Synthesis and characterization of novel halloysite-incorporated adhesive resins

Objective To investigate the effects of Halloysite^® aluminosilicate clay nanotubes (HNTs) addition on selected physical, mechanical, and biological properties of experimental adhesive resins. Methods Experimental dentin adhesive resins were prepared by mixing Bis-GMA, TEGDMA, HEMA (50/25/25 wt.%), and photo-initiators. As-received HNTs were then incorporated into the resin mixture at distinct concentrations: 0 (HNT-free, control), 1, 2.5, 5, 7.5, 10, and 20 wt.%. The degree of conversion (DC), radiopacity (RP), Knoop hardness (KHN), flexural strength (FS), and cytotoxicity analyses were carried out for each adhesive formulation. The adhesive resin of Adper Scotchbond Multi-Purpose (SBMP) was used as the commercially available reference for both the RP and cytotoxicity tests. Data were statistically analyzed using One-Way ANOVA and Tukey's test (p ≤ 0.05). Results All adhesives exhibited similar DC (p = 0.1931). The RP of adhesives was improved with the addition of up to 5 wt.% of HNTs (p < 0.001). Adhesives containing 5-10 wt.% of HNTs led to greater KHN when compared to the control (p < 0.001). The FS was reduced only when 20 wt.% of HNTs was added (p ≤ 0.001). None of the prepared adhesives was cytotoxic. Conclusion The incorporation of up to 10 wt.% of HNTs into the adhesive resins did not jeopardize the tested physical and biological properties. Clinical significance When using HNTs as carriers of drugs/bioactive compounds, the amount of the former added into adhesive resin materials should not exceed 10 wt.%; otherwise, a significant reduction in physicomechanical properties may be expected.