Primary + Mixed Dentition

Why this matters

 Identify primary vs permanent teeth on radiographs

 Avoid confusing normal growth with pathology

 Detect abnormalities or disturbances

 Essential for charting and pediatric/adolescent DHD

Learning objectives

1. Identify the primary teeth and eruption patterns of the permanent teeth as viewed on dental images.

2. Identify and describe the radiographic appearance of primary and mixed dentition.

3. Identify and describe the radiographic appearance of the following structures: primary root, root canal, crown, enamel

4. Explain the different radiographic appearance between the primary and permanent dentition

5. Explain eruption sequence of primary and permanent dentition

Three periods of dentition

Primary

Mixed

Permanent 

Primary Dentition Stage

Mixed dentition stage

Permanent dentition stage 

Tooth eruption sequence

Eruption sequence (permanent teeth)

Morphological differences

Primary:

• shorter

• narrow occlusal table

• constricted in the cervical portion 

Permanent:

• bigger

• broad occlusal table

• cervical constriction is not well marked 

Primary characteristics

 Thinner enamel and dentin layers

 Enamel rods in the cervical area directed occlusally

 Broad flat contacts

 Color is usually lighter

 Mesio-buccal cervical bulge seen in primary molars

 Incisors have no developmental grooves

• Mamelons

Permanent Characteristics

 Thick enamel and dentin

 Enamel rods in the cervical are directed gingivally

 Point contacts

 Color is much darker (not as white)

 Have mamelons

 Less prominent cervical bulge in molars

How to use the differences in identifying the dentition in radiographs: start with the roots 

How to use the differences in identifying the dentition in radiographs: look at the pulp

Key differences to identify primary vs permanent dentition

 Enamel and dentin are thinner in primary

 Pulp chamber is wider

 Pulp horn is more prominent

 Smaller root trunk for primary

Normal eruption patterns

 As a permanent tooth develops, the root length increases and it moves into position by “pushing out” the primary tooth

 While this is happening, the primary tooth root starts to resorb and shorten

 What is happening in this radiograph?

 Primary molars

• Flared roots

• Resorption

 Permanent molars

• Straighter, longer roots

• Roots still forming

• Apical foramen open & wide

Follicular space

• RL area surrounding developing tooth

• Normal

Dental charting