Exploring the retention properties of CaF2 nanoparticles as possible additives for dental care application with tapping-mode atomic force microscope in liquid

Abstract

Amplitude-modulation atomic force microscopy (AM-AFM) is used to determine the retention properties of CaF2 nanoparticles adsorbed on mica and on tooth enamel in liquid. From the phase-lag of the forced cantilever oscillation the local energy dissipation at the detachment point of the nanoparticle was determined. This enabled us to compare different as-synthesized CaF2 nanoparticles that vary in shape, size and surface structure. CaF2 nanoparticles are candidates for additives in dental care products as they could serve as fluorine-releasing containers preventing caries during a cariogenic acid attack on the teeth. We show that the adherence of the nanoparticles is increased on the enamel substrate compared to mica, independently of the substrate roughness, morphology and size of the particles.

Keywords: AM-AFM in liquid; nanodentistry; nanoparticles.

Figure 1

(a) Theoretically predicted trajectory angles of nanoparticles manipulated on an arbitrary surface as a function of the particle–substrate contact radius with b = 39 nm. (b) Calculated particle radius and energy dissipation obtained by using Equation 2 with an experimentally determined phase-lag and trajectory angle of the manipulated particles adsorbed on mica. The amplitude was A = 23 nm, the Q-factor = 7 and A₀ = 1.2A.

Figure 2

SEM images of the three morphologies of nanoparticles explored in this work. A certain size distribution of the particles was achieved with the synthesis method described in the text. The diameters vary from 50–100 nm for (A), 100–150 nm for (B) and 200–250 nm for (C). The shape varied from cubic (A) to polyhedral (B) and oblate cubic (C). The scale bar for all images is 200 nm.

Figure 3

(a) Phase image of nanoparticles (B) adsorbed and manipulated on mica substrate. (b) Topography image of nanoparticles (A) adsorbed on enamel substrate. Scan size is for both images 10 μm.

Figure 4

Calculated energy dissipation histograms obtained for the nanoparticles A, B and C from Figure 3 on mica (a) and tooth enamel (b). The dissipated power was calculated per oscillation cycle of the cantilever. Amplitude and set point were comparable for all experiments.