For lower mandibular swelling extending to the floor of the mouth, which space is MOST likely infected when the swelling originates from the LOWER FIRST MOLAR?

Correct answer: A. Submandibular space (roots of lower molars extend below mylohyoid — spread to submandibular space)

• A. Correct. Infection from the MANDIBULAR FIRST MOLAR most commonly spreads to the SUBMANDIBULAR SPACE because the molar roots (especially second and third molars) extend BELOW the mylohyoid muscle attachment — infection perforates the lingual plate below the mylohyoid, entering the submandibular space.
• B. Deep cervical space is secondary spread from other spaces.
• C. Submental space infections arise from mandibular INCISORS.
• D. Sublingual space infections arise from teeth whose roots extend ABOVE the mylohyoid (premolars, first molar occasionally) — they appear as floor-of-mouth swelling intraorally.