The potency of propolis extract as anti-inflammatory agent for stimulation of reparative dentin formation

Background: As an effort to treat a deep caries lesion with a diagnosis of reversible pulpitis, one of the treatment options is pulp capping. For decades, calcium hydroxide has been considered the most acceptable pulp capping material and has been routinely used in dental practice, but it also has some weakness. To overcome that, alternative materials are needed that can provide a better effect. Recently, a lot of research has been done using natural ingredients, including Propolis. Propolis has been known to have strong antimicrobial and anti-inflammatory properties. Therefore, it is necessary to conduct a deeper study regarding the potency of propolis extract as an anti-inflammatory agent for the stimulation of reparative dentin formation so that it can be considered to be used as a pulp capping material. Purpose: The aim of this literature review is to highlight the potency of propolis extract as anti-inflammatory agent in the natural stimulation of reparative dentin formation. Methods: The search strategy consist of electronic research using databases such as PubMed, Google Scholar, Science Direct, dan Springer Link for studies published from 2003 to 2021 regarding the potency of propolis extract as anti-inflammatory agent for stimulation of reparative dentin formation, including review articles and research articles. Results: Propolis and its constituents have been proven to be used as a potent natural anti-inflammatory, it also considered to have the ability to promote reparative dentin formation. However, there are some literatures stated that reparative dentin does not form with the application of propolis, and the causes may vary. Conclusion: Propolis extract has a potency as an anti-inflammatory agent in dental pulp inflammation by inhibiting TNFα expression, and increasing TGF-β1 expression, as well as its potency in stimulating the formation of reparative dentin. Based on this review, further studies are needed.


INTRODUCTION
Minimal intervention in dentistry aims to be able to maintain tooth structure in an effort to prevent more complex decay. 1 As an effort to treat deep caries with a diagnosis of reversible pulpitis, one of the treatment options is pulp capping.Pulp capping treatment can be performed on teeth with dentinal caries that are close to the pulp but have not exposed the pulp, or on exposed pulp.Pulp capping treatment is done by placing a biocompatible material on the roof of the dental pulp, to maintain the vitality and normal function of the pulp.Pulp capping is divided into two, namely direct and indirect. 2or decades, calcium hydroxide has been the gold standard as a pulp capping material. 3Calcium hydroxide can stimulate the formation of reparative dentin which is an indication of the success of open pulp treatment. 4The use of calcium hydroxide in pulp capping has several weaknesses, namely it can induce pulp inflammation, unpredictable tissue response, irregularly formed reparative dentin, formation of tunnel defects, has high solubility properties, and does not provide good adaptation to dentin. 5,6o correct the weaknesses of calcium hydroxide, alternative materials are needed that can provide a better effect.Many studies have been carried out using natural materials, including Propolis.Propolis is a resin compound derived from honey bee wax (Apis mellifera), consisting of 55% resin, 30% wax and volatile oils, 5% bee pollen, and 10% organic and mineral materials.The diversity of bioactive compounds contained in propolis causes propolis to have several biological activities.][9] Based on the results of many studies, it was proven that the application of propolis extract could inhibit pulp inflammation, stimulate the formation of hard tooth tissue and stimulate reparative dentin. 10,11Some of the literature that discuss the potency of propolis extract shows the difference of opinion.In a study conducted by Sabir 12 application of propolis extract caused the inflammatory process that occurred in the dental pulp of rats to be inhibited but unable to stimulate the formation of reparative dentin.
Based on the differences of opinion in several studies that have been carried out as described above, a more in-depth discussion is needed through a literature review regarding the potential of propolis extract as an anti-inflammatory to stimulate reparative dentin formation so that it can be considered as an alternative candidate material for pulp capping.

METHODS
The search strategy consists of electronic research using databases such as Pubmed, Google Scholar, Science Direct, dan Springer Link regarding the potency of propolis extract as anti-inflammatory agent for stimulation of reparative dentin formation.Articles search using keywords such as propolis, CAPE, flavonoids, pulp inflammation, TNFα, TGF-β1, ERK, odontoblast-like cells, reparative dentin, and pulp capping.The inclusion criteria in searching for literature review sources were in the form of journals written in English and Indonesian, journals of research articles and review articles, and library sources from 2003-2021.Meanwhile, the exclusion criteria in the library sources were sources in the form of blogspot websites, news reports, journals that only included abstracts without the contents of the manuscript, as well as library sources under 2003.

RESULTS
After exclusion of irrelevant articles, 34 articles were included in this review.Information regarding authors, year of publication, the type of study, and main findings are depicted in Table 1 and 2 Propolis has the ability to stimulate the production of TGF-β1, inhibit pulp inflammation, and stimulate reparative dentin formation.

Widjiastuti et al., 2014 In vitro reearch
East Java Propolis Inhibits cytokine Proinflammatory in Odontoblast like cells Human Pulp.
Application of 3μg/ml East Java propolis extract can inhibit TNFα expression and increase TGF-β1 expression in odontoblast-like cell cultures of human dental pulp.

Widjiastuti et al., 2014 In vitro research
The expressions of NFκB and TGF-β1 on odontoblast-like cells of human dental pulp injected with propolis extracts Injection of 1.5μg/ml, 3 g/ml, and 6μg/ml East Java propolis extract into odontoblast-like cells culture proved that the higher the dose of propolis extract, the ability to inhibit NF-kβ expression and increase TGF-β1 expression increased.

