Bionanocomposites in Caries Prevention and Treatment: A Systematic Review

Abstract

Objective:

The aim of this systematic review was to assess the therapeutic effect of remineralizing and antibacterial potential of resin-based nanocomposites compared with conventional composite with/without fluoride release in naturally occurring and post-orthodontic carious lesions.

Data Sources:

The literature search covered the electronic databases, such as PubMed, EBSCO, and Google scholar, from 2012 to 2021. Only articles published in English were included. Randomized controlled trials (RCT) and in-vitro studies were included. All studies which met eligibility criteria were reviewed by two independent reviewers.

Study Selection:

The processes involved in the selection of studies were presented in Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines for study screening. Finally, based on the eligibility criteria, 13 studies were selected. The remineralizing effects of nanocomposites were compared with conventional composites in clinical trials and in-vitro studies.

Conclusion:

Nanotechnological interventions could be used to improve the therapeutic efficiency in reducing demineralization and growth of the biofilm. Further well-designed clinical trials with long-term follow-up are essential to elucidate the clinical relevance of remineralizing agents.

INTRODUCTION

The microbial population of the oral cavity is polymicrobial and occurs predominantly as biofilms on diverse surfaces of teeth, restorations, and mucosa.[1] The primary mechanism of development of dental caries is considered to be caused by the microbial imbalance of oral biofilm leading to demineralization of dental hard tissues. Henceforth, it will be beneficial to employ remineralizing agents such as fluorides in caries prevention. The salivary concentration of calcium and phosphate ions can also reduce the demineralization process.[2]

In the presence of progressive demineralization associated with carious lesions, tooth-colored restorations are the material of choice due to their enhanced esthetic properties. Restorative polymers include a set of materials such as direct resin composites, enamel-dentin adhesives, and dental primers with similar primary compositions. Studies have shown that resin-based composites foster the development of cariogenic biofilms resulting in caries around restorations and are considered as one of the major factors for the failure of resin-based restorations. In the light of these limitations, the establishment of novel treatment strategies augmenting conventional therapy is considered crucial for the efficient control of secondary caries.[3] The use of nanotechnology-based treatment could be a game-changer in restorative dentistry through its biomimetic approach in providing effective treatment of dental caries.[4] Dental nano-formulations has also grabbed attention in preventing dental caries around orthodontic brackets.[5,6]

Nanotechnology has been used in the production of bioactive dental materials for decades. Several novel techniques, such as metallic/calcium phosphate-based nanoparticles, have indicated possible benefits in the modulation of biofilm formation. The potential for therapeutic success using nanoparticles is largely determined by these nanoparticles' physical, chemical, and biological properties.[3] Bionanocomposites are derived from natural or synthetic biodegradable polymers integrating with nano-scale materials from 1 to 100 nm in size. These are exceptional green technology materials with adequate biodegradability and biocompatibility to mimic biomaterials. Nanocomposites differ mechanically from conventional composites due to their extremely high surface-to-volume ratio by penetrating the bacterial cell effectively, causing the breakdown of the extracellular polysaccharide matrix.[2,7,8]

The review provides an insight into the intrinsic plausibility of various types of resin-based nanocomposites in respect of anti-cariogenic agents based on inhibition of bacterial growth for use in restorative polymer treatment and its role in remineralization. The most recent available evidence derived from clinical trials is summarized. In-vitro studies account for the bulk of research studies conducted in dentistry research. Hence, if recent clinical studies were not available, the latest available evidence of in-situ/in-vitro is presented.

MATERIAL AND METHODS

Protocol and registration

This systematic review was conducted following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analyses) statement.[9]

Structured question

Do nanocomposites possess the remineralizing potential to be employed as an anti-cariogenic agent in naturally occurring and post-orthodontic carious lesions?

Search criteria for considering studies for this review

The eligibility criteria for our systematic review have been developed according to the Population, Intervention, Comparison and Outcomes (PICOS) acronym [Table 1]. A systematic literature search was conducted on three databases, namely PubMed, EBSCO, and Google Scholar. Articles in these databases were searched using the keywords (“nanoparticle” OR “nanomaterial” OR “nanotechnology”) AND (“metal” OR “metal oxide” OR “silver” OR “zinc” OR “titanium-dioxide” OR “hydroxyapatite” OR “amorphous calcium phosphate”) AND (“anti-bacterial” OR”anti-microbial” AND “demineralization” OR “remineralization”).

