ORIGINAL RESEARCH

https://doi.org/10.5005/jp-journals-10019-1428
International Journal of Prosthodontics and Restorative Dentistry
Volume 13 | Issue 4 | Year 2023

Dimensional Stability of Maxillofacial Prosthetic Room Temperature Vulcanized Silicones after Various Disinfection Protocols: An In Vitro Study

Neha Parmar¹, Sareen Duseja² https://orcid.org/0000-0002-2360-0899

^1,2Department of Prosthodontics and Crown & Bridge, Narsinhbhai Patel Dental College & Hospital, Sankalchand Patel University, Visnagar, Gujarat, India

Corresponding Author: Sareen Duseja, Department of Prosthodontics and Crown & Bridge, Narsinhbhai Patel Dental College & Hospital, Sankalchand Patel University, Visnagar, Gujarat, India, Phone: +91 9979961730, e-mail: drsareenduseja@gmail.com

Received: 09 September 2023; Accepted: 29 November 2023; Published on: 30 December 2023

ABSTRACT

Purpose: To determine the influence on the dimensional stability of silicone specimens treated with water, soap water, alcohol, and herbal disinfectant for 45 days.

Materials and methods: A total of 80 test specimens were prepared from room temperature vulcanizing (RTV) silicones using a metal die according to the American Dental Association (ADA) specification no. 19 and divided into four groups (n = 20). Each group’s samples were treated with a different disinfectant solution (normal water, soap water, herbal disinfectant, and alcohol disinfectant) twice a day for 45 days. Dimensional stability was analyzed by stereomicroscope in intervals of every 15 days. Repeated measure analysis of variance (ANOVA), one-way ANOVA, and post hoc Tukey test were used for statistical analysis.

Results: Initially, alcohol disinfectant causes more shrinkage of silicone, while herbal disinfectant results in less shrinkage of silicone prosthesis. Dimensional stability measurements of samples treated with normal water (24.91, 24.84, and 24.72 mm), soap water (24.94, 24.91, and 24.73 mm), herbal-based disinfectant (24.9, 24.87, and 24.78 mm), and alcohol disinfectant (24.96, 24.93, and 24.75 mm) at 15, 30, and 45 days, respectively revealed significant shrinkage of RTV silicones over time in each group (p < 0.05).

Conclusion: Herbal disinfectant can be a favorable disinfectant for maintaining dimensional stability of RTV silicone in comparison to soap water as well as alcohol-based disinfectant.

How to cite this article: Parmar N, Duseja S. Dimensional Stability of Maxillofacial Prosthetic Room Temperature Vulcanized Silicones after Various Disinfection Protocols: An In Vitro Study. Int J Prosthodont Restor Dent 2023;13(4):210–215.

Source of support: Nil

Conflict of interest: None

Keywords: Alcohol disinfectant, Coronavirus disease of 2019, Dimensional stability, Herbal disinfectant, Maxillofacial prosthesis

INTRODUCTION

Maxillofacial prosthetics is the branch of prosthodontics concerned with the restoration and/ or replacement of stomatognathic and craniofacial structures with prostheses that may or may not be removed on a regular or elective basis.¹ Congenital malformations, facial trauma, and surgery in the head and neck area often lead to loss of function and unesthetic appearance, which directly affects the social and mental well-being of a person.² Plastic reconstruction of such defects is a boon to avoid surgical procedures for maxillofacial defects. Earlier materials like wax, wood, ivory, etc., caused dissatisfaction and discomfort due to their hardness and unalluring appearance. Therefore, it was imperative to develop new prosthetic materials.³ With modernization, the choice of material for facial prostheses has changed. Latex, polymethacrylates, polyvinylchloride, chlorinated polyethylene, silphenylene, and silicone elastomers (polydimethylsiloxane) became the materials of choice.² Various types of medical-grade silicones are available in the market. Factor B (A-103) medical grade is popular as there are minimal changes with outdoor weathering in pairwise comparison with room temperature vulcanizing (RTV) (A-2000, A-2006, and A-103) and HTV (M-511) silicone.⁴

In 1960, Barnhart introduced silicone as the material of choice for facial prostheses for properties like good tear strength, dimensional stability, and durability.⁵ However, it has inherent limitations, too, in terms of surface hardness and roughness with time, repairing difficulties, and color alteration due to pigment loss, which often makes it unacceptable to the patient. Dimensional stability is an integral property for extending prosthesis fitting to protect body tissues and esthetics.⁶^,⁷ Hands and face are the most contaminated surfaces for transmission of any type of infection. Varieties of disinfectants are used to prevent infections, which may lead to the degradation of static and dynamic properties of silicones and prosthesis discoloration in the service environment.⁸^,⁹

