Introduction

The oral cavity represents the entry point to the gastrointestinal tract and is a dynamic biointerface continuously exposed to the external environment. In addition to food, it encounters ambient air, microorganisms, and a wide range of physicochemical stimuli. Saliva and the complex oral microbiota further establish a distinct local microenvironment. These conditions are neither spatially nor temporally uniform [1]. Nutrient availability and pH fluctuate with food intake and subsequent salivary buffering, while oxygen tension and redox conditions differ substantially among surfaces, the gingival sulcus, periodontal pockets, and peri-implant niches. At the same time, salivary secretion continuously regulates mucosal hydration, lubrication, buffering capacity, and microbial homeostasis, whereas disruption of salivary gland function can markedly alter the oral environment and contribute to xerostomia-associated complications [2]. The oral mucosa is likewise exposed to repetitive mechanical, chemical, and inflammatory insults [3], and loss of epithelial barrier integrity can create a local microenvironment characterized by oxidative stress and persistent inflammation, as observed in oral ulceration [4,5]. Thus, the heterogeneous oral microenvironment influences not only biofilm-associated diseases such as dental caries, periodontitis, and peri-implantitis, but also noninfectious conditions including salivary gland dysfunction and oral mucosal injury, through interactions among microbial, inflammatory, oxidative, and tissue-specific factors [6-8].

Reactive oxygen species (ROS) have a central but context-dependent role in oral diseases. At physiological levels, ROS participate in intracellular signaling and cellular homeostasis. When ROS generation exceeds antioxidant capacity during infection or persistent inflammation, however, oxidative stress develops and can accelerate tissue damage [9]. In periodontal disease, neutrophils and other immune cells generate substantial amounts of ROS in response to pathogenic microorganisms [10]. Sustained ROS accumulation damages the gingiva, periodontal ligament, and alveolar bone and can further amplify local inflammation [10]. ROS can also be therapeutically useful. Locally generated ROS damage bacterial cellular components and the extracellular polymeric substance (EPS) matrix of biofilms, providing a mechanism for eliminating pathogenic biofilms.

The therapeutic objective is therefore not simply to increase or remove ROS, but to direct redox reactions according to the underlying pathology and treatment target. This distinction is particularly relevant within periodontal pockets. Low oxygen tension and reducing conditions may favor anaerobic pathogens, whereas persistent immune activation produces excessive ROS in adjacent host tissues. Local oxidative attack can therefore assist microbial eradication, while ROS scavenging may be required in nearby tissues to limit host damage [11]. Therapeutic platforms capable of controlling the location and direction of redox reactions are well suited to this setting.

Nanoparticles have been widely investigated in drug delivery, diagnostics, and therapy because of their high specific surface area and tunable physicochemical properties [12]. Nanomaterials that catalyze reactions resembling those of natural enzymes are generally referred to as nanozymes [13]. Their catalytic behavior depends on elemental composition, oxidation state, crystal structure, surface defects, particle size, morphology, and local reaction conditions such as pH, substrate concentration, and oxygen tension [14]. Some nanozymes display multiple enzyme-mimetic activities, with the dominant reaction changing according to the surrounding conditions. They are therefore better viewed as catalytic platforms whose functions emerge from the interaction between intrinsic material properties and the local microenvironment rather than simply as oxidizing or antioxidant agents. This environmental dependence does not imply that all nanozymes switch between distinct catalytic activities. Effective therapy instead requires selection or design of a material that supports the reaction appropriate for a specific disease environment.

This dependence on the surrounding environment is particularly relevant in the oral cavity, where markedly different physicochemical conditions occur within a relatively small anatomical space. In cariogenic biofilms, bacterial carbohydrate metabolism produces an acidic microenvironment [15], and certain peroxidase (POD)-like nanozymes can activate H₂O₂ under these conditions to generate highly reactive ROS that attack bacterial cells and the EPS matrix [16]. Periodontal disease and salivary gland dysfunction present a different requirement. In these conditions, chronic inflammation and excessive oxidative stress contribute to pathology, making ROS scavenging through superoxide dismutase (SOD)- and catalase (CAT)-like activities potentially useful [7,17,18]. In peri-implant environments, O₂ produced by CAT-like decomposition of H₂O₂ has also been used to modify anaerobic niches, and rapid catalytic gas generation can physically disrupt biofilms [19]. The therapeutic behavior of a nanozyme therefore depends on the material, the microenvironment in which it operates, the catalytic activity expressed under those conditions, and the relevance of that activity to disease pathophysiology.

