Effekt von bioaktiven Nanopartikeln auf die Struktur, die physikalischen und die mechanischen Eigenschaften von dentalen Adhäsiven

In the present in vitro study, different nanoparticles were added to a commercial adhesive (Solobond Plus, VOCO GmbH, Cuxhaven, Germany). The modified adhesives were investigated with regard to their material properties and a possible bioactive reaction. Solobond Plus was mixed with 0.1 m% or 1 m% bioactive glass with bismuth trioxide (BG-Bi), 10 m% or 20 m% monofunctional polyhedral oligomeric silsesquioxanes (POSS-1) or 10 m% or 20 m% multifunctional polyhedral oligomeric silsesquioxanes (POSS-8). Pure Solobond Plus adhesive was used as a control.

The distribution and size of the different nanoparticles were investigated in the solvent of the adhesive (acetone) using dynamic light scattering. The degree of conversion was measured by Fourier transform infrared spectroscopy. Viscosity was investigated on samples of experimental Solobond Plus adhesive (without photoinitiators) using a rheometer. Water absorption and sol fraction were performed on standardized test specimens. For this purpose, the polymerized specimens were incubated in distilled water at 37 °C for 20 days and weighed every 2 - 3 days. Subsequently, the water uptake and the sol fraction were calculated. The bioactive potential was investigated on extracted bovine teeth. The modified adhesive was applied to dentin test specimens by the etch-and-rinse technique. The test specimens were incubated in artificial saliva at 37 °C for 13 weeks and then examined for the formation of superficial calcium phosphate precipitates by scanning electron microscopy. The viscosity, degree of conversion, water uptake, and sol fraction were statistically analyzed by one-way ANOVA and Tukey's post hoc test (α = 0.05).

POSS-1 and POSS-8 showed good dispersion in acetone and had a size of < 2 nm. The dispersion and size of BG-Bi could not be measured due to its strong tendency to aggregate. Measurement of viscosity showed no change for all groups except a high increase in viscosity for 1 m% BG-Bi. A light decrease in the degree of conversion was detected for POSS-8 and a high decrease for POSS-1. No change in the degree of conversion was detected by the addition of BG-Bi. A decrease in water uptake was measured for POSS-1 and 20 m% POSS-8. A reduction of the sol fraction was detected for 20 m% POSS-1 and POSS-8. BG-Bi did not show a reduction of water uptake or sol fraction. Formation of Calcium phosphate precipitates was detected in all groups.

Due to its multifunctional structure, low concentrations of POSS-8 seem most suitable to be applied in a commercial adhesive. POSS-1 seems to be less appropriate since the mono functionality of the particles is expected to result in considerable losses in the degree of conversion. Due to the strong tendency to aggregation and poor dispersibility, BG-Bi also seems unsuitable for use in the Solobond Plus adhesive.