Nanoneedle-like zinc oxide as a filler particle for an experimental adhesive resin

The aim of this study was to develop an experimental adhesive resin with nanoneedle-like zinc oxide (N-ZnO), an inorganic filler, that could avoid particle agglomeration and lead to a homogeneous stress distribution within the material and characterize it.

N-ZnO particles obtained by a thermal evaporation technique were characterized regarding size and surface area and added at 0 (control), 1, 2, 5, and 10 wt%, to an experimental adhesive resin. The following experimental adhesive resins' properties were assessed: radiopacity, contact angle to conditioned enamel and dentin, color, degree of conversion, flexural strength, resistance to degradation, and cytotoxicity. Statistical analysis was performed using one-way ANOVA and Tukey's post hoc test and paired Student's t-test.

Particles presented a mean particle size of 40 nm and a specific surface area of 16 m²/g. N-ZnO_10%showed an increased radiopacity when compared to N-ZnO_0%. Contact angles were significantly higher for N-ZnO_10%at enamel and N-ZnO_2%, N-ZnO_5%, and N-ZnO_10%at dentin. All groups showed color change when compared to N-ZnO_0%. Higher the N-ZnO concentration, lower the degree of conversion. There were no significant differences between the groups for flexural strength and resistance to degradation. The addition of N-ZnO showed no difference in cytotoxicity when compared to positive control, N-ZnO_0%, and all groups showed higher values than negative control.

N-ZnO possibly exceeded potential limitations due to particles' agglomeration and improved the transference and distribution of stress within the material. It could be effectively used as a filler for adhesive resins.