Cigarette staining and cleaning of a maxillofacial silicone

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.

Ultraviolet C as a method of disinfecting medical silicone used in facial prostheses: An in vitro study

STATEMENT OF PROBLEM

Hygiene and disinfection are important factors for preserving facial prostheses and supporting tissue health. However, a method that does not accelerate degradation or color change is necessary.

PURPOSE

The purpose of this in vitro study was to evaluate the effectiveness of irradiation with ultraviolet C light-emitting diode (UV-C LED) light in the disinfection and initial color stability of the silicone (A-588-1; Factor II) used in facial prostheses.

MATERIAL AND METHODS

One hundred and twenty specimens were made, contaminated by multispecies biofilm, and divided into 5 groups (n = 24) with different treatments: control, distilled water, 0.12% chlorhexidine, UV-C LED light, and dimethyl sulfoxide (DMSO) as the negative control. Cell viability was measured by the methyl tetrazolium salt method. Statistical analysis was performed by generalized linear models. Additional descriptive analysis was performed for color analysis by using 16 silicone specimens made with light and dark intrinsic coloring in 4 groups (controls and treatments n=4) submitted to UV-C LED light. The ΔE of the specimens was obtained by CIEDE200.

RESULTS

The results of cell viability demonstrated a statistically significant difference among the groups (P<.001), with a microbial reduction after UVC-LED exposure compared with the control group. Regarding the color, the groups presented an average ΔE (light 0.205 and dark 0.308) compatible with visually imperceptible changes (light < 0.7 and dark < 1.2).

CONCLUSIONS

Irradiation with UV-C LED light decreased the in vitro microbial cell viability of the medical silicone used in facial prostheses, demonstrating initial color stability.

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.

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.

Efficacy of cleansing agents in killing microorganisms in mixed species biofilms present on silicone facial prostheses--an in vitro study

OBJECTIVES

The purpose of this study was to assess the efficacy of different cleansing agents in killing mixed species biofilms on silicone facial prostheses.

MATERIALS AND METHODS

Two bacterial and three yeast strains, isolated from silicone facial prostheses, were selected for the mixed species biofilms. A variety of agents used to clean facial prostheses were employed, viz., antibacterial soap, essential-oil-containing mouth rinse, ethanol 27 %, chlorhexidine mouth rinse, and buttermilk. Colony forming units (CFUs) and live/dead staining were analyzed to assess the efficacy of these cleansing agents against 24-h and 2-week biofilms and regrown biofilms on silicone samples.

RESULTS

Chlorhexidine was the most effective cleansing agent. Chlorhexidine killed 8 log unit CFUs (>99.99 % killing) in a 24-h biofilm and 5 log unit CFUs (>99.99 % killing) in 2-week biofilms. Also, after regrowth and repeated treatment of the biofilm, chlorhexidine was the most effective cleansing agent showing no detectable CFUs. The essential-oil-containing mouth rinse (containing 26.9 % ethanol) showed a similar efficacy as ethanol (27 %) alone. Antibacterial soap and buttermilk were the least effective agents tested.

CONCLUSIONS

Chlorhexidine showed the highest reduction in CFUs in 24-h, 2-week, and regrown mixed species biofilm of microorganisms isolated from silicone facial prostheses.

CLINICAL RELEVANCE

Chlorhexidine mouth rinse (easy obtainable and relatively cheap) is very effective in killing bacteria and yeast present in biofilms on silicone facial prostheses. When applied on a regular basis, cleansing a facial prosthesis with chlorhexidine will presumably increase its lifetime and reduce skin irritations.

Effect of cigarette smoke on acrylic resin teeth

BACKGROUND

The discolouration of artificial teeth, which hampers aesthetics, is one of the negative effects of cigarette smoking. Therefore, the effect of cigarette smoke on the colour stability of commercially available acrylic resin teeth needs to be evaluated for clinical success and to ascertain as to which brand has superior properties.

MATERIAL AND METHODS

Three commercially available acrylic teeth were evaluated, after division into Group A (Premadent), Group B (Astra), and Group C (Sanyo- Dent). Selected brands were subdivided as study group and control group. Each set of acrylic resin teeth were stored in artificial saliva at 37±1°C for 24 hours. After 24 hours of immersion, the colour measurement of each tooth (T0) was performed. Second colour measurements were done after 21 days (T21) of exposure to cigarette smoke for study group and after immersion in artificial saliva for control group. All data was statistically analyzed by using Repeated Measures ANOVA and Two-way ANOVA (p<0.05).