Water and soap water have been recommended for cleaning silicone maxillofacial prostheses for ages, according to the Centers for Disease Control guidelines.¹⁰ Soap has been shown to be more effective than hand sanitizer, but it removes saliva and blood partially only because of salivary mucins and sticky protein sticking to the silicones and skin.¹¹ World Health Organization recommends alcohol-based sanitizers as the major preventive measure against disease transmission from hand to mucosal membrane and are effective against bacteria, fungi, and enveloped viruses except naked viruses.¹²^-¹⁶ Despite this, all of it contains harsh chemicals that affect the skin proteins and damage the natural barrier of the skin.¹⁷^,¹⁸

The purpose of the study was to evaluate and compare the dimensional stability of pigmented RTV silicones sprayed with water, soap water, herbal disinfectant, and alcohol disinfectant over a period of 45 days. The null hypothesis was that there was no significant difference in dimensional accuracy of maxillofacial silicone material when sprayed with water, soap water, herbal-based disinfectant, and alcohol disinfectant over a period of 45 days.

MATERIALS AND METHODS

The study was comparative in vitro research to evaluate the dimensional stability of commonly used RTV silicone used for maxillofacial prosthesis with a total sample size of 80. The sample size was calculated by using G*Power 3.1.9.7 software, keeping the significance level at 0.05 and the power of the study at 0.80. The effect size came to be 0.25 with a total sample size of 72 samples. So, the sample size was rounded off to 80. The study was approved under the Indian Council of Medical Research Short-Term Studentship Project 2022. (Approval number/reference ID: 2022-09637 and report approval date: 13^th March 2023)

The maxillofacial silicone material (A-103, Factor 2 Inc, Lakeside, United States of America) was evaluated for dimensional stability after treatment with various disinfectants. The study specimens were divided into four groups depending on the type of disinfectant used: group I (normal water), group II (soap water, Dettol, Reckitt Piramal Ltd, Haryana, India), group III (Herbal disinfectant, natural disinfectant spray, Apollo Pharmacy, Chennai, India), and group IV (alcohol disinfectant, Apollo life hand sanitizer liquid, Apollo Pharmacy, Chennai, India) with 20 samples in each group. The dimensional stability was evaluated at 15, 30, and 45 days. The herbal-based disinfectant contains benzalkonium chloride, neem oil, and water. The alcohol disinfectant contains ethanol, glycerol, and hydrogen peroxide. The soap water contains 20 gm of powdered soap and 100 mL of water, which is filled in a spray bottle. The soap contained aqua, ammonium lauryl sulfate, sodium laureth sulfate, glycerine, sodium chloride, cocamide monoethanolamine, citric acid, salicylic acid, tetrasodium ethylenediaminetetraacetic acid (EDTA), magnesium nitrate, EDTA, methylchloroisothiazolinone, magnesium chloride, and methylisothiazolinone.

A stainless-steel master die was fabricated using computer-aided design (CAD)/computer-aided manufacturing similar to American Dental Association (ADA) specification no. 19, which is used to make impression samples to gauge dimensional changes (Fig. 1).¹⁹ The master die consists of a ruled block and a mold ring. The ruled block was fabricated using Auto-CAD software and a laser cutting machine. The ruled block has a height of 31 mm, width of 38 mm, 3 mm height, and 29.97 ± 0.01 mm diameter. The step had been made on one side of the die to which the metallic mold ring fits. It has three horizontal lines, X, Y, and Z, and two vertical lines, CD and C’D’. The lines CD and C’D’ were separated from each other by 25 mm. Mold Ringhad an outer ring diameter of 38 mm, inner ring diameter of 30 mm, and height of 6 mm.¹⁹

Fig. 1: Stainless steel mold as per ADA specification 19 for preparation of specimens

Samples were prepared by thoroughly mixing one part of the curing agent with ten parts by weight of the base elastomer in order to get a viscosity that is about half that of the initial base viscosity. Care should be given to minimize air entrapment while mixing and placing in the master die. Material has to be cured for around 24 hours at 23°C (73°F) in order to be adequately cured. The pigments (Factor 2 Inc, Lakeside, United States of America) were incorporated intrinsically in 0.2% concentration by weight. The samples were inspected for voids, bubbles, and contaminants in the region of reference lines (Fig. 2).

Fig. 2: Samples of different groups; group I (normal water), group II (soap water), group III (herbal-based disinfectant), and group IV (alcohol-based disinfectant)

Each sample was sprayed with the disinfectant according to their corresponding groups—group I: normal water, group II: soap water, group III: herbal-based disinfectant, and group IV: alcohol disinfectant (Fig. 3) and were treated twice a day with contact time of 5 minutes, then wiped up with tissue paper and allowed to dry freely (Fig. 4). The storage was done at 23 ± 2°C room temperature wherein samples were not exposed to direct sunlight during the study period. The dimensional measurements were assessed on the 15th, 30th, and 45th day.

