ERUPTION & SHEDDING OF TEETH

Tooth eruption

Defined as “the axial movement of tooth from its developmental position in the alveolar socket into its functional position within the oral cavity”

Active eruption – vertical movement of the tooth due to actual movement of the teeth

Passive eruption – receding of the gingiva leading to exposure of crown in the oral cavity.

Tooth eruption Three distinct tooth movements are noticed during

development of dentition.

1. Pre-eruptive – these are the movements which begin before the actual axial movement of teeth

○ Tooth buds are initially crowded as the jaws (maxilla and mandible) are small and later as the jaw grows, these buds move away from each other and align themselves in their respective crypts.

○ Permanent tooth buds develop adjacent to deciduous teeth and later they move apically.

○ Permanent maxillary molars face distally in the maxillary tuberosity when they develop, as the maxilla grows in size they turn mesially and erupt

2. Eruptive movements – (pre functional eruptive phase)○ In this phase the actual eruption (axial movement) of

teeth takes place, the mechanism is explained by various theories

3. Post eruptive- (functional eruptive phase)

○ To compensate for occlusal and proximal wear of the teeth

○ To compensate for the growth of the jaws

Primary Tooth Eruption

Reduced enamel epithelium fuses with oral epithelium

Forms a epithelium lined tunnel

Reduced enamel epithelium converts into primary attachment epithelium

Gubernacular Cord and Canal

Eruption process is the same for the primary teeth – formation of an epithelium lined tunnel for eruption

Gubernacular cord and gubernacular canal -

Initially both permanent and decidous buds are in the same crypt

As the deciduous erupts the permanent tooth becomes completely enclosed by bone except for a small canal which is filled with connective tissue – this is gubernacular cord

The bony canal in which this is present is known as Gubernacular canal

Helps in guiding the permanent tooth to erupt

Mechanisms of tooth eruption: current research

• Theories of eruption-• Bone remodeling theory

• Root growth theory : Cushion Hammock ligament

• Vascular pressure theory

• Periodontal ligament traction theory: most accepted

Bone remodeling theory This theory states that the tooth erupts because

there is bone resorption above the tooth and bone deposition below the tooth – which pushes the tooth to its functional position.

Not accepted because bone remodeling occurs as an effect of tooth movement and not as a cause of it

Removal of dental follicle stops the bone remodeling hence the driving force is not within the bone

Rooth growth theory As the root grows, it exerts downward pressure on

the bone which pushes the tooth up (like a rocket). Not accepted because

No fixed baseThe tooth moves for a greater distance than the

length of the rootEruption continues even if the root is sectioned

(cut)

Cushion Hammock theory.

Vascular pressure theory The pressure exerted by the blood vessels at the

apex of the tooth help in eruption of teeth Not accepted -

The pressure exerted is not enough to help in eruption of teeth

Teeth erupt even when the vascular supply is cut

Periodontal Ligament Traction Theory

Most accepted theoryThe periodontal ligament fibroblast have

contractile propertyThe fibroblasts are inter connected to each other

- fibronexusThe contractile forces are transmitted to the

fibres to reorient them to help in eruption of teeth.

Experimentally proven that the dental follicle is the most important structure rsponsible for eruption of teeth

Shedding / Exfoliation of Teeth

The physiologic process resulting in the elimination of the deciduous dentition is called as shedding or exfoliation.

It is initiated either by the pressure exerted by the permanent successor or by increased occlusal forces.

The cell responsible for removal of hard tissues is ODONTOCLAST (structure and origin similar to osteoclast)

Applied aspects

Importance of chronology and sequence of eruption

Delayed eruption Impacted teeth Submerged teeth Retained deciduous teeth Remnants of deciduous teeth