Effect of Extraoral Aging Conditions on Mechanical Properties of Maxillofacial Silicone Elastomer

Frequently used extraoral maxillofacial prosthetic materials and their longevity - A comprehensive review

The longevity of an extraoral prosthesis depends on its physical and mechanical properties and user maintenance. Faced with multiple outcome measures, researchers find it difficult to determine the most appropriate extraoral prosthetic material. This comprehensive review evaluates the most used extraoral prosthesis materials and qualitatively assesses their longevity and function. The study aims to identify and interpret the results of current updates on the factors that affect longevity and functionality. This comprehensive review summarizes and evaluates differences in the properties of commonly used extraoral maxillofacial prosthetic materials. The review was planned to focus on all factors related to the longevity and function of the extraoral maxillofacial prosthetics. An electronic search covered English articles in PubMed, Scopus, Google Scholar, Web of Science, and grey literature. Manual searching was also performed. Six authors participated in the screening. Search engines extracted 1107 records, and 88 studies were included for qualitative and bias assessments. Silicones are the most frequently used extraoral maxillofacial prosthetic materials. Heat-cured silicones are more color-stable than those cured at room temperature. Additional ingredients and processing techniques affect prosthesis longevity.

In situ study of the effect of endogenous and exogenous agents on color stability, hardness, and surface roughness of an elastomer for facial prostheses

PURPOSE

To evaluate in situ the influence of sweat, oil, sunscreen, and disinfectant solution on the color stability, hardness, and roughness of elastomer for facial prostheses.

MATERIALS AND METHODS

Standardized and intrinsically pigmented specimens remained in contact with human skin from the same person for 30 days, considering exposures (n = 36 per group), absent of exposition (Control, C); sweat and oiliness contact (SO); sweat and oiliness associated with sunscreen (SOS); 0.12% chlorhexidine digluconate immersion (CD0.12%); and all agents exposed (SOSCD). The main variables were color change (CIELab and National Standard Bureau system, NBS), Shore A hardness, and surface roughness, measured at baseline and 30 days. Qualitative analyses were performed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The data were analyzed by Kruskal-Wallis tests (color) and two-way ANOVA (hardness and roughness) with Sidak post-test (α = 0.05).

RESULTS

CD0.12% (1.54 ± 0.49) and SOSCD (2.10 ± 1.03) had similar effects and caused the smallest color changes, considered mild and noticeable (NBS), respectively. SOS promoted the greatest color change (6.99 ± 1.43, NBS: large) and hardness (17.97 ± 0.56); SOS promoted intermediate roughness (3.48 ± 1.05) between SOSCD (2.25 ± 0.53), and two similar groups: C (4.46 ± 0.95), and CD0.12% (4.39 ± 1.26). The qualitative analysis showed an irregular, dense, dry, and whitish layer on the surface of the specimens exposed to sunscreen, which was reduced when in contact with 0.12% chlorhexidine digluconate.

CONCLUSIONS

Endogenous and exogenous factors are capable of altering elastomer properties. The 0.12% chlorhexidine digluconate minimized the changes caused by sweat, oil, and sunscreen.

Polymers in 3D printing of external maxillofacial prostheses and in their retention systems

Maxillofacial defects, arising from trauma, oncological disease or congenital abnormalities, detrimentally affect daily life. Prosthetic repair offers the aesthetic and functional reconstruction with the help of materials mimicking natural tissues. 3D polymer printing enables the design of patient-specific prostheses with high structural complexity, as well as rapid and low-cost fabrication on-demand. However, 3D printing for prosthetics is still in the early stage of development and faces various challenges for widespread use. This is because the most suitable polymers for maxillofacial restoration are soft materials that do not have the required printability, mechanical strength of the printed parts, as well as functionality. This review focuses on the challenges and opportunities of 3D printing techniques for production of polymer maxillofacial prostheses using computer-aided design and modeling software. Review discusses the widely used polymers, as well as their blends and composites, which meet the most important assessment criteria, such as the physicochemical, biological, aesthetic properties and processability in 3D printing. In addition, strategies for improving the polymer properties, such as their printability, mechanical strength, and their ability to print multimaterial and architectural structures are highlighted. The current state of the prosthetic retention system is presented with a focus on actively used polymer adhesives and the recently implemented prosthesis-supporting osseointegrated implants, with an emphasis on their creation from 3D-printed polymers. The successful prosthetics is discussed in terms of the specificity of polymer materials at the restoration site. The approaches and technological prospects are also explored through the examples of the nasal, auricle and ocular prostheses, ranging from prototypes to end-use products.

Biocompatibility profile of aged pigmented and non-pigmented silicone elastomer for combined maxillofacial defects

PURPOSE

To assess the biocompatibility of platinum silicone elastomer A-2000 used in combined maxillofacial defects prosthesis, after being deteriorated by an accelerated aging process resembling both the extra and intraoral environment. This assessment was done indirectly on human-derived dermal and gingival tissues.

MATERIALS AND METHODS

One hundred eight samples of room-temperature vulcanized A-2000 platinum silicone were equally divided into extrinsically pigmented and non-pigmented groups to replicate combined maxillofacial defects. Accelerated aging was applied to pigmented samples to mimic extra- and intra-oral conditions, while non-aged counterparts served as controls. After isolating human cell lineages, dermal and gingival fibroblasts were indirectly exposed to silicone sample media. Cytotoxicity to cultured fibroblasts was assessed via MTT assay. Statistical significance was determined by repeated measures of one-way ANOVA (p < 0.01), evaluating cytotoxicity on dermal and gingival fibroblasts.

