Is grinding down the natural bottom teeth to fit a too thick upper front bridge really necessary? (Photo)

I have a three unit dental bridge for my front upper teeth.my dentist can't seem to get it right due to the lab/impressions. To make this fourth bridge fit he wants to further reduce my lower teeth which he has already reduced.The bridge is very thick and can't be thinned more. He temporarily cemented it over night. He made me pay the full 4,000 up front. I feel he is trying to force a bad fitted bridge to work because he doesn't want to refund. This is bridge number 4 he has had to send back.

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