Effectiveness of Propolis on Oral Health: A Meta-Analysis : Journal of Nursing Research (2025)

Introduction

Propolis is a natural resinous substance that honeybees collect from various tree sources and use as a glue to build, repair, and protect hives. In general, this substance is composed of 50% resin and vegetable balsam, 30% wax, 10% essential and aromatic oils, 5% pollen, and 5% various other substances, including organic debris (^{Blonska et al., 2004; Kosalec, Pepeljnjak, Bakmaz, & Vladimir-Knežević, 2005}). The primary function of propolis in the hive is to act as a biocide, being active against invasive bacteria, fungi, and even invading larvae (^{Lofty, 2006}). Propolis and its constituent flavonoids exhibit an antitumor effect both in vivo and in vitro. Flavonoids have been reported to exhibit a wide range of biological activities, including antioxidant, antibacterial, antiviral, antifungal, anti-inflammatory, antiallergenic, and vasodilatory actions. In addition, flavonoids inhibit lipid peroxidation, platelet aggregation, capillary permeability and fragility, and the activity of enzyme systems, including cyclo-oxyglenase and lipoxygenase (^{Viuda-Martos, Ruiz-Navajas, Fernández-López, & Pérez-Álvarez, 2008}).

Many practitioners are interested in natural products to heal diseases. Propolis may be an important product for this purpose (^{Hegazi, 2002}). Propolis is found in pharmaceutical and cosmetic products such as anti-acne lotions and facial creams (^{Blonska et al., 2004; Herrera, Alvear, Barrientos, Montenegro, & Salazar, 2010; Kosalec et al., 2005}). It is found also in products such as toothpaste, mouthwash, throat lozenges, wine, cake, powder, jelly, tablets, and soap, among others (^{Parolia, Thomas, Kundabala, & Mohan, 2010; Selwitz, Ismail, & Pitts, 2007}).

The use of mouth rinses or gels containing propolis as a supplemental intervention has increased during the last decade in Taiwan, especially in oncology, hospice, and long-term care settings. However, no published articles have yet investigated the effectiveness of propolis on the oral health of patients. In addition, there are currently no clinical guidelines for propolis use. Therefore, a systematic review of the use and effectiveness of propolis is an important emergent issue.

Effects on Oral Infection

A number of studies have documented the biocidal functions of propolis, its extracts, and its constituents. Thirteen Gram-positive and Gram-negative bacteria and yeast-like fungi have been used in studies on the antimicrobial effects of propolis. All four showed strong antimicrobial activity effects on the Gram-positive bacteria and yeasts (^{Uzel et al., 2005}). ^{Stepanvić, Antić, Dadić, and Švabić-Vlahović (2003)} investigated the antimicrobial properties of the ethanolic extract of 13 propolis samples against 39 microorganisms and determined synergistic activity between antimicrobials and propolis. The results support the hypothesis that propolis has a significant antimicrobial effect on Gram-positive bacteria and yeasts and that Gram-negative bacteria are less susceptible.

Research into the antibacterial action of propolis found this substance very effective against certain anaerobic oral pathogens (^{Castaldo & Capasso, 2002}). Several studies have shown that Candida species are susceptible to propolis extract solution (^{Dias et al., 2007; Libério et al., 2009}). The antifungal activity of propolis is because of changes in the cell wall leading to an increase in volume and cell membrane rupture (^{Najafi, Vahedy, Seyyedin, Jomehzadeh, & Bozary, 2007}).

^{Chee (2002)} used an in vitro method to evaluate the antifungal function of propolis. Cell suspension of Cryptococcus neoformans and Candida albicans was treated with propolis and incubated for 48 hours at 37°C. Using scanning electron microscopy, the appearance of yeast cell rupture was observed when the cells were exposed to propolis. ^{Silici, KoC, Ayangil, and Cankaya (2005)} studied the antifungal effects of propolis collected from different subspecies of honeybees and found that C. albicans, C. glabrata, Trichosporon spp., and Rhodotorula sp. were susceptible to low concentrations of all propolis samples. Their research outcomes also found that a propolis sample from the Adana region in Turkey is more active than samples from other regions. However, Bankova pointed out that different types of propolis exhibit similar biological activities, including antibacterial, anti-inflammatory, antitumor, hepatoprotective, and antioxidant (^{Bankova, 2005}).

