Design and development of self-healing dental composites

Abstract

The purpose of this project is to design and develop a clinically applicable self-healing dental composite (SHDC). The value of resin-based dental restorations could be improved by increasing their service lives. One way to improve longevity is to obturate micro-cracks that form during or after the composite hardens in the dental cavity. Toward this end, we introduce here a new type of SHDC made with contemporary dental components plus two additional ingredients: a healing powder (HP, strongtium fluoroaluminosilicate particles) and a healing liquid (HL, aqueous solutions of polyacrylic acids) that is enclosed within silica microcapsules. As micro-cracks develop, they will break the microcapsules in their propagation path, thereby releasing HL. This liquid will then react with particles of HP exposed by the crack formation, forming an insoluble reaction product that fills and seals the cracks. The key factors to achieve this self-healing of cracks are discussed. The elastic modulus of a SHDC appeared to be satisfactory. The healing process was confirmed by means of mechanical, morphological, and chemical methods. The SHDC restored micro-cracks without external intervention, thereby showing potential for increasing the service lives of dental restorations. Importantly, this SHDC contains only clinically-tested, biocompatible materials, making it readily applicable.

Keywords: composite; dental material; encapsulation; self-healing.

Figure 1

Self-healing steps of SHDC. (A) A crack forms, and water comes in; (B) a microcapsule is broken due to crack propagation and HL is released; (C) the HL reacts with HP, and the product is GIC with ionic crosslinking network.

Figure 2

Characterization of microcapsules. (A) FTIR spectra of the microcapsules, indicating the presence of polyacid in HL or methylene blue aqueous solutions; and (B) TGA of water-containing microcapsules and HL-containing microcapsules

Figure 3

SEM images of SHDC cross-sections. (A) A cross-section of SHDC with unsilanized microcapsules. The components of SHDC are labeled, and the arrows point to pits left by microcapsules; (B) a cross-section of SHDC with silanized microcapsules.

Figure 4

Elastic moduli of SHDCs and control composites containing different mass percentages of microcapsule

Figure 5

(A) A model of the SEVNB process indicates the required geometry for the V-notch: S₀ = 20 mm, W = 4 mm, and B = 3 mm; and the load is applied from the center of the bar. (B) A stereo microscope image shows the notched specimen before fracture, and (C) a stereo microscope image shows the same specimen after reached the fracture load.

Figure 6

Stress-strain curves of a SHDC having 5 wt % of microcapsules before and after healing, in comparison to a control composed with the same mass fraction of water-containing microcapsules.

Figure 7

SEM images of the (A) non-healed SHDC surface, and (B) the healed SHDC surface. SEM-EDS images of (C) non-healed SHDC surface, and (D) the healed SHDC surface, artificially colored to match the signal count of Al and Sr; and the elemental analysis by EDS on sections of the (E) non-healed, and (F) healed regions of the SHDC.