Effect of opacifiers on color stability of pigmented maxillofacial silicone A-2186 subjected to artificial aging

PURPOSE: This study was designed to determine the effect of opacifiers used at different ratios on the color stability of pigmented A-2186 silicone maxillofacial elastomers and to evaluate the color spectrophotometrically before and after artificial aging. MATERIALS AND METHODS: Sixty experimental groups of elastomers were made using various concentrations (5%, 10%, and 15%) of 4 opacifiers (Georgia kaolin powder neutral, kaolin powder calcined, Artskin white, and dry pigment titanium white) with 1 of 5 dry earth cosmetic pigment groups (no pigment [control], red, yellow ochre, burnt sienna, and a mixture of all pigments). Five specimens of each elastomer were tested, for a total of 300 specimens. All specimens were placed in an aging chamber and artificially aged by exposure to light, water spray, fluctuating temperatures, and humidity. CIE L*a*b* values were measured by spectrophotometer. The color differences (Delta E*) at various exposure energies (150, 300, and 450 kJ/m(2)) were subjected to 4-way analysis of variance with repeated measures (super ANOVA). Mean values were compared with Tukey-Kramer intervals calculated at the 0.05 significance level. RESULTS: The trained human eye can detect color changes (Delta E*) greater than 1.0. Adding all pigments to any of the kaolin groups did not protect silicone A-2186 from color degradation over time. Mixing red pigment in all groups at all times drastically increased DeltaE* values ranging from 0.1 to 1.3 up to 16.6 to 49.6. Yellow ochre had an effect only with 10% and 15% concentrations of kaolin powder calcined, increasing the value of Delta E* to greater than 1.0. Burnt sienna had an effect only with a 15% concentration of kaolin powder calcined, increasing the value of Delta E* at 300 and 450 kJ/m(2) to greater than 11.0. At the 5% concentration, kaolin powder calcined had the smallest color changes, followed by, in order, dry pigment titanium white, Artskin white, and Georgia kaolin. At the 10% concentration, Artskin white had the smallest color changes, followed by, in order, dry pigment titanium white, kaolin powder calcined, and Georgia kaolin. At the 15% concentration, Artskin white again had the smallest color changes, followed by, in order, dry pigment titanium white, Georgia kaolin, and the kaolin powder calcined. The smallest color changes in each kaolin group were at the 10% concentration for Artskin white, dry pigment titanium white, and kaolin powder calcined and at the 5% concentration for Georgia kaolin. CONCLUSIONS: Mixing dry earth cosmetic pigments with opacifiers did not protect silicone A-2186 from color degradation over time, especially in the case of red pigment. The group in which pigments were mixed with 10% Artskin white had the smallest color changes over time, followed by, in order, the groups in which pigments were mixed with 10% dry pigment titanium white, 10% kaolin powder calcined, and 5% Georgia kaolin. Red pigment had a significant effect on all opacifiers, especially Georgia kaolin and kaolin powder calcined. Yellow ochre and burnt sienna had an effect only on 15% kaolin powder calcined. Among all the pigment groups tested, yellow ochre remained the most color stable over time.     

Accelerated color change in a maxillofacial elastomer with and without pigmentation

STATEMENT OF PROBLEM: Maxillofacial prostheses require frequent replacement because the elastomer and its color additives undergo changes. PURPOSE: This study attempted to determine whether predictable color changes occur when 3 pigments are individually incorporated into a specific silicone elastomer. MATERIAL AND METHODS: The materials included an RTV elastomer; 1 natural inorganic pigment, burnt sienna; and 2 synthetic organic pigments, Hansa yellow and alizarin red. Eight test groups of 10 polymerized specimens were established. Groups 1 and 2, acting as the control, involved only the elastomer. Groups 3 and 4 were composed of elastomer and burnt sienna. Groups 5 and 6 consisted of elastomer and Hansa yellow. Groups 7 and 8 comprised elastomer and alizarin red. Odd-numbered groups were assigned to a test site in Miami, Fla., whereas the even numbered groups went to Phoenix, Ariz. Specimens weathered in Miami and Phoenix received sunlight exposures of 1305.7 MJ/m2 and 1310.2 MJ/m2, respectively, over time. Before and after weathering, the L* a* b* color parameter (DeltaE*) of each specimen was determined spectrophotometrically. RESULTS: Mean color changes that occurred in Arizona were larger than those produced in Florida. Specifically, these differences ranged from 0.4 (alizarin red groups) to 2.36 units for the 2 unpigmented control groups. Other differences showed significance for the unpigmented (P=.001), burnt sienna (P=.006), and Hansa yellow groups (P=.001). CONCLUSION: Outdoor weathering tests in which documented ASTM methods were used provided a valid baseline for future research on color changes in maxillofacial prostheses.     

