Properties of silicone maxillofacial elastomer processed in stone and metal

Effect of different concentrations of titanium and silver nanoparticles on maxillofacial silicone MDX4-4210 on cell viability, tear bond strength, and shore strength: An in vitro study

Aim

The aim was to evaluate and compare the cell viability, tear bond strength, and shore hardness of MDX4-4210 silicone reinforced with titanium dioxide and silver nanoparticles in 1%, 2%, and 3%.

Settings and Design

The study design involves in vitro comparative study.

Materials and Methods

MDX4-4210 silicone incorporated with 1%, 2%, and 3% by weight of silver and titanium dioxide nanoparticles. A total of 112 specimens were prepared and grouped into 7, with 16 specimens in each group. Group 1 - control, Groups 2, 3, and 4 were 1%, 2%, and 3% silver, respectively. Groups 5, 6, and 7 were 1%, 2%, and 3% titanium dioxide nanoparticles, respectively. Cell viability was tested by MTT ASSAY on MG63 cell lines, tear bond strength was tested by peeling force in universal testing machine, and Shore A hardness was tested in durometer.

Statistical Analysis Used

The cell viability values were statistically analysed using one-way analysis of variance, and Tukey honestly significant difference test, tear bond strength and shore hardness values were analysed using Mann-Whitney test.

Results

Based on the MTT ASSAY test, 1% silver nanoparticles incorporated MDX4-4210 silicone showed maximum cell viability of 42.10%, whereas minimum cell viability was 18.06% for 3% of titanium dioxide-reinforced silicone. The mean value of tear bond strength of 1% silver and 1% titanium dioxide nanoparticles reinforced room temperature vulcanized maxillofacial silicone were 62.81 ± 3.637 N/m and 59.69 ± 5.313 N/m and the mean value of shore hardness of room temperature vulcanized of 1% silver and 1% titanium dioxide nanoparticles reinforced room temperature vulcanized maxillofacial silicone were 38.06 ± 1.237 and 36.75 ± 1.291.

Conclusion

Cell viability of 1% silver nanoparticles reinforced MDX4-4210 silicone was higher in comparison to the other groups, and tear bond strength and shore hardness were significantly higher in 1% silver nanoparticles reinforced silicone compared to 1% titanium nanoparticles reinforced MDX4-4210 silicone.

Effect of Thixotropic Agent on the Color Stability of Platinum-Based Silicone Maxillofacial Elastomers after Artificial Aging

Maxillofacial prostheses are essential for restoring natural appearance and function in individuals with defects in the head and neck regions. Thixotropic agents, as liquid additives, are known to increase the viscosity of silicone elastomers. However, color deterioration remains a challenge in facial prostheses, leading to the need for refabrication. Despite this, there is limited research on the effect of thixotropic agents on the color stability of silicone maxillofacial elastomers. This study aims to investigate the impact of different thixotropic agent amounts on the color degradation of various maxillofacial silicone elastomers. Three elastomers (A-2000, A-2006, and A-2186) were combined with five pigments (no pigment as control, red, yellow, blue, and a mixture of red, yellow, and blue), and mixed with six thixotropic agent quantities (0, 1, 2, 3, 4, and 5 drops). A total of 450 specimens were fabricated (n = 5) and aged in an artificial aging chamber. L*, a*, b* readings were obtained before and after aging using a digital spectrophotometer. Color difference (ΔE*) means and standard deviations for 150 kj/m2, 300 kj/m2, and 450 kj/m2 were calculated. Statistical analyses, including four-way ANOVA and Fisher's PLSD test, were conducted to determine any significant differences (p < 0.05) among the groups. A comprehensive analysis revealed significant four-way interactions among the groups. In the mixed-pigmentation group, adding 4 drops of thixotropic agent resulted in ΔE* above 3 only in A-2186 silicone at 300 and 450 kj/m2 energy levels. However, the color stability of mixed-pigmented A-2000 and A-2006 remained within the acceptable thresholds of 3 ΔE* at all irradiance levels in this study. At each energy level, A-2006 exhibited the highest color stability with an increasing thixotropic agent quantity among all the silicones. Conversely, A-2186 was more affected by the increased number of thixotropic agent drops in each pigmentation group, including the control group at 450 kj/m2. The quantity of thixotropic agent plays a crucial role in determining the color stability of different silicone elastomers pigmented with various intrinsic pigments. The thixotropic agent amount has a more significant impact on color stability than the type of pigment used in the silicone elastomers. A key overarching insight from this investigation is the identification of a safety threshold for the thixotropic agent quantity of 3 drops for each silicone type, pigmentation, and energy level. These findings highlight the importance of considering the proper combination of thixotropic agents, pigments, and silicone materials to achieve optimal color stability in maxillofacial prosthetic applications.

