MDP-containing Single-bottle Self-etch Adhesives Induce Biomimetic Mineralization Of Reconstituted Type ? Collagen

Objective:This study investigated the ability of different single-bottle self-etch adhesives containing 10-methacryloxydecyl dihydrogen phosphate(MDP)or not to induce the biomimetic mineralization of reconstituted type I collagen fibrils in artificial saliva.Materials and Methods:1.Preparation of a single-layer reconstituted type I collagen model:type I collagen solution derived from rat tail(3mg/L,Invitrogen,USA)was diluted to 50?g/ml in the buffer solution(pH 9.2,50 mM glycine,200 mM KCl)and kept at room temperature for 20 min.Three ?l of collagen solution was each dropped on one of 400-mesh Ni TEM grid.Subsequently,all the grids(n=98)were incubated at 37 ? overnight.Afterward the grids were immersed into 0.05wt%glutaraldehyde solution for crosslinking for 1h.Then,all the grids were washed thoroughly with distilled water and dried in air.Two randomly-selected grids were stained by 1%uranyl acetate for 10s to confirm whether or not collagen fibrils were reconstituted on the grids by transmission electron microscopy(TEM).2.The other 96 grids were randomly divided into following groups:(1)experimental groups:Three MDP-containing single-bottle self-etch adhesives were included(n=16):? Single bond universal(SBU,3M ESPE,USA);? Clearfil Universal bond(CUB,Kuraray-Noritake,Japan);? Clearfil S3 bond(CSB,Kuraray-Noritake,Japan).(2)control groups:Two single-bottle self-etch adhesives without MDP were included(n=16):? Tetric N-bond(TNB,Ivoclar Vivadent,Liechtenstein);? G-Bond(GB,GC,Japan).(3)blank control group(n=16):Grids covered with reconstituted collagen fibrils without any treatment were used as the blank control group.The adhesives were respectively gently brushed a cross on the surface of a grid and light-cured.Four grids were floated upside down on 2 ml artificial saliva in a petri dish.All the grids were incubated at 37? for 1,4,7 and 14 days.Four grids each group were retrieved and analyzed by TEM.The grids of the experimental groups after 14-day incubation were also analyzed by selected area electron diffraction(SAED).Results:TEM images show that the collagen fibrils were not mineralized in the blank control group and the control groups(TNB group and GB group)after 14-d incubation.In the SBU group,collagen fibrils were mineralized after 1-d incubation and heavily mineralized after 7-d and 14-d incubation.In the CSB group,collagen fibrils were not mineralized after 1-d incubation while a small part of the collagen fibrils was mineralized after 4-d incubation.Furthermore,the intrafibrillar mineralization was found after 7-d and 14-d incubation.In the CUB group,mineralization of collagen was not found till 14-d incubation.Only a few collagen fibrils were mineralized after 14-d incubation.The SAED patterns of the minerals within the collagen fibrils exhibited a characteristic of apatite.Conclusion:The MDP-containing single-bottle self-etch adhesives used in this study could induce the biomimetic mineralization of the reconstituted type I collagen fibrils.Their ability of mineralization depended on the individual adhesive used.