Color stability of a pigmented elastomer for maxillofacial appliances

An investigation of the effects of topical sunscreen protection products under natural weather conditions on intrinsic color stability in maxillofacial silicones

Aim

The relatively short lifespan of maxillofacial prostheses (ranging from 3-24 months) is mostly a result of colour instability of silicone elastomers caused by ultraviolet (UV) radiation, requiring frequent remakes. An improvement in colour preservation could result in fewer remakes, thus saving time and money for both clinician and patient. In the quest for a suitable colour protection method, sunscreen protection products were considered; the most recent study on this subject was carried out in 1994, albeit using a low protection factor. The aim of this research was to determine if there is value in using topical sun protection products on extraoral silicone prostheses to prevent colour degradation.

Settings and Design

This was an in vitro quantitative study.

Materials and Methods

Three commercially available sunscreen products were studied, Riemann P20, Boots Soltan, and Garnier Ambre Solaire all with a sun protection factor of 50. A total of 144 silicone elastomer samples were produced using a Caucasian (light) shade 1.2 (n = 72) and dark skin shade 3.2 (n = 72) from the Technovent Ltd. Reality Shade range. Each shade group (n = 72) was divided into three groups to be subjected to outdoor weathering (n = 24), indoor (n = 24), and dark storage (n = 24). Within each environmental group, samples were divided into groups of six samples (n = 6) to receive the three sunscreens plus a control group with no sunscreen. The CIEL* a* b* formula was used to obtain the color measurements.

Statistical Analysis Used

One way ANOVA test and Tukey's HSD test for multiple comparisons was used to analyse the data.

Results

The ΔE values had changed for all samples throughout the aging process.

Conclusion

Soltan showed promising results in protecting the dark-shaded samples in the outdoor environment only.

Effect of Thixotropic Agent on the Color Stability of Platinum-Based Silicone Maxillofacial Elastomers after Artificial Aging

Maxillofacial prostheses are essential for restoring natural appearance and function in individuals with defects in the head and neck regions. Thixotropic agents, as liquid additives, are known to increase the viscosity of silicone elastomers. However, color deterioration remains a challenge in facial prostheses, leading to the need for refabrication. Despite this, there is limited research on the effect of thixotropic agents on the color stability of silicone maxillofacial elastomers. This study aims to investigate the impact of different thixotropic agent amounts on the color degradation of various maxillofacial silicone elastomers. Three elastomers (A-2000, A-2006, and A-2186) were combined with five pigments (no pigment as control, red, yellow, blue, and a mixture of red, yellow, and blue), and mixed with six thixotropic agent quantities (0, 1, 2, 3, 4, and 5 drops). A total of 450 specimens were fabricated (n = 5) and aged in an artificial aging chamber. L*, a*, b* readings were obtained before and after aging using a digital spectrophotometer. Color difference (ΔE*) means and standard deviations for 150 kj/m2, 300 kj/m2, and 450 kj/m2 were calculated. Statistical analyses, including four-way ANOVA and Fisher's PLSD test, were conducted to determine any significant differences (p < 0.05) among the groups. A comprehensive analysis revealed significant four-way interactions among the groups. In the mixed-pigmentation group, adding 4 drops of thixotropic agent resulted in ΔE* above 3 only in A-2186 silicone at 300 and 450 kj/m2 energy levels. However, the color stability of mixed-pigmented A-2000 and A-2006 remained within the acceptable thresholds of 3 ΔE* at all irradiance levels in this study. At each energy level, A-2006 exhibited the highest color stability with an increasing thixotropic agent quantity among all the silicones. Conversely, A-2186 was more affected by the increased number of thixotropic agent drops in each pigmentation group, including the control group at 450 kj/m2. The quantity of thixotropic agent plays a crucial role in determining the color stability of different silicone elastomers pigmented with various intrinsic pigments. The thixotropic agent amount has a more significant impact on color stability than the type of pigment used in the silicone elastomers. A key overarching insight from this investigation is the identification of a safety threshold for the thixotropic agent quantity of 3 drops for each silicone type, pigmentation, and energy level. These findings highlight the importance of considering the proper combination of thixotropic agents, pigments, and silicone materials to achieve optimal color stability in maxillofacial prosthetic applications.

The color stability of maxillofacial silicones: A systematic review and meta analysis

Aim

This systematic review aims to identify and interpret results of studies that evaluated the changes in the color stability of maxillofacial prosthetic materials due to chemical instability of silicones and pigments and the effect of exposure to environmental conditions and aging factors on the same.

