Comparison of conventional and plant-extract disinfectant solutions on the hardness and color stability of a maxillofacial elastomer after artificial aging

Antimicrobial effects of nano titanium dioxide and disinfectants on maxillofacial silicones

STATEMENT OF PROBLEM

Deficient hygiene of maxillofacial prostheses can be a source of infection, and various disinfectants, including nano-oxides, have been suggested for the disinfection of silicone prostheses. While maxillofacial silicones involving nano-oxides at different sizes and concentrations have been evaluated in terms of their mechanical and physical properties, reports are lacking on the antimicrobial effect of nano titanium dioxide (TiO2) incorporated into maxillofacial silicones contaminated by different biofilms.

PURPOSE

The purpose of this in vitro study was to evaluate the antimicrobial effects of 6 different disinfectants and nano TiO2 incorporation into maxillofacial silicone contaminated with Staphylococcus aureus, Escherichia coli, and Candida albicans biofilms.

MATERIAL AND METHODS

A total of 258 silicone specimens (129 pure silicones and 129 nano TiO2-incorporated silicones) were fabricated. Specimens in each silicone group (with or without nano TiO2) were divided into 7 disinfectant groups (control, 0.2% chlorhexidine gluconate, 4% chlorhexidine gluconate, 1% sodium hypochlorite, neutral soap, 100% white vinegar, and effervescent) in each biofilm group. Contaminated specimens were disinfected, and the suspension of each specimen was incubated at 37 °C for 24 hours. Proliferated colonies were recorded in colony-forming units per mL (CFU/mL). The differences in microbial levels among specimens were evaluated to test the effect of the type of silicone and the disinfectant (α=.05).

RESULTS

Significant difference was found among disinfectants regardless of the silicone type (P<.05). Nano TiO2 incorporation showed an antimicrobial effect on S aureus, E coli, and C albicans biofilms. Nano TiO2 incorporated silicone cleaned with 4% chlorhexidine gluconate had statistically less C albicans than pure silicone. Using white vinegar or 4% chlorhexidine gluconate led to no E coli on either silicone. Nano TiO2 incorporated silicone cleaned with effervescent had fewer S aureus or C albicans biofilms.

CONCLUSIONS

The tested disinfectants and nano TiO2 incorporation into silicone were effective against most of the microorganisms used in this study.

Effects of different types of molds on the color difference, translucency, surface roughness, and hardness of a maxillofacial silicone elastomer

PURPOSE

The purpose of the present study was to evaluate the effects of dental stone molds and three dimensional (3D)-printed molds on the color difference, translucency, surface roughness, and hardness of maxillofacial silicones.

METHODS

To prepare molds, a rectangular body 20 mm in diameter and 2 mm in thickness, was designed with computer-aided design software. Two different dental gypsum molds were prepared with the lost-wax technique. Silicone mixture was poured into molds and polymerized at room temperature for 24 h. Color parameters were measured using a spectrophotometer. A profilometer was used for measuring surface roughness, and Shore A values were obtained with a durometer.

RESULTS

Color change (ΔE00) values of the 3D-resin group (1.53 ± 0.35) were significantly lower than others. The highest translucency parameter (TP) values belonged to the stainless steel group (12.44 ± 0.65). Surface roughness values (Ra) of the stainless steel group (0.28 ± 0.06) were significantly lower than other groups. The mean Shore A value of the 3D-resin group (23.90 ± 1.37) was significantly higher than the blue gypsum group (21.53 ± 0.93).

CONCLUSION

Lower color difference and higher Shore A values were examined with 3D-printed resin molds. The highest TP values and lowest Ra values were obtained when stainless steel was used for molding of maxillofacial silicone.

