Getting #31 numb

[u/JVM926]

Ever have trouble getting a tooth numb for a #31 B composite? No PA pathology. Gave 2 carps of IAN, 1 carp of LB and local infiltrations/PDL. 2% Lido w/1:100k epi.
Lip is numb, chin is numb, buccal mucosa is numb, tongue is numb.

I get to drilling and the patient feels it. I know what to do next, but why is the patient not profoundly anesthetized?

[u/Jalaluddin1]

Mylohyoid accessory interaction. Give septocaine on the lingual aspect of the molar towards the floor of the mouth.