Year : 2009 | Volume
: 20 | Issue : 1 | Page : 77--80
Visual evaluation of color stability after accelerated aging of pigmented and nonpigmented silicones to be used in facial prostheses
Daniela Nardi Mancuso, Marcelo Coelho Goiato, Stefan Fiuza de Carvalho Dekon, Humberto Gennari-Filho
Department of Dental Materials and Prosthodontics, Araçatuba Dental School, UNESP - Sao Paulo State University, Araçatuba, Sao Paulo, Brazil
Daniela Nardi Mancuso
Department of Dental Materials and Prosthodontics, Araçatuba Dental School, UNESP - Sao Paulo State University, Araçatuba, Sao Paulo
Objectives: The objective of this study was to evaluate by a visual method of comparison the color stability of nonpigmented and pigmented facial silicones after accelerated aging.
Materials and Methods: Two kinds of silicones were used in this study; one specifically formulated for facial prostheses and the other an acetic silicone for industrial use. Twenty-four trial bodies were made for each silicone. These were divided into colorless and intrinsically pigmented groups: ceramic, make-up, and iron oxide. The groups were submitted to accelerated aging for nonmetallic materials. An initial reading and subsequent readings were made at 163, 351, 692, and 1000 hours using a visual method of comparison. The values were annotated in a spreadsheet by two observers, according to scores elaborated for this study.
Results: All groups presented color stability in the visual method. According to the results obtained and analyzed in this study, we can conclude that both silicones, Silastic 732 RTV and Silastic MDX 4-4210, behaved similarly, they can therefore be indicated for use in maxillofacial prosthesis. The time factor of aging influenced negatively, independently of the pigmentation, or lack of it, and of silicones and no group had visually noticeable alterations in any of the accelerated aging time, independently of the addition or not of pigments.
|How to cite this article:|
Mancuso DN, Goiato MC, Dekon SF, Gennari-Filho H. Visual evaluation of color stability after accelerated aging of pigmented and nonpigmented silicones to be used in facial prostheses.Indian J Dent Res 2009;20:77-80
|How to cite this URL:|
Mancuso DN, Goiato MC, Dekon SF, Gennari-Filho H. Visual evaluation of color stability after accelerated aging of pigmented and nonpigmented silicones to be used in facial prostheses. Indian J Dent Res [serial online] 2009 [cited 2014 Dec 19 ];20:77-80
Available from: http://www.ijdr.in/text.asp?2009/20/1/77/49073
The prosthetic technician faces a challenge when fabricating prostheses. A prosthesis provides esthetics and functional stability along with a sense of secureness to the patient (wearer). For this, the material chosen for the prosthesis must have good mechanical and physical properties, must have a satisfactory life span in relation to resistance and edge deterioration, and above all, it must retain its color pattern during the time it is in use.
In addition to the need to choose an adequate material so that the prosthesis can be considered esthetically pleasing, it is also important to match the color of the missing part to allow blending with the surrounding tissues, making the prosthesis almost unnoticeable to anyone observing the wearer.  However, prosthetic technicians face great challenges in creating the correct coloring for a facial prosthesis to match it with the patient's skin color; and this is one of the most important steps in the manufacture of these alloplasts.
Karayazgan et al.  reported that although the objective of a facial prosthesis is to fulfill the patient's esthetic needs and to improve his/her quality of life, it is also important that the patient is informed about the possible outcome related to the esthetics, as well as the limitations of this material in exactly simulating natural features after finishing the prosthesis.
For maintenance of esthetics, the stability of the color of the prosthesis is critical. Hence, we evaluated color stability by a visual method following accelerated aging of silicones used in facial prostheses, varying the following factors: silicone (a siliconeth designed for maxillofacial and another silicone designed for experimental prostheses), nonpigmented silicones (colorless control), and pigmented silicones, utilizing the following coloring systems: make-up, ceramic, and iron oxide.
Materials and Methods
Taking into account the results obtained in an earlier study  , we used two different silicones to manufacture the trial bodies; one silicone was adequate for use in facial prosthesis (SILASTIC MDX 4-4210, USA) and the other silicone (acetic silicone) was developed for industrial use (SILASTIC 732 RTV, Brazil). For an intrinsic pigmentation of the silicones, three coloring systems were used: make-up (Payot, Brazil), ceramic (Corin, Brazil), and iron oxide (Bayer S.A., Brazil).
Manufacturing of trial bodies
To fabricate the master mold, a stainless steel box and a white orthodontic plaster were used (Orto-Rio Produtos Odontológicos, SP, Brazil). To obtain the trial bodies, master molds were prepared in plaster using molds in pink wax 7 Wilson (Polidental Indústria Comιrcio Ltda., SP, Brazil) with a length of 7 cm, width of 5 cm, and thickness of 2 mm.
The groups were divided as shown in [Table 1], comprising 48 trial bodies in total. In addition to the preparation of pigments, the silicones were weighed using a precision digital scale (BEL Equipamentos Analνtico, SP, Brazil). The pigment was used in a ratio of 0.2%  of the silicone's weight. The silicones were handled according to the manufacturers' instructions, that is, at room temperature of 23 ± 2oC and a relative humidity of 50 ± 10%. Each pigment was mixed with the silicone on a glass sheet with the aid of a stainless steel spatula until a homogenous mixture was obtained. The silicone was then inserted in the master mold and the excess was removed with a spatula to maintain uniformity. The Silastic 732 RTV silicone was placed in the master mold with the external surface exposed at room temperature for 24 hours. Silastic MDX 4-4210 was then applied to the master mold with the external surface exposed at room temperature for three days. According to the manufacturers, the final polymerization of each silicone occurs during this period of time. After this period, each trial body was carefully separated from the metallic master mold and the thickness of 2 mm was confirmed with a thickness meter.
