12. Morphology of primary (deciduous) teeth. Distinguishing marks for primary teeth.
Covers the eruption and shedding timeline of the primary dentition, from first teeth at about six months to replacement by permanent teeth through the mixed dentition. It also outlines the stages of tooth formation, from initiation to the advanced bell stage, and a theory summary on eruption. A comparison table sets out the distinguishing features of primary against permanent teeth, covering size, colour, cervix, enamel, pulp and roots. The note closes with why these differences matter clinically, such as rapid pulp exposure and space loss.
Topic 12 of 75 in the MU Sofia syllabus for Preclinics of Dental Prosthetics (Dental Medicine, Year 2). The free AceMed note covers it in 5 sections, about 257 words (3 min of reading), with 14 flashcards.
In this note
Introduction
When they come and go
How a tooth forms
Primary or permanent? How to tell
Why this matters
Introduction
The primary (deciduous) dentition has 20 teeth: in each quadrant two incisors, one canine and two molars. In the FDI system they are quadrants 5 to 8, so 51 is the upper right central incisor and 85 the lower right second molar. Over a lifetime a person grows 52 teeth: 20 primary and 32 permanent.
When they come and go
Primary teeth erupt from about 6 months (usually the lower central incisors first) until about 2½ years, when the second molars arrive.
At about 6 years the first permanent molar erupts behind the primary second molar, without replacing anything, and the mixed dentition begins.
From 6 to about 12 years the primary teeth are shed one by one as permanent successors push up under them: incisors replace incisors, the canine replaces the canine and the premolars replace the primary molars.
By 12–13 years the permanent dentition stands complete apart from the third molars, which follow at 17–21 years or never.
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