Fig. 3: Disinfectant agents group I (normal water), group II (soap water), group III (herbal disinfectant solution), and group IV (alcohol disinfectant)

Fig. 4: Sample treated with disinfectant

Samples were tested using a stereomicroscope (SZ2-ILST transmitted and reflected light LED illuminstor stand; Olympus, Tokyo, Japan; auxiliary objective 110 AL, 0.62 magnification) (Fig. 5). An image-analyzing computer software (Catymage) was utilized to digitalize the sample image and measurement of dimensional changes (Fig. 6). The distance between the reference lines CC’ and DD’ were measured three times and the mean of distance was compared with corresponding measurements on the standard die. The percentage dimensional change was measured by using the formula²⁰:

Fig. 5: Measurement of dimension between reference lines CC’ and DD’ under a microscope

Fig. 6: Sample under the measuring microscope

C = Standard measurement in the die
D = Observed measurements of the specimen under stereomicroscope

All tests were done using statistical Statistical Package for the Social Sciences (SPSS) software (IBM Corp. Released 2011. IBM SPSS Statistics for Windows, Version 20.0. Armonk, New York, United States of America: IBM Corp.). The level of significance was kept at p ≤ 0.05. Repeated measure analysis of variance (ANOVA) was done for the evaluation of dimensional measurements of samples treated with different sanitizers at different time intervals. One-way ANOVA was done for intergroup comparison between all the groups at different intervals. A post hoc Tukey test was done for the pairwise comparison of various groups.

RESULTS

Dimensional stability measurements of samples treated with normal water (24.91, 24.84, and 24.72 mm), soap water (24.94, 24.91, and 24.73 mm), herbal-based disinfectant (24.9, 24.87, and 24.78 mm), and alcohol disinfectant (24.96, 24.93, and 24.75 mm) at 15, 30, and 45 days, respectively (Table 1) revealed significant shrinkage of RTV silicones over time in each group (p < 0.05).

**Table 1:** Dimensional stability measurements of samples treated with different disinfectants at 15, 30, and 45 days
Group	Time period (days)	Number of specimens	Dimensional stability (mm)		p-value
Group	Time period (days)	Number of specimens	Mean	Standard deviation (SD)	p-value
Group I (normal water)	15	20	24.91	0.04	0.001*
	30	20	24.84	0.08
	45	20	24.72	0.11
Group II(soap water)	15	20	24.94	0.09	0.002*
	30	20	24.91	0.06
	45	20	24.73	0.10
Group III (herbal-based disinfectant)	15	20	24.93	0.05	0.003*
	30	20	24.87	0.08
	45	20	24.78	0.08
Group IV (alcohol disinfectant)	15	20	24.96	0.09	0.001*
	30	20	24.93	0.04
	45	10	24.75	0.07

*p ≤ 0.05 is significant

One-way ANOVA for intergroup comparison of dimensional stability among various disinfected samples depicted a statistically significant difference at 30 days (p = 0.038). However, the difference was insignificant statistically at 15 days (p = 0.476) as well as at 45 days (p = 0.514) (Table 2).

**Table 2:** Intergroup comparison of dimensional stability at 15, 30, and 45 days
Time period	Groups	Number	Dimensional stability (micrometer)		p-value
Time period	Groups	Number	Mean	SD	p-value
15 days	Normal water	20	24.91	0.04	0.476
	Soap water	20	24.94	0.09
	Herbal disinfectant	20	24.93	0.05
	Alcohol disinfectant	20	24.96	0.09
30 days	Normal water	20	24.84	0.08	0.038*
	Soap water	20	24.91	0.06
	Herbal disinfectant	20	24.87	0.08
	Alcohol disinfectant	20	24.93	0.04
45 days	Normal water	20	24.72	0.11	0.514
	Soap water	20	24.73	0.10
	Herbal disinfectant	20	24.78	0.08
	Alcohol disinfectant	20	24.75	0.07

*p ≤ 0.05 is significant

On further post hoc Tukey test (Table 3), it was observed that there was a statistically significant difference (p = 0.037) between silicone samples treated with normal water and alcohol disinfectant at 30 days; all other comparisons yielded statistically insignificant results.

