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A influência do envelhecimento na estabilidade química, cor e polimerização de materiais restauradores auto-adesivos : estudo exploratório
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Objetivos: Verificar, após envelhecimento acelerado, as alterações na estabilidade química, estabilidade de cor e polimerização de uma resina composta flowable auto-adesiva, em comparação com uma resina composta universal comercial.
Materiais e métodos: Foram confecionados 30 discos (em anéis metálicos; 10x1 mm), a partir das resinas compostas Filtek™ Z250 (3M™ ESPE™, St. Paul, Minesota, EUA), grupo de controlo, e Constic™ (DMG, Hamburgo, Alemanha), uma resina auto-adesiva comercial. Armazenaram-se durante 2 meses, numa estufa a 60ºC (Memmert INE 400, Alemanha), de modo a simular um envelhecimento acelerado usando um modelo de Arrhenius. Ambas as resinas foram testadas em 5 momentos temporais (tempo zero, 1 dia, 1 semana, 1 mês e 2 meses). Foi estudada a cinética de polimerização (n=3), pondo os discos não polimerizados em contacto com o cristal de ATR (técnica de reflexão total atenuada), adquirindo espectros contínuos de FTIR (Spectrum One, Perkin-Elmer, Beaconsfield, Reino Unido), durante 20 min, utilizando a região de 700-4000 cm-1, a uma resolução de 4 cm-1. Obteve-se espectros antes, durante e depois de 20 s de fotopolimerização. Com os dados espectrais, avaliou-se a a estabilidade química, taxa de conversão extrapolada (DC,max) e a taxa de polimerização (Rp,max), em tempo real. Para avaliar a estabilidade de cor, nos mesmos tempos de estudo (n=3), utilizou-se o espectrofotómetro SpectroShade™ Micro (MHT Optic Research, Suiça) registando a cada medição os três parâmetros de cor CIELAB (L*, a* e b*).
Resultados: Com base nos espectros de ATR-FTIR, nenhuma das resinas pareceu sofrer significativas alterações químicas, após 2 meses de envelhecimento acelerado. Houve um impacto significativo do envelhecimento sobre a média de taxa de conversão (p<0,001). De forma similar, também se notou uma redução nas taxas de polimerização máxima, medidas para ambas as resinas (ANOVA; Z=203,722; p<0,001). A ANOVA two-way confirmou que o tipo de resina composta não teve influência sobre a estabilidade de cor (F=0,94; p=0,34), enquanto que a variável tempo teve sim um impacto significativo sobre a variação de cor (E) (ANOVA two-way, F=4,6; p=0,013).
Conclusão: A técnica de ATR-FTIR mostrou-se indicada para avaliar a estabilidade química das resinas convencionais e auto-adesivas. Nas resinas compostas auto-adesivas verificaram-se alterações dos níveis de absorvância mas sem grandes alterações químicas. A presença de um monómero acídico não pareceu contribuir para a uma maior degradação das resinas. A alteração de cor foi potenciada pelo envelhecimento.
