Comparing Self-Etch Adhesives with Atomic Force Microscopy and Optical Profilometry

Objectives: To examine enamel surfaces treated with phosphoric acid and self-etch adhesives using atomic force microscopy[AFM] and optical profilometry[OP].
Methods: Three self-etch adhesives were evaluated: OptiBond XTR[XTR]; Prime & Bond elect[PE]; Scotchbond Universal[SU]; and compared to a conventional phosphoric acid (35%), Ultra-Etch[PA]. De-identified extracted human molar teeth (n=10/group) were mounted in custom fixtures and flat ground to 4,000 grit. Etching times followed manufacturers’ recommendations. A Proscan 2100 non-contact optical profilometer (OP, 1-5μm lateral resolution) with ProForm software, and an Agilent 5420 atomic force microscope (AFM, 5-10nm lateral resolution) with Gwyddion software characterized specimens. ANOVA and Tukey's post hoc tests were used for statistical analysis.
Results: OP and AFM demonstrated significant differences (p<0.05) in enamel roughness between PA, control, and surfaces treated with self-etch adhesives. OP showed a difference (p<0.05) between XTR, when compared to PE, SU and control, but AFM did not show a difference between XTR and other self-etch adhesives. This suggests that XTR’s etching ability exists on the lateral scale measured by OP. However, XTR’s etching does not exist exclusively on the microscale, as OP and AFM distinguished statistical Ra differences (p<0.05) between XTR and control, suggesting etching both in the micro- and nano-structure. The surface area of the PA group was significantly greater (p<0.05) than all other groups.
Conclusions: Combined, OP and AFM show unique insights into resulting micro- and nano-structure from etching techniques and further confirm the superior increased roughness of phosphoric acid etching of enamel compared to self-etch adhesives.