Many opportunistic microorganisms, especially the Candida fungal species in the oral cavity, may be harmful to human beings who are immunosuppressed. The most common antifungal drugs use imidazole compounds (miconazole), polyenic derivatives (nystatin), and amphotericin B as active ingredients. However, their toxicity and common resistance to these antifungal drugs result in a high rate of reinfection (^{Casaroto & Lara, 2010}). Natural products, which originate from medicinal plants, are an effective alternative to synthetic chemical substances as a source of antimicrobial agents (^{Parolia et al., 2010}).

Because propolis has antibacterial (^{Hegazi, 2002}), antifungal (^{Herrera et al., 2010}), anti-inflammatory (^{Borrelli et al., 2002}), antioxidant (^{Borrelli et al., 2002}), and immunomodulatory (^{Lotfy, 2006}) properties, it has been widely used in the maintenance of oral health.

Removal of Dental Plaque

Dental plaque is caused by the colonization and accumulation of oral microorganisms and extracellular polysaccharides that are synthesized from sucrose by the glucosyltransferase of Streptococcus mutans on the hard surface of teeth.

Dental plaque is a complex aggregate of oral bacteria, fungi, and other organisms; it is estimated to contain more than 10¹¹ (^{Casaroto & Lara, 2010}) organisms per milligram (net weight), involving more than 30 species (^{Koo et al., 2002}). Thus, control of the bacterial biofilm or plaque on teeth is essential to the maintenance of oral health. Control may be achieved by proper oral hygiene, use of fluoride products, and regular dental checkups (^{Libério et al., 2009}). In addition, there is strong evidence for the efficacy of using chemical agents, such as chlorhexidine, to inhibit plaque formation (^{Eberhard, Jepsen, Jervøe-Storm, Needleman, & Worthington, 2008; Scannapieco et al., 2009}) and the application of natural products with antimicrobial activities such as propolis onto dental surfaces to reduce biofilm formation (^{Nikawa, Hamada, & Yamamoto, 1998; Samet, Laurent, Susarla, & Samet-Rubinsteen, 2007}). Such agents have been frequently prescribed as adjuvants in the prevention or treatment of oral diseases because they inhibit bacterial colonization, growth, and metabolism and consequently interrupt the formation of mature biofilm, changing it at the biochemical and ecological levels (^{Dias et al., 2007; Silici et al., 2005}). Propolis has been reported to be protective against dental plaque because of its antimicrobial activity against a large array of oral microorganisms (^{Viuda-Martos et al., 2008}).

^{Hidaka, Okamoto, Ishiyama, and Hashimoto (2008)} studied the effects of propolis on the in vitro formation of calcium phosphate precipitates, with results suggesting that propolis may have potential as an anticalculus agent in mouthwashes. A systematic review discussed the in vitro and in vivo studies published in the period between 1978 and 2008. The results indicated that propolis in vivo studies showed reductions in the plaque index and insoluble polysaccharide (IP) formation (^{Libério et al., 2009}). Twenty-five subjects who used propolis mouthwash showed significantly reduced plaque and in the gingival index levels in comparison with samples obtained at baseline (^{Pereira et al., 2011}).

Effect on Stomatitis

The oral mucous membrane is composed of a stratified squamous epithelium that covers the mucocutaneous junction of the lips, tongue, buccal mucosa, gingiva, palate, uvula, and tonsillar fossa. Stomatitis is characterized by chronic erythema, edema, and ulcer of any part of the oral mucous membrane (^{Samet et al., 2007}).

Recurrent aphthous stomatitis (RAS) is a painful inflammatory ulcerative disorder of the nonkeratinized oral mucosa that may cause problems with eating, swallowing, and speaking. Denture stomatitis (DS) presents as an inflammatory reaction in denture-wearing individuals under maxillary prosthesis, with Candida albicans being the principal etiological agent (^{Casaroto & Lara, 2010}). Propolis is claimed to be useful as an antifungal agent in the treatment of DS and RAS (^{Samet et al., 2007; Santos et al., 2005}).

