Permanent premolars

Why this matters

The premolars are the teeth where 'what the textbook says' and 'what is in front of you' part company most often. Whether an upper first premolar has one root or two is a statement about a population, not about the tooth: in one standardised 22-country protocol the proportion of single-rooted upper first premolars ranged from 10% to 75.7%. A lower first premolar can carry one root and two canals. A 2 mm bump on a newly erupted lower second premolar can contain a pulp horn.

The big picture

Four tooth types, described for a century in words with no denominators and measured for twenty years by CBCT taken for other reasons. This lesson puts the two side by side: descriptive sources for what to look for, imaging series for how often it is there - and where neither exists, it says so.

The 15 cards in this lesson

1. 01Eight premolars, four types, and a vocabulary that starts counting in three places
2. 02The maxillary first premolar: one central groove with two ends that are named separately
3. 03The most-taught feature of the upper 4 rests on one prevalence study, in one population
4. 04The mesial cervical concavity: essentially universal as a shape, roughly 62-74% as a measurement
5. 05Maxillary first versus second premolar: everything separates them except width
6. 06Three examinable premolar facts that no one has measured
7. 07The mandibular first premolar: a transverse ridge and a lingual half that never finished
8. 08The lower second premolar: read the groove pattern before you count the cusps
9. 09Root number is a distribution, and the distribution moves between countries
10. 10Roots and canals are two different counts, and the second one is the dangerous one
11. 11Clinical alert — in the lesson
12. 12On the lower first premolar, a groove you can see predicts a canal system you cannot
13. 13Four pulp chambers, four different problems
14. 14Dens evaginatus: a 2 mm tubercle with a pulp horn inside it
15. 15Five premolar variations, and one rule for reading them all

You have got it when

You can (1) name each of the four premolar types from its crown outline, cusp pattern and groove pattern; (2) say which classic 'distinguishing features' have a measured prevalence and which are descriptive conventions with no denominator; (3) state root number as a distribution with its population attached, and explain why root number does not predict canal number; and (4) recognise a radicular groove, a dens…