Jacob et al., 2015 In vitro research
The effects of Malaysian propolis and Brazilian red propolis on connective tissue fibroblasts in the wound healing process Application of 500μg/ml Malaysian propolis extract on fibroblast cell culture can induce optimal cell proliferation at 48 hours.Application of 90 mg/ml Thai Propolis extract did not cause inflammation and could stimulate pulp healing.

Sabir, 2019 In vivo research
Indonesian propolis suppressed the expression of COX-2 in inflamed rat dental pulp in direct capping treatment Application of 0.5 mg South Sulawesi propolis extract showed better anti-inflammatory properties in the inflamed pulp than the application of flavonoid propolis and non-flavonoid propolis.

Shi et al., 2019
In vitro research

Effects of MTA and Brazilian propolis on the biological properties of dental pulp cells
The application of 10μg/ml Brazilian propolis extract showed an increase in ALP expression after 21 days, and causing a decrease in TNFα expression although it was not significant.

Widjiastuti et al., 2019
In vivo research

Proliferation of odontoblast-like cells following application of a combination of calcium hydroxide and propolis
Application of a combination of Ca(OH)2 and propolis showed a significant increase in the proliferation of odontoblast-like cells on day 3 and 7 compared to the application of Ca(OH)2 alone.

Widjiastuti et al., 2020 In vivo research
Propolis extract as pulp capping material enhances odontoblast-like cell thickness and type 1 collagen expression (in vivo) Application of propolis extract did not show any significant difference in the thickness of odontoblastlike cells compared to CAPE application on days 7 and 14.A significant difference was seen on day 28, where the thickness of odontoblast-like cells after propolis extract application was thicker.There is a significant difference in the expression of type 1 collagen on day 7, 14 and 28 after propolis extract application compared to CAPE.The effectiveness of propolis extract compared with Ca(OH) 2 in the stimulation of reparative dentin formation is still debated because the stimulative effect on dental pulp depends on the flavonoid contained in propolis extract.

Jacob et al., 2015 In vitro research
The effects of Malaysian propolis and Brazilian red propolis on connective tissue fibroblasts in the wound healing process Application of 1,10,100,250,500 and 1000μg/ml Brazilian red propolis extract showed no significant cell proliferation.

Gamal et al., 2017 In vivo research
Histological evaluation of response to direct pulp capping with propolis: Experimental study in rabbit.
Application of propolis showed minimal inflammatory response on week 1,2, and 4 of observation period

DISCUSSION
Inflammation is a beneficial body response that indicates that the body is being exposed to injury, but inflammation should not occur excessively because it will hinder the healing process, so inflammation must be regulated or inhibited.If immune cells are unable to repair through homeostatic mechanisms, the damage will be widespread, and can continue to be irreversible and can even cause cell death.Likewise, the response of the dental pulp, injury to the pulp can result in an inflammatory response in the pulp or called pulpitis). 12,13here have been many studies aimed at treating vital pulps that have perforated, among others, using propolis.The composition of propolis varies greatly depending on the origin of propolis based on its geographical location.5][16] The content of propolis consists mostly of resins, bees wax and fatty acids, aromatic oils, pollen, and other components such as minerals and vitamins.These components are rich in mineral elements such as Mg, Ca, I, K, Na, Cu, Zn, Mn, and Fe.The composition of propolis also contains lots of vitamins A, C, B1, B2, B6, C, D, and E. These various ingredients will work together synergistically to become antibacterial, antibiofilm, anti-fungal, anti-viral, and anti-inflammatory agents. 17,18ropolis has several important pharmacological effects, including immunomodulatory activity that promotes the healing process, and induces collagen formation.Propolis is thought to have a fairly good adaptability to the dentin surface due to the presence of bees wax as one of the chemical elements contained in propolis.In addition, propolis also contains flavonoids which are thought to produce crystals if they react with dentin so that they will bind and close the open dentinal tubules. 19n the inflammatory process caused by mechanical injury and microorganisms, it will cause phosphorylation of IκB so that NF-κB bonds from IκB are released and translocation occurs into the cell nucleus and secretes pro-inflammatory cytokines, including TNFα which plays the most role in acute inflammation.Propolis inhibit inflammation because CAPE, which is the active ingredient of propolis extract, works by inhibiting the IκB signaling pathway, so there is no addition of phosphate groups, as a result, phosphorylation of IκB is inhibited and causes NF-κB activity, as well, become obstructed.][22][23][24] Some references state that reparative dentin can be formed after administration of propolis extract.[27][28][29] In conclusion, propolis extract has a potency as an anti-inflammatory agent in dental pulp inflammation by inhibiting TNFα expression, and increasing TGF-β1 expression, as well as its potency in stimulating the formation of reparative dentin.Based on this review, further studies are needed.

Table 1 .
. Summary of research results that show the potency of propolis extract as anti-inflammatory agent for stimulation of reparative dentine formation

Author, year of publication, and type of studies Title Main Findings
"Propolis" And Its Potential in Dentistry: A Review Propolis shows anti-inflammatory effects.Ahangari et al., 2012 In vivo research Effect of Propolis on Dentin Regeneration and the Potential Role of Dental Pulp Stem Cell in Guinea Pigs Application of Azerbaijani propolis extract showed the formation of odontoblast-like cells and reparative dentin in the observation period of 10, 15 and 30 days.Sabir, 2014 Article review Prospect of using propolis in conservative dentistry and endodontic treatment (Basic research vs clinical application) Application of MTA, propolis or a combination of both can increase the phosphorylation of ERK.

Table 2 .
Summary of research results that does not show the potency of propolis extract as anti-inflammatory agent for stimulation of reparative dentine formation