62ª Reunião Anual da SBPC

A. Ciências Exatas e da Terra - 3. Física - 4. Física da Matéria Condensada

Electron Paramagnetic Resonance (EPR) in the characterization of the shade effect on translucence, remaining free radicals, and polymerization depth of commercially available resin composites

Adriana da Silva Fontes 1 Walter Sano 2 Luis Henrique Dall´Antonia 3 Eduardo Di Mauro 4

1. Universidade Tecnológica Federal do Paraná - UTFPR, Campo Mourão - PR 2. Depto. de Física Aplicada, Instituto de Física, Universidade de São Paulo - USP 3. Depto. de Química, Universidade Estadual de Londrina - UEL 4. Prof. Dr./Orientador - LAFLURPE, Universidade Estadual de Londrina - UEL

INTRODUÇÃO:

Dental restorations with composite resins are naturally imperceptible nowadays due to the available options in color and translucence. Despite this progress, residual monomer in the cured composite still leads to the incomplete double bond conversion and probably interferes in restoration performance and longevity. Polymerization occurs when the initiator agent absorbs energy from the applied light and passes to a triplet excited state. The initiator agent then interacts with a proton-donor molecule such as a tertiary amine, and generates Amine and Ketyl free radicals. The amine radicals formed in the process interact with the monomers and produce a chain reaction. In chain reaction, the radicalized monomers combine to form progressively longer polymer chains which make up the polymer matrix. Free radicals are electrons with unpaired spin located on a molecule or a molecule fragment. Information on these radicals are of high importance because the polymerization of these resins is incomplete and is conducted by free radicals.  Anterior studies have not reported on the influence of color or translucence on free radical formation nor on the way these factors affect the polymerization process. Our work aimed to study precisely this phenomenon.

METODOLOGIA:

The objects of our study are two Brazilian commercial brands of microhybrid resin composites used for teeth restoration: Master Fill (Biodinâmica, Ibiporã, PR, Brazil) and Opallis (FGM, Joinville, SC, Brazil). To study the influence of color in resin polymerization, we used Master fill resins with variations in the quantity of color pigments (M, MA2 e MA4), and Opallis resin in shades DA2 and DB3.To study the influence of translucence, we used Opallis resin with variations in the quantity of opacity components, one for enamel (OE) and the other for dentine (OD), both in shade A2. The main composition difference in Master Fill products is lack of color pigment in colorless M, a small quantity of color pigment in MA2, and a large quantity in MA4. Among Opallis products, the amount of opacity components is larger in dentine than in enamel application. The amount of color pigment in dentine resin is larger in ODB3 than in ODA2. EPR spectra were recorded in the X-band (9.6 GHz) in a spectrometer (JEOL, JES-PE-3X, Germany) to study the radicals during the resin polymerization. EPR quantified the radical populations through relative intensity (Ir) of free radicals generated and radical decay was monitored.

RESULTADOS:

The analysis indicated that resin with more color pigments (MA4, Ir = 0.73 a.u) or more opacity components (ODA2, Ir = 0.84 a.u) generated smaller populations of free radicals and have lower polymerization depth than clearer (M, Ir = 1.20 a.u and MA2, Ir = 1.02) or more translucent (OEA2, Ir = 1.00 a.u) composites for the same light-curing time. It seems that irradiation doses have to be adequate to more colored and less translucent resins. The scraping test for the Master fill resin indicated that polymerization depth of the colorless resin (M) was 55 % larger than in the more pigmented MA4. Similar results are shown for color in Opallis resins such as the light color ODA2 and the dark color ODB3, where the former performed better than the latter. As far as translucency, Opallis resin for enamel (OE) had better properties than for dentine (OD) in the same color (A2) because the resin for enamel is more translucent and irradiation penetrated 16 % more deeply, resulting in better polymerization. As a result of generation insufficient radicals for the polymerization, only short polymer chains are formed and many monomers remain in the structure. Such a composite has insufficient mechanical properties and could fail when applied in restorative dentistry.

CONCLUSÃO:

Translucence, even more so than color, may be a limiting factor with regard to the polymerization depth of some resin systems. A more translucent material allows better light transmission from the LED device, resulting in a higher degree of conversion and consequently higher hardness. Light transmission through darker colors is diminished because of less translucence. Such results suggest an inversely proportional relationship between the amount of additive substance of color and translucence controls, and polymerization depth. Our results indicate that darker shades or more opaque dental resins lead to lower polymerization depth compared to clearer or more translucent resins. This is clearly indicated by the smaller radical production caused by the role of additive pigments and opacity components in reducing the light intensity required by the initiator agent of polymerization. Therefore, resins need to have different values for irradiation doses in function of the variation in color and translucence because the quality performance of dental restorations can improve with ideal irradiation doses being defined for each resin. These results show how EPR spectroscopy can provide new information which may lead to a better understanding of the phenomena existing in dental resins.

Instituição de Fomento: Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES

Palavras-chave: Composite resins, Translucence, Polymerization depth.