Structure of Cementum Flashcards
Where is the alveolar bone?
What is the purpose of alveolar bone?
What does it depend on?
Boundary at the level of root apices of teeth.
- Mineralised tooth support.
- Muscle attachment
- Bone marrow
- Reservoir for ions (calcium)
- Plasticity and remodelling
Depends on:
- Tooth eruption for development and tooth retention for maintenance
- Requires functional stimuli to maintain bone mass
Are what fetal age does alveolar bone develop?
Explain how this occurs
Second month of life.
Developing tooth buds are enclosed by grooves that are open to the oral cavity.
Major portion of the alveolar process begins with root formation and eruption of the teeth.
Give details about the inside of alveolar bone
Two layers of compact (cortical) bone.
Spongey bone inside - higher SA to mass ratio. This is to make the bone lighter and to allow blood vessels&nerves to innovate.
On the inside, compact bone gives attachment to the fibres of the periodontal ligament. This is sometimes called ‘bundle bone’ due to bundles of fibres attaching from the periodontal ligament.
What are the 3 layers on the alveolar bone coming from the root outwards towards the bone?
What connects cementum to alveolar bone?
- Bone lining the alveolus (compact bone)
- Central spongiosa
- Outer cortical plates (vary in thickness, thicker in mantle than maxilla, thicker in premolar and molar regions). This makes the mandible more heavy than the maxilla.
Collagen fibres to help withstand pressures.
Explain the parts of bundle/compact bone
It is the part of the alveolar bone where periodontal ligament fibres are inserted.
There are bundles of fibres and Sharpey’s fibres (principal fibres of the periodontal ligament that are
embedded in the bone or cementum).
Sharpey’s fibres are seen perpendicular to the bundle bone.
Other fibrils are arranged parallel to the bundle bone surface.
What is lamina dura called?
Radiographically is more radiodense due to presence of thick bone without trabeculations.
What is the cribriform plate?
Alveolar bone proper has many openings for blood vessels and nerves – is perforated.
What does interradicular septum and interdental septum separate?
Interradicular - separates roots of multi-root tooth
Interdental separates two adjacent teeth.
Give the 5 features of the nerve that comes into the bottom of the tooth
- Mesencephalic sensory neurons of the trigeminal nerve
- Motor nucleus of the trigeminal
- Sensory nucleus of the trigeminal
- Spinal sensory trigeminal nucleus
- Fibres of the masticatory musculature
What are the 3 sources of blood supply to the alveolar bone?
- Peridontal
- Alveolar
- Supraperiostal/mucogingival
What are features of the two types of spongey bone found in the alveolar bone?
Type 1 - trabecular are regular and horizontal like a ladder. Seen commonly in the mandible
Type 2 - irregularly arranges delicate and numerous trabecular. Commonly seen in maxilla.
Where is the trabecular bone the most dense?
Between the teeth, where is the bone most dense?
Next to the teeth where it forms the cribiform plate.
Near the crest and least dense at the apex.
Why are there canals in the alveolar bone?
Nutrient canals are anatomic structures of the alveolar bone through which neurovascular elements transit to supply teeth and supporting structures.
What affect does tooth loss have on alveolar bone?
Degradation of the bone
Explain what injury does to the alveolar bone
Injury can lead to triggers causing building up of bone.
Initially it causes little formation and lots of absorption which can be due to inflammation.
Then during repair, bone formation peaks and bone resorption goes down.
What 5 cells regulate bone loss and deposition?
Osteoprogenitor cells: Naïve osteoblasts Osteoblasts: bone forming Osteocytes: encased osteoblasts Osteoclasts: bone degrading Bone-lining cells: regulate movement of calcium and phosphate into and out of bone
Explain some features of osteoclasts
- Large, mulinucleate cells
- Dissolve both mineral and organic matrix
- Unusual polarised morphology
- Specialised membrane areas
- Secrete unique markers
Explain resting lines and reversal lines
When bone deposition by osteoblasts is halted temporarily then resumed, a resting line is formed.
Resorption by osteoclasts results in reverse lines which are scalloped - these represent the limit of a phase of resorption on which new bone deposition has occurred.
What is cementum?
Functions?
It is a bonelike tissue which covers teeth roots.
- Joins the enamel at the cervix of the teeth
- Anchors the teeth to the bony walls of the tooth socket
- Anchors gingival and periodontal fibres
- Protects dentine
Where does cementum come from?
- Formed continuously, slowly
- Compensated for tooth wear
- Thickest at apex
- Not vascularised unlike bone
What are 3 possible places for cementoblasts to come from?
- Pulp cells (make odontoblasts which become cementoblasts)
- HERS cells: epithelial-mesenchymal transformation
- Dental follicle cells: fragmentation of HERS cells allows dental follicle to contact the dentine surface.
What is the composition of cementum?
How about bone?
65% inorganic (hydroxyapatite)
23% organic (type 1 collagen, proteoglycans, glycoproteins)
12% water
60% inorganic (hydroxyapatite)
25% organic
15% water
Cementum is harder than bone.
Give the mineral content of cementum
Enamel = 95% Dentine = 70% Cementum = 65% Bone = 60%
What are the 4 types of cementum?
What is this due to?
- Acellular, afibillar
- Acellular, extrinsic-fiber
- Cellular, intinsic-fiber
- Cellular mixed fibre
Due to the faster rate of matrix formation for cellular cementum.
Compare acellular and cellular cementum
Acellular:
No cells slow rate of deposition, close incremental lines, thin precementum layer
Cellular:
Cementocyte cells, fast rate of deposition, far apart incremental lines, thick precementum layer.
Ground section through it shows lucunae (space that cementocytes occupy) and canaliculi (channel for their processes)
Explain extrinsic and intrinsic cementum
types of fibrillar cementum
Extrinsic: fibres come from outside such as Sharpey’s fibres from the periodontal ligament perpendicular to cementum, major role in anchoring teeth
Intrinsic: fibres are produced by cementoblasts, parallel to cementum surface, found at sites undergoing repair (following resorption), does not anchor teeth
Mixed fibre contains both of these.
What are clinical considerations of alveolar bone and cementum?
- Essential for anchorage
- Protection to root dentine (preventing sensitivity) • scaling/root planing removes cementum!
- new cementum is important for new attachments
- slow deposition at apical root
- Hypercementosis (oral surgery aspect)
- Applied forces-Tooth movement and Orthodontic treatment
- Importance of quality/quantity of alveolar bone (Creating a biological base for dental implants)
