http://informahealthcare.com/jmt ISSN: 0309-1902 (print), 1464-522X (electronic) J Med Eng Technol, 2014; 38(2): 67–75 ! 2014 Informa UK Ltd. DOI: 10.3109/03091902.2013.864715
INNOVATION
Microstructural characterization and evaluation of the properties of polymeric materials for maxillofacial prosthetics
Department of Dental Materials and Prosthodontics, Ribeira˜o Preto Dental School, University of Sa˜o Paulo, Ribeirao Preto, Brazil
Abstract
Keywords
This study evaluated the Shore A hardness, colour and microstructural alterations of an experimental silicone for maxillofacial prostheses. As a control, the MDX 4-4210 silicone was used. Eighty specimens of each material were randomly divided into groups of pigmentation and ageing. For microstructural analysis by Thermogravimetry, Fourier Transform Infrared Spectroscopy and Differential Scanning Calorimetry, three specimens of each group were used. Anova and Tukey test (p50.05) was used in statistical analysis. There was significant difference in hardness depending on the materials, pigmentation and ageing and interaction between all the factors evaluated (p ¼ 0.00). The colour change was significant due to ageing ( p ¼ 0.00) and the interaction between the factors evaluated (p ¼ 0.00). The microstructural analyses have shown that ageing methods and pigmentations did not cause structural alterations. The results suggest that the alterations in hardness and colour do not represent important structural changes.
Dfferential scanning calorimetry, fourier transform infrared spectroscopy, maxillofacial prostheses, thermogravimetry
1. Introduction Maxillofacial deformities can profoundly affect quality-of-life due to functional, social and psychological impairments [1,2]. Despite medical advances and plastic surgery, the attempt to recover lost or altered functional and aesthetics aspects due to trauma, birth defects or onco-surgery is still performed by maxillofacial prostheses, mainly because of the extent of these lesions and radiotherapy treatments [3]. Different materials have been used in the past for the fabrication of maxillofacial prostheses, including wood, ivory, wax and metals [4], and the most commonly used currently are heat polymerized acrylic resins and silicones [5]. Although resin has excellent properties [6], the main advantage of silicones regards a better simulation of the tissues lost, as they follow muscle contraction movements and have similar facial skin texture [3,7]. In addition to this, as it is a rubber material, it could contribute to the comfort, fit and quality-of-life improvements for patients [1,2] Surface hardness is an attribute directly related to these materials [2,3], which can be altered by temperature and humidity depending on the environmental conditions the prostheses are exposed to and by the addition of pigments in order to obtain adequate colouring to blend with the skin colour [2,3,8].
*Corresponding author. Email: [email protected]
History Received 22 July 2013 Revised 6 November 2013 Accepted 6 November 2013
Also, accurately correlating facial prosthesis to the patient’s skin has been a challenge to prosthetic manufacturers [9], leading to various studies found in the literature that evaluate colour stability [8,10,11], which is very important given that the ultimate aesthetic result and the prostheses’ colour stability are among the most significant factors in terms of clinical success or failure of the facial prostheses. However, there is limited literature concerning the physicochemical properties of the wide range of maxillofacial silicones used in clinical practice. There are several studies in the literature that evaluate different materials after ageing and pigmentation [1,2,8]; however, their results do not suggest structural alterations in these materials when they do not achieve satisfactory performance. Thermal analyses are very important as they provide an association among the composition, physical properties and structural characteristics of the materials, thereby provide valuable information on the occurrence of degradation in the structure of these materials [12–16] when subjected to various treatments, which could contribute to modifications of existing materials and to the development of new ones and ensure greater safety in clinical indication of new materials. These analyses can be defined as a group of techniques which evaluate the thermal characteristics of polymers under a controlled temperature programme [17]. The changes in the properties of the sample during the heating process can be monitored using this analysis. These measurements are shown thermal analysis curves, and thermal events in the sample are
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Juliana Barchelli Pinheiro, Andre´a Caˆndido Reis, Marina Xavier Pisani, Vanessa Maria Fagundes Leite, Raphael Freitas Souza, Helena Freitas Oliveira Paranhos, and Silva-Lovato Cla´udia Helena*
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Table 1. Materials used in this study. Material
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Experimental silicone Silicone MDX 4-4210 (gold standard) Makeup powder – intrinsic pigmentation (Colour 07) Makeup powder – extrinsic pigmentation (Colour 01)
Manufacturer
City/State/Country
Ortho Pauher Ind. Com. e Dist. Ltda. Dow Corning do Brasil Ltda. Marchetti Cosme´ticos Ltda Koloss Cosme´ticos Ltda – ME
Sa˜o Paulo/SP/Brazil Sa˜o Paulo/SP/Brazil Carazinho/RS/Brazil Jau´/SP/Brazil
related to the trends of these curves [17,18]. Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy and Thermogravimetry (TGA) are three wellknown analytical methods for evaluating the thermal characteristics of polymers [17,18]. Therefore, this in vitro study investigated the physical, mechanical and thermal properties as an experimental material with potential use in Maxillofacial Prosthodontics after ageing and pigmentation, comparing it with a standard silicone as a control. The response variables were the surface hardness, colour change and microstructural characteristics.
2. Materials and methods Table 1 shows the materials used in this study. 2.1. Preparation of specimens One hundred and sixty disk-shaped specimens were fabricated (16 mm diameter 3 mm thick) from a pre-fabricated plex glass matrix (Plex Glass, polymethylmethacrylate, Day SA Brazil, Ribeirao Preto, Brazil). All specimens received intrinsic pigmentation with makeup powder. The pigment was weighed in an analytical balance for accuracy (Metler Toledo GmbH, Laboratory and Weighing Technologies, Greifensee, Switzerland) and incorporated into the silicone in the ratio of 2:100 [19]. The mass was vacuum spatulate (Turbomix, EDG, Sa˜o Bernardo do Campo, Sa˜o Paulo, Brazil) to prevent the incorporation of bubbles and the mixture was then taken to the respective matrices. The silicone polymerization was performed in a stove (Odontobra´s Trade and Ind. Equip. Odont Med. Ltda, EL-11, Ribeira˜o Preto, Sa˜o Paulo, Brazil) for 30 min, at 100 C for the MDX 4-4210 and 50 C for the experimental silicone, according to the manufacturer’s instructions. After polymerization, half of the sample (n ¼ 80) received a uniform layer of the silicone for extrinsic pigmentation (EP group), which was realized with 20 g of silicone mix with 2 g of pigment [19]. This mixture was performed with a brush (Kolibri Flat brush, size 06, Feure Sohn, Germany) over one of the surfaces of the specimens and placed again in the oven following the aforementioned protocol. After polymerization, each specimen was carefully separated from the matrix, the excesses were removed with a scalpel and the dimensions were checked with a digital caliper (CD-6-B CSX, Mitutoyo Corporation Ltda. Suzano, Sa˜o Paulo, Brazil). A total of 160 specimens were fabricated due to the factors of variation and combination, namely 2 materials 2 pigmentations 4 ageing methods 10 repetitions.
Batch number 1002/05302 5324394 020309 01-L: 014
2.2. Groups Each pigmentation group (IP, n ¼ 80; EP, n ¼ 80) was randomly distributed into four sub-groups according to the ageing methods: (1) Thermocycling ageing (T): 1000 cycles with temperature variation ranging between 5–55 C per minute in a testing machine MSCT-3 (accelerated ageing machine, MSCT-3, Sa˜o Carlos, Sa˜o Paulo, Brazil), simulating 1 year of use [20]. (2) Ageing by ultraviolet light (UV): maintain samples under ultraviolet-B (UV-lamp TL 40 W/12RS B medical, Phillips, The Netherlands, Amsterdam) in accelerated ageing camera (UV Cond, Comexim And Raw Materials Industry Commerce Ltda, Sa˜o Paulo, Sa˜o Paulo, Brazil), with 240 h of UV and 240 h of condensation at constant temperature of 50 C, simulating 1 year of use [21]. (3) Ageing by natural light (NL): maintain specimens in an open window sill 24 h a day, for 12 consecutive months [7]. (4) Control (C): maintain specimens in a sealed glass container and stored in the dark at room temperature for 12 consecutive months [7]. 2.3. Shore A hardness assay The Shore A hardness was used in order to verify the degree of softness of silicones. The hardness assay was conducted using a Shore A durometer (Instrument and Manufacturing Co Inc, Freeport, NY). This instrument consists of a bluntpointed indenter attached to a scale by lever arrangement with a recording scale from 0–100 Shore A units. The higher the indenter penetrates the specimen, the lower the hardness value is. Silicones with a Shore A hardness of less than 40 are considered very soft, while a hardness of between 40–60 Shore A units is considered as soft only. A 1-kg load for 5 s weight was centred over the indenter and the reading was taken immediately after the pressure foot was in firm contact with the soft liner surface. The formula for calculating the Shore A hardness is: F/E0 ¼ (0.038) (R0,65) (P1,65), where F ¼ penetration force in newtons; E0 ¼ Young modulus, in MPa; R ¼ radius of the spherical indenter, in millimetres; and P ¼ depth of penetration, in millimetres. Five measurements were conducted for each specimen before (Ti, baseline) and after (Tf) ageing. The means of the results were provided in units of Shore A and the variation (Tf – Ti) was considered in the statistical analysis. 2.4. Colour change assay The colour change assay was performed in a spectrophotometer (Color Eye 7000; Macbeth, Newburgh, NY), using the Color System Standart Commission Internationale de L
Polymeric materials for maxillofacial prosthetics
DOI: 10.3109/03091902.2013.864715
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Eclairage (CIE LAB), recommended by the American Dental Association. This system represents a three-dimensional space with colour components of clarity (L), red-green (a) and yellow-blue (b). An important aspect of the CIE-LAB system is that the colour difference between the times can be given using a parameter, DEab. The colour change in each sample, each given in terms of L, a and b, was performed immediately after obtaining the samples and after ageing processes and calculated by the following formula: DEab ¼ [(DL)2 þ (Da)2 þ (Db)2]. Measurements were conducted for each specimen before (Ti, baseline) and after (Tf) ageing. The variation (DE) was considered in the statistical analysis.
