Newly synthesized or modified resin-based materials to improve the longevity of dental restorations

• Ano de defesa: 2022
• Autor(a) principal: Lucena, Fernanda Sandes de
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Composite resins; Dental bonding; Mechanical tests; Resinas compostas; Testes mecânicos; União à dentina
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/25/25148/tde-18112022-163721/

The focus of the investigations presented in this thesis was the development of new strategies to improve the quality and the longevity of resin-based materials, once polymerization shrinkage and induced stresses during the curing procedures are inherent characteristics of composites that might compromise their success. Moreover, the bonded interface is also a weak link of adhesive restorations, since it can undergo hydrolytically and enzymatic degradations. In the first study, a triacrylamide-based adhesive (TMAAEA) and a thiourethane-based (TU) composite were tested on a bioreactor system under mechanical and bacterial challenges and compared to HEMAbased materials. Marginal integrity was assessed through scanning electron microscopy (SEM) and demineralization and bacterial infiltration were evaluated on confocal laser scanning microscopy (CLSM). The materials were also tested for microtensile bond strength (TBS), where the beans were tested before and after 7- days storage in water or biofilm. HEMA-based materials exhibited greater initial gaps. After water testing, TMAAEA adhesive presented significantly smaller gaps, and for the samples tested with the presence of biofilm, the TMAAEA/TU combination produced smaller gaps for the bioreactor. For TBS, HEMA and TMAAEA adhesives showed similar immediate values, however, after 7-days of biofilm-challenge, TMAAEA-adhesive was the only one to preserve the initial bond strength values. The second study characterized a new BisGMA-free monomer, with high molecular weight (734.98 g/mol), PG6EMA, synthesized through a mixture of isomers, as an unfilled material (resin) with serial amounts of ethanol (3, 6 and 9% EtOH) and as filled material (composite). Resins were evaluated regarding polymerization kinetics, viscosity () and shear storage modulus (G) and, in addition, the composites were evaluated for water sorption and solubility, wet/dry flexural strength/modulus (FS/E) and polymerization stress. The materials were compared to BisGMA/TEGDMA (BTEG) mixtures. PG6EMA resins showed lower polymerization rates, but higher degrees of conversion (DC) when compared to BTEG (80.7±5.2-90.7±0.5 %, versus 73.5±3.2 - 84.4±1.7 %, respectively). The viscosity of PG6EMA resins was higher than the BTEG and, for PG6EMA resins, the amount of EtOH added to the formulation was inversely proportional to the viscosity values. The composites presented a similar behavior than the resins regarding polymerization kinetics, since PG6EMA/TEGDMA composite showed slower polymerization rates and higher final DC (9.1±0.1 %.s-1 and 93.4±1.6 %) in comparison to BTEG (9.7±0.1 %.s-1 and 87.8±2.7 %). As for the mechanical properties, besides the higher conversion, PG6EMA/TEGDMA group showed lower dry and wet FS, but similar elastic modulus. PG6EMA composite produced 18.4% lower polymerization stress than the BTEG formulation. As for the third article, dioxide titanium nanotubes (TiO2-nts) were synthesized, functionalized with 3-aminopropyl trimethoxysilane (APTMS) and loaded with chlorhexidine digluconate (CHX) ou doxycycline hyclate (DOX). The characterization of the unloaded and loaded nanotubes was performed through X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). These methods confirmed the tubular and hollow morphology of TiO2-nts, the effectiveness of the functionalization, and the presence of the inhibitors in the samples. All groups were able to inhibit the total activity of MMP between 65-72%. The adhesives modified by non-functionalized TiO2-nts presented lower DC compared to the control, meanwhile the functionalized groups were statistically similar to the non-modified adhesive. Nonfunctionalized groups loaded with CHX or DOX tested in etch-and-rinse and self-etch modes were able to sustain the TBS after 6 months storage in saliva, but this trend was not followed by functionalized groups. The cell viability of HDPC cells was not affected by the modified adhesives. The current results demonstrated that: 1) TMAAEA-based adhesives were able to produce a stable bond after mechanical and bacterial challenges, 2) PG6EMA, a novel monomer synthesized from the mixture of isomers, demonstrated higher conversion and lower polymerization stress when compared to a BisGMA/HEMA formulation without jeopardize the FS and E in dry conditions, and 3) The adhesives modified by CHX or DOX-loaded TiO2-nts were able to inhibit total MMP activity, producing a stable bond to dentin after 6 months storage, without compromise cell viability.