Treatment with propolis by oral supplementation to improve oral health has not been well established. The purpose of this review was to synthesize the best available evidence on whether daily oral use of propolis improves oral health through reduced rates of oral infection, dental plaque, and stomatitis.

Methods

Inclusion Criteria

Types of participants

Patients of either gender in both inpatient and outpatient settings were included in this review. Studies involving oncology patients were excluded, as these patients may be immunocompromised from their oncology therapy, which may impact their oral health status.

Types of intervention(s)/phenomena of interest

The interventions considered for inclusion involved daily oral use of propolis mouthwashes, gels, or capsules for the improvement of oral health. The comparators were usual care, placebo, or other mouthwashes/gels. Studies on propolis mouthwashes or gels conducted in vitro were not considered.

Types of studies

Only randomized controlled trials (RCTs) and clinical trials were included in this review, including both crossover and parallel group studies.

Types of outcomes

The outcome measures included were the effectiveness of oral infection reduction (e.g., decrease in the number of Candida, S. mutans), the score of supragingival dental plaque, and the effectiveness of stomatitis treatment (e.g., the complete remission of lesions, decrease in recurrence).

Search Strategy

Before beginning this systematic review, the Cochrane Library, Database of Abstracts of Reviews of Effects, Joanna Briggs Institute Library of Systematic Reviews, MEDLINE, and CINAHL databases were searched. No previous published systematic reviews on this topic were identified.

The search strategy was designed to identify all published articles and unpublished papers (e.g., conference proceedings) in either English or Chinese. The search proceeded in three stages as follows: an initial limited search of MEDLINE and CINAHL was undertaken followed by analysis of the text words contained in the title and abstract and of the index terms used to describe articles. The purpose of this initial search was to identify search terms. A second search using all identified keywords, index terms, and MeSH headings identified was then undertaken across all included databases. Third, the reference lists of all identified reports and articles were searched for additional studies.

The databases searched were the Cochrane Database of Systematic Reviews, CINAHL, PubMed, ScienceDirect, Conference Proceedings, Oral Health Journal Index, and Chinese Electronic Periodical Services. The relevant articles were published in English or Chinese between 1969 and 2012. The search terms/keywords used included propolis, oral health, plaque, oral ulcer, stomatitis, and oral infection.

All studies identified during the database search were assessed for relevance to the review based on information provided in the title, abstract, and descriptor/MeSH terms. A full-text report was retrieved for all studies that met the inclusion criteria. Studies identified from reference list searches were also assessed for relevance.

Two independent reviewers used the standardized critical appraisal instrument, Joanna Briggs Institute Meta Analysis of Statistics Assessment and Review Instrument (JBI-MAStARI), to assess the methodological validity of the retrieved article before inclusion in the review. For this review, at least 5 of 10 questions such as blind allocation, random assignment, or reliable measurement had to earn a “yes” from both reviewers for the study to be included. Any disagreements were resolved through discussion or by a third reviewer.

Data Collection

The data for each included article were extracted and tabulated using the standardized data extraction tools from the JBI-MAStARI. Because all included articles were randomized/ pseudorandomized studies, the JBI Data Extraction Form for Randomized and Pseudo-Randomized controlled trials was utilized. Data extracted from experimental studies included specific details about the interventions, populations, study methods, and outcomes of significance to the review question and specific objectives. All results were subject to double data entry to minimize the risk for errors.

Data Synthesis

Quantitative data were pooled, where possible, in a meta-analysis using the JBI-MAStARI. When appropriate, relative risks and/or odds ratios and their associated 95% confidence intervals were calculated for analysis of categorical data. The weighted mean differences and standard deviation were calculated for continuous data that used the same scale. Statistical heterogeneity was assumed at p < .1 using the χ² test for homogeneity and I² > 50% using I² statistics. Because of the complexity of outcomes measured in the variety of settings, heterogeneity was anticipated in the meta-analysis results. A random effects meta-analysis was performed to manage this issue. Thus, the overall effect does not show the best estimate of the intervention effect but rather the average intervention effect. Where statistical pooling was not possible because of variability in outcome measures or because of a lack of studies investigating the same outcomes, the findings are presented in narrative form.

