OE L15 Cementum and Root Formation

Question 1

What tissues is the periodontium comprised of?

Answer 1

• Cementum
• Periodontal ligament
• Bone lining alveolus (socket)
• Gingiva

Question 2

What are the 3 key roles of the periodontium?

Answer 2

• Apical deposition of cementum in response to occlusal force
• PDL has a high turnover in response to force
• Bone resorbed on pressure side and added to tension side

Question 3

What stage does root formation begin at?

Answer 3

Root formation begins at the apposition stage. After the completion of enamel formation.

Question 4

The IEE and OEE meet in the cervical loop region to form what?

Answer 4

Form a double layer of epithelial cells called HERS: Hertwig’s Epithelial Root Sheath

Question 5

What is the role of HERS?

Answer 5

HERS formation leads to root formation.
It increases odontoblast differentation and produces dentine matrix.
Many epithelial cells of the sheath undergo apoptosis leaving gaps for cells from dental follicle to migrate to new matrix.

Question 6

What are the remaining epithelial cells of the HERS called?

Answer 6

Epithelial rests of Malassez.

Reside in the PDL close to the cementum.

Question 7

What is the clinical relevance of the epithelial rests of Malassez?

Answer 7

They are a potential cause of radicular cysts.

Question 8

Summarise the 3 stages of root formation.

Answer 8

1. Apical extension of IEE and OEE forming HERS
2. HERS induces differentiation of odontoblasts from radicular pulp, produces dentine
3. Roots almost completely formed when HERS is just a small tag of epithelium at rim of apical foramen

Question 9

When does cementum formation occur?

Answer 9

Almost immediately following root formation.

Initiated by breakdown of HERS.

Question 10

What is the composition of cementum?

Answer 10

Thin layer of calcified tissue.
50% organic material
50% inorganic material (HAP)

Question 11

Describe the organic component of cementum.

Answer 11

• 90% type I collagen
• 10% type III and XII collagen
• Non-collagenous proteins e.g. cementum attachment protein (CAP) and cementum protein 1 (CEMP-1)

Question 12

What are the 3 sources of cementoblasts?

Answer 12

• Infiltrating dental follicle cells recieve signals from pre-dentine or HERS to differentiate
• HERS cells can transdifferentiate into mesenchymal stem cells and then into cementoblasts
• Stem cells from blood can differentiate to cementoblasts

Question 13

What signals do cells recieve that cause them to differentiate into cementoblasts?

Answer 13

• Loss of stellate reticulum, may withdraw some suppressing signal for cementoblast formation
• HERS
• Pre-dentine, contains growth factors that may provide signals to differentiate

Question 14

There are many factors regulating cementogenesis, name some.

Answer 14

• Cementum protein 1 (CEMP-1)
• BMPs
• Platelet derived and insulin growth factors
• FGFs
• Adhesion molecules
• Collagens
• Matrix Gla proteins
• Transcription factors

Question 15

What is cementum classification based on?

Answer 15

Time of formation:

• Primary
• Secondary

Presence or absence of cells in matrix:

• Cellular (secondary)
• Acellular (primary)

Origin of collagen fibers in matrix:

• Intrinsic
• Extrinsic

Question 16

What is meant by primary vs secondary cementum?

Answer 16

Primary: formed before eruption

Secondary: formed after eruption

Question 17

What is meant by intrinsic vs extrinsic fiber cementum?

Answer 17

Intrinsic: collagen fibers formed by cementoblasts (usually in cellular cementum)

Extrinsic: fibres derived from the PDL, between the cementum and alveolar bone (usually in acellular cementum)

Question 18

Describe acellular cementum.

Answer 18

• Also called primary cementum
• Found in upper 2/3rds of root
• Strong union at cementodental junction
• More mineralised than cellular cementum

Question 19

Describe cellular cementum.

Answer 19

• Also called secondary cementum
• Found in lower 1/3rd of root
• Less mineralised than primary cementum
• Formed rapidly, traps cementoblasts (osteocytic lacunae) and PDL fibres

Question 20

What are osteocytic lacunae?

Answer 20

When cementoblast cells are trapped in cellular cementum they occupy a lacuna.

Question 21

What type of cementum is found at the very top of the root at the cervical enamel surface?

Answer 21

Acellular afibrillar cementum:

• Highly mineralised
• Low protein content
• No cells
• No collagen fibres
• No role in tooth attachment

Question 22

What is acellular or cellular mixed cementum?

Answer 22

Acellular or cellular mixed cementum:

• Find intrinsic fibres and extrinsic Sharpey’s fibres
• Intrinsic fibres run parallel to root
• Extrinsic fibres run perpendicular to root

Question 23

What are the 3 types of cementoenamel junction?

Answer 23

• Overlap junction: acellular fibrillar cementum lays on top of enamel
• Butt joint: perfect connection between cementum and enamel
• Gap junction: cementum and enamel not connected

Question 24

Can root fractures be resolved?

Answer 24

Root fractures may remodel, but not to the original dimensions of the tooth.

Question 25

How does periodontal disease affect cementum?

Answer 25

Periodontal disease can damage the cementum which exposes dentine causing sensitivity.

Question 26

What may happen to cementum of deciduous teeth when permanent teeth erupt?

Answer 26

The cementum may resorb under the excessive pressure.

Question 27

What is ankylosis?

Answer 27

Ankylosis: cementum fusing to bone.

May happen with age as the PDL is worn away.

Question 28

What can happen to cementum in chronic inflammation and autoimmune diseases?

Answer 28

Enhanced cementum formation.