1 1DDS, MSc, Assistant professor, Department of Prosthodontics, School of dentistry, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran
2 2DDS, MSc, Assistant professor, Dental research center, Dentistry research institute, Department of prosthetics, School of dentistry, Tehran University of Medical Sciences, Tehran, Iran
3 3Dentist, Private practice, Tehran, Iran
4 4DDS, MS, PHD, FACP, Assistant Professor, Department of prosthetics, School of dentistry, University of California , Los Angeles, US
5 5Ph.D. student, Industrial Engineering and Management department, Oklahoma State University, US.
66DDS, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran, Tehran, Iran
Submission: July 17, 2019; Published: August 07, 2019
*Corresponding author:Maryam Baghizadeh, Tehran University of Medical Sciences, 1208 N. Knoblock, Stillwater, Oklahoma, US, Iran
How to cite this article: Sara M, Safoura G, Maryam J, Alireza M, Ahmadreza H, et al. Evaluating the Effect of Low Concentrations of Common Chemical
Solutions on Disinfecting Heat-Cured Acrylic-Resin. Adv Dent & Oral Health. 2019; 11(1): 555804. DOI: 10.19080/ADOH.2019.11.555804
Purpose: Dental prostheses are exposed to different microbial contaminant that potentially leads to prosthesis-related infections. This study aimed to evaluate the effectiveness of low concentrations of antimicrobial solutions on disinfecting heat-cured acrylic resin.
Materials and Methods: 188 acrylic (KAVO EWL 5518, Automatic curing device, Germany) specimens were fabricated (17×6×1mm), and sterilized. Two specimens (Brain-Heart Infusion Broth, Merk, type 110493, Germany) were kept ensuring the process validation while the remaining specimens were randomly divided in to 3groups (n=62). Each group was immersed in fresh colony suspensions of either Candida-albicans, Staphylococcus-aureus, or Streptococcus-mutans. Two specimens were kept in sterilized culture media (Brain- Heart Infusion Broth, Merk, type 110493, Germany) for ensuring the process validation while the remaining specimens were divided to 4 groups according to subsequent disinfecting procedure (n=15). Each group was immersed either in 0.5% sodium-hypochlorite solution, 0.2% chlorhexidine solution, vinegar, or water. The turbidity measurement of culture media was evaluated at interval time of 30 minutes, 2, and 4 hours. Student T-test, Chi-square and Fisher-exact test were used for results comparison (P<0.05).
Results: Chlorhexidine showed maximum effectiveness on eliminating candida-albicans at all time intervals. For Staph aureus, chlorhexidine was completely effective after two hours. 0.5% Hypochlorite solution eliminated 40% of Staph aureus colonies after 2 hours and retained this effect for 4 hours. All disinfectants were equally effective in eliminating Strep mutans.
Conclusion: Using chlorhexidine, disinfection of acrylic resin from Strep-mutans and Candida-albicans requires less time compare to Staph-aureus. Hypochlorite and vinegar were only effective in complete elimination of Strep-mutans.
Dental prosthesis could be highly contaminated as it is exposed to different infected sources and conditions . Biofilms formation in oral environment may cause different health complications , one of the most important of which is denture stomatitis that affects about two-thirds of full denture wearers [3,4]. Infectious agents can also lead to meningitis, pneumonia, and even heart diseases if swallowed or enter oral
mucosal lesions . Different microorganisms may play role in the formation of such infections, the most important of which are Candida albicans, Staphylococcus aureus, and Streptococcus
mutans [5,6]. Several procedures have been proposed to eliminate these microorganisms; the most prevalent have been reported to be mechanical hygienic procedures, and use of solutions like vinegar, Castrol oil, glutaraldehyde, sodium hypochlorite and chlorohexidine [7-16].
Each suggested material has its own advantages and problems. Among the most commonly used solutions, the benefits of organic vinegar are its lower price, availability, and lower toxicity [8,9].
Chlorhexidine 0.2% is an antimicrobial agent, commonly used in dentistry. It has low systemic toxicity and price; however, the adverse effects include mucosal erosion, unilateral or bilateral
parotid swelling, and bitter taste that cannot be eliminated [8,9].
Hypochlorite alkaline solution has also shown good results for
disinfecting the denture. It has anti-bacterial and antifungal
properties, but in long-term use, may change the color of the
denture base and corrode the denture metallic elements [15,17].
Several studies have evaluated the effect of different concentrations
of various solutions on eliminating denture microorganisms; the
results of studies are summarized in Table 1. [8-14]
Increased concentrations of disinfecting solutions could
increase the effectiveness of antiseptic agents, but at the same
time, increase the material side effects. The present study aimed
to evaluate the effectiveness of lower concentrations of easily
accessible materials commonly used for denture disinfection, on
most common microorganisms contaminate acrylic denture bases.
