i know their fillings do not last 18 months because i have had some for over 5 yrs with no problems. if you study the toxicity of other fillings, you will find the same toxins or worse. onlays/inlays do require big cavities, so for small ones, they are just not feesible. that is what i was taught by biologic dentists. onlays/inlays, some may have a very tough time convincing their dentist to put them in. i was taught inlays/onlays are hard to get a good seal on and can leak, but the cerec may be better, just that not all dentists are good at doing them.