Antimicrobial properties of nano-poly (d,l- lactic acid) [poly lactic acid] and zinc oxide nanofiller denture base resins: a systematic review and meta-analysis

Abstract

Purpose:

This systematic review and meta-analysis aimed to evaluate the antimicrobial properties and mechanical performance of denture base resins incorporating nano-poly (D,L-lactic acid) (PLA) and zinc oxide (ZnO) nanofillers compared to conventional denture base materials.

Materials and methods:

A comprehensive literature search was conducted across PubMed, Scopus, Web of Science, Cochrane Library, Embase, and Google Scholar for studies published between 2017 and 2024. The PICOS framework guided study selection:P: PMMAbased denture base resins; I: PLA/ZnO nanocomposite denture base resins; C: Conventional denture base resins; O: Antimicrobial efficacy, mechanical properties; S: Randomized controlled trials, cohort studies, case-control studies, and in vitro studies. Studies were screened according to PRISMA guidelines. Relevant data were extracted on study design, interventions, antimicrobial testing, microorganisms tested, mechanical outcomes, and biocompatibility. Quality was assessed using the QUIN tool, and risk of bias was evaluated for each domain.

Results:

From an initial 438 records, 11 studies met inclusion criteria and 8 were eligible for quantitative analysis. The included studies demonstrated that PLA/ZnO nanocomposites significantly reduced microbial growth and biofilm formation against common oral pathogens (Streptococcus mutans, Candida albicans, Escherichia coli). Higher ZnO concentrations correlated with larger inhibition zones and increased antibacterial efficacy. Mechanical properties, including flexural strength and impact strength, were notably improved in PLA/ZnO composites compared to conventional resins, with flexural strength values reaching up to 103.8 MPa. Biocompatibility assessments indicated minimal cytotoxicity and favourable tissue compatibility, with controlled degradation rates between 2–10% over six months. Quality assessment rated most studies as moderate to good quality, although some risk of bias was present.

Conclusion:

PLA/ZnO nanofiller denture base resins exhibit promising antimicrobial properties and enhanced mechanical performance compared to conventional materials. These findings support their potential for improving denture hygiene, durability, and patient outcomes. Further well-designed clinical trials are needed to confirm long-term safety and effectiveness.

Introduction

Dental prosthetics, including dentures, are highly susceptible to microbial colonization, which can lead to infections such as denture stomatitis. To mitigate these risks and improve oral health outcomes, incorporating antimicrobial agents like ZnO nanofillers into denture base materials has become essential for reducing microbial adherence and infection-related complications (1).

PLA, a biodegradable polymer, is widely recognized for its excellent biocompatibility and strong mechanical properties, which make it suitable for various medical and dental applications (2). Its ability to degrade into non-toxic by-products within the body further increases its appeal. Incorporating antimicrobial nanoparticles like ZnO into PLA matrices through nanotechnology has led to the development of advanced nanocomposites (3). Zinc oxide nanoparticles have an2timicrobial properties effective against a wide range of microorganisms, including bacteria, fungi, and viruses, making them ideal for enhancing dental materials (4, 5). In PLA-based denture resins, ZnO nanoparticles can significantly inhibit bacterial growth and prevent biofilm formation by inducing reactive oxygen species (ROS), which damage microbial cell membranes and cause cell death, effectively targeting pathogens such as Candida albicans and Streptococcus mutans (6, 7).

Antibacterial testing methods

A range of laboratory methods is used to screen or evaluate the in vitro antimicrobial activity of an extract or pure compound. The most common methods are the disk-diffusion and broth or agar dilution techniques. Other methods are used especially for antifungal testing, such as the poisoned food technique. To further study the antimicrobial effect of an agent in depth, time-kill tests and flow cytofluorometric methods are recommended, as they provide information on the nature of the inhibitory effect (bactericidal or bacteriostatic), whether it is time-dependent or concentration-dependent, and the extent of cell damage inflicted on the test microorganism.

Mechanical properties and biocompatibility

PLA/ZnO nanocomposites offer superior mechanical properties compared to traditional denture base materials, while retaining their antimicrobial benefits. The addition of ZnO nanoparticles improves the overall strength and toughness of the material, which is critical for the longevity and reliability of dental prosthetics (8). This improvement results from the uniform dispersion of nanoparticles within the polymer matrix, enabling better load transfer and greater resistance to fracture. Alongside mechanical strength, biocompatibility is vital to ensure dental materials do not harm oral tissues. Studies have confirmed that ZnO nanoparticles, when incorporated into dental materials, display minimal cytotoxic effects, with PLA further supporting the composite’s overall biocompatibility (9). The synergy between PLA and ZnO offers a promising approach for producing denture base resins that are both safe and effective for long-term use.

