Oral Anatomy & Histology (Review: Outcome 8)

Question 1

What structures make up the Periodontium?

Answer 1

• Cementum
• Periodontal ligaments
• Alveolar bone
• Gingiva (more of a minor role)

Question 2

Cementum

Answer 2

• 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

Question 3

What is the chemical composition of cementum?

Answer 3

65% - inorganic substance
23% - organic substance (proteins)
12% - water

Question 4

Physical characteristics of cementum

Answer 4

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

Question 5

Histological structure of Cementum

Answer 5

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

Question 6

Sharpey’s Fibers

Answer 6

• 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

Question 7

Formation of Cementum

Answer 7

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

Question 8

Clinical importance of cementum

Answer 8

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

Question 9

Clinical Considerations for Cementum

Answer 9

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

Question 10

Periodontal Ligament (PDL)

Answer 10

• 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

Question 11

Formation of PDL

Answer 11

i. Forms from the Dental Sac
- process begins after cementum formation begins

ii. Fibroblasts

iii. Intercellular substance

iv. Collagen

v. Periodontal ligament

Question 12

Other components of PDL

Answer 12

1. Cementoblast
2. Osteoblasts
3. Nerves
   - sensory nerves (provides sense of touch)
4. 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
5. Cementicles: small calcified bodies in the PDL
   - no clinical significance
6. Specialized cells
   - osteoclasts, osteoblasts which react to the demands of the adjacent environment (bone)

Question 13

Principle Fiber Groups of PDL

Answer 13

1. Gingival fibers
2. Transseptal fibers
3. Alveolar crest fibers
4. Horizontal fibers
5. Oblique fibers
6. Apical fibers
7. Interradicular fibers

Question 14

Gingival Fibres

Answer 14

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

Question 15

Transseptal Fibers

Answer 15

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

Question 16

Alveolar Crest Fibers

Answer 16

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

Question 17

Horizontal Fibers

Answer 17

i. Location:
- apical to alveolar crest fibers

ii. Connection:
- cementum to bone

iii. Purpose:
- resists horizontal (lateral) pressures applied to crown of tooth

Question 18

Oblique Fibers

Answer 18

i. Location:
- apical to horizontal fibers

ii. Connection:
- cementum to bone

iii. Purpose:
- resist forces places on the long axis of the tooth

Question 19

Apical Fibers

Answer 19

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

Question 20

Interradicular Fibers

Answer 20

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

Question 21

What are the functions of PDL?

Answer 21

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

Question 22

Clinical Considerations for PDL

Answer 22

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

Question 23

Alveolar Process

Answer 23

• 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

Question 24

What is the alveolar bone composition?

Answer 24

60% inorganic substance
25% organic substance
15% water

Very similar to cementum but not as hard as dentin or enamel

Question 25

Supporting Alveolar Bone

Answer 25

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

Question 26

Bone cells

Answer 26

1) Osteocytes: bone cells
- osteo = bone
- cyte = cell

2) Lacunae: “little spaces”
- where osteocytes are located

3) Canaliculi: “little canals”
- connect lacunae-to-lacunae

Question 27

Bone: Nutrient Transport

Answer 27

i. Very vascular = high blood supply
ii. High communication through many canals and systems
iii. Haversian Canal System
- carries blood supply (veins and arteries)

Question 28

Bone Connective Tissue Coverings

Answer 28

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

Question 29

Bone: Growth

Answer 29

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

Question 30

Clinical Considerations for Alveolar Bone

Answer 30

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