Impacted wisdom tooth. Buried its way under the root of the molar in front of it, causing the good molar to eventually abscess. Let me tell you, the pain across my lower face and jaw was unbearable. Had to get the good molar extracted and the partially erupted wisdom tooth needed filling. Any cold drink or hot food touching it immediately was hell. All sorted for years now. Lesson learned? Don't put off a dentist checkup , not worth the pain.