The 1951-P Roosevelt Dime has one of the higher mintages from 1946 to the 1950's. It's mintage is well over 100 million coins struck. Compare this to the mintage of the 1949-S for example and it is obvious that a mintage of over 100 million is extremely high. After 1955, it appears that mintages higher than 100 million are more common.
Despite its large mintage, the 1951-P Roosevelt Dime is scarce in MS66 condition especially with Full Band details on the torch features on the reverse of the coin. At PCGS, we have seen less than 300 examples in total that have graded MS66 with Full Band details. In MS67 we have seen far fewer and there are probably less than 100 examples that remain in MS67 with Full Bands. There are also a few known examples that have graded MS67+ but it's less than a handful and there are probably no MS68's that exist or in any higher grade.