Table 1.

Inclusion and exclusion criteria

Domain	Inclusion	Exclusion
Participants	Human in-situ model, patients above 6 years of age with carious lesions induced by fixed orthodontic treatment or natural process. No restrictions on gender, age, city/country, and socioeconomic status.	Animal studies, patients with any illness affecting the study outcome, such as enamel hypoplasia, craniofacial deformities, and/or ongoing medication.
Interventions	Resin-based nanocomposites	Non-remineralized methods for prevention and treatment of carious lesions such as bleaching and micro-abrasion.
Comparisons	Glass ionomer or commercial composite with/without fluoride release	-
Outcome	Carious lesion severity/progression measured by enamel surface roughness, biofilm inhibition and eluted component test, DIAGNOdent pen, disc diffusion, MTT assay, CFU, confocal laser scanning, and polarized light microscopy	-
Study design	Randomized controlled trials and in-vitro studies	Non-randomized studies, pilot studies, Case reports/case series, systematic review.
Timing	Studies from 2012 to 2021	-

Data collection and analysis

Two reviewers independently screened the titles and abstracts of all identified studies based on predetermined eligibility criteria. Any disagreement during study selection and data extraction was resolved by consensus after consulting a third reviewer. The processes involved in the selection of studies were presented in a PRISMA flow diagram for study screening [Figure 1].

Figure 1.

PRISMA flow chart of the included studies

Data extraction

The two reviewers extracted data from each included study using Microsoft Excel 2010 with a specifically developed data extraction form, independently. The summary of the details of the included studies was tabulated in Table 2.

Table 2.