Results

Description of Studies

The literature search identified 128 potentially relevant articles. Of these, 78 were excluded based on assessment of the titles, and the abstracts of the remaining 50 articles were retrieved (see Figure 1). Next, both the primary and secondary reviewers assessed the abstracts of the 50 studies, resulting in 32 articles selected for further assessment. The full texts of these 32 articles were subsequently obtained. Of the 32 articles, 23 were excluded because they did not meet the specified inclusion criteria.

The methodological quality of the remaining nine articles was assessed by critical appraisal using JBI-MAStARI. Disagreements were resolved by discussion. One article was excluded for its methodological quality under 5 points. Both reviewers agreed by consensus that eight articles should be included in the review. These articles were all research papers and included four RCTs and four pseudorandomized controlled trials.

The included studies were published between 1997 and 2011. They were conducted in various countries such as Brazil, the United Kingdom, India, and the United States. The studies include participants from a variety of cultural, chronological, and socioeconomic backgrounds. All studies measured the effectiveness of propolis on oral health, which allowed the pooling of available research data for the topic. For the purpose of this review, two articles focused on oral infection, three focused on dental plaque, and three focused on stomatitis. Detailed information about the participants, intervention, and outcomes is given in Table 1.

Methodological Quality of Included Studies

It has been observed that relatively few of the research studies conducted thus far have focused on the effectiveness of propolis in oral health in combination with other interventions. Some of the studies did not specifically set out to investigate the stated aims attempted in this review. In addition, incomplete reporting of studies increased the difficulties of this systematic review. Despite this, each included study contained adequate findings that allowed a narrative summary to be presented. The four RCTs met stringent standards of quality. ^{Koo et al. (2002)} adopted a crossover, double-blind research design to ensure random allocation of the treatment order of the mouth rinse formulations. ^{Dodwad and Kukreja (2011)} designed a single-blind parallel study to ensure that subjects were assigned randomly. In the third study conducted by Murray et al., participants were randomly assigned to either the experimental or control group and were blinded to treatment allocation (^{Murray et al., 1997}). In the fourth RCT (^{Samet et al., 2007}), participant assignments were randomized to receive either the propolis or the placebo.

Four pseudorandomized studies were included in this review. Three studies (^{Ota et al., 2001; Santos et al., 2008, 2005}) did not report the randomization technique and whether the assessors were blinded. One study (^{de Carvalho Duailibe, Gonćalves, & Ahid, 2007}) was a one-group pretest/posttest design; with the exception of that study, all of the eight studies selected as qualified for review used comparable groups at baseline and treated intervention and control groups identically. However, ^{Koo et al. (2002)} described a crossover effect at the 3-day follow-up. As nystatin and miconazole are the antifungal of choices for DS, Santos et al., in two separate studies (^{Santos et al., 2008, 2005}), used these drugs as comparators to investigate the effects of propolis. Lesion regression in propolis-treated patients similar to that observed in those patients treated with nystatin or miconazole was considered to indicate the efficacy of propolis in treating stomatitis. All studies presented reliable outcome measures and applied appropriate statistics.

The methodological quality of all the included studies ranged from high (10 points) to medium (5 points), as determined using the JBI-MAStARI critical appraisal checklist.

Findings of the Review

The study findings are presented according to the three objectives set out in this review. Outcomes of oral health are manifested in the number of colonies, the amount of dental plaque, and the remission of stomatitis. Two of the included studies (^{de Carvalho Duailibe et al., 2007; Ota et al., 2001}) revealed the effect of propolis on oral infection. ^{Koo et al. (2002), Dodwad and Kukreja (2011), and Murray et al. (1997)} investigated the effect of propolis on dental plaque. The other three studies by ^{Santos et al. (2005, 2008) and Samet et al. (2007)} analyzed the effect of propolis on stomatitis.

Effectiveness of Propolis on Oral Infection

The original objectives stated for this systematic review specified the severity of oral infection as one of the outcomes of oral health. There were no suitable studies to include in the systematic review that addressed this outcome measure, as the relevant studies identified were either incomplete or used in vitro models.

The following studies discussed below supported the efficacy of propolis in decreasing the counts of bacteria or fungi.

