Sorry to hear about Momo having problems...hope he's feeling better soon...
I use probiotics w/enzymes from Nature's Farmacy: (1/8 tsp daily for small dogs)(small container lasts a long time)
Nature's Farmacy - Store - Product Details=
And a product like this or Petzlife gel to help clean his teeth:
Nature's Farmacy - Store - Product Details
Apply to the gumline (no brushing required)