Summary of the included studies

Author and year	Study design	Participants and groups	Intervention	Comparative/control	Outcome/Result
Vineesha 2021[10]	In-vitro study	176 disk specimens 11 groups	TransbondXT Primer with 2.5%, 5% benzalkonium chloride, 0.2%, 2.5% chlorhexidine, 1%, 3% titanium dioxide nanoparticles, 0.2%, 0.5% nanohydroxyapatite, 0.2%, 0.5% silica-doped nanohydroxyapatite powder	TransbondXT Primer	Evaluation by disc diffusion method. The silica-doped nanohydroxyapatite at 0.5% had the greatest inhibition zone.
Nanda 2020[11]	Randomized, controlled single-blind in-vitro study	Extracted premolars 4 groups n=40	NanoSilverFluoride pre-treatment +GIC restoration, NSF pre-treatment +composite restoration.	Glass ionomer cement restoration, composite restoration	Vickers microhardness test showed lesser demineralization following NSF pre-treatment
Wu 2019[12]	In-vitro study	Enamel specimens from bovine incisors n=13; 8 groups	Inoculation of S. mutans in different concentrations Group 2-4: 0.08, 0.12, 0.16 mg/ml rGO/Ag + Brain Heart Infusion containing 1% sucrose (BHIS) Group 5-7:(0.16 mg/mL rGO, 0.16 mg/mL AgNPs, 10 ppm NaF) +1% BHIS	Negative control: (inoculation of S. mutans in 1% BHIS) Positive control: 1% BHIS, without inoculation.	Evaluated by confocal laser scanning, atomic force and Polarized light microscopy. Use of rGO/Ag can reduced enamel surface roughness and demineralization.
Wang 2019[13]	In-vitro study	Planktonic and biofilm phase	Ag/ZnO nanocomposites with a light-emitting diode (LED)	biofilms without Ag/ZnO and LED treatment	The combined Ag/ZnO with LED irradiation reduced the EPS matrix formation and useful in dental caries prevention
Salas-Lopez 2017[14]	Split-mouth double-blind clinical study	40 children 6-10 years	Silver nanoparticles-added sealant	Conventional sealant	Assessed using the DIAGNOdent pen. The silver nanoparticle-added sealant significantly increased remineralization.
Sodagar 2016[6]	In-vitro study	162 composite discs	Transbond XT composite containing 1%, 5%, and 10% silver/hydroxyapatite nanoparticles	Transbond XT composite	Disk agar diffusion, biofilm inhibition and eluted component test used. The orthodontic adhesives containing 5% and 10% Ag/HA nanoparticles reduced growth of cariogenic bacteria.
Li 2013[15]	In-situ study	Extracted third molars n=40	Primer +10% QADM, SBMP adhesive + QADM Primer +0.05% NAg SBMP adhesive +0.05% Nag	SBMP primer and adhesive	The live/dead assay, MTT, CFU, lactic acid, and gtf gene expression results demonstrated that QADM-containing bonding agent had antibacterial activity
Zhang 2013[16]	In-situ study	Plaque microcosm biofilms -cultured using saliva from 10 donors.	Five systems were tested: SBMP adhesive (A) + 2.5% 12-methacryloyloxydodecyl pyridinium bromide (MDPB); A +0.1% Nag; A+2.5% MDPB+0.1% NAg; primer“P” + MDPB+NAg together with A +MDPB+ NAg	ScotchbondMulti-Purpose (SBMP) adhesive control (A)	Metabolic activity, CFU, and lactic acid production of biofilms were investigated. The dual agent (MDPB + NAg) method inhibits biofilm and caries.
Melo 2013[17]	In-vitro study	Human in-situ model 2 groups n=25	40% NACP +20% glass (NACP nanocomposite)	Control composite with 60% glass particles	Evaluated using transverse microradiography. Release of Ca and P ions from NACP composite was significantly increased at cariogenic pH (P<0.05).
Cheng 2012[18]	In-vitro study	Human saliva microcosm model 3 groups n=18	Nanoparticles of amorphous calcium phosphate (NACP) and quaternary ammonium dimethacrylate (QADM)	Negative control: Commercial composite with methacrylate-ester Positive control: composite with silica/ytterbium-trifluoride	NACP-QADM nanocomposite had strong antibacterial properties and inhibit S. mutans biofilm viability, metabolic activity, CFU, and acid production by 3 fold (P<0.05)
Cheng 2012[19]	In-vitro study	Human saliva microcosm model 6 groups n=6/group	NACP +0% NAg, NACP +0.028% NAg, NACP +0.042% NAg, NACP +0.088% NAg, NACP +0.175% Nag	Commercial composite with methacrylate-ester	Live/dead assay of biofilm and CFU revealed that the antibacterial properties significantly increased with higher NAg mass fraction. The NACPnanocomposite + NAg is useful for caries-inhibiting restorations.
Cheng 2012[20]	In-vitro study	Human saliva microcosm model 6 groups n=6 per group	NACP, NACP + QADM, NACP + NAg, and NACP + QADM + NAg	Two commercial composites with low fluoride release and no fluoride release	The MTT assay and lactic acid production of biofilms on NACP + QADM + NAg composite were significantly less than the controls and has stronger remineralization effect than either composite alone (P<0.05).
Weir 2012[21]	In-vitro study	Caries-free molars 3 groups n=18	Nanoparticles of amorphous calcium phosphate (NACP)	Control enamel without composite and commercial fluoride releasing composite	Mineral profiles of enamel section were measured using quantitative analysis of contact microradiographs. NACP nanocomposite was effective in remineralizing enamel 4-fold than fluoride-releasing composite.

Quality assessment

Apparently, there are no standardized checklists for reporting in-vitro experiments. The concept note of CRIS guidelines[22] would rather assist in meeting standard reporting criteria of the in-vitro studies. Thus, the quality and transparency of the systematic reviews and meta-analyses of specific topics will be facilitated. In the present review, quality assessment of the included studies was undertaken independently by two reviewers. Sample preparation and handling were elaborated in detail in all the studies. The domains such as randomization, sample size calculation, allocation concealment, blinded assessment, and reporting of statistical methods need improvisation in the majority of the studies.

Statistical analysis

Meta-analyses could not be performed due to the heterogeneity between the studies.

RESULTS

The 13 studies that met the inclusion criteria were taken for the present systematic review [Table 1].

