Anatomy of the mandibular first molar
- The mandibular first molar has five cusps: mesiobuccal (MB), mesiolingual (ML), distolingual (DL), distobuccal (DB), and distal (D).
- The cusps are listed in order of decreasing size: ML, DL, DB, MB, and D.
- The occlusal surface of the mandibular first molar is pentagonal in shape and tapers toward the lingual.
- The tooth has four grooves: central groove, distobuccal groove, lingual groove, and buccal groove.
- The mandibular first molar has two roots, with the distal root generally being straighter.

Pathology of the mandibular first molar
- The shape of the developmental and supplementary grooves on the occlusal surface is described as being M-shaped.
- Mandibular first molars are the most common carious teeth.
- They are also the most common teeth to undergo endodontic treatment or extraction.
- Up to 45% of all extracted teeth are mandibular first molars.

References
- Zadik Y, Sandler V, Bechor R, Salehrabi R (August 2008). Analysis of factors related to extraction of endodontically treated teeth.
- Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 106 (5): e31–e35. doi:10.1016/j.tripleo.2008.06.017. PMID18718782.
- Ash, Major M. and Stanley J. Nelson, 2003. Wheelers Dental Anatomy, Physiology, and Occlusion. 8th edition.
- Rodriguez-Florez, C.D. et al., 2006. Occurrence of an Eighth Cusp on Primary Second Mandibular Molars of a Contemporary Argentinean Child. Dental Anthropol 19(3): 83-85. (http://anthropology.osu.edu/DAA/back%20issues/DA%20Vol%2019%203.pdf)

Notation for deciduous teeth
- In the universal system of notation, the deciduous mandibular first molars are designated by a letter written in uppercase.
- The right deciduous mandibular first molar is known as S, and the left one is known as L.
- The international notation uses a different system, with the right deciduous mandibular first molar known as 84 and the left one known as 74.

Notation for permanent teeth
- In the universal system of notation, the permanent mandibular first molars are designated by a number.
- The right permanent mandibular first molar is known as 30, and the left one is known as 19.
- The Palmer notation uses a number in conjunction with a symbol designating the quadrant the tooth is found in.
- For this tooth, the left and right first molars would have the same number (6), with the right one having the symbol ┐ and the left one having ┌.
- The international notation has a different numbering system, with the right permanent mandibular first molar known as 46 and the left one known as 36.

Mandibular first molar (Wikipedia)

The mandibular first molar or six-year molar is the tooth located distally (away from the midline of the face) from both the mandibular second premolars of the mouth but mesial (toward the midline of the face) from both mandibular second molars. It is located on the mandibular (lower) arch of the mouth, and generally opposes the maxillary (upper) first molars and the maxillary 2nd premolar in normal class I occlusion. The function of this molar is similar to that of all molars in regard to grinding being the principal action during mastication, commonly known as chewing. There are usually five well-developed cusps on mandibular first molars: two on the buccal (side nearest the cheek), two lingual (side nearest the tongue), and one distal. The shape of the developmental and supplementary grooves, on the occlusal surface, are described as being 'M' shaped. There are great differences between the deciduous (baby) mandibular molars and those of the permanent mandibular molars, even though their function are similar. The permanent mandibular molars are not considered to have any teeth that precede it. Despite being named molars, the deciduous molars are followed by permanent premolars.

Mandibular first molar
Mandibular first molars of permanent and primary teeth marked in red.
Identifiers
FMA	290275
Anatomical terminology [edit on Wikidata]

In the universal system of notation, the deciduous mandibular first molars are designated by a letter written in uppercase. The right deciduous mandibular first molar is known as "S", and the left one is known as "L". The international notation has a different system of notation. Thus, the right deciduous mandibular first molar is known as "84", and the left one is known as "74".

In the universal system of notation, the permanent mandibular first molars are designated by a number. The right permanent mandibular first molar is known as "30", and the left one is known as "19". The Palmer notation uses a number in conjunction with a symbol designating in which quadrant the tooth is found. For this tooth, the left and right first molars would have the same number, "6", but the right one would have the symbol, "┐", over it, while the left one would have, "┌". The international notation has a different numbering system than the previous two, and the right permanent mandibular first molar is known as "46", and the left one is known as "36". Mandibular permanent first molars usually have four pulp horns.

The first molar is usually the first permanent tooth to erupt at 6–7 years and has adult undertones.