Distinct photopolymerization efficacy on dentin of self-etch adhesives

Abstract

The effect of application mode on polymerization effectiveness of self-etch adhesives with different pHs has rarely been studied. We applied 2 self-etch adhesives-Adper Prompt L-Pop (APLP, pH ~ 0.8) and Adper Easy-Bond (AEB, pH ~ 2.5)-to dentin with or without agitation (dynamic or static application), to investigate photopolymerization efficacy on dentin, and to understand the role of chemical interaction/reaction between adhesives and dentin. Micro-Raman spectra and imaging were acquired across the dentin/adhesive (D/A) interface. The degree of conversion (DC) of each adhesive as a function of position was calculated. SEM-EDS was used to obtain the elemental distribution along the interface. Photopolymerization efficacies of the two self-etch adhesives on dentin were apparently different. APLP exhibited decreasing DCs as the distance from the D/A interface became greater for both application modes, while the DCs for the dynamic mode were much higher than those for the static mode. As for AEB, the DCs remained almost constant across the adhesive layer and showed no significant difference between two modes. Raman spectral analysis disclosed that the chemical interaction between dentin and adhesives was responsible for the observations. We also verified this by tracking the distribution of the elements Ca and P in the adhesive layers.

Figure 1.

Micro-Raman images of the band area ratios of 1640 cm⁻¹ (stretching υ of C=C) to 1458 cm⁻¹ (deformation δ of CH₂) (R_1640/1458) as a function of spatial position for (a) Adper Prompt L-Pop applied with agitation (APLP-WA), (b) Adper Prompt L-Pop applied without agitation (APLP-WOA), (c) Adper Easy-Bond applied with agitation (AEB-WA), and (d) Adper Easy-Bond applied without agitation (AEB-WOA). (e) Profiles of degrees of conversion for (a), (b), (c), and (d) adhesives as a function of spatial position. The degrees of conversion of the adhesives were calculated based on the band area ratios of 1640 cm⁻¹ to 1458 cm⁻¹ by use of the Equation.

Figure 2.

Representative micro-Raman spectra of Adper Prompt L-Pop (with and without agitation, APLP-WA and APLP-WOA) and Adper Easy-Bond (with and without agitation, AEB-WA and AEB-WOA) collected at positions 7 µm away from the dentin/adhesive (D/A) interfaces.

Figure 3.

Micro-Raman images of the band area ratios of 960 cm⁻¹ (stretching υ₁ of PO₄) to 1458 cm⁻¹ (deformation δ of CH₂) (R_960/1458) as a function of spatial position for (a) Adper Prompt L-Pop applied with agitation (APLP-WA), (b) Adper Prompt L-Pop applied without agitation (APLP-WOA), (c) Adper Easy-Bond applied with agitation (AEB-WA), and (d) Adper Easy-Bond applied without agitation (AEB-WOA). (e) Profiles of band area ratios of 960 cm⁻¹ to 1458 cm⁻¹ (R_960/1458) for (a), (b), (c), and (d) adhesives as a function of spatial position.

Figure 4.

Energy-dispersive x-ray spectrometry (EDX) as a function of spatial position. (a) Profiles of contents of the elements calcium (Ca) and phosphorus (P) as a function of spatial position. EDX spectra of (b) Adper Prompt L-Pop (with and without agitation, APLP-WA and APLP-WOA) and (c) Adper Easy-Bond (with and without agitation, AEB-WA and AEB-WOA) collected at positions 7 µm away from the dentin/adhesive (D/A) interfaces.