Wow- I didn't realize it could be so frequently. I was aiming for getting it done once, practising "brushing" every day and then not having to get the full dental again. Silly me.
Well, if you use an enzyme toothbrush and are faithful about brushing daily (something I admit I'm not), you can probably get away with less than yearly, but I doubt you won't have to do it again. That said, every dog is different.