Tooth Development Flashcards
what is the pattern of tooth eruption of the primary dentition with timeline
- mandibular central incisors: 5-8 mo.
-maxillary central incisors: 6-10 months
-mandibular lateral incisors: 7-10 mo. - maxillary lateral incisors: 8-12 months
- mandibular canine: 16-20 months
- maxillary canine: 16-20 months
- mandibular first molars: 11-18 months
- maxillary first molars: 11-18 months
- mandibular second molars: 20-30 months
- maxillary second molars: 20-30 months
when does calcification of the permanent dentition begin
- central incisors: 3-4 months
- maxillary lateral incisors: 10-12 months
- mandibular lateral incisors: 3-4 months
- canines: 4-5 months
- first premolars: 18-24 months
- second premolars: 24-30 months
- first molars: birth
- second molars: 30-26 months
- maxillary third molars: 7-9 years
- mandibular third molars: 8-10 years
when is the crown completely calcified in permanent dentition
- central incisors: 4-5 years
- lateral incisors: 4-5 years
- canines: 6-7 years
- first premolars: 5-6 years
- second premolars: 6-7 years
- first molars: 30-36 months
- second molars: 7-8 years
when is the first sign of tooth development in utero
6-7 weeks
when do deciduous teeth begin to calcify in untero
13-20 weeks
how long in utero for all deciduous teeth have begun to calcify
18-20 weeks
when do deciduous teeth erupt
6-30 months
what part of the tooth is the first to calcify
the crown
what gene is responsible for tooth development in the dental mesenchyme stage
msx1
what are the stages of tooth development in order
- crown formation
- root formation
- supporting structures
what are the steps in crown formation
-initiation
- bud stage
-cap stage
- bell stage
- enamel and dentin formation
describe the primary epithelial band
-horseshoe shaped
- correspond to future dental arches
what does the primary epithelial band give rise to
dental lamina and vestibular lamina
what is expressed in the epithelium where the tooth bud would form
SHH
what is expressed in the mesenchyme where the tooth bud would form
Pax9
describe the initiation of tooth development
- placode formation- epithelial thickening
- epithelial outgrowth into the mesenchyme
- initial odontogenic potential lies in the epithelium subsequently shifts to mesenchyme - the neural crest mesenchyme induces the oral ectoderm to become the dental lamina
what happens in the bud stage
-epithelial cells show no major changes
- Shh, Lef-1 and Eda-Edar involved in placode formation
- mesenchyme beneath starts to condense by the factors secreted by the epithelium
- cross talk between the epithelium and the mesenchyme
-odontogenic potential in the epithelium
what happens in the cap stage
- epithelium proliferates, mesenchyme continue to condense. looks like cap sitting on a ball of mesenchyme
- tooth germ: enamel organ and dental papilla
what is the bud to cap stage regulated by
signaling molecules and transcription factors
what does the enamel organ become
enamel of the tooth
what does the dental papilla form
dentin (outer) and pulp ( inner)
what does the dental follicle or dental sac differentiate into
supporting structures such as cementum/ periodontium/ alveolar bone proper
what is the enamel knot
a key signaling center consisting of cluster of non dividing cells that determine cusp formation
describe cap stage histodifferentiation
-cells in the enamel organ synthesize glycosaminoglycans in the ECM. hydrophilic and pull water in to the enamel organ
- increase in fluid volume forces the cells apart leading to formation of star shpaed stellate reticulum cells
what do the enamel organ epithelial cells form
- inner enamel epithelium
-outer enamel epithelium
whats happening in the bell stage
- under surface of the epithelium deepens and resembles a bell
- stratum intermedium formation
- crown attains full size and shape
where does permanent dentition form in relation to the deciduous dentition
lingual to deciduous
in the bell stage what does the OEE and IEE look like
-OEE: low cuboidal shaped outer enamel epithelium
- IEE: short columnar shaped inner enamel epithelium
what will the IEE differentiate into
ameloblasts
what is the junction of IEE and OEE called
the cervical loop
- future site of the CEJ
what happens during the late bell stage
- dental lamina breaks and separates the tooth from oral epithelium
- IEE completes folding forming the future crown pattern
- folding is due to differential rates of mitotic division in IEE
- under the influence of IEE mesenchymal cells differentiate into odontoblasts that makes dentin
- IEE differentiates in to ameloblasts and make enamel
what determines future cusp formation
site at which IEE differentiates
what are the stages in the life cycle of ameloblasts
- morphogenetic stage
- histodifferentiation stage
- initial secretory stage
- secretory stage (tome’s processes present)
- ruffle ended ameloblast of the maturation stagae
- smooth ended ameloblast of the maturation stge
- protective stage
what happens in secreotry stage ameloblasts
- intense synthetic and secretory activity
- forms enamel rod and inter rod
- secrete granules on the newly formed mantle dentin
what are the secretory products of the secretory stage ameloblasts
- proteins: amelogenin, ameloblastin, enamelin
- proteases: enamelysin (MMP20), and kallikrein
under the influence of epithelial cells, mesenchymal cells differentiate into:_____
odontoblasts that make dentin
what is mantle dentin
- first layer of dentin formed by the enwly differentiated odonotblasts, hypomineralized and only in the crown of the tooth 30-50 um thick)
what is primary dentin
formed during tooth development - 4 um/day
what is secondary dentin
dentin formed after tooth eruption (0.4 um/day)
what is tertiary dentin
dentin produced in response to injury to protect the pulp
describe root formation
- IEE and OEE form the cervical loop proliferate downward to form double layered structure called Hertwig’s epithelial root sheath
- odontoblasts differentiation and dentin formation
- completion of root formation
when is Hertwigs epithelial root sheath removed
mostly removed before cementum is laid down
what do cementoblasts differentiate from
HERS or dental follicle cells
what are remnants of HERS called
epithelial rests of Malassez
what are the 2 types of cementum
acellular and cellular
