Kelley -- It's not just your dentist, it happens here too. My 3 year old had root canals on his two top front teeth a year ago after a fall damaged them both. The dentist was not sure she could save the teeth, as she thought there was a pretty good chance of abcess, so they were filled rather than capped after the root canal. We've had to replace the fillings twice so far, and the dentist said that it was quite common. In my ds's case, it's made worse because one of the teeth was broken -- almost half of the tooth was broken off when he fell. So there's very little tooth there to keep the filling in.
I am super careful about what he bites into -- he's not allowed to eat anything hard or sticky. He's very aware of his tooth issues, so he actually will ask me before he eats anything new he is offered. "Is it too hard for my teeth, Mommy?" He eats apple slices, but I cut them into very small wedges and remind him to bite them with his side teeth rather than in front. Anything that's liable to be a bit tough (like bagels) where he'd have to exert a good bit of force to bite a piece off, I cut thin enough that he can bite off pieces with the side teeth.
I don't know if your little one every uses spill-proof sippy cups, but my son lost his filling the first time right after taking a sip of water from one of them. You have to such pretty hard to get the liquid with those valves, and I wondered if the amount of suction could have been a problem. Our dentist wasn't sure, but after that, I stopped giving him the spill-proof cups.
It's incredibly frustrating, isn't it? The dentist tried to cap ds' teeth last time the fillings fell out, as it had been a year with no sign of abcess, but when she started to prepare the broken tooth, it turned out to be loose, so that was out.
My dh and I came to the decision that if ds loses his fillings again, we're going to ask the dentist to extract the teeth. Her original goal had been to try and preserve the teeth at least until he turns 4, to minimize the effects of losing the front teeth too early, and ds is already 3 and a half. Each time we go in, it's a huge ordeal with the papoose board, etc. Our dentist is very kind, gentle, and compassionate with ds, (when he initially went in at with the tooth injury age 2 and a half, she managed to do X-rays, an exam, and a cleaning, without a single tear from him!) but he is just too traumatized at this point by all the dental work he's had done. It's so hard to make these decisions!
I will say that one thing that has really helped my ds from the beginning is really talking to him about what's going on as much as we can. "The dentist will fix your broken tooth so that it won't hurt." I would tell him he'd lost a filling and that the dentist needed to fix it. These things don't help much when he's actually at the dentist, but when she's done, he'll actually give her a hug when he says goodbye! And he explains to people that the dentist fixed his tooth. We also explain that someday he'll get new big teeth that won't be broken anymore (it helps that he has a big sister that's in the middle of that process). He also is really good at the doctor these days, where he used to be afraid -- as soon as we explain that the doctor isn't going to look at his teeth, he's happy!
Anyway, lots of sympathy here -- hope your little one's fillings stay in better next time.