Oral Anatomy & Histology (Review: Outcome 8) Flashcards
What structures make up the Periodontium?
- Cementum
- Periodontal ligaments
- Alveolar bone
- Gingiva (more of a minor role)
Cementum
- Part of the periodontium that attaches the teeth to the alveolar process by anchoring the periodontal ligaments (PDL)
- Hard dental tissue that covers the root and joins the enamel at the CEJ
What is the chemical composition of cementum?
65% - inorganic substance
23% - organic substance (proteins)
12% - water
Physical characteristics of cementum
1) Colour
- yellowish (clinically looks like dentin)
2) Thickness
- 1 hair (16-60 microns) in coronal half
- thicker in apical half
3) Resistance
- may be removed by brushing
- decays easily
Histological structure of Cementum
i. Composed of mineralized fibrous matrix and cells
ii. Cementoblasts (come from dental sac)
- found in the periodontal ligament (PDL)
- form cementum
- some become embedded in the cementum (become cementocytes = cementum cells)
- 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
1) Forms in layers
- cementoblasts in the PDL start at CEL and move downwards secreting a ground substance for the full length of the root
- ground substance eventually calcifies
- towards apex, cementoblasts become trapped in the calcifying cementum, making it a thick layer
2) 3 relationships with enamel and dentin
i. overlaps enamel at CEJ - 15%
ii. meets enamel at CEJ - 52%
iii. does not meet enamel at CEJ - 33%
- cause of sensitivity
- exposing dentinal tubules
See image on powerpoint
3) Acellular 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 1/2 to 1/3 of the tooth
4) Cellular Cementum
- sometimes called secondary cementum
- apical portion of the tooth
- thicker, contains cementocytes
- allows for production of more cellular cementum
See image on powerpoint
Clinical importance of cementum
1) Anchors tooth to bony socket
- PDL fibers suspend the tooth into the socket
- connect cementum to bone (through Sharpey’s fibres)
- no cementum (no attachment)
2) Compensates for loss of enamel
i. produces intermittently throughout life of tooth
- due to occlusion/attrition
- adding of layers of cementum at root apex
ii. keep max. and mand. teeth in contact/occlusion
- very slight movement
- causes natural gingival recession (overeruption)
3) Repairs damaged tooth root
- replaces resorbed dentin due to trauma
- ex. 3rd molar impacted
- pushing on tooth
- can cause resorption of bone and root of tooth in front
Clinical Considerations for Cementum
1) Resorption 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
2) During cementum formation
Hypercementosis/Cementum Hyperplasia
- thickening of cellular cementum
- at the root apex
- causes no problem unless being extracted
Periodontal Ligament (PDL)
- Part of the periodontium that provides for the attachment of the teeth to the surround alveolar bone by way of cementum
- Connective tissue around the root of the tooth
(peri = around; odontos = tooth) - Main suspensory tissue of periodontium
i. At root: cementum to bone (Sharpey’s fibers: bundles of collagen fibers trapped in cementum)
ii. At cervical of tooth: connective tissue of gingiva
Formation of PDL
i. Forms from the Dental Sac
- process begins after cementum formation begins
ii. Fibroblasts
iii. Intercellular substance
iv. Collagen
v. Periodontal ligament
Other components of PDL
- 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)
Principle Fiber Groups of PDL
- Gingival fibers
- Transseptal fibers
- Alveolar crest fibers
- Horizontal fibers
- Oblique fibers
- Apical fibers
- Interradicular fibers
Gingival Fibres
i. Location:
- cervical part of root
ii. Connection: tooth to gingiva
- extends into interdental papilla
- do not insert into the alveolar bone
iii. Purpose: holds gingiva close to tooth
- pulled tight with incisal/occlusal forces
Transseptal Fibers
i. Location: apical to the gingival fibers
- only on mesial and distal surfaces
ii. Connection:
- tooth to tooth via cementum
iii. Purpose:
- ensures teeth remain in proper relationship to one another and support the interproximal gingiva
Alveolar Crest Fibers
i. Location: at level of alveolar crest
- margin of bone around tooth root
- all around the tooth
ii. Connection: cementum to bone
- tooth root to alveolar crest
iii. Purpose:
- resists horizontal movements and maintain tooth in socket
Horizontal Fibers
i. Location:
- apical to alveolar crest fibers
ii. Connection:
- cementum to bone
iii. Purpose:
- resists horizontal (lateral) pressures applied to crown of tooth
Oblique Fibers
i. Location:
- apical to horizontal fibers
ii. Connection:
- cementum to bone
iii. Purpose:
- resist forces places on the long axis of the tooth
Apical Fibers
i. Location:
- around apex of tooth
ii. Connection:
- cementum to bone
iii. Purpose:
- prevent the tooth from tipping
- resist twisting (luxation)
- protect the blood, lymph, and nerves supply to the tooth
Interradicular Fibers
i. Location:
- in the furcations between roots
ii. Connection: cementum to bone
- tooth root to interradicular septum
iii. Purpose: stabilize tooth
- resist tipping and tiliting
What are the functions of PDL?
