Shear Bond Strength of Adhesives Placed Following Selective Removal of Red-Fluorescing Carious Dentine in Vitro.

Red-fluorescing dentine indicates bacterial contamination [Lennon et al.: Caries Res 2002;36:315-319]. We investigated effect of removal of red-fluorescent dentine-caries on shear-bond-strength and fracture-mode of 4 adhesive approaches. Sixty-five carious teeth and 50 non-carious controls were distributed into 4 groups: ClearfilTM self-etch (CSE), OptibondTM FL total-etch (OTE), ScotchbondTM Universal total-etch (STE) and self-etch (SSE). Samples were excited at 405nm and viewed through 530nm filter. Carious samples were ground flat exposing strongly red-fluorescing-dentine (StrongRF), on which a composite-cylinder was placed, using one of 4 adhesives. After 22 hours in water shear-bond-strength and fracture-mode were analysed. StrongRF was removed composite-cylinders were placed on weakly-red-fluorescing dentine (WeakRF) and tested as described above. Finally, red-fluorescing dentine was removed, composite-cylinders were placed on non-fluorescing dentine (NonRF) and tested. Composites were placed at 3 corresponding heights in controls. After 22 hours in water, shear-bond-strength testing and fracture-mode analysis were performed. Differences were tested using Mann-Whitney or Wilcoxon tests (p <= 0.05). Median(Q1,Q3) shear-bond-strength on StrongRF was: SSE 14.4(9.2, 18.2)MPa >CSE 10.2(6.4, 17.3)MPa >STE 9.1(6.9, 11.2)MPa >OTE 6.8(4.0, 10.8)MPa. Shear-bond-strength increased statistically significantly for all adhesives on WeakRF (p<0.001-p=0.013): SSE 19.8(13.6, 24.3)Mpa >STE 19.5(12.7, 23.1)MPa >CSE 17.5(12.0, 22.5)MPa >OTE 15.8(11.9,20.9)MPa. Only STE 25.6(22.4,29.1)MPa and CSE 22.1(17.6,24.6)MPa were significantly different on NonRF compared to WeakRF. For controls tested at corresponding depths, superficial shear-bond-strength was: OTE 18.7(16.0,22.1)MPa >STE 18.4(12.0,25.9)MPa >CSE 18.1(12.7,20.7)MPa >SSE 13.0(9.6,17.8)MPa. This was significantly higher compared to StrongRF except for SSE. Central shear-bond-strength was not significantly different to WeakRF, deep shear-bond-strength was significantly lower for SSE and CSE but higher for OTE compared to carious. Conclusion: strongly red-fluorescing dentine should be removed for higher shear bond strength, but weakly red-fluorescing dentine can be preserved without compromising adhesive bond strength.