The Effect of Cigarettes Smoke on the Color and Properties of a Silicone for Maxillofacial Prostheses

Although deterioration of silicone maxillofacial prostheses is severely accentuated in smoking patients, the phenomenon has not been systematically studied. To address a gap in the literature concerning the stability of maxillofacial prostheses during service, in this contribution, the effect of cigarette smoke on the aspect and physical properties of M511 silicone elastomer was evaluated. The aspect, surface, and overall properties of the silicone material, pigmented or not, were followed by AFM, color measurements, FTIR, water contact angle measurements, TGA-DTG and DSC, hardness and compression stress-strain measurements. The types of the contaminants adsorbed were assessed by XRF, ESI-MS, MALDI-MS, and NMR spectral analyses. Important modifications in color, contact angle, surface roughness, local mechanical properties, and thermal properties were found in the silicone material for maxillofacial prostheses after exposure to cigarettes smoke. The presence of lead, nicotine, and several other organic compounds adsorbed into the silicone material was emphasized. Slight decrease in hardness and increase in Young's modulus was found. The combined data show important impact of cigarette smoke on the silicone physical properties and could indicate chemical transformations by secondary cross-linking. To our knowledge, this is the first study making use of complementary physical methods to assess the effect of cigarette smoke on the aspect and integrity of silicone materials for maxillofacial prostheses.

Color Modifications of a Maxillofacial Silicone Elastomer under the Effect of Cigarette Smoke

Although it is known (from the observations of medical professionals) that cigarette smoke negatively affects maxillofacial prostheses, especially through staining/discoloration, systematic research in this regard is limited. Herein, the color modifications of M511 maxillofacial silicone, unpigmented and pigmented with red or skin tone pigments, covered with mattifiers, or with makeup and mattifiers, and directly exposed to cigarette smoke, were investigated by spectrophotometric measurements in the CIELab and RGB color systems. The changes in color parameters are comparatively discussed, showing that the base silicone material without pigmentation and coating undergoes the most significant modifications. Visible and clinically unacceptable changes occurred after direct exposure to only 20 cigarettes. By coating and application of makeup, the material is more resistant to color changes, which suggests that surface treatments provide increased protection to adsorption of the smoke components. The dynamic water vapor sorption (DVS) measurements indicate a decrease of the sorption capacity in pigmented versus unpigmented elastomers, in line with the changes in color parameters.

The Effect of Chemical Disinfectants on Maxillofacial Silicone With the Addition of Silver Nanoparticles: An Original Research

Background and objective Silicone has emerged as the most widely accepted material for facial prosthesis fabrication. However, silicone materials have certain limitations. Several techniques have been investigated to lessen the degradation of the polymer, such as the use of nanoparticles and nano-oxides, etc. In this study, we aimed to evaluate the effect of various chemical disinfectants on color stability, hardness, and surface roughness of maxillofacial silicone, after the addition of silver nanoparticles. Materials and methods This was an in vitro study carried out in the Department of Prosthodontics, Sharad Pawar Dental College and Hospital; 80 samples of maxillofacial silicone incorporated with silver nanoparticles (in a concentration of 20 ppm) were fabricated in a mold of 3 x 10 mm dimension disc. The samples were then tested for surface roughness (using a digital roughness tester), Shore A hardness (using a durometer), and color stability (using a spectrophotometer). The samples were then classified into four groups according to various disinfectants used: sodium hypochlorite (1% w/w), chlorhexidine gluconate (0.2%), and neutral soap, and distal water was deemed the control group. After 48 hours, the samples underwent retesting to assess for changes in readings under the same parameters (i.e., surface roughness, Shore A hardness, and color stability) to obtain results, i.e., the samples were tested after fabrication, before immersion, and 48 hours after immersion in disinfectants. Results When taking into account the surface roughness, the maximum roughness value was observed in the sodium hypochlorite group and the least roughness value in distilled water (mean % change of 38.359 to negligible change in the distilled water group). As for the Shore A hardness, the maximum hardness value was seen in the sodium hypochlorite group and the least hardness value in distilled water (mean % change of 15.780 to 2.125 in distilled water). Regarding color stability, the maximum increase in color values was seen in the sodium hypochlorite group (mean: 2.4) followed by the neutral soap group (mean: 1.653); the chlorhexidine gluconate group (mean: -0.287) showed the maximum decrease in color value from the initial to the final phase. Conclusions Based on our findings, surface roughness altered the most when samples were immersed in 1% sodium hypochlorite disinfectant and the least when samples were immersed in neutral soap disinfectant. Shore A hardness altered the most when samples were immersed in 1% sodium hypochlorite disinfectant, but altered the least when samples were immersed in neutral soap disinfectant. Color stability altered the most when samples were immersed in neutral soap disinfectant, but altered the least when samples were immersed in 0.2% chlorhexidine gluconate. Disinfection with neutral soap seems to lead to fewer changes in physical properties (i.e., surface roughness and Shore A hardness) and hence is recommended as a disinfectant for silicone prosthesis. However, our study also showed that 0.2% chlorhexidine gluconate had the least effect on the parameter of color stability, and hence it could be the disinfectant of choice for prostheses with high esthetic requirements.

