thanks for your query, i have gone through your query. the small hole could be a pus discharging sinus tract from a periapical abscess or cyst secondary to tooth infection. or it can be a oroantral fistula or communication secondary to infection in the tooth. consult a oral physician and take radiograph like occlusal, PNS view and CT if necessary. later find out the cause and treat the infection. you can take a course of antibiotics and do saline gargling. i hope my answer will help you. take care.