JIOH on LinkedIn JIOH on Facebook
  • Users Online: 999
  • Home
  • Print this page
  • Email this page
Home About us Editorial board Ahead of print Current issue Search Archives Submit article Instructions Subscribe Contacts Login 


 
 Table of Contents  
ORIGINAL RESEARCH
Year : 2021  |  Volume : 13  |  Issue : 4  |  Page : 378-385

Influence of weather in Saudi Arabia on mechanical properties of maxillofacial elastomeric materials: An in vitro study


1 Department of Prosthetic Dental Sciences, College of Dentistry, Jouf University, Sakakah 42421, Jouf Province, Saudi Arabia
2 Department of Prosthetic Dental Sciences, College of Dentistry, Jouf University, Sakakah 42421, Jouf Province, Saudi Arabia; Fixed Prosthodontics Department, Tanta University, Tanta, Egypt
3 Prosthodontic Unit, School of Dentistry, International Medical University (UMI), Jalan Jalil Perkasa 19, Bukit Jalil, Kuala Lumpur 5700, Malaysia
4 Department of Restorative Dentistry, School of Dental Medicine, University of Nevada, Las Vegas, NV, USA

Date of Submission11-Feb-2021
Date of Decision13-Apr-2021
Date of Acceptance22-Apr-2021
Date of Web Publication19-Aug-2021

Correspondence Address:
Dr. Mohammed A Mousa
Department of Prosthetic Dental Sciences, College of Dentistry, Jouf University, Sakakah 42421, Jouf Province.
Saudi Arabia
Login to access the Email id

Source of Support: None, Conflict of Interest: None


DOI: 10.4103/JIOH.JIOH_30_21

Rights and Permissions
  Abstract 

Aim: The aim of this article was to analyze the influence of Saudi Arabia climate on the mechanical characteristics of two room-temperature (RV)- and heat-temperature-vulcanized (HV) medical silicone materials. Materials and Methods: In this in vitro study, 160 specimens of four different elastomeric materials, two RV (A-2000 and A-2186) and two HV (TechSil S-25 and Cosmesil M-511), were exposed to natural weather of Jouf Area in Saudi Arabia for 6 months. The mechanical tests, including tear resistance, tensile strength, and percentage of elongation, were performed using a universal testing machine. A t-test and analysis of variance followed by a post hoc test with α<0.05 were used to analyze the results. Results: The weather statistically influenced the mechanical properties of the silicone materials. A-2000 showed the highest tear resistance (37.34 ± 2.36, P < 0.05). TechSil S-25 showed the highest tensile strength (57.34 ± 1.92, P < 0.05) and percentage of elongation (888.20 ± 13.83, P < 0.05). The least tensile strength and percentage of elongation were found in Cosmesil M-511 among all test specimens (P < 0.05). Conclusion: After 6 months of natural weathering in hot and dry climates, A-2000 exhibited the highest tear strength values among all test specimens, whereas TechSil S-25 achieved the best results for tensile strength and percentage of elongation.

Keywords: Maxillofacial Prostheses, Silicone Elastomers, Tensile Strength, UV Radiation, Weather


How to cite this article:
Mousa MA, Alzarea BK, Sghaireen MG, Sultan S, Hamza MO, Jamayet NB, Lynch E. Influence of weather in Saudi Arabia on mechanical properties of maxillofacial elastomeric materials: An in vitro study. J Int Oral Health 2021;13:378-85

How to cite this URL:
Mousa MA, Alzarea BK, Sghaireen MG, Sultan S, Hamza MO, Jamayet NB, Lynch E. Influence of weather in Saudi Arabia on mechanical properties of maxillofacial elastomeric materials: An in vitro study. J Int Oral Health [serial online] 2021 [cited 2022 Jan 29];13:378-85. Available from: https://www.jioh.org/text.asp?2021/13/4/378/324138




