HI Paul - thanks again for your reply. I have some good news to report and must confess that it wasn't me I was treating, but my beloved dog. I didn't know whether all life forms were considered worthy of help on this forum so I posted it was about me.
Despite the MMS&DMSO taking the skin off her gum and making the hole next to the tooth where the pus was coming up, around 10 times larger than it was before, yesterday afternoon the pus was greatly reduced. I kept persevering dropping the mixture directly into the hole (trying to avoid the rest of the gum as the skin is hanging off it) and keeping it there for about 3 minutes. My dog is a star and just let me do it, even though it must have stung like crazy. This morning, there was hardly any pus and later in the day the cause of the infection came up and was sat in the hole - it was yet another fragment of bone from the extraction that my vet didn't remove out of the extraction site. The tooth was removed on January 16. This fragment was 2 1/2 mm long... there is now no pus, but I will continue to use the MMS&DMSO for another few times to make sure we got al the bacteria.
Today has been a great day, and I'm looking forward to seeing the gum heal very soon - it is such a mess, but was a means to an end.
Thank you for your encouragement and advice.