thanks for your query, i have gone through your question, the mass on the submandibular gland
could be secondary to the ductal obstruction by a stone in the duct....you have to take a mandibular occlusal radiograph to rule out stone...the numbness
in the lower third of the face could be because of the pressure over the nerve
particularly mandibular division by any mass like tumor
or any growth or even trauma... consult a oral physian and you need to take OPG to rule out any odontogenic infection
resulting in swelling in the submandibular region.. i hope my answer will help you...take care..