Original Article |
Corresponding author: Abbas Bahador ( abahador@sina.tums.ac.ir ) © 2023 Zeinab Imani, Ahmad Sodagar, Maryam Pourhajibagher, Armin Hosseinpour Nader, Abbas Bahador.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Imani Z, Sodagar A, Pourhajibagher M, Nader AH, Bahador A (2023) Evaluation of antibacterial effect of the orthodontic composite containing propolis nanoparticles in rat as an animal model. Folia Medica 65(1): 131-139. https://doi.org/10.3897/folmed.65.e67782
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Aim: The present study aimed to assess the antimicrobial effects of orthodontic primer containing nano-propolis against the cariogenic bacteria in а rat model.
Materials and methods: Transbond XT orthodontic primer containing 0%, 1%, 5%, and 10% nano-propolis was experimentally prepared in-house. The Wistar rats we used in the study were randomly divided into four groups and their oral cavities were colonized with Streptococcus mutans, Streptococcus sanguinis, and Lactobacillus acidophilus. After anesthetizing the rats, one drop (10 µL) of primer containing different concentrations of nano-propolis was applied to the labial surface of the maxillary incisor and light-cured. The orthodontic composite was applied on the primer and light-cured. One drop (10 µL) of primer containing the same concentrations of nano-propolis was again applied on the surface of composite and light-cured. The number of S. mutans, S. sanguinis, and L. acidophilus colonies in the saliva of rats was quantified at 24 h, at days 4 and 7 using plate counting.
Results: Primer containing 1%, 5%, and 10% of nano-propolis significantly reduced the S. mutans colony count at 24 h compared with the control group (p<0.05). At day 4, the mean S. mutans colony counts in the 5% and 10% nano-propolis groups were significantly lower than that in the control group (p<0.05). Primer containing 1%, 5%, and 10% (all (p<0.05) of nano-propolis significantly reduced the L. acidophilus at 24 hours. Also, at day 4 the mean L. acidophilus colony counts in the 5% and 10% nano-propolis groups were significantly lower than that in the control group (p<0.05). At 24 h and 4 days, the mean S. sanguinis colony count in the 1%, 5%, and 10% nano-propolis group was significantly lower than that in the control group (p<0.05). No significant difference was observed in the presence of all concentrations of nano-propolis at day 7 (p>0.05).
Conclusions: Orthodontic primer containing nano-propolis significantly reduced the colony count of cariogenic bacteria in a rat model.
cariogenic bacteria, nano-propolis, composite, orthodontic adhesive, primer, rat
White spot lesions (WSLs) around the brackets are a sequela of fixed orthodontic treatment, which is aggravated by poor oral hygiene.[
Nanotechnology and nanoscience, the use of matter with dimensions on the atomic, molecular, and supramolecular scale, has become increasingly utilized for medical and clinical applications and has recently attracted much interest as an approach to killing or reducing the virulence of numerous microorganisms.[
Propolis is a mixture of buds, exudates, and other parts of plants as well as beeswax substances, and bee salivary enzymes used by bees to protect the hive from cavities and intruders. It has various activities such as antibacterial, antiviral, antifungal, antiparasitic, antioxidant, anti-inflammatory, and antiproliferative effects. In terms of antibacterial effect, the content including phenolic and flavonoids compounds is important.[
No research has been conducted on combining the orthodontic composite with nano-propolis to obtain an antimicrobial effect in an animal model and improved fixed orthodontic treatment outcomes.
The purpose of the current study was to explore a combinational orthodontic composite with nano-propolis to reduce cariogenic S. mutans, S. sanguinis, and L. acidophilus in oral cavity of rat as an animal model. It was hypothesized that there was a significant difference between the antimicrobial property of the orthodontic composite containing nano-propolis and the original orthodontic composite against S. mutans, S. sanguinis, and L. acidophilus in a rat model.
