Primary Teeth & the Mixed Dentition

Primary vs permanent teeth

Feature	Primary teeth	Clinical meaning
Enamel and dentin	Thinner, more uniform enamel; less dentin	Carious lesions reach the pulp faster
Pulp	Larger chambers; tall pulp horns, especially mesiobuccal	Easy to expose the pulp during preparation
Crown	Constricted at the CEJ with a prominent cervical bulge (most marked on the buccal of first molars)	Matrix and crown adaptation need care
Roots	Long, thin and flared (to hold the permanent tooth bud between them)	Fracture risk during extraction
Color	Whiter (more opaque)	Shade matching
Cervical enamel rods	Slope occlusally	Gingival floor of a Class II box needs no bevel

Primary tooth	Resembles
Maxillary first molar	A premolar
Maxillary second molar	Permanent maxillary first molar (smaller)
Mandibular first molar	No other tooth; prominent mesial cervical ridge and well-developed mesial marginal ridge
Mandibular second molar	Permanent mandibular first molar, but its three buccal cusps are nearly equal in size

Primary eruption order: central incisors (mandibular first, about 6–10 months) → lateral incisors → first molars → canines → second molars (about 2–2.5 years).
Permanent eruption order commonly taught: maxillary 6-1-2-4-5-3-7; mandibular 6-1-2-3-4-5-7 (the mandibular central may erupt before the first molar).
Primate spaces: mesial to the maxillary primary canines and distal to the mandibular primary canines.
Leeway space: primary canine + first molar + second molar are wider than the permanent canine + premolars; textbook figures range from about 1–1.5 mm per side in the maxilla to 2–2.5 mm per side in the mandible.
Terminal plane of the primary second molars: flush (most common), mesial step (favors Class I), distal step (leads to Class II).

Comparing the primary mandibular FIRST molar to the permanent mandibular first molar: it is the primary SECOND molar that resembles it.
Putting the mandibular primate space mesial to the canine: in the mandible it is distal.
Forgetting the tall mesiobuccal pulp horn when preparing a primary molar.
Assuming a distal step will self-correct to Class I.

Pick an answer to see right away whether it is correct and why.

Which primary tooth does not resemble any other primary or permanent tooth?
The primary mandibular second molar differs from the permanent mandibular first molar mainly in that:
Where are the primate spaces in the MANDIBULAR primary dentition?
Why are primary molar roots long, thin and flared?
A primary second molar relationship most likely to lead to a Class II permanent molar relationship is:

0 of 5 answered

Answer key: 1 B · 2 B · 3 C · 4 B · 5 A