RESULTS

MTT assay showed increased cytotoxicity in pigmented silicon samples subjected to extraoral aging compared to non-aged counterparts (p < 0.01). Non-pigmented silicon, modeling intraoral conditions, exhibited cytotoxicity after 48 h (p < 0.05). Both aged and non-aged silicon extracts equally sensitized gingival fibroblasts at 72 h (p < 0.001). Negative correlations between pigmented and non-pigmented silicon were observed in dermal cell growth (p > 0.05, except at 24 h, r = 0.2), with accelerated aging showing minimal impact on the pigmentation effect (p > 0.05).

CONCLUSION

The retrieved diminished cellular metabolic activity of platinum silicone elastomer was in an acceptable clinical range, pointing out the importance of periodic assessments of the maxillofacial prosthesis for replacement depending on aging and cytotoxic harmful cellular responses.

Fabrication of Implant-Supported Auricular Prosthesis Using Artificial Intelligence

The absence of any organ of the facial region causes an asymmetrical appearance. This asymmetrical appearance can cause social dilemmas for the patient. The maxillofacial technician, the prosthodontist, and the patient must work closely together to fabricate an epithesis. On the implants, a superstructure is first constructed. Most of it is made up of rings and a bar that joins the implants. The firm acrylic resin base of the epithesis is equipped with clips that serve as the epithesis's retention mechanism. The actual epithesis is made of silicone rubber. The epithesis has to be shaped and colored with extreme caution. An appropriate substitute is an auricular prosthesis that is implant-retained. Microtia, deformity, malformation, and loss of the external ear, either partially or completely, can result from a variety of inherited genetic conditions. To evaluate the symmetry of both ears, artificial intelligence (AI) software is used. An Instagram lens Gridset by crystalwavesxx was used to correct and verify the bilateral symmetry of the patient. This case report primarily focuses on the fabrication of implant-supported auricular prostheses using AI.

Maxillofacial prosthetics and digital technologies: Cross-sectional study of healthcare service provision, patient attitudes, and opinions

PURPOSE

Digital technologies are continuously improving the accuracy and quality of maxillofacial prosthetics, but their impact on patients remains unclear. This cross-sectional study aimed to analyze the impact of facial prosthetics service provision, patients' perception, and digital technology on prostheses construction.

MATERIALS AND METHODS

All patients who presented for evaluation and management of facial defects between January 2021 and December 2021 at the ENT clinic were eligible for study enrollment. Patients requiring prosthetic reconstruction of their missing facial parts were included in the study. Forty-five questionnaires were delivered, inquiring about the patients' prosthetic demographics, prosthesis manufacture using 3D technologies, and their perceptions and attitudes.

RESULTS

A total of 37 patients responded (29 males, eight females; mean age 20.50 years). The congenital cause was the highest among other causes (p = 0.001) with auricular defects being the highest (p = 0.001). A total of 38 prostheses were constructed and 17 prostheses were retained by 36 craniofacial implants (p = 0.014). The auricular and orbital implants success rates were 97% and 25%, respectively. The implant locations were digitally planned pre-operatively. Digital 3D technologies of defect capture, data designing, and 3D modeling were used and perceived as helpful and comfortable (p = 0.001). Patients perceived their prosthesis as easy to handle, suited them, and they felt confident with it (p = 0.001). They wore it for more than 12 h daily (p = 0.001). They were not worried that it would be noticed, and found it comfortable and stable during various activities (p = 0.001). Implant-retained prosthesis patients were more satisfied with it, and found it easy to handle and stable (p = 0.001).

CONCLUSIONS

Congenital defects are the main cause of facial defects in the study country. The overall acceptance of maxillofacial prostheses was good, showing high patient perception and satisfaction. Ocular and implant-retained silicone prostheses are better handled, more stable, and the latter is more satisfying than traditional adhesive prostheses. Digital technologies save time and effort invested in manufacturing facial prostheses.

Effect of in vivo aging on the surface and electrochemical properties of magnetic attachments used in facial prostheses: A retrieval analysis study

STATEMENT OF PROBLEM

Reasons associated with the failure of facial prosthesis are of major concern and may be associated with deterioration of both elastomeric materials and magnetic attachments. However, the extent of deterioration of these components is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate selected retrieved facial prostheses and provide information regarding the electrochemical characterization of the recovered magnetic attachments.

MATERIAL AND METHODS

Five facial prostheses (RP1, RP2, RP3, RP4, RP5) fabricated at the University of Texas, M.D. Anderson Cancer Center were retrieved following clinical use. The intaglio and external surfaces of the prostheses along with the incorporated magnetic attachments were photographed. The areas with the detected failures on the retrieved prostheses, as well as the recovered magnetic attachments, were evaluated under a reflected light stereomicroscope at ×16 nominal magnification and photographed with a digital camera. Five magnetic attachments recovered from the prostheses (retrieved group RT) were evaluated for degradation of their corrosion resistance after electrochemical testing in artificial sweat solution and were compared with 5 unused magnetic attachments (control group, CT). To identify the elemental composition of the intact magnet surface, 1 specimen from the control group was investigated by X-ray energy dispersive spectroscopy (EDS). Means and standard deviations of the open circuit potential (EOCP), the zero-circuit potential (Ecorr), and Icorr were calculated and statistically analyzed by a t test (α=.05 for all tests).