In vitro evaluation of color change in maxillofacial elastomer through the use of an ultraviolet light absorber and a hindered amine light stabilizer

STATEMENT OF PROBLEM: External prostheses composed of silicone elastomers exhibit an unwanted color change over time. PURPOSE: This study evaluated color stability when an ultraviolet light absorber and hindered amine light stabilizer were mixed in the maxillofacial elastomer containing either organic or inorganic pigments. MATERIAL AND METHODS: The materials used were an RTV silicone elastomer, 1 natural inorganic dry-earth pigment (burnt sienna) and 2 synthesized organic pigments (hansa yellow and alizarin red), ultraviolet light absorber (UVA) and hindered amine light stabilizer (HALS). Specimens (n=160) were fabricated in a custom mold and randomly assigned and exposed to weathering sites in Miami and Phoenix for approximately 3 months. Eight test groups (2 of each 4 material types with or without additives) of 10 specimens each were assigned to each site. L*, a*, b* readings were obtained before and after weathering from a spectrocolorimeter. Nonpigmented elastomers served as the control. Three-factor ANOVA was conducted to examine interaction effects between weathering sites, specimen type, and the presence of additive (alpha=.05). Overall color change (Delta E) and change in color coordinates (Delta L*, Delta a*, Delta b*) of specimen groups with and without additive were analyzed with independent sample t tests. RESULTS: In specimen groups with the additives (UVA and HALS), color change decreased significantly (P<.05) in burnt sienna and hansa yellow in Phoenix and in the control and hansa yellow in Miami. Additives did not affect color change in the alizarin red group. CONCLUSION: UVA and HALS were shown to be effective in retarding color change in some circumstances.     

Interactions of pigments and opacifiers on color stability of MDX4-4210/type A maxillofacial elastomers subjected to artificial aging

STATEMENT OF PROBLEM: The color instability and degradation of maxillofacial elastomers limit the function and cosmetic quality of facial prostheses. PURPOSE: The purpose of this study was to measure the interactions of oil pigments plus dry earth opacifiers at 5%, 10%, and 15% by volume in stabilizing the color of MDX4-4210/type A silicone elastomers before and after artificial aging. MATERIAL AND METHODS: In the first part of the study, each of 5 opacifiers (Georgia kaolin powder neutral, kaolin powder calcined, Artskin white, dry pigment titanium (Ti) white, or Ti white artists' oil color) at 10% concentrations were combined with each of 5 oil pigment types (no pigment, cadmium-barium red deep, yellow ochre, burnt sienna, or a mixture of the 3 pigments), for a total of 25 experimental groups of elastomers. In the second part of the study, 50 experimental groups of elastomers were made by combining 1 of 5 opacifiers at 5% and 15% concentrations with 1 of 5 oil pigments as in Part 1. Five specimens of each elastomer were tested, for a total of 375 specimens. In each part of the study, all specimens were aged in an artificial aging chamber. CIE L*a*b* values were measured by a spectrophotometer. The color differences (DeltaE*) were subjected to repeated-measures analysis of variance. Mean values were compared by Tukey-Kramer intervals (alpha = .05). RESULTS: In Part 1, when the opacifiers were tested at 10% concentration, Ti white oil color had the most color change, and dry pigment Ti white had the least; all other opacifiers were not significantly different from each other. In Part 2, at 5%, Ti white oil color had the most color change; all other opacifiers were not significantly different from the others. At 15%, Ti white oil color again had the most color change, followed by Artskin white, kaolin powder calcined, and Georgia kaolin; Ti white dry earth pigment had the least color change. Overall, 5% Artskin white had less color change than the 15%, whereas 15% dry pigment Ti white had less color change than the 5% (P < .001). The 5% and 15% of other opacifiers were not significantly different. CONCLUSIONS: At all 3 concentrations, oil pigments mixed with opacifiers helped protect the MDX4-4210/type A silicone elastomer from color degradation over time. Dry pigment Ti white remained the most color stable over time, followed by the pigments mixed with kaolin powder calcined, Georgia kaolin, Artskin white, and Ti white artists' oil color.     