  Introduction Top


Maxillofacial prostheses (MFPs) have been used for functional and cosmetic restoration of missing parts of maxilla, mandible, and other facial parts when surgical procedures are unable to restore the missing parts.[1] Chlorinated polyethylene, polyvinyl chloride, polymethyl methacrylate, vinyl plastisols, polyurethanes, and silicone materials are all, but not limited to, materials used to fabricate MFP.[2],[3],[4],[5] An ideal maxillofacial prosthetic material should have a stable surface morphology, good mechanical properties, sufficient hardness, and it should not be affected by local environmental factors, such as solar radiation, thus achieving a satisfactory lifespan for prolonged use.[5],[6],[7],[8]

The most common materials used to fabricate MFP are the elastomeric silicone materials (dimethylsiloxane) owing to their high tear strength, percentage of elongation, and adequate tear resistance. In addition to that, the coloring compatibility with the tissue, the chemical inertness, high elongation, ease of fabrication, and patient comfort render them as the current material of choice for the management of maxillofacial defects.[9],[10],[11],[12] According to the type of chemical reaction, elastomeric silicone materials can be classified into room temperature-vulcanized (RV) and heat temperature-vulcanized (HV).[13] Both types vary in terms of physical and mechanical properties, to a lesser degree in physical properties. The quality of the different types of these materials mainly depends on the polydimethylsiloxane chains and the silica fillers and affects the overall strength and serviceability of these materials. Lontz[14] found that the color stability, thermal properties, and physical properties are superior in HV when compared with RV.

Facial prostheses made from maxillofacial silicone elastomers are exposed to a variety of environmental conditions such as sunlight, high temperature, ultraviolet radiation, moisture, wind, dust, and pollutants. Despite the advantages of these silicone elastomers, they show low solar radiation resistance and low thermal stability.[15] These disadvantages lead to degradation, particularly at the edge of the prosthesis, and, accordingly, to the limitation of the service life of silicone elastomeric prostheses.[15],[16],[17],[18],[19],[20],[21]

Various studies on silicone elastomers have inspected the influence of weather on their properties.[5],[22],[23],[24] However, to the best of our knowledge, experience with longevity in terms of mechanical strength of these MFPs in the north area of Saudi Arabia, which has a hot and dry climate on the nominated maxillofacial silicone materials, has not been evaluated. Thus, the performance of elastomeric materials is estimated based on the studies, which evaluated the influence of weather in climates with different thermal and solar radiations and some, but not all, elastomeric materials. This may provide inaccurate data about the real performance of these materials. It is, therefore, essential to understand the mechanical behavior of these materials to allow clinicians to choose the best materials for prostheses. It is assumed that hot and dry weather would not affect the mechanical and physical properties of maxillofacial elastomeric materials (H0). This assumption was examined in the present study (H1).


  Materials and Methods Top


Specimen selection and preparations

In this study, 160 specimens of four different maxillofacial silicone elastomers were used to study the effect of the weather on their tear, tensile strength, and percentage of elongation. Two materials of them were RV including A-2186 (Code A) and A-2000 (Code B). The other two materials were HV and included Cosmesil M-511 (Code C) and TechSil S-25 (Code T) as shown in [Table 1]. [Figure 1] shows the flowchart of sample distribution and study design. The sample size was based on PS 2009 software, the guidelines for the determination of effective sample size in observational studies,[25],[26] and previous studies that stated nine samples as sufficient for the detection of differences depending on calculation with 0.05 alpha errors and 0.8 power of the test.[5],[19],[27],[28],[29]
Table 1: The type and properties of the specimens involved in the study