Advances in nanocomposite denture base resins

The evolution of dental materials is demonstrated by the introduction of PLA/ZnO nanocomposite denture base resins, designed to address the limitations of traditional materials such as poor antimicrobial properties and insufficient mechanical durability (10). By embedding antimicrobial nanoparticles like ZnO into the polymer framework, these composites reduce microbial colonization and enhance critical physical properties (11).

Techniques including melt blending, solvent casting, and in situ polymerization have been used to ensure the uniform dispersion of ZnO within the PLA matrix, optimizing both antimicrobial performance and mechanical integrity (12, 13). Furthermore, advancements in surface modification have improved the interaction between ZnO nanoparticles and the PLA polymer, leading to better nanoparticle distribution and improved material performance (14). Preclinical studies on PLA/ZnO nanocomposite denture base resins are promising and indicate potential for clinical applications, although further research is needed to fully assess long-term effects and refine formulations (15). Clinical trials will be crucial to confirm the safety and effectiveness of these materials and to address any practical challenges that may arise (16). Antimicrobial denture liners made with these nanocomposites provide ongoing protection against microbial growth and biofilm formation (17). These innovations also show potential improvements in other dental applications such as crowns and bridges, offering enhanced antimicrobial properties and durability (18). Compared to conventional materials, PLA/ZnO nanocomposites provide clear advantages in antimicrobial efficacy and mechanical performance, offering greater resistance to microbial colonization and increased longevity (19). The addition of ZnO nanoparticles to PLA denture base resins effectively addresses the limitations of conventional materials. Future research should focus on optimizing formulations and production methods to maximize clinical safety and efficacy. This systematic review provides a comprehensive overview of current research, highlighting the potential benefits and challenges of incorporating PLA/ZnO nanocomposites into dental practice, with the goal of improving oral health outcomes.

Materials and methods

Research question

“What are the antimicrobial properties and mechanical performance of nano-Poly (D, L-lactic acid) (PLA) and zinc oxide (ZnO) nanofiller denture base resins?” was the research topic that this systematic review and meta-analysis attempted to answer.

PICOS design

Population (P): Studies using PMMA based denture-based resins, Intervention (I): Using denture base resins that are PLA/ ZnO nanocomposite, Comparison (C): Conventional denture base resins, Outcome (O): Antimicrobial efficacy, mechanical properties, Study Design (S): Randomized controlled trials, cohort studies, case-control studies.

Study timeline

The study was conducted from 2017 to 2024. This included literature search, selection, data extraction, synthesis, and quality assessment.

Search strategy

Careful planning of the search strategy was conducted, adhering to PRISMA guidelines, to guarantee a thorough and systematic literature review. PubMed, Scopus, Web of Science, Cochrane Library, Embase, and Google Scholar were all included in the search for databases. This comprehensive array of databases was designed to encompass a broad spectrum of pertinent publications through December 2023. The exploration utilized both controlled vocabulary (MeSH terms) and free-text terms to encompass all applicable research. Utilizing Boolean operators (AND, OR, NOT) assisted in improving and fine-tuning the search outcomes. The terms and phrases utilized were “nano-Poly(D,L-lactic acid)”, “PLA”, “zinc oxide”, “ZnO”, “nanofiller”, “denture base resins”, “antimicrobial properties”, “mechanical performance”, “dental materials”, “biofilms”, “nanotechnology”, “biocompatibility”, “polymer composites”, “nanocomposite dental materials”, “PLA/ZnO interactions”, and “denture base nanotechnology”. The search criteria were created to guarantee thorough identification of pertinent research. As an illustration, the search conducted in PubMed was organized as: (nano-Poly(D,L-lactic acid) OR PLA) AND (zinc oxide OR ZnO) AND (nanofiller OR nanocomposite) AND (denture base resins) AND (antimicrobial properties OR mechanical performance). Comparable methods were utilized in the rest of the databases, employing different versions of the keywords and Boolean operators to enhance the scope and thoroughness of the search. This thorough search strategy guaranteed a comprehensive examination of the literature, encompassing all pertinent studies on the antimicrobial properties and mechanical performance of PLA/ZnO nanofiller denture base resins (Table 1).

Table 1.

