1. The groove pattern resembles a “Y”.
2. The cusp sizes are: MB > ML > DL > DB > D.
3. They have the largest MD crown dimension and root separation of any other teeth in the mouth.
4. They usually have two roots and three canals (two mesial canals and one distal canal).
5. The occlusal outline is pentagonal.
6. They have the largest faciolingual crown dimension of any other mandibular tooth.
7. There is a developmental groove between the DF and D cusp.
8. They have the longest root of any molar.

Pictured here: Tooth #30

Mandibular Second Molars (#18, #31)

1. The occlusal groove pattern is cruciform (see blue +).
2. From the occlusal, the faciolingual diameter is greater in the mesial 1/3 than in the distal 1/3.
3. They are the only posterior teeth and mandibular teeth wider MD than FL.
4. The crown inclines to the mesial and to the lingual.
5. There is a prominent groove on the buccal.
6. The roots that are less divergent than those of mandibular first molars

Pictured here: Tooth #31

Mandibular Third Molars (#17, #32)

1. They have the most variation in crown morphology (even more than maxillary wisdom teeth!)
2. They have the greatest distal root inclination of any other tooth.
3. They have the shortest root of any other mandibular tooth.
5. Abnormalities of occlusion and eruption often occur.
6. Keep in mind: the third molars have the most variation of anatomy of any tooth in the mouth!

Pictured here: Tooth #32