RESULTS

Group A showed least total colour change on exposure to cigarette smoke, followed by Group B and Group C had the highest total colour change. In control group, after immersion in artificial saliva, a slight increase in total colour change was observed for all groups, which was clinically acceptable.

CONCLUSION

Group A (crosslinked acrylic resin teeth) was more colour stable and more resistant to the discolouration which was caused by cigarette smoke, followed by Group B (crosslinked acrylic resin teeth). Group C (Non-crosslinked acrylic resin teeth) was least colour stable and most susceptible to discolouration which was caused by cigarette smoke.

Influence of pigments and opacifiers on color stability of silicone maxillofacial elastomer

OBJECTIVES

To determine the effects of opacifiers and silicone pigments on the color stability of silicone A-2000 maxillofacial prosthetic elastomers subjected to artificial aging.

METHODS

Seventy-five groups (n=5) were made by various combinations (5%, 10%, and 15%) of four dry earth opacifiers (Georgia kaolin, Gk; calcined kaolin, Ck; Artskin white, Aw; titanium white dry pigment, Td); and 1 silicone pigment white (Sw) with one of 5 silicone pigments (no pigment (control), red (Pr), yellow (Py), burnt sienna (Po), and a mixture of Pr+Py+Po). A reflection spectrophotometer was used for color measurements. Color differences (DeltaE*) between baseline and after an energy exposure of 450kJ/m(2) in an artificial aging chamber were calculated. A DeltaE*=3.0 was used as 50:50% acceptability threshold in result interpretation, while DeltaE*=1.1 was used as 50:50% perceptibility threshold. Means were compared by Fisher's PLSD intervals at the 0.05 level of significance. Color differences after aging were subjected to three-way analysis of variance.

RESULTS

Yellow ochre mixed with all opacifiers at all intervals had increased DeltaE* values significantly from 0.7-2.1 up to 3.8-10.3. When mixed groups were considered, at 5%, Gk exhibited the smallest color changes, followed by Td<Aw=Sw<Ck, respectively. At 10%, Aw<Td<Gk<Sw=Ck. At 15%, Td<Aw<Gk=Sw<Ck (< indicates p<0.0001 and = indicates p>0.05). The smallest color differences, observed for opacifier groups, were recorded for Gk at 5%, and Td and Aw at 10% and 15%. Overall, 15% Td exhibited the smallest, whereas 5% Ck exhibited the most pronounced color change after artificial aging. All DeltaE* values were below the 50:50% acceptability threshold, indicating acceptable color stability. Color differences for 10% and 15% of Aw and Td were below 50:50% perceptibility thresholds, indicating excellent color stability.

CONCLUSION

Silicone pigments mixed with 10% and 15% Artskin white and titanium white dry pigment opacifiers protected silicone A-2000 from color degradation over time. Yellow silicone pigment significantly affected color stability of all opacifiers especially silicone pigment white and calcined kaolin.

Facial prosthetic rehabilitation: preprosthetic surgical techniques and biomaterials

PURPOSE OF REVIEW

Attention to detail ensuring a successful facial prosthetic rehabilitation must be considered a priority at the time of presurgery, surgery, and at every stage in fabricating the prosthesis. Teamwork between the surgeon and maxillofacial prosthodontist will ensure an optimal surgical preparation and definitive prosthesis.

RECENT FINDINGS

Evidence of interaction between team members can most certainly be encouraging to the patient. During the prosthetic phase of treatment, focusing on tissue assessment, impression making, sculpting, mold fabrication, familiarity with materials, appreciation of color, delivery of instructions, and patient education will ensure a satisfactory outcome. With the desire, determination, and encouragement from the restorative team to make the most of this artificial replacement, a patient can have a higher quality of life and a more normalized lifestyle.

SUMMARY

This review presents current concepts regarding facial prosthetic rehabilitation of patients with head and neck cancer and facial prosthetic biomaterials.

Effects of environmental factors on maxillofacial elastomers: Part III--Physical properties

The physical properties of four currently used and two recently introduced maxillofacial prosthetic materials were evaluated after the materials were subjected to the following seven environmental variables: natural weathering, normal aging, two types of adhesives, two types of cleaning agents and cosmetics. Ultimate tensile strength, percent elongation, tear strength, and Shore A hardness were evaluated. The physical properties recorded for the currently used materials were consistent with previous studies. Although the properties of the recently introduced materials were similar to those currently in use, one of the new materials, A-2186, showed high strength values, although it was one of the softest materials tested. Unfortunately, this new material lost these advantageous characteristics as it was weakened and made harder by most of the tested environmental variables.