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2.5.3. Differential scanning calorimetry (DSC) DSC is a thermal analysis which aims to provide the glass transition temperature (Tg), which is fundamental in comprehension of the behaviour of polymeric materials when subjected to high temperatures [17]. DSC was carried out in order to determine the transition temperatures of the specimens using the equipment DSC 882 (Mettler-Toledo Ind. e Com., Barueri, Sa˜o Paulo, Brazil) and a heating rate of 20 C min1, under a dynamic atmosphere of nitrogen gas. The specimens were subjected to heating and cooling cycles ranging from 70 C to 150 C. The heat flow (Q) was recorded as a function of temperature and enthalpy variations (DH) were obtained [16,17].
2.5. Microstructural analysis
2.6. Data analysis
The thermal properties of the samples were determined by Thermogravimetric analysis (TG), Fourier Transform Infrared Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC). For each thermal analysis, a sample size of 4 mg (n ¼ 3) was used for each study group.
For data analysis, the hardness and colour change variations were calculated for each specimen. Confirmed normal (Shapiro-Wilk’s) and homogeneous (Levene’s test) distribution of the data, 3 way-ANOVA test was selected for the statistical analysis of the data. For significant effects, post-hoc tests were conducted using Tukey’s test (p50.05). The results of the microstructural analysis are shown in the tables and figures, for interpretation and discussion.
2.5.1. Thermogravimetric analysis (TG) Thermogravimetric analysis allows the measurement of the variation of a material as a function of temperature or time. Therefore, it is a system with a wide field application in the characterization of the thermal behaviour of materials [12]. The thermogravimetric curves (TG) and its derivatives as a function of temperature were obtained in a thermal analyser Q500 TGA (TA Instruments, 2000 Du Pont, New Castle, DE, USA) using a heating rate of 20 C min1. The sample was heated from room temperature (23 C) to 550 C in an N2 atmosphere. After reaching this temperature, the atmosphere used was oxygen (O2), with an average flow of 50 ml min1 to 850 C [12]. 2.5.2. Fourier transform infrared spectroscopy (FTIR) A Nexus 4700 FTIR spectrophotometer (Thermo Nicolet, Berkeley, CA) was used in this study. The samples were analysed using the accessory Thunder Dome and readings varied from 4000–400 cm1 with a resolution of 4 cm1. This technique consisted of focus electromagnetic radiation corresponding to the infrared range (4000–400 cm1) on the specimens’ surface. The energy associated with these wavelengths, once absorbed by the molecule, is converted into energy of molecular vibration–rotation, in order to identify the chemical groups present in the structure of materials [13–15].
3. Results 3.1. Shore A hardness Table 2 shows the values of Shore A hardness (results provided in Shore A units) of MDX 4-4210 and experimental silicone of the IP and EP groups, immediately after obtaining the specimens (Ti, baseline) and after the ageing methods (Tf). For the MDX 4-4210 silicone with intrinsic pigmentation (IP), the hardness decreased in control groups, thermocycling and natural light. In those with extrinsic pigmentation (EP), similar behaviour occurred in the control groups and thermocycling. For the experimental silicone, hardness decreased only in the specimens with IP after thermocycling. For other ageing methods, the material exhibited increased hardness. The hardness variation was calculated from the data of Table 2 and was used in the analysis of variance (Table 3). Significant differences were observed in the materials, pigmentation, ageing and their interactions (p50.05) (Table 4). Among the ageing methods (p ¼ 0.00), the natural light (NL ¼ 3.34 3.17) and ultraviolet light (UV ¼ 3.81 3.94) caused the highest variations in hardness compared with thermocycling (T ¼ 2.19 3.51). The experimental silicone (E ¼ 4.57 4.25) showed the greatest variations in hardness
Table 2. Mean (SD) Shore A hardness (results provided in Shore A units) of MDX 4-4210 and experimental silicone of IP and EP groups, immediately after obtaining the specimens (Ti) and after ageing (Tf). Control
Thermocycling
UV
Natural light
Ti
Tf
Ti
Tf
Ti
Tf
Ti
Tf
MDX 4-4210
IP EP
41.02 1.99 36.4 2.04
38.78 0.90 28.8 1.35
39.98 1.94 30.84 1.84
36.52 1.47 25.08 1.27
42.74 1.90 29.1 2.56
44.36 2.47 33.12 2.08
43.14 2.10 37.08 2.06
42.66 1.30 42 1.00
Experimental
IP EP
23.2 1.74 20.04 1.54
31.88 1.05 28.96 1.36
23.38 2.39 21.52 1.32
23.04 1.75 22.32 1.24
29.62 2.05 24.76 1.32
30.88 3.30 33.12 1.97
23.46 1.84 21.5 2.41
28.3 0.97 25.58 1.22
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compared with the MDX 4-4210 (M ¼ 1.12 4.80; p ¼ 0.00), as an EP (EP ¼ 2.21 6.12) and IP (IP ¼ 1.23 4.42; p ¼ 0.005). For the MDX 4-4210 silicone with intrinsic pigmentation, the greatest variation in hardness was promoted by thermocycling and the lowest for NL. When pigmented extrinsically, the material presented higher hardness variation when kept in the dark (control) and lower when subjected to thermocycling and UV light. The experimental silicone with intrinsic pigmentation showed higher hardness variation in the control group and decreased after UV light, whereas, with EP, the highest alteration occurred in control and UV and the lowest after thermocycling. For the pigmentation factor, the intrinsic pigmentation promoted a difference between the material as a function of control, thermal cycling and natural light, while the extrinsic pigmentation promoted difference between the materials in the control group, thermocycling and ultraviolet light.
and UV light (p ¼ 0.004). For the intrinsically pigmented experimental material, the greatest change was due to the UV light and, for the EP group, it was due to thermal cycling and ultraviolet light. Comparing the materials of the PI group, the experiment was different from MDX 4-4210 only after ageing by UV and, in the EP group, after thermocycling and UV light (p ¼ 0.000). 3.3. Microstructural analysis 3.3.1. Thermogravimetric analysis (TG) Table 7 shows the results of thermogravimetric analysis (TG). Since the amount of residue remaining at the end of the test is related to the amount of inorganic matter present in the sample polymer [12], Table 7 indicates that both materials evaluated had a large quantity of inorganic compounds. It can also be noted that silicone MDX 4-4210 presents no initial decomposition peak, demonstrating stable behaviour at high temperatures.
3.2. Colour change Analysis of variance (Table 5) showed significant differences between ageing and their interactions (p50.05). There was a significant colour change difference between the materials (E ¼ 1.4 0.8; M ¼ 1.23 1.6) and pigmentation (IP ¼ 1.3 0.6; IEP ¼ 1.4 0.8). For ageing, UV light (UV ¼ 1.7 1.3) and control (C ¼ 1.2 0.5) were significantly different. There was no difference between UV light and other ageing processes (T ¼ 1.3 1.9; NL ¼ 1.3 0.5). For the interaction between factors (Table 6), for the MDX 4-4210 silicone in the IP group, there was no colour change resulting from any of the ageing processes, while, in the EP group, the major changes were promoted by thermocycling Table 3. Analysis of variance.
Source Material (M) Pigment (P) Ageing (A) A*P M*T P*T M*P*T Error Total
3.3.2. Fourier transform infrared spectroscopy (FTIR) Figures 1 and 2 and Table 8 show the results obtained from the Fourier transform infrared (FTIR) spectroscopy. The similarity between the peaks of silicones evaluated were observed when compared with the standard material (polydimethylsiloxane, represented on the last figure spectrum), and the absence of formation of new peaks, indicating that the different ageing pigmentations did not promote the formation of new products in the silicone compositions, hence without the degradation of the product. The result also shows that the polymerization reaction of both silicones was complete [13–15]. Table 5. Analysis of variance.
Type III sum of squares
df
1298.460 38.612 893.991 35.910 907.957 309.737 222.163 846.740 5030.360
1 1 3 1 3 3 3 144 160
Mean square 1298.460 38.612 297.997 35.910 302.652 103.246 74.054 5.880
F
Sig.
220.821 6.567 50.679 6.107 51.470 17.558 12.594
0.000* 0.011* 0.000* 0.015 0.000 0.000 0.000*
*Significant difference.
Source Material (M) Pigment (P) Ageing (A) A*P M*T P*T M*P*T Error Total
Type III sum of squares
df
Mean square
0.002 1.771 6.744 35.414 11.512 5.954 9.900 65.561 420.598
1 1 3 1 3 3 2 135 150
0.002 1.771 2.248 35.414 3.837 1.985 4.950 0.486
F
Sig.
0.003 3.647 4.629 72.924 7.902 4.086 10.193
0.955 0.058 0.004* 0.000 0.000 0.008 0.000*
*Significant difference.
Table 4. Comparison of means (SD) of the hardness variation (results provided in Shore A units) for the interaction between the factors evaluated. IP
EP
C
T
UV
MDX 4-4210
2.24 1.9 Aag
3.46 0.47 Aag
1.62 0.57 Bag
Experimental
7.6 0.7 Abg
5.76 0.6 Bbg
4.02 0.5 Cag
NL 0.48 0.8 Bag 4.92 1.06 Bbg
C
T
UV
NL
8.68 0.7 Aa
0.34 0.64 Ca
1.26 1.25 Ca
4.84 0.87 Ba
8.9 0.2 Cag
0.8 0.08 Ab^
8.36 0.65 Cb
4.08 1.19 Bag
Equal letters ¼ statistical equality. Capitalized letters: comparison between columns of the same block. Lowercase: comparison between lines. Symbol: comparison between columns of different blocks. Negative sign indicates decreased hardness.
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Table 6. Comparison of means (SD) of colour change (DE) for the interaction between the factors evaluated. PI
PIE
C
T
UV
NL
C
T
UV
NL
MDX 4-4210
0.783 0.29 Aa
0.895 0.76 Aa
0.291 0.12 Aa
0.922 0.30 Aa
1.322 0.41 Aa
2.525 1.25 BA
2.524 1.38 BA
1.324 0.20 Aa
Experimental
1.07 0.53 Aa
0.91 0.62 Aa
1.36 1.35 Bb
1.32 0.68 Aa
1.18 0.48 Aa
1.62 1.26 Bb
1.88 1.15 Bb
1.20 0.37 Aa
Equal letters ¼ statistical equality. Capitalized letters: comparison between columns of the same block. Lowercase: comparison between lines. Symbol: comparison between columns of different blocks.