The null hypothesis was that these materials could effectively
eliminate the microorganisms without any significant difference.
188 rectangular acrylic specimens were made in the same
shape, size, and thickness (17×6×1 mm), and processed (KAVO
EWL 5518, Automatic curing device, Germany) at 70°C for 9
hours using standard procedure recommended by manufacturer.
The acrylic specimens were immersed in a sterile distilled water
container; and autoclaved at 121°C for 15 minutes. Two specimens
were transferred to sterilized culture media (Brain-Heart Infusion
Broth, Merk, type 110493, Germany) to validate sterilization
accuracy. After 24 hours incubation at 37 °C the specimens were
evaluated for turbidity and cultivate in blood agar. Turbidity is
the quality of being cloudy or hazy caused by particles basically invisible to naked eyes. Turbidity was used as a criterion to assess
the microbial infection . Any growth at this stage, called for
revision and repeating the sterilization procedure.
The remaining 186 specimens were divided into three
groups (n=62); and each group was transferred to one of three
microorganism suspension to form an experimental biofilm. After
24 hours, the specimens were removed from the suspension and
washed with sterile water. Two specimens from each group were
transferred to the Brain-Heart Infusion (BHI) medium to ensure
the expected contamination; two samples from each mold were
needed to demonstrate the solutions’ efficiency and confirm
whether the molds had been disinfected . After 24 hours
incubation at 37 °C and cultivation in a blood agar, the turbidity
was evaluated. Each group was redistributed into four subgroups
(n=15), that were immersed in sterile containers containing either
sodium hypochlorite 0.5%, chlorhexidine 0.2%, vinegar 100%,
or water (as control). The reasons of using these disinfecting
materials are the prevalence and availability for patients .
After validation of sterilizing procedure, fresh colonies of
standard strain of 3 microorganisms were prepared with the
concentration of 0.5 McFarland (1.5×108cells/mL): Staphylococcus
aureus (ATCC29213), Streptococcus mutans (ATCC1683), and
Candida albicans (ATCC10231).
Five specimens were randomly selected from each subgroup
at 30 minutes, 2 hours, and 4 hours, rinsed, and immersed in 10cc
of BHI liquid culture medium. The randomly selected specimens
were incubated (Brinsea OvaScope Egg Viewer, Titusville, FL, USA)
at 37°C for 24 hours, and the turbidity results were recorded. In
order to ensure the accuracy of results, the specimens were also
cultured in blood agar solid medium. The procedure was performed
using loop, next to the flame, observed the preventive principles.
The media were incubated at 37 °C for 24 hours and the results
were recorded (finding colonies on the crop line indicated the
presence of microorganisms while the absence was an indicator
for acceptable disinfection). The results were recorded as growth
(+) or non-growth (-) of three microorganisms (Staph aureus,
Strep mutans, and Candida albicans) in the culture medium
SPSS 23 was used for data analysis (P<0.05), and Chi square
and Fisher exact test were applied to compare the results.
Figure 1 summarizes the results after 30 minutes: Chlorhexidine
0.2% was significantly more effective than hypochlorite 0.5%
and pure vinegar in eliminating Candida albicans (P=0.008).
Chlorhexidine 0.2% was more effective on Staph aureus (80%
disinfection) compared to two other solutions (0% disinfection)
(P=0.048). There was no significant difference in the effect of
three disinfectants on Strep mutans (100% disinfection) (P= 1.00
for comparison between Chlorohexidine and Vinegar, P= 1.00 for
comparison between Chlorohexidine and Hypochlorite).
Figure 2 shows the materials effects after two hours:
Chlorhexidine 0.2% eliminates 80% of Candida albicans colonies,
that was significantly more than pure vinegar and hypochlorite
0.5% (P=0.44). The effect of chlorhexidine 0.2% on Staph aureus
(100% disinfection) was significantly more than hypochlorite
(40% disinfection) (P=0.008). However, all three solutions
were completely effective on Strep mutans after 2 hours (100%
Figure 3 summarized the effects after 4 hours: Chlorhexidine
0.2% was more effective on Candida albicans and Staph
aureus microorganisms (P= 0.048 for comparison between
Chlorohexidine and Vinegar, P= 0.048 for comparison between
Chlorohexidine and Hypochlorite). All three solutions showed
acceptable effect on Strep mutans, and there was no statistically
significant difference (Negative percent in all solutions= 100%)
The overall resistance of the body to infectious diseases
reduces with the age, and the importance of prevention
increases consequently . On the other hand, local infections
can play an important role in systemic complications [2-5], and
removable prostheses could be an active source of such infectious
contaminations. The clinicians prefer to recommend safe,
accessible, easily applicable, and less expensive disinfectants in
low concentrations as preventive approach for decontamination
of removable prostheses to increase patient cooperation and
reduce the reverse effects. Strep mutans, Staph aureus, and
Candida albicans are among the most prevalent microorganisms
that could result in health problems in old age [6,14]. The present
study aimed to evaluate the effectiveness of low concentration
of prevalent and routine disinfectant solutions on disinfecting
acrylic part of prostheses from these common microorganisms at
different timeframes (30 minutes, 2 hours, and 4 hours).