RESULTS

The main reasons of failure were discoloration, degradation and rupture of the silicone elastomer, marginal misfit, and delamination of the polyurethane sheet. Additional findings were tarnish and discoloration of the magnetic attachments accompanied by considerable smear build-up. EDS results verified the Ni plating of tested magnets. Electrochemical testing revealed that retrieved magnets showed significantly lower OCP (P<.001) and Ecorr (P<.001) but similar Icorr (P=0.083) while the pseudopassivity region of unused magnets vanished in the retrieved group, denoting a degradation of electrochemical properties after clinical use.

CONCLUSIONS

In vivo aging exerts extended degradation on the elastomer part of facial prostheses as well as deterioration of their surface integrity and electrochemical properties.

Evaluation of the Mechanical and Physical Properties of Maxillofacial Silicone Type A-2186 Impregnated with a Hybrid Chitosan-TiO2 Nanocomposite Subjected to Different Accelerated Aging Conditions

The effects of incorporating a pioneer chitosan-TiO2 nanocomposite on the mechanical and physical properties of room-temperature vulcanization (RTV) maxillofacial A-2186 silicone under accelerated aging protocols were rigorously examined. This investigation utilized 450 samples distributed across five distinct silicone classifications and assessed their attributes, such as tensile strength, elongation, tear strength, hardness, and surface roughness, before and after various accelerated aging processes. Statistical methodologies, including a one-way ANOVA, Tukey's HSD, and Dunnett's T3, were employed based on the homogeneity of variance, and several key results were obtained. Silicones infused with 1 wt.% chitosan-TiO2 showed enhanced tensile strength across various aging procedures. Moreover, the 1 wt.% TiO2/Chitosan noncombination (TC) and 2 wt.% TiO2 compositions exhibited pronounced improvements in the elongation percentage. A consistent rise was evident across all silicone categories regarding tear strength, with the 1 wt.% chitosan-TiO2 variant being prominent under certain conditions. Variations in hardness were observed, with the 1 wt.% TC and 3 wt.% chitosan samples showing distinctive responses to certain conditions. Although most samples displayed a decreased surface roughness upon aging, the 1 wt.% chitosan-TiO2 variant frequently countered this trend. This investigation provides insights into the potential of the chitosan-TiO2 nanocomposite to influence silicone properties under aging conditions.

Cohesive Zone Modeling of Pull-Out Test for Dental Fiber-Silicone Polymer

BACKGROUND

Several analytical methods for the fiber pull-out test have been developed to evaluate the bond strength of fiber-matrix systems. We aimed to investigate the debonding mechanism of a fiber-silicone pull-out specimen and validate the experimental data using 3D-FEM and a cohesive element approach.

METHODS

A 3D model of a fiber-silicone pull-out testing specimen was established by pre-processing CT images of the typical specimen. The materials on the scans were posted in three different cross-sectional views using ScanIP and imported to ScanFE in which 3D generation was implemented for all of the image slices. This file was exported in FEA format and was imported in the FEA software (PATRAN/ABAQUS, version r2) for generating solid mesh, boundary conditions, and material properties attribution, as well as load case creation and data processing.

RESULTS

The FEM cohesive zone pull-out force versus displacement curve showed an initial linear response. The Von Mises stress concentration was distributed along the fiber-silicone interface. The damage in the principal stresses' directions S11, S22, and S33, which represented the maximum possible magnitude of tensile and compressive stress at the fiber-silicone interface, showed that the stress is higher in the direction S33 (stress acting in the Z-direction) in which the lower damage criterion was higher as well when compared to S11 (stress acting in the XY plane) and S23 (stress acting in the YZ plane).

CONCLUSIONS

The comparison between the experimental values and the results from the finite element simulations show that the proposed cohesive zone model accurately reproduces the experimental results. These results are considered almost identical to the experimental observations about the interface. The cohesive element approach is a potential function that takes into account the shear effects with many advantages related to its ability to predict the initiation and progress of the fiber-silicone debonding during pull-out tests. A disadvantage of this approach is the computational effort required for the simulation and analysis process. A good understanding of the parameters related to the cohesive laws is responsible for a successful simulation.

Hybrid Chitosan-TiO2 Nanocomposite Impregnated in Type A-2186 Maxillofacial Silicone Subjected to Different Accelerated Aging Conditions: An Evaluation of Color Stability

This study explores the impact of the incorporation of a chitosan-TiO2 nanocomposite on the color stability of pigmented room-temperature vulcanization maxillofacial silicone under various accelerated aging conditions. Five hundred disk-shaped specimens were formed with type A-2186 silicone elastomer, and they were distributed into groups based on pigment types and nanoparticle treatments. The color difference (ΔE) was assessed using a colorimeter in the CIELAB color system before and after exposure to aging conditions, including UV-accelerated aging and outdoor weathering. ANOVA, Dennett's T3, and Tukey HSD tests revealed significant color alterations across all silicone types, with the most pronounced being in the red-colored 3% chitosan specimens and the least pronounced being in the 2% TiO2 specimens that underwent UV-accelerated aging. Outdoor weathering consistently increased the ΔE values across all categories. This study suggests that while nanoparticles may offer some resistance against accelerated aging, they fall short in adequately defending against UV radiation during outdoor weathering.