Nano-propolis was prepared as described previously.[
Transbond XT orthodontic primer (3M Unitek, Monrovia, CA, USA) was used for the preparation of the modified orthodontic composite (MOA) containing 0%, 1%, 5%, and 10% nano-propolis. Twenty drops (50 µl ≈ 0.05 g per drop) of Transbond XT orthodontic primer were mixed with 0.00, 0.01, 0.05, and 0.1 g of nano-propolis for the preparation of the control (no nano-propolis), 1%, 5%, and 10% nano-propolis groups, respectively, using an ultrasonic bath for 30 minutes. The prepared experimental primers were transferred into microtubes, which were covered with aluminum wraps to prevent exposure to the light.
The animal experiments were done in accordance with the Animal Ethics Committee of Tehran University of Medical Sciences guideline (IR.TUMS.DENTISTRY.REC.1396.2773) Male Wistar rats (200–250 g; Pasteur Institute, Tehran, Iran) were housed one rat per cage, at 22–25°C and at 12 h light/dark cycles, under sanitary conditions with free access to water and sanitized pellet food. Rats were allowed to adapt to the animal room conditions for 1 week to the test day. All methods in the current study were carried out in accordance with relevant guidelines and regulations. To increase the accuracy of microbiological assessments, the bedding materials were autoclaved and replaced every day as well as the cages were disinfected with 10% povidone iodine solution. Based on the previous studies, the effect size (No. of rat in experimental groups) was estimated as nine rats per each nano-propolis concentrations, using power analysis with power arbitrarily set at 90%.[
Rats were randomly assigned to either test (modified orthodontic composite containing 1, 5, and 10% of nano-propolis) or control groups (same as test without nano-propolis). Cariogenic bacteria-infected rat receiving original Transbond XT orthodontic primer instead of modified orthodontic composite containing nano-propolis served as controls (group A). The control group was set up with no nano-propolis (0%) applied. Test groups (B-D) were exposed to different concentrations of nano-propolis (1, 5, and 10%, respectively), while a control group (A) was not exposed (Fig.
An animal model for assessment of the antimicrobial activity of orthodontic primer containing nano-propolis.
Since the oral microbiome of the rats is different from that of human, the microbiome of the rats was removed based on the previous study.[
Rats were anesthetized using intraperitoneal injection of a ketamine-xylazine cocktail. The rats were then fixed on an operating table in the supine position, their maxillary central incisor was etched with phosphoric acid (37%) for 20 s after which the central incisor was washed gently, and then dried with a cotton pellet. Next, 10 µL of primer containing nano-propolis was applied on the labial and proximal surface of central incisor and cured for 20 s using LED irradiation. A thin layer (2×2 mm) of adhesive (Transbond XT; 3M Unitek, Monrovia, CA, USA) was then applied to the area of the tooth that was primed and cured for 20 s using LED irradiation. Next, 10 µL of primer containing nano-propolis was again applied over the layer of adhesive and cured for 20 s using LED irradiation.[
To prevent separation of the adhesive from the surface of central incisors in occlusion, the central incisors of the mandible were shortened by 2 mm. The presence of adhesive on the surface of the teeth was checked after 24 h, 4 days, and 7 days, and saliva samples were collected from all rats at the designated time points (24 h, 4 days, and 7 days). To count the test bacteria (CFU/mL), plate counting method using brain heart infusion (BHI) agar (Merck, Germany) was done as described previously.[
One-way ANOVA was run to compare the CFU/mL of test bacteria at each time point. Tukey’s post hoc test was applied to compare each two means on each dependent variable for pairwise comparisons. Data were analyzed using SPSS version 23.0 (SPSS Inc., IL, USA) and a p-value of 0.05 was considered statistically significant.
As shown in Fig.
Mean and standard deviation of the number of S. sanguinis CFU/mL in terms of nanopropolis concentration and evaluation time.
According to the data in Fig.
Mean and standard deviation of the number of S. mutans CFU/mL in terms of nanopropolis concentration and evaluation time.
