Consideration of Dental Tissues and Composite Mechanical Properties in Secondary Caries Development: A Critical Review.

Different kinds of interactions between the restorative material and mineralized dental tissues result in secondary caries around dental composites. Of these, the mechanical interactions have to be carefully investigated. Due to the elastic mismatch between dental tissues and the composite restoration, complex stresses and strains develop at their interface. This complex mechanical environment disturbs the demineralization-remineralization equilibrium of dental hard tissues. The fluid flow both over and within enamel and dentin, associated with their complex ultrastructure and mechanical behavior, is a key factor. It is known that external mechanical loading can indirectly promote the dissolution of enamel and dentin through a pumping action of cariogenic fluids in and out of microgaps at the interface between mineralized tissues and composite. Mechanical loading can also directly influence the physicochemical behavior of dental hard tissues by inducing complex strain and stress fields on the crystal scale. It is important to consider both the direct and indirect paths by which mechanical loading can influence the apatite dissolution kinetics. Therefore, a systematic approach should be used to investigate the mechanism of secondary caries formation considering the tooth-composite interface as a unique complex in which each element has an influence on the other.

Effectiveness of the DHMAI monomer in the development of an antibacterial dental composite.

OBJECTIVE: Development of antibacterial dental composites is the ultimate goal to decrease carious disease occurrence and increase the restoration longevity. For this purpose, the quaternary ammonium dimethyl-hexadecyl-methacryloxyethyl-ammonium iodide (DHMAI) and the methacryloyloxyethylphosphorylcholine (MPC) have been incorporated in experimental methacrylate-based composite resins. This aims to first investigate the effect of each alone and then their combined effect. METHODS: Synthesized DHMAI and commercial MPC were added either alone or combined at different concentrations to experimental dental composite. Flexural strength (FS) and modulus (FM) were tested to select the optimal concentrations. Only selected composites were evaluated for Vickers hardness (HV) and the degree of conversion (DC) using fourier transform infrared spectroscopy analysis (FTIR-ATR). Antibacterial activity was assessed using tests on colony-forming unit (CFU), scanning electron microscopy (SEM) and Alamarblue assay to measure the metabolic activity. Streptococcus mutans biofilm was chosen to be grown on the composite surfaces during 96h at 37°C. RESULTS: Incorporation of 7.5% DHMAI in composite improved the degree of conversion and gave a strong antibacterial effect with a reduction of (∼98%) in CFU and (∼50%) of metabolic activity with acceptable mechanical properties. Addition of MPC to DHMAI affects mechanical properties of composites without providing a better antibacterial activity. SIGNIFICANCE: Composites with DHMAI greatly reduced S. mutans biofilm and improved the degree of conversion without scarifying the composites' mechanical properties. DHMAI may have wide applicability to other dental materials in order to inhibit caries and improve the longevity of restorations.