teeth

tooth development from embryonic layers

1. tooth development begins in the oral epithelium (ectodermal in origin.) signals exchanged between the oral epithelium and NCC derived mesenchyme underneath initiate odontogenesis

2. localised thickening of oral epithelium occurs forming the labiogingival band. this separates into the labiogingival lamina and the dental lamina.

3. thickening of dental laminae on medial aspect of the labiogingival band

4. mesenchyme underneath each laminae condenses

5. dental lamina invaginates forming the dental bud

6. dental bud expands and branches to form an enamel organ to surround a NCC derived dental papilla

7. this dental papilla enamel organ complex will form the deciduous tooth

8. a small mass of cells bud off from the dental lamina of the deciduous enamel organ, this cell cluster is the primordium of the permanent tooth.

what do the inner enamel epithelium differentiate into, how are odontoblasts derived, what does dentine and cementoblasts do?

• budding off of permanent tooth primordium continues

• inner enamel epithelium (derived from oral epithelium) differentiates into ameloblasts.

• cells in the dental papilla which are neural crest cell derived mesenchyme differentiate into odontoblasts.

• as odondoblasts lay down dentine, central part of the dental papilla remains as the pulp and the dentine surrounds the pulp and extends downwards to form tooth rot.

• later epithelial cells near distal part of tooth known as cementoblasts secrete cementum aorund tooth rot

ameloblasts

• what do they secrete

• how do they maintain contact with new unmineralised enamel

• what characteristic do they form

• what do they produce

• what happens after they erupt

secrete enamel which forms the outer covering of the tooth crown

maintain contact with new unmineralised enamel via cellular projections called thomes fibres

form crown characteristc of each tooth type

produce matrix which is not remodelled

are lost upon tooth eruption

odontoblasts- what do they do and what type of cell are they

secrete dentine which forms before enamel and induces enamel formation

columnar

role of mesenchyme, how are tooth tissues laid down

• mesenchymal cells can differentiate but have stable morphogenetic properties

• experimentally molar tooth mesenchyme and non oral ectoderm was combined resulting in a tooth shaped structure, showing that mesenchyme carries instructures for tooth morphology

• neural crest derived mesenchyme determines tooth type

• when molar mesenchyme is paired with incisor epithelium in culture the tooth that forms is a molar

• tooth tissues are laid down from the crown to the root

• tooth does not reach its final length while still embedded in jaw, achieved after eruption begins

tooth eruption- temporary

• eruption after crown is fully formed but before complete formation of the root

• eruption provides space for completion of root

• epithelial covering is continuous with gums upon eruption

• wear removed epithelium

permanent tooth eruption

• migrates into socket of temporary tooth

• increasing pressure from tooth

• resorption of temporary tooth root

• loosening

• shedding

• permanent tooth replaces

what aids tooth eruption?

• osteoclasts and odontoclasts resorb alveolar bone and root of the deciduous tooth to allow space for permanent tooth to move upward

• bone remodeling occurs to allow the tooth to move upward

• at the bottom of the developing root there is tissue fluid and blood supply which create hydrostatic pressure pushing the tooth upward as the root grows

• the periodontal ligament remodel collagen fibres and generate contractile forces to help pull the tooth upwards

Poll

dentine

• nature of production and rate

• contents

• produced continually

• rate increases during repair

• innervated

• mineralised matrix- collagen type i, dentine, specific protein

• odontoblasts recede from newly formed surfaces

• like bone but acellular

peridontal ligament

• where does it suspend tooth from

• what do the PDL fibres bridge

• shape

• what is it lined by

• suspends tooth in its alveolar socket

• fibres bridge alveolar bone and cementum

• shaped to accomodate tooth root-may be branched

• lined by compact bone

cementum

• what does it surround

• properties

• what collagen

• surrounds dentine of root

• mostly acellular

• not readily resorbed

• type i collagen

• not remodelled

can alveolar bone be remodelled

yes

what is the furcation angle

point where roots diverge in teeth with two or more roots

where does the crown meet the root

cemento enamel junction

what does the enamel consist of

hexagonal prisms or rods of hydroxyapatite crystals held together by cementing organic matrix

pulp

• connective tissue, nerves, lymph, blood vessels, collagen and undifferentiated reserve mesenchymal cells

what causes dentine to be sensitie to pain

Odontoblasts line the pulp cavity and branch into the dentine tubules. These branches, together with the fine nerve endings, cause the dentine to be sensitive to temperature and pain.