Two articles (^{de Carvalho Duailibe et al., 2007; Ota et al., 2001}) examined the numbers of bacteria colonies in the saliva of volunteer patients. Ota et al. investigated whether propolis had antifungal activity and verified the influence of hydroalcoholic propolis extract on the number of Candida in saliva. Adult volunteer patients who had full dentures and who were showing symptoms of stomatitis were screened. Patients with Candida concentrations of more than 400 colony-forming units (CFU)/ml in their saliva were chosen and received mouth rinse twice daily for 2 weeks. The concentration of Candida suspension is expressed in CFU/ml saliva. In this article, M₂O agar (Difco Laboratories, Detroit, MI, USA) was used to culture the Candida strains. A 24-hour culture was suspended is sterile saline solution to obtain a suspension of 105 CFU/ml, evaluated by spectrophotometer (Beckman Du-640, Beckman Coulter, Inc., USA). The experimental group consisted of 12 patients using a hydroalcoholic solution of propolis. The control group consisted of five patients receiving the same mouth rinse but without propolis. All the patients in the experimental group showed a significant reduction in the number of Candida yeast in the saliva after 1 week. The patients in the control group did not show a significant difference in the number of Candida yeast in the saliva during the experiment.

^{de Carvalho Duailibe and colleagues (2007)} conducted a study to evaluate the in vivo antimicrobial activity of the propolis extract mouth rinse on the concentration of Streptococcus mutans present in the oral cavity of young individuals. Forty-one volunteers of both genders were recruited, ranging in age from 11 to 30 years. The participants were asked to perform a propolis-extract mouth rinse three times per day for 7 days, with no other changes in their oral hygiene and dietary habits. Saliva was collected at three times before the first rinse (sample 1), and 1 hour (sample 2) and 7 days after the first rinse (sample 3). One hundred twenty-three samples were obtained. Of the 123 saliva samples collected from the 41 volunteers, those from 21 volunteers presented Streptococcus mutans ranging from 1250 to 1,000,000 CFU/ml saliva, whereas no bacterial growth was observed in 20 participants before or after the use of the propolis mouth rinse. Among 21 participants showing growth of S. mutans between saliva samples 1 and 2, a decrease in the number of colonies was observed in 62% of the participants (13/21). A comparison between saliva samples 1 and 3 revealed a reduction in bacterial concentration in 81% (17/21) of the participants. There were significant differences in the number of S. mutans between saliva samples 1 and 2 (t = 2.8783, p = .0031) and between saliva samples 1 and 3 (t = 4.8589, p < .0001). These results indicate that the propolis extract possesses in vivo antimicrobial activity against S. mutans present in the oral cavity. Because propolis extract is easily obtained, is low cost, and shows long-term beneficial effects, it may represent a new option for health promotion in terms of preventing dental caries and promoting oral health.

Effectiveness of Propolis on Dental Plaque

^{Koo et al. (2002)} evaluated the effectiveness of a mouth rinse containing propolis on 3-day dental plaque accumulation. The plaque index for the experimental group was significantly less than for the placebo group. In addition, the experimental mouth rinse reduced the IP concentration in dental plaque by 61.7% compared with the placebo. An experimental mouth rinse containing propolis was thus efficient in reducing the formation of supragingival plaque and IP under conditions of high plaque accumulation. ^{Dodwad and Kukreja (2011)} evaluated the effect of propolis mouth rinse on plaque accumulation and gingivitis. They compared the plaque and gingival indices at baseline and 5-day intervals, and the mouth rinse was compared with saline controls. Twenty subjects were selected and assigned randomly to two groups of 10 subjects each. Propolis mouthwash was found to be better than saline at inhibiting plaque formation.

^{Murray et al. (1997)} conducted a study involving the de novo plaque formation design. This study incorporated a double-blind parallel design to permit the comparison of similar groups of subjects. As part of the study protocol, all participants had their teeth professionally scaled and polished 3 weeks and 1 week before commencing the study. Oral hygiene instructions were given in an attempt to improve their oral hygiene before their enrollment in the study. The mouth rinses (with and without propolis) were randomly allocated to subjects. All subjects were instructed to rinse twice per day with the mouth rinse for 1 minute. Final examination plaque scores were recorded 5 days after the conclusion of the intervention. There was a statistically nonsignificant 14% reduction in plaque for the group that used the propolis mouth rinse in comparison with the group that used the placebo mouth rinse, suggesting that propolis may have limited efficacy.