Ultraviolet radiation-induced color shifts occurring in oil-pigmented maxillofacial elastomers.

STATEMENT OF PROBLEM: Oil-based pigments are added to a maxillofacial prosthesis either as base colorants present within the elastomer or as surface tints that are painted on with an adhesive. Color stability of the pigments and pigmented prosthetic materials on exposure to ultraviolet radiation are unknown. PURPOSE: This study measured DeltaE* color changes caused by ultraviolet radiation for materials colored with 5 oil pigments, applied either as base colorants (intrinsic) or surface tints (extrinsic) to a silicone elastomer. MATERIAL AND METHODS: One of 5 oil pigments was added to polydimethyl siloxane disks to serve as a base colorant (0.2 weight percent present throughout a 2 mm thick disk) or as a concentrated surface tint (2.0 weight percent concentrated in upper 0.3 mm thickness). Pigmented disks, along with pigment-only and elastomer-only control disks, were exposed to ultraviolet radiation for 400, 600 and 1800 hours. DeltaE* color changes were measured at baseline and for each time interval. RESULTS: Control samples underwent minimum color changes after 1800 hours (DeltaE* 相似文献   

三种颌面赝复硅橡胶吸水率、溶解率的对比测定

目的:对比研究ZY-1、SY-1及A-2186三种赝复硅橡胶的吸水率和溶解率,评价ZY-1硅橡胶的对水的稳定性.方法:在相同条件下对三种硅橡胶材料进行吸水率和溶解率测定,并对结果进行统计学分析.结果:ZY-1的吸水率及溶解率与A-2186无显著性差异,而明显低于SY-1.结论:赝复硅橡胶材料ZY-1具有良好的水解稳定性.     

Effect of Extraoral Aging Conditions on Color Stability of Maxillofacial Silicone Elastomer

Purpose: Maxillofacial prostheses require enhancement or replacement due to deterioration in their color during service. The purpose of this study was to investigate color stability of pigmented and nonpigmented maxillofacial silicone elastomer exposed to different human and environmental aging conditions. Material and Methods: One hundred and twelve disk‐shaped silicone (TechSil S25, Technovent, Leeds, UK) specimens were prepared and equally divided into pigmented (using intrinsic rose‐pink skin shade, P409, Principality Medical, Newport, UK) and nonpigmented categories of seven groups (n = 16; 8 pigmented and 8 nonpigmented): dark storage (control) (group 1), sebum solution storage (group 2), acidic perspiration storage (group 3), light aging (group 4), natural outdoor weathering (group 5), silicone‐cleaning solution (group 6), and mixed conditioning of sebum storage and light aging (group 7). Conditioning periods (groups) were 6 months (groups 1, 2, 3, 5), 360 hours (groups 4, 7), and 30 hours (group 6). Color change (ΔE) was measured at the start and end of conditioning. In addition, for groups 1, 2, and 4, ΔE was measured at fixed intervals of 30 days, 15 days, and 30 hours, respectively. Data were analyzed with one‐way analysis of variance (ANOVA), Dunnett’s‐T3 post hoc, and independent t‐tests (p < 0.05). Linear regression was implemented to investigate ΔE with time for groups 1, 2, and 4. Results: Six of the seven treatment conditions induced perceivable color change (ΔE > 3). Within the nonpigmented category, specimens stored in the dark for 6 months (group 1) exhibited high ΔE (6.17), which was greater (p < 0.05) than that produced by silicone‐cleaning solution for 30 hours (group 6) (ΔE = 2.08). Within the pigmented category, light aging (group 4), outdoor (group 5), and mixed (group 7) conditionings induced greatest color changes (ΔE = 8.26, 8.30, 9.89, respectively) (p < 0.05); however, there was a strong positive linear function of log‐time after dark storage (group 1) and light aging (group 4). Conclusions: There is inherent color instability of nonpigmented silicone elastomer, which adds to the overall color change of silicone prostheses. Storing silicone elastomer in simulated sebum under light aging induced the greatest color changes. Overall, the color stability of TechSil S25 maxillofacial heat‐temperature‐vulcanizing (HTV) silicone elastomer was unacceptable (ΔE > 3.0, range from 3.48 to 9.89 for pigmented and 3.89 to 10.78 for nonpigmented) when subjected to six of the seven extraoral aging conditionings used in this study. Inherent color instability of nonpigmented facial silicone elastomers primarily contributes to the color degradation of extraoral facial prostheses. Sebaceous skin secretions along with daylight radiation cause the greatest perceivable color change to the silicone and pigment used in this study.     

