It's interesting to come across this post (I don't know how I missed it earlier!). Our local Sheltie club had a visit in January from a vet here in town who has a small practice and a special interest in dentistry. He brought along one of his techs and gave a really great presentation on preventative dental care - its importance, and how to do it properly.
He recommended that any toothpaste for dogs can be used, as long as it is an enzymatic paste. Look for the key word "enzymatic"; beyond that, brand isn't really important. The enzyme activity and the mechanics of brushing the teeth are what count!
According to him, studies show that, in dogs, optimal results come from brushing every other day. Every day won't hurt (and it might be easier to remember), but it doesn't show much improvement over every other day.
When you brush, use any soft-bristled toothbrush (kid-sized brushes are great for Sheltie-sized dogs). Make sure you angle the bristles at 45 degrees to the tooth - you want to brush right along the gumline, not just the visible surface of the teeth.
Like Brad, I (and many of the other club members!) had been scaling the teeth at home - but it turns out that this really only has cosmetic effects. It takes the tartar off, but it doesn't clean under the gumline (and if you tried to with a home scaler, you'd hurt the dog). This is why regular brushing, at an angle to the gum, with an enzymatic toothpaste, are so important.
He also recommended using a chlorhexidine rinse in addition to brushing. This is squirted along the gumline, and it distributes itself around the mouth and has excellent antibacterial properties, which helps prevent gum disease. Again, the real worry with dogs isn't the part of the teeth you can see - it's what's under the gums that needs to be kept clean and healthy.
When you have your dog's teeth cleaned under anaesthesia, they are using a curette to clean along and under the gums, in addition to cleaning the visible surfaces of the teeth. If you can keep bacteria and infection under the gums at bay through regular brushing and rinsing, you'll go a longer way towards keeping the whole mouth healthier.
I had been brushing and scaling Betty's teeth semi-regularly, but since this presentation I've really stepped it up (I added the rinse, too - it was $10 for a big bottle, and she doesn't mind it, so why not try?). Her mouth was in pretty good shape to start with, but I'm hoping I can keep it that way longer by making brushing/rinsing part of our routine. She doesn't love it, but I figure it's worth the trouble to spare her pain and discomfort.