Research on oral nanozymes initially centered on catalytic antimicrobial therapy but has since expanded to other diseases and therapeutic mechanisms [20,21]. Caries studies have primarily exploited the acidic biofilm environment to drive POD-like ROS generation and selective biofilm removal [20,22]. In periodontitis and peri-implantitis, approaches now include ROS scavenging, regulation of the inflammatory microenvironment, oxygenation of anaerobic niches, and physical decontamination of implant-associated biofilms [17,23]. Antioxidant nanozymes have also been investigated in conditions in which infection is not the primary cause, including Sjögren’s disease-associated salivary gland dysfunction, xerostomia [24], and oral ulceration [25,26]. In these settings, therapeutic strategies mainly aim to reduce oxidative stress and inflammatory dysregulation while preserving glandular or mucosal tissue function.

Previous reviews of oral nanozymes have largely focused on antibacterial and antibiofilm mechanisms [27] or on the therapeutic application of nanozymes within a single disease, particularly periodontitis [28]. Recent work has extended these materials to salivary gland dysfunction and other settings in which host oxidative stress, rather than microbial elimination alone, is the primary therapeutic target, such that nanozyme catalysis can be directed toward opposing therapeutic goals depending on the lesion. An integrated framework linking nanozyme catalytic function to the distinct pathophysiological and physicochemical microenvironments of oral diseases has not yet been systematically established, and quantitative standardization of catalytic activity across these applications remains largely unaddressed. This review therefore considers oral nanozymes from the perspective of the relationship between catalytic function and disease pathophysiology, on the premise that therapeutic benefit depends not only on the material itself, but also on whether its dominant catalytic reaction is suited to the pathophysiological and physicochemical conditions of the target lesion.

Nanozymes for Oral Applications

Nanozymes investigated for oral diseases include materials with diverse compositions whose catalytic behavior is determined by both intrinsic material properties and the surrounding physicochemical environment [14,29]. Oxidation state, crystal structure, surface defects, and local reaction conditions can substantially alter activity even among materials of similar composition [29,30]. Unlike nanoparticles used mainly as drug carriers or for their intrinsic biological effects, nanozymes actively catalyze biochemical reactions through enzyme-mimetic activity [31]. Depending on composition and reaction conditions, they can promote ROS production or ROS removal. These reactions have been applied to pathogenic biofilm elimination [20], suppression of excessive oxidative stress and inflammation [17], and protection or recovery of damaged tissues [17,25]. Because oral sites differ considerably in pH, oxygen and substrate availability, and biological interfaces, this environment-dependent behavior is particularly relevant to oral applications [32].

1. Types of nanozymes

This section first surveys the material classes relevant to oral applications and the enzyme-like activities they express, then examines the structural and chemical variables that determine which activity dominates, and finally considers how the microenvironments of oral disease sites modify catalytic behavior and delivery in practice (Table 1) [17,19,20,22,23,30,33-41].

Iron oxide-based materials commonly exhibit POD-like activity through Fe²⁺ /Fe³⁺ redox cycling [33]. Fe₃O₄ nanozymes can activate H₂O₂ to generate highly reactive oxidizing species that damage bacterial cells and disrupt EPS-rich biofilms [20]. This reaction is particularly relevant to cariogenic biofilms because some iron oxide nanozymes show increased catalytic activity under acidic conditions [20]. Ferumoxytol, a clinically used iron oxide formulation, has also been examined for this purpose. Its use is of translational interest because it represents repurposing of the catalytic properties of an existing pharmaceutical product for oral therapy. Ferrite and multimetallic systems containing Fe together with Cu, Co, Mn, or other metals can further alter electron transfer and redox cycling, thereby enhancing POD-like activity or introducing ROS-scavenging functions [34].