1) Supportive
- transmits occlusal forces from teeth to the bone allowing for small movement
- shock absorption
2) Formative
- throughout life
- tension (pull) on PDL –> cementum + bone formation
a) Fibroblasts –> cementoblasts –> cementum (additive effect)
b) Fibroblasts –> osteoblasts –> bone (replacement effect)
3) Resorptive
- Pressure on PDL -> becomes narrower
- severe pressure can cause: bone resorption, cementum resorption, destroys PDL
4) Sensory
- determines pressure and touch (pain determined from tooth pulp)
5) Nutritive
- presence of blood vessels provide essential nutrients to area
Clinical Considerations for PDL
1) Main purpose is to anchor tooth in socket
2) Maintains the gingival tissues in proper relationship to the teeth
3) Transmits occlusal forces from the teeth to the bone (shock absorber)
4) Cells found within contribute to the development and resorption of the hard tissues of the periodontium
5) Blood vessels within provide nutrients
6) Nerve supply - sensation of pressure
7) Periodontal Disease
- can cause destruction of the PDL fibres causing tooth mobility
8) 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 x-rays
9) Clinically, occlusal trauma is noted by the late manifestation of increased mobility of the tooth
10) Clinically, occlusal trauma is also noted possibly by the presence of pathological tooth migration (PTM)
11) 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
Alveolar Process
- The part of the maxilla or mandible that supports and protects the teeth
- Part of the periodontium to which the cementum of the tooth is attached through the PDL
- Hard mineralized tissue with all the other components of other bone tissues
—-> connective tissues
—-> made of: osteocytes (bone cells), organic matrix that mineralizes - Makes up the lining of the tooth socket
- Lamina Dura (cribiform plate): part of the alveolar bone that is uniformly radiopaque
- Alveolar Crest: the most cervical part
What is the alveolar bone composition?
60% inorganic substance
25% organic substance
15% water
Very similar to cementum but not as hard as dentin or enamel
Supporting Alveolar Bone
1) Cortical bone
- a plate of compact bone on both the facial and lingual surfaces of the alveolar process
2) Trabecular/spongy bone
- consists of cancellous or spongy bone that is located between the alveolar bone and the plates of cortical bone
See image on powerpoint
Bone cells
1) Osteocytes: bone cells
- osteo = bone
- cyte = cell
2) Lacunae: “little spaces”
- where osteocytes are located
3) Canaliculi: “little canals”
- connect lacunae-to-lacunae
Bone: Nutrient Transport
i. Very vascular = high blood supply
ii. High communication through many canals and systems
iii. Haversian Canal System
- carries blood supply (veins and arteries)
Bone Connective Tissue Coverings
i. Periosteum
- tough connective tissue
- outside of bone
ii. Endosteum
- delicate connective tissue
- location:
a. inner surface of compact bone
b. surface of trabeculae
c. lines Haversian and Volkmann’s canals
Bone: Growth
Formation and resorption is a process
- occurs throughout life
- intermittent
Formation: new bone forms from periosteum or endosteum
- osteoblasts: form bone
Resorption: removes mineral and organic matrix of bone
- osteo: bone
- clasts: to break
Clinical Considerations for Alveolar Bone
1) Orthodontics
- the bands, wires, or appliances put pressure on one side of the tooth and adjacent alveolar bone, creating a compression zone in the PDL
- this compression in the PDL leads to bone resorption. On the opposite side of the tooth and bone, a tension zone develops in the PDL and causes the deposition of new bone
2) Mesial drift or physiological drift is a normal, natural movement phenomenon in which all teeth move slightly toward the midline of the oral cavity over time
- this can cause crowding, late in life, in a once-perfect dentition
3) Periodontal Disease
- bone loss caused by chronic periodontal disease or periodontitis
- bone loss involved the alveolar crest and moved apically as the periodontal disease progressed
4) Density of bone
- the density of the alveolar bone in an area also determines the route that dental infection takes with abscess formation
- also the efficacy of local infiltration during the use of local anesthesia
5) Tooth Loss
- after extraction of a tooth, the clot in the alveolus fills in with immature bone, which later is remodeled into mature secondary bone
- however, with the loss of teeth, a patient becomes edentulous, either partially or completely, and the alveolar bone undergoes resorption