The odontoblasts lay down dentine and reduce the pulp cavity in size as the animal ages.

dangers to pulp

• Physical trauma: may cause bruising, haemorrhage or pulpitis.

• Accidental over-heating from polishing or scaling: may cause pulp necrosis.

• Pulp exposure after tooth fracture: may cause pulpitis and possibly pulp necrosis.

• Loss of blood supply following trauma: will cause ischaemic necrosis

dentine tubu;e

• extends from external surface to the pulp

• can transmit pain to pulp if the dentine is exposed

primary dentine

forms before tooth eruption

secondary dentine

forms after eruption

develops from odontoblasts living within pulp and laid down in layers within pulp cavity

reparative/tertiary dentine

forms as a result of trauma to the odontoblasts- can be thermal, chemical, bacterial, mechanical

few tubules and darker and dense

cribiform plate

densest bone that lines the alveolus

it may be seen radiograpically as a white line called lamina dura

periodontal ligament

• what is it comprised of

• where does it insert

• 3 type

• comprised of taut collagen fibre bundles called sharpeys fibres- inserted into cementum and alveolar bone which are anchored to cementum of tooth and alveolar bone

• gingival, trans septal and alveolodental fibres

• blood vessels within periodontal ligament which are evenly dstributed

• nerves capable of transmitting heat cold pain and pressre

cementum

• what does it cover

• what does it provide a point of attachment for

• what is the composition similar to

• how is it nourished

• covers the enamel free root

• provides a point of attachment for periodontal ligament

• similar in composition to woven bone

• capable of formation, destruction and repar

• remodels continually throughout life

• nourished from vessels within periodontal ligament

gingival sulcus

• sulcus lining epitheium (junctional epithelium) renews more rapidly than oral

• bathed in crevicular fluid which contains antibodies, neutrophils, lymphocytes

• depth of more than 4mm in dogs is dangerous- sign of active disease and attachment loss

interdental papilla

• prevents impaction of food and devris between closely adjaent teeth

• should be preserved during surgery

• when viewed from coronal aspect there is an indentation called the col (the epithelium of this is not keratanised)

junctional epithelium

• where is it located

• why is it important

• what does it attach, and using what

• where is the apical extent of it

• bottom of the sulcus

• important in control of periodontal disease

• attaches the gingival tissues to the tooth using hemidesmosomes

• apical extent usually the cemento enamel juncion

what does the free gingiva suround

surrounds the crown of the tooth

cemento enamel junction

• between anatomical root and crown

• not visible in health

• so sight indicates recession of attachment of tooth

attached gingiva

• what does it adhere to and how

• properties

• tightly adherent to subgingival connective tissue and bone via deep rete pegs

• keratinised- withstand stress and ripping and tearing food

mucogingival junction

• properties

• reasons why is might change in height

• between mucus membrane of the oral cavity and gingiva

• remains stationary throughout life

• may change in height de to hyperplasia, recession or attachment loss

function of the alveolar bone

provide structural support to the root

gingival fibres

• where are they

• where do they extend

• what do they do

• in the gingiva above the alveolar crest

• extend from cementum into gingival tissue

• attach gingiva to tooth and bone

transseptal fibres

• run interdentally

• extend from cementum of one tooth to cementum of adjacent, over the alveolar crest

• maintain tooth to tooth alignment

• stabilise the dental arch

alveolodental fibres

• where do they run

• what do they do

• what do they attach

• true periodontal ligament fibres

• run between cementum and alveolar bone

• attach tooth to the alveolar bone

• absorb and distribute occlusal force during chewing