Methods: Discs of root dentine were demineralised in a lactic acid buffer (pH4) for 4 days. Bonding agents (ProtectBond (PB); Kuraray, OptiBond (OB); Kerr, XenoIII (X); Dentsply) were applied to overwet dentine, using 2 coats of the hydrophilic component and light cured for 30 seconds. Specimens were sectioned and microRaman spectroscopy performed at 8µm intervals across the hybrid layer. The height of 1610cm-1 (phenyl C=C) and 1640cm-1 peaks (C=C) were calculated and ratios compared to indicate degree of cure.
Results: Molecules associated with adhesive were detected to ~110µm into dentine for PB and ~160µm for OB and X. An inconsistent hybrid layer was observed for PB and OB with a reduced 1610:1640 ratio after 50-70µm accompanying an apparent change in molecular structure. X hybrid layers demonstrated a gradual dilution of adhesive resin. The nature of the hybrid layer differed for different materials.
Conclusions: A thick hybrid layer was observed with adequate degree of cure in superficial layers. The reduction in 1610:1640 ratio within PB and OB hybrid layers may be a consequence of reduced degree of cure, phase separation, enhanced penetration of primer (PB) and may be affected by peaks overlapping with dentine components (1667cm-1). PB and OB hybrid layers appear to have a high proportion of aliphatic groups at the base. The hybrid layer in X appears to be rapidly diluted, possibly leaving collagen exposed.
Project supported by ODRT 3M ESPE Dental Biomaterials Research Award 2007