RE: My 5 yr. old has 8 cavities!!
DS had a cavity filled (w/ the "white" composite filling material) on the back of his upper central incisor at 18 months or so. He ate almost no sugar, we have a very healthy diet, and he never had juice. We brushed regularly. He never went to bed with a bottle (never had a bottle LOL) So...first, let me say, don't blame yourself, because I know how hard it is!!! Some kids are just naturally prone to decay. I felt kind of insulted when my ped dentist handed me a sheet saying "no juice, no candy, no sugary cereal or crackers, no bottles after 12 months etc." because we didn't eat that way. He then tried to tell me that it was because I was a "stay at home mom" and my kid "wasn't on a schedule like daycare" because obviously since I'm a SAHM my kid walks around with a sippy cup of juice and cheerios all day long (insert eyeroll). After I basically gave him the lowdown of how thing were at our house, he backed off on the blame, and we get along a lot better now ;)
DS did fine w/ his filling. It was a small one and we did it without novacaine or a sedative.
From what I read, some cavities do remineralize to a degree or don't get any larger, so some dentists will do a wait and see approach. I wanted to get DS's taken care of right away, but in some cases I might have opted to wait assuming the cavity was small and I really, really trusted my dentist. I think a 2nd opinion can be helpful when you are talking about that amount of work regardless.
Just something else you might want to look into is Xylitol, which is a sweetener derived from corn that can help fight the bacteria that causes tooth decay (strep mutans). Some people are more succeptible to strep mutans, and even w/ good hygeine, etc. they are more prone to get cavities. The strep mutans basically tries to feed on the xylitol like it would on sugar, but it can't process it, and it causes the bacteria to die off. There is actual research coming out about its effectiveness (you can search www.pubmed.com for xylitol, etc. to see actual studies).
We use Spry toothpaste and Spry gum for DS and for DH and I. It tastes good (the fruit flavor of gum is DS's favorite) and can be helpful. It has more xylitol in it than some of the brands like Trident, etc. that add a bit of it to their gum now. We usually find vitamin shoppe online has good prices. Obviously, if your kid is prone to cavities, a lot of brushing, etc. is needed, and gum isn't going to replace that, but xylitol has been a good edition for us. They are finding it also helps kill bacteria associated w/ ear and sinus infections.
Hugs. I hope you get some answers and that your little one does well. It is so traumatic for us as parents as well.
Mama to DS-2004
DD-2006
and a new addition-ds born march 2010