Periodontal Ligament and Cementum

Question 1

What is the periodontal ligament (PDL)?

Answer 1

A thin sheet of fibrous conenctive tissue, thickness varies depending on age and function of tooth

Fibroblasts are responsible for the production of fibrous matrix and ground substance

Fibres are arranged in bundles located within the alveolar bone proper and cementum

Question 2

What are the functions of the PDL?

Answer 2

1. Attaches tooth to its bony socket
2. Supportive = suspends pressure and pain
3. Sesonry = tactile pressure and pain
4. Nutritive
5. Formative
6. Remodelling

Question 3

What are the 5 dentoalveolar fibre groups?

Answer 3

1. Alveolar crest fibres
2. Horizontal fibres
3. Oblique fibres
4. Apical fibres
5. Inter-radicular fibres

Question 4

What are Sharpey’s fibres?

Answer 4

Ends of PDL fibres

Embedded in the cementum and alveolar bone

Question 5

How does the PDL get its blood supply?

Answer 5

Rich supply originates primarily from the dental arteries that enter through the apical foramen and from blood vessels in the adjacent bone marrow spaces

Heavily anastomosed

Question 6

What are the two kinds of nerves in the PDL and what do they do?

Answer 6

Mechanoreceptors

Pain sensing nerve endings

Transmit information about jaw position, tooth movements and contact, injuries, etc

Question 7

What are the physical characteristics of the cementum?

Answer 7

Thin layer of calcified tissue covering the dentine of the root

Pale yellow with a dull surface

More permeable and softer than dentine = readily removed by abrasion due to softness and thinness of cementum around the cervical region

Question 8

What is the function of cementum?

Answer 8

Maintains the integrity of the root

Helps maintain the tooth’s functional position in the mouth

Seals the dentinal tubules

Involved in tooth repair and regeneration

Question 9

How is the cementum formed?

Answer 9

Cementoblasts lay down cementoid (uncalcified matrix), which is subsequently mineralised to form cementum

As a new layer of cementoid is laid down, the old one is mineralised

A thin layer of cementoid can always be found on the surface of cementum, which is lined by cementoblasts

Question 10

What are the two types of cementum?

Answer 10

1. Acellular cementum = covers the cervical one third of the root
2. Cellular cementum = covers the apical third and overlying the acellular cementum

Question 11

How are the two types of cementum formed?

Answer 11

Once the tooth comes into occlusaion, cementum starts to form more rapidly

Cementoblasts become trapped in the forming mineralised tissue

This results in the two types of cementum (acellular and cellular)

Question 12

What are the characteristics of acellular cementum?

Answer 12

Formed prior to the tooth becoming functional

Does not increase in thickness with age

Laid down in layers resulting in incremental lines which run parallel to the root surface indicating slow formation

Question 13

What are the characteristics of cellular cementum?

Answer 13

Less calcified and up to 10 times thicker than a cell

Cementoblasts trapped in the rapidly forming cellular cementum are known as cementocytes

Incremental lines are further apart, thicker, and more irregular

Question 14

Cementum is a continuous process that proceeds at varying rates throughout life. What are some common attributes of cementum thickness?

Answer 14

Most thickness at apical and furcation of multi-rooted teeth

Thicker in the dsital surfaces than the mesial surface

Thickness on coronal half equates to the thickness of one hair

Question 15

What are the three patterns in cementum-enamel relationships and how common are they?

Answer 15

Enamel overlaps the cementum (60 - 65% of the time)

Edge to edge (30% of the time)

Enamel and cementum do NOT meet (5 - 10% of the time)

Question 16

How does resorption and repair affect cementum?

Answer 16

Odontoclasts can resorb through thin cementum and penetrate the dentine and pulp

Cementoblasts deposit thin layers of precementum in the deficiency to repair the tissue

Question 17

What is the purpose of cementum?

Answer 17

Cementum is essential for tooth anchorage, it mediates attachment of the tooth to the gingival conenctive tissue as well as the periodontal ligament and alveolar bone

Cementum protects the tooth as it is less susceptible to resorption (loss of substance) allowing for safe orthodontic movement without damage

During the removal of calculus and bacterial deposits, thin layers of cementum are removed

Question 18

What is ankylosis and when does it occur?

Answer 18

The fusion of cementum and alveolar bone (no presence of periodontal ligaments)

Post chronic periapical inflammation
Tooth reimplantation, occlusion trauma, and impacted teeth
Common in primary dentition

Question 19

What are the characteristics of ankylosis?

Answer 19

Metallic percussion sound
Infraocclusion
No pressure receptors
No drifting
No eruption of teeth
Periodontal ligament is missing

Question 20

What is hypercementosis?

Answer 20

Abnormality in cementum thickness (abnormal thickening of cementum), specifically thickening with nodular enlargement of the apical third of the root

Age related phenomenon which can be localised or generalised

Associated with neoplastic or non-neoplastic conditions

Question 21

What can cause hypercementosis?

Answer 21

Excessive tension from orthodontic appliances or occlusal forces

Generalised form occurs when keeping pace with excessive tooth eruption (over eruption)

Pulp disease, compensation for the destroyed fibrous attachment to the tooth