A step toward bio-inspired dental composites

Abstract

This feasibility study aimed to develop a new composite material of aligned glass flakes in a polymer resin matrix inspired by the biological composite nacre. The experimental composite was processed by an adapted method of pressing a glass flake and resin monomer system. By pressing and allowing the excess monomer to flow out, the long axis of the flakes was aligned. The resultant anisotropic composite with silanized and non-silanized glass flakes were subjected to fracture toughness tests. We observed increasing fracture toughness with increasing crack extension (Δa) known as resistance curve (R-curve) behavior. Silanized specimens had higher stress intensity K_R-Δa over non-silanized specimens, whereas non-silanized specimens had a much lower Young's modulus, and higher nonlinear plastic-elastic J_R-Δa R-curve. In comparison with conventional composites, flake-reinforced composites can sustain continued crack growth for more significant extensions. The primary toughening mechanism seen in flake-reinforced composites was crack deviation and crack branching. We produced an anisotropic model of glass flake-reinforced composite showing elevated toughening potential and a prominent R-curve effect. The feasibility of flake reinforcement of dental composites has been shown using a relatively efficient method. The use of a biomimetic, nacre-inspired reinforcement concept might guide further research toward improvement of dental restorative materials.

Keywords: Composite materials; R-curve; bioinspiration; biomaterials; dental materials; mechanical properties.

Figure 1.

Structure of nacre; (a) natural nacre in an abalone shell (Halitosis iris); (b,c) aragonite platelets in brick-and-mortar structure; (d) arrows showing the nano-asperities on the surface of platelets providing a rough surface and increasing friction; (e) fracture pattern of nacre showing platelet pull out and bridging as well as crack deviations (arrows), more clearly seen in (f), schematic of nacre failure on the microscopic level.

Figure 2.

(a) Method of processing the experimental flake-reinforced composites; (b) SEM of fracture surface of the flake-reinforced composite; (c) SEM of surface after removing polymer.

Figure 3.

R-curves of silanized and non-silanized experimental flake-reinforced composites. Fracture toughness is shown in terms of stress intensity K_R (a) and nonlinear elastic fracture, J_R (b). Included were data on conventional composites (particles, grey dots):K_R data taken from Shah et al. [22] (see Figure 3(a)) and J_R data from Wendler et al. [6] and De Souza et al. [21] (see Figure 3(b)). Glass-reinforced composite data (particles + orientated short-fibers, red dots) K_R and J_R from Tiu et al. [5] were added.

Figure 4.

Micrographs of crack patterns along the surface of the flake-reinforced composites.