Databases searched and the key words.

Database	Keywords
PubMed	“nano-Poly(D,L-lactic acid)”, “PLA”, “zinc oxide”, “ZnO”, “nanofiller”, “denture base resins”, “antimicrobial properties”, “mechanical performance”
Scopus	“nano-PLA”, “zinc oxide nanoparticles”, “ZnO”, “nanocomposite”, “denture resins”, “antibacterial properties”, “mechanical strength”, “dental materials”
Web of Science	“poly(D,L-lactic acid) nanocomposites”, “PLA”, “ZnO”, “nanoparticles”, “denture base materials”, “antimicrobial efficacy”, “mechanical properties”
Cochrane Library	“PLA nanocomposites”, “zinc oxide nanofiller”, “ZnO”, “denture base resins”, “antimicrobial activity”, “mechanical properties”, “dental prosthetics”
Embase	“nano-Poly(D,L-lactic acid)”, “PLA”, “zinc oxide”, “ZnO nanocomposite”, “denture base materials”, “antibacterial performance”, “mechanical properties”, “dental applications”
Google Scholar	“PLA/ZnO nanocomposites”, “zinc oxide nanofiller”, “ZnO nanoparticles”, “denture resins”, “antimicrobial properties”, “mechanical performance”, “nanotechnology in dentistry”

Inclusion criteria

Studies involving PLA/ZnO nanocomposite denture base resins, studies reporting antimicrobial properties and mechanical performance, randomized controlled trials, cohort studies, case-control studies, and in vitro studies, full-text articles published in English were included in this research.

Exclusion criteria

Studies not involving PLA/ZnO nanocomposite denture base resins, studies not reporting on antimicrobial properties or mechanical performance, Reviews, editorials, and opinion pieces, Articles written in languages other than English or abstracts were excluded.

Data extraction, synthesis, and quality assessment

This process was carried out in a methodical manner by 5 authors A,B,C,D,E adhering to established protocols to ensure thoroughness and dependability in the evaluation process. Out of a total of 438 articles that were screened, 11 of them were included in the review and only 8 were eligible for quantitative analysis as per PRISMA flowchart by authors A and B (Figure 1). Data relevant to chosen studies was obtained using predefined extraction forms. This included key variables like study design, sample size, interventions (e.g. types of PLA/ZnO nanocomposites), outcomes (e.g. antimicrobial properties, mechanical performance), and any adverse events reported. The gathered data was combined to uncover common themes, patterns, and discrepancies among various studies on the effectiveness and safety of PLA/ZnO nanocomposite materials for dental use. Evaluation of the studies’ quality was conducted to assess their methodological rigor and potential bias, utilizing specific tools designed for different study types. This methodical process guaranteed that only research that met established quality standards was included in the ultimate analysis, thereby increasing the trustworthiness and accuracy of the results.

Figure 1.

Flowchart of the research protocols.

Risk of bias assessment

The other three reviewers (C,D and E), assessed the bias risk on their own. By debate or consultation with a fourth reviewer, disagreements were settled. Selection bias, performance bias, detection bias, attrition bias, and reporting bias were among the variables considered in the assessment. The antibacterial qualities and mechanical performance of PLA/ZnO nanocomposite denture base resins were reviewed and analysed using a strict and methodical process, which produced solid and trustworthy results.

Results

Table 2 shows that adding these nanomaterials to denture base resins greatly improves their ability to fight off common oral pathogens like Streptococcus mutans, Candida albicans, and Escherichia coli. Significant decreases in biofilm formation and microbial growth were observed when higher concentrations of ZnO nanofillers were used, demonstrating their efficacy. Table 3 provides additional evidence by demonstrating the antibacterial effectiveness of ZnO and other nanoparticles in PMMA and PLA materials. Higher concentrations of ZnO nanoparticles led to larger inhibition zones and reduction in CFU, with 40% concentration showing the most prominent antimicrobial effects. These findings highlight the ability of ZnO and nano-PLA to improve the antimicrobial properties and mechanical strength of denture base resins, showing promise for use in clinical settings.

Table 2.

Antimicrobial properties of dental nanomaterials: studies on nano-PLA and zinc oxide nanofiller denture base resins.

