Eruption and Shedding of Teeth

What are the three phases of tooth eruption

preeruptive, prefunctional eruptive, functional eruptive

What happens in the preeruptive phase

tooth crowns move from formation to crown completion, adjust position in jaws

When is the preeruptive phase finished

early root formation

How do permanent anterior teeth develop

lingual to primary incisors

How do permanent premolars move

from near occlusal area of primary molars to within roots of primary molars

How do maxillary molars develop

in maxillary tuberosities, occlusal surface slanted distally

How do mandibular molars develop

occlusal surface slanted mesially

When does the prefunctional eruptive phase start

initiation of root formation

When does the prefunctional eruptive phase end

when tooth reaches occlusal contact

What are the four major events in prefunctional eruptive phase

root formation, movement to oral mucosa, crown penetration, intraoral movement

What causes root formation

proliferation of epithelial root sheath

Why does tooth move during prefunctional eruptive phase

need space for root elongation

How does penetration occur

crown tip moves through fused epithelial layers into oral cavity

What covers enamel initially

primary organic cuticle from ameloblasts

What is clinical crown

part of tooth exposed in mouth

What is anatomic crown

entire crown from cusp tip to CEJ

What changes occur in overlying tissues

dental follicle forms eruption pathway, fibers and connective tissue degenerate, bone remodels

What is gubernacular cord

follicular fibers pointing toward mucosa in eruption path

What causes bone resorption

osteoclasts from monocytes, ruffled border modifies membrane

How does resorption occur

extracellular phase separates minerals, intracellular phase ingests fragments

What happens to collagen fibers

fibroblasts destroy remaining collagen, reuse amino acids for bone formation

Which permanent teeth erupt through alveolar bone

only posterior molars

What changes occur in surrounding tissues

fibers attach to tooth, extend to periodontium, alveolar crypt height increases

What changes occur in underlying tissues

crown moves occlusally to allow root lengthening, fibroblasts form collagen around apex, bony trabeculae form

When does functional eruptive phase occur

after teeth begin functioning, continues lifelong

How long for root completion after eruption

~1–1.5 years for primary, 2–3 years for permanent

What causes tooth eruption

root growth, pulpal pressure, cell proliferation, vascularity, bone formation, endocrine/enzymatic factors

What is shedding

loss of primary teeth

Why does shedding occur

root resorption, bone loss, primary pulp degeneration, inability to handle forces

How many teeth in primary dentition

20

How many teeth in permanent dentition

32

What are successional teeth

permanent teeth replacing primary teeth

What are accessional teeth

permanent teeth with no predecessors

Which permanent teeth are larger than primary

most, including incisors and canines

What is leeway space

difference between mesiodistal size of primary molars/canines and permanent molars/canines

How do primary roots compare to permanent

shorter, more divergent, flat curved

What is difference in root canals

primary teeth have ribbon-shaped canals, permanent have tube-shaped

Why is primary enamel harder to etch

may have prismless surface

How thick is enamel in permanent teeth

~2x primary teeth, more pigmented

How does primary dentin compare

slightly softer than permanent

How does pulp size compare

primary coronal pulps relatively larger

Where are accessory canals located

primary teeth in furcation, permanent at apical third

How do arch shapes compare

similar anteriorly, permanent extends further distally

What is incisor liability

replacement of smaller primary incisors with larger permanent incisors

What happens during root resorption

pulp cells decrease, nerves degenerate, fibers reorganize

Do blood vessels remain during resorption

yes, until exfoliation

Why are primary teeth less sensitive at exfoliation

nerve fibers lost