If you have a child with special needs, then you have to put in a lot of extra thought and work into doing everything, up to and including taking them to the dentist. You know you need to take them to the dentist regularly, so what can you do to make it easier for yourself?
The office should be accessible, but it may be harder for exam rooms to be accessible because of limited space. Check with the dentist's office to see if they have a room that is large enough for a wheelchair to get into and maneuver into place. You should also check with the dentist to see if it will be easy for your child to transfer from their wheelchair to the exam chair. That would mean the chair would need to be at a particular height and the arm would need to be completely out of the way so that the wheelchair would line up exactly with the exam chair. If your child is in a specialized wheelchair and can't really transfer, you will want to talk to the dentist and see if they have a problem with examining your child while they are in their wheelchair.
Autistic kids or kids with other sensory issues can have a really hard time with all kinds of noise levels. Your child may have issues with some of the sounds that you can hear around the dentist's office. You should check with your pediatric dental clinic to see if they have an exam room that works well for kids who have sensory disorders. That includes having one that is set back and away from other rooms or sone that has extra soundproofing on it so that sounds from the other rooms can't get into that exam room and disturb your child. You may also want to talk to them about whether or not they are OK with your child wearing noise-canceling headphones. Those headphones are thicker and have special dampening materials in the makeup to keep noises from outside getting through and disturbing the person wearing the headphones. Your child may listen to some favorite music at the same time, which can really help to block any noises and keep your child calmer.
As a parent of a child with special needs, you know that you have to put a lot of work and planning into anything you do, including taking them to the dentist.