Click here to view
Figure 1: Flowchart of sample distribution and testing

Click here to view


To fabricate the test specimens, wax patterns (Cavex, The Netherlands) were invested in dental stone with high strength (Dentsply International, Canada) to form the molds in which the mixed silicone elastomers were packed using plastic syringes and a vibrator (Sirio, Italy). For the RV silicone types, the molds were placed in hydraulic press 660 (Silfradent, Italy) and maintained on bench for 24 h for polymerization. For the HV silicones, the flask was placed in a heat oven (Memmert, Germany) at 100°C for 2 h for curing. After complete polymerization for RV, or curing for HV, the test specimens were removed from the molds and examined for any excess or deficiencies to be trimmed with scissors or even remade, if necessary. To test the tensile strength and percentage of elongation, 20 dumbbell-shaped specimens were fabricated for each material according to the International Standards Organization ISO 37 [Figure 2].[30] For tear strength testing, 20 trouser-shaped specimens (100 × 15 × 2 mm) were fabricated for each material according to ASTM D624 [Figure 3].[31] For each test, 10 specimens were used as a control and wrapped with coats, placed in suitable plastic containers, and kept in a Stainless Steel waterproof humidity control electronic cabinet (Yunboshi, Jiangsu, China) at 24 ± 1°C and 50 ± 5% relative humidity, and the other 10 specimens were tested after weathering.[32],[33]
Figure 2: Steps of dumbbell shape fabrication. A, wax pattern; B, mold fabrication; C, the final shape of dumbbell while A = B = C=25 mm, D=12.5 mm, and E=4 mm

Click here to view
Figure 3: Steps of trouser shape fabrication. A, wax pattern; B, mold fabrication; C, the final shape of trouser while A = B= 51 mm, and C=19 mm

Click here to view


Weathering

Weathering of specimens was conducted in 1–3 days following their preparation, by hanging and keeping them on the rooftop of Jouf dental College for 6 months (May 2019 to October 2019). The specimens were then cleaned for 10 min in bottled water (Aquafina, Aljomeh Water Factory, Boradah, Saudi Arabia), and were subsequently wiped, dried, and prepared for different tests.

Climate and environmental data

The monthly average environmental data including daily temperature, wind, rain, humidity, pressure, and ultraviolet (UV) index scales were collected from World Weather Online (Manchester, UK)[34] and from the study of Mousa that had been done at the same time and in the same region of Saudi Arabia.[8]

Testing tear strength

The computer-controlled Universal Testing Machine (UTM) (GT-C01-1, Gester International Co., Quanzhou, China) was switched on while the length of the testing specimens was gaged with a ruler to adjust the distance between the grips through up/down button. The test specimens were then placed and clamped in axial alignment for a pull direction. The test program was selected, including test method (pull direction), test speed, end method, and test steps. The tearing force was set at a constant rate of 5 mm/min until each test specimen broke. At the point of breakage, the tear strength was expressed in kilonewtons per meter (kN/m) and obtained by the machine software [Figure 4].[31] The output file was exported to excel format file for statistical analysis.
Figure 4: The test specimen during clamping in the UTM

Click here to view


Testing tensile strength

The tensile strength of the control and test specimens was determined using the same UTM (GT-C01-1, Gester International Co., Quanzhou, China). The test specimens were clamped by the same way explained in testing of tear strength, whereas the program test was selected according to manufacturer’s instruction. At the point of breakage, the tensile strength was expressed in megapascals (MPa) and obtained using machine software.[30]

Testing percentage of elongation

The percentage of elongation was determined on the same specimens that were used to test the tensile strength. The length of the test specimens was recorded initially and at the time of fracture, it is recorded using a digital vernier caliper (Model CD-6, Mitutoyo, Japan) to determine the percentage of elongation. At the point of breakage, the percentage of elongation was obtained using machine software.[30]

Statistical analysis

Data were analyzed using IBM SPSS software version 21.0 (IBM Corp., Armonk, NY, USA). The mean and standard deviations (SDs) were described for quantitative data. The comparison between the independent variables was performed using the t-test for two variables and F-test (analysis of variance (ANOVA)) for more than two variables. ANOVA was done followed by a post hoc test for identification of level of significance between every two groups. For all evaluation, α < 0.05 was considered as statistically significant.