Evaluation of some mechanical properties of a new silicone elastomer for maxillofacial prostheses after addition of intrinsic pigments

Objective

The approximate life span of a silicone maxillofacial prosthesis is as short as 1.5–2?years of clinical service, then a new prosthesis should be fabricated. The most common reason for re-making the prosthesis is silicone mechanical properties degradation. The aim of this study was to assess some mechanical properties of VST-30 silicone for maxillofacial prostheses after addition of intrinsic pigments.

硅橡胶中纳米二氧化钛对白色念珠菌生长影响的初探

目的 通过研究纳米二氧化钛对硅橡胶体外抗白色念珠菌性能的影响,探讨用纳米二氧化钛改善硅橡胶抗白色念珠菌性能的可靠性.方法 硅橡胶中加入质量分数分别为0.5%、1.0%、1.5%、2.0%的纳米二氧化钛抗菌剂,分别记为A、B、C、D组,对照组硅橡胶不加纳米二氧化钛,采用薄膜密着法在光照和无光照条件下测定各组硅橡胶对白色念珠菌的抗菌作用.结果 光照条件下,A、B、C、D组菌落数[分别为(439.0±21.9)CFU、(289.3±7.8)CFU、(173.0±7.6)CFU、(86.7±3.9)CFU]与对照组[(597.3±5.5)CFU]的差异均有统计学意义(P<0.05);非光照条件下,A、B、C、D组菌落数[分别为(543.7±22.8)CFU、(478.0±17.0)CFU、(422.7±21.8)CFU、(283.0±12.1)CFU]与对照组[(611.3±10.0)CFU]的差异均有统计学意义(P<0.05).D组抗菌性能最好,无光照条件下,抑菌率为53.7%;光照条件下,抑菌率可达85.9%.结论 添加了纳米二氧化钛抗菌剂的硅橡胶在光照和无光照条件下均能抑制白色念珠菌生长,随着纳米二氧化钛质量分数的增加,硅橡胶抑菌效果增强.纳米二氧化钛质量分数相同时,光照下硅橡胶的抑菌性比无光照强.     

Color stability of facial silicone prosthetic polymers after outdoor weathering.

STATEMENT OF PROBLEM: Color deterioration of silicone prosthetic elastomers affects the life expectancy of facial prostheses in a service environment. PURPOSE: This study investigated the color stability of 3 nonpigmented silicone elastomers (Silskin 2000, Elastosil M3500, Ideal) exposed to outdoor weathering for 1 year. MATERIAL AND METHODS: A tristimulus colorimeter was used to evaluate the color differences (DeltaE*) of the silicone elastomers every 2 months. Ten disk-shaped specimens for each material were tested. Data were analyzed with a repeated measures ANOVA and Student-Newman-Keuls test at a significance level of alpha = .05. RESULTS: All silicone elastomers showed visually detectable, mean color differences (DeltaE* > 2.0), that ranged from 2.13 to 3.98. Silskin 2000 showed greater color differences (P <.05) compared with Elastosil M3500 and Ideal, which showed similar behavior (P >.05). CONCLUSION: Outdoor exposure of silicone facial elastomers for 1 year resulted in visually detectable color differences. Duration of exposure and silicone elastomer were significant factors that affected color stability. Silskin 2000 was significantly less color stable than Elastosil M3500 and Ideal, which were not statistically significantly different from each other.     