Silicones for Maxillofacial Prostheses and Their Modifications in Service

The biomedical applications of silicones are countless due to their outstanding properties. In dentistry, silicone for maxillofacial and plastic surgery has become indispensable, from both physiological and aesthetic points of view. In this mini-review, silicone materials for dentistry and facial prostheses are discussed, focusing on their properties and alterations when exposed for long periods to different environments. A significant number of studies reported in the literature have been conducted in vitro, mimicking some of the main degradative factors which have been identified as triggers for discoloration and deterioration of the mechanical properties. Among these, in artificial aging and accelerated natural aging studies, UV radiation is considered the most important. Other weathering factors, biological contamination, and disinfection agents may have dramatic effects as well. Several general properties of silicones are described at the beginning, with a focus on biocompatibility, cross-linking mechanisms, and applications in dentistry and maxillofacial prosthetics. We discuss the ongoing cross-linking and/or possible exudation after manufacturing, which also affects the stability of the prosthesis over time, and possibly the patient. Next, the main environmental factors that affect the prostheses in service are presented, including the role of cigarettes smoke, which has been discussed very little so far. A few aspects, such as biofilm formation, its negative effects, and proposed solutions to overcome this phenomenon regarding silicones, are also described. We conclude by proposing a set of topics for future research and development based on the gaps that have been identified in the literature. Although silicones are probably irreplaceable in maxillofacial prosthetics, improvements in terms of base materials, additives, surface treatments, and maintenance are possible and necessary for long-lasting and safer prostheses.

The impact of zirconium dioxide nanoparticles on the color stability of artificially aged heat-polymerized maxillofacial silicone elastomer

The limited service life of craniofacial prostheses due to degradation and color instability is a significant challenge. This in vitro study aimed to determine how zirconium dioxide (ZrO2) nanoparticles affect the color stability of M511 heat temperature vulcanizing (HTV) maxillofacial silicone elastomers after artificial aging. ZrO2 nanoparticles were added at concentrations of 1, 2, and 3 wt% to M511 HTV silicone elastomer. Two intrinsic silicone pigments were used (red and mocha). Silicone with pigment and without ZrO2 nanoparticles were used as the control. Eighty disk-shaped specimens were fabricated and divided into eight experimental groups, each containing ten specimens (n = 10). All specimens were subjected to artificial aging, and color changes were recorded at 252, 504, and 1008 h intervals. The L*a *b * values were measured using a colorimeter and the CIE-Lab system. To interpret the recorded color differences, a 50:50 percent perceptibility threshold (ΔE* = 1.1) and acceptability threshold (ΔE* = 3.0) were implemented. A one-way analysis of variance and Tukey's post hoc test at a significance level of 0.05 were used for the statistical analysis. We found that every evaluated specimen group exhibited a chromatic change (ΔE* > 0). The ΔE* values for the mocha pigments with and without ZrO2 nanoparticles were below the perceptible threshold (1.1 units). The ΔE* values of the red pigment with and without ZrO2 nanoparticles were significantly higher than the acceptable threshold (P < 0.000). According to the findings of this in vitro study, all the specimens underwent color changes (ΔE* > 0). The red pigment exhibited highly significant chromatic alterations. In contrast, mocha pigments with and without ZrO2 nanoparticles exhibited the least color change and were below the perceptible threshold. ZrO2 nanoparticles provided important protection and showed a reduction in color change.

