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The restoration of facial aesthetics and improvement of quality of life are primary goals for patients with facial deformities requiring maxillofacial prostheses [1].https://doi.org/10.3390/ma16165580 https://www.mdpi.com/journal/materials Materials 2023, 16, 5580 2 of 10 a growing interest in improving the mechanical or physical properties of elastomers by incorporating nano-oxide particles, such as ZnO, TiO2, and CeO2, as fillers in silicone-based elastomers [1,9,10].The physical and chemical properties of silicone elastomers, which are commonly used in facial prostheses, are influenced by factors such as crosslinking within their structure and the type and concentration of fillers in the elastomer network, as well as thermal initiators, other additives, polymerization time, and temperature [4-6].By utilizing unpigmented silicone elastomers and considering various materials, this research aims to contribute valuable insights into the field of maxillofacial prosthetics and enhance our understanding of how these treatments can impact color stability in different clinical scenarios.In this regard, the evaluation of disinfectants and nano-oxides on unpigmented silicone elastomers serves the purpose of achieving better standardization and facilitating data interpretation across various elastomer types.However, to achieve better standardization and facilitate data interpretation across various elastomer types, it is essential to evaluate the effects of disinfectants and nano-oxides on unpigmented silicone elastomers as well.In this regard, the first part of our study aimed to evaluate the antimicrobial properties of incorporating nano-oxides and different disinfectants in unpigmented maxillofacial silicone elastomers [18].Cleaning of silicone prostheses can be achieved through various methods, including mechanical cleaning using manual brushing or hand washing with neutral soap, as well as chemical cleaning with nontoxic disinfectants [14].Furthermore, when selecting a disinfectant, consideration should be given to its antimicrobial properties, compatibility, and inertness, in order to minimize any adverse impact on the physical properties of the material's surface and preserve them to the greatest extent possible.Moreover, mechanical cleaning methods may contribute to the deterioration of the silicone material and may not effectively eliminate all accumulated bacterial colonies [1,13,15].Differences observed in studies investigating the color and mechanical properties of maxillofacial silicones after disinfection can be attributed to variations in study design and the materials used.It was reported that the use of a reflection spectrophotometer as a method has been widely utilized for assessing the color stability of maxillofacial elastomers.On the other hand, colorimeters also provide color measurements in the CIE Lab* format, which allows for mathematical analysis and facilitates the comparison of color parameters between different objects [11].This investigation helped to establish the efficacy of these treatments in providing antimicrobial protection to silicone, which is crucial for its clinical application in maxillofacial prosthetics.The second part focused on examining how the incorporation Materials 2023, 16, 5580 3 of 10 of these disinfectants and nano-oxides influenced the color stability of different types of maxillofacial silicone.Studies have reported the colonization of complex microbial biofilms in maxillofacial prostheses.

The restoration of facial aesthetics and improvement of quality of life are primary goals
for patients with facial deformities requiring maxillofacial prostheses [1]. Despite significant advancements in plastic and reconstructive applications, the demand for maxillofacial
prosthetics remains constant, especially for patients with unrestorable defects. To address
this need, recent developments in maxillofacial prosthodontics have embraced the integration of 3D printing technologies in both the design and fabrication of prostheses [2–4]. The
physical and chemical properties of silicone elastomers, which are commonly used in facial
prostheses, are influenced by factors such as crosslinking within their structure and the type
and concentration of fillers in the elastomer network, as well as thermal initiators, other
additives, polymerization time, and temperature [4–6]. These factors collectively impact
the strength and durability of the silicone material, thus affecting its overall lifespan [2,5].
Recently, most studies have aimed to identify the most biocompatible materials with the
longest lifespan for use in maxillofacial prostheses [6–8]. In this regard, there has been
Materials 2023, 16, 5580. https://doi.org/10.3390/ma16165580 https://www.mdpi.com/journal/materials
Materials 2023, 16, 5580 2 of 10
a growing interest in improving the mechanical or physical properties of elastomers by
incorporating nano-oxide particles, such as ZnO, TiO2, and CeO2, as fillers in silicone-based
elastomers [1,9,10]. It was reported that the use of a reflection spectrophotometer as a
method has been widely utilized for assessing the color stability of maxillofacial elastomers.