  Results Top


The recorded data from the World Weather Online website and from the study of Mousa reported high temperatures ranging from 34°C to 41.1°C (with a mean ± SD of 39.1 ± 2.56).[8] Humidity showed a low percentage ranging from 13% to 27% (17.7 ± 4.45), whereas the UV scale was high in all months of the test showing 8–9 scales, except for October when it was moderate (6 scales) (8.2 ± 1.16).[8],[34] In hot, dry, and high UV weather, all test specimens showed significant changes in their mechanical properties at the time of examination.

Concerning the tear resistance, as shown in [Table 2], the t-test showed a significant decrease, within the same group, in the tear resistance in all weathered specimens when compared with the non-weathered specimens (P < 0.05), except for T, which expressed no significance between the weathered and non-weathered specimens (P > 0.05). Comparing the non-weathered groups, ANOVA revealed that T showed the least tear resistance (P < 0.05), whereas B showed the highest tear resistance among all control and test specimens when comparing the weathered and non-weathered specimens. However, there were no significant differences between the weathered specimens other than B (P > 0.05).
Table 2: Comparison between tear resistance (kN/m) in the weathered and non-weathered test materials

Click here to view


[Table 3] shows the mean and standard deviations of the tensile strength and the comparison of different test specimens. The t-test revealed that both B and C showed a significant reduction in their tensile strength when comparing the weathered with the non-weathered specimens (P < 0.05), whereas A and T showed no significance. Comparing the groups, ANOVA revealed that C showed the least tensile strength, whereas T showed the highest tensile strength specimens when comparing the groups in weathered and non-weathered specimens (P < 0.05).
Table 3: Comparison between tensile strength (kg/cm2) in the weathered and non-weathered test materials

Click here to view


Regarding the percentage of elongation, [Table 4] shows the mean and standard deviations of different types of test specimens. When comparing the groups, both B and T showed a significant decrease in the percentage of elongation, whereas A and C showed an insignificant difference between the weathered and non-weathered specimens. When comparing the groups, T showed the highest percentage of elongation (941.40 ± 8.50 and 888.20 ± 13.83) in weathered and non-weathered specimens, respectively (P < 0.05).
Table 4: Comparison between percentage of elongation in the weathered and non-weathered test materials

Click here to view



  Discussion Top


Exposure to UV radiation can cause significant degradation to medical silicone elastomers, leading to the need for replacement every 3–12 months mainly due to color degradation and physical properties.[35] UV radiation was found to cause photooxidative degradation in elastomeric materials in the form of elaboration of free radicals. The free radicals react with oxygen, producing oxy- and peroxy-radicals. The oxy- and peroxy-radicals break the chains in the polymer and are linked with each other. This process leads to a reduction in the molecular weight because of the production of volatile degradation products, leading to changes in physical and mechanical characteristics of the material.[36],[37] These changes depend on whether the dominant mechanism inside the polymer is cross-link or breaking the chain. When the cross-linking is the dominant mechanism, the link between the existing chain segments becomes harder, and, consequently, the density of the structural network increases. Finally, the material becomes harder. When the breaking of the chain is the dominant mechanism, the link between the chains becomes weak, and the material becomes softer.[29] In the last 10 years’ published literature, few studies focussed on the mechanical properties of the silicone elastomeric materials,[19],[29] whereas most of the researches focus on color degradation.[16],[22],[24]

Saudi Arabia has two main seasons: summer and winter. The climate of Saudi Arabia is characterized by high temperatures during the day and low temperatures at night. The country follows the pattern of the desert climate, except for the southwest, which features a semi-arid climate. The weather of the north area of Saudi Arabia is characterized by high temperature, ranging from 37oC to 41oC in summer, which decreases to become 20–35oC in winter; the humidity levels are very low (very dry), ranging from 13% to 18%, with moderate to high pressure and high to extreme UV index radiation (8+). Jouf Province was selected as the location of the outdoor weathering tests as representative of the environmental conditions of the north area of Saudi Arabia, as the climate in the Kingdom is highly variable between areas. The most significant impact of weather on the mechanical behavior of elastomeric materials is due to UV radiation, which is high during summer. For this, the authors chose to conduct outdoor weathering in the months that are usually associated with high UV radiation.

