Development of monomeric blends containing methacrylates with elastomeric behavior in association with photoinitiated alternative systems for application in dental materials

Abstract

The purpose of this research proposal will be to develop and evaluate the performance of monomeric blends containing low elastic modulus-methacrylate (exothane), in association with alternative water-soluble initiator systems. Blends with different exothane monomers will be formulated in combination with methacrylates commonly used in dental formulations: bisphenol A glycidyl dimethacrylate, ethoxylated bisphenol A glycidyl dimethacrylate, 2-hydroxyethyl methacrylate and triethylene glycol dimethacrylate. For the photoinitiaton systems, mixtures of traditional camphorquinone/amine binary system will be formulated, as well as alternative initiators and co-initiators: thioxanthone derivative (QTX), diphenyliodonium hexafluorophosphate, barbituric and sulfinic acid derivatives. Emission spectra of light curing units (LCU) and absorption of the evaluated initiators will be obtained. Absorption spectra will be determined in the 200-600 nm range using a UV-Vis spectrophotometer from solutions of photoinitiators prepared in methanol. The spectra will be obtained using a 1.0 cm path length quartz-cell. Fourier-transformed infrared (FTIR) spectra will be obtained in the spectral range between 1750 and 1550 cm-1 at a resolution of 4 cm-1. Each monomer solution will be placed on a diamond surface of an attenuated total reflectance unit (ATR) attached to infrared spectrophotometer and exposed to light emitted by the LCUs for 40 seconds (n=7). The degree of conversion will be calculated based on the comparison between aliphatic/aromatic double carbon bond ratios obtained before and after polymerization. Differential scanning calorimetry (DSC) will be performed on 10 mg of each sample (n=5), which will be placed in aluminium sample holders. The holders will be left open into the DSC sample compartment. Real-time heat flow data will be obtained during exposure to curing light to determine acceleration and deceleration curves during monomer conversion. Disc-shaped (15 mm x 1 mm) specimens will be fabricated for sorption and solubility test. The samples will be stored in a desiccator until a constant mass is obtained. The specimens will be immersed in distilled water for 7 days and the new mass will be measured. Water sorption and solubility will be determined using specific formulas. For cohesive strength, hourglass shape specimens (n=20) will be tested in tension in a universal testing machine. Cohesive strength will be calculated from the force required to fracture the specimens and specimen fractured area. Flexural strength and Young's modulus will be measured by three-point bending test (n=10), in a universal testing machine. Afterwards, experimental self-etching primer or adhesive system Clearfil SE Bond (Kuraray, Japan) will be applied to flat medium depth dentin surfaces of bovine incisors (n=20). Resin composite blocks will be incrementally build-up on the bonded dentin surface and the restored teeth will be sectioned to obtain beams with cross-sectional area of approximately 0.5 mm2. The specimens will be tested in tension after 24 hours, 6 months, and 1 year of storage in distilled water at 37 °C. The beams will be attached to a microtensile bond strength device and tested at 0.5 mm/min until failure. Thermomechanical cycling (n=20) will be also conducted using 200,000 mechanical and 2,500 thermal cycles, followed by microtensile strenght test after storage in distilled water at 37 °C for 24 hours. Analysis of the hybrid layer quality will be performed by scanning electron microscopy. All data will be submitted to statistical analyses. (AU)