Based on the results, pure vinegar, hypochlorite 0.5%, and
chlorhexidine 0.2% were completely effective on Strep mutans in
all timeframes. Therefore, 30-minute immersion in one of these
disinfectants is enough to eliminate Strep mutans disinfection.
When it came to Staph aureus bacteria, pure vinegar did not show
any significant effect; Chlorhexidine 0.2% had ascending effect
and eliminates 80% of Staph aureus colonies in 30 minutes, that
increased to 100% at 2 and 4 hours. Hypochlorite 0.5% did not
show an acceptable effect on these bacteria at 30 minutes; however,
it eliminates 40% of colonies in 2 and 4 hours. Therefore, in order
to eliminate this resistant bacterium from acrylic prostheses,
Chlorhexidine 0.2% can be recommended for 30 minutes or more;
while, Hypochlorite 0.5% should be applied for at least 2hours.
Candida albicans impregnated specimens, were only
surrendered to chlorhexidine 0.2%, and this solution showed
complete effectiveness at 30 minutes. As this microorganism
causes the most common complication in denture wearers
(denture stomatitis), the application of chlorhexidine 0.2% for 30
minutes or more could be effective and reliable [3,4].
In one study, Lavania examined the effectiveness of sodium
hypochlorite 1%, chlorhexidine 2%, vinegar 100%, and sodium
perborate 3.8% on disinfecting acrylic specimens infected with
Staph aureus, Escherichia coli, and Candida albicans in a timeframe
of 10 minutes. The source of microorganisms in the study was
clinical specimens of patients ; In the present study, fresh
colonies from international standard strains were used, and, the
study was performed with lower materials concentrations as the
higher solutions’ concentration could result in more damage to the
prosthesis components. The present investigation results showed
that vinegar cannot be considered as an acceptable prosthesis
disinfectant. However, Chlorohexidine 0.2%, and Hypochlorite
0.5% could provide enough effect on eliminating microorganisms
in 2 hours, and Chlorohexidine 0.2% is acceptable and reliable
disinfectant for common denture infectious contaminations.
Several agents have been suggested for prosthesis disinfection
like castor oil , glutaraldehyde , vinegar , sodium
hypochlorite , and chlorohexidine . Each has its own advantages and problems. Knowing about the material efficiency,
commercially availability, and the least effective concentration/
time along with the cognition of material characteristics
is necessary to prescribe a patient specific material. More
investigations focused on the least effective concentration/time
for sodium hypochlorite and chlorohexidine considering the
material effects on mechanical and physical properties of denture
Considering the limitations of the present study, the following
conclusions can be made:
1. Chlorhexidine 0.2% was significantly more effective than
hypochlorite 0.5% and pure vinegar in eliminating Candida
albicans (P=0.008 in 30 mins, and P=0.44 in 2 hours).
2. In 30 minutes, Chlorhexidine 0.2% was significantly
more effective on Staph aureus compared to two other solutions
3. Chlorhexidine 0.2% was more effective on Candida albicans
and Staph aureus microorganisms at 4-hours timeframe (P<0.05).
4. There was no significant difference in the effect of three
disinfectants on Strep mutans (P>0.05).
5. Chlorhexidine 0.2% was the most effective option between
disinfecting solutions tested.
6. Chlorhexidine 0.2% caused complete elimination of Strep
mutans and Candida albicans after 30 minutes, and Staph aureus
after 2 hours.
7. Hypochlorite 0.5% was 100% effective on Strep mutans
after 30 minutes and eliminated 40% of Staph aureus colonies
after 2 hours.
8. Pure vinegar showed the least effectiveness as disinfectant
material and was effective only on Strep mutans (100%).
Ebadian B, Pursina F, Saghaee S (2007) In Vitro Evaluation of the Atimicrobial Effect of Two Disinfectant Chemical Solutions on Conventional Heat- Cured AcrylicDenture Base Resin. Mashhad Journal of dental research 31(3): 217-222.