Improved degree of conversion of model self-etching adhesives through their interaction with dentine

Abstract

Objective: To investigate the correlation of the chemical interaction between model self-etching adhesives and dentine with the degree of conversion (DC) of the adhesives.

Methods: The model self-etching adhesives contained bis[2-methacryloyloxy)ethyl] phosphate (2MP) and 2-hydroxyethyl methacrylate (HEMA) with a mass ratio of 1/1, and 0-40% water contents, respectively. The adhesives were applied either onto the prepared dentine surface or unreactive substrates (such as glass slides), agitated for 15s, then light-cured for 40s. The DCs of the adhesives were determined using micro-Raman spectral and mapping analysis.

Results: The DCs of the adhesives cured on the dentine substrate were found to be significantly higher than those on the unreactive glass substrate. Moreover, the DCs of the adhesives displayed a decreasing trend as the distance from the dentine surface became greater. The chemical interaction of the acidic 2MP/HEMA adhesives with the mineral apatite in dentine was proposed to play a significant role for the observations. The chemical interaction could be validated by the spectral comparison in the phosphate regions of 1100 cm(-1) and 960 cm(-1) in the Raman spectra. The results also revealed a notable influence of water content on the DC of adhesives. The DCs of the adhesive at 10% water content exhibited the highest DC level for both substrates.

Conclusions: Interaction with dentine dramatically improved the degree of conversion of self-etching adhesives. Our ability to chemically characterise the a/d interface including in situ detection of the DC distribution is very important in understanding self-etching adhesive bonding under in vivo conditions.

Figure 1

Representative Raman spectra of the 2MP/HEMA adhesives with different amount of water light-cured on glass and dentin for 40 s, respectively. The arrows indicate the Raman bands used for the DC calculation. For the specimens cured on glass, the spectra shown were collected from the adhesive surface in contact with glass slides. For the specimens cured on dentin, the spectra were acquired from the adhesive in contact with dentin.

Figure 2

Comparison of degree of conversions for the light-cured 2MP/HEMA adhesives (with different amount of water) on glass and dentin

Figure 3

Representative Raman spectra of the light-cured 2MP/HEMA adhesive (containing 30% water) on glass and dentin

Figure 4

(a) Representative micro-Raman mapping spectra in the region of 1300-1900 cm⁻¹ across from the dentin surface into the adhesive layer (containing 30% water); the arrows indicate the Raman bands used for the DC calculation. (b) Degree of conversion plots of the light-cured 2MP/HEMA adhesives with different amount of water as a function of location across the dentin surface and bulk adhesive layer.

Figure 5

(a) Representative micro-Raman mapping spectra in the region of 900-1600 cm⁻¹ across from the dentin surface into the adhesive layer (containing 30% water); the arrows indicate the Raman bands used for the 960/1458 calculation. (b) 960/1458 plot of the light-cured 2MP/HEMA adhesive (containing 30% water) as a function of location across the dentin surface and bulk adhesive layer.