Peptides in Dentistry: A Scoping Review

Currently, it remains unclear which specific peptides could be appropriate for applications in different fields of dentistry. The aim of this scoping review was to scan the contemporary scientific papers related to the types, uses and applications of peptides in dentistry at the moment. Literature database searches were performed in the following databases: PubMed/MEDLINE, Scopus, Web of Science, Embase, and Scielo. A total of 133 articles involving the use of peptides in dentistry-related applications were included. The studies involved experimental designs in animals, microorganisms, or cells; clinical trials were also identified within this review. Most of the applications of peptides included caries management, implant osseointegration, guided tissue regeneration, vital pulp therapy, antimicrobial activity, enamel remineralization, periodontal therapy, the surface modification of tooth implants, and the modification of other restorative materials such as dental adhesives and denture base resins. The in vitro and in vivo studies included in this review suggested that peptides may have beneficial effects for treating early carious lesions, promoting cell adhesion, enhancing the adhesion strength of dental implants, and in tissue engineering as healthy promotors of the periodontium and antimicrobial agents. The lack of clinical trials should be highlighted, leaving a wide space available for the investigation of peptides in dentistry.


Introduction
Dental plaques contain over 750 different bacterial species, which are the major reason for dental caries, with streptococci being the most predominantly present. These bacteria, due to the production of acids, can demineralize and affect mineralized tooth tissues [1]. Different additives and biomaterials were used in dental treatments in order to eliminate and decrease the number of bacteria in the oral cavity and teeth tissues. Some dental materials, such as calcium silicate-based products, have been introduced in the dental market due to their antibacterial, antioxidant and remineralization properties [2]. Other solutions ( Table 1). The MEDLINE search strategy was then adapted to other electronic databases. The reviewers also hand-searched the reference lists of the included articles to identify additional manuscripts.

Selection Process and Data Collection Process
After running the search strategy, a reference management program was used (End-Note X9, Clarivate Analytics, Philadelphia, PA, USA) to store the files of all databases. Then, duplicate articles were removed, followed by manual removal after the organization of titles in alphabetical order. All studies were initially scanned for relevance by title followed by abstract using an online software program (Rayyan, Qatar Computing Research Institute, HBKU, Doha, Qatar). The titles and abstracts of the articles were screened according to the following inclusion criterium: in vitro or in vivo studies that evaluated or reported the use of peptides for dental applications. The search was carried out on documents published in any language without restrictions on their date of publication. Reviews, case reports, case series, pilot studies, and conference abstracts were excluded. If the review authors were not sure about the eligibility of any study, it was kept for the next phase. All phases were carried out by two independent reviewers (RB and CECS) to check whether they met the inclusion criteria. The same two reviewers summarized and categorized the data using a standardized form. The information collected included the type of study, the peptide used, the application proposed and the main results.

Characteristics of Studies
The main characteristics of the studies included in the present review are presented in Table 2. Bröseler, 2020 [43] Randomized clinical trial Self-assembling peptide (SAP) P11-4 Early buccal carious lesions Self-assembling peptide regenerated enamel caries lesions          There is an interaction between substance P and enkephalin systems in the superficial layer of the brain-stem trigeminal sensory nuclear complex for the regulation of dental pain transmission. In addition, the native application of naloxone (5 × 10 −7 M) partly antagonized the inhibitory effects of locally applied morphine and the opioid peptide Yoshinari, 2005 [161] In vitro Antimicrobial peptide histatin 5 Poly (methyl methacrylate) denture base C. albicans colonization on histatin-adsorbed PMMA was knowingly less than the control

Characteristics of Studies
The main characteristics of the studies included in the present review are presented in Table 2. It was observed that there was a capacity of the peptides to promote enhanced cell adhesion The studies included experiments in animals and/or using bacteria or cells; also, several clinical trials were found. Most of the applications of the peptides included caries management, implant osseointegration, guided tissue regeneration, vital pulp therapy, antimicrobial activity, enamel remineralization, occlusion of dentin tubules, periodontal therapy, the surface modification of dental implants, and the modification of dental materials such as dental adhesives and denture base resins.