Comparative evaluation of tensile strength, tear strength, color stability and hardness of conventional and 1% trisnorbornenylisobutyl polyhedralsilsesquioxane modified room temperature vulcanizing maxillofacial silicone after a six month artificial aging period

Aims

Silicone elastomers, chemically known as polydimethylsiloxane used in maxillofacial rehabilitation, over a period of time, undergo degradation and discoloration once aged, thereby reducing clinical longevity. Many previous studies reinforced the maxillofacial silicone material with stronger materials to increase its mechanical properties. However, no studies have been conducted to evaluate all the primary properties using single reinforcing agent. This study was conducted to evaluate and compare the tensile strength, tear strength, color stability, and Shore A hardness of conventional and 1% trisnorbornenylisobutyl polyhedralsilsesquioxanes (POSS) modified room temperature vulcanizing (RTV) maxillofacial silicone after a 6 - month artificial aging period.

Setting and Design

In vitro comparative study.

Materials and Methods

Eighty-eight silicone samples were fabricated. Therefore for each parameter of tensile strength, tear strength, color stability and hardness, twenty two samples comprising of 11 samples of conventional RTV silicone (Group 1) and 11 for POSS modified RTV silicone (Group 2) were fabricated in stainless steel molds using ASTM D 412-06, ASTM D 624, and ASTM D 2240-15 Standards. Baseline measurements for Shore A hardness and color values were recorded. Samples were then exposed to 6 months of natural weathering process and evaluated for tensile and tear strengths, color stability (ΔE), and hardness.

Statistical Analysis Used

Paired and unpaired t-test.

Results

Intragroup and intergroup comparison was done using unpaired and paired t-test. At the end of 6-month aging period, the tensile strength and tear strength of POSS-modified RTV silicone were significantly higher than conventional RTV silicone (P < 0.0001 and P = 0.00014, respectively). Intragroup comparison of conventional group showed highly statistically notable changes in L, a, and b values (P = 0.01631, > 0.0001, and = 0.0.0067, respectively), whereas the POSS-modified RTV silicone showed statistically nonsignificant results in L, a, and b values' (P = 0.91722, 0.15174, and 0.10847, respectively) comparisons after aging. Intergroup ΔE value comparisons showed an extremely statistically difference (P < 0.0001) within the groups. Intergroup comparisons postaging hardness showed a high statistical difference between both the groups, indicating a significant increase in hardness in the conventional group (P < 0.0001). However, intragroup comparison for hardness values showed a statistically highly significant difference for Group 1 (P < 0.0001) and a nonsignificant difference (P = 0.4831) for Group 2.

Conclusion

After the simulated 6-month aging procedure, 1% NB 1070 trisnorbornenylisobutyl POSS-incorporated RTV maxillofacial silicone showed better tensile strength, tear strength, Shore A hardness and color stability as compared to conventional RTV silicone. Hence, trisnorbornenylisobutyl POSS is a potent cross-linking agent which enhances the primary mechanical properties of RTV silicone can result in in significant increase in the mean life expectancy of RTV silicone even after 6 months of weathering.

Effect of ultraviolet protective agents on maxillofacial silicone elastomer, part 2: Mechanical properties after artificial aging

STATEMENT OF PROBLEM

The addition of ultraviolet (UV) protectives may affect the materials' mechanical properties, which can limit the service life of facial prostheses.

PURPOSE

The purpose of this in vitro study was to investigate the effect of UV protectives on the mechanical properties of maxillofacial silicones after artificial aging.

MATERIAL AND METHODS

Six color groups (unpigmented, white, yellow, red, blue, and mixed) of addition-type maxillofacial silicone were prepared. Four UV protectives, benzophenone-3 (UV-BP), ethylhexyl methoxycinnamate (UV-EM), titanium dioxide (UV-TD), and ethylhexyl salicylate (UV-ES), at 0.5% and 1% concentrations by weight were incorporated into the silicone before polymerization. The specimens were subjected to accelerated aging in a weathering chamber for 300 and 600 hours and to thermocycling. The tensile strength and percentage elongation, tear strength, and hardness of maxillofacial silicones were evaluated. Data were analyzed by using 4-way ANOVA. The differences were compared by the Tukey honestly significant difference test (α=.05).

RESULTS

Tensile strength decreased after 300 and 600 hours of UV aging in 0.5% and 1% UV-BP protective-added groups and increased in thermocycled groups (P<.05). Aging conditions generally showed no effect on the tensile strength of UV-EM, UV-TD, and UV-ES added groups (P>.05). Aging generated a decrease in percentage elongation values compared with nonaged specimens of groups (P<.05). The addition of UV protectives generally did not significantly affect the tear strength of specimens compared with control in the aged groups (P>.05). The hardness of UV protective-added groups increased when compared with that of nonaged groups after 300 and 600 hours of UV aging (P<.05). Also, thermally aged groups showed increased hardness than nonaged groups (P<.05).

CONCLUSIONS

The protective UV-BP addition caused decreased tensile strength, percentage elongation, and tear strength in both concentrations. The UV-EM and UV-ES provided increases in tensile strength and percentage elongation of the silicone in the 0.5% concentration. The addition of UV-BP, UV-EM, and UV-ES did not make significant differences; however, UV-TD significantly decreased the hardness values of the silicone.