Table 7. Results of thermogravimetric analysis. % Decomposed material Pick of decomposition
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Material M C IP M C EP M T IP M T EP M UV IP M UV EP M NL IP M NL EP E C IP E C EP E T IP E T EP E UV IP E UV EP E NL IP E NL EP
1a loss 9.72% 10.00% 8.75% 9.96% 10.02% 9.01% 9.10% 8.83% 20.00% 20.18% 21.79% 21.31% 24.96% 22.23% 23.63% 20.22%
2a loss 36.78% 37.48% 23.81% 33.30% 22.53% 29.81% 14.30% 14.25% 11.36% 11.51% 12.44% 12.35% 10.10% 12.11% 8.35% 11.09%
1a loss – – – – – – – – 421 C 420 C 434 C 429 C 428 C 431 C 420 C 431 C
2a loss
556 C 558 C 558 C 558 C 558 C 559 C 562 C 563 C 563 C 562 C 560 C 564 C 562 C 562 C 565 C 562 C
Residue (%) 53.50% 52.55% 67.49% 56.76% 67.49% 61.18% 76.56% 76.94% 68.68% 68.35% 65.82% 66.39% 65.00% 65.67% 68.00% 68.71%
M, MDX 4-4210; E, experimental; C, control; T, thermocycling; UV, ultraviolet light; NL, natural light; IP, intrinsic pigmentation; EP, extrinsic pigmentation.
3.3.3. Differential scanning calorimetry (DSC) The results of Differential Scanning Calorimetry assay (Figure 3) indicated that the extrinsically pigmented (EP) samples showed higher melting enthalpy (DH). High values of melting enthalpy are directly related to the presence of crosslinks in polymers, which are indicative of stability [16].
4. Discussion Understanding the mechanical, physical and thermal properties of materials is essential for the correct selection and clinical indication. Although maxillofacial rehabilitation materials have evolved in recent years, they still exhibit alterations influenced by time and pigmentation [2,3,8]. Moreover, the commercial options regarding these materials are still limited and expensive. The two silicones evaluated showed hardness changes. Similarly, Pesqueira et al. [9] found hardness changes in the maxillofacial silicones when they were subjected to accelerated ageing and pigmentation; however, despite the alterations, the surface hardness values were satisfactory. In this present study, silicone MDX 4-4210 showed changes ranging from 25.08–44.36 Shore A units (Table 2) of hardness and the experimental silicone showed a variation of 20.04–33.12 (Table 2), which can be considered acceptable hardness values [2,22], thus enabling its clinical indication based on
hardness. In addition, the hardness values found in silicones evaluated allowed classifies them as very soft, which is a very significant finding because it allows prosthesis made from both materials accompanying facial movements during speech, chewing and other functional movements [1]. The increased hardness of the silicone can promote change of the edges of the prosthesis, and the consequent mismatch with the peripheral tissue of the lesion. Additionally, there is decreased muscle movement, aesthetics and acceptance by patients [1,2]. It was observed that, in general, the experimental silicone presented lower hardness values than those of silicone MDX 4-4210. These differences could be a result of different components used in the original formulation and/or due to differences in the cross-linking system of each polymer, differences in density, molecular weight and the degree of concentration of silicones [23]. These characteristics, associated with ageing, leading to the formation of free radicals, which react with oxygen and the formation of secondary polymer radicals, promote chain scission and consequently polymeric chain cross-linking [23], which could undermine the penetration tip of the durometer Shore A. Regarding the pigmentation, the highest hardness variation in the EP group may have occurred because this group underwent dual polymerization, which could alter the polymeric chain of the materials. The continuous polymerization process could favour the formation of a more complex polymer chain, making the surface of the material less susceptible to penetration tip of the durometer Shore A [24]. A lower density of cross-links between the polymer chains is indicative of shorter distance between these cross-links, which makes the material more rigid and resistant to penetration [23]. Furthermore, the high-temperature polymerized silicones exhibit excellent thermal stability and superior mechanical properties when compared with the polymerized ones at room temperature [2,3,23]. In general, the highest mean variation with increasing hardness occurred when the materials were subjected to ageing by ultraviolet light and natural light. According to Rabek [25], photo exposure causes deterioration in the physical, chemical and mechanical properties of the materials due to the formation of free radicals, resulting in chain scission of the polymers which, in turn, leads to changes in properties. Specifically for silicone MDX4-4210 with intrinsic and extrinsic pigmentation, the greatest hardness variation was promoted by thermocycling. In this process, the specimens were submitted to long periods of immersion in distilled water with variations in temperature between 5–55 C [20,23],
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1 2 3 4
5
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Wavenumber (cm−1)
Figure 1. Infrared absorption spectra of the analysed sample. Curve 1: Absorption spectra of the experimental silicone, EP Group - T; Curve 2: Absorption spectra of the experimental silicone, IP Group - NL; Curve 3: Absorption spectra of the silicone experimental, EP Group - NL; Curve 4: Absorption spectra of the silicone MDX 4-4210, IP Group - NL; Curve 5: silicone standard used for comparison.
Figure 2. Curve 2: Absorption spectra of the experimental silicone, IP Group – NL.
Table 8. Identification of the chemical grouping, according to the number of the peak and wave number of the peak, relative to Figure 2. Peak 1 2 3 4 5 6
Wave number of the peak (cm1) 2962, 2906 1412 1259 1081, 1016 794 699
Chemical grouping –CH3 Si–CH3 –Si(CH3)–O– –Si–O– Si–CH3 Si–C
which may cause water sorption and hardness alteration of the silicone. For the intrinsically pigmented experimental silicone, the greatest hardness variation occurred after ageing for natural light, while, for EP, the greatest variation occurred with UV light. The incidence of light, heat and humidity are important factors that can change the hardness of the material, since it promotes the separation of the main polymer chain
and contributes to the production of volatile degradation products [24]. Evaluation of colour change is important as it is one of the most limiting aspects regarding treatment with facial prostheses. According to Villalta et al. [26], the silicones undergo colour change with ageing and this change may be caused by intrinsic and extrinsic factors. The intrinsic factors include discolouration of the material [26], which includes changes in its polymer matrix, while the extrinsic factors may be related to the absorption of substances, for example, water during the thermocycling test and/or also the thermal and humidity changes [24,27], as in the UV ageing and NL test. The results of this study indicated that the specimens subjected to ageing by thermal cycling, UV light and natural light underwent greater colour change when compared with the specimens of the control group, which suggests that the ageing methods interfered in the material’s colour stability.
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PI O LN PI PE
LN O
VP IP E U
VP I
O
U O
O TP I
O TP IP E
O
C
PI PE
PI C O
PI PE
PI
M LN
M LN
VP IP E
VP I M U
M TP I
PI PE
M TP IP E
M U
−20
M C
M
C
−10
PI
0
−30 −40 −50 −60 Fusion Temperature (°C)
Fusion enthalpy (J/g)
−70
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Figure 3. Results of differential scanning calorimetry. M, MDX 4-4210; E, experimental; C, control; T, thermocycling; UV, ultraviolet light; NL, natural light; IP, intrinsic pigmentation; EP, extrinsic pigmentation.
The experimental silicone underwent IP and EP pigmentation influence as a function of ageing processes by thermocycling and ultraviolet light. This material is commonly used in medical orthopaedic rehabilitations that do not require pigmenting agents and this could explain the colour changes and also suggest the need for modifying its original formulation to withstand the staining procedures and exposure to inherent environmental conditions, such as changes in temperature, humidity and ultraviolet rays. The association of intrinsic and extrinsic pigmentation promoted greater colour change in silicon MDX4-4210, suggesting that the pigment types negatively affect the colour stability of silicones. Furthermore, the extrinsic pigment layer is located externally to the specimen, thereby more susceptible to changes for being more exposed to the environment. The use of makeup powder as pigment can promote greater colour changes when its composition has large-size organic particles [2,3,24]. Small pigment particles tend to aggregate, while the bigger ones are separated from the main polymer chain [24]. According to Goiato et al. [1], small but continuous release of sub-products during the polymerization of silicones, associated with factors such as material surface roughness, water absorption during the ageing processes, stain accumulation, dehydration, oxidation during double carbon reactions to produce peroxide compounds, infiltration of fluids and chemical degradation also interfere with colour characteristics. It should be noted that, although both silicones displayed colour changes after ageing, these may be clinically acceptable in all groups studied, since they were less than or equal to 3.3 [28]. Polyzois [5] reported that the exposure of maxillofacial silicones in the environment for a 1-year period resulted in visually detectable colour changes (DE43.3), which does not corroborate our results. Although studies agree that varying degrees of clinically observable colour changes in silicone prostheses are caused by weathering or ageing, it is difficult to compare and identify the most degrading factor, since the methodologies vary in terms of the pigments used, the experimental protocols, the silicone type tested and climatic conditions for the ageing process in the natural environment. Thus, further studies are required to investigate the improvement of colour stability for the clinical
application, possibility so as not to compromise the aesthetics of the prosthesis. Thermal stability is a general term used to describe the potential changes of a material and it has a significant implication as far as polymer fabrication processes are concerned [29–31]. The thermogravimetry showed that silicone MDX4-4210 exhibited mass loss and low constant from the initial heating up to the approximate temperature of 560 C (Table 7). This feature is observed for materials with large amounts of crosslinks in the polymer chain and contributes to the material’s stability [12]. As the experimental material underwent greater weight loss at lower temperatures (Table 7), the addition of inorganic additives could be suggested in order to prevent oxidation of the material and increase its durability and stability. Thermogravimetry indicated that the samples pigmented extrinsically had larger amounts of residue, suggesting that the pigments added to the sample behaved as inorganic compounds fully integrating with the material during handling and polymerizing, showing a highly favourable result. In Fourier Transform Infrared Spectroscopy (FTIR) the samples were compared to a standard polymethylsiloxane and a number of peaks exhibited similar characteristics (Figures 1 and 2 and Table 8). This result suggests that no new components or by-products were formed by double-change or addition reactions after the different pigmentations, ageing and immersion in water for prolonged periods, indicating that the polymerization reaction of the materials was complete [13–15]. The test also showed that both silicones studied have similar chemical groups, even if they present different forms and viscosity in clinical practice, and also that they are stable and their unique thermal formulation properties are satisfactory. The Differential Scanning Calorimetry (DSC) confirmed the effectiveness of the silicones reaction through its melting enthalpy values, which corroborates the data verified by FTIR. The crystallinity of a polymer sample is directly related to the amount of cross-linked polymer it has. Thus, the greater the crystallinity of the polymer, the higher the stability of the mechanical properties [16]. The aspect responsible for the crystallinity of a polymer sample is the enthalpy of fusion, where higher temperatures indicate higher crystallinity and,
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therefore, better performance of the material, in addition to the efficiency of the polymerization process [16] When the silicones were extrinsically pigmented, the melting enthalpy values were higher (Figure 2), suggesting increased stability of the samples pigmented in this manner. Since the DSC test demonstrates the degradation temperature of the sample, correlating it with possible chemical structural changes [16], it is observed that the silicones were influenced by both the pigmentation and ageing methods; however, none of these processes promoted microstructural changes. When a material is heated in an inert atmosphere, as was done in this study for tests of Thermogravimetry (TG), Fourier Transform Infrared Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC), the increase in molecular motion or atomic ion can lead to changes in the crystalline structure of the material evaluated, which can decompose and form new fragments of molecules. When more than one substance is present (in this case, makeup powder and water during thermal cycling tests and accelerated ageing by ultraviolet light), there are even more possibilities for interaction by heating and the formation of new compounds for addition reactions and double replacement. These reactions are accompanied by changes in enthalpy (as measured in Differential Scanning Calorimetry) and, in some cases, change of mass (measured as the thermogravimetry). Accordingly, the realization of such thermal analysis was very important, because it was possible that the silicones tested suffered no structural changes after incorporation of pigments and ageing for long periods [32,33].
