Try not to beat yourself up for shouting, forgive yourself...it's a normal reaction. I know this is hard, and I do understand how it feels. I used to expect myself to be superwoman-mum, someone who would always take the therapeutic appraoch, which demands that I remain calm and in control and thinking about what to do next, and expected myself to refrain from things like shouting lots. Years down the line, I think differently. To expect ourselves to be parenting perfectly all the time is setting ourselves up for failure, because it's an impossible feat. We're human, and pretty much every human after this much stressful situations, reaches shouting point/piling on the consequences point etc. We will ALL do it, because it's normal and natural to get to this point. We have to find a way to accept that it's normal and natural and we will do it, and we have to find a way to forgive ourselves for not being superhero strength parents, and let ourselves be normal people who try our very best but inevitably have bad days and bad moments
I love Dan Hughes advice on this (thanks for that MrsBW ), and I'm pretty sure he also said that it's not the arguments/shouting etc that matters, it's the "making up" afterwards, because if you can make up, cuddle etc, then that's what will probably stick in your childs head and enable them to move on and forget about the shouting match.
With teeth brushing, I go more for Kristina's approach, because that's what fits my 2 older kids better, more likely to end well for us all if I take that approach.
Because of the control taking attempts, I used to simply have a 10 minute slot for teeth cleaning, and during those 10 minutes, the children have to get their teeth done. If they refuse and refuse, I then say "okay you've missed the slot, time for bed". And if someone then starts up a "oh now I've changed my mind, I'll do my teeth now" I say, "you've missed tonights slot, but you get to brush your teeth tomorrow morning!".
I restrict sweeties etc until teeth are brushed, as a logical consequence. "Mum, I want the sweets!", "Yes, DD2, of course you may have the sweets, just as soon as your teeth are brushed!". And I explain briefly why sweeties can't be eaten if teeth aren't being cleaned, but refuse to go over it again and again, because repeated "but WHY?"'s after i've aleady explained twice is an attempt to ignite a shouting match on the childs part.