Meta-analysis of dental plaque data revealed that the studies of ^{Koo et al. (2002), Dodwad and Kukreja (2011), and Murray et al. (1997)} all identified a positive although not statistically significant reduction in dental plaque (see Figure 2). The meta-analysis showed significant heterogeneity (p = .02, χ² = 7.81). The overall effect size was −1.24 (95% CI [−2.51, 0.04], p = .06), indicating that, although propolis reduced dental plaque, the reductions were not statistically significant (see Figure 2).

Effectiveness of Propolis on Stomatitis

Three studies were included to analyze the effectiveness of propolis on improving stomatitis. Meta-analysis was not possible because of the heterogeneity in outcome measurements. Therefore, all findings are presented in a narrative summary. RAS is a common, painful, and ulcerative disorder of the oral cavity of unknown etiology. Propolis is a bee product used in some cultures to treat mouth ulcers. One pilot study (^{Samet et al., 2007}) was conducted to evaluate if propolis was able to reduce the number of outbreaks of RAS ulcers. The sample consisted of 19 patients experiencing RAS at a minimum frequency of four outbreaks per year. Patients were divided randomly into two subgroups: a propolis group (n = 10) that received a daily dosage of 500 mg/day of bee propolis and a placebo group (n = 9) that received a daily placebo capsule of a calcium-based food supplement. As this was a double-blind study, neither the participants nor the investigators knew the identity of the product distributed. The proportion of patients in the propolis group with a 50% or greater reduction in frequency in outbreaks of stomatitis was greater than that in the placebo group. Patients in the propolis group also reported improved quality of life, compared with their placebo counterparts. Although a study with a larger sample size is necessary, this trial shows that daily ingestion of 500 mg of propolis may lead to a decrease in aphthous ulcer incidence and an improvement in quality of life.

^{Santos et al. (2005)} investigated the efficacy of treating stomatitis patients with propolis and nystatin. Eighteen patients were selected from a dental clinic, with 12 receiving propolis and six receiving nystatin. After drying the infected area using a swab, propolis or nystatin was applied topically four times a day for 7 days. The results showed that the absence of lesions for propolis and nystatin was 7 of 12 and four of six, respectively, demonstrating similar rates of effectiveness for the two treatments.

In the other study, ^{Santos and colleagues (2008)} analyzed the effects of propolis gel and miconazole gel for patients with stomatitis. Thirty patients were recruited from a dental clinic, with 15 receiving propolis gel and 15 receiving miconazole gel. After drying the infected area using a swab, propolis or miconazole was applied topically four times a day for 7 days. The subjects in the intervention and control groups achieved complete remission of palatal edema and erythema after 1 week. This pilot study offered evidence that propolis is as effective as the pharmaceutical miconazole for the topical treatment of stomatitis.

Discussion

The current review found that propolis is better than standard care in achieving certain treatment targets (e.g., reducing oral infection, dental plaque, and stomatitis). In addition, this review found evidence to conclude that propolis is as effective as the current pharmaceutical treatments of choice (nystatin and miconazole). Significantly, none of the outcomes included in this review indicated poorer results or harmful effects for participants treated with propolis.

Mouth rinses containing propolis were prepared at four different concentrations: 10%, 5%, 2.5%, and 1%. Mouth rinse containing 0.2% chlorhexidine was used as the comparator. The antibacterial effects of the five solutions on oral microorganisms were tested, and their cytotoxic effects on human gingival fibroblasts were evaluated. The results suggest that, although the inhibitory activity of the experimental mouth rinse solutions against oral microorganisms was not as effective as chlorhexidine, these solutions were found to be noncytotoxic to human gingival fibroblasts (^{Özan et al., 2007}).

With regard to efficacy in decreasing colonies of Candida (^{Ota et al., 2001}) and Streptococcus mutans (^{de Carvalho Duailibe et al., 2007}), the reviewed research indicated that propolis may be effective in improving oral infections. Furthermore, propolis use seems to be effective in supporting the philosophy of health promotion because it is easily obtained, is low cost, and shows long-term beneficial effects (^{de Rezende, Pimenta, & da Costa, 2006}).

