Call your dentist and ask them what they do for little kids, and when they like to start seeing them. My dentist is great with kids. They have a prize box and toothbrushes to give them that are all geared to kids. They even have little kid movies that they can play on their computers for them to watch.
They had my youngest come in when he was three, but mostly they asked me about his personality. They had a "happy visit" which meant that when he came in with his big brother, they just rode on the chair and got to check everything out. Then, based on his reaction, they brought the dentist in and had him count his teeth. He got a little toothbrush and a toy.
They pretty much started all over then next time we went, going very slowly with him and gauging his reaction. When he decided to cooperate, they pulled out the "tooth tickler" to clean his teeth. He did okay, so they went ahead and did the whole cleaning.
Best of all, they didn't charge us for the happy visits. They were willing to do several of those to get him comfortable with visiting the dentist. Now he loves going to the dentist!
If you aren't comfortable with how your dentist handles kids, or if they say that they usually don't see kids (we had that happen--a previous dentist wasn't comfortable with tiny mouths), call a pediatric dentist and ask them when a kid should get his first visit and what they do.
But we've been very happy with our regular dentist, and it's nice to all go together as a family.