It doesn't matter if rats have phytase or not, controlled trials trump mechanistic speculation and rats apparently do accumulate IP6 and it's derivatives but only if they consume a diet with enough IP6 (i.e. the phytase is apparently not inactivating the IP6 as your hypothesis would require; alternatively, IP6 is re-synthesised from the break-down products). I don't have time to find out right now why your speculation is wrong (and I'm not sure what it's meant to imply), even though I'm very interested in destroying this myth more thoroughly. I'll be back in some weeks.
Well with the teeth I guess there are many variables involved and its true I haven't seen any studies pointing to IP6 causing deficiencies, just speculation.
However in the study pointed out at the blog Whole Health Source the diet without grains reversed tooth decay the best, however I havent seen any controlled trials showing IP6 causing mineral deficiencies, but it does decrease the absorption of magnesium and calcium.
John G. Reinhold2, Bahram Faradji3, Parichehr Abadi and Framarz Ismail-Beigi4
Medical Research Unit, Institute of Nuclear Medicine, Nemazee Hospital, and the Departments of Biochemistry and Medicine, School of Medicine, Pahlavi University, Shiraz, Iran
During a 20 day period of high fiber consumption in the form of bread made partly from wheaten wholemeal, two men developed negative balances of calcium, magnesium, zinc and phosphorus due to increased fecal excretion of each element. The fecal losses correlated closely with fecal dry matter and phosphorus. Fecal dry matter, in turn, was directly proportional to fecal fiber excretion. Balances of nitrogen remained positive. Mineral elements were well-utilized by the same subjects during a 20 day period of white bread consumption.