**Table 3:** Pairwise comparison of various groups at different time intervals
Time period	Groups		p-value
15 days	Normal water	Soap water	0.774
		Herbal disinfectant	0.932
		Alcohol disinfectant	0.416
	Soap water	Herbal disinfectant	0.984
	Soap water	Alcohol disinfectant	0.932
	Herbal disinfectant	Alcohol disinfectant	0.774
30 days	Normal water	Soap water	0.166
		Herbal disinfectant	0.776
		Alcohol disinfectant	0.037*
	Soap water	Herbal disinfectant	0.652
	Soap water	Alcohol disinfectant	0.893
	Herbal disinfectant	Alcohol disinfectant	0.258
45 days	Normal water	Soap water	0.995
		Herbal disinfectant	0.505
		Alcohol disinfectant	0.875
	Soap water	Herbal disinfectant	0.655
	Soap water	Alcohol disinfectant	0.956
	Herbal disinfectant	Alcohol disinfectant	0.915

*p ≤ 0.05 is significant

Though these results were statistically insignificant, it can be seen that mean dimensional measurements were closer to original measurements when RTV silicones were treated with herbal-based disinfectants over a longer period of time, that is, 45 days. As compared to the original die measurements of 25 mm, the mean corresponding measurements on samples after spraying with herbal-based disinfectants for 45 days were closer (24.78 mm), followed by measurements on samples treated with alcohol disinfectants (24.75 mm), soap water (24.73 mm), and normal water (24.72 mm).

DISCUSSION

The research hypothesis is accepted as there is a significant difference in the dimensional accuracy of maxillofacial silicone material when sprayed with various disinfectants over a period of time. On the other hand, these results were statistically insignificant; it can be seen that mean dimensional measurements were closer to original measurements when RTV silicones were treated with herbal-based disinfectants over a longer period of time, that is, 45 days. As compared to the original die measurements of 25 mm, the mean corresponding measurements on samples after spraying with herbal-based disinfectants for 45 days were closer (24.78 mm), followed by measurements on samples treated with alcohol disinfectants (24.75 mm), soap water (24.73 mm), and normal water (24.72 mm). Conversely factors like skin secretions, environmental conditions and temperature, atmospheric changes and material type, characteristics of disinfectant, relaxation of stresses, and water imbibition have additional effects on the mechanical and physical properties of silicone, which leads to two types of dimensional changes, inherent polymerization shrinkage and form of evaporation shrinkage.⁵^,¹⁴^,²¹

The present study shows significant shrinkage of samples over a period of 45 days, irrespective of disinfection and cleansing protocol. The initial shrinkage is attributed to that occurring during polymerization. The use of various disinfectants yielded statistically insignificant changes in dimensional stability. However, these changes may be clinically significant over a longer period. After initial polymerization shrinkage, the evaporation shrinkage may vary among prostheses treated with different groups. The least shrinkage of silicone was observed with the use of herbal disinfectant over a period of 45 days. During the initial 30 days, dimensional changes were more evident in specimens treated with normal water because silicone swells in contact with water; when water evaporates, silicone contracts and this often results in shrinkage of the prosthesis.²² The least dimensional shrinkage of silicones with herbal disinfectant over a longer period of time (45 days) may be attributed to the least evaporation shrinkage because of neem oil in herbal disinfectants that reduces viscosity acting as a plasticizer. Low-viscosity liquids may have the least evaporation once they are imbibed in a porous material, showing the least dimensional changes in silicone-based prostheses treated with herbal disinfectants.²²

After a period of 45 days, maximum dimensional shrinkage was found with the use of normal water, followed by soap water and alcohol-based disinfectants. Herbal disinfectant resulted in the least dimensional changes. The polymerization reaction is over in the initial hours and is the main cause of the instability of silicone-based polymers, but the constituent evaporation’s contribution, if it exists, can play a substantial long-term role. Aging causes continuous polymerization shrinkage in silicone prosthesis.²³ Evaporation often leads to loss of plasticizers, dibutyl phthalate catalysts, low-molecular-weight polymers, and byproducts of polymerization reaction. Herbal sanitizers contain volatile oil with extremely substantial antimicrobial effects and are less irritating to skin adjacent to prosthesis margins than alcohol-based disinfectants.²⁴^-²⁹

There is a significant contraction of intrinsic pigment incorporated silicone after thermocycling, as reported in a study by Goiato et al.³⁰ However, extrinsic pigmentation did not show a negative effect on dimensional stability, and therefore it can be indicated.³⁰ Many previous studies evaluated that medical grade silicon degrades with time, and prosthesis may need replacement within 6 months.⁶^,³¹^-³⁵

The incorporation of nanoparticles may lead to lesser changes in physical and mechanical properties. Therefore, the further scope of research may be an incorporation of different concentrations of nanoparticles to evaluate dimensional stability over time.³⁶ The limitation of the present study was that it’s an in vitro study done on specimens. Future in vivo studies to evaluate various physical as well as mechanical properties over a longer duration of time may be conducted to determine the actual shelf life of silicone prostheses.

CONCLUSION

Room temperature vulcanizing (RTV) silicones exhibit dimensional shrinkage in spite of the disinfection method employed. It is prudent to note that herbal disinfectant emerges as a promising alternative for effective cleaning protocol. This finding suggests that the herbal disinfectant offers a more reliable solution for maintaining the integrity of silicone prosthetic material in a clinical scenario.

ORCID

Sareen Duseja https://orcid.org/0000-0002-2360-0899

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