Hi Sue! It's good to talk with you. I am here to help you anytime so don't feel bad about asking anything you need to.
Oh Sue, I am so sorry that you went through such horrible abuse. It is very understandable that you fear the dentist because of what you experienced as a child. I believe that you are experiencing PTSD. Post traumatic stress often develops because of child abuse. Flashbacks are very common and can continue if not treated. Being at the dentist, which is normally an unnerving experience for most people, would be much worse when it triggers your memories of abuse.
The first thing to do is accept that what you feel is very normal. Anyone would feel as you do in the same circumstances. Give yourself permission to feel afraid. It will help your fear dissipate.
The second step is to understand flashbacks as being a part of your trauma. They are triggered by similar situations to the trauma you experienced. Being at the dentist feels similar to you. What we need to do is make the dentist seem different to you so you no longer associate the two.
Three, think of props you can use while at the dentist to help you change the association. Take headphones and an IPOD and play music or watch a show for example. Or take along something to play with in your hands, like a smooth stone or something with texture. Ask to have the seat changed to your liking or bring along something to focus on like a picture.
Four, enlist the help of your dentist. You don't have to share the whole story, just let him/her know you are extra anxious. Ask for more control over your appointment, like the ability to stop any time you need to take a breath.
You can also ask about being put to sleep, if that does not bother you. That way, you can get the work done without having to sit through it.
Just remember, you are normal. This is not an unexpected or unusual problem.