Sorry for replying so late. (This site was so full of spam that I stopped visiting it for a while.)
Just curious to find out if you went ahead with the dental work/surgery?
I have tonkinese cats (half burmese, half siamese). Siamese cats have issues with anesthesia. One of them has bad breath caused by both gingivitis and stomach issues and he too has thyroid issues (he is on medication for that and on hyperallergenic food for his stomach issues). He had dental work done when he was 8. Now he is 12 years old and, though he may need it, the vet doesn't recommend having it done because of the risk of anesthesia.
I wish I had seen your post earlier. Will probably visit this site more regularly again.