Anatomy - Week 9 PP Flashcards
What is the periodontium consist of?
The periodontium consists of..
- cementum
-periodontal ligaments
-alveolar bone
-gingival - more of a minor role
Cementum Characteristics
-part of the periodontium that attaches the teeth to the alveolar process by anchoring the periondtal ligaments (PDL)
-hard dental tissue that covers the root and joins the enamel at the CEJ
- softer than dentin
Cementum physical characteristics
colour: yellowish - clinically looks like dentin
Thickness: 1 hair (16-60 microns) in coronal half
thicker in apical half (150-200 microns)
Resistance: may be removed by brushing, decays easily
Chemical composition of cementum
65 % inorganic substance
23% organic substance (proteins)
12 % water
Histological Structure of Cementum
- Composed of a mineralized fibrous matrix and cells
- Cementoblasts (come from dental sac) ◦ Found in the periodontal ligament (PDL) ◦ Form cementum ◦ Some become embedded in the cementum –become
cementocytes ◦ The cementocytes are housed in a lacunae and have
canals (canaliculi) ◦ Canaliculi are oriented towards the PDL and have a
cementocyte process that derive nutrients for the PDL
Sharpey’s Fibers
- Ends of the fibers of the PDL that become trapped in the developing cementum
- Attach the PDL firmly to the tooth and suspend the tooth in the socket
Formation of Cementum
- Forms in Layers
◦ Cementoblasts in the PDL start at CEJ and move
downwards secreting a ground substance for the full
length of the tooth
Ground substance eventually calcifies Towards apex, cementoblasts become trapped in the calcifying
cementum making it a thicker layer - three relationships with enamel and dentin
-1. Overlaps Enamel at CEJ – 15%
-2. Meets Enamel at CEJ – 52%
-3. Does not meet Enamel at CEJ – 33%
* Cause of sensitivity
* Exposing dentinal tubules
*decided by genetics - Accellular cementum
◦ First layer of cementum deposited at the DCJ ◦ Also considered primary cementum
◦ Has no embedded cemetocytes
◦ At least one layer of acellular cementum covers the entire tooth
◦ Thin cementum in coronal ½ to 1/3 of the tooth - Cellular Cementum
◦ Sometimes called secondary cementum
◦ Apical portion of the tooth
◦ Thicker, contains cementocytes Allows for the production of more cellular cementum
Clinical Importance of Cementum
- more succeptible to decay if there is recession
- Anchors tooth to bony socket * PDL fibers suspend the tooth into the socket * Connect cementum to bone
- Through Sharpeys fibres
- No cementum
- no attachment
NO CEMENTUM = NO ATTACHMENT
Compensates for loss of enamel
* Produces intermittently throughout life of tooth
* Due to occlusion/attrition
* Adding of layers of cementum at root apex
* Keep max and mand teeth in contact/occlusion
* Very slight movement occlusally
* Causes natural gingival recession
(overeruption - when there is no opposing tooth in other arch)
Clinical Importance of cementum.. continued
-Repairs damaged tooth root
-Replaces resorbed dentin due to trauma
-Examble - 3rd molar impacted
-pushing on tooth
- can cause resorption of bone and root of tooth in front
Clinical Considerations for Cementum
-Resporption of the cementum at the apex of the roots on maxillary anteriors can occur with trauma such as with rapid orthodontic movement
- May cause tooth mobility due to root resorption
During Cementum Formation
* Hypercementosis/Cementum Hyperplasia
Thickening of cellular cementum
At the root apex Causes no problem unless being extracted
Periodontal Ligaments
The PDL is part of the periodontium that provides for the attachment of the teeth
to the surrounding alveolar bone by way of the cementum
- Connective tissue around the root of the tooth
◦ Peri = around
◦ Odontos = tooth - Main suspensory tissue of periodontium
◦ At root: cementum to bone
Sharpey’s fibers: bundles of collagen fibers
trapped in cementum
◦ At cervical of tooth: Connective tissue of gingiva
PDL Formation
Forms from the Dental Sac - process begins after cementum formation begins > Fibroblasts > Intercellular substance > collagen > periodontal ligament
PDL: Other components
- Cementoblast * Osteoblasts
- Nerves
◦ Sensory nerves Provides sense of touch - Rests of Malassez: small groups of epithelial cells
◦ Remnants of Hertwig’s root sheath during development ◦ May have a role in formation of cysts/tumors - Cementicles: small calcified bodies in the PDL
◦ No clinical significance - Specialized cells
◦ Osteoclasts, osteoblasts which react to the demands of the
adjacent environment (bone)
PDL: Principal fiber groups
- Gingival fibers
- Transseptal fibers
- Alveolar crest fibers
- Horizontal fibers
- Oblique fibers
- Apical fibers
- Interradicular fibers
Gingival Fibres
- Location: cervical part of root
- Connection: tooth to gingiva
- Extends into interdental papilla
- DO NOT insert into the alveolar bone
- Purpose: holds gingiva close to tooth
- Pulled tight with incisal/occlusal forces
- takes you from tooth to gingiva
-purpose is to hold gingiva close to tooth
-fibers extend from cementum into the gingiva
Transseptal Fibers
- Location: apical to the gingival fibers
- Only on mesial and distal surfaces
- Connection: tooth to tooth via cementum
- Purpose: ensures teeth remain in proper relationship to one another and support the
interproximal gingiva - cementum from one tooth to cementum to the next tooth
-helps keep teeth in the right positon
-No bone!
