|Year : 2017 | Volume
| Issue : 2 | Page : 110-115
Effect of denture cleansers and accelerated aging on the color stability of maxillofacial silicone: An in vitro study
Department of Prosthodontics, V S Dental College and Hospital, Bengaluru, Karnataka, India
|Date of Web Publication||28-Dec-2017|
Department of Prosthodontics, V S Dental College and Hospital, Bengaluru, Karnataka
Source of Support: None, Conflict of Interest: None
Aim: Evaluate the effect of denture cleansers and accelerated aging on the color stability of a commercially available maxillofacial silicone.
Materials and Methods: A commercially available maxillofacial silicone cosmesil M511 was mixed according to manufacturer's instruction with the incorporation of three pigments, namely, Burnt sienna, Hansa Yellow, and Alizarin red and packed into the stone molds prepared using metal dies according to ASTM standards. After processing, initial color measurement was carried out 72 h following processing using a spectrophotometer. The samples were later subjected to disinfection and accelerated aging for 504 h and 1008 h following which color measurement was carried out. The results were analyzed using one-way ANOVA and Tukey's multiple comparison test (P < 0.001).
Results: There was a statistically significant difference in the color stability of the silicone samples pigmented with Hansa Yellow than with Burnt Sienna and Alizarin Red after disinfection and 504 h of accelerated aging. Silicone samples disinfected with Fittydent denture cleanser showed better color stability than samples disinfected with neutral soap. There was a statistically significant difference in the color stability of the samples after 1008 h of accelerated aging irrespective of pigmentation and disinfection method.
Conclusions: Silicone samples pigmented with Hansa Yellow had greater color stability than the samples pigmented with other two pigments after disinfection and 504 h of accelerated aging. After 1008 h of aging, all samples showed poor color stability irrespective of pigmentation and disinfection method.
Keywords: Alizarin red; burnt sienna; cosmesil M511; Hansa Yellow; spectrophotometer
|How to cite this article:|
Manjula N. Effect of denture cleansers and accelerated aging on the color stability of maxillofacial silicone: An in vitro study. Indian J Multidiscip Dent 2017;7:110-5
|How to cite this URL:|
Manjula N. Effect of denture cleansers and accelerated aging on the color stability of maxillofacial silicone: An in vitro study. Indian J Multidiscip Dent [serial online] 2017 [cited 2019 Jul 21];7:110-5. Available from: http://www.ijmdent.com/text.asp?2017/7/2/110/221766
| Introduction|| |
A large number of people acquire facial defects, unfortunately, as a result of ablative surgery, trauma, and congenital deformity., Although modern plastic surgical technique, in particular microsurgery, can help restore some lost tissues, patient's age and general medical condition may preclude major reconstructive surgery. It therefore follows that these patients should be offered prosthetic rehabilitation as an alternative. A facial prosthesis restores the normal function and anatomy, protects the tissue of the defects, and provides great benefits to the patients allowing improvement in self-esteem and help the patient lead as normal a life as possible., The most important objective is fabrication of the prosthesis with optimal esthetics and function.
Restoration of facial defects is a difficult challenge for both the surgeon and the prosthodontist. The prosthodontist is limited by the inadequate materials available for facial restoration, movable tissue beds, difficulty in retaining large prosthesis, and patient acceptance. Maxillofacial silicone is one such material available for restoring these facial defects. Its first use for facial prostheses was presented in 1960 by Barnhart.
Today, silicones have 50 years of safety and efficiency in their application. Despite their development since the past 4 decades, most commonly used silicones still have some disadvantages, such as discoloration with time, technique sensitivity, lack of reparability, extrinsic color peel/fade, and lack of longevity. Hence, this reduces the mean lifespan of a facial prosthesis to 6–14 months.,,, To date, the effects of many popular coloring agents, different reinforcement materials such as glass fiber, nanoparticles, on the color stability of the maxillofacial polymers have been evaluated. Till date, none of the facial prosthetic material, including silicone, fulfills all the requirements of a satisfactory prosthesis.,, The principal reason for the replacement of facial prostheses is degradation in appearance because of changes in color and physical properties. Frequent replacement of the prosthesis becomes less cost-effective.
In addition, failure to maintain facial prosthesis hygiene causes infection of the subjacent tissues. Hence, facial prosthesis disinfection is essential for maintenance of the surrounding tissues. The routine use of immersion denture cleansers is recommended as an effective way to minimize biofilm accumulation. However, this disinfection may alter the physical properties of the facial silicone, particularly the color stability. Hence, the aim of the present study is to evaluate the effect of denture cleansers on the color stability of a commercially available maxillofacial silicone following accelerated aging.
| Materials and Methods|| |
According to ASTM specification D2244-85 for testing the color stability of maxillofacial silicone, metal dies were prepared with a dimension of 7 cm × 5 cm × 2 mm [Figure 1]. These metal dies were then used to prepare stone molds for the fabrication of samples. Each of these samples was later cut to the dimension of 3.5 cm × 5 cm × 2 mm.