Cerium oxide (CeO₂ ) has been widely investigated as an antioxidant nanozyme in oral applications [17,30,35]. Reversible Ce³⁺ /Ce⁴⁺ redox cycling and surface oxygen vacancies provide broad ROS-scavenging capacity, including SOD- and CAT-like activities [42]. CeO₂ has therefore been studied in periodontal disease, oral ulceration and salivary gland dysfunction, where excessive oxidative stress and chronic inflammation contribute to tissue damage. Its catalytic activity can be altered by particle morphology [30], surface area [30], Ce oxidation state [43], and surface defects and oxygen vacancies [44], making ceria a useful model for examining nanozyme structure – activity relationships.

Manganese-based nanozymes can exhibit CAT-, POD-, and oxidase (OXD)-like activities depending on Mn oxidation state and the local chemical environment [45]. CAT-like decomposition of H₂O₂ by MnO₂ generates H₂O and O₂ , allowing simultaneous H₂O₂ removal and oxygen production. In oral biofilms, this reaction can alter anaerobic conditions. When oxygen is generated rapidly and locally, it can also form microbubbles capable of mechanically disrupting biofilms. In mixed oxides such as manganese ferrites, interactions between Mn and Fe provide an additional means of adjusting antioxidant activity [36].

Noble metals including Pt, Pd, and Au also show multiple enzyme-mimetic activities because of their high surface catalytic activity. Pt and Pd are commonly associated with CAT- and POD-like H₂O₂ conversion [46]. Au is frequently incorporated into composite systems in which its catalytic or photothermal properties, together with surface functionalization, are used to alter catalytic reactions or regulate drug release.

More recent material designs have moved beyond conventional single-metal oxides toward structures that provide greater control over catalytic reactions. Single-atom nanozymes disperse individual metal atoms within defined coordination environments, resulting in high atomic utilization and relatively uniform catalytic sites. Their coordination chemistry can be adjusted to favor specific enzyme-like reactions. Metal nitrides such as Mo₅N₆ have also been reported to combine POD-, OXD-, and CAT-like activities through metal – nitrogen coordination and the resulting electronic structure [37]. These approaches increasingly focus on matching catalytic behavior to the pathophysiological requirements of a disease rather than simply introducing additional catalytic materials.

2. Enzyme-like activities

Nanozyme activities relevant to oral therapy can be broadly grouped into ROS-generating and ROS-scavenging reactions [32]. ROS-generating activity mainly involves POD- and OXD-like catalysis and is used to damage pathogenic microorganisms and biofilms. ROS-scavenging activity primarily involves SOD- and CAT-like reactions that reduce excessive oxidative stress. These categories are not mutually exclusive. A single nanozyme may exhibit several enzyme-mimetic activities, with one becoming dominant under particular reaction conditions.

POD-like activity uses H₂O₂ as a substrate to produce highly reactive oxidizing species, including hydroxyl radicals ( •OH). These ROS damage bacterial membranes, proteins, and nucleic acids and can weaken the EPS matrix that supports biofilm architecture [47]. POD-like catalysis is therefore one of the most common nanozyme-mediated antimicrobial mechanisms used in oral biofilm-associated diseases, particularly dental caries [27,32]. Some iron-based POD-like nanozymes are more active at low pH, allowing the acidic environment generated by cariogenic bacteria to increase catalytic activity locally.

OXD-like activity uses molecular O₂ as an electron acceptor and can generate ROS without H₂O₂ [48]. This decreases reliance on externally supplied H₂O₂ , but introduces dependence on local oxygen availability [48]. OXD activity may therefore be limited in deep biofilms and periodontal niches with low oxygen tension [49].

SOD-like activity converts •O₂⁻ into H₂O₂ and O₂ . Because H₂O₂ can itself contribute to oxidative injury, efficient ROS detoxification generally benefits from subsequent CAT-like conversion of H₂O₂ into H₂O and O₂ [50]. SOD- and CAT-like activities have been applied to periodontitis and Sjögren’s disease-associated salivary gland dysfunction, where excessive ROS contributes to tissue injury.

