When infiltrating lingual of molars, where should you inject?

• A. 5-10 millimeters from the free gingival margin
• B. 1-2 millimeters from the free gingival margin
• C. Directly at the free gingival margin
• D. At the apex of the tooth root

Answer: (A)

Effective lingual infiltration for molars relies on placing the anesthetic in the submucosa near the lingual root area so it can diffuse through the dense lingual bone to reach the tooth’s nerve supply. About five to ten millimeters from the free gingival margin on the lingual side positions the needle tip in the right vicinity—near the lingual cortical plate and into the underlying cancellous bone—allowing the anesthetic to diffuse toward the apical nerves that service the molar. Injecting too close to the margin (one to two millimeters) or directly at the margin tends to keep the solution in superficial soft tissue, which doesn’t provide adequate pulpal anesthesia for molars. Injecting at the apex isn’t ideal for this technique because the goal is diffusion through bone to reach the nerve endings rather than delivering directly into the apical area.