Mandibular third molar: FDI 38 and 48

The numbers on both sides

In FDI the first digit is the quadrant and the second is the position counted from the midline. 38 is quadrant 3, position 8: the lower left third molar. 48 is the same position in quadrant 4, on the lower right. 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 17 on the lower left and 32 on the lower right. Palmer writes the position inside a bracket that shows the quadrant. In plain text that gives LL8 and LR8.

Crown surfaces: mesial, distal, buccal, lingual and occlusal.

The ADA chart also uses the older name wisdom tooth.

Development and eruption

Calcification starts at 8 to 10 years and the crown is complete at 12 to 16 years. The tooth erupts at 17 to 21 years, if it erupts, and the root is not finished until 18 to 25 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 highly variable. Many have five or more cusps, and some are larger than the second molar. A well-developed third molar closely resembles the second molar, with short, rounded buccal cusps. The outline is often more rounded, with a smaller cheek to tongue dimension at the back.

The crown is wider at its contact areas than at the cervix.

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

In a study of 639 extracted mandibular third molars from northern Jordan, 89.7 percent had two roots, 7.4 percent three, 2.5 percent one and 0.47 percent four. Canal counts were three in 55.71 percent, two in 29.42 percent, four in 13.61 percent and one in 1.09 percent.

Roots are shorter and less developed than on other molars, and can be separate or fused along their length. A pooled analysis reports C-shaped canals in 8.4 percent of lower third molars from five studies.

Read on 24 October 2026. Sources: Al-Qudah and others, Root and canal morphology of third molar teeth, Scientific Reports 2023; Yousefi and others, Prevalence of c-shaped canal morphology in premolar and molar teeth assessed by CBCT, BMC Oral Health 2025; 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.

Neighbors and why no baby tooth comes first

The second molar in front of it has a tidy four-cusp crown, while the third molar may have five or more cusps. Cervical enamel projections are least frequent on this tooth: 5.5 percent in a dry-skull study.

It has no predecessor. Space is often inadequate for it, so impaction is 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); Bhusari and others, Prevalence of enamel projections and its co-relation with furcation involvement in maxillary and mandibular molars, J Indian Soc Periodontol 2013; 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

An inferior alveolar block numbs the pulp, the lower lip and the chin. The lingual nerve lies alongside the inferior alveolar nerve in the pterygomandibular space and is reached by the same deposit, though a smaller one. The buccal gingiva of the molar belongs to the long buccal nerve, which the inferior alveolar block misses, so a separate injection is added for surgery.

The Gow-Gates technique anesthetizes the inferior alveolar, lingual, mylohyoid and in most patients buccal nerves from one deposit, at the price of a slower onset of about 5 minutes.

Read on 24 October 2026. Sources: MolarPath note Mandibular 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 2024 meta-analysis found impacted third molars in 36.9 percent of people, with the mandible affected more often than the maxilla. The inferior alveolar canal runs close to the roots, and a cohort of 165 impacted mandibular third molars found a neurosensory deficit after surgery in 7.3 percent: 5.5 percent transient and 1.8 percent permanent.

In that cohort, deep impaction, horizontal angulation and radiographic overlap with the inferior alveolar canal were each linked to deficits, with adjusted odds ratios of 5.10, 3.80 and 4.20. It is a retrospective cohort of 135 patients, so the figures show direction more than a rate to quote to a patient.

Read on 24 October 2026. Sources: Pinto and others, Worldwide Prevalence and Demographic Predictors of Impacted Third Molars, J Clin Med 2024; Yadav and others, Risk Factors Associated With Inferior Alveolar and Lingual Nerve Injury Following Surgical Extraction of Impacted Mandibular Third Molars, Cureus 2026. 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); Al-Qudah and others, Root and canal morphology of third molar teeth, Scientific Reports 2023; Yadav and others, Risk Factors Associated With Inferior Alveolar and Lingual Nerve Injury Following Surgical Extraction of Impacted Mandibular Third Molars, Cureus 2026. Figures are usual values, and teeth vary from person to person.