Settings and Design

This systematic review was conducted in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines (PRISMA).

Materials and Methods

Relevant articles written in English only, before November 15, 2019, were identified using an electronic search in the PubMed/Medline conducted to identify pertinent articles. The relevancy of the articles was verified by screening the title, abstract, and full text, if they met the inclusion criteria. A total of 42 articles satisfied the criteria, from which data were extracted for qualitative synthesis. This review protocol was registered in the International Prospective Register of Systematic Reviews (PROSPERO registration number CRD42019124562).

Statistical Analysis Used

Since considerable data heterogenicity was present in all studies except the ones on incorporation of TiO2 for which meta-analysis using random effects model was performed.

Results

The database search resulted in 234 studies, of which 202 articles were excluded due to lack of relevance, duplication, and unavailability of data. The remaining 32 fulltext articles were assessed for eligibility, out of which 2 articles were excluded. Twelve articles were yielded by manual search. A total of 42 studies were included in the present systematic review. Due to heterogeneous data, meta-analysis could be only carried out with the effect of TiO2 nano particle on color stability.

Conclusions

Although there has been extensive amount of research in this field, an ideal maxillofacial silicone exhibiting good color stability in various human and environmental aging conditions is yet to be identified. Human and environmental aging conditions have an adverse effect on the color stability and addition of TiO2 nano particle seems to improve the same.

Color stability of nonpigmented and pigmented maxillofacial silicone elastomer exposed to 3 different environments

STATEMENT OF PROBLEM

The color degradation of maxillofacial prostheses in clinical service requires their frequent renewal. How different materials compare is unclear.

PURPOSE

The purpose of this in vitro study was to investigate the color stability of a nonpigmented and pigmented maxillofacial silicone when stored in darkness and exposed to accelerated aging in a weathering chamber and natural outdoor weathering.

MATERIAL AND METHODS

M511 elastomer was colored with Spectromatch Pro colorants, stored in darkness, and exposed to accelerated aging and natural outdoor weathering for 1500 hours. Test groups included nonpigmented specimens (n=18), individually pigmented specimens (n=90), and Caucasian skin tone-colored specimens (n=18). The CIELab values of the test specimens were measured using the CM-2600d spectrophotometer (Konica Minolta Sensing) at base line (0 hours) and then every 100 hours up to 1500 hours of aging. Color changes (ΔE) were calculated based on the recorded CIELab values. All data were analyzed by using linear mixed models and the Šídák multiple comparison of means test (α=.05).

RESULTS

A significant effect of time was found on the ΔE of all test specimens in all environments (P=.001). All pigmented M511 specimens demonstrated good color stability with maximum ΔE below the acceptability threshold of 2 ΔE when stored in darkness and exposed to outdoor weathering. However, nonpigmented specimens crossed this acceptability threshold when exposed to outdoor weathering with maximum ΔE values of 3.65. The greatest color changes were observed for all specimens when exposed to accelerated aging and most exceeded the acceptability threshold. Nonpigmented (ΔE, 4.86) and Indian yellow (ΔE, 5.20) demonstrated the highest color changes after 1500 hours.

CONCLUSIONS

All environments resulted in visible color changes of nonpigmented and pigmented M511 elastomer. The lowest ΔE values were observed for specimens stored in darkness and the greatest for specimens exposed to accelerated aging. The organic pigment Logwood maroon demonstrated the best color stability with maximum ΔE values below the perceptibility threshold (PT) of 1 ΔE.

Refabrication of an implant-retained auricular prosthesis using clip attachment pickup technique

Increased patient acceptance and widespread use have led to a greater demand for refabrication of existing maxillofacial prostheses exhibiting wear and tear. Refabricating an osseointegrated implant-retained silicone auricular prosthesis on the existing Hader bar is a challenging task if it is performed without removing it. Therefore, an attachment level impression method is utilized for the refabrication of a new prosthesis on an existing Hader bar framework without removing it from the patient's defect. This case report discusses a modification of the Mahidol University technique. This modification provides a simple, speedy, and convenient method through which the relation between the metal framework and attachments could be obtained precisely. This precision allowed for easy fabrication of the acrylic housing, which in turn results in better adaptation of the auricular prosthesis to the patient's face. Therefore, this technique offers advantages to both the prosthetist in fabrication and the patient in facilitating him continue to wear his existing implant-retained prosthesis during refabrication process.

