What are the boundaries of the retro molar trigone?

Anatomical Boundaries of the Retromolar Trigone

The retromolar trigone is a triangular anatomical region located posterior to the last mandibular molar, bounded anteriorly by the distal surface of the last molar tooth, laterally by the anterior border of the ascending ramus of the mandible, and medially by the lingual mucosa and anterior tonsillar pillar. 1

Detailed Anatomical Boundaries

Anterior Boundary

• The distal surface of the third mandibular molar (or second molar if the third molar is absent) forms the anterior limit 2, 1
• When measuring from the last tooth socket, the retromolar foramen (when present) is located approximately 11.91 ± 6.71 mm from the distal edge of the last socket 3

Lateral Boundary

• The anterior border of the ascending ramus of the mandible defines the lateral extent 1, 4
• This boundary corresponds to the external oblique ridge of the mandible 5

Medial Boundary

• The lingual mucosa and anterior tonsillar pillar form the medial border 1
• This area includes the attachment of the pterygomandibular raphe 5

Superior Boundary

• The occlusal plane level or slightly above, extending to the level of the mandibular notch 2, 4

Inferior Boundary

• The floor of the mouth and lingual gingival reflection 5

Clinical Dimensions

Spatial Measurements

• Bone depth in this region averages more than 10 mm at most insertion sites, with measurements taken parallel to the occlusal plane showing approximately 3 mm greater depth than those at 45° angles 4
• Cortical bone thickness ranges from 3-5 mm on average 4
• The vestibulolingual bone dimension shows significant reduction (approximately 10 mm decrease) in the posterior aspect of the retromolar region 4

Distance from Key Landmarks

• From the mandibular foramen: approximately 12.27 ± 12.13 mm on the right side and 12.13 ± 2.35 mm on the left side to the apex of the retromolar trigone 2
• The retromolar foramen, when present (in 25% of mandibles), is located 4.23 ± 2.30 mm from the third molar 3

Important Clinical Considerations

Neurovascular Structures

• The retromolar canal and foramen are present in approximately 25% of mandibles, containing a neurovascular bundle with striated muscle fibers, thin myelinated nerve fibers, venules, and a muscular artery 3
• The lingual nerve courses through this region and can be compressed by dental prostheses, causing pain in its distribution territory 5
• These neurovascular structures must be considered during any surgical or anesthetic procedures in this area 3

Surgical Relevance

• The retromolar trigone serves as a critical landmark for inferior alveolar nerve blocks, mandibular implant placement, and osteotomies 2
• Large mandibular tori in this region can create narrow working spaces and difficult retractor positioning during transoral surgical procedures 6
• The dimensions of the retromolar trigone are not dependent on the presence or absence of the last teeth in the arch 3

Oncological Implications

• Tumors of the retromolar trigone are rare and aggressive malignancies that spread rapidly into surrounding structures including the anterior ramus, buccal mucosa, and tonsillar pillars 1
• Understanding these precise boundaries is essential for surgical planning and reconstruction following tumor resection 1