CAT-like activity can also have effects beyond ROS scavenging. O₂ generated through H₂O₂ decomposition can modify the environment of anaerobic biofilms [51]. In MnO₂ -based systems, rapid local O₂ production can generate oxygen bubbles that contribute directly to biofilm disruption and surface decontamination [19]. The therapeutic consequence of a given enzyme-like reaction therefore depends strongly on where the reaction occurs and how the material is configured.

3. Determinants of catalytic activity

The enzyme-mimetic activity of a nanozyme cannot be predicted from elemental composition alone. Two distinct sets of variables govern catalytic performance. The first is largely determined during synthesis and includes particle size, morphology, exposed crystal facets, specific surface area, oxidation state, and surface defect density. These features define the number, nature, and electron-transfer characteristics of the available catalytic sites. The second is imposed by the surrounding environment and includes pH, substrate concentration, and oxygen tension. These conditions determine the relative rates and dominant pathways of the reactions supported by those sites. A material may therefore possess the capacity for several enzyme-like reactions, while one activity becomes predominant under a given set of local conditions. CeO₂ provides a clear example. The Ce³⁺ /Ce⁴⁺ distribution and abundance of oxygen vacancies are closely associated with redox cycling and ROS-scavenging activity [44]. Particle morphology further changes exposed crystal facets, surface defect density, and specific surface area. As a result, CeO₂ particles with the same nominal composition can differ considerably in SOD-and CAT-like activities and therapeutic performance. Structural control can therefore improve intrinsic catalytic performance without introducing additional components.

Electron transfer between metal ions provides another level of control in multimetallic nanozymes. Metals such as Fe, Cu, and Mn can access multiple oxidation states, and their combination can accelerate redox cycling, enhance H₂O₂ activation, or alter the dominant catalytic pathway [52]. In single-atom nanozymes, the coordination environment surrounding the central metal atom similarly influences electron density, substrate binding, and catalytic selectivity [53].

These examples illustrate why nominal composition alone is insufficient for comparing nanozyme performance across studies. A practical consequence follows for reporting: characterization limited to elemental composition and particle size is insufficient either to compare studies or to reproduce a described effect. Relevant structural and surface characteristics, together with experimentally measured catalytic activity under defined reaction conditions, should therefore be reported alongside composition, as discussed further in the Challenges and Future Perspectives section.

4. Catalytic behavior and delivery in oral disease microenvironments

For intrinsic nanozyme activity to produce a therapeutic effect, the target lesion must provide conditions that support the intended reaction and allow sufficient material exposure. Oral disease sites differ substantially in pH, oxygen availability, substrate concentration, biofilm architecture, and fluid flow [54]. These conditions can either favor or limit catalysis.

Cariogenic biofilms illustrate how the lesion environment itself can contribute to catalytic selectivity. Carbohydrate metabolism by acidogenic bacteria, including Streptococcus mutans, generates an acidic microenvironment, and H₂O₂ activation by some iron oxide-based POD-like nanozymes is enhanced at low pH. Higher catalytic antimicrobial activity can therefore occur within cariogenic biofilms even without a separate targeting mechanism [20]. Early nanozyme-based caries studies largely exploited this acid-dependent POD activity [20,55], whereas later approaches combined environmental responsiveness with bacterial binding or multimetallic redox cycling [38].

The situation is more complex in periodontal and peri-implant niches. Deep periodontal pockets and implant-associated biofilms may have limited oxygen availability and support anaerobic microbial communities [56]. At the same time, persistent immune activation can produce excessive ROS in adjacent host tissues [57]. ROS generation may therefore be useful against pathogens but detrimental to nearby tissue. Some nanozyme systems address these opposing requirements by spatially separating POD-like pathogen-directed activity from SOD/ CAT-like antioxidant activity in host tissues.

Peri-implantitis introduces the additional constraint of a biomaterial interface. Rough implant surfaces and fixture–abutment microgaps promote persistent biofilm attachment and are difficult to decontaminate completely with chemical antimicrobials [23]. Catalytic reactions have therefore been used to generate mechanical forces. CAT-like MnO₂ catalysis, for example, produces O₂ microbubbles from H₂O₂ , and bubble movement can physically disrupt attached biofilms.

