Chapter 6: The Functional Biology Of the Dentine/Pulp Complex

BASIC DENTINE STRUCTURE and COMPOSITION

Physical characteristics:

• Forms bulk of tooth, is considered a vital tissue with the pulp providing nutrition, sensation, resistance to breakdown.
• Provides a base for the enamel and forms the tooth root(s).
• Yellow in colour, perforated throughout by tubules, continuous from pulp to outer surface and is therefore porous.
• A resilient material with no preferential fracture lines.

Chemical composition:

• 70% inorganic, 20% organic and 10% water - by weight.
• 45% " 33% " 22% " - by volume.
• Inorganic phase is hydroxyapatite, the organic is mainly collagen.

Structure:

• Dentine can be divided up into mantle dentine - 10µm thick outer layer under enamel - and circumpulpal dentine.
• Dentine also divided into coronal and radicular, primary and secondary, intertubular and peritubular.
• The tubules are curved, both primary and secondary curvatures beeing seen. Their diameter varies and reduces with age by deposition of peritubular dentine until total blockage occurs and the dentine becomes sclerotic. Mineralisation and composition differs from intertubular dentine.
• Tubules branch throughout their length in varying amounts.
• Interglobular dentine, granular layer of Tomes. Predentine seen at pulp margin - it is non-calcified
• Incremental lines seen named - Von Ebner, Owen and Schreger.
• Neo-natal line seen in deciduous teeth.
• Form of the dento-cemental junction - hyaline layer.

Age changes:

• Increase of volume at the expense of pulp, increase of secondary and tertiary dentine, more dead tracts and sclerotic dentine found.

PULP and PAIN

Functions of pulp:

1. nutritive and sensory for dentine.
2. development of dentine.

Develops from: - dental papilla.

Components:

1. cells - odontoblasts, fibroblasts (less with age),defence cells
2. matrix - collagen (more with age) + G.S.
3. nerves
4. blood vessels

Major structure:

1. odontoblast layer
2. cell free layer (of Weil)
3. cell rich layer
4. loose vascular connective tissue
5. Raschkow's plexus
6. (pulp stones)

Sensation of pain:

• Myelinated axons (1-4 µ_m) - sharp pain
• Unmyelinated (<0.5 µ_m) - low, dull sensation.

Mechanisms of dentine sensitivity:

1. direct innervation of dentine
2. odontoblasts sensitive to pain stimulus
3. fluid flow within tubules (hydrodynamic theory)

DENTINE CARIES (Coronal)

Smooth surface/fissure caries

Similarities and differences to enamel caries

Effect of dentine structure on progress of lesion

Recognisable zones of dentine lesion:

1. Changes in the mineral phase
2. Changes in the matrix

Defence mechanisms:

1. Within dentine
2. Within the pulp

DENTINE CARIES (Root)

Specific properties and problems of root caries