A spectrophotometric analysis of extraoral aging conditions on the color stability of maxillofacial silicone

Context:

Surveys have reported color fading as the most frequent reasons patients given for disliking their prostheses.

Aim:

The aim of the study is to compare the color variation between two maxillofacial silicone elastomers after subjecting them to extraoral aging conditions.

Subjects and Methods:

A total of 80 samples were made from M511 Maxillofacial Rubber (Part A: Part B = 10:1) and Z004 Platinum Silicone Rubber (Part A: Part B = 1:1) and divided into two main Groups A and B (40 each). These main groups were then subdivided into five subgroups (A₁B₁, A₂B₂, A₃B₃, A₄B₄, and A₅B₅) (n = 8); outdoor weathering, acidic perspiration, sebum (for 6 months), and neutral soap and disinfectant (for 30 h), respectively. Baseline L*a*b* values were recorded. The samples were subjected to the extraoral aging conditions, and the L* a*b* values were recorded after the aging period using a spectrophotometer.

Statistical Analysis:

The intergroup comparison was done by Kruskal–Wallis test, whereas the intragroup comparison was done by Mann–Whitney test.

Results

All groups exhibited visually detectable, mean color differences that ranged from 3.06–5.21, except for A₄B₄. There was no statistical significance between the two materials when subjected to extraoral aging conditions.

Conclusions:

Visually perceptible and clinically unacceptable color changes occur when exposed to various extraoral aging conditions except for neutral soap solution immersion, for which values of Δ E* were clinically acceptable (ΔE < 3). It can be said for all practical purposes, clinically, the choice between M511 Maxillofacial Rubber (Part A: Part B = 10:1) and Z004 Platinum Silicone Rubber (Part A: Part B = 1:1) would yield more or less the same results, with unacceptable norms in terms of color stability under extraoral aging conditions.

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.

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

OBJECTIVES

To determine the effects of opacifiers and silicone pigments on the color stability of silicone A-2000 maxillofacial prosthetic elastomers subjected to artificial aging.

METHODS

Seventy-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 (DeltaE*) between baseline and after an energy exposure of 450kJ/m(2) in an artificial aging chamber were calculated. A DeltaE*=3.0 was used as 50:50% acceptability threshold in result interpretation, while DeltaE*=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.

RESULTS

Yellow ochre mixed with all opacifiers at all intervals had increased DeltaE* 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 DeltaE* 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.

CONCLUSION

Silicone 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.

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.

Facial prosthetic rehabilitation: preprosthetic surgical techniques and biomaterials

PURPOSE OF REVIEW

Attention to detail ensuring a successful facial prosthetic rehabilitation must be considered a priority at the time of presurgery, surgery, and at every stage in fabricating the prosthesis. Teamwork between the surgeon and maxillofacial prosthodontist will ensure an optimal surgical preparation and definitive prosthesis.

RECENT FINDINGS

Evidence of interaction between team members can most certainly be encouraging to the patient. During the prosthetic phase of treatment, focusing on tissue assessment, impression making, sculpting, mold fabrication, familiarity with materials, appreciation of color, delivery of instructions, and patient education will ensure a satisfactory outcome. With the desire, determination, and encouragement from the restorative team to make the most of this artificial replacement, a patient can have a higher quality of life and a more normalized lifestyle.

SUMMARY

This review presents current concepts regarding facial prosthetic rehabilitation of patients with head and neck cancer and facial prosthetic biomaterials.

Color Stability of Dry Earth Pigmented Maxillofacial Silicone A-2186 Subjected to Microwave Energy Exposure

PURPOSE

The purpose of this study was to measure spectrophotometrically the color stability of pigmented A-2186 silicone maxillofacial elastomer with 10% by volume of titanium white dry earth opacifier before and after exposure to microwave energy over a simulated 1.5-year period of microwave sterilization.

MATERIALS AND METHODS

A-2186 silicone elastomer opacified with titanium white dry earth pigment, pigmented with 5 cosmetic dry earth pigment colors [no pigment (control) group (Pc), red (Pr), yellow ochre (Py), burnt sienna (Po), and a mixture of Pr + Py + Po color group (P3)], was used in this study. Each of the 5 experimental groups consisted of 5 specimens. All specimens were placed in a 250 ml glass beaker filled with 150 ml of water (replenished for each microwave exposure). An exposure of 6 minutes was used 18 times (simulating 1.5 years of microwave sterilization with one 6 minute exposure monthly). Reflectance values were measured by spectrophotometer. Three- and two-way analyses of variance with repeated measures were performed for the color difference (DeltaE*) with the factors of group/color/months, and group/months, respectively. Means were compared by Tukey Honest Significant Difference (HSD) multiple range test calculated at the 0.05 level of significance using SPSS.