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.

Influence of ozone and paracetic acid disinfection on adhesion of resilient liners to acrylic resin

PURPOSE

The aim of this study was to evaluate the effect of paracetic acid (PAA) and ozone disinfection on the tensile bond strength (TBS) of silicone-based resilient liners to acrylic resins.

MATERIALS AND METHODS

One hundred and twenty dumbbell shaped heat-polymerized acrylic resins were prepared. From the mid segment of the specimens, 3 mm of acrylic were grinded off and separated parts were reattached by resilient liners. The specimens were divided into 2 control (control1, control7) and 4 test groups of PAA and ozone disinfection (PAA1, PAA7, ozone1 and ozone7; n=10). While control groups were immersed in distilled water for 10 min (control1) and 7 days (control7), test groups were subjected to PAA (16 g/L) or ozone rich water (4 mg/L) for 1 cycle (10 min for PAA and 60 min for ozone) per day for 7 days prior to tensile tests. Measurements of the TBS were analyzed using 3-way ANOVA and Tukey's HSD test.

RESULTS

Adhesive strength of Mollosil decreased significantly by application of ozone disinfection. PAA disinfection had no negative effect on the TBS values of Mollosil and Molloplast B to acrylic resin. Single application of ozone disinfection did not have any negative effect on TBS values of Molloplast B, but prolonged exposure to ozone decreased its adhesive strength.

CONCLUSION

The adhesion of resilient liners to acrylic was not adversely affected by PAA disinfection. Immersion in ozonated water significantly decreased TBS of Mollosil. Prolonged exposure to ozone negatively affects adhesion of Molloplast B to denture base materials.

Effects of the Addition of Titanium Dioxide and Silaned Silica Nanoparticles on the Mechanical Properties of Maxillofacial Silicones

PURPOSE

Silicone-based elastomeric materials are commonly used to fabricate maxillofacial prostheses. The aim of this study was to evaluate the effect of different types of silica and nanosized titanium dioxide addition on the mechanical properties of two RTV silicone elastomers.

MATERIALS AND METHODS

A-2000 and A-2006 silicone elastomers were used, and each was divided into four subgroups (n = 5). The first group was the control without additives. Other groups were titanium dioxide, fumed silica, and silaned silica. Each specimen was prepared in compliance with the manufacturer's instructions for the tensile strength, percent elongation, tear resistance, and the hardness tests according to ISO and ASTM standards. A factorial ANOVA with pairwise interaction indicated that the pattern for all four outcomes of the materials was different for A-2000 and A-2006 (p < 0.05). Therefore, the average outcome values for the materials within silicone elastomers were then analyzed by Tukey HSD. For the hardness test results, Kruskal-Wallis and Mann-Whitney U test methods were used. The level of statistical significance was p < 0.05.

RESULTS

There was a statistically significant interaction (p < 0.05) between materials and silicone type for all four tests (tensile strength, tear, hardness, percent elongation). The hydrophobic silica group had significantly higher tensile strength than TiO₂ for A-2000. The fumed hydrophilic silica group had significantly higher tensile strength than TiO₂ for A-2006. Most of silica specimens had higher tensile strength when compared with the control and TiO₂ groups for A-2000 and A-2006 silicones. The TiO₂ group had the highest hardness value for A-2000 while the lowest hardness value for A-2006 (p < 0.05). There was no significant difference of tear strength among the type of additives (p > 0.05) for A-2000. The fumed silica and TiO₂ groups had significantly higher tear strength than the control group for A-2006. The fumed silica and the hydrophobic silica groups had significantly higher percent elongation than the control group (p < 0.05) for A-2000. The TiO₂ group had the lowest percent elongation for A-2006.

