Prevention of water-contamination of ethanol-wet dentine and hydrophobic hybrid layers

Objectives: This study examined, with two-photon laser microscopy, the water contamination induced by simulated pulpal during application of a hydrophobic resin on ethanol-saturated deep or middle dentine pre-treated with or without 3% mono-potassium/mono-hydrogen oxalate. Methods: Crown segments were prepared in middle dentine (RDT=1.5±0.5 mm) and in deep dentine (RDT=0.8±0.3 mm) and divided into two principal groups: deep dentine; middle dentine (n=16/each). Two sub-groups were further created for each principal group: water-treated control dentine; oxalate-treated experimental specimens (n=8/each). Each specimen was connected to a hydraulic pressure source (20cmH₂O) containing 0.2 mg/mL of Lucifer Yellow during dentine bonding procedures. The ethanol wet-bonding substrate was achieved by covering dentine surfaces in absolute ethyl-alcohol for 5min. Two consecutive coats of the hydrophobic ethanol-primer (30 wt% ethanol/70% BisGMA/TEGDMA) were applied and light-cured for 20s. Five-mm resin build-ups were constructed incrementally. Two-photon microscopy was performed using a Zeiss Model 510-LSM equipped with a femtosecond/Ti:Sapphire-laser pumped by an argon ion laser. A region of interest (ROI: 2300 µm²) was drawn around each hybrid layer to quantify the intensity of the fluorescence emission of the dye that was taken up by the hybrid layer. Statistical differences were determined using Sidak's test(a=0.05). Results: The control middle and deep dentine hybrid layers showed values of fluorescence emission intensity of 1164±114 and 1627±271, respectively. In oxalate-pre-treated middle and deep dentine the values of intensity were only 227±42 and 274±41, respectively. No significant difference was found between oxalate-pre-treated middle and deep dentine. The other groups were statistically different (p<0.05). Conclusion: The results of this study showed that pulpal pressure may induce large water contamination of hydrophobic-hybrid layers. Little contamination was observed when oxalate was used to occlude the tubules prior the bonding procedures. Supported: grant R01 DE 01411 from the NIDCR to DHP (PI); Dickinson-USA-fund of King's College London Dental Institute.