Coloring Effects of Disinfectants on Pure or Nano-TiO2-Incorporated Maxillofacial Silicone Prostheses

Silicone elastomers play a crucial role in the field of maxillofacial prosthodontics. To maintain optimal hygiene, various disinfectants have been reported to clean silicone prostheses. Nevertheless, when selecting a disinfectant, it is important to consider not only its antimicrobial efficacy, but also its compatibility with the materials, to minimize any potential impact on the physical properties of the material surfaces. The coloring effect of such disinfectants on different types of silicone is of interest. A total of 144 silicone specimens (72 pure silicones, 72 nano-TiO2-incorporated silicones, from A-2000 and A-2006 silicones) were fabricated in this study. The spectrophotometric analysis was carried out, and the initial CIE L*a*b* color values were measured prior to disinfection. Specimens in each silicone group (with or without nano-TiO2) were subjected to a 30-h disinfection period simulating 1 year of disinfection with the following disinfectants: Control (tap water), 0.2% chlorhexidine gluconate, 4% chlorhexidine gluconate, 1% NaOCl, neutral soap, and effervescent. After the second color values were recorded, the color change (∆E*) was calculated. Significant differences were observed among the disinfectants for both the A-2000 and A-2006 silicone groups. Nano-TiO2 did not show a color protection effect in A-2000 silicone. In contrast, nano-TiO2 incorporation provided color protection against CHG 0.2%, CHG 4%, and NaOCl in A-2006 silicone. Most of the disinfectants did not show acceptable color stability over time. In pure A-2000 silicone, except for 0.2% chlorhexidine, all disinfectant groups demonstrated a color change within the acceptability threshold of 50:50% (∆E* = 3.0). On the other hand, in nano-TiO2-incorporated A-2006 silicone, only 0.2% and 4% chlorhexidine demonstrated an acceptable color change. Overall, chlorhexidine could be used as a suitable disinfectant in maxillofacial silicone prostheses.

Complete Denture - Border Molding Technique Using a Laboratory Condensation Silicone Putty: Review

During the fabrication of a complete denture, functional impression is taken. Literature studies show that polydimethylsiloxane (condensation silicone) has not been reported by United States dental schools to perform border molding. Thus, the purpose of this article is to review the functional impression technique when border molding is performed with a laboratory condensation silicone putty.

Fungicidal Effect of Lemongrass Essential Oil on Candida albicans Biofilm Pre-established on Maxillofacial Silicone Specimens

Aims:

This in-vitro study aimed to evaluate the efficacy of lemongrass (Cymbopogon citratus) essential oil in eradicating Candida albicans biofilm pre-established on the maxillofacial silicone specimens.

Materials and Methods:

Two maxillofacial silicones, namely, MDX4-4210 and Multisil Epithetik, were used for the fabrication of 6 mm diameter disks (n = 21 for each brand of silicone). A 48-h mature C. albicans ATCC 10231 biofilm was pre-established on sterile silicone specimen. These disks were then exposed to various concentrations of lemongrass essential oil ranging from 0.31% to 5% (v/v), 20% (v/v) nystatin, and RPMI-1640 medium for 18–20 h. After exposure, the remaining viable fungal biofilm was examined by the XTT [2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide]-reduction assay. All data were analyzed by using a regression coefficient and a post hoc Tukey HSD multiple comparisons test (α = 0.05).

Results:

Different brands of silicone used for fabrication did not significantly affect the formation of mature C. albicans biofilm (P =0.302). A 5% (v/v) lemongrass essential oil significantly eliminated fungal biofilm by approximately 95% (P =0.031). However, less than 50% of the fungal biofilm was eliminated by the tested oil at a concentration as low as 0.31% (v/v). Furthermore, the fungicidal efficacy against C. albicans biofilm of lemongrass essential oil at 2.5% (v/v) was as potent as that of 20% (v/v) nystatin suspension (P = 0.99).

