Resinas para restauração dentária baseadas em cerâmicas organicamente modificadas - ORMOCER®

Abstract

In this work we developed a hybrid organic-inorganic polymer (pMEMO) via a sol-gel process from the precursor 3 - metacriloiloxipropil trimethoxysilane (MEMO). The material was characterized by FTIR, and nuclear magnetic resonance H1 NMR. The data confirmed the achievement of a hybrid polymer with a very organized three-dimensional structure of siloxane bonds (Si-O-Si). Both neat and in combination with other monomers, the material was used as organic matrix in dental restorative resins, and the physico-chemical properties of the resins were evaluated. In all resins was used 70 % by weight of silanized silica (mean size of 7.5 ?m). The effect of Lucirin (LR samples), as an alternative photoinitiator system, was evaluated in comparison with that one used in most commercial resins (Camphoroquinone, RE samples). A mixed factorial design was done in order to optimize the composition between pMEMO and conventional monomers by monitoring the response of these formulations in relation to the main tests used for characterization of dental resins. In the optimized composition of resins prepared with Camphorquinone the monomers showed little influence of Bis-GMA, with best values of Vickers hardness (48,88 HV) and degree of conversion of monomer (72.36 %) consisting of about 50% of pMEMO and 50% of TEGDMA (diluent). The results for resins cured with Lucirin showed a very large dependence with the pMEMO content, especially with a composition higher than 70%, which showed a hardness of 60.78 HV and a degree of monomer conversion of 67.88%. For formulations containing only pMEMO cured with both systems photoinitiation (RE1 and LR1) the flexural strength (FS) values were smaller than established by ISO 4049 for dental restorative resins. This aspect was expected due to the ceramic characteristics of these materials. The presence of the diluent monomer TEGDMA in combination with resins containing pMEMO caused a plasticizing effect in such formulations, thereby increasing the FS values (RE1 = 36.83; RE4 = 44.43 MPa - LR1 = 33.37; LR4 = 73.87 MPa). Shrinkage was relatively low in systems consisting solely by pMEMO (ca. 3 %). This was assigned to the inorganic three-dimensional polymer network which prevents shrinkage even at higher degrees of conversion as observed for the samples cured with Lucirin. SEM analyzes associated with sorption and solubility data indicated a very pronounced deleterious effect on samples containing only TEGDMA. Noteworthy is the fact that cracks were observed due to the leaching of microgel regions rich in diluent monomers for the RE4 sample (cured with Camphorquinone), which contains, besides pMEMO, 50% of TEGDMA. This was not observed in the sample cured with LR4 Lucirin due to this photoinitiator be generating a better structured three-dimensional network and therefore less susceptible to sorption processes