Study On The Effect Of Opacifiers On The Color Stability Of Maxillofacial Elastomers

Purpose.The purpose of this study was to measure color differences(â–³E^*) caused by exposure to ultraviolet-A,exposure to weathering and time passage on maxillofacial elastomers when mixed with several concentrations of opacifiers and pigments.Material and Methods.Experiment 1:Five ZY-1 elastomer specimens were fabricated for each of the combinations of the five opacifiers(nanometre TiO₂,nanometre TiO₂ coated with Si and Al,dry pigment titanium white,Ti white oil color,and no opacifier) and three pigments(oil pigment scarlet,gouache color crimson red,and no pigment),for a total of 75 specimens.The specimens were exposed to ultraviolet-A for 200h.CIE L^* a^* b^* values were measured before and after exposure,the color differences(â–³E^*) were calculated. Experiments 2 and 3:In part 1 of the studies,15 elastomer specimens were fabricated for each combination of 4 pigments(0.2%by weight)(cadmium red,yellow ochre,burnt sienna,and no pigment(control)) and various concentrations(0.1%,0.2%,0.3%by weight) of 4 opacifiers(nanometre TiO₂ coated with Si and Al,dry pigment titanium white,oil pigment titanium white,and no opacifier(control)).In part 2,the combinations were made of 1 of 4 opacifiers(0.2%by weight) and various concentrations(0.1%,0.2%,0.3%by weight) of 1 of 4 pigments as in part 1.For a total 64 groups(eliminated the repeated ones) and 960 specimens.The 15 specimens of each group were separated into 3 test condition groups at random.The UVA exposure groups were exposed to ultraviolet-A for 1000 hours;the weathering exposure groups were exposed to direct out door weathering;the time passage group was sealed in glass containers and kept in dark for 1000 hours and 6 months(about 4300h).Color differences(â–³E^*) were measured by a spectrophotometer before and after testing.The color differences(â–³E^*) were subjected to 4-way analysis of variance(ANOVA). Mean values were compared with Tukey's HSD post hoc test calculated at the 0.05 significance level.Results.Experiment 1:After 200h's exposure,no pigment specimens had the least color change,gouache color crimson red had the biggest.Among the five opacifiers,nanometre TiO₂ coated with Si and Al had the smallest color change,followed by,in order,nanometre TiO₂ and Ti white oil color(there are no difference between the two types),no opacifier,dry pigment titanium white.Experiments 2 and 3:In part 1,Along with the increase of opacifier concentration,cadmium red-UVA exposure group and burnt sienna-weathering exposure group showed an upward tendency for color change.In part 2,Along with the increase of pigment concentration,cadmium red-UVA exposure group,cadmium red-weathering exposure group,yellow ochre and no pigment(control)-1000 h-time passage group,showed an upward tendency for color change;burnt sienna-weathering exposure group showed a downward tendency for color change.After 1000 h of UVA exposure or stored in darkness: For all the pigments,nanometre TiO₂ coated with Si and Al had the least color change;for most of the pigments,no opacifier(control) had the most color change,within the 4 pigments, only burnt sienna caused less color change than no pigment(control),in both condition groups.After 6 months of weathering exposure or stored in darkness:Burnt sienna had the least color change,followed by,in order,yellow ochre,no pigment(control),and cadmium red.Most opacifiers had protected oil-pigmented elastomers from color change in time passage group,while the opacifiers showed an concentration-related effect on color stability of oil-pigmented elastomers,in weathering exposure group.Nanometre TiO₂ coated with Si and Al protected cadmium red from color degradation in a lower concentration of 0.1 wt%and 0.2 wt%.When the comparison was conducted between the 1000 h-time passage group and 6 months-time passage group,the most alter ofâ–³E^* were occur in cadmium red and nanometre TiO₂ coated with Si and Al with increasing amplitudes of 53.60%and 69.90% respectively.Conclusions.Nanometre TiO₂ coated with Si and Al,with a character that the lower concentration the more color stability,protected pigmented elastomers,especially red pigmented,from color degradation on some conditions,it was better than the rest of opacifiers. Burnt sienna increased the color stability of maxillofacial elastomers and the higher concentration the more color stability;cadmium red which was the most cause for color degradation of maxillofacial elastomers,decreased the color stability of maxillofacial elastomers and the higher concentration the less color stability.Most color degradation of oil-pigmented elastomers occured in the early stage after fabricated.