Theme II: Part 2 Flashcards
How does the PDL develop and form. Are there more fibers in cementum or bone
- After induction of dentine formation, HERS stretches and disintegrates and dental follicle cells differentiate into cementoblasts, fibroblasts and osteoblasts.
- cementum and bone form with a ligament space in between. Short fibre bundles emerge from these tissues and form a continuous attachment to each other.
- Cementum: there are more fibres and closely spaced. Thinner.
- Bone: fewer, thicker and spaced wider
Functions of the PDL
- Tooth attachment: Mineralised sharpey’s fibres from cementum and bone insert here
- Withstands forces of mastication acting as a shock absorber
- Remodels to reposition teeth to achieve occlusion
- Nutritive: highly vascular
- Senses pain and tension
Which type of PDL fibers develop first. Where do they insert
-Alveolar crest fibres form first. From CEJ to rim of alveolus
-Develop obliquely then horizontal then oblique again
[- As the root forms, fibre formation proceeds apically.]
Describe the 5 PDL fibre groups and their functions. Which is most abundant
- Alveolar crest fibres: resist extrusive forces
- Horizontal fibres: resist horizontal tipping forces
- Oblique fibres: Resist intrusive compressive forces
- Apical fibres: resists extrusive forces
- Interradicular fibres: (only when multiple roots) Resist extrusive forces
-Oblique are most abundant
What is the PDL composed of. Cell types and ECM
-Fibroblasts, osteoclasts, osteoblasts, cementoblasts, cementoclasts, Rests of Malassez, mesenchymal stem cells, immune cells
- 60% ground substance (ECM): glycosaminoglycans (hyaluronic acid) proteoglycans and glycoproteins that bind water and ions for shock absorption.
- Collagen fibres (I & III). Fibronectin attaches cells to collagen fibrils for migration and wound healing
- Elastic fibres (oxytalan) containing fibrillin but no elastin. Regulate blood flow. Perpendicular to collagen fibres
What do fibroblasts in the PDL do. What are perivascular and endosteal fibroblasts
- Secrete collagen fibrils, growth factors and ground substance.
- Remodel the PDL
- Possible role in eruption: mechanical forces acting on the collagen mediate onto the fibroblasts which then contract.
- Functional in tooth movements: mesial and vertical tooth drift
- Perivascular: around vessels
- Endosteal: align along the bone
What arteries supply the PDL. What unique capillaries are present and why
- Branches of Superior and inferior alveolar arteries through apex
- Interalveolar vessels through the alveolar process
- Branches of the lingual and palatine arteries entering through the gingiva
- Interstitial areas are usually located near the bone and contain neuromuscular bundles.
-Fenestrated capillaries are usually not in connective tissue but are in PDL to increase diffusion capacity. As high metabolic rate of PDL requires larger molecules.
How PDL changes with age. When remodelling occurs
- Thickness decreases. More fibrotic, less cells
- Loss of bone and decreased function decreases its thickness.
- Hyaluronic acid decreases. Proteoglycan increases
-Remodelling is induced by mastication which increases thickness. Thickest in areas under tension, compared to compression
Innervation of the PDL. How it compares in incisor and molars
- Myelinated sensory afferent fibers sense pain (free nerve endings) and pressure (Ruffini’s corpuscles)
- Autonomic fibres regulate blood flow
-Denser innervation in upper incisors, as this is where initial contact with food is so requires more sensation as more force
Function of the 2 types of collagen in PDL
- Type I (80%): forms the fibre bundles
- Type III (15%): from reticular bundles that crosslink to form a collagen meshwork that supports vessels when PDL is compressed, and also interact with platelets to form clots
What is an osteon and its structure. What is an osteocyte
- Osteon= cylinder units of bone. Consist of central Heversian canal with a capillary in it, surrounded by 3 layers of lamellar bone (circumferential, concentric, interstitial)
- Adjacent canals connected by Volkmann’s canals.
- osteoblasts align the canal. They enter the inside of the osteon through the blood vessel and produce bone matrix that is later mineralised to bone.
-When osteoblasts become trapped in the bone it is termed an osteocyte
What is Bundle bone and lamellar bone
- Bundle bone is always found near the PDL, where sharpey’s fibers insert. Constantly remodelled in response to tooth movements.
- Regions further away from the PDL consist of lamellar bone that forms the majority of the alveolar process.
Howship’s lacunae
- Bone remodelling at the reversal stage.
- Osteoclasts have stopped resorbing bone and have disappeared from the region, leaving behind resorption bays termed Howship’s lacunae.
What happens to the PDL and bone when you tap your tooth. What is the piezoelectric effect
- The force lasts less than second
- PDL incompressible
- Alveolar bends due to the Piezoelectric signal: the force causes a movement of electrons causing a short flow of current. Bone bends to prevent atrophy.
What happens to blood flow in the PDL in areas under tension and in compression
- Tension/ stretching= blood flow increases, vasodilation
- Compresssion/ under pressure= vessels occluded so decreases in blood flow. Cell death
Difference in response to heavy and light orthodontic forces
- Light= slow continuous tooth movement by remodelling of bone so less destructive. Discourages resorption. Takes about 2 days.
