Deciduous vs. Permanent Teeth

I. General Characteristics & Development

Feature	Deciduous Teeth	Permanent Teeth
Number	20 teeth	32 teeth (including third molars)
Types of Teeth	Incisors, Canines, Molars (Premolars are absent)	Incisors, Canines, Premolars, Molars
Size & Morphology	– Generally smaller in all dimensions. – Crowns have a more bulbous contour. – Marked cervical constriction. – Mamelons are absent on newly erupted incisors.	– Larger in all dimensions. – Cervical constriction is less pronounced. – Mamelons are present on newly erupted incisors.
Development	– Develop directly from the dental lamina. – Often not fully covered by a bony crypt. – A neonatal line is present in all teeth, marking the boundary between pre-natal and post-natal enamel formation.	– Develop from extensions of the dental lamina. – Develop within and are covered by bony crypts. – A neonatal line is typically absent, except in the first permanent molars.
Eruption & Lifespan	– Full eruption by ~2.5-3 years of age. – Root completion takes 1-1.5 years after eruption. – Average lifespan in the mouth is 6-10 years.	– Full eruption (excluding 3rd molars) by ~12-13 years. – Root completion takes 2-3 years after eruption. – Designed for a lifetime (60+ years).
Occlusal Relationship	– End-to-end (tooth-to-tooth) relationship is common.	– Intercuspal relationship (cusp-to-fossa).

II. Crown & Enamel

Feature	Deciduous Teeth	Permanent Teeth
Enamel Thickness	Thinner (approx. 1mm).	Thicker.
Enamel Mineralization	Less mineralized, appears whiter and more opaque.	Highly mineralized, appears more translucent.
Acid Resistance	More prone to acid attack; demineralizes faster.	Less prone to acid attack.
Enamel Rod Direction	At the cervical area, rods slope occlusally.	At the cervical area, rods slope gingivally.
Etching Time	Requires longer acid-etching time for bonding due to lower mineralization.	Requires standard or shorter etching time.

III. Roots & Supporting Structures

Feature	Deciduous Teeth	Permanent Teeth
Root Shape	– Longer and more slender relative to crown size. – Roots of molars flare markedly apically to accommodate developing permanent tooth buds. – Root trunk is absent or minimal; bifurcation/trifurcation begins near the cervix.	– Roots are proportionate to crown size. – Flaring is less pronounced. – A distinct root trunk is present.
Periodontal Ligament (PDL)	– Total PDL area is smaller. – The lamina dura (bony lining of the socket) is relatively thick.	– Total PDL area is larger. – The lamina dura is relatively thin.

IV. Dentin

Feature	Deciduous Teeth	Permanent Teeth
Thickness	Dentin thickness is less. The ratio is approximately 1:2 (deciduous:permanent).	Dentin is significantly thicker.
Mineralization	Less mineralized and softer.	More highly mineralized and harder.
Dentinal Tubules	Number of dentinal tubules per mm² is less.	Number of dentinal tubules per mm² is greater (50,000-90,000).
Dentinoenamel Junction (DEJ)	The DEJ is relatively flat and less scalloped.	The DEJ is scalloped (with convexities toward the pulp).

V. Pulp

Feature	Deciduous Teeth	Permanent Teeth
Pulp Chamber	– Pulp volume is larger relative to tooth size. – Mesial pulp horn in molars is higher and more prominent, increasing risk of exposure. – No marked cervical constriction between chamber and canals.	– Pulp volume is smaller relative to tooth size. – A distinct cervical constriction is present.
Root Canals	– Number of accessory canals is greater, especially in the furcation area. – Apical foramen position is variable due to physiological root resorption.	– Fewer accessory canals. – Apical foramen position is fixed.
Innervation & Repair	– Nerves end at the pulpodentinal junction; few penetrate far into dentin. – Reparative capacity is lower; formation of reparative dentin is less.	– Nerves can extend further into the dentinal tubules. – Reparative capacity is higher.