Effect of delayed light-curing on solubility, color stability, and opacity of Fuji II LC glass ionomer cement: original article / Efeito da fotopolimerização tardia na solubilidade, estabilidade de cor e opacidade do cimento de ionômero de vidro Fuji II LC: artigo original

Objective: Resin-modified glass ionomer (RMGI) cements are among the commonly used restorative materials in low stress-bearing areas and also for temporary restorations. The competition between acid-base reactions and light polymerization reactions in delayed curing of RMGIs can affect their physical and mechanical properties, as well as their degree of conversion. Since solubility, color stability, and opacity are among the main physical properties affecting the durability and clinical service of RMGI restorations, this study aimed to assess the effect of delayed curing on solubility, color stability, and opacity of Fuji II LC RMGI. Material and Methods: This in vitro, experimental study evaluated 80 Fuji II LC RMGI specimens (10 specimens per each in 4 groups) in terms of solubility, color stability, and opacity at 6 months later. Specimens were cured immediately or were cured with 1, 5 and 10 min delay. Results: Maximum solubility and minimum change in opacity and color stability at 6 months were noted in the group with delayed curing by 10 min. A significant difference was noted in the solubility of specimens cured after 10 min and 1 min. Significant differences were also noted in the opacity and color stability of specimens cured after 10 min and all other groups (P < 0.05). Conclusion: Delayed curing by 1 min decreased the solubility of RMGI specimens compared with immediate curing or curing after 5 min. Although this difference did not reach statistical significance. Color stability and changes in opacity are mainly influenced by the acid-base reactions rather than polymerization reactions.(AU)

Objetivo: Cimentos de ionômero de vidro modificado por resina (CIVMR) estão entre os materiais restauradores mais comumente utilizados em áreas de baixa tensão e também para restaurações temporárias. A competição entre reações ácido-base e reações provenientes da fotopolimerização tardia dos CIVRMs podem afetar suas propriedades físicas e mecânicas, bem como seu grau de conversão. Uma vez que a solubilidade, estabilidade de cor e opacidade estão entre as principais propriedades físicas que afetam a durabilidade e o tempo de serviço clinico de restaurações de CIVMR, este estudo teve como objetivo avaliar o efeito da fotopolimerizaçao tardia na solubilidade, estabilidade de cor e opacidade do CIVMR Fuji II LC. Material e Métodos: Este estudo experimental in vitro avaliou 80 espécimes de CIVMR Fuji II LC (4 grupos com 10 espécimes cada) em termos de solubilidade, estabilidade de cor e opacidade apos 6 meses. As amostras foram fotopolimerizadas imediatamente ou com 1, 5 e 10 min de atraso. Resultados: Máxima solubilidade e mínima alteração na opacidade e estabilidade da cor em 6 meses foram observadas no grupo com fotopolimerização tardia em 10 min. Uma diferença significativa foi observada na solubilidade das amostras fotopolimerizadas após 10 min e 1 min. Diferenças significativas também foram observadas na opacidade e estabilidade de cor das amostras fotopolimerizadas após 10 min e em todos os outros grupos (P <0,05). Conclusão: A fotopolimerizaçao tardia em 1 min diminuiu a solubilidade das amostras CIVMR em comparação com a fotopolimerizaçao imediata ou após 5 min. Embora essa diferença não tenha alcançado significância estatística. A estabilidade da cor e as mudanças na opacidade são influenciadas principalmente por reações ácido-base, em vez de reações causadas pela polimerização(AU)

Degree of Conversion of Resin-Modified Glass Ionomer Cement Containing Hydroxyapatite Nanoparticles.

OBJECTIVES: Hydroxyapatite (HA) nanoparticles are used to improve the physical and mechanical properties of glass ionomers (GIs). This study aimed to assess the effect of addition of different weight percentages of nano-HA on degree of conversion (DC) of Fuji II LC GI cement using a spectrometer. MATERIALS AND METHODS: In this in vitro experimental study, 30 samples were fabricated of Fuji II LC (improved) GI cement in six groups (n=5) containing 0%, 1%, 2%, 5%, 7% and 10wt% nano-HA. The obtained paste in each group was subjected to Fourier-transform infrared spectroscopy (FTIR) before curing to assess the monomer to polymer DC percentage. The paste was then light-cured and underwent FTIR again. One-way ANOVA was applied to compare the DC percentage of different groups. Pairwise comparisons were performed using the Tukey's test. RESULTS: The DC was 57.88±0.57% in 0%, 60.04±0.63% in 1%, 66.92±0.54% in 2%, 65.5±0.71% in 5%, 51.49±0.24% in 7% and 50.09±0.32% in 10% nano-HA group. The difference in DC among the groups was statistically significant (P<0.0001). The highest DC was noted in 2% nano-HA and the lowest DC was found in 10% nano-HA group. Pairwise comparisons revealed significant differences between the groups in DC (P<0.0001). CONCLUSION: Increasing the weight percentage of nano-HA to 2% increased the DC but increasing the nano-HA weight percentage over 5% decreased the DC of resin-modified glass ionomer cement (RMGIC). The highest DC was noted in 5w% and 2w% nano-HA groups. Thus, 5w% and 2w% nano-HA can be used to improve the DC of RMGIC.