Tooth Eruption and Exfoliation

Learning Outcomes

• Three phases of tooth eruption should be described
• How the dento-gingival junction originates should be described
• The process of tooth exfoliation should be described
• Theories of tooth eruption should be outlined
• A link between the processes, developmental timeline of teeth, and eruption and exfoliation ages for teeth should be identified

Eruption Process

• The eruption process of teeth begins before birth and continues throughout life.
• The eruption process does not complete when all teeth are present, it continues after they have appeared.
• The eruption process is not completed once primary teeth erupt, because permanent dentition grows afterwards.
• Eruptive processes start much earlier than 6 months of age
• Eruption starts early in embryological development

Eruption of Teeth

• There are three phases involved in eruption
• Tooth crown development must be complete during the bell stage alongside root development
• The first instance of tooth visibility in the oral cavity is around 6 months old
• It is a continuous process throughout life
• It is a multi-factorial process

Physiological Foundation of Oral Health advice

• Knowing this allows the physiological provision of oral health advice for teething, wobbly teeth, and erupting wisdom teeth
• Allows clinical distinction between normal and abnormal tooth eruption and exfoliation
• Allows to identify a supernumerary / missing tooth
• Allows to be able to refer for orthodontics

Definitions

• Eruption represents the physiological movement of teeth from their developmental position in the alveolar bone, through soft tissues, to the position of function in the oral cavity
• The process of eruption has three phases
• Exfoliation is the physiological resorption of primary teeth
• Exfoliation involves teeth being lost

Embryological Links

• Eruption and exfoliation begins during the tooth's bell stage
• Ameloblasts, cells of the enamel organ, osteoclasts, odontoclasts, and oral epithelium play a role in eruption and exfoliation
• Underpinning knowledge explains the various theories on the mechanisms of the erupting tooth

Clinical Links

• The developmental timeline during embryology links into life with the eruption timeline that is essential
• These links are essential to identify the presence and position of missing teeth, supernumerary teeth, crowding of teeth, and the need for orthodontic referral

Eruption Process: 3 Phases

• There are 3 phases of eruption -> pre-eruptive, eruptive and post-eruptive tooth movement

The Pre-Eruptive Phase

• Involves the movement of the developing tooth, within the alveolar bone, specifically until crown formation is complete.
• This starts during the bell stage, which remodels in the bony crypt to allow more space for the developing tooth.

Active Eruption Phase

• Movement of teeth through the alveolar bone, then soft tissue.
• The teeth move through intraosseous and then supraosseous to the oral cavity
• This phase starts around the same time as the root formation, and ends when the tooth reaches occlusion.
• Root formation continues after this phase

Post-Eruptive Phase

• Teeth move after active eruption, to maintain occlusion, and compensate for occlusal and proximal tooth wear, and growth
• This occurs through life when an opposing tooth is removed

Eruption Process Answer

• The eruption process starts during the bell stage of tooth development

Active Eruption Phase Detail

• Before the active eruption phase oral epithelium must fuse with the reduced enamel epithelium

Reduced Enamel Epithelium

• After amelogenesis is complete, ameloblasts shrink and combine with: outer enamel epithelium, stratum intermedium, residual stellate reticulum to form reduced enamel epithelium
• Functions: Protects the developing tooth crown, fuses with oral epithelium to make an eruption pathway, forms the dento-gingival junction

Eruption Pathway Detail

• Movement occurs via complex signaling from cells.
• Reduced enamel epithelium protects tooth crown from odontoclasts and osteoclasts
• The bone overlying the developing crown is resorbed by osteoclasts (and odontoclasts of predecessor teeth)

Modified Eruption pathway

• There are no blood vessels or nerves present during eruption phase
• The reduced enamel fuses with oral epithelium to create an eruption pathway
• Stimulation and trauma occurs to promote ectomesenchyme fusion
• The fusion forms a seal which prevents exposure of the underlying tissue and haemorrhage

Dento-Gingival Junction

• Forms when the reduced enamel epithelium and oral epithelium seal off the oral cavity from the body via the dento-gingival junction
• Significant for periodontal disease (relates to clinical significance)
• The junction also forms a shallow trough that will create the gingival sulcus

Rate of eruptive movement

• Tooth moves slowly through bone at a rate of 1-10um per day
• Teeth move through soft tissue at a rate of 75um per day
• Muscular forces of the tongue, cheek, and lips guide the tooth into position
• A sustained force of 4-5g is required

Reduced Enamel Epithelium

• The reduced enamel epithelium surrounds the developing tooth crown during eruption

Exfoliation of Teeth

• Permanent successor teeth develop (positioned lingually, increase in size and start the eruptive phases)
• Odontoclasts resorb the roots of the primary teeth up to the crown
• The pattern is usually the same thus any variations are a key indicator of abnormalities clinically
• Masticatory forces help push out primary teeth by applying pressure

Tooth Eruption Theories

• The exact mechanism is unknown
• Root formation theory states the tooth is elevated by thrust of root development, but it is now refuted
• Bone remodeling occurs, but it is unsure whether bone resorption and deposition cause teeth to erupt, or vice versa
• Dental follicle theory states signals between the dental follicle and the reduced enamel epithelium have been found to induce bone re-modelling
• Periodontal ligament theory involves fibroblast formation but it has been refuted like the root formation theory
• Various molecules are thought to be involved
• There are also more recent theories under investigation: bite forces on the soft tissues and neuromuscular forces

Summary of Tooth Eruption

• The eruption and exfoliation processes are complex and multi-factorial
• There are three phases of eruption
• We have discussed the active phase in detail
• The phases are all linked to embryological development
• The different theories of eruption were outlined

Explore the three phases of tooth eruption, the origin of the dento-gingival junction, and the process of tooth exfoliation. Learn about the theories of tooth eruption and the developmental timeline of teeth. Develop a link between the processes, developmental timeline of teeth, and eruption and exfoliation ages for teeth.