Synthesis of Results and Summary of Evidence
The in vitro and in vivo studies included in the present review stated that peptides may have beneficial effects for treating early carious lesions. Additionally, the use of peptides seems to be beneficial for promoting cell adhesion and enhancing the adhesion strength of dental implants. In addition, peptides were useful for tissue engineering for cell-based pulp regeneration. Peptides were also successfully used as healthy promotors of the periodontium, acting as inflammatory mediators. Finally, most peptides were used as effective antimicrobial agents.

Discussion
A scoping review was performed regarding the use and applications of peptides in the dental field at present. Appropriately, most of the applications of the peptides included caries management, implant osseointegration, guided tissue regeneration, vital pulp therapy, antimicrobial activity, enamel remineralization, occlusion of dentin tubules, periodontal therapy, the surface modification of dental implants, and the modification of dental materials such as dental adhesives and denture base resins.
One should keep in mind that dental caries is considered the most common disease worldwide [171], and it can lead to the destruction of dental surfaces by means of acidogenic bacteria changing sugars to acids [43]. Dissolution of the mineral tooth structure begins with caries formation, therefore generating a demineralized subsurface lesion body, similar to white spots [172], followed by the development of irreversible cavitation of the mineralized surface layer [173,174]. Treatment of manifested caries involves an oral hygiene regulation and a follow-up visit to identify whether the caries has been prevented or has advanced into a cavity, which is subsequently treated by means of restoration [173]. The use of fluoride varnish can prevent caries formation by reinforcing the inorganic surface layer, consequently inhibiting the progression of caries [175][176][177]. Fluoride ions are preserved within the inorganic surface layer covering the demineralized carious lesion due to the high correspondence to hydroxyapatite [178]. Subsequently, the demineralized subsurface zone is not penetrated by fluoride; yet this is where remineralization would be essential in an attempt to regenerate decayed enamel tissue [43]. For this reason, novel methods for the treatment of caries have been introduced to mimic the structure of the enamel matrix, such as guided enamel regeneration (GER) [179].
It should be noted that self-assembling peptide (SAP) technology was designated on the reasonable design of a short hydrophilic peptide in combination with GER that builds into fibers, establishing a three-dimensional (3D) scaffold [180][181][182]. The surface features of the fibers might fluctuate, concurring with the physiological desires of the treated tissue [66,183]. This could be explained by the rational design criteria [183]. When treating early caries lesions, SAP P11-4 fibers have been adjusted to suitably bind ionic calcium and template hydroxyapatite formation, thus, accompanying remineralization in a comparable approach of amelogenin that supports the construction of the enamel. From this analysis, the SAP P11-4 fibers might be known as a biomimetic agent [66,74]. This could be in agreement with the finding of this review that demonstrated the potential effect of peptide P11-4 in caries management.
With regards to implant osseointegration, pure titanium is commercially used for implants in the dental field due to its possible resistance to corrosion, biocompatibility, and suitable mechanical properties [184][185][186]. Researchers have detected peri-implant bone resorption produced by peri-implantitis, which is considered the key reason for the failure of osseointegrated dental implants [187,188]. In this manner, surface modification of dental implants has been a topic of interest for researchers since titanium is an inert material that decreases the aptitude for remedial tissue therapy to succeed and resists bacterial settlement [189][190][191]. To counteract peri-implantitis and advance osseointegration, different type of coatings have been investigated [192]. Surfaces incorporating chlorhexidine, antimicrobial agents and antibiotics such as gentamicin, and surfaces incorporating chlorhexidine, poly-lysine, sliver, and chitosan have all been established for coating the titanium surface of implants [52]. However, some drawbacks could be noted with antibiotic-coated titanium, such as the controversial opinion about their bacterial resistance and host cytotoxicity [193]. In 2015, Zhou et al. demonstrated that antimicrobial peptides