Oral Biology - Development Of Teeth

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1st-6th Weeks of Pregnancy

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initial development of teeth

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3 Phases of Tooth Development

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Initiation - Initiates sites for teeth, already have oral cavity (stomodeum)
Morphogenesis - growing of teeth
Histogenesis - add enamel/dentin

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@6th Week of Pregnancy

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12 mm CRL
Oral Cavity is lined with low columnar cells

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Low Columnar Cells

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2-3 layers on mesoderm where teeth will develop
1 layer everywhere else

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@6th Week of Pregnancy: 1st Primordia

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1st recognizable hist. significant differenti. of an organ
1. Primary Epithelial Band
2. Proliferation of these cells across the midline
3. PEB starts to sink into mesodermal tissue

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7th-8th Week of Pregnancy

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-PEB becomes vestibular band and dental lamina
-tongue & lip are larger
-PEB is buccally situated in maxilla
-Maxillary PEB is wider

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Buccal Band of PEB

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Becomes Vestibular Band
(lip furrow band)
Marks separation of cheek and gums, thicker process

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Lingual Band of PEB

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Becomes Dental Lamina
Gives rise to teeth
Grows to be larger than vestibular band
folds into mesoderm

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Dental Lamina

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@7/8 Weeks - distinguished
small ovoid swellings that involve whole thickness of lamina, ectodermal, are enamel organs of deciduous teeth (dental organs)

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Enamel Organs

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7th-8th Week, 4 enamel organs in each quadrant, dM2 & M1 grow off distal edge of dM1, 6 dental organs in each quadrant

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10th - 11th Week of Development/Pregnancy

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40 mm CRL
dM2 Appears

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15th-16th Week of development/pregnancy

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100mm CRL
M1 Appears

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Enamel organs of other permanent teeth appear _____.

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AFTER birth

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Production of Dental Papilla

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Mesoderm massing occurs
Makes up primitive dentin, cementum, pulp chamber, dental follicle

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Ectoderm gives rise to

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enamel and dental organ

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Mesoderm gives rise to

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dental papilla (dentin region, pulp, cementum), dental follicle (vascular cocoon that everything is in)

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______ triggers the enamel organ.

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Dentin

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Bud Stage: DentinEnamel Junction

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is the fossilized basil membrane /papillary region btw enamel and dentin (where the two were together during formation)

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Bell Stage

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continuity of meso & ecto @ base
continuity is in the very tip (gubernacular core)
upper region is a guid to the oral cavity, tip will use it as a guide to know where to go

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Bell Stage: Dental Lamina

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dental lamina grows into the jaws, creates a ledge w/swllings (den organs), @ Bell stage ledge dissolves except for region at tip (guide for emergence), creates isolated tooth germs

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Distal side of dM1 has a remant of the gubernacular cord

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it is a deteriorated remnant of the dental lamina

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Permanent teeth form...

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on the lingual side of deciduous developing tooth germ, occurs in 4th Fetal month, 100mm CRL

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Enamel Organ has 4 cell types

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Innerenamel epitheliam (along inside on DEJ), In that are the Stellate reticulum and stratum intermedium (layer in betw innerenamel cells and stellate), Outerenamel epithelium (outside of DEJ)

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Cervical Loop

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where all growth takes place in tooth formation, inner and outer epith. cells come together, determining the shape of the tooth

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Innerenamel epithelial cells during bell stage

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convert into ameloblasts and deposit enamel, when enamel is secreted maybe half the crown is mapped out at the cervical loop, nutrients are taken out of the mesoderm

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Enamel & dentin formation begin after

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enamel organ takes on cellular differentiation

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Fibroblasts

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are maintenance cells, main structures in dental follicle to form periodontal ligament

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Mesodermal tissue during Bell Stage

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dental papilla - capillary appearance and collagen fibers appear, this is in the region where entin will arise

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2 Purposes of Dental Follicle

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keep tooth in contact w/oral cavity, nurish what is on the inside

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Dental follicle is the byproduct of

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mesoderm

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Dental follicle is the

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fibrovascular cocoon hanging from the gubernaculum

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the Dental Follicle houses the

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tooth germ

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5 Key Components

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Enamel Organ, inner epith, out epith, stratum/stellate, dental pathway

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Inner Enamel Epithelium Functions

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-determined the form of the crown
-evokes cells in dental pap to become odontoblasts (then odontoblasts lay dentin, then IEE becomes ameloblasts which cover dentin w/enamel)
-maps the root in conjunction with the outer enamel epithelium

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Dentin & Enamel form in Crown

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4-6 months in deciduous teeth, mineralization of tooth, continue 8-11 months after birth

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Lag btw completion of crown & root growth because

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root growth CAUSES emergence

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Eruption/emergence

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1st movement of completed crown
entails remodeling of surrounding tissue
hole for grubunacular

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emergence is not complete until

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it meets the antagonists

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4 Mechanisms w/tooth Emergence

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1. Pulpal Growth
2. Root Formation
3. Periodontal Ligament Formation
4. Bone deposition & resorption

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5 Theories for Eruption

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1. Root Growth
2. Bone Growth
3. Growth of Pulp
4. Increase in Blood Pressure
5. Periodontal Ligament Form.

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Clinical Practice includes

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tooth measurements (x-rays)

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Histology

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#/frequency of cells in mitosis in pulpal region

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Experiments with rats and rabbits because

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they have continuously growing incisors

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When the Sheath of Hertwig breaks down

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the exposed dentin triggers a response from dental follicle (undifferentiated mesodermal cells become cementecytes and secrete cementum)

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Hertwig has

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2 layers and grows the root (coninuation of dentin)

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After cementum -->

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-pulls in collagen fibers through follicle
-other end of fibers are attached to alveolar bone
-follicle becomes part of the alveolar bone

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The crown NEVER

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touches the mesoderm because it emerges through ectodermally lined pathway (no bleeding)

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3 Things for functional occlusion

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1. early tooth development (initiation and morphogenesis) (crown and root development)
2. formation of hard tissues (histogenesis)
3. root formation