New organosilicon maxillofacial prosthetic materials.

OBJECTIVES: The silicone elastomer A-2186 is a widely used maxillofacial prosthetic material. It is a pourable two-component silicone rubber cured by a platinum catalyst. Used as a prosthetic material, A-2186 has short working time and because of its hydrophobic nature, poor adhesion to non-silicone based adhesives. The purpose of this study is to evaluate the physical properties of new prosthetic materials based on methacryloxypropyl-terminated polydimethylsiloxane (MPDS-MF), and to compare the properties with those of A-2186. METHODS: Hardness, tensile strength, ultimate elongation, tear strength and adhesive bonding strength of MPDS-MF and A-2186 with and without additives were determined and compared. The bonding strengths of the extrinsic colorant carrier with the prosthetic materials were also determined. Statistical analyses were done using a two-way analysis of variance (ANOVA). For significant effects, post-hoc tests were done using the Bonferroni correction. RESULTS: The hardness of MPDS-MF is similar to A-2186. However, tensile strength, tear strength, ultimate elongation, and adhesive bonding strength of MPDS-MF are higher than those of A-2186. SIGNIFICANCE: MPDS-MF is cured by free radical thermal polymerization and crosslinking. The working time of MPDS-MF, unlike A-2186, is long. The presence of methacrylate groups in MPDS-MF enhances its adhesion to non-silicone based adhesive. Based on the present study, it appears that MPDS-MF is suitable for use in fabricating of clinical prostheses.     

Influence of pigments and opacifiers on color stability of silicone maxillofacial elastomer

ObjectivesTo determine the effects of opacifiers and silicone pigments on the color stability of silicone A-2000 maxillofacial prosthetic elastomers subjected to artificial aging.MethodsSeventy-five groups (n = 5) were made by various combinations (5%, 10%, and 15%) of four dry earth opacifiers (Georgia kaolin, Gk; calcined kaolin, Ck; Artskin white, Aw; titanium white dry pigment, Td); and 1 silicone pigment white (Sw) with one of 5 silicone pigments (no pigment (control), red (Pr), yellow (Py), burnt sienna (Po), and a mixture of Pr + Py + Po). A reflection spectrophotometer was used for color measurements. Color differences (ΔE*) between baseline and after an energy exposure of 450 kJ/m² in an artificial aging chamber were calculated. A ΔE* = 3.0 was used as 50:50% acceptability threshold in result interpretation, while ΔE* = 1.1 was used as 50:50% perceptibility threshold. Means were compared by Fisher's PLSD intervals at the 0.05 level of significance. Color differences after aging were subjected to three-way analysis of variance.ResultsYellow ochre mixed with all opacifiers at all intervals had increased ΔE* values significantly from 0.7–2.1 up to 3.8–10.3. When mixed groups were considered, at 5%, Gk exhibited the smallest color changes, followed by Td < Aw = Sw < Ck, respectively. At 10%, Aw < Td < Gk < Sw = Ck. At 15%, Td < Aw < Gk = Sw < Ck (< indicates p < 0.0001 and = indicates p > 0.05). The smallest color differences, observed for opacifier groups, were recorded for Gk at 5%, and Td and Aw at 10% and 15%. Overall, 15% Td exhibited the smallest, whereas 5% Ck exhibited the most pronounced color change after artificial aging. All ΔE* values were below the 50:50% acceptability threshold, indicating acceptable color stability. Color differences for 10% and 15% of Aw and Td were below 50:50% perceptibility thresholds, indicating excellent color stability.ConclusionSilicone pigments mixed with 10% and 15% Artskin white and titanium white dry pigment opacifiers protected silicone A-2000 from color degradation over time. Yellow silicone pigment significantly affected color stability of all opacifiers especially silicone pigment white and calcined kaolin.     