The effect of weather on elastomeric materials can be investigated either by outdoor weathering or virtually through accelerated aging. Accelerated aging is used to estimate the performance of the medical silicone elastomers after virtual weathering and can also estimate the lifetime of the materials.[38] However, the main drawback of accelerated aging is that it can lead to an inaccurate estimation of the life time of silicone materials because it cannot provide a real environment for outdoor weathering.[35],[39] Thus, data on the performance of silicone materials after outdoor weathering are more preferable, compared with artificial aging, to predict their lifetime under regional service conditions.

In this study, varying weather conditions led to significant changes in tear resistance of all test materials except for T, and so the null hypothesis was rejected. For tensile strength, the null hypothesis was confirmed for B and T, whereas for percentage of elongation, the null hypothesis was rejected for B and T.

The tear strength of a material is the resistance of the material to the force of tearing. From a clinical point of view, the tear strength is considered the most critical property of maxillofacial prosthetic materials, particularly when used in thin sections such as eyelid and nasal prostheses, due to susceptibility to tearing upon frequent removal.[6],[22] Although the weathered B specimens showed significant decrease in the tear strength when compared with the non-weathered, it had the highest tear strength when compared with the other weathered specimens. This increase in tear strength of B specimens can be attributed to the continuous polymerization of silicone associated with exposure to UV rays which result in more strong association between polymer chains (the cross-linking is the dominant mechanism). The results from the previous studies regarding the behavior of silicone materials due to weathering showed contradictory results. One results showed no significant differences in mechanical strength between elastomeric materials, which have A and C in between.[32] These findings were in contradictory with other study which examined the influence of weather on three different silicone materials with A and T in between, whereas T specimens showed highest tear, tensile strength, and percentage of elongation when compared with A and MED-4210.[19] The differences in the results among the studies can be attributed to the differences in testing environments and protocols. According to these results, B elastomeric material is advised for managing the deficiency involving thin section such as the eyelid and nose.

Tensile strength is the ability of a material to withstand a pulling force without fracture. It specifies the point when a material goes from elastic to plastic deformation, whereas the percentage of elongation is a measure of the amount of ductility of a material. The tensile strength and percentage of elongation are important in terms of the elasticity of the elastomers. The tensile strength of different elastomers ranged from 21 to 70 kg/cm2.[40] A material with a high percentage of elongation and low hardness is preferred when restoring areas of the head and neck that need stretching or movement during functioning.[13],[32] T had the highest tensile strength and percentage of elongation values. This agrees with a study that compared the effect of weathering on the mechanical properties and color changes of three maxillofacial materials: T, MED-4210, and A silicone elastomers.[19] There was no way to compare the present study with other on the same basis due to the diversity of the test specimens, additive materials to the specimens, and the variables that have been tested.[29],[33],[41],[42] These results can be interpreted as the main dominant reaction between the hydroxyl-groups on the filler and chains of the polydimethylsiloxane in TechSil S-25 (T) materials is the cross-linking. This makes the T material strong enough to resist the rupturing under the applied force. This result makes both B and T materials preferable for the management of different thin maxillofacial defects.

This study will assist prosthodontist in making adequate decisions when selecting the type of maxillofacial materials in the restoration of maxillofacial defects. According to the results of the present study, A-2000 TechSil S-25 showed that the most appropriate materials can be used for the restoration of most of the area in the face and head, particularly the area of part defects that can be moved or stretched, as they showed favorable tensile strength and percentage of elongation. These results can be applied, with some limitation, to areas in the world with hot and dry weather, such as most of the Gulf areas, Northern Australia, and southern India.

