Primary maxillary second molar: FDI 55 and 65

The numbers on both sides

In FDI the first digit is the quadrant and the second is the position counted from the midline. 55 is quadrant 5, position 5: the upper right primary second molar. 65 is the same position in quadrant 6, on the upper left. Universal gives baby teeth the letters A to T, from the upper right second molar around to the lower right second molar, which makes this tooth A on the upper right and J on the upper left. Palmer writes the letter for the position inside a bracket that shows the quadrant. In plain text that gives URE and ULE.

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

Development and eruption

Calcification starts at about 19 weeks in utero and the crown is complete at 11 months. The tooth erupts at 25 to 33 months, the last primary tooth to appear, and the root is complete at 3 years. It is shed at 10 to 12 years, which makes it one of the longest-kept baby teeth. The primary dentition is normally complete by about 2.5 to 3 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); 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.

Crown

The crown resembles a small permanent maxillary first molar, and it is the primary tooth most likely to have an oblique ridge. It may carry a cusp of Carabelli on the lingual surface of the mesiolingual cusp. In the primary dentition the cusp of Carabelli is found on this tooth. The lower second molar has none.

The second molar is larger than the first molar and wider than the premolar that will replace it.

Read on 24 October 2026. Sources: MolarPath note Primary tooth morphology (built on McDonald and Avery's Dentistry for the Child and Adolescent, 11th ed.); 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.

Roots and canals

The roots are three, like the first molar, but more consistent. The same CBCT study found three roots in 79.2 percent of 510 second molars, against 57.9 percent of first molars. A second canal in the mesiobuccal root was found in 21.2 percent of second molars, and 15.3 percent of the three-rooted ones had four canals with two in the mesiobuccal root.

A micro-CT paper on 38 extracted primary molars summarizes earlier work: maxillary molars more often have one canal per root, with three to four canals overall, the palatal root is the longest and the distobuccal root the shortest.

Read on 24 October 2026. Sources: Kim and others, Root and Canal Morphology of Maxillary Primary Molar using CBCT and 3D CT, Journal of the Korean Academy of Pediatric Dentistry 2021; Kirilova and others, Micro-CT Assessment of Dentin Mineral Density and Furcation Morphology in Primary First and Second Molars, Dentistry Journal 2026. Figures are usual values, and teeth vary from person to person.

Neighbors and the tooth that replaces it

The permanent first molar erupts behind this tooth at about 6 years, as it does not replace any baby tooth. The AAPD describes ectopic eruption of the first permanent molar as an abnormal mesioangular path that locks the molar under the distal prominence of the primary second molar crown. It affects up to three percent of the population, is more common in the maxilla, and 71 percent correct themselves by age nine.

The premolar that replaces the tooth is the second premolar, at 10 to 12 years.

Read on 24 October 2026. Sources: American Academy of Pediatric Dentistry, Management of the Developing Dentition and Occlusion in Pediatric Dentistry (2024 revision); American Dental Association, Tooth development charts (primary and permanent); 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 maxillary technique is infiltration. A buccal deposit reaches the pulp through thin, porous bone, and a molar procedure may need a small palatal deposit when the margin lies on the palatal side.

Infiltration is routine for every maxillary tooth, which keeps the injection simple in a young child.

Read on 24 October 2026. Sources: MolarPath note Maxillary techniques, local anesthesia (built on Malamed's Handbook of Local Anesthesia, 7th ed.); 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

The terminal plane, the relation of the distal surfaces of the upper and lower primary second molars, predicts the first molar relationship. A flush plane becomes a mesial step when the lower first permanent molars erupt and push the primary molars forward into the primate space.

When a second primary molar is lost early, the AAPD says it is prudent to consider space maintenance, weighing the tooth lost, the time since loss, dental age and the root development of the successor. The guideline also states that evidence on how well maintainers work is limited.

Read on 24 October 2026. Sources: MolarPath note Eruption sequence and chronology (built on McDonald and Avery, 11th ed., and Proffit's Contemporary Orthodontics, 7th ed.); 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); Kim and others, Root and Canal Morphology of Maxillary Primary Molar using CBCT and 3D CT, Journal of the Korean Academy of Pediatric Dentistry 2021; MolarPath note Primary tooth morphology (built on McDonald and Avery's Dentistry for the Child and Adolescent, 11th ed.). Figures are usual values, and teeth vary from person to person.