5. Conclusion Within the limitations of present in vitro study, although the experimental silicone showed greater hardness and colour changes, the microstructural analysis showed that it has stable thermal properties. However, considering that mechanical and physical properties were evaluated under controlled laboratory conditions, the performance of the experimental material should be clinically evaluated before it can be considered an option for maxillofacial rehabilitation.
Acknowledgements This investigation was supported by the State of Sa˜o Paulo Research Foundation (FAPESP), Brazil (Grant number 2010/ 50787-9).
Declaration of interest The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.
References 1. Goiato, M.C., Pesqueira, A.A., Dos Santos, D.M., and Dekon, S.F.C., 2009, Evaluation of hardness and surface roughness of two maxillofacial silicones following disinfection. Brazilian Oral Research, 23, 49–53. 2. Goiato, M.C., Pesqueira, A.A., Silva, C.R., Gennari-Filho, H., and Dos Santos, D.M., 2009, Patient satisfaction with maxillofacial prosthesis: Literature review. Journal of Plastic, Reconstructive & Aesthetic Surgery, 62, 175–180.
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3. Guiotti, A.M., Goiato, M.C., and Dos Santos, D.M., 2010, Evaluation of the Shore A hardness a silicone for facial prosthesis as to the effect of storage period and chemical disinfection. Journal of Craniofacical Surgery, 21, 323–327. 4. Haug, S.P., Andres, C.J., Munoz, C.A., and Bernal, G., 1992, Effects of environmental factors on maxillofacial elastomers part IV - optical properties. Journal of Prosthetic Dentistry, 68, 820–823. 5. Polyzois, G.L., 1999, Color stability of facial silicone prosthetic polymers after outdoor weathing. Journal of Prosthetic Dentistry, 82, 447–450. 6. Polyzois, G.L., Tarantili, P.A., Frangou, M.J., and Andreopoulos, A.G., 2001, Fracture force, deflection at fracture, and toughness of repaired denture resin subjected to microwave polymerization or reinforced with wire or glass fiber. Journal of Prosthetic Dentistry, 86, 613–619. 7. Hatamleh, M.M., Polyzois, G.L., Silikas, N., and Watts, D.C., 2011, Effect of extraoral aging conditions on mechanical properties of Maxillofacial Silicone Elastomer. Journal of Prosthodontics, 20, 439–446. 8. Kiat-Amnuay, S., Mekayarajjananonth, T., Powers, J.M., Chambers, M.S., and Lemon, J.C., 2006, Interactions of pigments and opacifiers on color stability of MDX4-4210/type A maxillofacial elastomers subjected to artificial aging. Journal of Prosthetic Dentistry, 95, 249–257. 9. Pesqueira, A.A., Goiato, M.C., Dos Santos, D.M., Haddad, M.F., Ribeiro, P.P., Sinhoreti, M.A.C., and Sundefeld, M.L., 2011, Effect of disinfection and accelerated aging on color stability of colorless and pigmented facial silicone. Journal of Prosthodontics, 20, 305–309. 10. Mancuso, D.N., Goiato, M.C., Dekon, S.F., and Gennari-Filho, H., 2009, Visual evaluation of color stability after accelerated aging of pigmented and nonpigmented silicones to be used in facial prostheses. Indian Journal of Dental Research, 20, 77–80. 11. Aziz, T., Waters, M., and Jagger, R., 2003, Development of a new poly(dimethysiloxane) maxillofacial prosthetic material. Journal of Biomedical Materials Research Part B Applied Biomaterials, 5, 252–261. 12. Nam, K.Y., Lee, C.H., and Lee, C.J., 2012, Antifungal and physical characteristics of modified denture base acrylic incorporated with silver nanoparticles. Gerodontology, 29, E413–E419. 13. Kontonasaki, E., Kantiranis, N., Papadopoulou, L., Chatzistavrou, X., Kavouras, P., Zorba, T., Sivropoulou, A., Chrissafis, K., Paraskevopoulos, K.M., and Koidis, P.T., 2008, Microstructural characterization and comparative evaluation of physical, mechanical and biological properties of three ceramics for metal-ceramic restorations. Dental Materials, 24, 1362–1373. 14. Lewis, R.N., and McElhaney, R.N., 2013, Membrane lipid phase transitions and phase organization studied by Fourier transform infrared spectroscopy. Biochimica et Biophysica Acta, 1828, 2347–2358. 15. Faria-e-Silva, A.L., Piva, E., Lima, G.S., Boaro, L.C., Braga, R.R., and Martins, L.R., 2012, Effect of immediate and delayed light activation on the mechanical properties and degree of conversion in dual-cured resin cements. Journal of Oral Science, 54, 261–266. 16. Laino, G., De Santis, R., Gloria, A., Russo, T., Quintanilla, D.S., Laino, A., Martina, R., Nicolais, L., and Ambrosio, L., 2012, Calorimetric and thermomechanical properties of titanium-based orthodontic wires: DSC–DMA relationship to predict the elastic modulus. Journal of Biomaterials Applications, 26, 829–844. 17. Aydogan Ayaz, E., Durkan, R., and Bagis, B., 2013, The effect of acrylamide incorporation on the thermal and physical properties of denture resins. Journal of Advanced Prosthodontics, 5, 110–117. 18. Aouachria, K., and Bensemra, N.B., 2006, Miscibility of PVC/ PMMA blends by vicat softening temperature, viscometry, DSC and FTIR analysis. Polymer Testing, 25, 1101–1108. 19. Yu, R., Koran, A., and Craig, R.G., 1980, Physical properties of maxillofacial elastomers under conditions of accelerated aging. Journal of Dental Research, 59, 1041–1047. 20. Abu-Baker, R., Han, L., Okamoto, A., and Iwaker, M., 2000, Color stability of compomer after immersion in various media. Journal of Esthetic Dentistry, 12, 258–263. 21. Tran, N.H., Scarbecz, M., and Gary, J.J., 2004, In vitro evaluation of color change in maxillofacial elastomer through the use of an ultraviolet light absorber and a hidered amine light stabilizer. Journal of Prosthetic Dentistry, 91, 483–490.
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22. Polyzois, G.L., Tarantili, P.A., Frangou, M.J., and Andreopoulos, A.G., 2000, Physical properties of a silicone prosthetic elastomer stored in simulated skin secretions. Journal of Prosthetic Dentistry, 83, 572–577. 23. Mancuso, D.N., Goiato, M.C., and Santos, D.M., 2009, Color stability after accelerated aging of two silicones, pigmented or not, for use in facial prostheses. Brazilian Oral Research, 23, 144–148. 24. Seluk, L.W., Yu, R., and Koran, A., 1987, Stability of ceramic pigments for maxillofacial applications. Journal of Oral Rehabilitation, 14, 309–313. 25. Rabek, J.F., 1995, Polymer photodegradation: Mechanisms and experimental. (New York: Chapman and Hall). pp. 4–5. 26. Villalta, P., Lu, H., Okte, Z., Garcia-Godoy, F., and Powers, J.M., 2006, Effects of staining and bleaching on color change of dental composite resin. Journal of Prosthetic Dentistry, 95, 137–142. 27. Wilson, N.H., Burke, F.J., and Mjor, J.A., 1997, Reasons for placement and replacement of restorations of direct restorative
28. 29. 30. 31. 32. 33.
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materials, by a selected group of practitioners in the United Kingdom. Quintessence International, 28, 245–248. Takamata, T., Moore, B.K., and Chalian, V.A., 1989, Evaluation of color changes of silicone maxillofacial materials after exposure to sunlight. Dental Materials Journal, 8, 260–270. Mutlu-Sagesen, L., Ergun, G., Ozkan, Y., and Semiz, M., 2005, Color stability of a dental composite after immersion in various media. Dental Materials Journal, 24, 382–390. Davy, K.W., Anseau, M.R., and Berry, C., 1997, Iodinate methacrylate copolymers as X-ray opaque denture base acrylics. Journal of Dentistry, 25, 499–505. Nam, K.Y., Lee, C.H., and Lee, C.J., 2012, Antifungal and physical characteristics of modified denture base acrylic incorporated with silver nanoparticles. Gerodontology, 29, e413–e419. Pope, M.I., 1980, Differential thermal Analysis: A guide to the technique and its applications. (London, Philadelphia, PA: Heyden). Turi, A., 1981, Thermal characterization of polymeric materials. (New Jersey: Academic Press).
