Puppies start getting their adult teeth somewhere around 4-6 months I think.
If you feed them a good food and give them lots of good things to chew on (or brush them yourself), you should never have to take them in for a dental cleaning. It's not very good for the dog's teeth, as it will strip away the enamel after a period of time, not to mention the fact that they anesthitize (sp?) the dog to do it.