Impacted third molars: Winter and Pell & Gregory
What you need to know
- Third molars, if they come in, appear roughly between the ages of 17 and 21. Some stay inside the bone: they're said to be retained or impacted.
- Winter classifies them by how the third molar is tilted compared with the second: vertical (parallel), mesioangular (tilted forward), horizontal (lying down) and distoangular (tilted backward). There's also the inverted type (with the crown facing down).
- In studies, the most common are mesioangular and vertical; which one comes out on top depends on the population. In a study of 1,055 molars, mesioangular made up 41.8%.
- Pell and Gregory look at 2 things. The space in front of the mandibular ramus: Class I (plenty of space), Class II (a bit short of space) and Class III (no space).
- And the depth compared with the second molar: position A (level with its chewing surface), B (between that surface and the cervical line of the tooth) and C (below the cervical line).
- Problems they can cause: pericoronitis (infection of the gum covering the tooth), caries on the back surface of the second molar, pain, swelling and wearing away of neighboring roots (resorption).
Winter's classification
| Type | How the tooth sits |
|---|---|
| Vertical | Parallel to the second molar |
| Mesioangular | Tilted forward, toward the second molar |
| Horizontal | Lying down, perpendicular to the second molar |
| Distoangular | Tilted backward, toward the ramus |
| Inverted | The crown faces down |
Terms in plain words
Impacted toothA tooth that doesn't fully erupt because something blocks it (also called a retained tooth).
PericoronitisInflammation or infection of the gum covering a molar that's erupting.
Mandibular ramusThe vertical part of the mandible, behind the molars.
MesioangularTilted forward (mesially).
For the exam
A lower third molar is tilted forward, resting against the second molar. What is it called according to Winter?
Show answerHide answer
Mesioangular.
Sources
- Santos KK, et al. Prevalence of Mandibular Third Molars According to the Pell & Gregory and Winter Classifications. J Maxillofac Oral Surg. 2022;21(2):627–633. View source
- American Dental Association (MouthHealthy): eruption charts. View source
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