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00001665-201109000-0001600001665_2011_22_1612_haddad_maxillofacial_5article< 101_0_7_4 >Journal of Craniofacial Surgery© 2011 Mutaz B. Habal, MDVolume 22(5)September 2011pp 1612-1616Influence of Pigment and Opacifier on Dimensional Stability and Detail Reproduction of Maxillofacial Silicone Elastomer[Original Articles]Haddad, Marcela Filié DDS, MS; Goiato, Marcelo Coelho DDS, PhD, MS; dos Santos, Daniela Micheline DDS, PhD, MS; Pesqueira, Aldiéris Alves DDS, PhD, MS; Moreno, Amália DDS, MS; Pellizzer, Eduardo Piza DDS, PhD, MSFrom the Department of Dental Materials and Prosthodontics, Araçatuba Dental School, UNESP. Araçatuba, São Paulo, Brazil.Received April 4, 2011.Accepted for publication July 8, 2011.Address correspondence and reprint requests to Marcelo Coelho Goiato, DDS, PhD, MS, Faculty of Dentistry of Araçatuba, Department of Dentistry Materials and Prosthesis, Rua José Bonifácio, 1193-Vila Mendonça, CEP 16015-050, Araçatuba, São Paulo, Brasil; E-mail: goiato@foa.unesp.brThis investigation was supported by a research grant (2008/52766-9) from Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP).The authors report no conflicts of interest.AbstractWe evaluated the influence of chemical disinfection and accelerated aging on the dimensional stability and detail reproduction of a silicone elastomer containing an opacifier and/or a pigment. A total of 120 samples were fabricated from Silastic MDX 4-4210 silicone and divided into groups (n = 10) according to pigment and/or opacifier (ceramic powder and/or barium sulfate) and disinfectant solution (neutral soap, Efferdent, or 4% chlorhexidine). The specimens were disinfected 3 times per week during 60 days and then subjected to accelerated aging for 1008 hours. Dimensional stability and detail reproduction tests were performed after specimens' fabrication (baseline) and chemical disinfection and periodically during accelerated aging (252, 504, and 1008 hours). The results were analyzed using 3-way repeated-measures analysis of variance and the Tukey Honestly Significant Difference test (a = 0.05). All groups exhibited dimensional changes over time. The disinfectant, pigment, and time (P < 0.0001) affected the dimensional stability of silicone. Statistically significant dimensional differences were not observed between the tested groups. Accelerated aging influenced the dimensional stability of the samples. All groups scored 2 in the detail reproduction tests, which represents the full reproduction of 3 test grooves with accurate angles. Incorporation of opacifier and/or pigment alters the dimensional stability of silicones used in facial prosthetics but seems to have no influence on detail reproduction. Accelerated aging is responsible for most of the dimensional changes in Silastic MDX4 4210, but all dimensional changes measured in this study remained within the limits of stability necessary for this application.Maxillofacial prosthesis is included in prosthetic dentistry area, used to replace missing facial parts that have been lost through congenital diseases, tumors, or traumas through artificial substitutes.1-3 Prosthetic rehabilitation is a surgical alternative in functional aesthetic facial reconstruction when conventional reconstructive surgery cannot be applied.3-5The material most widely used for fabrication of facial prostheses is silicone1,2,5-27 because of its ease of manipulation and it offers physical properties better than other materials, such as good stability, chemical inertness, repels water and blood, and is fairly flexible, an essential characteristic to achieve good aesthetic appearance and to provide comfort to the patient.5,11,12,20,21,24,26,27Despite the considerable advances in the treatment of patients with facial defects and the advantages provided by the silicone material, there is an increasing need to enhance the material's properties used to fabricate those facial prostheses because of the limited lifetime of such prostheses. It is the result of degradation of the elastomer, color instability, and physical property changes.1,4,5,8,12,15,22,24,28 To increase the durability of these prostheses, several efforts have been done by researchers9,24,28,29 that advocate the chemical and dimensional stability and minimal or no water absorption as the most important properties related to the longevity of maxillofacial prosthesis.The facial prosthesis can be pigmented intrinsically or extrinsically by using several organic and inorganic materials. It is a consensus