- Heavy= Movement occurs in steps, by undermining resorption. Takes 7-14 days.
What are the 5 types of tooth movements. What takes the most and least force. What are the forces required
- Intrusion (force concentrated on apex) -15-25g
- Tipping: 50-75
- Rotation: 50-100
- Extrusion: (pulling out, tension on PDL) 50-100
- Translation: whole tooth moves side ways through the bone with PDL uniformly loaded 100- 150
Adverse effects of orthodontic forces
- Compressed pulp causing transient inflammation leading to discomfort or even loss of vitality
- Excessive root resorption causing thin and distorted roots
- PDL can damage if existing periodontal disease
What are the main afferent nerve endings in the PDL
- Free-ending: sense pain and pressure. Unmyelinated
- Ruffini’s corpuscles: sense pressure. Myelinated
What is endochondral and intramembranous bone. Which bone type is alveolar bone
1-Endochondral ossification occurs where chondrocytes make cartilage which is then replaced by bone. =in long bones
2-Intramembranous: Mesenchymal cells in the periosteum differentiate into osteoblasts which make bone = alveolar bone
What are the different bone types and layers in alveolar bone
- Dense outer layer= compact/ cortical bone:
- 3 lamellae layers with Haversian canals in the centre, and numerous vascular Volkmann’s canals passing to PDL - Cancellous/ trabecular bone (air filled)
- Alveolar/ cribriform plate: lining the socket (compact)
4: alveolar crest: upper most outer portion
Composition of alveolar bone. Functions of some proteins
- mineralised living connective tissue
- type 1 collagen
- Non-collagenous proteins:
1. proteoglycans: bind to collagen, role in mineralisation.
2. glycoproteins
3. osteocalcins: bind to Ca and collagen so role in mineralisation - Inorganic = HA, deposited by collagen
- Osteoblasts, osteoclasts, osteocytes
Function of alveolar bone
- support teeth roots, protection, locomotion, mineral reservoir, attachment for muscles and tendons, remodelling
- regulating metabolic processes, regulating Ca and PO4
What molecules control formation and resorption of bone
- Formaiton = calcitonin, vit D, oestrogen
- Resorption= PTH, glucocorticoids
What is periosteum and endosteum
- Periosteum: connective tissue membrane surrounding bone
- Endosteum= loose connective tissue lining the inside of medullary cavity, separating bone and marrow
What are osteoclasts, osteoblasts and osteocytes. [Where they are derived from, where they are found, what they make, and what they do]
- Osteoblasts: from mesenchymal cells in follicle.
- Active are cuboidal, inactive are flat.
- Sit on bone surface producing bone matrix.
- Make alkaline phosphatase which promotes mineralisation and produce growth factors for bone repair.
- Osteoclasts: from monocytes. Produce howship’s lacunae during bone Resorption. Produce acid phosphatase to demineralise, and lysosomal enzymes to degrade.
- osteocytes: osteoblasts trapped in bone matrix with a lacunae chamber and communicate via canaliculi processes. Detect load. 90% of bone cells.
Different stages of alveolar process development in utero
- Mesenchymal cells make osteoblasts which secrete bone
- Mandible initially makes a trough shape underneath the inferior alveolar nerve and tooth germ
- Process grows upwards and almost surrounds the incisor germ. IAN is enclosed in bony canal
- to make room for the growing germ and stellate reticulum, inner bone is resorbed and is deposited on the outside.
Describe some examples of bone defects. Perioapical abscess, infraocclusion, alveolar osteitis, ankylosis, sinus perforation
- Bone resorption from chronic periodontal disease or extraction makes implants difficult as unsupported
- Ankylosis: fusion of bone to root due to trauma or infection. No exfoliation
- Infraocclusion: further growth of bone during ankylosis submerges the tooth causing malocclusion or PDL issues if not extracted
- Periapical abscess: (pus at root apex) Noticed on Xray if lamina dura (alveolar plate) is interrupted
- Alveolar osteitis: socket should fill with blood after extraction, however the clot can detach and expose the bone causing inflammation
- Maxillary sinus perforation: during extraction roots can fracture the sinus floor causing a fistula between sinus and oral cavity and lead to infection.
What are the stages of bone remodelling. What happens during tooth drift
- Occurs during mesial drift (inter proximal tooth wear) or orthodontic treatment resorption and deposition is needed
- On Alveolar (inner) and cortical (outer) plates
- Resting stage: inactive osteoblasts are flat
- Resorption: migration and activation of osteoclasts to create space where tooth is moving to, to remove excess bone
- Formation: cuboidal active osteoblasts make bone to fill gaps and compensate loss
Difference between resting and reversal lines in bone
- Resting line: Pauses in bone deposition. Straighter and less pronounced.
- Reversal line: pronounced wavy lines in bone indicating increase in production of bone. A change from bone resorption to deposition has occurred here.
Where is the lamellar bone the thickest
Thickest on buccal aspect of mandibular premolars and molars