The samples were flasked in the normal conventional manner using type III dental stone as an investing medium. The dental stone (investment medium) was contoured such that the top surface of the metal dies was level with the investing medium. The lid of flask was gently tapped onto place and the investing medium was allowed to set under clamp pressure.
After the investing medium reached its final set, the clamps were removed and the two portions of the flask were gently separated with the help of a plaster knife. The metal dies were also lifted from the investing medium along the edges, thereby creating a mold space into which silicone could be packed.
An alginate-based separating medium was coated onto the walls of the mold cavity with the help of a sable brush and it was allowed to dry.
Cosmesil M511 is available as a two part system, part A and part B. Both the parts were digitally weighed before mixing in a ratio of 10:1, according to the manufacturer's instructions. 0.2% of the silicone by weight of pigment Burnt sienna was added using a digital precision balance to the weighed silicone [Figure 3]. A vacuum mixer was used to mix part A and part B with the pigments to minimize the air bubble incorporation. The mixture was then injected into the prepared plaster molds and the flask assembly was placed on a hydraulic press and pressure was applied incrementally. This slow application of pressure permits the silicone to flow evenly throughout the mold space. Excess material was displaced eccentrically. Pressure was applied till the major portion of the flasks closely approximated one another. The flasks were placed in a hot air oven for 1 h at 100°C to accelerate curing [Figure 2].
After curing, the samples were retrieved from their molds and inspected for surface irregularities and internal defects. Excess flash was trimmed with scissors and the samples were cleaned by soaking in warm water. A total of 180 samples were fabricated of which 60 samples were pigmented using Burnt sienna [Figure 4], 60 samples using Hansa yellow [Figure 5], and 60 samples using Alizarin red [Figure 6].
Testing the color stability
Once the samples were fabricated, they were exposed to the environment for 72 h. Following this, the initial color measurement was done for all the samples using visible UV spectrophotometer [Figure 7]. The L, a, and b values were measured according to the CIE L* a* b* system.
The color alterations were calculated by the CIE Lab system. Variation of the color was calculated using the formula
ΔE = ([ΔL]2+ [Δa]2+ [Δb]2)1/2
where L* stands for lightness, a* for redness-greenness, and b* for yellowness-blueness. ΔL, Δa, and Δb were changes in L*, a*, and b*, respectively, between the interval of interest and baseline, and ΔE was the color difference. This formula is designed to provide numeric data that represent the magnitude of the color difference perceived between two objects.
After the initial color measurement, the samples were disinfected using Fittydent denture cleanser and also with water and neutral soap. Twenty samples from each group were immersed in a receptacle containing the effervescent tablets of Fittydent denture cleanser dissolved in warm water. This was done for 30 min. Later, the samples were removed and the procedure was repeated 3 times a week for 60 days.
Another 20 samples from each groups were rubbed with neutral soap using digital friction for 30 s followed by washing with water. This procedure was also carried out 3 times/week for 60 days. The remaining 20 samples from the groups were not subjected to any disinfection and acted as the control group.
After 60 days of disinfection, the samples were measured for color changes using the visible UV spectrophotometer.
Accelerated aging process
After the samples were disinfected and the color variations were calculated, the samples were subjected to the accelerated aging process. Ten samples from each group were placed in the accelerated aging chamber and submitted to alternate periods of UV light and condensed distilled water [Figure 8]. Each cycle of aging was carried out for 12 h. During the first 8 h, UV light was applied at 60°C ± 3°C. Then, the samples were subjected to a period of condensation without light at 45°C ± 3°C for 4 h. This process was carried out for 504 h and 1008 h.
The remaining 10 samples from each group were not subjected to accelerated aging. After 504 h of aging, the color variations were calculated. The samples were again placed in the aging chamber and the process was carried out for 1008 h. After 1008 h, the samples were again measured for color variations.
The remaining 10 samples of each group were not subjected to aging but were exposed to the environment for 3 months and the color variations were calculated. The data for color change (ΔE) are statistically analyzed using ANOVA followed by Tukey's test (P< 0.01).
| Results|| |
After disinfection, increase in ΔE values was observed in samples pigmented with Burnt Sienna and Alizarin Red, as compared to samples pigmented with Hansa Yellow. The increase in ΔE values was more after disinfection with neutral soap, as compared to the disinfection with Fittydent denture cleanser. One-way ANOVA and Tukey's multiple comparison test showed that the difference was not statistically significant among the samples irrespective of pigmentation.
