Had a nightmare trip to the dentist yesterday. My DS(7) has been to the dentist a few times, started taking him when he was very small just to get used to the idea and he was fine then. But then last year when we took him he had to have his teeth cleaned and a temporary filling in a milk tooth. He completely freaked out but the dentist managed to do the work required (I was mortified that we hadn't noticed that he wasn't cleaning his teeth properly
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The dentist then advised that DS went to see her again in 3 months just to get him used to going to the dentist, and that trip was not too bad, a few tears but nothing horrendous.
Then yesterday, he was happy enough for the dentist to look into his mouth but when she said that he had to have another temporary filling he freaked out again and refused to open his mouth. Dentist was lovely, but firm with him, tried 3 times to do the filling but with no success. So told him that she wouldn't be able to do it then as she had other people waiting, and that he would have to come back in a couple of months to have it done. Cue hysterical screaming as we took him out of the surgery, screaming that he "wanted it done now!" Cue even more mortified parents 
We have similar problems with just cleaning his teeth, and have been for a few months, which I think has really started since getting wobbly teeth. We usually end up shouting at him, which I know is so wrong and unhelpful, but just get so stressed with it.
I too have a phobia about dentists, so I know where DS is coming from, but I have tried to hide it from him in the past. Always go to the dentist as a family, and DH will take DS out of the room when I am being treated so DS does not see my fear. I have explained to DS that it is ok to not like going to the dentist, as I don't, but it is necessary to go.
We have started a sticker chart to help with the brushing of teeth, and I am thinking that we start a jar of money for all the stickers he gets, and hopefully the growing pile of money will encourage him more. Then when he has been to the dentist and successfully had the treatment he can then go and spend this money.
Sorry this is so long, but if you have managed to read to the end has anyone got any further ideas?