Conclusion:

Lemongrass essential oil expressed fungicidal effect on C. albicans biofilm pre-established on the disks fabricated from different brands of silicone. Additionally, the fungicidal effectiveness of the oil against the mature fungal biofilm was dose-dependent.

Classification, History, and Future Prospects of Maxillofacial Prosthesis

This review presents a classification system for maxillofacial prostheses, while explaining its types. It also aims to describe their origin and development, currently available materials, and techniques, predicts the future requirements, and subsequently discusses its avenues for improvement as a restorative modality. A literature search of the PubMed/Medline database was performed. Articles that discussed the history, types, materials, fabrication techniques, clinical implications, and future expectations related to maxillofacial prostheses and reconstruction were included. Fifty-nine articles were included in this review. Maxillofacial prostheses were classified as restorative or complementary with subclassifications based on the prostheses finality. The origin of maxillofacial prostheses is unclear; however, fabrication techniques and materials have undergone several changes throughout history. Currently, silicones and acrylic resins are the most commonly used materials to fabricate customized prostheses. Maxillofacial prostheses not only restore several types of orofacial defects but also improve the patients' quality of life. Although the current clinical scenario concerning the field of maxillofacial prostheses is promising, improvements in material quality and techniques for maxillofacial prostheses may be expected in the future, to produce better results in the treatment of patients.

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 some mechanical properties of a new silicone elastomer for maxillofacial prostheses after addition of intrinsic pigments

OBJECTIVE

The approximate life span of a silicone maxillofacial prosthesis is as short as 1.5-2 years of clinical service, then a new prosthesis should be fabricated. The most common reason for re-making the prosthesis is silicone mechanical properties degradation. The aim of this study was to assess some mechanical properties of VST-30 silicone for maxillofacial prostheses after addition of intrinsic pigments.

METHODS

Two types of intrinsic pigments (rayon flocking and burnt sienna); each of them was incorporated into silicone. One hundred and twenty samples were prepared and split into 4 groups according to the conducted tests (tear strength, hardness, surface roughness, and tensile strength and elongation percentage) with 30 samples for each test. Each group was equally split into three subgroups. Group (A) was without pigment (control group), group (B) was with rayon flocking and group (C) was with burnt sienna.

RESULTS

Samples with rayon flocking showed a highly significant decrease in hardness and there was a significant increase in tear strength, while there were non-significant differences in surface roughness, tensile strength and elongation percentage. Samples with burnt sienna showed a highly significant increase in tear strength and a highly significant decrease in hardness, but surface roughness, tensile strength and elongation percentage showed non-significant differences. However, there were non-significant differences between experimental groups in all tests.

CONCLUSIONS

The addition of each of rayon flocking and burnt sienna changed the mechanical properties of the VST-30 silicone, while no superior pigment-silicone combination was revealed in all the conducted tests.

Fabrication of a custom pediatric nasal mask for noninvasive ventilation using a maxillofacial elastomer: A straightforward technique

The facial masks commercially available for noninvasive positive pressure ventilation therapy for children with clinical conditions of hypoventilation are limited by size and hardness. The present report describes a straightforward method of developing a nasal mask from a room-temperature vulcanizing silicone elastomer for daily contact with the nasal mucosa of babies during noninvasive positive pressure ventilation. The fabrication of the silicone mask with nasal tubes is based on maxillofacial prosthesis techniques, with retention with steel prongs and elastics.

Effect of nano-titanium oxide addition on some mechanical properties of silicone elastomers for maxillofacial prostheses

OBJECTIVE

This study evaluated the effects of adding titanium oxide (TiO2) nanofillers on the tear strength, tensile strength, elongation percentage, and hardness of room-temperature-vulcanized (RTV) VST50F and high-temperature-vulcanized (HTV) Cosmesil M511 maxillofacial silicone elastomers.