Significant reductions were seen in L. acidophilus CFU/mL in the presence of 1%, 5%, and 10% nano-propolis at 24 h (p<0.05) in comparison with the control group. Exposure to 5% and 10% nano-propolis at day 4 had no significant reduction in L. acidophilus CFU/mL when compared with the control group. No significant reduction was observed in L. acidophilus CFU/mL in the presence of 1%, nano-propolis at day 4 (p>0.05), and in the presence of 1%, 5%, and 10% nano-propolis at day 7 (p>0.05) in comparison with the control group. As shown in Fig.
There are some concerns about the incidence of white spots as well as dental caries lesions during fixed orthodontic treatment.[
The main constituents of propolis associated with antimicrobial effects include flavonoids and cinnamic acids.[
In the present study, three bacteria S. mutans, S. sanguinis, and L. acidophilus were used to evaluate the effects of different concentrations of nano-propolis used in orthodontic composites. S. mutans is usually involved in the onset of dental caries, and L. acidophilus is rarely seen in the early stages of caries. S. sanguinis is also associated with plaque biofilm and is one of the bacteria that is colonized in the oral cavity and helps to bind other microorganisms and plays a key role in the development of oral biofilm.[
The results of the present study showed that the use of composites with concentrations of 1%, 5%, and 10% of nano-propolis had specific antibacterial effects against S. mutans, S. sanguinis, and L. acidophilus at each time of day 1, day 4, and day 7. Also, the antibacterial effects of composites with concentrations of 5% and 10% nano-propolis were stronger than those of composites with concentrations of 1% nano-propolis, but the effects of composites with concentrations of 5% and 10% nano-propolis were estimated to be equal to each other, which indicates that the effects are dose dependent. These results are consistent Lactobacilliwith the results reported by Akhavan et al.[
Over time, the CFU concentrations of test bacteria showed a tendency of nonsignificant decrease in all control groups at days 1, 4, and 7. It is possible that the exposure to environmental microbial strains and reversion of the natural oral microbiome in rats during the study period interfere with the prior implanted S. mutans. On the other hand, we cannot exclude the possibility that the change in rat saliva composition throughout the study period in the presence of orthodontic composite was responsible for the changes in CFU concentrations of test bacteria.[
Most research on the antibacterial effects of propolis has resulted in products such as mouthwash and toothpaste, and to our knowledge, this is the first report that attempts to show the antimicrobial effect of an orthodontic composites containing different concentrations of nano-propolis against cariogenic microorganisms.
Vanni et al.[
In another study, Netto et al.[
In the current study, with increasing time, the antibacterial effects of composites containing different concentrations of nano-propolis have decreased. The increase in the number of cariogenic microorganisms on day 7 compared to days 1 and 4 indicates that the antimicrobial properties of nano-propolis decreased over time to day 7, due to insufficient release of propolis nanoparticles. It seems that with increasing the concentration of nano-propolis, it may continue to release and induce antimicrobial effects, although the use of high concentrations of nano-propolis can also weaken the mechanical properties and bond strength of the orthodontics composite contain nano-propolis.
According to the results of the present study, the highest levels of microbial inhibition occurred in all three bacteria, S. mutans, S. sanguinis, and L. acidophilus, at a concentration of 10% nano-propolis. Also, concentrations of 5% and 10% of nano-propolis were significantly different only in the first day of exposure. On other days (i.e., days 4 and 7), no significant differences were observed in L. acidophilus and S. mutans CFU/mL, in terms of bacterial inhibition. In other words, the antibacterial effects of these two concentrations were equal to each other. Since the use of various compounds such as nano-propolis can affect other physical and mechanical properties, including bond strength to the tooth, it seems that the best concentration for antibacterial effects is 5% nanoparticles.
Malhotra et al.[
The results of this study are consistent with a recent report[
Our data support the finding that orthodontic composite containing 10% nano-propolis demonstrated antibacterial activity against S. mutans, S. sanguinis, and L. acidophilus up to day 7 in a rat model. To fully assess the viability of nano-propolis, future studies will focus on gauging the physical properties of orthodontic composite containing nano-propolis, such shear bond strength and adhesive remnant index.
This research was supported by Tehran University of Medical Science as a part of Dr. Zeinab Imani’s thesis (DDS).
No potential conflict of interest was reported by the authors.