INNOVATION
Microstructural characterization and evaluation of the properties of polymeric materials for maxillofacial prosthetics
Department of Dental Materials and Prosthodontics, Ribeira˜o Preto Dental School, University of Sa˜o Paulo, Ribeirao Preto, Brazil
Abstract
Keywords
This study evaluated the Shore A hardness, colour and microstructural alterations of an experimental silicone for maxillofacial prostheses. As a control, the MDX 4-4210 silicone was used. Eighty specimens of each material were randomly divided into groups of pigmentation and ageing. For microstructural analysis by Thermogravimetry, Fourier Transform Infrared Spectroscopy and Differential Scanning Calorimetry, three specimens of each group were used. Anova and Tukey test (p50.05) was used in statistical analysis. There was significant difference in hardness depending on the materials, pigmentation and ageing and interaction between all the factors evaluated (p ¼ 0.00). The colour change was significant due to ageing ( p ¼ 0.00) and the interaction between the factors evaluated (p ¼ 0.00). The microstructural analyses have shown that ageing methods and pigmentations did not cause structural alterations. The results suggest that the alterations in hardness and colour do not represent important structural changes.
Dfferential scanning calorimetry, fourier transform infrared spectroscopy, maxillofacial prostheses, thermogravimetry
1. Introduction Maxillofacial deformities can profoundly affect quality-of-life due to functional, social and psychological impairments [1,2]. Despite medical advances and plastic surgery, the attempt to recover lost or altered functional and aesthetics aspects due to trauma, birth defects or onco-surgery is still performed by maxillofacial prostheses, mainly because of the extent of these lesions and radiotherapy treatments [3]. Different materials have been used in the past for the fabrication of maxillofacial prostheses, including wood, ivory, wax and metals [4], and the most commonly used currently are heat polymerized acrylic resins and silicones [5]. Although resin has excellent properties [6], the main advantage of silicones regards a better simulation of the tissues lost, as they follow muscle contraction movements and have similar facial skin texture [3,7]. In addition to this, as it is a rubber material, it could contribute to the comfort, fit and quality-of-life improvements for patients [1,2] Surface hardness is an attribute directly related to these materials [2,3], which can be altered by temperature and humidity depending on the environmental conditions the prostheses are exposed to and by the addition of pigments in order to obtain adequate colouring to blend with the skin colour [2,3,8].
*Corresponding author. Email: [email protected]
History Received 22 July 2013 Revised 6 November 2013 Accepted 6 November 2013
Also, accurately correlating facial prosthesis to the patient’s skin has been a challenge to prosthetic manufacturers [9], leading to various studies found in the literature that evaluate colour stability [8,10,11], which is very important given that the ultimate aesthetic result and the prostheses’ colour stability are among the most significant factors in terms of clinical success or failure of the facial prostheses. However, there is limited literature concerning the physicochemical properties of the wide range of maxillofacial silicones used in clinical practice. There are several studies in the literature that evaluate different materials after ageing and pigmentation [1,2,8]; however, their results do not suggest structural alterations in these materials when they do not achieve satisfactory performance. Thermal analyses are very important as they provide an association among the composition, physical properties and structural characteristics of the materials, thereby provide valuable information on the occurrence of degradation in the structure of these materials [12–16] when subjected to various treatments, which could contribute to modifications of existing materials and to the development of new ones and ensure greater safety in clinical indication of new materials. These analyses can be defined as a group of techniques which evaluate the thermal characteristics of polymers under a controlled temperature programme [17]. The changes in the properties of the sample during the heating process can be monitored using this analysis. These measurements are shown thermal analysis curves, and thermal events in the sample are
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Juliana Barchelli Pinheiro, Andre´a Caˆndido Reis, Marina Xavier Pisani, Vanessa Maria Fagundes Leite, Raphael Freitas Souza, Helena Freitas Oliveira Paranhos, and Silva-Lovato Cla´udia Helena*
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Table 1. Materials used in this study. Material
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Experimental silicone Silicone MDX 4-4210 (gold standard) Makeup powder – intrinsic pigmentation (Colour 07) Makeup powder – extrinsic pigmentation (Colour 01)
Manufacturer
City/State/Country
Ortho Pauher Ind. Com. e Dist. Ltda. Dow Corning do Brasil Ltda. Marchetti Cosme´ticos Ltda Koloss Cosme´ticos Ltda – ME
Sa˜o Paulo/SP/Brazil Sa˜o Paulo/SP/Brazil Carazinho/RS/Brazil Jau´/SP/Brazil
related to the trends of these curves [17,18]. Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy and Thermogravimetry (TGA) are three wellknown analytical methods for evaluating the thermal characteristics of polymers [17,18]. Therefore, this in vitro study investigated the physical, mechanical and thermal properties as an experimental material with potential use in Maxillofacial Prosthodontics after ageing and pigmentation, comparing it with a standard silicone as a control. The response variables were the surface hardness, colour change and microstructural characteristics.
2. Materials and methods Table 1 shows the materials used in this study. 2.1. Preparation of specimens One hundred and sixty disk-shaped specimens were fabricated (16 mm diameter 3 mm thick) from a pre-fabricated plex glass matrix (Plex Glass, polymethylmethacrylate, Day SA Brazil, Ribeirao Preto, Brazil). All specimens received intrinsic pigmentation with makeup powder. The pigment was weighed in an analytical balance for accuracy (Metler Toledo GmbH, Laboratory and Weighing Technologies, Greifensee, Switzerland) and incorporated into the silicone in the ratio of 2:100 [19]. The mass was vacuum spatulate (Turbomix, EDG, Sa˜o Bernardo do Campo, Sa˜o Paulo, Brazil) to prevent the incorporation of bubbles and the mixture was then taken to the respective matrices. The silicone polymerization was performed in a stove (Odontobra´s Trade and Ind. Equip. Odont Med. Ltda, EL-11, Ribeira˜o Preto, Sa˜o Paulo, Brazil) for 30 min, at 100 C for the MDX 4-4210 and 50 C for the experimental silicone, according to the manufacturer’s instructions. After polymerization, half of the sample (n ¼ 80) received a uniform layer of the silicone for extrinsic pigmentation (EP group), which was realized with 20 g of silicone mix with 2 g of pigment [19]. This mixture was performed with a brush (Kolibri Flat brush, size 06, Feure Sohn, Germany) over one of the surfaces of the specimens and placed again in the oven following the aforementioned protocol. After polymerization, each specimen was carefully separated from the matrix, the excesses were removed with a scalpel and the dimensions were checked with a digital caliper (CD-6-B CSX, Mitutoyo Corporation Ltda. Suzano, Sa˜o Paulo, Brazil). A total of 160 specimens were fabricated due to the factors of variation and combination, namely 2 materials 2 pigmentations 4 ageing methods 10 repetitions.
Batch number 1002/05302 5324394 020309 01-L: 014
2.2. Groups Each pigmentation group (IP, n ¼ 80; EP, n ¼ 80) was randomly distributed into four sub-groups according to the ageing methods: (1) Thermocycling ageing (T): 1000 cycles with temperature variation ranging between 5–55 C per minute in a testing machine MSCT-3 (accelerated ageing machine, MSCT-3, Sa˜o Carlos, Sa˜o Paulo, Brazil), simulating 1 year of use [20]. (2) Ageing by ultraviolet light (UV): maintain samples under ultraviolet-B (UV-lamp TL 40 W/12RS B medical, Phillips, The Netherlands, Amsterdam) in accelerated ageing camera (UV Cond, Comexim And Raw Materials Industry Commerce Ltda, Sa˜o Paulo, Sa˜o Paulo, Brazil), with 240 h of UV and 240 h of condensation at constant temperature of 50 C, simulating 1 year of use [21]. (3) Ageing by natural light (NL): maintain specimens in an open window sill 24 h a day, for 12 consecutive months [7]. (4) Control (C): maintain specimens in a sealed glass container and stored in the dark at room temperature for 12 consecutive months [7]. 2.3. Shore A hardness assay The Shore A hardness was used in order to verify the degree of softness of silicones. The hardness assay was conducted using a Shore A durometer (Instrument and Manufacturing Co Inc, Freeport, NY). This instrument consists of a bluntpointed indenter attached to a scale by lever arrangement with a recording scale from 0–100 Shore A units. The higher the indenter penetrates the specimen, the lower the hardness value is. Silicones with a Shore A hardness of less than 40 are considered very soft, while a hardness of between 40–60 Shore A units is considered as soft only. A 1-kg load for 5 s weight was centred over the indenter and the reading was taken immediately after the pressure foot was in firm contact with the soft liner surface. The formula for calculating the Shore A hardness is: F/E0 ¼ (0.038) (R0,65) (P1,65), where F ¼ penetration force in newtons; E0 ¼ Young modulus, in MPa; R ¼ radius of the spherical indenter, in millimetres; and P ¼ depth of penetration, in millimetres. Five measurements were conducted for each specimen before (Ti, baseline) and after (Tf) ageing. The means of the results were provided in units of Shore A and the variation (Tf – Ti) was considered in the statistical analysis. 2.4. Colour change assay The colour change assay was performed in a spectrophotometer (Color Eye 7000; Macbeth, Newburgh, NY), using the Color System Standart Commission Internationale de L
Polymeric materials for maxillofacial prosthetics
DOI: 10.3109/03091902.2013.864715
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Eclairage (CIE LAB), recommended by the American Dental Association. This system represents a three-dimensional space with colour components of clarity (L), red-green (a) and yellow-blue (b). An important aspect of the CIE-LAB system is that the colour difference between the times can be given using a parameter, DEab. The colour change in each sample, each given in terms of L, a and b, was performed immediately after obtaining the samples and after ageing processes and calculated by the following formula: DEab ¼ [(DL)2 þ (Da)2 þ (Db)2]. Measurements were conducted for each specimen before (Ti, baseline) and after (Tf) ageing. The variation (DE) was considered in the statistical analysis.