Objectives: To determine, after accelerated aging, the changes in chemical stability, colour stability and polymerization kinetics of a flowable self-adhesive resin composite, compared to a conventional commercial universal composite resin. Materials and Methods: 30 discs (in metal circlips; 10x1 mm) were made from Filtek™ Z250 resin composites (3M™ ESPE™, St. Paul, Minnesota, USA), the control group, and Constic™ (DMG, Hamburg, Germany), a commercial self-adhesive composite. They were stored for 2 months in a 60°C incubator (Memmert INE 400, Germany) in order to simulate accelerated ageing, using an Arrhenius model. Both composites were tested at 5 time intervals (time zero, 1 day, 1 week, 1 month and 2 months). The polymerization kinetics (n=3) was studied by placing the unpolymerized discs in contact with the ATR crystal (attenuated total reflection technique), acquiring continuous FTIR spectra (Spectrum One, Perkin-Elmer, Beaconsfield, UK), for 20 min, using the region of 700-4000 cm-1, at a resolution of 4 cm-1. Spectra were obtained before, during and after 20 s of photopolymerisation. With the spectral data, chemical stability, extrapolated conversion rate (DC,max) and polymerization rate (Rp,max) were evaluated in real time. To evaluate colour stability, at the same study times (n=3), a SpectroShade™ Micro spectrophotometer (MHT Optic Research, Switzerland) was used recording at each measurement the three CIELAB colour parameters (L*, a* and b*). Results: Based on the ATR-FTIR spectra, none of the composites appeared to undergo significant chemical changes after 2 months of accelerated ageing. There was a significant impact of aging on the mean DC,max (p<0.001). Similarly, a reduction in Rp,max, measured for both composites, was also noted (ANOVA; Z=203.722; p<0.001). The two-way ANOVA confirmed that the type of resin composite had no influence on the colour stability (F=0.94; p=0.34), while the time variable did have a significant impact on colour variation (E) (ANOVA two-way, F=4.6; p=0.013). Conclusion: ATR-FTIR seems to be indicated to study the chemical stability of conventional and self-adhesive resin composites. Regarding self-adhesive composites changes in absorbance levels were noted, without major chemical changes in functional groups. The presence of an acidic monomer does not seem to potentiate the degradation of these composites. Changes in colour stability were potentiated by the ageing factor.
Objectives: To determine, after accelerated aging, the changes in chemical stability, colour stability and polymerization kinetics of a flowable self-adhesive resin composite, compared to a conventional commercial universal composite resin. Materials and Methods: 30 discs (in metal circlips; 10x1 mm) were made from Filtek™ Z250 resin composites (3M™ ESPE™, St. Paul, Minnesota, USA), the control group, and Constic™ (DMG, Hamburg, Germany), a commercial self-adhesive composite. They were stored for 2 months in a 60°C incubator (Memmert INE 400, Germany) in order to simulate accelerated ageing, using an Arrhenius model. Both composites were tested at 5 time intervals (time zero, 1 day, 1 week, 1 month and 2 months). The polymerization kinetics (n=3) was studied by placing the unpolymerized discs in contact with the ATR crystal (attenuated total reflection technique), acquiring continuous FTIR spectra (Spectrum One, Perkin-Elmer, Beaconsfield, UK), for 20 min, using the region of 700-4000 cm-1, at a resolution of 4 cm-1. Spectra were obtained before, during and after 20 s of photopolymerisation. With the spectral data, chemical stability, extrapolated conversion rate (DC,max) and polymerization rate (Rp,max) were evaluated in real time. To evaluate colour stability, at the same study times (n=3), a SpectroShade™ Micro spectrophotometer (MHT Optic Research, Switzerland) was used recording at each measurement the three CIELAB colour parameters (L*, a* and b*). Results: Based on the ATR-FTIR spectra, none of the composites appeared to undergo significant chemical changes after 2 months of accelerated ageing. There was a significant impact of aging on the mean DC,max (p<0.001). Similarly, a reduction in Rp,max, measured for both composites, was also noted (ANOVA; Z=203.722; p<0.001). The two-way ANOVA confirmed that the type of resin composite had no influence on the colour stability (F=0.94; p=0.34), while the time variable did have a significant impact on colour variation (E) (ANOVA two-way, F=4.6; p=0.013). Conclusion: ATR-FTIR seems to be indicated to study the chemical stability of conventional and self-adhesive resin composites. Regarding self-adhesive composites changes in absorbance levels were noted, without major chemical changes in functional groups. The presence of an acidic monomer does not seem to potentiate the degradation of these composites. Changes in colour stability were potentiated by the ageing factor.
Descrição
Dissertação para obtenção do grau de Mestre no Instituto Universitário Egas Moniz
Palavras-chave
FTIR Estabilidade química Estabilidade de cor Auto-adesiva