Not sure if there are real good clinical studies on that. There is a controversy of thought in that area and I understand the reason why coming from a biomaterials background of 5 years. When you placed a margin on composite or any adhesive bonded restoration, it is difficult to have proper and ideal isolation subgingivally. Therefore, you are bound to have some microleakage and eventually bacteria and saliva seeping underneath your composites. If that happens, you lose your composite and your crown. Whereas, you can use RMGI with recurrent release of fluoride to help prevent some of that recurrent decay underneath crowns. Also, crowns are theoretically to have better marginal adaptation with minimum cement gap.