Color stability and colorant effect on maxillofacial elastomers. Part I: colorant effect on physical properties

STATEMENT OF PROBLEM: The average clinical life span of a maxillofacial prosthesis is approximately 6 months, at which point it needs to be refabricated, mainly because of degradation of the color and physical properties of the prosthesis. PURPOSE: This first part of a 3-part study evaluated the effect of coloring agents on the physical properties of maxillofacial elastomers. METHODS AND MATERIAL: Five dumbbell-shaped and 5 trouser-shaped specimens were fabricated for each of the combinations of the 3 elastomers (Silastic medical adhesive type A, Silastic 4-4210, and Silicone A-2186) and 6 colorants (dry earth pigments, rayon fiber flocking, artist's oil paints, kaolin, liquid cosmetics, and no-colorants), for a total of 180 specimens. Evaluations of hardness and tear strength were made with the trouser-shaped specimens. Evaluations of the ultimate tensile strength and the percentage elongation were made with the dumbbell-shaped specimens. A within elastomer analysis compared the 6 colorants using a 1-way analysis of variance for each of the 4 physical properties. When significant differences were observed, the Student-Newman-Keuls multiple range test was used to identify differences between groups at a significance level of.05. RESULTS: Physical properties of maxillofacial elastomers were changed by the incorporation of coloring agents. Dry earth pigments, kaolin, and rayon flocking acted as a solid filler without bonding to the Silicone, and artists' oils and liquid cosmetics acted as a liquid phase without bonding to the silicone matrix. CONCLUSION: No clearly superior colorant-elastomer combination was demonstrated in all the tests in this study.     

Parylene coating hinders Candida albicans adhesion to silicone elastomers and denture bases resin

Objective

To investigate whether parylene coatings over denture bases and silicone elastomers can effectively reduce Candida albicans adhesion and thus to decrease the incidence of denture stomatitis.

Design

Specimens of silicone elastomers A-2186 or lucitone 199 resin were prepared, and the measurements of contact angle, assay of XTT reduction and cell count of C. albicans adhesion were taken before and after parylene treatment. Furthermore, morphology of C. albicans adhesion for 48 h was observed by scanning electron microscope (SEM), and C. albicans adhesion for 4 h was illustrated by confocal scanning laser microscopy (CLSM) in combination with fluorescent dyes FUN-1 and Concanavalin A.

Result

There was a statistical difference between mean contact angles of silicone elastomer A-2186 before and after parylene coating (P < 0.05). The amount of C. albicans adhesion to the surface of silicone elastomer A-2186 and lucitone 199 resin after parylene treatment was significantly less than before parylene treatment by cells count and XTT reduction assay (P < 0.05). In SEM and CLSM analysis, C. albicans biofilm was more apt to generate on the surface of silicone elastomer A-2186 than other three groups, and more C. albicans aggregation formed on the surface of silicone elastomer A-2186 and lucitone 199 resin before parylene treatment than after parylene treatment.

Conclusion

Parylene coating reduced C. albicans adhesion and aggregation on the surface of silicone elastomer A-2186 and lucitone 199 resin, and improved the wettability of silicone elastomer A-2186.     