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2.5.3. Differential scanning calorimetry (DSC) DSC is a thermal analysis which aims to provide the glass transition temperature (Tg), which is fundamental in comprehension of the behaviour of polymeric materials when subjected to high temperatures [17]. DSC was carried out in order to determine the transition temperatures of the specimens using the equipment DSC 882 (Mettler-Toledo Ind. e Com., Barueri, Sa˜o Paulo, Brazil) and a heating rate of 20 C min1, under a dynamic atmosphere of nitrogen gas. The specimens were subjected to heating and cooling cycles ranging from 70 C to 150 C. The heat flow (Q) was recorded as a function of temperature and enthalpy variations (DH) were obtained [16,17].
2.5. Microstructural analysis
2.6. Data analysis
The thermal properties of the samples were determined by Thermogravimetric analysis (TG), Fourier Transform Infrared Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC). For each thermal analysis, a sample size of 4 mg (n ¼ 3) was used for each study group.
For data analysis, the hardness and colour change variations were calculated for each specimen. Confirmed normal (Shapiro-Wilk’s) and homogeneous (Levene’s test) distribution of the data, 3 way-ANOVA test was selected for the statistical analysis of the data. For significant effects, post-hoc tests were conducted using Tukey’s test (p50.05). The results of the microstructural analysis are shown in the tables and figures, for interpretation and discussion.
2.5.1. Thermogravimetric analysis (TG) Thermogravimetric analysis allows the measurement of the variation of a material as a function of temperature or time. Therefore, it is a system with a wide field application in the characterization of the thermal behaviour of materials [12]. The thermogravimetric curves (TG) and its derivatives as a function of temperature were obtained in a thermal analyser Q500 TGA (TA Instruments, 2000 Du Pont, New Castle, DE, USA) using a heating rate of 20 C min1. The sample was heated from room temperature (23 C) to 550 C in an N2 atmosphere. After reaching this temperature, the atmosphere used was oxygen (O2), with an average flow of 50 ml min1 to 850 C [12]. 2.5.2. Fourier transform infrared spectroscopy (FTIR) A Nexus 4700 FTIR spectrophotometer (Thermo Nicolet, Berkeley, CA) was used in this study. The samples were analysed using the accessory Thunder Dome and readings varied from 4000–400 cm1 with a resolution of 4 cm1. This technique consisted of focus electromagnetic radiation corresponding to the infrared range (4000–400 cm1) on the specimens’ surface. The energy associated with these wavelengths, once absorbed by the molecule, is converted into energy of molecular vibration–rotation, in order to identify the chemical groups present in the structure of materials [13–15].
3. Results 3.1. Shore A hardness Table 2 shows the values of Shore A hardness (results provided in Shore A units) of MDX 4-4210 and experimental silicone of the IP and EP groups, immediately after obtaining the specimens (Ti, baseline) and after the ageing methods (Tf). For the MDX 4-4210 silicone with intrinsic pigmentation (IP), the hardness decreased in control groups, thermocycling and natural light. In those with extrinsic pigmentation (EP), similar behaviour occurred in the control groups and thermocycling. For the experimental silicone, hardness decreased only in the specimens with IP after thermocycling. For other ageing methods, the material exhibited increased hardness. The hardness variation was calculated from the data of Table 2 and was used in the analysis of variance (Table 3). Significant differences were observed in the materials, pigmentation, ageing and their interactions (p50.05) (Table 4). Among the ageing methods (p ¼ 0.00), the natural light (NL ¼ 3.34 3.17) and ultraviolet light (UV ¼ 3.81 3.94) caused the highest variations in hardness compared with thermocycling (T ¼ 2.19 3.51). The experimental silicone (E ¼ 4.57 4.25) showed the greatest variations in hardness
Table 2. Mean (SD) Shore A hardness (results provided in Shore A units) of MDX 4-4210 and experimental silicone of IP and EP groups, immediately after obtaining the specimens (Ti) and after ageing (Tf). Control
Thermocycling
UV
Natural light
Ti
Tf
Ti
Tf
Ti
Tf
Ti
Tf
MDX 4-4210
IP EP
41.02 1.99 36.4 2.04
38.78 0.90 28.8 1.35
39.98 1.94 30.84 1.84
36.52 1.47 25.08 1.27
42.74 1.90 29.1 2.56
44.36 2.47 33.12 2.08
43.14 2.10 37.08 2.06
42.66 1.30 42 1.00
Experimental
IP EP
23.2 1.74 20.04 1.54
31.88 1.05 28.96 1.36
23.38 2.39 21.52 1.32
23.04 1.75 22.32 1.24
29.62 2.05 24.76 1.32
30.88 3.30 33.12 1.97
23.46 1.84 21.5 2.41
28.3 0.97 25.58 1.22
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compared with the MDX 4-4210 (M ¼ 1.12 4.80; p ¼ 0.00), as an EP (EP ¼ 2.21 6.12) and IP (IP ¼ 1.23 4.42; p ¼ 0.005). For the MDX 4-4210 silicone with intrinsic pigmentation, the greatest variation in hardness was promoted by thermocycling and the lowest for NL. When pigmented extrinsically, the material presented higher hardness variation when kept in the dark (control) and lower when subjected to thermocycling and UV light. The experimental silicone with intrinsic pigmentation showed higher hardness variation in the control group and decreased after UV light, whereas, with EP, the highest alteration occurred in control and UV and the lowest after thermocycling. For the pigmentation factor, the intrinsic pigmentation promoted a difference between the material as a function of control, thermal cycling and natural light, while the extrinsic pigmentation promoted difference between the materials in the control group, thermocycling and ultraviolet light.
and UV light (p ¼ 0.004). For the intrinsically pigmented experimental material, the greatest change was due to the UV light and, for the EP group, it was due to thermal cycling and ultraviolet light. Comparing the materials of the PI group, the experiment was different from MDX 4-4210 only after ageing by UV and, in the EP group, after thermocycling and UV light (p ¼ 0.000). 3.3. Microstructural analysis 3.3.1. Thermogravimetric analysis (TG) Table 7 shows the results of thermogravimetric analysis (TG). Since the amount of residue remaining at the end of the test is related to the amount of inorganic matter present in the sample polymer [12], Table 7 indicates that both materials evaluated had a large quantity of inorganic compounds. It can also be noted that silicone MDX 4-4210 presents no initial decomposition peak, demonstrating stable behaviour at high temperatures.
3.2. Colour change Analysis of variance (Table 5) showed significant differences between ageing and their interactions (p50.05). There was a significant colour change difference between the materials (E ¼ 1.4 0.8; M ¼ 1.23 1.6) and pigmentation (IP ¼ 1.3 0.6; IEP ¼ 1.4 0.8). For ageing, UV light (UV ¼ 1.7 1.3) and control (C ¼ 1.2 0.5) were significantly different. There was no difference between UV light and other ageing processes (T ¼ 1.3 1.9; NL ¼ 1.3 0.5). For the interaction between factors (Table 6), for the MDX 4-4210 silicone in the IP group, there was no colour change resulting from any of the ageing processes, while, in the EP group, the major changes were promoted by thermocycling Table 3. Analysis of variance.
Source Material (M) Pigment (P) Ageing (A) A*P M*T P*T M*P*T Error Total
3.3.2. Fourier transform infrared spectroscopy (FTIR) Figures 1 and 2 and Table 8 show the results obtained from the Fourier transform infrared (FTIR) spectroscopy. The similarity between the peaks of silicones evaluated were observed when compared with the standard material (polydimethylsiloxane, represented on the last figure spectrum), and the absence of formation of new peaks, indicating that the different ageing pigmentations did not promote the formation of new products in the silicone compositions, hence without the degradation of the product. The result also shows that the polymerization reaction of both silicones was complete [13–15]. Table 5. Analysis of variance.
Type III sum of squares
df
1298.460 38.612 893.991 35.910 907.957 309.737 222.163 846.740 5030.360
1 1 3 1 3 3 3 144 160
Mean square 1298.460 38.612 297.997 35.910 302.652 103.246 74.054 5.880
F
Sig.
220.821 6.567 50.679 6.107 51.470 17.558 12.594
0.000* 0.011* 0.000* 0.015 0.000 0.000 0.000*
*Significant difference.
Source Material (M) Pigment (P) Ageing (A) A*P M*T P*T M*P*T Error Total
Type III sum of squares
df
Mean square
0.002 1.771 6.744 35.414 11.512 5.954 9.900 65.561 420.598
1 1 3 1 3 3 2 135 150
0.002 1.771 2.248 35.414 3.837 1.985 4.950 0.486
F
Sig.
0.003 3.647 4.629 72.924 7.902 4.086 10.193
0.955 0.058 0.004* 0.000 0.000 0.008 0.000*
*Significant difference.
Table 4. Comparison of means (SD) of the hardness variation (results provided in Shore A units) for the interaction between the factors evaluated. IP
EP
C
T
UV
MDX 4-4210
2.24 1.9 Aag
3.46 0.47 Aag
1.62 0.57 Bag
Experimental
7.6 0.7 Abg
5.76 0.6 Bbg
4.02 0.5 Cag
NL 0.48 0.8 Bag 4.92 1.06 Bbg
C
T
UV
NL
8.68 0.7 Aa
0.34 0.64 Ca
1.26 1.25 Ca
4.84 0.87 Ba
8.9 0.2 Cag
0.8 0.08 Ab^
8.36 0.65 Cb
4.08 1.19 Bag
Equal letters ¼ statistical equality. Capitalized letters: comparison between columns of the same block. Lowercase: comparison between lines. Symbol: comparison between columns of different blocks. Negative sign indicates decreased hardness.
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Table 6. Comparison of means (SD) of colour change (DE) for the interaction between the factors evaluated. PI
PIE
C
T
UV
NL
C
T
UV
NL
MDX 4-4210
0.783 0.29 Aa
0.895 0.76 Aa
0.291 0.12 Aa
0.922 0.30 Aa
1.322 0.41 Aa
2.525 1.25 BA
2.524 1.38 BA
1.324 0.20 Aa
Experimental
1.07 0.53 Aa
0.91 0.62 Aa
1.36 1.35 Bb
1.32 0.68 Aa
1.18 0.48 Aa
1.62 1.26 Bb
1.88 1.15 Bb
1.20 0.37 Aa
Equal letters ¼ statistical equality. Capitalized letters: comparison between columns of the same block. Lowercase: comparison between lines. Symbol: comparison between columns of different blocks.
