The flesh at the back of the tooth is called the posterior molar pad. Swelling and pain of the posterior molar pad may be due to the impending eruption of the wisdom tooth under normal circumstances, and may be due to pericoronitis or periodontitis of the wisdom tooth in case of disease, as follows. 1. Under normal circumstances: when wisdom teeth are about to erupt, the mucous membrane on them may be swollen and painful to varying degrees, and the symptoms will usually disappear after the wisdom teeth erupt. 2. In case of disease: (1) Wisdom tooth pericoronitis: If there is a gingival flap covering the erupted wisdom tooth, it will form a blind pocket, which is prone to the accumulation of food debris and plaque, causing wisdom tooth pericoronitis, and swelling and pain in the surrounding soft tissues. (2) Periodontitis: Periodontal inflammation of the second molar may lead to swelling and pain in the gums around it, with pus overflow in severe cases. There may be other reasons for the swelling and pain of the back cushion of the molar. It is recommended to visit the hospital in time for treatment according to the cause of the disease and removal of the wisdom teeth if necessary.