Past, Present, and Future of Soft-Tissue Prosthetics: Advanced Polymers and Advanced Manufacturing

Millions of people worldwide experience disfigurement due to cancers, congenital defects, or trauma, leading to significant psychological, social, and economic disadvantage. Prosthetics aim to reduce their suffering by restoring aesthetics and function using synthetic materials that mimic the characteristics of native tissue. In the 1900s, natural materials used for thousands of years in prosthetics were replaced by synthetic polymers bringing about significant improvements in fabrication and greater realism and utility. These traditional methods have now been disrupted by the advanced manufacturing revolution, radically changing the materials, methods, and nature of prosthetics. In this report, traditional synthetic polymers and advanced prosthetic materials and manufacturing techniques are discussed, including a focus on prosthetic material degradation. New manufacturing approaches and future technological developments are also discussed in the context of specific tissues requiring aesthetic restoration, such as ear, nose, face, eye, breast, and hand. As advanced manufacturing moves from research into clinical practice, prosthetics can begin new age to significantly improve the quality of life for those suffering tissue loss or disfigurement.

Influence of Different Pigmentations and Accelerated Aging on the Hardness and Tear Strength of the A-2186 and MDX4-4210 Silicones

Objective

To evaluate the influence of different pigmentations and accelerated aging on the hardness and tear strength of the A-2186 and MDX4-4210 silicones.

Materials and Methods

The samples A-2186 and MDX4-4210 were manufactured without and with pigmentations (black, bronze, and pink). For the Shore A hardness test, 80 samples of each silicone were fabricated, and for the tear strength test, 320 samples of each silicone were fabricated. Eight groups were created for each test (n = 10). These tests were performed before and after 252, 504, and 1008 hours of aging. Three-way repeated-measures analysis of variance and the Tukey test were performed (α = 0.05).

Results

The A-2186 silicone showed higher hardness and tear strength when compared with the MDX4-4210 silicone (p < 0.05), except in the hardness of the A-2186 and MDX4-4210 groups without pigmentation after 1008 hours (p > 0.05). All hardness values were between 25 and 35 units, regardless of the silicone type, period, and pigmentation (or no pigmentation). In most situations, the hardness of silicones used increased after 252 hours (p < 0.05). The nonpigmented MDX4-4210 group and all A-2186 groups showed an increase in tear strength after 252 hours (p < 0.05). For the nonpigmented MDX4-4210 group, from 252 to 1008 hours, there was no change in tear strength (p > 0.05). All pigmented MDX4-4210 groups showed no change in tear strength from 0 (initial) to 1008 hours of aging (p > 0.05). In all A-2186 groups, from 252 to 504 hours, there was a reduction in tear strength (p < 0.05), and from 504 to 1008 hours, there was an increase in tear strength (p < 0.05), except in the bronze A-2186 group (p > 0.05).

Conclusion

In most situations, the A-2186 silicone showed significantly higher values of hardness and tear strength than the MDX4-4210 silicone. All hardness values were considered clinically acceptable. Accelerated aging could increase, decrease, or not significantly change the hardness and tear strength of the silicones used. The results of hardness and tear strength suggest that MDX4-4210 was more influenced by the presence of pigmentation after aging.

Advancements in Soft-Tissue Prosthetics Part B: The Chemistry of Imitating Life

Each year, congenital defects, trauma or cancer often results in considerable physical disfigurement for many people worldwide. This adversely impacts their psychological, social and economic outlook, leading to poor life experiences and negative health outcomes. In many cases of soft tissue disfigurement, highly personalized prostheses are available to restore both aesthetics and function. As discussed in part A of this review, key to the success of any soft tissue prosthetic is the fundamental properties of the materials. This determines the maximum attainable level of aesthetics, attachment mechanisms, fabrication complexity, cost, and robustness. Since the early-mid 20th century, polymers have completely replaced natural materials in prosthetics, with advances in both material properties and fabrication techniques leading to significantly improved capabilities. In part A, we discussed the history of polymers in prosthetics, their ideal properties, and the application of polymers in prostheses for the ear, nose, eye, breast and finger. We also reviewed the latest developments in advanced manufacturing and 3D printing, including different fabrication technologies and new and upcoming materials. In this review, Part B, we detail the chemistry of the most commonly used synthetic polymers in soft tissue prosthetics; silicone, acrylic resin, vinyl polymer, and polyurethane elastomer. For each polymer, we briefly discuss their history before detailing their chemistry and fabrication processes. We also discuss degradation of the polymer in the context of their application in prosthetics, including time and weathering, the impact of skin secretions, microbial growth and cleaning and disinfecting. Although advanced manufacturing promises new fabrication capabilities using exotic synthetic polymers with programmable material properties, silicones and acrylics remain the most commonly used materials in prosthetics today. As research in this field progresses, development of new variations and fabrication techniques based on these synthetic polymers will lead to even better and more robust soft tissue prosthetics, with improved life-like aesthetics and lower cost manufacturing.

Tear Strength Analysis of MDX4-4210 and A-2186 Silicones with Different Intrinsic Pigments Incorporated by Mechanical and Industrial Methods

Objective

The aim of this study was to evaluate the tear strength of MDX4-4210 and A-2186 silicones with different intrinsic pigments incorporated by mechanical and industrial methods, comparing nonaged and aged groups.

