Maxillary first molar: FDI 16 and 26

The numbers on both sides

In FDI the first digit is the quadrant and the second is the position counted from the midline. 16 is quadrant 1, position 6: the upper right first molar. 26 is the same position in quadrant 2, on the upper left. Universal numbers adult teeth from 1 at the upper right third molar around to 32 at the lower right third molar, which makes this tooth 3 on the upper right and 14 on the upper left. Palmer writes the position inside a bracket that shows the quadrant. In plain text that gives UR6 and UL6.

A plain number can name two different teeth, so the system matters. Universal 16 is the maxillary left third molar, which is FDI 28. Universal 26 is the mandibular right lateral incisor, which is FDI 42.

Crown surfaces: mesial, distal, buccal, palatal (lingual) and occlusal.

Development and eruption

Calcification begins at about birth, earlier than any other permanent tooth, and the crown is finished at 2.5 to 3 years. The tooth erupts at 6 to 7 years behind the primary second molar and replaces no baby tooth. The root closes at 9 to 10 years.

Read on 24 October 2026. Sources: Human tooth development, tables citing Ash and Nelson, Wheeler's Dental Anatomy, Physiology and Occlusion (Wikipedia); American Dental Association, Tooth development charts (primary and permanent). Figures are usual values, and teeth vary from person to person.

Crown

The crown is the largest in the upper arch and is broader cheek to tongue than front to back, usually by about 1 mm. Four major cusps carry the table: mesiobuccal, distobuccal, mesiolingual and distolingual. The mesiolingual cusp is the largest.

A fifth, variable cusp of Carabelli can sit on the lingual surface of the mesiolingual cusp. It ranges from a full cusp to a ridge, groove or pit. Its frequency differs by population: high in Americans of northwest European origin and absent in unmixed Eskimo groups, as one chapter summarizes.

An oblique ridge runs across the table from the mesiolingual cusp to the distobuccal cusp and separates the central fossa from the distal fossa. It is the landmark that identifies an upper molar, and it can be crossed by a groove.

Read on 24 October 2026. Sources: Mufadhal and others, External and internal anatomy of maxillary permanent first molars (IntechOpen, 2019); Craciunescu and others, Dental Anatomy and Morphology of Permanent Teeth, in Human Teeth, From Function to Esthetics (IntechOpen, 2023); MolarPath note Permanent tooth morphology (built on Wheeler's Dental Anatomy, 11th ed., and Sturdevant's Operative Dentistry, 8th ed.). Figures are usual values, and teeth vary from person to person.

Roots and canals

Three well-spread roots hold the tooth: mesiobuccal, distobuccal and palatal. Mean lengths in one chapter are 12.9 mm for the mesiobuccal root, 12.2 mm for the distobuccal root and 13.7 mm for the palatal root. A Saudi CBCT sample found three separate roots in 94 percent of teeth.

The usual pattern is three roots and four canals. The second mesiobuccal canal, MB2, lies palatal and mesial to the main mesiobuccal orifice. A review of 21 regions gave a global proportion of 73.8 percent, with a range from 48.0 to 97.6 percent, and a pooled analysis in the Han population found 63.7 percent. The distobuccal and palatal roots hold a single canal in 98.3 and 99 percent of teeth.

The palatal canal often curves toward the cheek near its tip. That bend lies in the buccolingual plane, so a standard periapical film hides it and the working length can be underestimated.

Read on 24 October 2026. Sources: Mufadhal and others, External and internal anatomy of maxillary permanent first molars (IntechOpen, 2019); Wu and others, Prevalence of second mesiobuccal canal in maxillary first and second molar detected using CBCT in the Han population, J Dent Sci 2026; Number of roots and canals, from Ingle's Endodontics (animated-teeth.com); MolarPath note Pulp chambers and root canal morphology (built on Cohen's Pathways of the Pulp, 12th ed.). Figures are usual values, and teeth vary from person to person.

Neighbors and why no baby tooth comes first

The second molar is smaller, with a reduced distolingual cusp, and its roots lie closer together. In the baby teeth, the primary maxillary second molar resembles a small first permanent molar.

The first permanent molar erupts distal to the primary second molar, behind the baby teeth. This accessional eruption is easy to confuse with replacement eruption, but no primary tooth precedes this molar.

Read on 24 October 2026. Sources: Craciunescu and others, Dental Anatomy and Morphology of Permanent Teeth, in Human Teeth, From Function to Esthetics (IntechOpen, 2023); Chussid, Anatomy of Primary Teeth, Columbia University College of Dental Medicine lecture; MolarPath note Eruption sequence and chronology (built on McDonald and Avery, 11th ed., and Proffit's Contemporary Orthodontics, 7th ed.). Figures are usual values, and teeth vary from person to person.

Local anesthesia

The posterior superior alveolar nerve supplies the molar pulps and the buccal tissue. It may leave the mesiobuccal root sensitive, because that root receives the middle superior alveolar nerve, and a buccal infiltration over the root is the usual supplement. The zygomatic buttress over the first molar is dense and slows diffusion.

Palatal tissue is separate: an extraction needs a posterior superior alveolar block for the buccal side and pulp, plus a greater palatine block for the palate.

Read on 24 October 2026. Sources: MolarPath note Maxillary techniques, local anesthesia (built on Malamed's Handbook of Local Anesthesia, 7th ed.). Figures are usual values, and teeth vary from person to person.

Clinical and exam points

The mesial furcation entrance sits palatal to the middle of the mesial surface, so a curved probe placed from the palatal side reaches it best. The buccal furcation lies between the two buccal roots.

One summary of Ingle's Endodontics cites MB2 detection of 73 percent by visual inspection and 93 percent under the microscope. A chapter on this tooth advises assuming MB2 is present until clinical and radiographic evidence shows otherwise.

The AAPD records ectopic eruption of first permanent molars in up to three percent of the population. It is more common in the upper arch, and 71 percent correct themselves by age nine.

Read on 24 October 2026. Sources: MolarPath note Permanent tooth morphology (built on Wheeler's Dental Anatomy, 11th ed., and Sturdevant's Operative Dentistry, 8th ed.); Number of roots and canals, from Ingle's Endodontics (animated-teeth.com); Mufadhal and others, External and internal anatomy of maxillary permanent first molars (IntechOpen, 2019); American Academy of Pediatric Dentistry, Management of the Developing Dentition and Occlusion in Pediatric Dentistry (2024 revision). Figures are usual values, and teeth vary from person to person.

Questions and answers

Read on 24 October 2026. Sources: American Dental Association, Tooth development charts (primary and permanent); Mufadhal and others, External and internal anatomy of maxillary permanent first molars (IntechOpen, 2019); Wu and others, Prevalence of second mesiobuccal canal in maxillary first and second molar detected using CBCT in the Han population, J Dent Sci 2026; Craciunescu and others, Dental Anatomy and Morphology of Permanent Teeth, in Human Teeth, From Function to Esthetics (IntechOpen, 2023). Figures are usual values, and teeth vary from person to person.