CONCLUSIONS

Results in this in vitro study may clarify future studies about the effect of different additives on the physical and mechanical properties of maxillofacial elastomers. There is a great interest in the effect of a new-generation hydrophobic silica incorporation into A-2000 silicone as well as the effect of fumed hydrophilic silica incorporation into A-2006 silicone. Future research should be supported with more in vitro trials in different percentages of such additives used in this study.

Bond strength of silicone to polyurethane following immersion of silicone in cleaning solutions

STATEMENT OF PROBLEM

The use of polyurethane liners beneath silicone facial prostheses is recommended to improve the effectiveness of water-based adhesives, reduce bacterial colonization, and allow very thin margins. Patients using silicone prostheses with a polyurethane lining often observe different degrees of debonding which may lead to failure of the prosthesis. Aggressive cleaning may be associated with debonding of the silicone to polyurethane.

PURPOSE

The purpose of this investigation was to determine the effect on bond strength of soaking specimens of silicone to polyurethane in hot or room-temperature soapy water.

MATERIAL AND METHODS

Specimens of silicone to primed polyurethane were divided into 3 groups of 16 specimens for testing: control (no soak), room-temperature soapy water soak, and hot soapy water soak. The soaked specimens were placed in soapy water at different temperatures for 1825 minutes to simulate 1 year of a 5 min/day cleaning cycle. One examiner performed the assessment of T-peel strength (N/mm) for all specimens. Each specimen was attached to an adhesive testing machine and separated in tension at the crosshead speed of 25.4 mm/min. Data were analyzed with a 1-way ANOVA followed by post hoc pairwise testing using the Tukey test (alpha=.05).

RESULTS

A significant difference in bonding strength between the 3 groups was found (P<.001), with post hoc tests indicating that the control group bonding strength (6.06 +/- 1.84 N/mm) was significantly higher than both room-temperature water soapy soak (3.93 +/- 1.84 N/mm; P=.005) and the hot soapy water soak group values (2.49 +/- 1.75 N/mm; P<.001). However, there was no significant difference found between the hot and room-temperature soapy soak values.

CONCLUSION

Within the limitations of this study, soaking in hot or room-temperature soapy water produced a significant reduction of bond strength of silicone to polyurethane.

Comparison of tensile and peel bond strengths of resilient liners

Previous studies have shown little agreement between the test methods used to assess the bond strength and the mode of failure of resilient liners. This study evaluated the bond strength characteristics of resilient liners by means of 180-degree peeling and butt tensile strength testing. Seventy-two specimens were divided into peel bond and tensile bond specimen groups and were then subdivided into four test groups to evaluate each resilient liner. Tests were conducted with an Instron universal testing machine at a cross-head speed of 2 mm/minute for the tensile specimens and 5 mm/min for the peel specimens. Tensile bond strength and peel bond strength varied significantly among resilient liners except between Novus and Palasiv-62 liners in tensile testing. The mode of failure of Molloplast-B and Novus liners was significantly different between the tensile bond and peel bond test methods. It was concluded that bond strength characteristics can vary according to the test method used.

Simplified fabrication of orbital prostheses using posterior attachment for the artificial eye

The ocular component of an orbital prosthesis can be held firmly during fabrication by attaching a plastic needle cover with autopolymerizing acrylic resin to the posterior surface of the eye in the wax-sculpted prosthesis. This index is subsequently embedded in the master cast. Compared with other techniques described in the literature, this technique spares the corneal surface of the artificial eye and allows duplicate fabrication of silicone orbital prostheses in nonmetal durable molds.

An evaluation of the surface characteristics of a facial prosthetic elastomer. Part I: Review of the literature on the surface characteristics of dental materials with maxillofacial prosthetic application

Silicone elastomers are used to construct a wide variety of maxillofacial prostheses and appliances. These applications dictate that an elastomer-tissue interface is present. The behavior of this interface will vary according to the method of retention of the prosthesis, the nature of the tissue surface, and whether the prosthesis is externally applied or occupies an intratissue location. Understanding the behavior of the silicone-tissue interface is consequently important. Part I of this series of three articles is a review of the literature on the surface characteristics of dental materials with maxillofacial prosthetic application. The review considers surface texture, indentation hardness, wettability, and reaction of tissues to surface texture of restorative materials.