Sl. no	Author and Year	Study design	Methodology used	Antimicrobial Testing	Microorganisms Tested	Antimicrobial properties of nano- PLA & zinc oxide nanofiller denture base resins
1.	Kamonkhantikul et al., 2017 (10).	In Vitro	Preparation of denture base resin samples with nano-PLA & zinc oxide nanofillers. Characterization of physical and mechanical properties.	Agar diffusion method, biofilm formation analysis, and zone of inhibition testing.	Streptococcus mutans, Candida albicans, and Escherichia coli.	Enhanced antimicrobial activity with significant reduction in biofilm formation and clear zones of inhibition against all tested microorganisms.
2.	Shafiee Nasab et al. 2018 (20).	Experimental in vitro study	Fabrication of denture base resins with nano-PLA and zinc oxide nanofillers; characterization using SEM, FTIR, and XRD	Disc diffusion method; MIC (Minimum Inhibitory Concentration) and MBC (Minimum Bactericidal Concentration) tests	Staphylococcus aureus, Candida albicans, Escherichia coli, Pseudomonas aeruginosa	Nano-PLA and zinc oxide nanofiller resins exhibited significant antimicrobial activity against tested microorganisms; showed effective inhibition of bacterial and fungal growth; enhanced mechanical properties compared to control resins
3.	Lipovsky et al., 2011 (6).	Experimental	Synthesis and characterization of nanofillers; incorporation into resins; testing	Growth inhibition, minimum inhibitory concentration (MIC), colony counting	Candida albicans, Staphylococcus aureus, Escherichia coli	Nano-PLA and ZnO nanofillers exhibit enhanced antimicrobial activity against tested microorganisms, with ZnO showing greater efficacy.
4.	Mousavi et al., 2020 (15).	Experimental study	Incorporation of Ag, ZnO, and chitosan nanoparticles into tissue conditioners; antimicrobial testing via turbidity measurements	Spectrophotometric assessment of microbial growth inhibition at various nanoparticle concentrations and incubation times	Candida albicans, Streptococcus mutans, Enterococcus faecalis, Pseudomonas aeruginosa	Effective in reducing growth of tested microorganisms; optimal inhibition at 5% concentration
5.	Abd Alwahab et al. 2020 (21).	Experimental study	Preparation of PMMA with varying percentages of Nano ZrO2 and ZnO; Testing for thermal conductivity, compression, and roughness.	Not conducted	Not tested	The study focused on thermal conductivity, compression strength, and surface roughness, not on antimicrobial properties.
6.	Fahmi et al. 2019 (16).	Experimental study	Addition of ZrO2 to PMMA at 0.5%, 1%, 3% concentrations	Not tested	Not tested	Not applicable
7.	Collares et al. 2020 (22).	In vitro study	Formulation of methacrylate-based dental sealers with ZnO nanostructures; physical, chemical, and antibacterial evaluations	Agar diffusion test, CFU count	Enterococcus faecalis	ZnO nanostructures provided significant antimicrobial effects, particularly at higher concentrations (30% and 40%).
8.	Raj et al. 2018 (23).	Experimental study	Fabrication of denture base resins with varying concentrations of nano-PLA and zinc oxide nanofillers	Agar diffusion method	Candida albicans and Streptococcus mutans	Nano-PLA and zinc oxide nanofillers enhanced antimicrobial properties against C. albicans and S. aureus, with higher concentrations showing increased effectiveness.

Table 3.

Antimicrobial efficacy of different nanocomposites in PMMA and PLA matrices.

Author and Year	Nanoparticle Used		Concentration (%)	Microorganisms Tested
Kamonkhantikul et al., 2017 (10).	Zinc Oxide Nanofiller		2% - 5%	Streptococcus mutans, Candida albicans, Escherichia coli
Shafiee Nasab et al. 2018 (20).	Nano-PLA, Zinc Oxide Nanoparticles		1%, 3%, 5%	Staphylococcus aureus, Candida albicans, Escherichia coli, Pseudomonas aeruginosa
Lipovsky et al., 2011(6).	ZnO, ZnO (various sizes), ZnO + Histidine, ZnO + Blue Light		0.1 mg/ml (ZnO), Various sizes (ZnO), 0.05 mg/ml (ZnO + Histidine), 0.1 mg/ml (ZnO + Blue Light)	Candida albicans
Mousavi et al., 2020 (5).	Silver (Ag), Zinc Oxide (ZnO), Chitosan		0.625% to 5%	Candida albicans, Enterococcus faecalis, Pseudomonas aeruginosa, Streptococcus mutans
Abd Alwahab et al. 2020 (21).	Nano ZrO2		0.02%, 0.04%, 0.06%, 0.08%, 1.0%	Not tested
	Nano ZnO		0.02%, 0.04%, 0.06%, 0.08%, 1.0%
Fahmi et al. 2019 (16).	Zinc Oxide		1%, 2%, 3%	Not tested
Collares et al. 2020 (22).	Zinc Oxide Nanostructures (ZnO-NN)		20%, 30%, 40%	Enterococcus faecalis
Raj et al. 2018 (23).	Zinc oxide (ZnO)		1%, 2%, and 3%	Streptococcus mutans and Candida albicans

