Cementum

Question 1

What is the composition of cementum?

Answer 1

65% inorganic, 23% organic and 12% water, mineral is hydroxyapatite crystals, the matrix is particularly type 1 extrinsic and intrinsic fibres of type 1 collagen

Question 2

What differentiates cementum from bone?

Answer 2

Cementum is devoid of blood vessels and nerves and is less readily resorbed. Cementum does not have a lamellar appearance and has no marrow spaces.

Question 3

What non collagenous components does cementum have?

Answer 3

Sialoproteins, glycosaminoglycans, proteoglycans, growth factors and osteopontin

Question 4

What two sources does cementum derive its collagen fibres from?

Answer 4

1) Sharpey’s fibres of the periodontal ligament (extrinsic)

2) Cementoblasts (intrinsic - run parallel to the root surface and at right angles to the extrinsic fibres)

Question 5

How is acellular cementum formed?

Answer 5

Mesenchymal cells of the inner layer of the dental follicle come to lie close to the surface of the newly formed un-mineralised dentine, differentiate into cementoblast like cells, secrete collagen fibrils and begin forming acellular cementum. The fibres intermingle with the hyaline layer, at the superficial end they run perpendicularly into the periodontal space and provide attachment for fibres of the PDL

Question 6

Where does cellular cementum form?

Answer 6

Apical region at about the time the tooth erupts, acellular is at the cervical region

Question 7

How is cellular cementum formed?

Answer 7

Large basophilic cells differentiate from the adjacent cells of the dental follicle (or acellular cementum), these cells form a distinct cuboidal layer of cementoblasts adjacent to the root surface and secrete intrinsic collagen fibres that do not extend into periodontal ligament and run parallel to the root surface.

Question 8

What is the thin layer of uncalcified matrix on the surface of the cellular variety of cementum called?

Answer 8

Precementum

Question 9

What out of primary (acellular) or secondary (cellular) cementum is formed first?

Answer 9

Primary

Question 10

What does cementum do?

Answer 10

Mineralised connective tissue that lines the root of the tooth, via the periodontal ligament, to alveolar bone, continuous through life allowing continual reattachment of the periodontal ligament fibres

Question 11

If resorption occurs due to microtrauma how does this occur?

Answer 11

Carried out by multinucleated odontoclasts and may carry out into the root dentine

Question 12

How do cementoblasts repair trauma?

Answer 12

A layer of cementoblasts deposit a thin layer of matrix (precementum) in the deficiency, the repair tissue can resemble cellular cementum with evidence of appositional growth.

Question 13

Is cementum deposited regularly?

Answer 13

No, deposited in an irregular rhythm resulting in unevenly spaced incremental lines of Salter (precise incremental lines is unknown)

Question 14

How do the lines of acellular and cellular cementum differ?

Answer 14

Acellular - close together, thin and even

Cellular - further apart, thicker and more irregular

Question 15

Are Sharpey’s fibres mineralised?

Answer 15

In the cementum but not in the periodontal ligament

Question 16

Where are Sharpey’s fibres formed from?

Answer 16

Periodontal fibroblasts

Question 17

What are the differences between cellular and acellular cementum?

Answer 17

Acellular - No cells, border with dentine not clearly demarcated, rate of development relatively slow, incremental lines relatively close together, precementum layer virtually absent
Cellular - Contains cementocytes, border with dentine clearly demarcated, rate of development relatively fast, incremental lines relatively wide apart and precementum layer is present

Question 18

Is cementum normally subject to resorption?

Answer 18

No

Question 19

Does cementum formation continue following root completion?

Answer 19

Yes