Materials and Methods

Twenty-four groups were created according to the American Society for Testing and Materials D-624/type C, half nonaged and half aged (n = 10): bronze mechanical MDX4-4210, bronze industrial MDX4-4210, black mechanical MDX4-4210, black industrial MDX4-4210, pink mechanical MDX4-4210, pink industrial MDX4-4210, bronze mechanical A-2186, bronze industrial A-2186, black mechanical A-2186, black industrial A-2186, pink mechanical A-2186, and pink industrial A-2186. All specimens were submitted to tear strength analysis. Data were submitted to the ANOVA and Tukey test (p < 0.05).

Results

An increase in the tear strength values was observed only for the bronze and black MDX4-4210, comparing nonaged and aged silicones (p < 0.05), regardless of the manufacturing method. There was a difference in all comparisons between MDX4-4210 and A-2186 silicones with the same pigment type (p < 0.05), regardless of the manufacturing method. In all cases, there was no difference in the manufacturing method comparing the MDX4-4210 or A-2186 groups with the same pigment.

Conclusion

Accelerated aging did not influence the tear strength in all aged A-2186 silicones and in aged pink industrial and mechanical MDX4-4210 silicones. The other MDX4-4210 groups had an increase in the results after aging. In all cases compared, the A-2186 groups had higher tear strength values than the MDX4-4210 groups. Mechanical and industrial methods can be used for silicone preparation, without changing the tear strength.

Comprehensive prosthetic rehabilitation of a case of the orofacial digital syndrome

Maxillofacial defects can result from trauma, treatment of neoplasm, or congenital malformations. Many a time due to the size, location of the defect, or because of the patient's medical condition, surgical reconstruction may not be possible. In these cases, rehabilitation is indicated with the help of a maxillofacial prosthesis. Orofacial digital syndrome (OFDS) is a congenital anomaly that affects the development of the mouth, face, and digits. Such abnormalities or defects compromise form, function, esthetics, and social acceptance and deeply affect the psychological status of an individual. This report describes the comprehensive prosthetic rehabilitation of a case of OFDS with bilateral cleft lip and palate as well as syndactyly and brachydactyly of the foot. The individual was rehabilitated with a definitive obturator and a custom-made foot prosthesis using room-temperature-vulcanizing silicone. The prosthetic rehabilitation significantly improved esthetics, phonetics, and function as well as social and psychological status of the patient.

In vitro study of effects of aging and processing conditions on colour change in maxillofacial silicone elastomers

Background

The inherent colour change in maxillofacial silicone elastomers becomes perceptible 6–12 months after fabrication. Determining the factors that accelerate the degradation of the prosthesis can help the clinicians increase its life span. Therefore, the aim of the study was to investigate the effect of time passage, processing temperature, and molding-stone colour on the colour change of maxillofacial silicone elastomers after darkroom storage for 6000 h.

Methods

A total of ten study molds, each incorporating ten specimen gaps were fabricated using five different colors of dental stones. The gaps were filled with coloured Cosmesil M511 maxillofacial silicone elastomer. Five of the study molds, one of each stone color, were processed at room temperature (25 °C) for 24 h while the remainder were vulcanized at 100 °C for 1 h. Two stainless-steel molds were also fabricated to obtain a total of twenty control-group specimens of the same dimensions that were processed under the same conditions as the study molds. Colour measurements of the vulcanized silicone samples were performed using a Konica Minolta spectrophotometer. Initial measurements were obtained after the blocks were removed from the molds and the final measurements were recorded 6000 h after storage in the dark at 25 °C and 40% relative humidity. The CIEDE2000 colour-difference formula was used to measure the changes in the colour. One-way and two-way ANOVA, and an independent-sample t-test were used for statistical assessments.

Results

For every group, the colour change exceeded the perceptible thresholds. Thus, either the vulcanization temperature or the colour of the molding stone has a significant effect on the colour change over time. Those samples vulcanized in green and white molding stones at 100 °C exhibited a significantly higher ∆L*, ∆a*, and ∆b* values relative to the samples vulcanized at room temperature.

Conclusion

The molding-stone colour and vulcanization temperature both affect the degree of colour change after storage in a dark environment. The L*, a*, and b* values for the maxillofacial silicone elastomers are influenced by the direction of the increase or decrease according to the selected colour. This effect varies as the temperature increases.

Evaluation of Shore A hardness of maxillofacial silicones: the effect of dark storage and nanoparticles

Purpose

Little has been reported how the addition of nanoparticles could affect the hardness of maxillofacial silicones. The purpose of this study was to evaluate the effects of different types of nanoparticle additives and dark storage for 2-years on the Shore A hardness of two types of maxillofacial silicone elastomers.

Materials and Methods

A-2000 and A-2006 Room Temperature Vulcanized (RTV) silicone elastomers were tested in this study. Silaned silica, fumed silica and titanium dioxide nanoparticles at concentrations of 10% by volume were used as fillers for the maxillofacial silicone elastomers. A total of 64 silicone specimens were fabricated, which includes 8 samples, 30 × 10 mm in size, from each silicone elastomers for each subgroup and also controls. After the initial Shore A hardness measurements, specimens were kept in dark conditions at room temperature for 2 years. The final measurements were then taken from the silicone specimens. All data were statistically analyzed.

Results

For both types of silicones, there was statistically significant differences among study groups (p<0.001). Fumed silica group showed the lowest hardness values in A-2000 after storage. However, no significant difference was observed between control and fumed silica groups. Control group showed the lowest hardness values in A-2006, while the highest hardness values were found in fumed silica group; there was no significant difference between silica and silane groups.

Conclusion

Shore A values of the specimens were within the acceptable range for the maxillofacial silicones after aging. Nanoparticle addition did not prevent hardening of the silicone elastomers with time.

