It is great you are taking him now! Early exposure will help a ton. Both of mine started going at 18 mos!
The great thing about a pediatric dentist is they specialize in kids of all varied personalities.
Talk to your son about expectation way beforehand. Why he has to sit still, etc. I was paranoid the first time my son went thinking there is NO WAY he will sit for xrays, I walked out of the room and the nurse was there with him and he did fabulous!!!!!
Show him how to look inside your mouth, put a flashlight up to his mouth and show him a mirror so he knows what the dentist is looking at, have him practice saying Ahh and stuff like that. Let him brush your teeth for you and check your mouth out. Take along his favorite stuffed animal, favorite book or something. As long as you are super relaxed about it so will he be. They are usually so great at pedatric dentists with the kids! :)
To be honest, the first few times our pediatric dentist had me go in with them, keeping them busy with handheld toys and so on, then by the third visit the dentist prefers the child to go in alone (or they went in together without me)as sometimes kids act much better when the parents aren't around. Also helps as you cannot be in the room with more evasive procedures.
Both of my kids LOVE the dentist. I go to one where I can see them at all times, they know where I am at and love our dentist so much they actually get excited when it is time to go get their teeth cleaned. So much so my 7 year old wants to be a dentist when she gets older! :) Prepare him with conversation, go with him the first time or two but after that give him the chance to go alone, seeing that the dentist is a great guy, keeping his teeth healthy and there is nothing to be afraid of.