Study characteristics

The included studies were compared regarding the number of the participants, study design, main findings examination, and treatment methods. The studies included were published from 2012 to 2021. All the included studies were in-vitro studies wherein only one study was a clinical study (RCT) to evaluate the effects of sealant with silver nanoparticles on dental caries. Two of the in-vitro studies evaluated the antibacterial properties of nanoparticles incorporated in orthodontic primer.[6,10] Of the included studies, the study conducted by Nanda et al.[11] was single-blinded and Salas-Lopez et al.[14] was a split-mouth double-blinded study. Remaining studies included in the review have not mentioned explicitly the blinding in the methodology. The review comprised of studies on resin-based nanocomposites incorporating silver-nanofluoride, reduced graphene oxide-silver nanocomposite, calcium phosphate, quaternary ammonium compounds, titanium-oxide, zinc oxide, and hydroxyapatite nanoparticles.

Primary outcome

The primary outcome for assessment was the remineralization potential of resin-based nanocomposite on the human in-situ model. The measurement methods used included a combination of International Caries Detection and Assessment System II (1 study), disc diffusion assay (2 studies), MTT assay (3 studies), microradiography (2 studies), confocal laser scanning, atomic force and Polarized light microscopy (1 study), microhardness test (2 studies), DIAGNOdent (1 study), CFU (5 studies), and eluted component test (1 study) [Table 2]. All the included studies showed a significant reduction in demineralization using nanocomposites compared with conventional composites.

Secondary outcome

The study conducted by Li et al.[15] reported that the quaternary ammonium dimethacrylate (QADM), nanoparticles of silver (NAg) nanocomposites had eluent cytotoxicity against fibroblasts.

DISCUSSION

The review disclosed that nanocomposites had promising results in terms of remineralizing and antimicrobial properties. Biofilms on NACP nanocomposite restorations in-situ exhibited considerably greater Ca⁺ and P⁺ ion concentrations than that on the control at local cariogenic pH levels which is effective for caries prevention.[17,19] Graphene-oxide and silver nanoparticles composites have been employed in recent years for their long-term antibacterial action.[19]

Nanotechnology aids in the treatment of dental caries in two ways. The first method involves remineralization, with the use of nanomaterials that release fluoride and calcium, such as calcium phosphate, calcium fluoride, hydroxyapatite, and fluoro-hydroxyapatite. The other method employs the use of antibacterial nanoparticles such as silver, quaternary ammonium polyethylene amine, and zinc oxide. Better results are attained when both approaches are combined.[2,4,8,17,23] Also, the nanocomposites with NACP + QADM + NAg not only have the dual benefits of remineralization and antibacterial effect but also possesses mechanical properties similar to conventional composites.[20] Application of MDPB + Nag into adhesives, sealants, cements, and composites act as anti-biofilm agents.[16]

Several nanoparticles (zinc oxide and silver) have indeed been integrated into dental composites to inhibit microbial growth through various mechanisms such as disruption of the bacterial cell walls, suppression of active transport and sugar metabolism, production of reactive oxygen species, and dispersion of magnesium ions necessary for oral biofilm enzyme production. Nanocomposites releasing high concentrations of Ca²⁺ and PO4^3- have been formulated to aid in the prevention of recurring caries around the restorations. The size of silver nanoparticles has an inverse relationship with their antimicrobial activity.[22] QADM and NAg potentially serve as complementary antibacterial agents, both on and away from the resin surface.[19] Weir et al.[21] stated that NACP nanocomposite has four times the remineralizing capability than fluoride-releasing composite.

Nanodentistry will be economical, time-saving, and will arrest the progress of caries in its early stage. Although there have been several studies that reveal nanoparticles to be beneficial, there is a dearth of documented clinical trials on nanocomposites and their clinical applications for caries prevention.[2] Further research is necessary to disclose the performance of nanoparticles in the oral environment.

CONCLUSION

Nanotechnological interventions could be used to improve the therapeutic efficiency in reducing demineralization and growth of the biofilm. As a result, newer nano-sized formulations offer substantial benefits over conventional restorative materials. However, there is a need for more in vivo or clinical studies for the judicious use of bionanocompistes in caries control and prevention.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.