Table 4shows that the inclusion of ZnO nanoparticles typically enhances the mechanical characteristics of these materials. Research conducted by Shafiee Nasab et al. (20). has shown substantial improvements in flexural strength, impact strength, and elastic modulus as the concentration of ZnO increases, with flexural strength reaching as high as 103.8 MPa and impact strength up to 9.1 kJ/m². Other research also showed comparable enhancements, suggesting that ZnO nanocomposites improve the longevity and robustness of dental materials, rendering them suitable for clinical application. Table 5 examines the biocompatibility and degradation rates of these nanocomposites. The study consistently shows strong biocompatibility, with low levels of toxicity and positive tissue compatibility in different testing methods, including cell viability assays and ISO cytotoxicity tests. For instance, Kamonkhantikul et al.(10). and Shafiee Nasab et al. (20) discovered that cell viability remained high and degradation rates were controlled between 2% and 10% for six months. These findings showcase the capability of ZnO and other nanocomposites to offer both durability and extended biocompatibility for dental uses.

Table 4.

Mechanical properties of PMMA and PLA nanocomposites incorporating metal oxide nanoparticles.

Author and Year	Nanoparticle Used	Polymer Matrix	Concentration (%)	Flexural Strength (MPa)	Impact Strength (kJ/m²)	Elastic Modulus (GPa)
Kamonkhantikul et al., 2017 (10).	Zinc Oxide Nanofiller	Polylactic Acid (PLA)	2% - 5%	85 - 95 MPa	3.5 - 4.2 kJ/m²	2.1 - 2.5 GPa
Shafiee Nasab et al. 2018 (20).	Zinc Oxide Nanoparticles	Poly(methyl methacrylate) (PMMA)	1%, 3%, 5%	97.5, 100.2, 103.8	8.4, 8.9, 9.1	2.8, 3.0, 3.2
Lipovsky et al., 2011 (6).	ZnO	PMMA	1-4%	93.3-107.5	0.89-1.22	4.0-4.8
Mousavi et al., 2020 (15).	Silver (Ag), Zinc Oxide (ZnO), Chitosan	Poly-L-lactic acid (PLA)	0.625% to 5%	Typically increased	Typically increased	Typically increased
Vikram S et al. 2020 (24).	Zinc Oxide (ZnO)	PMMA	0.4 to 1.4%	71.73 to 91.31	Not provided	Not provided
Aboshama M et al. 2022 (25).	Zirconium Oxide (ZrO₂) and Titanium Oxide (TiO₂)	PMMA	1.5 to 5%	63.96 to 110.95 Mpa, 61.46 to 126.94 Mpa, 53.34 to 96.84 Mpa	Not reported	Not reported
	Zinc Oxide (ZnO)
Abd Alwahab et al. 2020 (21).	Nano ZrO2	PMMA	0.02%, 0.04%, 0.06%, 0.08%, 1.0%	Not provided	Not provided	Not provided
	Nano ZnO		0.02%, 0.04%, 0.06%, 0.08%, 1.0%	Not provided	Not provided	Not provided
Fahmi MK et al. 2019 (16).	Zirconium Oxide	Heat-polymerized PMMA	0.5%, 1%, 3%	Not mentioned	1.95, 2.93, 3.89	Not mentioned
Collares FM et al. 2020 (22).	Zinc Oxide Nanostructures (ZnO-NN)	Methacrylate-based dental sealer	20%, 30%, 40%	Approximately 85-90 MPa (non-significant variation among concentrations)	Not reported	Approximately 2.5-3.0 GPa (non-significant variation among concentrations)
Raj et al. 2018 (23).	Zinc oxide (ZnO)	Polylactic acid (PLA	1%, 2%, 3%	Increased with higher concentrations of ZnO	Enhanced at optimal concentration	Increased with ZnO addition

Table 5.

Biocompatibility and degradation rate of PMMA and PLA-based nanocomposites.