provided a promising bifunctional titanium surface and enhanced its bactericidal activity and cytocompatibility [168]. Likewise, a previous report suggested that after 6 weeks of implantation in rabbit femurs, titanium dental implants with an antimicrobial peptide GL13K coating allowed in vivo dental implant osseointegration at similar bone growth rates to gold-standard non-coated dental implants [52]. This could be explained by the fact that GL13K is bactericidal in solution against Escherichia coli, Pseudomonas aeruginosa, Porphyromonas gingivalis and Streptococcus gordonii [83,194,195]. Similarly, Yoshinari et al. proved that the antimicrobial and titanium-binding peptides were favorable for the diminution of biofilm formation on titanium surfaces [162]. In addition, a laminin-derived peptide was demonstrated to improve and enhance the integration of soft tissue on dental titanium implants [143].
Furthermore, an epithelial basement membrane was formed on a titanium surface when platelet-activating peptide was used [135]. All in all, this could clearly support the result of this review that the use of peptides seems to be beneficial for promoting cell adhesion and enhancing the adhesion strength of dental implants.
In addition, this analysis determined that peptides were useful for guided tissue regeneration [42]. This could be achieved when a combination of a synthetic peptide named P-15 (analog of collagen) and an anorganic bovine bone mineral (ABM) was used. ABM enhanced cell attachment by differentiation and cell binding, thus enhancing osseous formation and ensuing an accelerated periodontal ligament fibroblast attachment [109,196]. Adding to P-15, biocompatible and osteoconductive filler material was thus detected [42].
A major task in the use of tissue engineering for therapy in dentistry involves the initiation of tooth and bone regeneration. The dentin phosphophoryn-derived arginine-glycineaspartic acid-containing peptide was demonstrated as a biodegradable, biocompatible, and bioactive material for dentin regeneration. These results could be clarified by the short AA sequences of the peptide used and by its 3D conformation essential for acquiring this function [46]. Accordingly, the peptide can be used in vital pulp therapy when a specific sequence is used.
Further, most peptides were used as effective antimicrobial agents. Peptide hydrogels have shown that ultrashort peptides (<8 amino acids) might self-assemble into hydrogels. These ultrashort peptides might be intended to integrate antimicrobial motifs, such as positively charged lysine residues; thus, the peptides have integral antimicrobial features [47]. The scheme and synthesis of biocompatible hydrogels with antimicrobial activity are of numerous interests for tissue engineering drives comprising the replacement of tissue in infected root canals [65,197,198]. Moreover, antimicrobial peptides were used in coated titanium surfaces [168], dental adhesives [147], caries infection [102], and plaque biofilm inhibition [36].
Peptides were also successful for enamel remineralization. It is imperative to note that the acidic nature of dental cavities created by a massive amount of sugar intake leads to bacterial colonization and a reduction in the pH. Accordingly, the demineralization of the enamel surface begins [48]. In order to prevent this issue, numerous remineralizing agents were presented [48]. A perfect agent should be free of toxicity and qualified to initiate remineralization without any harm to the dental surface. Matrix-facilitated mineralization equal to a natural process should be carried out, though this ability is absent in almost all these agents [199]. The arrival of SAP P11-4 has overwhelmed this restriction. It has the ability to regenerate enamel. In addition, these agents initiate remineralization by making 3D constructions mimic the extracellular matrix of the dental surface [200]. Therefore, when talking about enamel remineralization, clinicians should focus on SAP due to its efficient and effective outcomes obtained in this review.
The occlusion of dentin tubules is considered possible with the help of peptides. This theory became conceivable when mineral particles were observed on dentinal tubules, thus reducing dentinal permeability and enhancing the seal of the material-tooth interfaces [57]. Bonding agents and desensitizers have been demonstrated to be effective for occluding tubules by mineral precipitation; however, these techniques are sensitive, and the longterm performance of the resin is doubtful [201,202]. As a balancing method for the protein mediation of hydroxyapatite mineralization, streamlined synthetic cationic macromolecules comprising poly(L-lysine) (PLL) that cover primary and secondary amine groups are organizationally comparable to the functional areas of the natural proteins and have further been presented to encourage silicification [203]. This review implies that this peptidecatalyst-mediated method of mineral formation for occluding tubules and/or reinforcing dentin-bonding resins might retain function on the dentin surface, advising a wide range of protective and treatment plans.