METHODS

Two types of maxillofacial elastomers, VST50F RTV and Cosmesil M511 HTV, were used. Nano-TiO2 powder was applied as a nanofiller. A total of 120 specimens were fabricated, 60 each of VST50F and Cosmesil M511. The specimens of each type of elastomer were divided into three equal groups on which tests were conducted for tear strength, tensile strength, and hardness i.e., 20 specimens were used for each test. Each group of 20 specimens was further divided into two equal subgroups: (A) control i.e., silicone without nano-TiO2, and (B) experimental i.e., VST50F and Cosmesil M511 silicone incorporated with 0.25 wt% and 0.2 wt% nano-TiO2, respectively. Each subgroup thus had 10 specimens. The specimens were evaluated, and data were studied using descriptive statistical analysis and two-way analysis of variance (ANOVA).

RESULTS

The addition of 0.25 wt% and 0.2 wt% TiO2 nanofiller into VST50F and Cosmesil M511 elastomers, respectively, resulted in a statistically significant increase in the mean values (p < 0.01) of tear strength, tensile strength, elongation percentage, and hardness of the materials.

CONCLUSION

The mechanical properties of the VST50F and Cosmesil M511 maxillofacial silicone materials improved with the addition of select concentrations of nano-TiO2.

Synthesis of Novel Reactive Disperse Silicon-Containing Dyes and Their Coloring Properties on Silicone Rubbers

Novel red and purple reactive disperse silicon-containing dyes were designed and synthesized using p-nitroaniline and 6-bromo-2,4-dinitro-aniline as diazonium components, the first condensation product of cyanuric chloride and 3-(N,N-diethyl)amino-aniline as coupling component, and 3-aminopropylmethoxydimethylsilane, 3-aminopropylmethyldimethoxysilane, and 3-aminopropyltrimethoxysilane as silicone reactive agents. These dyes were characterized by UV-Vis, ¹H-NMR, FT-IR, and MS. The obtained reactive disperse silicon-containing dyes were used to color silicone rubbers and the color fastness of the dyes were evaluated. The dry/wet rubbing and washing fastnesses of these dyes all reached 4–5 grade and the sublimation fastness was also above 4 grade, indicating outstanding performance in terms of color fastness. Such colored silicone rubbers showed bright and rich colors without affecting its static mechanical properties.

Effect of different types of disinfection solution and aging on the hardness and colour stability of maxillofacial silicone elastomers

INTRODUCTION

Understanding the effect of aging and different disinfecting agents on the physical properties of pigmented maxillofacial silicones may help eliminate the current uncertainty as to the best follow-up suggestions for the patients treated with silicone prostheses.

METHODS

One hundred fifty specimens (14 × 2 mm) were evaluated for colour and 75 specimens (30 × 10 mm) for hardness (total, 225 specimens). Five specimens were used for hardness testing in each disinfecting solution while 10 silicone specimens were used for colour evaluation. The samples were separated into 5 groups and the initial hardness and colour evaluations were performed and placed in disinfectant solution (neutral soap, effervescent tablet, 0.2% chlorhexidine, 4% chlorhexidine, sodium hypochlorite). A second set of colour and hardness measurements was taken after 48 hours of disinfection and 1,008 hours of artificial aging in a QUV-accelerated weathering tester. Two-way and 1-way analysis of variance with Tukey tests and paired t-test were used for statistical analysis (α = 0.05).

RESULTS

Before artificial aging, the hardness value of the red pigment group was found to be significantly lower than that of the brown pigment group. After aging, the lowest Shore A value was seen in the neutral soap group, while the highest was seen in the effervescent tablet.

CONCLUSIONS

Based on the results of this study, chlorohexidine 0.2% was found to be most suitable agent for disinfection of the prostheses. Washing with neutral soap caused loss of pigment from the surface of the silicones. Sodium hypochlorite was found to have a colour-fading effect on silicone specimens.

Effect of vulcanization temperature and dental stone colour on colour degradation of maxillofacial silicone elastomers

Background

Colour degradation is a major problem in maxillofacial silicone elastomers. Recent studies have focused on colour stability and the mechanical properties of the silicone elastomers. A colour match is also essential for the acceptance of the prosthesis by the patient. The aim of this study is to assess the colour degradation of the silicone elastomer after being moulded in different colours of dental stones at two different vulcanization temperatures.