Author and Year	Biocompatibility Assessment Method	Results	Degradation Rate (% weight loss over time)
Kamonkhantikul et al., 2017 (10).	Cell viability assays (MTT, Live/Dead staining)	High cell viability, minimal cytotoxicity	5% - 10% weight loss over 6 months
Shafiee Nasab et al. 2018 (20).	ISO 10993 cytotoxicity test	Non-cytotoxic	2% over 6 months
Lipovsky et al., 2011 (15).	In vitro cytotoxicity tests, In vivo animal studies, Histological analysis	No significant cytotoxicity observed,	0.5% after 6 months,
		Good tissue compatibility, No adverse reactions	1.2% after 6 months,
			0.8% after 6 months
Mousavi et al., 2020 (15).	PMMA-Based Nanocomposites	Generally high, with good tissue integration and minimal cytotoxicity	Degrades slowly over time; rate dependent on environmental conditions and additives
	PLA-Based Nanocomposites
Raj et al. 2018 (23).	MTT assay (cell viability assay)	Non-toxic, maintained cell viability	Slow degradation rate; minimal weight loss over the tested period

Table 6 displays the evaluation of the quality of the in vitro research studies included, using the QUIN (Quality Index) tool to assess methodological rigor in various important areas. These areas consist of defined objectives, calculation of sample size, selection of sample method, utilization of control groups, thorough description of methods, operator information, random assignment, assessment methods for outcomes, details of assessors, masking, data analysis, and reporting of findings. Research articles were classified according to their scores: moderate quality (scores 18, 19) included studies such as Lipovsky et al. (15) and Kamonkhantikul et al. (10 ) while good quality (scores 20-22) encompassed studies like Fahmi MK et al. (16) and Mousavi et al. (15) . These evaluations showcase the dependability and accuracy of the results, guaranteeing that the conclusions of the examination are based on strong evidence.

Table 6.

Quality assessment done using QUIN tool for the in vitro studies.

S.no	Author (Year)	Clearly stated aims/objectives	Sample size calculation	Sampling technique	Comparison group	Explanation of methodology	Operator details	Randomization	Method of measurement of outcome	Outcome assessor details	Blinding	Statistical analysis	Presentation of results	Total	Quality
1.	Lipovsky et al., (2011)	*	*	**	**	**	*	**	*	**	**	*	*	18	Moderate
2.	Kamonkhantikul et al., (2017)	*	*	**	**	**	*	**	**	**	**	*	*	19	Moderate
3.	Shafiee Nasab et al. (2018)	*	*	**	**	**	*	**	**	**	**	*	*	19	Moderate
4.	Raj et al. (2018)	**	*	**	*	**	*	**	*	**	**	*	*	18	Moderate
5.	Fahmi et al. (2019)	**	*	**	**	**	*	**	**	**	**	*	*	20	Good
6.	Abd Alwahab et al. (2020)	**	*	**	**	**	*	**	**	**	**	**	*	21	Good
7.	Collares et al. (2020)	**	**	**	**	**	*	**	**	**	**	**	*	22	Good
8.	Mousavi et al., (2020)	**	**	**	**	**	*	**	**	**	**	*	**	22	Good

Risk of bias assessment

Figure 2 displays a visual representation of the bias risk for each study in different domains, such as selection, performance, detection, attrition, and reporting bias. The color- coded system, with green representing low risk, yellow representing some concerns, and red representing high risk, points out specific methodological strengths and weaknesses in each study, enabling a more thorough examination of potential biases. Figure 3 provides a summarized view of bias risk in all studies, classifying them as low, moderate, or high risk. This summary is crucial for assessing the overall standard of the evidence. Study that has a low risk of bias is seen as methodologically strong, whereas studies with moderate risk raise some concerns but are still mostly trustworthy. However, study with a high risk of bias identifies important methodological errors that might impact the credibility of their results. This thorough evaluation of bias is essential for determining the robustness and dependability of the evidence, helping to explain the review’s findings. Table 7 depicts the list of articles excluded from the present analysis based on the inclusion criteria stated earlier.

Figure 2.

Risk of bias assessment for individual studies.

Figure 3.

Overall risk of bias assessment.

Table 7.

List of articles excluded from the analysis.

