Incorporation of cellulose nanocrystals into dental resins for denture base and relining. Chemical characterization and effect on physical, mechanical and biological properties.

Abstract

The materials for the preparation and relining of complete or partial dentures are constantly subjected to repeated forces originating from mastication or parafunctional habits, as well as variations in temperature and exposure to solvents and oral fluids, which may lead to changes in the physical and mechanical properties of these materials. The use of biopolymers from renewable sources as nanometric reinforcing agents can represent an important innovation in dental materials. Cellulose nanocrystals (CNC) isolated from wood pulp through acid hydrolysis will be used as reinforcing agents in acrylic resins for denture base (Lucitone 550-LU, water-bath thermopolymerizable, and Onda-Cryl -OC, activated by microwave energy) and relining (Kooliner - KL and Soft Confort Dura - SC). Mechanical properties (viscoelastic and flexural strength), physical (roughness, hardness, surface free energy and color stability), and biological properties (biofilm formation) of the four dental resins after CNC incorporation will be evaluated. Twenty experimental groups (n = 10), according to the type of acrylic resin (LU, NC, KL or TR) and agent concentration (0%, 0.25%, 0.5%, 0.75% and 1.00%). The characterization of the resins, for all groups (n = 1), will be performed by Fourier Transform Infrared Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC). Rectangular specimens (64 x 10 x 3.3 mm) will be obtained for dynamic-mechanical thermal analysis (DMTA) and flexural strength (FS). Acrylic resin discs (15 x 3 mm) will be prepared for the evaluation of roughness, hardness, surface free energy, color stability and biofilm formation. The color stability readings will be carried out by means of a spectrophotometer (E), the roughness will be measured in a digital rugosimeter Ra (¼m), the Vickers hardness in the microdrometer Micromet 2100, and the surface free energy will be measured from contact angle measurements, obtained by means of a goniometer connected to a computerized system. To evaluate the simple and mixed biofilm formation of C. albicans and S. mutans, the specimens will be inoculated and incubated at 37ºC for 48h. After this period, each specimen will be transferred to tubes containing saline solution. Serial dilutions of the resulting suspension will then be performed and aliquots of these dilutions will be seeded into Petri dishes. After 48h at 37ºC incubation, counts of colony forming units/mL (UFC / mL) will be performed and the characterization of the specimens (n = 2) will be carried out by Scanning Electron Microscopy (SEM) in each experimental condition. For all variables, the data will be tabulated and submitted to adequate statistical tests, according to adherence to normality, at 5% of significance level. (AU)