Alveolar Crest Fibres
- very top of the alveolar bone (crest means top!)
-inserts into the bone
-fibers reaching right from the cementum to the top of the bone
-purpose is to resist horizontal movements of the tooth - Location: at level of alveolar crest
- Margin of bone around tooth root * All around the tooth
- Connection: cementum to bone
- Tooth root to alveolar crest
- Purpose: resists horizontal movements and maintain tooth in socket
Horizontal Fibers
- go horizontally from cementum to bone
-resisting horizontal pressures
-just under alveolar crest fibers - Location: apical to alveolar crest fibers
- Connection: cementum to bone
- Purpose: resists horizontal (lateral) pressures applied to crown of tooth
Oblique
-Slanted fibers
-resisting up and down forces on teeth
- Location: apical to
horizontal fibers - Connection: cementum to bone
- Purpose: resist forces places on the long axis of the tooth
Apical fibers
- Location: around apex of
tooth - Connection: cementum to
bone * Purpose: * Prevent the tooth from
tipping - Resist twisting (luxation) * Protect the blood,
lymph and nerves
supply to the tooth
-closer to apices of the tooth
-right under oblique, closer or attached to apex of the tooth
-help to prevent tooth from tipping from one direction or another
-help supply nerve and blood vessels to the tooth
-help prevent twisting of the tooth
Interradicular fibers
in between the furcation of roots
- helps with stabalizing (no tipping, twisting)
-only the tooth that have two or more roots (or a furcation)
* Location: in the furcations between roots
* Connection: cementum to bone
* Tooth root to interradicular septum
* Purpose: stabilize tooth (resist tipping and tilting
PDL Functions
- Supportive
Transmits occlusal forces from teeth to the
bone allowing for small movement Shock absorption - Formative
◦ Throughout life
◦ Tension (pull) on PDL cementum+bone formation - Resorptive
* Pressure on PDL
becomes narrower
* Severe pressure can cause
* Bone resorption
* Cementum resorption
* Destroys PDL
Ortho is controllled trauma - Sensory
◦ Determines pressure and touch
Pain determined from tooth pulp - Nutritive
◦ Presence of blood vessels provide essential nutrients to area
Clinical Considerations for the Periondtal Ligament
Main purpose is to anchor tooth in socket
Maintains the gingival tissues in proper relationship to the teeth
transmits occulsal forces from the teeth to the bone (shock absorber) Cells found within contribute to the development and resorption of the hard tissues of the periodontium
Blood vessels within provide nutrients Nerve supply – sensation of pressure
Peridontal disease and PDL?
Periodontal Disease can cause destruction of the PDL fibers causing tooth mobility
Occlusal Trauma
- The PDL will widen in response to occlusal trauma
- Thickening of the lamina dura is also possible with early occlusal trauma.
- This will appear in xrays
- Clinically, occlusal trauma is noted by the late manifestation of increased mobility of the tooth.
- Clinically, occlusal trauma is also noted possibly by the presence of pathological tooth migration (PTM). If you have spacing throughout dentition it is not always due to disease but typically it is something pathological meaning it can be problematic. (Sometimes ppl have natural spacing between teeth with healthing gums, no pockets, etc)
Orthodontics
- To a lesser extent, orthodontic therapy also affects the PDL similar to its response to occlusal trauma or periodontal disease but in a more controlled manner.
- On the side under tension, the periodontal ligament space will become wider; on the side under pressure, it will become narrower.
- The interdental ligament is also responsible for the memory of tooth positioning within each dental arch.
essentially you are destroying PDL, by putting tension on it.. and build up bone on other side.. There is memory in fibers so you will have to wear a retainer to keep them from going back to original place