RESULTS

The trained human eye can detect color changes (DeltaE*) greater than 1.0. Most DeltaE* values of the red pigment group at all intervals and the mixed pigment group at 15- and 18- month intervals increased significantly greater than 1.0 (p < 0.001) compared with the control group. Yellow and burnt sienna groups remained the most color stable over time with DeltaE* values below 0.35.

CONCLUSIONS

Lack of color stability of red dry earth pigmented A-2186 silicone maxillofacial elastomers was clinically significant after 12-month exposure to microwave energy as compared with yellow, burnt sienna, and opacified A-2186 dry earth pigments.

Colourfast pigments in silicone hand and maxillofacial prostheses

This study addresses the clinical problem of long-term discolouration of silicone hand and maxillofacial prostheses. Seven (7) pigment hues, considered essential for achieving a suitable tissue colour-matched prosthesis, were compared for their colourfast property, across three selected proprietary formulations. In all, a series of 21 pigments, were tested for colourfastness. The pigments, presenting as suspensions (PS), pastes (PP) and dry pigments (PD), were exposed, over nine months, to ultraviolet light, elevated temperatures and varying concentrations of salinity. Colour change of the pigments was measured and expressed as Commission International de l'Eclairage (CIE) (L*, a*, b*) units. Pigment discoloration was significantly attributed to ultraviolet light. Pigmented and clear silicone samples showed a "yellowing" (+delta b*) effect. Lighter pigments became darker (-delta L*) in shade. Pigment samples at the elevated temperature of 50 degrees C showed significant but small colour change (delta E, 0.77 to 3.63). Only the master blue pigment (PS-4) recorded a higher delta E, 6.26 at 50 degrees C. At a moderate temperature of 35 degrees C, both pigmented and clear silicone test samples remained relatively colourfast. Comparison was made to control samples, stored in darkness, at 26 degrees C. The pigments were generally colourfast (deltaE<6 units) to saline solutions of 0.15 M and 5.0 M concentrations. Only the monastral red (PD-3) pigment recorded a delta E of 9.33, in 0.15 M normal saline, simulating the vulnerability of this pigment to the salinity of human sweat. Pigment hues were systematically ranked according to colourfastness. Pigment suspensions were more colourfast than pigment pastes.

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* </= 2.0), whereas samples containing oil pigments as base colorants demonstrated a wide range of susceptibility to ultraviolet radiation, with the greatest changes occurring for pigments cadmium red, cadmium yellow, and yellow ochre (7.1 </= DeltaE* </= 9.4). Elastomers coated with the same oil pigments as concentrated surface tints demonstrated significantly lower color shifting after 1800 hours of radiation exposure (maximum DeltaE* = 4.2, P </= .05).

CONCLUSION

Customizing a prosthesis with an oil-pigmented surface tint may reduce the incidence of color change, provided a sufficient amount of pigment is present.

Color stability and colorant effect on maxillofacial elastomers. Part III: weathering effect on color

STATEMENT OF PROBLEM

Maxillofacial prostheses are serviceable for approximately 6 months, after which they need to be refabricated because of the deterioration of color and physical properties.

PURPOSE

This third article in a 3-part series evaluated the color stability of commonly used colorant-elastomer combinations as a result of exposure to weathering.

METHODS AND MATERIAL

Fifteen specimens were fabricated for each 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 colorant) for a total of 270 specimens (18 groups of 15 specimens). The 15 specimens of each elastomer-colorant combination were separated into 3 test condition groups (control, time passage, and natural weathering) of 5 specimens per test condition group. Control specimens were evaluated within 1 month of fabrication. The time passage group was sealed in glass containers and kept in the dark for 6 months before testing. The natural weathering groups were placed on the roof of the dental school for 6 months and exposed to sunlight and weathering. Color and optical density data for each elastomer-colorant combination were subjected to a 1-way analysis of variance to examine effects among test conditions (control, time passage, and weathering). When significant differences were observed, the Student-Newman-Keuls multiple range test was performed to identify differences in elastomer-colorant combinations among each test condition at a significance level of .05.

