Growth and Development Part III

neural crest forms

• cranial and sensory ganglia and nerves

• medulla of suprarenal (adrenal) gland

• pigment cells

• pharyngeal arch cartilages (maxillary and mandible)

• head mesenchyme and CT

• bulbar and conal ridges in heart

neural tube forms

• central nervous system

• retina

• pineal body

• posterior part of pituitary gland

ectoderm → epithelial layer →

dental laminae → bud → cap → bell

ectoderm → neural crest →

ectomesenchyme → dental mesenchyme → dental papilla or embyronic dental pulp

primary teeth and permanent molars come from

general lamina

succedaneous teeth come from

successional lamina

hypodontia

• 1-5 teeth missing

• MSX1, PAX9

oligodontia

• more than 6 teeth missing

• MSX1, PAX9

anodontia

• all teeth missing

• AXIN2

conical shape

• small, peg-shaped

• most common in anterior maxilla

tuberculate shape

• barrel-shaped

• rarely erupt; commonly block eruption

supplemental tooth

extra lateral incisor or premolar

compound odontoma

• multiple, small tooth-like structures

• common in anterior maxilla; blocks eruption

complex odontoma

• mass of dental tissues

• common in posterior mandible; blocks eruption

mesiodens location

• between maxillary central incisors

• often conical

• causes midline diastema or impaction

paramolar location

• buccal/lingual to molars

• small, rudimentary

distomolar location

• distal to 3rd molars

• may be unerupted

• rarely symptomatic

parapremolar location

often supplemental in shape

bilateral fusion is more common in

primary dentition

fusion in permanent dentition

more frequent in maxilla, usually involving central incisor

geminated teeth are mostly

unilateral

a fused tooth has

two pulp chambers and root canals

a geminated tooth has

one pulp chamber and root canal

fusion

• fusion of cementum, dentin, and enamel

• one less tooth in arch

gemination

• one large shared pulpal canal and bifid crown

• normal number of teeth

twinning

• complete gemination

• supernumerary → one extra tooth in arch

concrescence

union of adjacent teeth with cementum only

proliferation occurs at

9-10 weeks

differentiation occurs in

cap stage

morphogenesis occurs in

early bell stage

natal teeth

supernumerary or central incisor

eruption of primary teeth complete within

24-30 months of age

spacing at anterior segment of primary dentition

increases w/ age and is important for permanent teeth alignment

outcome of crowding

almost certain extraction

primate space in maxillary arch is located

between lateral incisors and canines

primate space in mandibular arch is located

between canines and first molars

pre-emergent eruption starts

when crown formation is complete, and root development starts

steps of pre-emergent eruption

1) resorption of overlying tissues— path of eruption

2) eruptive forces— move tooth towards path of eruption

resorption of overlying tissues is dependent on

dental follicle; regulated by TGF-B1 and EGF

signal for bone resorption is activated by

crown completion

controlling factor of eruption path

resorption (root formation is not necessary)

stages of post-emergent eruption

1) post-emergent spurt

2) juvenile occlusal equilibrium

3) adult occlusal equilibrium

post-emergent spurt

• once tooth emerges, it erupts rapidly to reach occlusal level

• growth peaks at 8 PM - 1 AM; circadian rhythm and growth hormone match

• mainly collagen crosslinking in PDL

juvenile occlusal equilibrium

teeth continue to erupt as vertical growth of ramus continues

adult occlusal equilibrium

• after pubertal spurt, teeth continue to erupt extremely slowly

• wear and tear

transition from primary to permanent teeth begins at

about 6 years

at dental age 6

eruption of mandibular incisors and first molars

at dental age 7

• eruption of maxillary centrals & mandibular laterals

• canines and premolars are in crown competition or beginning root formation

• advanced root formation of maxillary laterals

at dental age 8

eruption of maxillary laterals

at dental age 9

• teeth CDE present

• 1/3 root of mandibular #3 and #4 formed

most permanent teeth begin to erupt when

about 2/3 of root is formed

by the time a tooth reaches occlusal plane

root is usually about ¾ complete

at dental age 10

• root resorption of primary canines and molars

• ½ of mandibular #3 and #4 complete

• root of mandibular incisors is complete

root completion occurs

2-3 years after eruption

at dental age 11

• eruption of mandibular #3 and #4, maxillary #4

• only remaining teeth: maxillary canines and second premolars

at dental age 12

all succedaneous teeth erupt

at dental age 15

all roots of permanent teeth are complete, except 3rd molars

disturbances in sequence

• eruption of 2nd molars before premolars in mandibular arch

• eruption of canines before premolars in maxillary arch

• asymmetry in eruption

permanent incisors are each

2-3 mm wider than their primary

incisor liability

primate space in distal to the canine in mandibular arch

resolution of incisor liability

• permanent teeth erupt upwards and outwards

• permanent incisors more labially inclined

• repositioning of mandibular canines into primate space

ugly duckling stage

maxillary incisors flare laterally and are widely spaced when they first erupt

leeway space

extra space due to primary molars being larger than premolars

when 2nd primary molars are lost

1st permanent molars rapidly move forward (mesially) into leeway space → loss of arch length and circumference

significance of leeway space

space bank to relieve moderate incisor crowding

maintain leeway space by

preventing mesial movement of permanent 1st molar into space

normal relationship of primary molar teeth

flush terminal plane relationship

distal step is equivalent to

angle class II

mesial step is equivalent to

angle class I

equivalent to class III is never found in primary dentition because

normal pattern of growth where mandible lags behind maxilla