Study No	Author	Title of the study	Reason of exclusion of the study
1.	Hussain et al. (26).	A review on PLA-based biodegradable materials for biomedical applications	Review article
2.	Lodi et al. (27).	Mechanical, chemical and biological properties of PLA 3D printer	Systematic Review
3.	Xu et al. (28).	Clinical evaluation of resorbable polylactic acid (PLA) intracanal posts for primary incisor restoration	Out of topic of interest
4.	Jockusch et al. (29).	An overview on processes, materials and applications.	Review article
5.	Barcena et al. (30).	Emerging Biomedical and Clinical Applications of 3D-Printed Poly (Lactic Acid)-Based Devices and Delivery Systems.	Review article
6.	Sebbar et al. (31).	Greener Approaches to Combat Biofilm’s Antimicrobial Resistance on 3D-Printed Materials: A Systematic Review	Systematic Review

Discussion

Prosthodontics has advanced significantly because of the increased interest in using nanotechnology to improve dental materials, especially in the creation of denture base resins. The objective of this systematic review was to evaluate the impact of incorporating ZnO and PLA nanocomposites on the properties of denture base resins. By addressing persistent challenges in dental materials, such as limited antibacterial activity and mechanical strength, this review aims to provide a comprehensive understanding of how these nanomaterials enhance resin performance. Through an integration of existing research findings, the study offers a critical analysis of the efficacy and potential therapeutic benefits of these advanced nanocomposites in improving the functionality of denture base resins.

The capacity of this review to compile and evaluate information on the most recent developments is what makes it significant; it will direct future studies and clinical procedures in dental material science.

It has been shown that adding ZnO and nano-PLA to denture base resins greatly improves their antibacterial capabilities against common oral pathogens as Escherichia coli, Candida albicans, and Streptococcus mutans. This result is consistent with previous research on ZnO nanoparticles’ antibacterial properties. The broad-spectrum antibacterial activity of polymeric dental nanoparticles, such as ZnO, was emphasized by Yudaev et al. (Figure 1), underscoring its effectiveness against a range of microbes. Similarly, Gonzalez-Garzon et al. (32) observed that the melt-processed PLA/PMMA blends exhibit enhanced antibacterial and mechanical properties, complementing the findings of this review. A study observed notable enhancements in the biological characteristics of polymer-based dentures when antimicrobial agents were incorporated (33). Previous research demonstrated that ZnO nanoparticles improve both the mechanical and antifungal properties of PMMA materials (10). Additionally, the integration of ZnO into PLA/PMMA blends was reported to enhance mechanical properties and foaming behavior (34). PLA’s ability to improve the mechanical performance and biocompatibility of dental materials has been well-documented (2). In line with Jones et al. (2008), who emphasized the broad-spectrum antibacterial activity of ZnO nanoparticles (4),the present study’s results, as shown in Table 1, show that the integration of ZnO and nano-PLA greatly lowers biofilm formation and microbial growth.

ZnO nanoparticles exhibit strong antibacterial activity and effectively target bacterial pathogens, with an observed reduction in microbial growth as the concentration of ZnO nanofillers increases (5, 6). The enhancement of multifunctionality in PLA-ZnO nanocomposites through alternative manufacturing methods plays a crucial role in improving their application in dental materials (35).These findings underscore the therapeutic potential of incorporating nano- PLA and ZnO into denture base resins. Table 2 illustrates the efficacy of ZnO nanoparticles in PLA and PMMA matrices, especially at higher concentrations, aligning with previous research that demonstrated improved antibacterial activities and mechanical performance in ZnO nanocomposite films (20, 3).The integration of PLA into PMMA matrices enhances thermal properties and crystallinity, further supporting the mechanical benefits observed with ZnO (36). ZnO nanoparticles have been shown to enhance key mechanical properties, including flexural strength, impact strength, and elastic modulus, particularly with higher ZnO content (20).

Improvements in the mechanical properties of dental materials with the addition of ZnO have been consistently observed, enhancing their suitability for clinical applications where strength and durability are crucial (10, 24). PLA/PMMA blends have been found to maintain transparency and ultraviolet transmittance, which are important for dental applications requiring both aesthetic and protective qualities (37). The cumulative findings suggest that ZnO nanocomposites offer enhanced mechanical robustness, making them ideal for demanding clinical settings. The biocompatibility and degradation rates of PLA/ZnO nanocomposites, as shown in Table 4, demonstrate good biocompatibility across various testing conditions. Studies have consistently shown that these nanocomposites exhibit low cytotoxicity and good tissue compatibility (10, 20). Additionally, there is evidence of low deterioration and no adverse reactions in vivo, supporting their suitability for long-term dental use (6). This is in agreement with earlier research emphasizes the strong biocompatibility and long-term viability of these nanocomposites in dental settings. The QUIN tool’s evaluation of study quality, which is presented in Table 5, reveals a range of methodological rigor in the examined research. Studies by Lipovsky et al. (6) and Kamonkhantikul et al. (10), for example, obtained good quality scores, indicating a range of methodological robustness, whereas Fahmi MK et al. (16) and Mousavi et al. (15) had middling quality scores. This variation highlights the need for rigorous study approaches to guarantee the validity and dependability of findings. Apart from these investigations, Yudaev et al. research from 2022 highlights the antibacterial activity of polymeric dental nanoparticles, highlighting the significance of nanocomposites in improving dental material attributes (1).

