Embryological Development of the Tooth “Odontogenesis”

Three Stages: Bud stage Cap stage Bell stage

Bud Stage and Dental Lamina Epithelial thickening (dental lamina) starts at 6 - 8 weeks of fetal development Lamina differentiates into tooth buds Enamel organ ➙ ameloblasts Dental papilla ➙ odontoblasts Dental follicle ➙ cementoblasts, osteoblasts, & fibroblasts Bud Stage: buds are round or ovoid

Cap Stage Round form starts to invert Appearance of a cap - cap stage

Bell Stage Concavity deepens - bell stage Most of enamel and coronal dentin laid down; DEJ identifiable Connection with dental lamina disintegrates Permanent tooth bud starts forming

A: Enamel organ (ameloblasts) B: Dental papilla (odontoblasts) C: Dental follicle (cementoblasts, osteoblasts, fibroblasts)

Root Development Bell stage ends with formation of CE line Enamel organ differentiates into Hertwig’s sheath, which forms the root structure

Root Completed Deciduous teeth: at about age 3 (one year from eruption to completion) Apical foramen becomes constricted

Eruption Active eruption: Passive eruption: Entry of tooth into oral cavity until contact with opposing tooth Passive eruption: Continuing adaptation of tooth to changing occlusal relationships Continues throughout life of the tooth

Deciduous Eruption Sequence 1. Central incisors 2. Lateral incisors 3. First molars 4. Canines 5. Second molars *Rule: mandibular precedes maxillary

Positioning of Developing Permanent Teeth Permanent anteriors develop lingual to primary roots Premolars develop within root furcations of primary molars

Mixed Dentition Period Presence of both deciduous and permanent dentition (ages 6 - 12) Mandible/maxilla start growth spurt (age 5) “Primate” spaces form between teeth Permanent first molars erupt (age 6) - cornerstones in permanent occlusion

Resorption Permanent teeth start resorption of primary roots (osteoclastic process) Resorption starts at least one year prior to exfoliation Ankylosis: root fused to bone, disrupts resorption and exfoliation

Exfoliation Root structure mostly resorbed, tooth is loose Mandibular teeth precede maxillary in exfoliation except: Primary second molars, all four are lost about same time

Deciduous Dentition

General descriptions: Twenty primary teeth (A - T) Dental formula: I C M No premolars Important in maintaining arch space for permanent dentition 2 1 2

Comparisons With Permanent Dentition Generally smaller than permanent Crowns are shorter relative to total tooth length Crowns wider M-D relative to height Facial & lingual HOC closer to cervical line

More comparisons… Crowns exhibit more F and L convexity Crowns more constricted cervically and occlusally in F-L dimensions Presence of a cervical ridge on facials of all teeth as well as linguals of all anteriors* Fewer anomalies - shapes more consistent

Still more comparisons… Deciduous roots longer relative to crown height Roots are smaller in other dimensions Apices of anterior roots are facially inclined Molar roots are flared - more space for permanent buds No root trunks - branching occurs close to crown

Finally… Deciduous crowns have milk-white color Pulp cavities larger Enamel and dentin layers thinner

Tooth ID #2 Anteriors + Premolars

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