that inorganic pigments (such as ceramic powder) are more stable than organic pigments (powder makeup). However, even using inorganic powders, the color of the maxillofacial prosthesis is prone to change over time.20,21,24,25,28,30 To enhance its color stability, the intrinsic addition of opacifiers to silicone has been suggested,17-19,24,28 but their effects on dimensional stability and detail reproduction and maintenance of pigmented facial silicone remains an unexplored issue.In addition, the poor hygiene of patients with facial prosthesis contributes to the infection of the supporting tissues. Therefore, disinfection procedures for such facial prosthesis are of fundamental importance to the maintenance of healthy supporting tissues.10-12,28,29 However, those disinfectants may change the physical properties of the facial silicone.1,7,9,10,28,29The aims of this study were to investigate the dimensional stability and detail reproduction of facial silicone prostheses fabricated with and without the incorporation of opacifier and/or pigment and to determine the influence of disinfection and accelerated aging on these parameters.METHODSThe samples were fabricated using Silastic MDX4-4210 (Dow Corning Corporation, Midland, MI). Barium sulfate (Wako, Osaka, Japan) and titanium dioxide (Homeofar, Catanduva, São Paulo, Brazil) were used as opacifier.29A cylindrical metal mold 30 mm in diameter and 3 mm in thickness was used to cast the samples.1,12,28,29 A total of 120 samples were divided into 12 groups (n = 10) according to opacifier and/or pigment content (none [L], ceramic powder [Ce], barium sulfate [Ba], ceramic powder and barium sulfate [CeBa]) and disinfection method (soap [S], Efferdent [E] [Pfizer Consumer Health, Morris Plains, NJ], or chlorhexidine [C]) (Table 1).TABLE 1. Mean Values (SDs) of Dimensional Change in Absolute Value (%)The materials were weighed using a precision digital scale (BEL Equipamentos Analíticos, Piracicaba, São Paulo, Brazil). The pigment and/or opacifier was added at a concentration of 0.2 wt% of silicone.21,24,25,28-30Silicone was formulated and mixed according to the manufacturer's instructions at 23°C ± 2°C. The pigment and/or opacifier was added to silicone using a stainless steel spatula on a glass plate to obtain a homogenous mass. After manipulation, the mixture was placed in the mold and cured at room temperature during 3 days according to the manufacturer's instructions.1,10,21,28,29 The sample was carefully removed from the mold to avoid distortions.1,29,30 Dimensional stability and detail reproduction tests were carried out initially, after 60 days of disinfection, and after different times of accelerated aging (252, 504, and 1008 hours).For the dimensional stability test, samples were digitalized using a scanner (Genius; Langenfeld, Nordrhein-Westfalen, Germany) with a resolution of 800 dpi. To standardize the measurement, a metallic block with 2 vertical lines (C-D) 25 mm apart was scanned with each sample. The measurements were performed using AutoCAD 2008 software (R16 version N63.0; Autodesk Inc, San Rafael, CA). Both sample's and matrix's images were imported into the software using the "Raster image" tool.1,29 This tool allows working with bitmap images within vector-based files constructed using straight lines. The vertical lines of the block were used as a 25-mm dimensional reference (C-D) within the software. Vertical lines inscribed on the samples (C'-D') were compared against this reference.29Each sample was measured 3 times. The following formula was applied to determine dimensional changes1,29:where A = original distance of the block between edges C and D = 25 mm; B = distance between edges C′ and D′ in the samples.Equation (Uncited)In the detail reproduction test, the angular accuracy of 3 grooves (20, 50, and 75 μm wide) molded in each sample was recorded. Detail reproduction was examined using a stereo microscope (Olympus, Tokyo, Japan) under low-angle illumination at 13× magnification. To classify the accuracy of detail reproduction, the scores suggested by Goiato et al1 were used as described below: X: no groove reproduction; 0: full reproduction of 2 of the 3 grooves; 1: full reproduction of the 3 grooves, with inaccurate angles; and 2: full reproduction of the 3 grooves, with accurate angles.Samples were disinfected 3 times per week during 60 days.1,9,10,27-29 Ten samples of each group were disinfected with Efferdent (Pfizer Consumer Health),1,9,12,27-29 10 with neutral soap,1,12,27-29 and 10 with 4% chlorhexidine gluconate (Naturativa, Araçatuba, São Paulo, Brazil).28,29The groups disinfected with water and neutral pH soap (Johnson & Johnson, São José dos Campos, São Paulo, Brazil) were rubbed with the fingertips during 30 seconds, then rinsed with water.1,9,10,27-29 The samples disinfected with Efferdent (Pfizer Consumer Health) were immersed in a solution containing Efferdent tablets dissolved in 250 mL of warm water during 15 minutes.1,9,10,28,29 Samples disinfected with chlorhexidine were immersed in this solution for 10 minutes and then rinsed with water.12,28,29Accelerated aging treatments were carried out using an aging chamber (Equilam, Diadema, São Paulo, Brazil).21,24,28,29 Each aging cycle lasted 12 hours. In the first 8 hours, the samples were exposed to UV light at a temperature of 60°C ± 3°C. In the remaining 4 hours, samples were subjected to oxygen-saturated distilled water condensate in the absence of light at a temperature of 45°C ± 3°C. The samples underwent 1008 hours of accelerated aging. Both disinfection and accelerated aging processes simulated 1 year of patient's clinical use of silicone.21,28,29The effect of opacifiers, disinfection, and aging on dimensional stability (interactions among these factors) was analyzed by 3-way repeated-measures analysis of variance. Means were compared using the Tukey Honestly Significant Difference test (a = 0.05). As all of the samples achieved the same detail reproduction score, no statistical analysis was performed for this variable.RESULTSResults are summarized in Tables 1 to 3. Table 1 lists the means and SDs of the dimensional change values of silicone for each period of analysis. All groups exhibited dimensional changes over the course of the experiment (Table 1). In general, the colorless and ceramic + barium groups exhibited the lowest dimensional changes. Similar dimensional change behavior was observed among groups regardless of the disinfectant type (Table 1).TABLE 2. Results of 3-Way Repeated-Measures Analysis of Variance for Dimensional ChangesTABLE 3. Mean Values of Dimensional Change in Module (%) for Each Material in Different Periods, Regardless of DisinfectantBoth the pigment (P = 0.35) and time (P < 0.0001) statistically affected the dimensional stability of silicone when they were not associated (Table 2). Statistically significant dimensional changes occurred among the initial measurement, after 60 days of disinfection and after 1008 hours of accelerated aging (Table 3). The ceramic + barium group showed lower values of dimensional change when compared with ceramic and barium groups and higher values versus colorless group. However, this difference was not statistically significant. All groups scored 2 in the detail reproduction test, showing full reproduction of the 3 test grooves with accurate angles.DISCUSSIONAll groups exhibited dimensional changes over the experiment (Tables 1-3). At the initial period, the dimensional changes may be attributed to the polymerization shrinkage of the elastomer.1,9,10,12,30 The increased dimensional changes observed during other periods (60 days, 252, 504, and 1008 hours) can be explained by the release of formaldehyde, a byproduct of silicone's curing process.1,10,31 It is well known that elastomers can contract during polymerization. Anusavice31 stated that there are 5 main reasons to promote dimensional changes in elastomeric materials: polymerization shrinkage; byproduct release during condensation reactions; thermal shrinkage due to temperature changes; sorption after exposure to water, disinfectants, or high humidity environments for long periods; and incomplete elastic deformation recovery due to viscoelastic behavior.Color change is the easiest alteration observed in facial prosthesis and occurs over a long period of use. Several studies have been conducted to investigate the most suitable pigment and pigmentation technique to obtain good aesthetic appearance of the prosthesis over time.7,8,10,11,13-15,17,21-24,28,29 There is a consensus that the inorganic pigments (such as ceramic powder used in this study) are more stable than the organic ones as affected by environmental factors and that the technique of intrinsic pigmentation, applied in this study, is better than the extrinsic technique regarding color stability.7,8,10,20,21,24,26,28 Recent studies17-19,24,28 also suggested that the intrinsic addition of opacifiers can improve the color stability of facial prosthesis for a long period of use.Barium sulfate is a white powder used to help doctors to examine the esophagus, stomach, and