Process of aging of trial bodies
After the manufacture of trial bodies, five trial bodies from each subgroup were submitted to accelerated aging by means of the accelerating system of aging for nonmetallic materials ultraviolet B / water condensation (Comexim Matιrias Primas Ind. Com. Ltda., SP, Brazil). However, one trial body from each subgroup was not submitted to accelerated aging. These specimens were stored in a closed box in a well-ventilated area, without the interference of direct or indirect light, for later analysis by a visual method of comparison. This analysis was carried out with the trial bodies that were submitted to the accelerated aging process and the trial body that did not go through this process.
After initial color measurements, the trial bodies were positioned in an accelerated aging chamber, where they were submitted to alternate periods of ultraviolet light and distilled water condensation in an oxygen-saturated environment, under heat and humidity conditions of 100%. Each aging cycle took 12 hours. For the first eight hours, the ultraviolet light was applied at a temperature of 60 ± 3°C. During the following four hours, a period of condensation without light was applied at a temperature of 45 ± 3°C. The aging process was performed for 1000 hours, the equivalent of 83 cycles and 42 days. This simulated the deterioration caused by rain water, dew, and ultraviolet light from the sun (as indirect and direct solar energy), and simulated the equivalent of one year of constant use of the prosthesis by the patient. After using the prostheses for one year, visible color alterations often occur in prostheses. ,,,
After each of the accelerated aging periods, 163, 351, and 692 hours, the trial bodies were removed and submitted to the reading process with a reflection spectrophotometer (ultraviolet-visible model UV - 2450 Shimadzu, Japan), after which they were replaced in the chamber for a new period of aging until 1000 hours were completed.
Trial body visual evaluation
a) Visual method of comparison
Trial bodies were visually compared following their submission to the accelerated aging process, to a trial body that did not go through this aging process.
For the evaluation of this method, scores varying from -5 to +5 were created:
-5 -4 -3 -2 -1 0 +1 +2 +3 +4 +5
-5, extremely dark;-4, very dark; -3, dark; -2, fairly dark; -1, slightly darker; 0, trial body has not suffered aging; -1, slightly clearer; +2, fairly clear; +3, clear;+4, very clear; and +5, extremely clear.
The trial bodies from each group were placed in pairs (control and aged), side by side, on the top of a white metallic plaque and were analyzed by two observers at each reading time (0, 163, 351, 692, and 1000 hours); results were recorded according to the scores.
The visual reading was carried out among trial bodies of the same silicone and not among the different silicones, since even during the initial period we were unable to visually compare the different silicones due to the small differences in texture and shade of the materials.
The accelerated aging process lasted 42 days in total. The trial bodies that were not submitted to the accelerated aging were stored inside a closed box in a well-ventilated place without interference of indirect or direct light during the period in which the other trial bodies underwent accelerated aging.
The data comparing trial bodies not submitted to accelerated aging (0) to the trial bodies that were submitted to accelerated aging (1, 2, 3, 4, and 5) are shown in the [Table 2],[Table 3],[Table 4],[Table 5],[Table 6],[Table 7],[Table 8],[Table 9], according to the scores (-5 to +5). Visual comparison of all the groups demonstrated that none of the groups had presented noticeable visual alterations following the periods of accelerated aging.
Visual method of comparison
Many authors have studied the ideal replacement time for prostheses and reported several different periods, due to the diversity of the material studied. The majority of authors agree, however, that prostheses should be replaced in a maximum period of one year, due to the color alteration detected by reflection spectrophotometry. ,, As such, a visual evaluation of color alteration in facial silicones exposed to the environment in a maximum period of a year was recommended by Polyzois. 
In this context, one of the factors that contributes to the constant refabrication of the prosthesis is the instability of its color due to the effect of ultraviolet rays on facial silicones and pigments. Although, the trial bodies suffered color alterations, as shown by reflection spectophotometry in a previous study (REF); in the present study, these alterations were not considered to be clinically visibly noticeable in the groups studied, independently of time exposed to accelerated aging or the addition or not of pigments. This finding demonstrates the successful maintenance of the color stability of facial prosthesis during clinical use for approximately a year.
Method of exposure of trial bodies
Another important factor, to be taken into consideration in the present study, is the exposure method used for trial body aging. Some authors have suggested the use of artificial luminous sources, exposure chamber rooms for an artificial time of 900- ,,,, 2000 hours,  while others demonstrated trial body aging as a consequence of direct exposure to solar light and environment conditions from 3- , 6 months. 
Thus, these data lead us to question the possibility that differences exist between color alterations resulting from exposure in accelerated aging chambers and from direct exposure to the solar light and environment conditions. Takamata et al.  and Lemon et al.  reported that color changes occurred in the polymer bases of materials and that artificial aging caused a greater color alteration than aging in the open air. Lemon et al.  affirmed that the time of use of prosthesis varies on an average from three months to one year, resulting in elastomer degradation and color instability. Sweeney et al.  suggested that the majority of patients need to replace their prostheses at between six to eight months.
We utilized accelerated aging chambers in this study for aging nonmetallic materials, a method that is most commonly used as reported in the published literature. ,,,,,,,, Furthermore, these chambers simulate situations in which facial prostheses are used for a period of one year.
According to the results obtained and analyzed in this study, we can conclude thatboth silicones, Silastic 732 RTV and Silastic MDX 4-4210, behaved similarly, they can therefore be indicated for use in maxillofacial prosthesis. The time factor of aging influenced negatively, independently of the pigmentation, or lack of it, and of silicones and no group had visually noticeable alterations in any of the accelerated aging time, independently of the addition or not of pigments.
Based on a dissertation submitted to the graduate faculty, UNESP - Sγo Paulo State University, in partial fulfilment of the requirements for the M.S. degree.
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