On the other hand, colorimeters also provide color measurements in the CIE Lab* format,
which allows for mathematical analysis and facilitates the comparison of color parameters
between different objects [11].
Studies have reported the colonization of complex microbial biofilms in maxillofacial
prostheses. This colonization can lead to various issues, such as skin irritation and disuse of
the prosthesis, ultimately resulting in the need for prosthesis replacement [12,13]. Cleaning
of silicone prostheses can be achieved through various methods, including mechanical
cleaning using manual brushing or hand washing with neutral soap, as well as chemical
cleaning with nontoxic disinfectants [14]. Conventional cleaning processes such as scrubbing with soap have the potential to degrade the surface of the prosthesis, which can result
in colonization by microbes. Moreover, mechanical cleaning methods may contribute to the
deterioration of the silicone material and may not effectively eliminate all accumulated bacterial colonies [1,13,15]. In addition, repeated mechanical scrubbing should be avoided, as
it may lead to the dissolution and removal of pigments present on the external surface [16].
In contrast, chemical disinfectants offer a viable solution, as they can effectively reduce the
risk of infection without causing any adverse alterations to the physical properties of the
silicone [16,17]. Based on the current literature, chlorhexidine at various concentrations
seems to be the gold standard for disinfecting maxillofacial prostheses [13,14,18]. In recent
years, several studies have been conducted to investigate the effects of various disinfectants on the color stability of maxillofacial silicone elastomers [1,13,14,18,19]. Differences
observed in studies investigating the color and mechanical properties of maxillofacial
silicones after disinfection can be attributed to variations in study design and the materials
used. Furthermore, when selecting a disinfectant, consideration should be given to its
antimicrobial properties, compatibility, and inertness, in order to minimize any adverse
impact on the physical properties of the material’s surface and preserve them to the greatest
extent possible.
The specific chemical composition and processing methods of various silicone elastomers play a critical role in influencing their physical and mechanical properties. Due to
the distinct matrix structure found in different silicones [8,20,21], each silicone can exhibit
varied physical properties. Additionally, the presence of different chemical bonds in each
silicone group may contribute to varying color stability results. Consequently, conducting a
study that tests disinfecting agents and their physical effects using different types of silicone
is essential. Understanding potential differences between materials and disinfectants can
provide valuable insights into their interactions and implications for practical applications.
By investigating these aspects, we can gain a deeper understanding of the relationship
between silicone types and disinfectant effects, which will be beneficial for future research
and clinical use.
Pigments are known to provide color protection in specific scenarios [10,20], and their
presence in silicone elastomers can influence color stability. However, to achieve better standardization and facilitate data interpretation across various elastomer types, it is essential
to evaluate the effects of disinfectants and nano-oxides on unpigmented silicone elastomers
as well. In this regard, the evaluation of disinfectants and nano-oxides on unpigmented
silicone elastomers serves the purpose of achieving better standardization and facilitating
data interpretation across various elastomer types. Consequently, utilizing unpigmented
silicones in such studies can lead to a better understanding of the effects of these treatments.
In this regard, the first part of our study aimed to evaluate the antimicrobial properties of
incorporating nano-oxides and different disinfectants in unpigmented maxillofacial silicone
elastomers [18]. This investigation helped to establish the efficacy of these treatments in
providing antimicrobial protection to silicone, which is crucial for its clinical application in
maxillofacial prosthetics. The second part focused on examining how the incorporation
Materials 2023, 16, 5580 3 of 10
of these disinfectants and nano-oxides influenced the color stability of different types of
maxillofacial silicone.
Therefore, the objective of this study was to investigate the potential effects of nanooxide incorporation and disinfectant type on the color stability of different types of maxillofacial silicone. By utilizing unpigmented silicone elastomers and considering various
materials, this research aims to contribute valuable insights into the field of maxillofacial prosthetics and enhance our understanding of how these treatments can impact
color stability in different clinical scenarios. The null hypotheses of this study were that
(1) the disinfectants used to clean the silicone elastomers would not have any effect on the
color stability of the silicone elastomers, and that (2) nano-TiO2 would not affect the color
stability of different silicone elastomers after being subjected to disinfection for 30 h.