What is the limitation of pervious study？（)

A.Promising laboratory test results still need to be confirmed by clinical studies before clinical recommendation could be given.

B.It really is still a significant problem in dentistry to bond reliably to oxide ceramics such as alumina and zirconia ceramics.

C.Most original laboratory research reports on bonding to zirconia ceramics start in their introduction with a statement pointing more or less out that achieving a reliable and predictable bond to this ceramic would be a major problem in dentistry.

D.No clinical trials with alumina ceramic IRFDFs or with RBFDPs made from densely sintered alumina ceramic were foun