Effect of the simulated Indian and Mediterranean climates on the Shore A hardness of maxillofacial silicone

Purpose:

The purpose of this study was to assess and compare the effect of the simulated Indian and Mediterranean climates on the Shore A hardness of a commercially available nonpigmented room temperature vulcanizing maxillofacial silicone.

Materials and Methods:

Sixty specimens were fabricated from A-2000 silicone material (Factor II), using a stainless steel mold of dimension 20 mm × 2 mm. The initial Shore A hardness was noted using a digital durometer. Thirty samples were subjected to the simulated Mediterranean climate (Group I), and the remaining thirty samples were subjected to the Indian tropical climate (Group II) in an accelerated weather chamber to simulate 1 year of clinical use. Final Shore A hardness was noted. A one-way ANOVA and Bonferroni post hoc tests were performed for the Shore A hardness at P < 0.05.

Results:

The mean initial Shore A hardness for both the groups was 24.9833. After accelerated weathering, Group I showed mean Shore A hardness of 33.0000 whereas Group II showed mean Shore A hardness of 38.0000.

Conclusions:

The Shore A hardness of Factor II, before and after accelerated artificial weathering, was statistically significant at 0.05 level (P < 0.05). The change in Shore A hardness was greater in the simulated tropical climate group (Group II) as compared to the simulated Mediterranean climate group (Group I) but within clinical limits.

Fabrication of an Orbital Prosthesis Combined With Eyebrow Transplantation

Fabrication of an orbital prosthesis is considered as a challenging procedure as compared to the other facial prosthesis due to the presence of inactive eye movements and the need of artificial hair in order to mimic eyelashes and eyebrows. Generally these structures are sewed or bonded in the silicone. However, deformation or hair loss is observed within time. This deformation is visible especially in the eyebrow. This clinical report represents a patient with an implant supported orbital prosthesis. Patient was not satisfied with the nature of her eyebrow that was sewed in the silicone. Therefore, an alternative approach of eyebrow transplantation was used for the patient. The patient expressed her better satisfaction of this definitive prosthesis supported with eyebrow transplantation.

A spectrophotometric analysis of extraoral aging conditions on the color stability of maxillofacial silicone

Context:

Surveys have reported color fading as the most frequent reasons patients given for disliking their prostheses.

Aim:

The aim of the study is to compare the color variation between two maxillofacial silicone elastomers after subjecting them to extraoral aging conditions.

Subjects and Methods:

A total of 80 samples were made from M511 Maxillofacial Rubber (Part A: Part B = 10:1) and Z004 Platinum Silicone Rubber (Part A: Part B = 1:1) and divided into two main Groups A and B (40 each). These main groups were then subdivided into five subgroups (A₁B₁, A₂B₂, A₃B₃, A₄B₄, and A₅B₅) (n = 8); outdoor weathering, acidic perspiration, sebum (for 6 months), and neutral soap and disinfectant (for 30 h), respectively. Baseline L*a*b* values were recorded. The samples were subjected to the extraoral aging conditions, and the L* a*b* values were recorded after the aging period using a spectrophotometer.

Statistical Analysis:

The intergroup comparison was done by Kruskal–Wallis test, whereas the intragroup comparison was done by Mann–Whitney test.

Results

All groups exhibited visually detectable, mean color differences that ranged from 3.06–5.21, except for A₄B₄. There was no statistical significance between the two materials when subjected to extraoral aging conditions.

Conclusions:

Visually perceptible and clinically unacceptable color changes occur when exposed to various extraoral aging conditions except for neutral soap solution immersion, for which values of Δ E* were clinically acceptable (ΔE < 3). It can be said for all practical purposes, clinically, the choice between M511 Maxillofacial Rubber (Part A: Part B = 10:1) and Z004 Platinum Silicone Rubber (Part A: Part B = 1:1) would yield more or less the same results, with unacceptable norms in terms of color stability under extraoral aging conditions.

In Vitro Cytotoxicity of Maxillofacial Silicone Elastomers: Effect of Nano-particles

PURPOSE

Silicone elastomers are generally used for maxillofacial extraoral prostheses. The purpose of this in vitro study was to evaluate the cytotoxicity of different kinds of nanoparticles added to two types of maxillofacial elastomers.

MATERIALS AND METHODS

A-2000 and A-2006 silicone elastomers were used. The silicone specimens were divided into eight groups according to the presence of additional nanoparticles (n = 18). The following represents the groups in the study: Group A: A-2000 silicone (control group); Group B: A-2006 silicone (control group); Group C: A-2000 silicone and the addition of titanium dioxide (TiO₂ ); Group D: A-2006 silicone and the addition of TiO₂ ; Group E: A-2000 silicone and the addition of fumed silica; Group F: A-2006 silicone and the addition of fumed silica; Group G: A-2000 silicone and the addition of silaned silica; Group H: A-2006 silicone and the addition of silaned silica. A paired sample t-test was used to analyze the cytotoxicity of each group after 24, 48, and 72 hours.

RESULTS

Based on the results of the 24-hour analysis, the biocompatibility values of the (A-2006) fumed silica group were higher than those of the control groups. There was no statistically significant difference in A-2006 and A-2000 groups. The cytotoxicity values of the control groups and TiO₂ (A-2000 silicone) elastomer groups increased at all test times; however, the cytotoxicity values of the TiO₂ (A-2006), fumed silica (A-2006), silaned silica (A-2006), fumed silica (A-2000), and silaned silica (A-2000) groups increased significantly only from 24 to 48 hours.