Table 7. Results of thermogravimetric analysis. % Decomposed material Pick of decomposition
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Material M C IP M C EP M T IP M T EP M UV IP M UV EP M NL IP M NL EP E C IP E C EP E T IP E T EP E UV IP E UV EP E NL IP E NL EP
1a loss 9.72% 10.00% 8.75% 9.96% 10.02% 9.01% 9.10% 8.83% 20.00% 20.18% 21.79% 21.31% 24.96% 22.23% 23.63% 20.22%
2a loss 36.78% 37.48% 23.81% 33.30% 22.53% 29.81% 14.30% 14.25% 11.36% 11.51% 12.44% 12.35% 10.10% 12.11% 8.35% 11.09%
1a loss – – – – – – – – 421 C 420 C 434 C 429 C 428 C 431 C 420 C 431 C
2a loss
556 C 558 C 558 C 558 C 558 C 559 C 562 C 563 C 563 C 562 C 560 C 564 C 562 C 562 C 565 C 562 C
Residue (%) 53.50% 52.55% 67.49% 56.76% 67.49% 61.18% 76.56% 76.94% 68.68% 68.35% 65.82% 66.39% 65.00% 65.67% 68.00% 68.71%
M, MDX 4-4210; E, experimental; C, control; T, thermocycling; UV, ultraviolet light; NL, natural light; IP, intrinsic pigmentation; EP, extrinsic pigmentation.
3.3.3. Differential scanning calorimetry (DSC) The results of Differential Scanning Calorimetry assay (Figure 3) indicated that the extrinsically pigmented (EP) samples showed higher melting enthalpy (DH). High values of melting enthalpy are directly related to the presence of crosslinks in polymers, which are indicative of stability [16].
4. Discussion Understanding the mechanical, physical and thermal properties of materials is essential for the correct selection and clinical indication. Although maxillofacial rehabilitation materials have evolved in recent years, they still exhibit alterations influenced by time and pigmentation [2,3,8]. Moreover, the commercial options regarding these materials are still limited and expensive. The two silicones evaluated showed hardness changes. Similarly, Pesqueira et al. [9] found hardness changes in the maxillofacial silicones when they were subjected to accelerated ageing and pigmentation; however, despite the alterations, the surface hardness values were satisfactory. In this present study, silicone MDX 4-4210 showed changes ranging from 25.08–44.36 Shore A units (Table 2) of hardness and the experimental silicone showed a variation of 20.04–33.12 (Table 2), which can be considered acceptable hardness values [2,22], thus enabling its clinical indication based on
hardness. In addition, the hardness values found in silicones evaluated allowed classifies them as very soft, which is a very significant finding because it allows prosthesis made from both materials accompanying facial movements during speech, chewing and other functional movements [1]. The increased hardness of the silicone can promote change of the edges of the prosthesis, and the consequent mismatch with the peripheral tissue of the lesion. Additionally, there is decreased muscle movement, aesthetics and acceptance by patients [1,2]. It was observed that, in general, the experimental silicone presented lower hardness values than those of silicone MDX 4-4210. These differences could be a result of different components used in the original formulation and/or due to differences in the cross-linking system of each polymer, differences in density, molecular weight and the degree of concentration of silicones [23]. These characteristics, associated with ageing, leading to the formation of free radicals, which react with oxygen and the formation of secondary polymer radicals, promote chain scission and consequently polymeric chain cross-linking [23], which could undermine the penetration tip of the durometer Shore A. Regarding the pigmentation, the highest hardness variation in the EP group may have occurred because this group underwent dual polymerization, which could alter the polymeric chain of the materials. The continuous polymerization process could favour the formation of a more complex polymer chain, making the surface of the material less susceptible to penetration tip of the durometer Shore A [24]. A lower density of cross-links between the polymer chains is indicative of shorter distance between these cross-links, which makes the material more rigid and resistant to penetration [23]. Furthermore, the high-temperature polymerized silicones exhibit excellent thermal stability and superior mechanical properties when compared with the polymerized ones at room temperature [2,3,23]. In general, the highest mean variation with increasing hardness occurred when the materials were subjected to ageing by ultraviolet light and natural light. According to Rabek [25], photo exposure causes deterioration in the physical, chemical and mechanical properties of the materials due to the formation of free radicals, resulting in chain scission of the polymers which, in turn, leads to changes in properties. Specifically for silicone MDX4-4210 with intrinsic and extrinsic pigmentation, the greatest hardness variation was promoted by thermocycling. In this process, the specimens were submitted to long periods of immersion in distilled water with variations in temperature between 5–55 C [20,23],
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1 2 3 4
5
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Wavenumber (cm−1)
Figure 1. Infrared absorption spectra of the analysed sample. Curve 1: Absorption spectra of the experimental silicone, EP Group - T; Curve 2: Absorption spectra of the experimental silicone, IP Group - NL; Curve 3: Absorption spectra of the silicone experimental, EP Group - NL; Curve 4: Absorption spectra of the silicone MDX 4-4210, IP Group - NL; Curve 5: silicone standard used for comparison.
Figure 2. Curve 2: Absorption spectra of the experimental silicone, IP Group – NL.
Table 8. Identification of the chemical grouping, according to the number of the peak and wave number of the peak, relative to Figure 2. Peak 1 2 3 4 5 6
Wave number of the peak (cm1) 2962, 2906 1412 1259 1081, 1016 794 699
Chemical grouping –CH3 Si–CH3 –Si(CH3)–O– –Si–O– Si–CH3 Si–C
which may cause water sorption and hardness alteration of the silicone. For the intrinsically pigmented experimental silicone, the greatest hardness variation occurred after ageing for natural light, while, for EP, the greatest variation occurred with UV light. The incidence of light, heat and humidity are important factors that can change the hardness of the material, since it promotes the separation of the main polymer chain
and contributes to the production of volatile degradation products [24]. Evaluation of colour change is important as it is one of the most limiting aspects regarding treatment with facial prostheses. According to Villalta et al. [26], the silicones undergo colour change with ageing and this change may be caused by intrinsic and extrinsic factors. The intrinsic factors include discolouration of the material [26], which includes changes in its polymer matrix, while the extrinsic factors may be related to the absorption of substances, for example, water during the thermocycling test and/or also the thermal and humidity changes [24,27], as in the UV ageing and NL test. The results of this study indicated that the specimens subjected to ageing by thermal cycling, UV light and natural light underwent greater colour change when compared with the specimens of the control group, which suggests that the ageing methods interfered in the material’s colour stability.
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PI O LN PI PE
LN O
VP IP E U
VP I
O
U O
O TP I
O TP IP E
O
C
PI PE
PI C O
PI PE
PI
M LN
M LN
VP IP E
VP I M U
M TP I
PI PE
M TP IP E
M U
−20
M C
M
C
−10
PI
0
−30 −40 −50 −60 Fusion Temperature (°C)
Fusion enthalpy (J/g)
−70
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Figure 3. Results of differential scanning calorimetry. M, MDX 4-4210; E, experimental; C, control; T, thermocycling; UV, ultraviolet light; NL, natural light; IP, intrinsic pigmentation; EP, extrinsic pigmentation.
The experimental silicone underwent IP and EP pigmentation influence as a function of ageing processes by thermocycling and ultraviolet light. This material is commonly used in medical orthopaedic rehabilitations that do not require pigmenting agents and this could explain the colour changes and also suggest the need for modifying its original formulation to withstand the staining procedures and exposure to inherent environmental conditions, such as changes in temperature, humidity and ultraviolet rays. The association of intrinsic and extrinsic pigmentation promoted greater colour change in silicon MDX4-4210, suggesting that the pigment types negatively affect the colour stability of silicones. Furthermore, the extrinsic pigment layer is located externally to the specimen, thereby more susceptible to changes for being more exposed to the environment. The use of makeup powder as pigment can promote greater colour changes when its composition has large-size organic particles [2,3,24]. Small pigment particles tend to aggregate, while the bigger ones are separated from the main polymer chain [24]. According to Goiato et al. [1], small but continuous release of sub-products during the polymerization of silicones, associated with factors such as material surface roughness, water absorption during the ageing processes, stain accumulation, dehydration, oxidation during double carbon reactions to produce peroxide compounds, infiltration of fluids and chemical degradation also interfere with colour characteristics. It should be noted that, although both silicones displayed colour changes after ageing, these may be clinically acceptable in all groups studied, since they were less than or equal to 3.3 [28]. Polyzois [5] reported that the exposure of maxillofacial silicones in the environment for a 1-year period resulted in visually detectable colour changes (DE43.3), which does not corroborate our results. Although studies agree that varying degrees of clinically observable colour changes in silicone prostheses are caused by weathering or ageing, it is difficult to compare and identify the most degrading factor, since the methodologies vary in terms of the pigments used, the experimental protocols, the silicone type tested and climatic conditions for the ageing process in the natural environment. Thus, further studies are required to investigate the improvement of colour stability for the clinical
application, possibility so as not to compromise the aesthetics of the prosthesis. Thermal stability is a general term used to describe the potential changes of a material and it has a significant implication as far as polymer fabrication processes are concerned [29–31]. The thermogravimetry showed that silicone MDX4-4210 exhibited mass loss and low constant from the initial heating up to the approximate temperature of 560 C (Table 7). This feature is observed for materials with large amounts of crosslinks in the polymer chain and contributes to the material’s stability [12]. As the experimental material underwent greater weight loss at lower temperatures (Table 7), the addition of inorganic additives could be suggested in order to prevent oxidation of the material and increase its durability and stability. Thermogravimetry indicated that the samples pigmented extrinsically had larger amounts of residue, suggesting that the pigments added to the sample behaved as inorganic compounds fully integrating with the material during handling and polymerizing, showing a highly favourable result. In Fourier Transform Infrared Spectroscopy (FTIR) the samples were compared to a standard polymethylsiloxane and a number of peaks exhibited similar characteristics (Figures 1 and 2 and Table 8). This result suggests that no new components or by-products were formed by double-change or addition reactions after the different pigmentations, ageing and immersion in water for prolonged periods, indicating that the polymerization reaction of the materials was complete [13–15]. The test also showed that both silicones studied have similar chemical groups, even if they present different forms and viscosity in clinical practice, and also that they are stable and their unique thermal formulation properties are satisfactory. The Differential Scanning Calorimetry (DSC) confirmed the effectiveness of the silicones reaction through its melting enthalpy values, which corroborates the data verified by FTIR. The crystallinity of a polymer sample is directly related to the amount of cross-linked polymer it has. Thus, the greater the crystallinity of the polymer, the higher the stability of the mechanical properties [16]. The aspect responsible for the crystallinity of a polymer sample is the enthalpy of fusion, where higher temperatures indicate higher crystallinity and,
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therefore, better performance of the material, in addition to the efficiency of the polymerization process [16] When the silicones were extrinsically pigmented, the melting enthalpy values were higher (Figure 2), suggesting increased stability of the samples pigmented in this manner. Since the DSC test demonstrates the degradation temperature of the sample, correlating it with possible chemical structural changes [16], it is observed that the silicones were influenced by both the pigmentation and ageing methods; however, none of these processes promoted microstructural changes. When a material is heated in an inert atmosphere, as was done in this study for tests of Thermogravimetry (TG), Fourier Transform Infrared Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC), the increase in molecular motion or atomic ion can lead to changes in the crystalline structure of the material evaluated, which can decompose and form new fragments of molecules. When more than one substance is present (in this case, makeup powder and water during thermal cycling tests and accelerated ageing by ultraviolet light), there are even more possibilities for interaction by heating and the formation of new compounds for addition reactions and double replacement. These reactions are accompanied by changes in enthalpy (as measured in Differential Scanning Calorimetry) and, in some cases, change of mass (measured as the thermogravimetry). Accordingly, the realization of such thermal analysis was very important, because it was possible that the silicones tested suffered no structural changes after incorporation of pigments and ageing for long periods [32,33].
