Periodontal Ligament and Cementum

Question 1

Describe the structure of the periodontal ligament

Answer 1

• It is a thin sheet of dense fibrous connective tissue
• Located between tooth and bony socket
• Thickness varies depending on age and function of tooth
• Fibroblasts are responsible for the production of fibrous matrix
• They reproduce and remodel themselves at a fast rate

Question 2

Describe the functions of the periodontal ligament

Answer 2

• Attaches tooth to its bony socket
• Suspension- suspends tooth in socket
• Sensory- tactile pressure and pain sensation
• Nutritive- to cementum and bone
• Formative- contains cementoblasts
* Resorptive- severe pressure initiates osteoclasts

Question 3

What are the 5 principle fibre groups of the PDL?

Answer 3

• Horizontal
• Oblique
• Alveolar crest
• Inter-radicular
• Apical

Question 4

Define ankylosis and discuss occurrence and characteristics of it

Answer 4

Ankylosis is the fusion of cementum and alveolar bone, because there is no presence of periodontal ligaments.

Occurrence:
• Post chronic periapical inflammation
• Tooth re implantation, occlusion trauma, and impacted teeth
* Common in primary dentition

Characteristics:
• If you use the handle of the mirror the tap on the occlusal surface of teeth, it has a metallic sound because of the lack of cushion
• Infra occlusion of opposite tooth
* Ankylosed teeth do not drift

Question 5

Recall the physical properties of cementum

Answer 5

Properties:
• A mineralized layer of connective tissue that covers the root of the tooth
* Thin, calcified, pale, yellow, dull, more permeable than dentine
• It has collagen fibers- oriented fairly parallel to long axis of tooth held together in gel-like ground substance
• Mineralized portion- made up of hydroxyapatite crystals (calcium & phosphate)

Question 6

How is cementum formed?

Answer 6

• Cementoblasts lay down cementoid, which is subsequently mineralised to form cementum
• As new layer of cementoid is laid down, the old one is mineralised
• Once the tooth comes into occlusion (the way in which upper and lower teeth meet), cementum starts to form more rapidly
• Cementoblasts become trapped in the forming mineralised tissue = cellular cementum

Question 7

Define hypercementosis and its aetiology

Answer 7

Hypercementosis is the overproduction of cementum.

Can happen because of:
• Age
• Medical conditions
• Previous trauma
• Excessive tensions from orthodontic appliances or occlusal forces
• Over eruption of teeth
* Pulp disease: body trying to compensate for destroyed fibres

Question 8

Explain the differences between cellular and acellular cementum

Answer 8

Acellular:

• Does not increase in thickness with age
• Formed prior to tooth becoming functional
• Covers the covers the cervical third
• Laid down in layers resulting in a series of lines which are parallel to the roots surface
• Layers are close together, thin and even
• These lines are evident because of the differences in the level of mineralisation
• Nutrients from dentine

Cellular:

• Up to 10 times thicker, but less calcified
• Formed throughout life
• Covers the apical third
• Contains cementocytes
• Lines are in series, but are further apart, thicker and more irregular
• Nutrients come from periodontal ligaments. It cannot obtain nutrients from dentine as it is too thick

Question 9

Recall the functions of cementum

Answer 9

• Maintains the integrity/shape of tooth
• Seals off the dentinal tubules within dentine
• Involved in tooth repair and regeneration
* Helps maintain tooths functional position in the mouth