In this study, only four maxillofacial silicone materials were examined to identify the influence of outdoor weathering on the performance of these materials. This can be considered a limitation of the present study. Moreover, human factors are not considered in the outcome of the prostheses. Future studies are required to examine the effect of these factors on the same materials.


  Conclusion Top


Within limitations of the present study, the hot and dry weather adversely affects the mechanical properties of the maxillofacial silicone materials. After weathering, A-2000 recorded the highest values for tear strength when compared with other specimens. TechSil S-25 achieved the highest values for tensile strength and percentage of elongation. With some modification and improvement of physical properties, TechSil S-25 can prove to be a promising material for the managing of maxillofacial defects.

Acknowledgements

None.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Authors contributions

All the authors of Jouf University have a major contribution in the work. M. A. M.: study conception, personal funding, data collection, data acquisition, and manuscript writing. B. K. A., M. G. S., Sh. S., M. O. H.: study conception, data collection, funding, and final approval of the manuscript. N. B. J.: statistical analysis, final approval of the manuscript. E. L.: manuscript language revision, final approval of the manuscript.

Ethical policy and Institutional Review board statement

Not applicable

Patient declaration of consent

Not applicable

Data availability statement

The data are available with the corresponding author.



 
  References Top

1.
Ariani N, Visser A, van Oort RP, Kusdhany L, Rahardjo TB, Krom BP, et al. Current state of craniofacial prosthetic rehabilitation. Int J Prosthodont 2013;26:57-67.  Back to cited text no. 1
    
2.
Huber H, Studer SP. Materials and techniques in maxillofacial prosthodontic rehabilitation. Oral Maxillofac Surg Clin North Am 2002;14:73-93.  Back to cited text no. 2
    
3.
Abraham HM, Krishanga S, Philip JM, Venkatakrishnan CJ, Chandran CR. A review of materials used in maxillofacial prosthesis — Part 2. Drug Invent Today 2018;10:1569-73.  Back to cited text no. 3
    
4.
Chalian VA, Phillips RW. Materials in maxillofacial prosthetics. J Biomed Mater Res 1974;8:349-63.  Back to cited text no. 4
    
5.
Eleni PN, Katsavou I, Krokida MK, Polyzois GL, Gettleman L. Mechanical behavior of facial prosthetic elastomers after outdoor weathering. Dent Mater 2009;25:1493-502.  Back to cited text no. 5
    
6.
Aziz T, Waters M, Jagger R. Analysis of the properties of silicone rubber maxillofacial prosthetic materials. J Dent 2003;31:67-74.  Back to cited text no. 6
    
7.
Mousa MA, Lynch E, Sghaireen MG, Zwiri AM, Baraka OA. Influence of time and different tooth widths on masticatory efficiency and muscular activity in bilateral free-end saddles. Int Dent J 2017;67:29-37.  Back to cited text no. 7
    
8.
Mousa MA. Influence of weather on hardness and surface roughness of maxillofacial elastomeric materials. J Contemp Dent Pract 2020;21:678-82.  Back to cited text no. 8
    
9.
dos Santos DM, Goiato MC, Sinhoreti MA, Fernandes AU, Ribeiro Pdo P, Dekon SF. Color stability of polymers for facial prosthesis. J Craniofac Surg 2010;21:54-8.  Back to cited text no. 9
    
10.
Mancuso DN, Goiato MC, Dekon SF, Gennari-Filho H. Visual evaluation of color stability after accelerated aging of pigmented and nonpigmented silicones to be used in facial prostheses. Indian J Dent Res 2009;20:77-80.  Back to cited text no. 10
[PUBMED]  [Full text]  
11.
Ryniewicz AM, Machniewicz T, Ryniewicz W, Bojko Ł. Strength tests of the polymers used in dental prosthetics. Arch Mech Eng 2018;65:515-25.  Back to cited text no. 11
    
