Figure 2. Laser-Raman analysis. (A) Raman spectra of the bonding resin layer, the central portion of the hybrid layer made with wet bonding and that made with dry bonding. Aromatic ring (1614-1620 cm^-1); C=C (1642-1644 cm^-1). (B) The amount of resin infiltration within the hybrid layer calculated by comparison based on the relative intensity of the peak area of the aromatic ring (1548-1624 cm^-1). The same letter indicates that there is no significant difference: Mann-Whitney U test. P < 0.05 was considered significant. n = 24 for each group.