Data for the dental plaque index (^{Dodwad & Kukreja, 2011; Koo et al., 2002; Murray et al., 1997}) provide limited evidential support for the effectiveness of propolis. Because clinical diversity occurs between any two studies included in a meta-analysis, statistical heterogeneity is inevitable. Therefore, the identified effect size of the meta-analysis for dental plaque is limited in its potential interpretation. However, because the accumulation of dental plaque with respiratory pathogens serves as a reservoir for recurrent lower respiratory tract infections and because the control of dental plaque has been effective in reducing the rate of pneumonia, especially for residents in nursing homes (^{EI-Solh, 2011}), incorporating propolis in daily oral care offers the potential to further reduce systemic diseases and promote overall quality of life.

In relation to stomatitis, propolis has been shown to affect the level (^{Santos et al., 2008, 2005}) and frequency (^{Samet et al., 2007}) of lesions experienced by participants. Other than the outcomes of oral health mentioned above, propolis also has an effect on dentinal hypersensitivity. The mechanism of dentinal hypersensitivity is the destruction of pulp mechanoreceptors because of the movement of dentinal fluid, resulting in pain. ^{Mahmoud, Almos, and Dahlan (1999)} conducted a clinical trial to evaluate the effect of propolis on subjects with dentinal hypersensitivity and to assess the level of satisfaction among subjects after the use of propolis. Twenty-six women of ages ranging between 16 and 40 years were recruited. All subjects were healthy except for the symptoms of dentinal hypersensitivity. Four of the 26 subjects were excluded from the study because of failure to complete the 4-week study period. The propolis was applied using a small paintbrush twice daily for 1 month. At the end of the first and fourth weeks, subjects were asked to fill a questionnaire with a special emphasis on their experience of using this material. Self-reported levels of pain decreased from severe to slight or moderate during the study period. Propolis also had a positive effect on teeth affected by dentinal hypersensitivity. Propolis was highly appreciated by subjects, and 94% of the subjects liked the taste, color, and flavor.

There were several limitations to this review. The number of studies available for inclusion in this review was small, which reduced the generalizability of conclusions. The inclusion of only three studies in the meta-analysis for dental plaque limited the options for investigating heterogeneity. Inconsistency in reporting and measuring of outcomes limited the possibility of pooling data in the meta-analysis for oral infection and stomatitis. Structured guidelines for propolis use and the standardized measurement of outcomes are suggested in future research.

In summary, propolis had a positive effect on dental plaque. However, this effect was not statistically significant. Findings from the present review suggest that propolis is safe to use and may improve oral health outcomes. However, the significant heterogeneity across studies precludes deriving any definite conclusions regarding the effect of propolis on oral health.

Conclusions

The overall methodological quality of the studies in this review was medium. This review shows that the effectiveness of propolis mouth rinse is comparable with other mouth rinses (e.g., chlorhexidine and nystatin). In light of the increasing popularity of complementary and alternative treatments, propolis provides an attractive alternative for the maintenance and promotion of oral health. Although only limited research has examined the effects of propolis on oral health, this systematic review using the best available evidence illustrates the effects of propolis on various oral health outcomes. Further studies are necessary to validate whether propolis products are equal or superior to conventional products in reducing oral infection, dental plaque, and stomatitis.

Implications for Practice

Studies included in this systematic review met appropriate levels of evidence as specified under JBI criteria (^{JBI, 2013}) and were only randomized control/quasirandomized trials. This bolsters the trustworthiness of findings that propolis is somewhat effective in improving oral health on the following points:

1. Propolis tends to reduce the level of oral infection (level of evidence 3).
2. Propolis decreases dental plaque (level of evidence 2).
3. Propolis improves stomatitis (level of evidence 3).

Implications for Research

Further RCTs with larger samples must be conducted to draw definitive conclusions regarding the effectiveness of propolis in oral care. Full-text trials presented in languages other than English and Chinese should be considered to provide additional data for meta-analysis and potentially reduce the problem of heterogeneity encountered in this review.

Acknowledgments

We would like to thank the staff at the Joanna Briggs Institute for their patience and suggestions. Particular gratitude goes to Dr. Attard and Dr. Stephenson for their detailed revision of this manuscript.

References