12.
Lee HH, Lee JH, Yang TH, Kim YJ, Kim SC, Kim GR, et al. Evaluation of the flexural mechanical properties of various thermoplastic denture base polymers. Dent Mater J 2018;37:950-6.  Back to cited text no. 12
    
13.
Begum Z, Kola MZ, Joshi P. Analysis of the properties of commercially available silicone elastomers for maxillofacial prostheses. Int J Contemp Dent 2011;2:1-5.  Back to cited text no. 13
    
14.
Lontz JF. State-of-the-art materials used for maxillofacial prosthetic reconstruction. Dent Clin North Am 1990;34:307-25.  Back to cited text no. 14
    
15.
Rosa D, Angelini J, Agnelli J, Mei L. The use of optical microscopy to follow the degradation of isotactic polypropylene (iPP) subjected to natural and accelerated ageing. Polym Test 2005;24:1022-6.  Back to cited text no. 15
    
16.
Kantola R, Lassila LV, Tolvanen M, Valittu PK. Color stability of thermochromic pigment in maxillofacial silicone. J Adv Prosthodont 2013;5:75-83.  Back to cited text no. 16
    
17.
Polyzois GL. Color stability of facial silicone prosthetic polymers after outdoor weathering. J Prosthet Dent 1999;82:447-50.  Back to cited text no. 17
    
18.
Artopoulou II, Chambers MS, Zinelis S, Eliades G. Peel strength and interfacial characterization of maxillofacial silicone elastomers bonded to titanium. Dent Mater 2016;32:e137-47.  Back to cited text no. 18
    
19.
Al-Harbi FA, Ayad NM, Saber MA, ArRejaie AS, Morgano SM. Mechanical behavior and color change of facial prosthetic elastomers after outdoor weathering in a hot and humid climate. J Prosthet Dent 2015;113:146-51.  Back to cited text no. 19
    
20.
Haug SP, Andres CJ, Munoz CA, Okamura M. Effects of environmental factors on maxillofacial elastomers: Part III — Physical properties. J Prosthet Dent 1992;68:644-51.  Back to cited text no. 20
    
21.
Farook TH, Mousa MA, Jamayet NB. Method to control tongue position and open source image segmentation for cone-beam computed tomography of patients with large palatal defect to facilitate digital obturator design. J Oral Maxillofac Surg Med Pathol 2020;32:61-4.  Back to cited text no. 21
    
22.
Hatamleh MM, Watts DC. Effect of extraoral aging conditions on color stability of maxillofacial silicone elastomer. J Prosthodont 2010;19:536-43.  Back to cited text no. 22
    
23.
Farah A, Sherriff M, Coward T. Color stability of nonpigmented and pigmented maxillofacial silicone elastomer exposed to 3 different environments. J Prosthet Dent 2018;120:476-82.  Back to cited text no. 23
    
24.
Han Y, Powers JM, Kiat-Amnuay S. Effect of opacifiers and UV absorbers on pigmented maxillofacial silicone elastomer, part 1: Color stability after artificial aging. J Prosthet Dent 2013;109:397-401.  Back to cited text no. 24
    
25.
Dupont WD, Dupont WD. Statistical Modeling for Biomedical Researchers: A Simple Introduction to the Analysis of Complex Data. Cambridge: Cambridge University Press; 2009.  Back to cited text no. 25
    
26.
Ahmad WMAW, Amin WAAWM, Aleng NA, Mohamed N. Some practical guidelines for effective sample-size determination in observational studies. Aceh Int J Sci Technol 2012;1:51-3.  Back to cited text no. 26
    
27.
Day SJ, Graham DF. Sample size estimation for comparing two or more treatment groups in clinical trials. Stat Med 1991;10:33-43.  Back to cited text no. 27
    