Peptides have also been successfully used as healthy promotors of the periodontium, acting as inflammatory mediators. Periodontitis is a chronic inflammatory and tissuedestructive illness. Meanwhile, the oral cavity with its polymicrobial effect makes it problematic to treat; thus, new healing approaches are mandatory. In a minimally invasive way, SAP delivers the benefit of being functional at a defect site without creating a toxic area [204]. Furthermore, their tunable mechanical characteristics and reasonably designed physicochemical features permit a high variety of encapsulated drugs [205]. Some peptides called P11-4 and P11-28/29 were considered SAP-applicable for periodontal therapy, due to their biocompatibility, injectability, tunable mechanical and physicochemical properties, and cargo-loading capacity [72].
Finally, peptides were used in the modification of dental materials such as dental adhesives and denture base resins. Recurrent decay that grows at the composite-tooth interface was demonstrated to be a disadvantage when using resin-based composite [163]. Primarily, the composite-tooth interface becomes coated by a low-viscosity adhesive system; however, when a fragile seal to the dentin is obtained, damage from enzymes, acids, and oral fluids will be achieved. This impairment is chief in crevices that are occupied by cariogenic bacteria such as Streptococcus mutans [206][207][208][209]. Various bacterial-inhibition strategies have been incorporated into adhesive systems, but none of these strategies address the multifaceted interplay of the mechanical and physicochemical influences of the durability of the adhesive seal at the composite-tooth interface. Antimicrobial peptides have been coupled into the adhesive system using non-bonded interactions [146], and subsequently, antimicrobial peptides were conjugated into the network of the adhesive system in order to improve the antimicrobials' effectiveness [147]. An antimicrobial peptide AMP2-derivative (AMPM7) sequence using a functional spacer was used for integration into a monomer site. This adhesive system formed of co-tethered peptides demonstrated both localized calcium phosphate remineralization and strong metabolic inhibition of S. mutans [163]. An adhesive system incorporated with an antimicrobial peptide inhibited bacterial attack, and a hydroxyapatite-binding peptide promoted the remineralization of damaged tooth structures [146,163]. In 2017, Su et al. demonstrated that a cured antimicrobial peptide with nisin-incorporated dental adhesive showed a significant inhibitory effect on the growth of S. mutans [133], and recently, a paper showed that 3% (w/v) of nisin-incorporated universal adhesive system substantially inhibited the growth of both saliva-derived multispecies biofilms and S. mutans monospecific biofilms without hindering the bonding performance [166].
Moreover, it was demonstrated that C. albicans colonization on the denture's base was significantly less than the control when histatin-adsorbed PMMA (poly methyl methacrylate), an antimicrobial peptide, was used [161]. Another report suggested that histidine-rich polypeptides were effective in the treatment of denture stomatitis [121], thus evidencing the important use of peptides in removable prostheses.
Some limitations relative to the applications of peptides in the dental field can be cited. One restriction is the absence of homogeneity of the type and obtention of the peptides used in the different applications described in the present review. Another limitation that can be highlighted is that due to the heterogeneity of the analytical techniques used for distinguishing the peptides, analyzing data using any statistical analysis was avoided.

Conclusions
The use of peptides has been gaining increasing attention in contemporary dentistry. Dental research evidence suggests that peptides have several applications, including osseointegration, guided tissue regeneration, vital pulp therapy, antimicrobial activity, enamel remineralization, and the surface modification of dental implants. The lack of clinical trials should be highlighted, leaving a wide space available for the investigation of peptides in dentistry.