5. Conclusion Within the limitations of present in vitro study, although the experimental silicone showed greater hardness and colour changes, the microstructural analysis showed that it has stable thermal properties. However, considering that mechanical and physical properties were evaluated under controlled laboratory conditions, the performance of the experimental material should be clinically evaluated before it can be considered an option for maxillofacial rehabilitation.
Acknowledgements This investigation was supported by the State of Sa˜o Paulo Research Foundation (FAPESP), Brazil (Grant number 2010/ 50787-9).
Declaration of interest The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.
References 1. Goiato, M.C., Pesqueira, A.A., Dos Santos, D.M., and Dekon, S.F.C., 2009, Evaluation of hardness and surface roughness of two maxillofacial silicones following disinfection. Brazilian Oral Research, 23, 49–53. 2. Goiato, M.C., Pesqueira, A.A., Silva, C.R., Gennari-Filho, H., and Dos Santos, D.M., 2009, Patient satisfaction with maxillofacial prosthesis: Literature review. Journal of Plastic, Reconstructive & Aesthetic Surgery, 62, 175–180.
J Med Eng Technol, 2014; 38(2): 67–75
3. Guiotti, A.M., Goiato, M.C., and Dos Santos, D.M., 2010, Evaluation of the Shore A hardness a silicone for facial prosthesis as to the effect of storage period and chemical disinfection. Journal of Craniofacical Surgery, 21, 323–327. 4. Haug, S.P., Andres, C.J., Munoz, C.A., and Bernal, G., 1992, Effects of environmental factors on maxillofacial elastomers part IV - optical properties. Journal of Prosthetic Dentistry, 68, 820–823. 5. Polyzois, G.L., 1999, Color stability of facial silicone prosthetic polymers after outdoor weathing. Journal of Prosthetic Dentistry, 82, 447–450. 6. Polyzois, G.L., Tarantili, P.A., Frangou, M.J., and Andreopoulos, A.G., 2001, Fracture force, deflection at fracture, and toughness of repaired denture resin subjected to microwave polymerization or reinforced with wire or glass fiber. Journal of Prosthetic Dentistry, 86, 613–619. 7. Hatamleh, M.M., Polyzois, G.L., Silikas, N., and Watts, D.C., 2011, Effect of extraoral aging conditions on mechanical properties of Maxillofacial Silicone Elastomer. Journal of Prosthodontics, 20, 439–446. 8. Kiat-Amnuay, S., Mekayarajjananonth, T., Powers, J.M., Chambers, M.S., and Lemon, J.C., 2006, Interactions of pigments and opacifiers on color stability of MDX4-4210/type A maxillofacial elastomers subjected to artificial aging. Journal of Prosthetic Dentistry, 95, 249–257. 9. Pesqueira, A.A., Goiato, M.C., Dos Santos, D.M., Haddad, M.F., Ribeiro, P.P., Sinhoreti, M.A.C., and Sundefeld, M.L., 2011, Effect of disinfection and accelerated aging on color stability of colorless and pigmented facial silicone. Journal of Prosthodontics, 20, 305–309. 10. Mancuso, D.N., Goiato, M.C., Dekon, S.F., and Gennari-Filho, H., 2009, Visual evaluation of color stability after accelerated aging of pigmented and nonpigmented silicones to be used in facial prostheses. Indian Journal of Dental Research, 20, 77–80. 11. Aziz, T., Waters, M., and Jagger, R., 2003, Development of a new poly(dimethysiloxane) maxillofacial prosthetic material. Journal of Biomedical Materials Research Part B Applied Biomaterials, 5, 252–261. 12. Nam, K.Y., Lee, C.H., and Lee, C.J., 2012, Antifungal and physical characteristics of modified denture base acrylic incorporated with silver nanoparticles. Gerodontology, 29, E413–E419. 13. Kontonasaki, E., Kantiranis, N., Papadopoulou, L., Chatzistavrou, X., Kavouras, P., Zorba, T., Sivropoulou, A., Chrissafis, K., Paraskevopoulos, K.M., and Koidis, P.T., 2008, Microstructural characterization and comparative evaluation of physical, mechanical and biological properties of three ceramics for metal-ceramic restorations. Dental Materials, 24, 1362–1373. 14. Lewis, R.N., and McElhaney, R.N., 2013, Membrane lipid phase transitions and phase organization studied by Fourier transform infrared spectroscopy. Biochimica et Biophysica Acta, 1828, 2347–2358. 15. Faria-e-Silva, A.L., Piva, E., Lima, G.S., Boaro, L.C., Braga, R.R., and Martins, L.R., 2012, Effect of immediate and delayed light activation on the mechanical properties and degree of conversion in dual-cured resin cements. Journal of Oral Science, 54, 261–266. 16. Laino, G., De Santis, R., Gloria, A., Russo, T., Quintanilla, D.S., Laino, A., Martina, R., Nicolais, L., and Ambrosio, L., 2012, Calorimetric and thermomechanical properties of titanium-based orthodontic wires: DSC–DMA relationship to predict the elastic modulus. Journal of Biomaterials Applications, 26, 829–844. 17. Aydogan Ayaz, E., Durkan, R., and Bagis, B., 2013, The effect of acrylamide incorporation on the thermal and physical properties of denture resins. Journal of Advanced Prosthodontics, 5, 110–117. 18. Aouachria, K., and Bensemra, N.B., 2006, Miscibility of PVC/ PMMA blends by vicat softening temperature, viscometry, DSC and FTIR analysis. Polymer Testing, 25, 1101–1108. 19. Yu, R., Koran, A., and Craig, R.G., 1980, Physical properties of maxillofacial elastomers under conditions of accelerated aging. Journal of Dental Research, 59, 1041–1047. 20. Abu-Baker, R., Han, L., Okamoto, A., and Iwaker, M., 2000, Color stability of compomer after immersion in various media. Journal of Esthetic Dentistry, 12, 258–263. 21. Tran, N.H., Scarbecz, M., and Gary, J.J., 2004, In vitro evaluation of color change in maxillofacial elastomer through the use of an ultraviolet light absorber and a hidered amine light stabilizer. Journal of Prosthetic Dentistry, 91, 483–490.
Polymeric materials for maxillofacial prosthetics
DOI: 10.3109/03091902.2013.864715
J Med Eng Technol Downloaded from informahealthcare.com by McMaster University on 01/14/15 For personal use only.
22. Polyzois, G.L., Tarantili, P.A., Frangou, M.J., and Andreopoulos, A.G., 2000, Physical properties of a silicone prosthetic elastomer stored in simulated skin secretions. Journal of Prosthetic Dentistry, 83, 572–577. 23. Mancuso, D.N., Goiato, M.C., and Santos, D.M., 2009, Color stability after accelerated aging of two silicones, pigmented or not, for use in facial prostheses. Brazilian Oral Research, 23, 144–148. 24. Seluk, L.W., Yu, R., and Koran, A., 1987, Stability of ceramic pigments for maxillofacial applications. Journal of Oral Rehabilitation, 14, 309–313. 25. Rabek, J.F., 1995, Polymer photodegradation: Mechanisms and experimental. (New York: Chapman and Hall). pp. 4–5. 26. Villalta, P., Lu, H., Okte, Z., Garcia-Godoy, F., and Powers, J.M., 2006, Effects of staining and bleaching on color change of dental composite resin. Journal of Prosthetic Dentistry, 95, 137–142. 27. Wilson, N.H., Burke, F.J., and Mjor, J.A., 1997, Reasons for placement and replacement of restorations of direct restorative
28. 29. 30. 31. 32. 33.
75
materials, by a selected group of practitioners in the United Kingdom. Quintessence International, 28, 245–248. Takamata, T., Moore, B.K., and Chalian, V.A., 1989, Evaluation of color changes of silicone maxillofacial materials after exposure to sunlight. Dental Materials Journal, 8, 260–270. Mutlu-Sagesen, L., Ergun, G., Ozkan, Y., and Semiz, M., 2005, Color stability of a dental composite after immersion in various media. Dental Materials Journal, 24, 382–390. Davy, K.W., Anseau, M.R., and Berry, C., 1997, Iodinate methacrylate copolymers as X-ray opaque denture base acrylics. Journal of Dentistry, 25, 499–505. Nam, K.Y., Lee, C.H., and Lee, C.J., 2012, Antifungal and physical characteristics of modified denture base acrylic incorporated with silver nanoparticles. Gerodontology, 29, e413–e419. Pope, M.I., 1980, Differential thermal Analysis: A guide to the technique and its applications. (London, Philadelphia, PA: Heyden). Turi, A., 1981, Thermal characterization of polymeric materials. (New Jersey: Academic Press).
