Maxillary second molar: FDI 17 and 27

The numbers on both sides

In FDI the first digit is the quadrant and the second is the position counted from the midline. 17 is quadrant 1, position 7: the upper right second molar. 27 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 2 on the upper right and 15 on the upper left. Palmer writes the position inside a bracket that shows the quadrant. In plain text that gives UR7 and UL7.

A plain number can name two different teeth, so the system matters. Universal 17 is the mandibular left third molar, which is FDI 38. Universal 27 is the mandibular right canine, which is FDI 43.

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

Development and eruption

Calcification starts at 2.5 to 3 years and the crown is complete at 7 to 8 years. The tooth erupts at 12 to 13 years, and the root closes at 14 to 16 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 about 0.5 mm shorter than the first molar's from the biting surface to the neck and about as wide cheek to tongue. The distobuccal cusp is smaller than on the first molar and the distolingual cusp is smaller still. No fifth cusp is evident in the usual form.

The outline is rhomboidal with smaller acute angles and larger obtuse angles than the first molar, and supplemental grooves and pits are more common.

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). Figures are usual values, and teeth vary from person to person.

Roots and canals

Most teeth have three roots and three canals. The roots are as long as the first molar's or longer, but they sit closer together and can be partly fused, which narrows the furcations.

A second mesiobuccal canal is less common here than in the first molar: a Han-population pooled analysis of 9,707 second molars found 23.3 percent. The pooled prevalence of a C-shaped canal is 4.8 percent in 12 studies.

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); MolarPath note Permanent tooth morphology (built on Wheeler's Dental Anatomy, 11th ed., and Sturdevant's Operative Dentistry, 8th ed.); 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; Yousefi and others, Prevalence of c-shaped canal morphology in premolar and molar teeth assessed by CBCT, BMC Oral Health 2025. Figures are usual values, and teeth vary from person to person.

Neighbors and why no baby tooth comes first

Next to the first molar, this tooth is smaller overall, with a tapered outline. Behind it, the third molar is more variable still.

No baby tooth precedes it. The permanent molars come in behind the primary teeth and replace none of them. The primary maxillary second molar resembles a small first permanent molar, and it is the primary tooth most likely to have an oblique ridge.

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; Maxillary second molar (Wikipedia). Figures are usual values, and teeth vary from person to person.

Local anesthesia

The posterior superior alveolar block is aimed at this tooth. The needle enters the mucobuccal fold above the second molar and follows the maxillary tuberosity upward, inward and backward, staying close to bone. A path that runs outward drifts into buccal fat, and one that goes too deep or too far back can tear the pterygoid venous plexus and cause a rapidly enlarging cheek hematoma.

The palatal side needs a greater palatine block. The greater palatine foramen usually lies distal to the second molar, and the needle goes in just in front of it.

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

A dry-skull study of 944 molars found cervical enamel projections on 14.6 percent of maxillary second molars. Enamel projections extend toward the furcation and cannot hold connective tissue fibers, so the gingiva beside them attaches by epithelium only. Of the molars with a projection, 87.5 percent also had furcation involvement.

The roots sit closer together than on the first molar, so the furcations are narrower and harder to reach with instruments.

Read on 24 October 2026. Sources: Bhusari and others, Prevalence of enamel projections and its co-relation with furcation involvement in maxillary and mandibular molars, J Indian Soc Periodontol 2013. 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); 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.