Porosity and Color of Maxillofacial Silicone Elastomer

Purpose: Prosthesis color production and stability as a result of pore entrapment during mixing has not been investigated for maxillofacial silicone prostheses. The purpose of this study was to investigate pore numbers and percentages of a maxillofacial silicone elastomer mixed by two different techniques, using X‐ray microfocus computerized tomography (Micro‐CT), and to investigate the effect of porosity on color reproducibility and stability after two different aging conditions. Materials and Methods: Sixty‐four disk‐shaped specimens were prepared (8‐mm diameter, 3‐mm thick) by mixing TechSil S25 silicone elastomer (Technovent, Leeds, UK) following two techniques: manual mixing (n = 32) and mechanical mixing under vacuum (n = 32). Half the specimens in each group were intrinsically pigmented, and the other half remained unpigmented. Pore numbers, volumes, and percentages were calculated using the Micro‐CT, and then specimens of each subgroup were stored in simulated sebum for 6 months (n = 8), and exposed to accelerated daylight aging for 360 hours (n = 8). Color change (ΔE) was measured at the start and end of conditioning. Pore numbers and percentages were analyzed using one‐way Analysis of Variance (ANOVA) and Dunnett’s‐T3 post‐hoc tests (p < 0.05). Independent t‐test was used to detect differences (p < 0.05) in ΔE between manually and mechanically mixed specimens, in both unpigmented and pigmented states and to detect differences (p < 0.05) in ΔE before and after conditioning within each mixing method. Results: Mechanical mixing under vacuum reduced the number and percentage of pores in comparison to manual mixing, within pigmented and unpigmented silicone specimens (p < 0.05). Perceptible ΔE between manual and mechanical mixing techniques were 5.93 and 5.18 for both unpigmented and pigmented specimens, respectively. Under sebum storage, manually mixed unpigmented specimens showed lower ΔE (p < 0.05) than those that were mechanically mixed; however, pigmented silicone specimens showed the same ΔE (p > 0.05). After light aging, mixing method had no effect on ΔE of unpigmented specimens (p > 0.05). Furthermore, mechanically mixed pigmented specimens showed lower ΔE (p < 0.05). Conclusions: Within silicone elastomers (whether pigmented or unpigmented), mechanical mixing under vacuum reduced pore numbers and percentages in comparison to manual mixing. For selected skin shade, pores affected the resultant color of prosthesis (color reproducibility). Additionally, silicone pores affected silicone color stability upon service. Clinical significance: In fabricating maxillofacial prostheses, mechanically mixing silicone under vacuum produces pore‐free prostheses, tending to enhance their color production and stability.     

The color accuracy of the Kubelka-Munk theory for various colorants in maxillofacial prosthetic material

The reflectance model developed by Kubelka and Munk was evaluated for agreement in color prediction of thick pigmented samples and for linearity of optical absorption and scattering coefficients with concentration of colorant in maxillofacial elastomer. The colorants tested were generic opacifiers, dry mineral earth pigments, and fibrous colorants. Significant linear relationships were commonly found between the optical coefficients and the concentration of the colorants. These relationships indicated occasional optical interaction between the colorants and the elastomer. Color differences between theoretical and observed colors of the thick samples averaged 2.96, 3.47, and 1.60 for the opacifiers, mineral earth pigments, and fibrous colorants, respectively, when measured using the CIELAB uniform-color space. The agreement between theoretical and observed colors was significantly closer for the fibrous colorants than for the dry mineral earth pigments of the same labeled color.     

Computerized Color Formulation for African-Canadian People Requiring Facial Prostheses: A Pilot Study

Purpose: The aim of this study was to investigate the effectiveness of spectrophotometry and a computerized color formulation system to predict pigment formulas for color mixing silicone elastomer to match the skin color of African-Canadian people.
Materials and Methods: In a prospective study, reflectance spectrophotometery was used to measure the skin color of 19 African-Canadian subjects. The spectral data for each subject was used in a computerized color formulation system to predict colorants required to mix silicone elastomer to match each subject's skin color. Delta-E values were recorded for each silicone sample in comparison to the subject's skin measurement. An analysis of variance was used to determine significance among variables, and a Tukey HSD post hoc test was used to assess paired comparisons.
Results: Delta-E decreased with iterative mixes of colored silicone for each subject, and pigment loading increased with iterative mixes. Delta-E values for the third iterative mix (fourth and final sample) ranged between 1.49 and 8.82.
Conclusion: Spectrophotometry and computerized color formulation provide a foundation in the color matching procedure for facial prostheses that offers objectivity to an otherwise subjective task. Through further study of spectrophotometry and computerized color formulation, and with the development of pigment databases appropriate for the African-Canadian population, it may be possible to establish a precise and repeatable color matching system that predicts required colorants and controls metamerism.     