intestine using x-rays or computed tomography. Also, it is added to root-end filling material to confer higher radiopacity to be visualized radiographically. Nowadays, barium sulfate has been used in cosmetic industry such as in sunscreen lotions to create a physical barrier against UV rays and to provide better appearance of the product.4,5,28 In the current study, the opacifier was added to silicone associated or not with the ceramic powder to analyze its effect on the dimensional stability and reproduction and maintenance of details of Silastic MDX 4-4210.Comparing the dimensional stability values exhibited by different groups (colorless, ceramic, barium, and ceramic + barium) for each of the disinfectants at different intervals, there is no difference in the initial period (Table 1). These results indicate that the ceramic pigment and barium sulfate, associated or not, can be intrinsically added to the MDX 4-4210 facial silicone, without causing dimensional changes.The disinfectant type did not significantly affect the dimensional stability of silicone (Table 2). Similar results were reported by Guiotti et al,12 who used a scanning electron microscope to evaluate the marginal deterioration of facial prostheses after chlorhexidine disinfection. The authors did not observe any significant alteration. Goiato et al1 examined the dimensional alteration and detail reproduction of 2 silicones used in facial prostheses, without pigmentation, after disinfection with neutral soap and alkaline peroxide effervescent tablets. Goiato et al29 evaluated the influence of chemical disinfection and accelerated aging on the dimensional stability and detail reproduction of a silicone elastomer containing 1 of 2 opacifiers. They did not find any significant alteration of these properties.It appears that period of time is responsible for the highest dimensional changes in all groups (Tables 1-3). This can be explained by the continuous extended polymerization of elastomeric materials9,31 with the release of formaldehyde.9 Most polymers contain aromatic rings and C - C bonds in their structures, which can absorb UV light during accelerated aging.31 When the polymer molecule absorbs UV light, this energy creates instability in the molecular structure. The excess of energy can be dissipated through several pathways, for instance, transfer of the excitation to another molecule.31 These functional groups may return to their ground state in steps, re-emitting the excess of energy at longer wavelengths such as visible or infrared light.31 If not dissipated, the excess energy may lead to bond cleavage (photochemical degradation). This degradation contributes to deterioration of the molecule, causing dimensional changes, color and brightness changes, loss of opacity, crack formation, and hardening.31The accelerated method used in the current study may be another possible reason. The accelerated aging chamber is a device where the specimens are exposed to conditions similar to the environment atmosphere, radiation, temperature, and humidity, simulating the natural aging of a facial prosthesis.6,8 Several studies6,8,20,21,28 suggested the UV radiation as a key contributor to the environmental changes that affect both the optical and mechanical properties of silicones with and without pigmentation.No significant change in the dimensional stability was observed among the disinfectants regardless of the period (Table 2), indicating that despite the difference in disinfection techniques, the materials used promote similar changes to silicone, pigmented, or not.In our study, the dimensional changes observed in all samples with or without pigmentation subjected to both disinfectants types and accelerated aging were considered adequate (Tables 1 and 3) and are in agreement with previous studies.1,2,5,13,14,30 Although there was contraction in the test specimens of all groups, they are within the recommendation of ISO specification,32 according to which contraction must not be more than 1% in 24 hours, because they do not present values higher than 0.117%, showing excellent dimensional stability of the present silicone (Tables 1 and 3).The use of AutoCAD software as a method to evaluate the dimensional stability of facial silicones appears to be satisfactory and produced accurate values. The applicability of this software in many areas of medicine and dentistry is unquestionable29 and highlights the possible contributions through the association of computational methods with the health sciences.Regarding detail reproduction, the