CONCLUSION

Nanoparticles of TiO₂ , fumed silica, and silaned silica added to a commercial silicone-based elastomer used for fabrication of maxillofacial prostheses are nontoxic.

Improved Construction of Auricular Prosthesis by Digital Technologies

Implant-retained auricular prostheses are a successful prosthetic treatment option for patients who are missing their ear(s) due to trauma, oncology, or birth defects. The prosthetic ear is aesthetically pleasing, composed of natural looking anatomical contours, shape, and texture along with good color that blends with surrounding existing skin. These outcomes can be optimized by the integration of digital technologies in the construction process. This report describes a sequential process of reconstructing a missing left ear by digital technologies. Two implants were planned for placement in the left mastoid region utilizing specialist biomedical software (Materialise, Belgium). The implant positions were determined underneath the thickest portion (of anti-helix area) left ear that is virtually simulated by means of mirror imaging of the right ear. A surgical stent recording the implant positions was constructed and used in implant fixtures placement. Implants were left for eight weeks, after which they were loaded with abutments and an irreversible silicone impression was taken to record their positions. The right existing ear was virtually segmented using the patient CT scan and then mirror imaged to produce a left ear, which was then printed using 3D printer (Z Corp, USA). The left ear was then duplicated in wax which was fitted over the defect side. Then, it was conventionally flasked. Skin color was digitalized using spectromatch skin color system (London, UK). The resultant silicone color was mixed as prescribed and then packed into the mold. The silicone was cured conventionally. Ear was trimmed and fitted and there was no need for any extrinsic coloring. The prosthetic ear was an exact match to the existing right ear in shape, skin color, and orientation due to the great advantages of technologies employed. Additionally, these technologies saved time and provided a base for reproducible results regardless of operator.

Outdoor weathering of facial prosthetic elastomers differing in Durometer hardness

STATEMENT OF PROBLEM

Facial prosthetic elastomers with wide ranges in hardness are available, yet material weatherability is unknown.

PURPOSE

The purpose of this study was to assess color, Durometer hardness, and tensile property changes after 3000 hours of outdoor weathering.

MATERIAL AND METHODS

Unpigmented elastomers with Durometer hardness 5, 30, 50, 70, and A-2186 were polymerized into dumbbells (ASTM D412) and disks, 34 mm in diameter by 6 mm thick. Materials were subjected to outdoor or time passage environments for 3000 hours. CIELab color (n=5), Durometer hardness (n=5), and tensile mechanical properties (n=10) were measured at 0 and 3000 hours, and group differences were assessed by material and weathering condition (ANOVA/Tukey, α=.05).

RESULTS

Except for A-2186, the mean Durometer changes for all materials were 1 unit or less, with no significant differences observed between time passage and weathered groups (P≥.05). Three-thousand-hour tensile mechanical property results demonstrated nonsignificant differences between time passage and weathered materials but significantly changed properties from immediately tested materials (P<.001). Outdoor weathering induced perceptible but acceptable color changes (1.7≤ΔE*≤2.6) for elastomers with Durometer hardness 5 and 30 and A-2186.

CONCLUSIONS

With a few exceptions, outdoor weathering produced relatively small changes in color, Durometer hardness, or tensile properties compared with time passage.

Effect of different disinfecting procedures on the hardness and color stability of two maxillofacial elastomers over time

OBJECTIVE

Disinfection procedures often cause deterioration in a maxillofacial prosthesis. Color and hardness alterations could lead to a replacement of the prosthesis.

MATERIAL AND METHODS

An experimental chlorinated polyethylene (CPE) and a commercial polydimethyl siloxane (PDMS) sample were treated with four different disinfection procedures for a period which simulates 1 year of clinical service. The applied disinfection procedures included microwave exposure and immersion in three solutions, sodium hypochlorite, neutral soap and a commercial disinfecting soap. Shore A hardness (∆H) and color differences (∆E) were determined before and after each procedure. All data were analyzed by Two Way Analysis of Variance (ANOVA) and Tukey's post hoc tests at a level of α=0.05.

RESULTS

The samples presented significant alterations in color and hardness after the different disinfection treatments. The color differences (∆E) were at least eye detectable in all cases and clinically unacceptable in most of the cases, with values ranging from 1.51 to 4.15 and from 1.54 to 5.92 for the PDMS and CPE material, respectively. Hardness was decreased after all the disinfection procedures in the PDMS, while for the CPE, a decrement was observed after disinfection with sodium hypochlorite and neutral soap and an increment after microwave exposure and the disinfection with a commercial antimicrobial agent. The PDMS samples presented greater alterations in color and hardness after disinfection with sodium hypochlorite solution, while the microwave exposure caused negligible effects. The CPE samples were affected most after disinfection when treated with neutral soap, and more slightly when disinfected with sodium hypochlorite solution.

CONCLUSIONS

The disinfection procedures caused alterations in color and hardness of the examined materials. The most suitable disinfection procedure for the PDMS material is microwave exposure, while disinfection with sodium hypochlorite solution is not recommended. The CPE material is suggested to be disinfected with sodium hypochlorite solution and the use of neutral soap is not recommended. Comparing the two materials, the PDMS material is most color stable, while the CPE material presented fewer changes in hardness.