Methods

Five different colours of dental stones were used to fabricate a total of 120 silicone blocks using a Cosmesil M511 maxillofacial silicone elastomer. Vulcanization was completed at two different temperatures (25 and 100° Celsius). Colour measurements were obtained with a Conica Minolta spectrophotometer. The CIEDE2000 formula was used to calculate the colour differences (∆E00). Two-way ANOVA, one-way ANOVA with Bonferroni corrected post-hoc p values and independent samples t-test were used for the statistical analyses.

Results

High temperature vulcanization causes lightening of the maxillofacial silicone elastomers without regard to the dental stone colour (p = 0.001). Specimens moulded in green stone lightened least at room temperature (p = 0.999). Compared to the control group, at high temperature, all specimens moulded in coloured dental stones darkened significantly (p < 0.001 for white, blue and yellow; p = 0.006 for green; p = 0.045 for reddish-brown). In the high temperature group, the shift to a green chroma was significant in the white, yellow and green dental stones groups (p = 0.001, p = 0.002, p < 0.001, respectively). The mean b* of the high temperature control group was higher than that of the room temperature control group (p < 0.001). The only ∆E00 score lower than the perceptibility threshold for dental materials (∆E00 = 1.30) was between the room temperature control group and the room temperature green dental stone group (∆E00 = 0.96).

Conclusions

Green and blue dental stones cause less colour degradation in silicone elastomers. Reddish-brown dental stones cause the most colour degradation in silicone elastomers. At 100 °C, the colour of the silicone elastomer lightens and yellows even if the elastomer is vulcanized in a stainless steel mould. White, yellow and reddish-brown dental stones make the silicone elastomer appear more yellow even if the elastomer is vulcanized at room temperature.

Antimicrobial activity of conventional and plant-extract disinfectant solutions on microbial biofilms on a maxillofacial polymer surface

STATEMENT OF PROBLEM

Dentists often note problems with infection in patients with maxillofacial prostheses. Conventional disinfection protocols are not always effective and may alter the properties of the polymer used in the prosthesis. Thus, the search for improved disinfection methods is important.

PURPOSE

The purpose of this in vitro study was to evaluate and compare the antimicrobial activity of conventional disinfectant solutions (water and neutral soap and 4% chlorhexidine) and plant extracts (Cymbopogon nardus and Hydrastis canadensis) on specimens of maxillofacial silicone contaminated with Candida albicans and Staphylococcus aureus biofilms.

MATERIAL AND METHODS

Seventy-two silicone (MDX4-4210) specimens were fabricated (5×2 mm) and sterilized. Thirty-six were contaminated with C albicans (10(6) cells/mL) and 36 with S aureus (10(8) cells/mL) to evaluate the antimicrobial activity of the cleaning protocols. After incubation (37°C/72 hours), the specimens were divided into 5 groups: not disinfected (positive control), soaking in saline solution for 10 minutes, soaking in 4% chlorhexidine for 10 minutes, soaking in C nardus for 10 minutes, soaking in H canadensis for 10 minutes, and washing by hand with water and neutral soap for 30 seconds. The viability of cells was evaluated by XTT (2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide) assay and by scanning electron microscope analysis. The results were analyzed by ANOVA and the Tukey HSD test (α=.05).

RESULTS

All disinfection solutions provided a statistically significant reduction in biofilm viability compared with the control group for both microorganisms (P<.05). Washing with water and neutral soap was significantly more effective in reducing biofilm viability than immersion in the disinfection solutions, with persistence of viable microorganisms between 1.05% for C albicans and 0.62% for S aureus after this cleaning protocol. Photomicrographs revealed that 4% chlorhexidine altered the surface of the polymer.

CONCLUSIONS

Within the limitations of this in vitro study, it was concluded that the cleaning protocols with different disinfectant solutions produced a significant reduction in the viability of C albicans and S aureus biofilms on the silicone polymer. Washing with water and neutral soap was the most effective protocol against both microorganisms.