加载载荷对钛锆铌锡合金摩擦磨损性能的影响

目的:探讨载荷变化对钛锆铌锡合金与滑石瓷对磨时摩擦磨损性能的影响.方法:使用MMV-1立式万能摩擦磨损试验机,以滑石瓷为对磨物,载荷设置为20、50、100 N,在37℃人工唾液润滑的试验工况下,对口腔修复用钛锆铌锡合金进行二体摩擦磨损试验.采用扫描电镜观察表面磨损形貌,电子天平得出磨损量.结果:钛锆铌锡合金与对磨物滑石瓷的磨损量随载荷的增加而增大.载荷20N,钛锆铌锡合金的磨损机制主要为磨粒磨损; 50N时,磨损机制是粘着磨损伴发磨粒磨损;100N时,钛锆铌锡合金磨损机制以粘着磨损为主.结论:载荷增加可增大钛锆铌锡合金的磨损量,导致磨损机制改变,在高载荷条件下可发生严重粘着磨损,缩短修复体的使用寿命.     

ZA-1偶联剂对赝复硅橡胶与丙烯酸树脂材料粘接强度的影响

目的：研究ZA-1偶联剂在两种加成型硅橡胶及两种丙烯酸树脂之间交叉使用时粘接强度的影响。方法：选择ZY—1硅橡胶与A-2186硅橡胶分别与临床中常用的热凝丙烯酸树脂和自凝型树脂制成硅橡胶一偶联剂一丙烯酸树脂粘接试件,分别测试试件粘接强度。选择ZY-1组进行热氧老化试验。结果：四组硅橡胶偶联剂粘接系统中,ZY-1硅橡胶与丙烯酸树脂的粘接强度显著高于A-2186组（P〈0．05）。热凝和自凝丙烯酸树脂对粘接系统的粘接强度无显著影响。所有实验组的破坏方式均为内聚破坏。热氧老化处理后ZY-1丙烯酸树脂粘接试件的粘接强度与未老化组相比有显著性提高。结论：丙烯酸树脂材料的种类对粘接强度的影响不大。两种不同的加成型硅橡胶与ZA-1偶联剂交叉使用时粘接强度略有下降,但粘接效果不影响临床使用。热氧加速老化实验使ZY-1加成型硅橡胶与丙烯酸树脂的粘接强度有所提高。     

Color stability of thermochromic pigment in maxillofacial silicone

PURPOSE

Maxillofacial silicone elastomer is usually colored intrinsically with color pigments to match skin colors. The purpose of this study was to investigate the color stability of a maxillofacial silicone elastomer, colored with a thermochromic, color changing pigment.

MATERIALS AND METHODS

Disc-shaped maxillofacial silicone specimens were prepared and divided into 3 groups: a conventionally colored control group, one group additionally colored with 0.2 wt% thermochromic pigment , and one group with 0.6 wt% thermochromic pigment. Half of the surface of each specimen was covered with an aluminium foil. All of the specimens were exposed to UV radiation in 6 hour cycles over 46 days. In between the UV exposures, half of the specimens were stored in darkness, at room temperature, and the other half was stored in an incubator, at a humidity of 97% and a temperature of +37℃. Color measurements were made with a spectrophotometer and registered according to the CIELAB L^*a^*b^* color model system. The changes in L^*, a^* and b^* values during artificial aging were statistically analyzed by using paired samples t-test and repeated measures ANOVA. P-values <.05 were considered as statistically significant.

RESULTS

The UV exposure resulted in visually noticeable and statistically significant color changes in the L^*, a^* and b^* values in both of the test groups containing thermochromic pigment. Storage in the incubator lead to statistically significant color changes in the a^* and b^* values of the specimens containing thermochromic pigment, compared to those stored at room temperature.

CONCLUSION

The specimens containing thermochromic pigment were very sensitive to UV radiation, and the thermochromic pigment is not suitable, as such, to be used in maxillofacial prostheses.