results show comparatively that all groups reproduced score level 2, regardless of chemical disinfection and exposure time to accelerated aging. According to the classification that Goiato et al1 used, level 2 means that all test specimens fully reproduced the 3 grooves with accurate angles. These results confirm the observations of Goiato et al1 and Guiotti and Goiato,5 who found that silicones (for impression) and facial silicones had excellent detail reproduction capacity, reproducing grooves of up to 20 μm wide.The maintenance of maxillofacial elastomer hygiene is important, yet there are no sufficiently effective methods for doing this. Brushing is not advisable because this repeated washing may dissolve and remove some pigments on the external surface.9 Rinsing with tap water is ineffective against calculus buildup and stains.9,28 A chemical soaking technique is primarily the method of choice for the disinfection of maxillofacial elastomer. Patients are advised not to clean the prosthesis using any solvents, such as isopropyl alcohol, which could cause dissolution of the pigments.9,28 For this reason, the solutions used in the current study were Efferdent tablets that act by saturation, but peroxides are present in their composition; the neutral soap acts by digital friction and has an inert chemical composition,28 and the 4% chlorhexidine acts by saturation but is chemically inert.28Data presented in Tables 1 to 3 showed that the disinfectants did not affect the clinical behavior of silicone regarding its dimensional stability and maintenance and detail reproduction independent of the addition or not of pigments and/or opacifier. Guiotti and Goiato5 also found that chemical disinfection did not affect the physical properties of facial silicones.On the other hand, studies from Gary et al7 and Goiato et al9,10,27 showed that chemical materials based on alkaline peroxide used to disinfect prosthesis can alter the chemical and physical properties of facial silicones and some pigments. Therefore, the possible changes in dimensional and color stability of facial silicones promoted by the disinfectants should be considered.The limitation of the current study relies on the mechanism of artificial aging used, which differs from the natural aging mechanism to which medical silicones are normally subjected. During normal function, most elastomers used in facial prostheses are not exposed to the wet environments or thermal cycling procedures used during the artificial aging process. Although artificial weathering causes a greater change than natural weathering,24 there is no definitive research examining the correlation between the aging chamber used in the current study and clinical changes in physical properties of silicones. Future research is warranted to investigate this correlation.CONCLUSIONSIncorporation of ceramic pigment and/or opacifier alters the dimensional stability of facial prosthesis silicone but seems to have no influence on detail reproduction. The disinfectants did not promote statistically significant changes in dimensional stability and detail reproduction of the facial silicone. Accelerated aging is responsible for most of the dimensional changes in Silastic MDX4 4210, but all dimensional changes measured in this study remained within the limits of stability necessary for this application.REFERENCES1. Goiato MC, Pesqueira AA, dos Santos DM, et al. Evaluation of dimensional change and detail reproduction in silicones for facial prostheses. 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ISO 4823. http://www.iso.org/iso/iso_catalogue [Context Link]Key Wordscolon;: Maxillofacial prostheses; silicone; opacifier; pigmentsovid.com:/bib/ovftdb/00001665-201109000-0001600001891_2008_21_85_goiato_reproduction_|00001665-201109000-00016#xpointer(id(R1-16))|11065405||ovftdb|SL000018912008218511065405P63[Medline Link]18841751ovid.com:/bib/ovftdb/00001665-201109000-0001600146796_2002_14_73_huber_rehabilitation_|00001665-201109000-00016#xpointer(id(R2-16))|11065213||ovftdb|SL001467962002147311065213P64[CrossRef]10.1016%2FS1042-3699%2802%2900018-3ovid.com:/bib/ovftdb/00001665-201109000-0001600146796_2002_14_73_huber_rehabilitation_|00001665-201109000-00016#xpointer(id(R2-16))|11065405||ovftdb|SL001467962002147311065405P64[Medline Link]18088612ovid.com:/bib/ovftdb/00001665-201109000-0001600136430_2007_8_101_goiato_maxillofacial_|00001665-201109000-00016#xpointer(id(R4-16))|11065405||ovftdb|SL001364302007810111065405P66[Medline 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