RESULTS

Changes in color, as a result of weathering, were noted in many of the colorant-elastomer combinations. Also, color change occurred not only to the colored, but also to uncolored materials over time without exposure to weathering.

CONCLUSION

Clinically, the addition of colorants could have a stabilizing effect on the elastomer color when it is exposed to weathering.

Using a colorimeter to develop an intrinsic silicone shade guide for facial prostheses

PURPOSE

To determine if using CIE L*a*b* color measurements of white facial skin could be correlated to those of silicone shade samples that visually matched the skin. Secondly, to see if a correlation in color measurements could be achieved between the silicone shade samples and duplicated silicone samples made using a shade-guide color formula.

MATERIALS AND METHODS

A color booth was designed according to ASTM specifications, and painted using a Munsell Value 8 gray. A Minolta colorimeter was used to make facial skin measurements on 15 white adults. The skin color was duplicated using custom-shaded silicone samples. A 7-step wedge silicone shade guide was then fabricated, representing the commonly encountered thicknesses when fabricating facial prostheses. The silicone samples were then measured with the Minolta colorimeter. The readings were compared with the previous L*a*b* readings from the corresponding patient's skin measurements, and the relative color difference was then calculated. Silicone samples were fabricated and analyzed for three of the patients to determine if duplication of the visually matched silicone specimen was possible using the silicone color formula, and if the duplicates were visually and colorimetrically equivalent to each other. The color difference Delta E and chromaticity was calculated, and the data were analyzed using a coefficient-of-variation formula expressed by percent. A Pearson Product Moment Correlation Coefficient was performed to determine if a correlation existed between the skin and the silicone samples at the p < or = .05 level.

RESULTS

The highest correlation was found in the b* dimension for silicone thicknesses of 1 to 4 mm. For silicone thicknesses of 6 to 10 mm, the highest correlation was found in the L* dimension. All three dimensions had positive correlations (R2 > 0), but only the 1-mm and 4-mm b* readings were very strong. Patient and silicone L*a*b* measurement results showed very little change in the a* axis, while the L* and b* measurements showed more change in their numbers, with changes in depth for all patient silicone samples. Delta E numbers indicated the lowest Delta E at the 1-mm depth and the highest Delta E at the 10-mm depth. All duplicated samples matched their original silicone samples to a degree that visual evaluation could not distinguish any color differences. Using volumetric measurements, a shade guide was developed for all 15 patients.

CONCLUSIONS

There was good correlation between the patient's colorimeter measurements and the silicone samples, with the b* color dimension the most reproducible, followed by the L* and the a*. Silicone samples at 6, 8, and 10 mm matched the patient the best, and this study showed that silicone samples can be duplicated successfully if a good patient-silicone match is obtained. Rayon flocking fibers and liquid makeup are effective at matching facial prostheses and can be used to develop a simple shade guide for patient application.

Pigments and their application in maxillofacial elastomers: a literature review

PURPOSE

This literature review provides information about pigments used for facial and somatoprostheses.

MATERIAL

This information includes common pigment and index names and numbers, lightfastness categories, chemical type and class, and the chemical formulas of the common pigments used in maxillofacial prosthetics.

CONCLUSION

It can be deduced from this review that the pigments used with silicone elastomers do exhibit a color change, and that a color change is to be expected.

Color stability of facial prostheses

The limited service of facial prostheses is the result of degradation of the elastomer and color instability. Deterioration may be caused by many factors, which include environmental exposure and changes in humidity. This investigation assessed the efficacy of an additive, intrinsic, broad-spectrum ultraviolet light absorber on the color stability of a pigmented facial elastomer. Samples were weathered artificially and outdoors at exposure levels of radiant energy of 150 to 450 kJ/m2. The samples changed color slightly but perceptibly. Artificial aging caused a greater change than outdoor aging. The ultraviolet light absorber UV-5411 did not protect the samples from color changes.

Color changes in dry-pigmented maxillofacial elastomer resulting from ultraviolet light exposure

Five dry pigments and one maxillofacial elastomer were evaluated for color changes (delta E) resulting from prolonged exposure to two types of ultraviolet light. The elastomer, pigments, and pigmented elastomers were subjected to each ultraviolet light source for 400, 600, and 1800 hours, and delta E color shifts were determined. The unpigmented elastomer underwent minimally perceptible color change after 600 hours of exposure to both types of ultraviolet light. Two pigments underwent substantial color change after 400 hours, whereas the remaining three pigments remained color stable after 1800 hours. It was concluded that for the materials tested, early color changes in a prosthesis may be the result of degradation of certain ultraviolet light-susceptible pigments, whereas longer term color shifts may be caused by color changes within the elastomer.