28.
Mousa MA, Patil S, Lynch E. Masticatory efficiency and muscular activity in removable partial dental prostheses with different cusp angles. J Prosthet Dent 2017;117:55-60.  Back to cited text no. 28
    
29.
Eleni PN, Krokida M, Polyzois G, Gettleman L, Bisharat GI. Effects of outdoor weathering on facial prosthetic elastomers. Odontology 2011;99:68-76.  Back to cited text no. 29
    
30.
ISO Standard. Rubber, vulcanized or thermoplastic-determination of tensile stress-strain properties. ISO 37, 2011. Available from: https://www.iso.org/standard/53023.html. [Last accessed on 2019 Apr 2].  Back to cited text no. 30
    
31.
D624-00 A. Standard Test Method for Tear Strength of Conventional Vulcanized Rubber and Thermoplastic Elastomers. ASTM International, West Conshohocken, PA: British Standards Publication; 2012.  Back to cited text no. 31
    
32.
Dootz ER, Koran A III, Craig RG. Physical properties of three maxillofacial materials as a function of accelerated aging. J Prosthet Dent 1994;71:379-83.  Back to cited text no. 32
    
33.
Cevik P, Eraslan O. Effects of the addition of titanium dioxide and silaned silica nanoparticles on the mechanical properties of maxillofacial silicones. J Prosthodont 2017;26:611-5.  Back to cited text no. 33
    
34.
WorldWeatherOnline. Sakaka Weather Forecast, Inc. [Internet]. 2020; Available from: https://www.worldweatheronline.com/sakaka-weather/al-jawf/sa.aspx. [Last accessed on 2019 Nov 5].  Back to cited text no. 34
    
35.
Sampers J. Importance of weathering factors other than UV radiation and temperature in outdoor exposure. Polym Degrad Stabil 2002;76:455-65.  Back to cited text no. 35
    
36.
Yousif E, Haddad R. Photodegradation and photostabilization of polymers, especially polystyrene. SpringerPlus 2013;2:1-32.  Back to cited text no. 36
    
37.
Guo JH. Aging processes in pharmaceutical polymers. Pharm Sci Technol Today 1999;2:478-83.  Back to cited text no. 37
    
38.
Mahomed A, Hukins DW, Kukureka SN. Effect of accelerated aging on the viscoelastic properties of a medical grade silicone. Biomed Mater Eng 2015;25:415-23.  Back to cited text no. 38
    
39.
Pospíšil J, Pilař J, Billingham N, Marek A, Horak Z, Nešpůrek S. Factors affecting accelerated testing of polymer photostability. Polym Degrad Stabil 2006;91:417-22.  Back to cited text no. 39
    
40.
Mitra A, Choudhary S, Garg H, Jagadeesh HG. Maxillofacial prosthetic materials — An inclination towards silicones. J Clin Diagn Res 2014;8:ZE08-13.  Back to cited text no. 40
    
41.
Bibars ARM, Al-Hourani Z, Khader Y, Waters M. Effect of thixotropic agents as additives on the mechanical properties of maxillofacial silicone elastomers. J Prosthet Dent 2018;119:671-5.  Back to cited text no. 41
    
42.
Shakir DA, Abdul-Ameer FM. Effect of nano-titanium oxide addition on some mechanical properties of silicone elastomers for maxillofacial prostheses. J Taibah Univ Med Sci 2018;13:281-90.  Back to cited text no. 42
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

Top
 
 
  Search
 
Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
Access Statistics
Email Alert *
Add to My List *
* Registration required (free)

 
  In this article
Abstract
Introduction
Materials and Me...
Results
Discussion
Conclusion
References
Article Figures
Article Tables

 Article Access Statistics
    Viewed330    
    Printed8    
    Emailed0    
    PDF Downloaded26    
    Comments [Add]    

Recommend this journal


[TAG2]
[TAG3]
[TAG4]