The dentist asked you to hold your nose and blow so she could check if you had an oro-antral fistula. The roots of maxillary molars are often very near or sometime actually inside the maxillary sinus. If interested, run "oro-antral fistula" through a search engine for some good information. Beware scary photos. Hot-salt-mouth-wash is used to keep the socket clean as it heals. Rinse carefully so as not to disturb the clot which is protecting the socket from becoming infected. It's thought that the heat dilates the blood vessels, allowing more healing cells into the area. Chlorhexidine mouthwash has its uses - but can cause staining of the teeth. This can be minimised by avoiding tea, coffee, red wine and cigarettes for a couple of hours after use. Hope things heal quickly for you.