Saliva imposes another limitation. Continuous fluid flow can dilute both nanozymes and reaction substrates and remove them rapidly from the target site. Adsorption of salivary proteins and other biomolecules may also alter particle surfaces and restrict access to catalytic sites. High intrinsic activity alone is therefore insufficient if the nanozyme cannot remain at the lesion long enough to act.

Several delivery strategies have been developed to address these problems. Selective accumulation in cariogenic biofilms can be achieved through interactions with bacterial surface proteins or biofilm components [58]. Injectable hydrogels improve local retention in periodontal pockets, while bacterial enzyme-responsive coatings can restrict catalytic activation to disease-associated environments [30,35,59]. For xerostomia, systemic administration followed by salivary gland accumulation and mucoadhesive microspheres for sustained local delivery of CeO₂ nanozymes have been investigated [18,24]. Microneedle and adhesive patch-based delivery has been explored for direct treatment of oral ulcer lesions [25,26].

Therapeutic efficacy therefore depends on more than catalytic activity measured under ideal experimental conditions. The required reaction must occur selectively within the disease microenvironment and persist at the relevant site for an adequate period. The relationship between the microenvironment of each oral lesion, the direction of catalysis required, and the delivery strategy needed to sustain it is summarized in Fig. 1. The following sections consider how catalytic properties and delivery strategies have been adapted to the pathophysiology of individual oral diseases.

Nanozyme-based Treatment of Oral Diseases

1. Dental caries

Dental caries is a biofilm-mediated oral disease that develops through sustained interactions between tooth-associated microbial communities and dietary fermentable carbohydrates [60]. Acidogenic and aciduric bacteria, including S. mutans, metabolize sugars and produce organic acids. Repeated acid production creates a persistently low-pH environment within dental plaque. When this acidification exceeds salivary buffering and tooth remineralization capacity, enamel hydroxyapatite progressively demineralizes and caries develops. Control of cariogenic biofilms is considered central to caries prevention and treatment. Mature dental biofilms, however, are difficult to eliminate because the EPS matrix restricts antimicrobial penetration, biofilm-associated bacteria show increased tolerance, and therapeutic agents are readily cleared by saliva.

Catalytic antimicrobial approaches have used the acidic environment of cariogenic biofilms as a local reaction condition [20,55]. POD-like nanozymes activate H₂O₂ to generate highly reactive ROS, including hydroxyl radicals, directly within the biofilm [20]. These species damage bacterial membranes and intracellular components and degrade the EPS matrix [61]. For nanozymes whose POD-like activity increases at acidic pH, catalytic activity is preferentially enhanced within cariogenic biofilms relative to the more neutral surrounding oral environment.

Gao et al. [20] provided an early demonstration of this approach using Fe₃O₄ catalytic nanoparticles (CAT-NPs). In the presence of H₂O₂ , CAT-NPs generated free radicals in situ, degraded the EPS matrix, and killed embedded S. mutans, producing a > 5-log reduction in bacterial viability. Catalytic activity increased markedly at the acidic pH characteristic of cariogenic biofilms. Short topical CAT-NP/H₂O₂ treatment also reduced caries initiation and severity in a rodent model and limited enamel destruction and cavitation.

Liu et al. [33] subsequently used ferumoxytol, an FDA-approved iron replacement formulation, to add biological selectivity to the iron oxide nanozyme strategy. Ferumoxytol nanoparticles (FerIONPs) bound preferentially to cariogenic biofilms through interactions with S. mutans glucan-binding proteins and activated H₂O₂ under acidic conditions. The resulting local ROS generation reduced S. mutans while producing comparatively limited effects on commensal streptococci. FerIONPs also reduced enamel demineralization in a human intraoral caries model. This work combined two levels of selectivity: an acidic environment that favored catalysis and bacterial binding that increased local nanoparticle accumulation [33].

