolar bone?
Similar to bone elsewhere in the body
Cortical (compact) plate forms inner lining of tooth socket
Inner cancellous bone containing marrow
Provides attachment for PDL fibres (sharpeys)
Has nutrient canals (volkmanns)
Supports the tooth
What happens to alveolar bone when teeth are lost?
Alveolar process is resorbed leaving a residual ridge
What part of the alveolar bone shows in radiographs?
Lamina dura
What perforates the inner cortical bone?
Nutrient Formina
What type of tissue is the PDL?
Fibrous connective tissue (derived from dental follicle)
What does the PDL contain?
Cells
Extracellular Matrix
Fibres
Nerves
Blood vessels
What is the ground substance of PDL made of and how does it behave?
Hyaluronate GAGs
Glycoproteins (fibronectin)
Proteoglycans (proteodermatan sulphate, dermatan sulphate, chondritin sulphate)
Behaves as a viscoelastic gel
What cells are present in PDL?
Fibroblasts
Cementoblasts
Osteoclasts and cementoclasts
Immune cells
Debris of malassez (epithelial cells)
What sensory nerves are present in the PDL?
Mechanoreceptors (a- beta, a- delta fibres)
Nociceptors (a-delta, C fibres)
What are the qualities of the mechanoreceptors?
Rapidly or slowly adapting
Proprioception; chewing control
What are the qualities of the nociceptors?
Protective reflexes; inhibit jaw elevator motor neurones
What are the autonomic nerves of the PDL
Sympathetic
For blood vessel control -vasoconstriction
What is the blood supply of the PDL?
Inferior/ superior alveolar arteries passing into PDL from alveolar bone
Lingual and palatine arteries supplying gingivae
What are the two types of PDL fibres?
True PDL fibres
Gingival ligament fibres
What are the true fibres?
Fibres connecting tooth to bone at or apical to alveolar crest
What are the gingival fibres?
Fibres mainly above the alveolar crest including free gingival fibres
What is the role of the PDL?
Attaches tooth to jaw
Transmits biting forces to alveolar bone
Organised regular connected tissue
What is the width of the PDL?
0.2mm
What are the fibres present in PDL
Collagen (types 1 and 3)
Oxytalan
What is the role of each fibres?
Collagen = principal fibres found in true periodontal ligament, support tooth in load bearing
Oxytalan = present in human PDL, function is uncertain
What are the fibre groups found in the alveolo-dental ligament? (In the tooth)
Alveolar crest
Horizontal
Oblique
Apical
Inter radicular (between roots of tooth)
What are fibres found in the interdental ligament (between teeth)?
Transseptal
What are the fibres found in the gingiva and where are the present?
Support the free gingiva
Present in lamina propria in marginal gingiva
-dento-gingival
-alveolo-gingival
-dentó-periosteal
-circular
What is the crevicular epithelium (oral sulcular epithelium)?
Epithelium that covers the sulcus. It is not attached to enamel (between the junctional epithelium and the gingival epithelium)
What is the junctional epithelium?
Epithelium that is attached to the enamel/tooth
What is the enamel cuticle?
Demineralised coating of enamel. Covers tooth once it has erupted by is worn away by mastication and cleaning
What are the histológicas features of the junctional epithelium?
Has gap junctions, hemidesmosomes, desmosomes
Has two basal laminas - one near the enamel, one near the lamina propria
What is the inter-dental col?
Non keratinised epithelium that in the Inter proximal valley between two teeth
What forces is the PDL subjected to?
Mastication
Swallowing
Speech
Para function (clenching, grinding)
What are horizontal, extrusive forces that the PDL is rarely subjected to?
Sticky foods
Orthodontic forces
What happens to a tooth when a load is applied initially?
Displaced initially into the socket
What happens to loading after a bit?
After the initial elastic component, viscous creep happens due to the viscoelastic properties of PDL
What happens in PDL during loading?
Tension in PDL fibres
Compression of ECF
In a displacement graph, what happens under disease conditions for the PDL?
Movement becomes linear
In which direction do the principal oblique fibres lie, relative to the alveolar bone and cementum?
They attach to the cementum apically and to the bone cervically
This arrangement facilitates the transfer of forces, applied to the tooth, to be absorbed to the bone.
What is the main protein in the principal (Sharpey’s) fibres?
Collagen, types I and III
What types of cementum can you see in the root of the tooth?
Acellular extrinsic
Cellular intrinsic
In which part of the root the cementum is thicker?
Apical part of the root
The shape of principal oblique fibres are?
Wavy
What cells lie in the cementum surface?
Cementocytes
What is the main cell type at the centre of the periodontal ligament ?
Fibroblasts
On which side of the periodontal ligament are the Sharpey fibres bundled more closely?
At the cementum
What is the name of these clusters of epithelial cells found near cementum?
Rests of malassez
What are the epithelial cells found in periodontal ligament responsible for?
Periaapical cyst