Similarly, Mohd Farid et al. (33) offers an update on the biological characteristics of dentures made of polymers, highlighting important discoveries and achievements in the field (33). These and other research, such as those conducted by An et al. (7) and Bikiaris et al. (12), highlight the increasing amount of data that supports the use of nanocomposites to enhance the biocompatibility and performance of dental materials. The risk of bias assessments, as seen in Figure 2 and Figure 3, are essential for placing the overall caliber of the evidence in this study in context. Figure 2 lists individual research biases in several domains, including as reporting, attrition, detection, performance, and selection. This figure’s usage of color-coded indicators offers a concise visual assessment of the methodological advantages and disadvantages.

FFigure 3 provides a thorough summary of the reliability of the evidence base by consolidating these assessments and classifying research into low, moderate, and high risk of bias. The discovery of high-risk biases in certain studies emphasizes the need to interpret the results with caution and points out areas where methodological advancements in further studies are needed. An elevated risk of bias resulted from Yudaev et al.’s (1) constraints when investigating the antibacterial activity of polymeric dental nanoparticles. These included variations in study design and sample sizes. Ali et al.’s (2) evaluation of the synthesis and biodegradability of polylactic acid revealed discrepancies in the reliability and caliber of results published, which may have an impact on the conclusions obtained from these investigations. The results of studies with differing degrees of methodological rigor also had an impact on the overall quality of the evidence, even though An et al.’s (7) systematic review on the integration of antimicrobial agents in denture base resins was presented. Even though these studies offer insightful information, one should interpret their results cautiously because some of them have high-risk biases. To improve the strength and consistency of the data pertaining to the mechanical performance and antibacterial qualities of polymeric dental materials, future studies should focus on addressing these methodological flaws.

Hence, this review offers a thorough summary of the developments in dental materials enhanced by nanotechnology, with a special emphasis on ZnO and PLA nanocomposites. The outcomes support the potential of these materials for clinical usage by showing notable increases in mechanical performance, biocompatibility, and antibacterial characteristics. The significance of methodological rigor in research is emphasized by the quality and risk of bias assessments, which provide insightful information about the dependability of the included studies. These results lay the groundwork for further research in this developing field and add to the increasing body of evidence promoting the use of nanocomposites in dental applications.

Advantages and disadvantages

This systematic review offers several advantages, including a comprehensive analysis of the antimicrobial properties and mechanical performance of PLA/ZnO nanocomposite denture base resins, supported by a systematic approach following PRISMA guidelines. The detailed risk of bias assessment and inclusion of recent studies from 2017 to 2024 enhance the reliability of the findings. However, the review’s limitations include potential variability in study methodologies and sample sizes, which may affect the generalizability of results. Additionally, the high risk of bias identified in some studies necessitates cautious interpretation and suggests that future research should address these methodological issues to strengthen the evidence base further. By investigating the incorporation of nano PLA into denture base resins, this review aims to enhance the properties and performance of denture materials. The outcomes will advance the field of prosthodontics, providing a foundation for the development of improved denture base materials with enhanced mechanical properties, biocompatibility, and patient satisfaction.

Conclusion

The systematic study concludes by emphasizing the therapeutic value of adding PLA/ZnO nanocomposites to denture base resins and their potential to improve mechanical performance and antibacterial qualities. According to the research, these nanocomposites may enhance denture hygiene and durability, which would be extremely advantageous for patients. To validate these advancements, future studies ought to concentrate on resolving the noted methodological shortcomings and investigating long-term therapeutic effects. This systematic review and meta-analyses propose an approach by incorporating cPoly Lactic Acid (PLA) into denture base resins. Nano PLA offers unique properties such as biocompatibility, biodegradability, and mechanical reinforcement potential. The use of PLA in denture base materials is relatively unexplored, providing an opportunity to investigate its potential in enhancing the performance of denture base resins.