The permanent maxillary left second molar is a large, multi-rooted posterior tooth situated in the upper left quadrant of the mouth, distal to the first molar and mesial to the third molar. Designated as tooth #15 in the Universal Numbering System (UNS) and 27 in FDI World Dental Federation notation, it erupts between ages 11 and 13 as part of the permanent dentition.

Anatomy and Structure

This tooth shares many morphological features with the permanent maxillary first molar but is generally smaller in overall dimension. Its occlusal surface typically bears four or five cusps — the mesiobuccal, distobuccal, mesiolingual, distolingual, and occasionally a fifth cusp of Carabelli variant. The crown is supported by three distinct roots:

• Mesiobuccal root — often the most curved, sometimes containing two separate canals
• Distobuccal root — generally the shortest of the three
• Palatal root — the longest and largest, with a single, well-defined canal

The enamel covering the crown is the hardest calcified tissue in the body, while the roots are anchored to alveolar bone through the periodontal ligament, which absorbs and distributes occlusal forces during chewing.

Clinical Significance

The permanent maxillary left second molar plays a critical role in mastication, contributing to the grinding of food before swallowing. Its posterior location makes it prone to plaque accumulation, raising the risk of caries and periodontal disease. Clinicians must also account for its proximity to the maxillary sinus — the palatal and mesiobuccal roots may approach or penetrate the sinus floor, a key consideration during extraction or endodontic treatment.

Common clinical concerns include:

• Occlusal and interproximal caries due to deep grooves and tight contact points
• Root canal therapy complicated by root curvature and potential canal calcification
• Crown fractures from heavy occlusal loading or parafunctional habits such as bruxism
• Impaction or tipping caused by inadequate arch space when a third molar erupts distally

Radiographic evaluation — typically periapical radiographs or cone-beam computed tomography (CBCT) — is essential for accurate diagnosis and treatment planning given the root complexity and sinus proximity.

Preserving the permanent maxillary left second molar through timely restorative care and consistent periodontal maintenance protects posterior occlusal function and prevents the bone resorption that follows tooth loss in the posterior maxilla.