The use of a photoprotective agent to increase the color stability of a tinted extraoral prosthetic silicone

PURPOSE

This study investigated the use of ultraviolet-absorbing or photoprotective agents as a method of decreasing the color changes caused by ultraviolet radiation on an intrinsically tinted facial prosthetic material.

MATERIALS AND METHODS

Silastic MDX 4-4210 (Dow Corning Corp, Midland, MI) was the facial prosthetic material studied. It was intrinsically tinted with talc and nylon flock to approximate the color of skin. Three brands of commercially available sunscreens with sun protective factor (SPF) of 15 were placed on the surface of the cured silicone samples. The samples were rotated in an ultraviolet radiation chamber for 300 hours. A control group was placed in the dark for 300 hours. The second phase of the experiment had para-aminobenzoic acid (PABA) added to the tinted silicone. All samples were measured with a spectrophotometer at the beginning and at the end of 300 hours, and a delta E was obtained.

RESULTS

None of the sunscreens provided any ultraviolet radiation protection to the silicone. The addition of PABA caused a significant color degradation of the silicone.

CONCLUSIONS

No photoprotective agent tested provided any significant level of ultraviolet radiation protection for silastic MDX 4-4210.

Effects of environmental factors on maxillofacial elastomers: Part I--Literature review

Part I of a four-part report presents a comprehensive review of the literature pertaining to physical property testing of materials for facial and somatoprostheses. The report was conducted in preparation for testing four current maxillofacial elastomers: MDX 4-4210, Silastic 4-4515, Medical Adhesive type A, and Epithane-3, and two recently introduced materials: Silicone A-2186 and Silicone A-102.

Stability of ceramic pigments for maxillofacial applications

In this study samples made from pigmented porcelain and Silastic 44210 were evaluated for colour stability after accelerated ageing in order to determine the potential of coloured ceramic powders as maxillofacial pigments. These pigments demonstrated good clear colour stability compared with the same pigments which were not incorporated into a porcelain matrix.

Effect of processing temperature on the properties of a polyvinyl chloride maxillofacial elastomer

Mechanical properties and color of a plasticized polyvinyl chloride (PVC) maxillofacial elastomer were evaluated at processing temperatures from 140 to 190 degrees C. The properties were dependent on processing temperature. Specimens prepared at 170 degrees C had optimum mechanical properties with minimal discoloration.

Stain removal from a pigmented silicone maxillofacial elastomer

The removal of environmental stains from a pigmented maxillofacial elastomer was carried out by solvent extraction under network swelling. Silastic 44210 was pigmented with 11 maxillofacial pigments prior to staining. Samples were stained with lipstick, methylene blue, and disclosing solution. These stains were then removed by solvent extraction with 1,1,1-trichloroethane. Color parameter measurements both before and after staining and after solvent extraction demonstrated the effectiveness of removing these stains by solvent extraction while causing little or no change in the color of the pigmented samples.

Stain removal from a silicone maxillofacial elastomer

In this study, environmental stains were removed from maxillofacial elastomers by solvent extraction. Silastic 44210, an RTV silicone with proven color and physical property stability, was stained with lipstick, disclosing solution, and methylene blue. These stains were then removed by solvent extraction with each of four chemically dissimilar solvents, namely: toluene, benzene, 1,1,1-trichloroethane, and n-hexane. An additional series of samples was prepared with 11 maxillofacial pigments, not for staining, but for evaluation of pigment stability. Results obtained from spectrophotometric measurements before and after solvent extraction demonstrated the effectiveness of solvent extraction in removing stains, while there was little or no change in the color of the pigments or the base elastomer.

Physical properties of a pigmented silicone maxillofacial material as a function of accelerated aging

The effects of accelerated aging on a pigmented elastomer were evaluated by using a weathering chamber. Silastic 44210, a maxillofacial material with proven color and physical property stability, was chosen for pigmentation with 11 maxillofacial pigments. The values of ultimate tensile strength, maximum percent elongation, shear strength, Shore A hardness, and permanent deformation were determined for the pigmented elastomer before and after accelerated aging for 900 h. Results obtained indicate that the incorporation of 0.2% by weight of pigments can alter the physical and mechanical properties of the base elastomer. Accelerated aging had no effect on the physical properties of the pigment/elastomer combinations.