TOOTH DEVELOPMENT REVISION By Calvin Wong BUD STAGE CAP STAGE BELL STAGE

Early Late Early Late

6 7 8 9 10 11 12 13 14 15 16 17 18

INITIATION MORPHOGENESIS HISTODIFFERENTIATION INITIATION

BUD STAGE CAP STAGE BELL STAGE

Early Late Early Late

6 7 8 9 10 11 12 13 14 15 16 17 18

INITIATION MORPHOGENESIS HISTODIFFERENTIATION INITIATION 6 7 Week 6 = Primary epithelial band (oral epithelium thickening which invaginates into underlying mesenchyme Week 7 = PEB develops into dental lamina and vestibular lamina

MORPHOGENESIS

BUD STAGE CAP STAGE BELL STAGE

Early Late Early Late

6 7 8 9 10 11 12 13 14 15 16 17 18

INITIATION MORPHOGENESIS HISTODIFFERENTIATION BUD STAGE

Week 8 - 10 = Tooth bud (enamel organ?) surrounded by condensed ectomesenchyme CAP STAGE Week 11 (Early Cap Stage) - Enamel organ becomes concave = cap shape HISTODIFFERENTIATION

BUD STAGE CAP STAGE BELL STAGE

Early Late Early Late

6 7 8 9 10 11 12 13 14 15 16 17 18

INITIATION MORPHOGENESIS HISTODIFFERENTIATION Week 12 - 13 (Late Cap Stage) - Dental papilla - Stellate reticulum formation begins in the enamel organ (cells connected by ______?) - External enamel epithelium and internal enamel epithelium begins forming from peripheral cells of EO - Enamel knot???

ENAMEL KNOT = for molars in late cap stage

‘Centre that releases genes controlling cuspal development’ BELL STAGE Week 14 - 16 (Early bell stage) 2 main markers: 1. Dental lamina degeneration begins 2. 4 distinct layers - SR - EEE - IEE - Stratum intermedium Cervical loop involved in root formation Week 17 – 18? (Late bell stage)

Permanent tooth germs For 1 – 5 = lingual down growth of EEE For 6 – 8 = posterior extension of EEE

Accessional lamina = Not preceded by a tooth (i.e. 6, 7, 8)

Successional lamina = precedes another tooth (i.e. 1 – 5 in normal development) Oral epithelium

Dental lamina

Stellate reticulum

Successional lamina (permanent tooth germ) AMELOGENESIS 1. PRE-SECRETORY STAGE

Reciprocal induction • Pre-ameloblasts in IEE begin differentiating into ameloblasts • Pre-ameloblasts release growth factors  induce ectomesenchyme in dental papilla to begin differentiating into odontoblasts • Ameloblasts in contact with pre-dentine matrix being secreting enamel matrix Begins at cusp tip 2. SECRETORY STAGE

What are perikymata? 3. TRANSITION STAGE

• Ameloblast apoptosis (~50% die) 4. MATURATION STAGE

• Enamel matrix proteins degraded by serine proteases

• Water and degraded protein out • Calcium, phosphate and carbonate ions in 5. POST-MATURATION STAGE

• Ameloblasts flatten and merge with everything above it = reduced enamel epithelium • Enamel mineralisation/maturation completed via demin and remin after birth

1 2 5

3

4 DENTINOGENESIS 1. ODONTOBLAST DIFFERENTIATION

• Reciprocal induction 2. DENTINE MATRIX DEPOSITION

Predentine • Collagen I (a bit of III initially) • Dentine phosphoprotein • Other organic products, etc, etc 3. MINERALISATION • Lags behind matrix deposition (hence pre-dentine) • Matrix deposited onto type I collagen framework controlled by DPP 4. SECONDARY DENTINE

• Laid down throughout life through same mechanism as primary dentine • Has tubular structure = intratubular dentine

Intratubular (peritubular) vs intertubular? 5. TERTIARY DENTINE

• Depends on severity of injury Reactionary - Odontoblasts not dead  secretes irregular/wavy tubular dentine Reparative - Odontoblasts die = newly differentiated odontoblasts secrete atubular dentine (known is osteodentin)