After 504 h of accelerated aging, increase in ΔE values was observed in samples pigmented with Burnt Sienna and Alizarin Red, as compared to samples pigmented with Hansa Yellow. The increase in ΔE values was more in the samples disinfected with neutral soap than those disinfected with Fittydent denture cleanser. One-way ANOVA and Tukey's multiple comparison test revealed that the difference in ΔE values after 504 h of accelerated aging was not statistically significant.
Increase in ΔE values was observed after 1008 h of aging in all 3 pigmented samples regardless of the disinfection method. One-way ANOVA revealed that there was a significant difference after 1008 h of aging in all samples irrespective of pigmentation.
Tukey's multiple comparison test revealed that after 1008 h of aging, there was a statistically significant difference in the samples pigmented with Alizarin red between the initial measurement and following disinfection with neutral soap [Table 1], [Table 2], [Table 3].
There was a statistically significant difference in the samples pigmented with Burnt sienna between initial measurement and following disinfection with neutral soap and between control and samples disinfected with neutral soap [Table 1], [Table 2], [Table 3].
There was a statistically significant difference in the samples pigmented with Hansa Yellow between initial measurement and following disinfection with neutral soap and Fittydent denture cleanser [Table 1], [Table 2], [Table 3].
| Discussion|| |
In 1972, Sweeny et al. reported the use of an accelerated aging chamber for evaluation of maxillofacial material color stability. Aging is the adverse response of a material to UV radiation, temperature, and water (moisture), often causing discoloration.
According to the results obtained in the present study, the specimens pigmented with Burnt Sienna and Alizarin Red showed color instability as compared to Hansa Yellow. There was an increase in ΔE values after disinfection. The ΔE values increased more in samples disinfected with neutral soap than those disinfected with Fittydent denture cleanser.
Neutral soap causes removal of pigments that accumulate on the surface of silicone, increasing the chromatic alteration. Andres suggested that digital friction on the prostheses removes the pigments. This removal causes color alteration.
Fittydent denture cleanser which is an alkaline peroxide product works through oxygen liberating mechanism that loosens the debris and removes the light stains. They also promote color alteration of the prosthesis by removing the pigments from the superficial layer of the silicone. They also whiten the prosthesis, thereby causing bleaching of the prostheses. However, in this study, there was no whitening of prosthesis, due to the composition of the colorless silicone.
The ΔE values of the samples disinfected with Fittydent denture cleanser were significantly lower than the values obtained in samples pigmented with neutral soap because the Fittydent denture cleanser did not expose the pigment or create porosities in the materials, which facilitate color degradation.
There was an increase in ΔE values after 504 h of accelerated aging for samples pigmented with Burnt Sienna and Alizarin Red. Whereas after 1008 h of accelerated aging, there was an increase in ΔE values for all the samples
Exposure to UV light alters the color of the elastomers due to inherent chemical alterations in silico ne or discoloration of some pigments that are not UV resistant. Photooxidation and hydrolysis of the silicone elastomer are the main degradation reactions that occur after exposure to sunlight, humidity, and temperature. These reactions produce changes in physical and chemical properties resulting in deterioration of the silicone. Many authors like Lemon et al. and Ishigami et al. have investigated the effect of UV light on pigmented silicone elastomers and have shown that samples pigmented with red pigments discolor at a higher rate than the ones with yellow pigments.,,,, Yellow pigments are stable in the presence of sunlight, moisture, and temperature below 177°C. This is mainly because the chemical incompatibility between pigment and elastomer permits migration of pigment during prolonged exposure to ultraviolet radiant energy.
The smaller the pigment particle, the higher is its interaction with the polymeric chain of the silicone. Organic pigments are difficult to incorporate into silicone. Therefore, easy release of oxygen during disinfection or accelerated aging may occur, leading to more deterioration of the silicone. Furthermore, silicone has weak molecular interactions, which allows higher particles to be more easily separated. This leads to further chromatic alterations in the silicone. The organic pigment exhibited greater degradation with accelerated aging, since these pigments dissolve in contact with UV light.
The limitations of the present study are incorporation of the pigments was done manually. This results in improper mixing of the pigments leading to uneven pigmentation. Since it is an in vitro study, the changes that are observed clinically will be different. The effect of accelerated aging on silicone is different from natural aging. Normally, most elastomers used in facial prostheses are not exposed to wet environments or thermal cycling procedures used during the artificial aging process. Artificial aging causes greater changes than natural weathering.
| Conclusion|| |
Within the limitations of this in vitro study, it can be concluded that as follows:
- Silicone pigmented with Hansa yellow was more color stable than the silicone pigmented with Burnt sienna and Alizarin red after disinfection and 504 h of accelerated aging
- Silicone disinfected with neutral soap and water was less stable than silicone disinfected with Fittydent denture cleanser
- Silicone subjected to accelerated aging for 1008 h was highly unstable.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]
[Table 1], [Table 2], [Table 3]