Desenvolvimento de materiais resinosos odontológicos utilizando monômeros metacrílicos derivados do cardanol: propriedades físico-químicas e mecânicas

Abstract

Triethylene glycol dimethacrylate (TEGDMA) and hydroxyethyl methacrylate (HEMA) are the most frequently employed diluent monomers in dental resin systems. However, they can lead to a reduction in mechanical properties, increased polymerization shrinkage, allergic reactions, and postoperative sensitivity. Consequently, various research efforts have been made to develop biocompatible organic matrices free from these monomers. A promising approach involves the use of cardanol, the main component of cashew nutshell liquid, for the synthesis of methacrylic monomers, as it presents several reactive sites, as well as a hydrophobic and flexible molecular structure. This thesis is composed of two chapters, which aim, respectively, to: 1) develop and file a patent for the invention of the synthesis and dental application of cardanol glycidylmethacrylate monomer (CGMA); 2) synthesize and characterize the cardanol trimethacrylate monomer (CTMA) to analyze the effect of partial or total replacement of TEGDMA by CTMA on the physicochemical and mechanical properties of experimental composite resins. In Chapter 1, a patent was filed with the National Institute of Industrial Property (INPI) concerning the synthesis and application of CGMA, obtained by incorporating a glycidyl methacrylate group into the phenolic hydroxyl of cardanol, with a focus on its use in dental resinous materials. Compared to HEMA, this monomer has the potential to confer greater hydrophobicity to dental materials, reducing water sorption, solubility, and polymer hydrolytic degradation. Additionally, the combination of the rigidity of the aromatic ring with the flexibility of the carbon chain provides high mechanical strength, and due to its high molecular weight, it can minimize polymerization shrinkage stress. In Chapter 2, CTMA was synthesized and characterized by Fourier-transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), and thermogravimetric analysis. Experimental composite resins were formulated with an organic matrix composed of Bis-GMA/TEGDMA (50/50% by weight) (Control) with CTMA gradually added, replacing TEGDMA: 10% (CTMA-10), 20% (CTMA-20), 40% (CTMA-40), and 50% (CTMA-50). The composite resins were evaluated for degree of conversion by FT-IR, water sorption and solubility, flexural strength, modulus of elasticity, and polymerization shrinkage stress. The data were analyzed with one-way ANOVA and Tukey's post hoc test (α=0.05), except for solubility data, which were evaluated by the Kruskal-Wallis test. Successful synthesis was confirmed by FT-IR and NMR spectra. Additionally, acceptable thermal stability was observed for safe use in the oral cavity. The CTMA-10 and CTMA-20 groups showed no statistically significant differences compared to the control in terms of degree of conversion, flexural strength, and modulus of elasticity. The incorporation of CTMA significantly reduced polymerization shrinkage stress in Class I restorations, did not affect water sorption, and reduced solubility in CTMA-10 and CTMA-40 compared to the control. Within the limitations of this in vitro study, the renewable CTMA monomer demonstrated favorable properties when incorporated at 20% to replace TEGDMA in composite resins, as it exhibited physicochemical and mechanical properties similar to the control, in addition to the ability to reduce polymerization shrinkage stress.