Session 2: Structures of the Periodontium: PDL & Cementum

Question 1

Describe the structure and function of the periodontal ligament

Answer 1

Thin sheet of fibrous C.T. 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.
Functions
• Attaches tooth to its bony socket
• Supportive - suspends tooth in socket
• Sensory- tactile pressure and pain sensation
• Nutritive- to cementum and bone
• Formative- builds and maintains cementum and alveolar bone
• Remodelling - severe pressure initiates osteoclast

Question 2

Define ankylosis and discuss occurrence and characteristics of it

Answer 2

Fusion of cementum and alveolar bone. 
Occurrence:
• Post chronic periapical inflammation
• Tooth re implantation, occlusion trauma, and impacted teeth
• Common in primary dentition
Characteristics:
• Metallic percussion sound
• Infra occlusion
• No pressure receptors
• No drifting
• No eruption of teeth
• Periodontal ligament space is missing

Question 3

Recall the physical properties and functions of cementum

Answer 3

Cementum is a thin layer of calcified tissue covering the dentine of the root. More permeable and softer than dentine
Functions
• 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 4

Describe the process of cementum formation

Answer 4

• Cementoblasts lay down cementoid (Uncalcified matrix), 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, cementum starts to form more rapidly. Cementoblasts become trapped in the forming mineralised tissue. Results in two types of cementum

Question 5

Explain the differences between cellular and acellular cementum

Answer 5

Acellular Cementum
- Covers the cervical 1/3 of the root
- Formed prior to the tooth becoming functional
- Laid down in layers resulting in incremental lines which run parallel to the root surface indicating slow formation
Cellular Cementum
- Less calcified and covers the apical third and overlying the acellular cementum
- Cementoblasts trapped in the rapidly forming cellular cementum (cementocytes)
- Incremental lines are further apart, thicker and more irregular

Question 6

Describe the relationship of cementum to enamel at the cementoenamel junction
(CEJ) and recall the classification system used to describe this relationship.

Question 7

Explain factors / conditions that affect cementum thickness and initiate formation

Question 8

Define hypercementosis and its aetiology

Answer 8

Hypercementosis is excessive deposition of cementum on the tooth roots
Aetiology of Hypercementosis
• Excessive tension from orthodontic appliances or occlusal forces
• Generalized form- keep pace with excessive tooth eruption (over-eruption)
• Pulp disease – compensation for the destroyed fibrous attachment to the tooth

Question 9

Explain key clinical considerations related to the composition and function of cementum

Answer 9

Clinical Considerations:
• Essential for tooth anchorage
• It mediates attachment of the tooth to the gingival connective tissue as well as the periodontal ligament and alveolar bone
• Protects the tooth as it is less susceptible to resorption (loss of substance)
• This allows for safe orthodontic movement without damage
• During the removal of calculus and bacterial deposits, thin layers of cementum are removed