Ferumoxytol has also been combined with established anticaries agents. Huang et al. [39] incorporated stannous fluoride (SnF₂ ) with ferumoxytol to couple catalytic biofilm removal with enamel protection. Sn²⁺ interacted with the carboxymethyldextran coating of ferumoxytol, which improved SnF₂ stability and enhanced the POD-like activity of the nanoparticles. The combination reduced S. mutans by more than 5 log units and nearly abolished EPS-rich biofilm formation. In a rodent caries model, it suppressed caries initiation and prevented cavitation at one-quarter of the conventional fluoride dose. This approach uses catalytic antimicrobial activity to complement the established mineral-protective function of fluoride [39].

Other studies have focused on bacterial selectivity rather than simply increasing ROS generation. Duan et al. [58] developed a Cu/Fe-doped chitosan nanozyme (CS@Cu,Fe) based on coupled Cu⁺ /Cu²⁺ and Fe²⁺ /Fe³⁺ redox cycling. Electron transfer between Cu and Fe enhanced POD-like activity under acidic conditions and promoted generation of •OH and •O₂⁻ at low H₂O₂ concentrations. CS@Cu,Fe preferentially penetrated S. mutans biofilms and inhibited S. mutans by 99.7%, while antibacterial activity against the commensal species Streptococcus oralis was comparatively limited. Similar selectivity was observed in mixed-species biofilms formed on saliva-coated hydroxyapatite. Combining bacterial targeting with catalytic ROS generation may therefore reduce disruption of non-target members of the oral microbiota [58].

Composite systems have also been evaluated in more complex biofilm models. Ghaffari et al. [38] developed a dextran/ chitosan-functionalized cobalt ferrite – graphene oxide nanozyme (CoFe₂O₄ /GO@Dex-CS) with strong POD-like activity under acidic conditions. In combination with H₂O₂ , the nanozyme produced more than a 3-log reduction in bacterial viability in S. mutans monospecies biofilms and retained substantial antibacterial activity in a six-species supragingival biofilm. The use of polymicrobial models represents an important extension beyond the single-species systems frequently used in early nanozyme studies.

Nanozyme catalysis has also been used for physical biofilm removal rather than ROS-dependent killing alone. Kim et al. [62] incorporated MnO₂ nanozymes into porous diatoms to generate a diatom microbubbler (DM). CAT-like decomposition of H₂O₂ generated O₂ microbubbles that propelled the diatoms and mechanically disturbed attached biofilms. In S. mutans biofilms grown on orthodontic brackets, DM/H₂O₂ removed biofilms more effectively than chlorhexidine (CHX) or H₂O₂ alone and also removed mature multispecies biofilms obtained from patient-used brackets. CHX caused strong bacterial killing but left a substantial portion of the biofilm structure attached, whereas the microbubbler physically disrupted the matrix through oxygen bubble-driven movement. Nanozyme catalysis can therefore be converted into mechanical action rather than being used solely for chemical bacterial killing [62].

Nanozyme approaches to caries have consequently expanded beyond acid-dependent ROS production. Current strategies include combination with fluoride, selective accumulation in cariogenic bacteria, treatment of polymicrobial biofilms, and bubble-mediated physical biofilm removal. At the same time, many POD-like systems remain dependent on externally supplied H₂O₂ . H₂O₂ availability, salivary dilution and clearance, catalytic efficiency within mature polymicrobial biofilms, and the effects of repeated treatment on the commensal microbiome remain important issues.

2. Periodontal and peri-implant diseases

Periodontitis and peri-implantitis are biofilm-associated inflammatory diseases characterized by dysbiotic polymicrobial communities and dysregulated host responses within periodontal or peri-implant niches [63]. Progression results from interactions between microbial dysbiosis and the host inflammatory response. Nanozyme therapy has therefore developed along two main lines: catalytic antimicrobial treatment directed toward the biofilm and regulation of the oxidative-inflammatory environment in host tissues.

The deep, confined anatomy of periodontal pockets and peri-implant sites limits the penetration and retention of conventional antimicrobials. Mature EPS-rich biofilms and anaerobic microbial communities add further barriers. Bacterial elimination alone, however, does not address the persistent host response. Excessive ROS production and dysregulated inflammation contribute directly to periodontal tissue destruction and alveolar bone loss and are therefore considered targets for ROS-scavenging nanozymes.

Yu et al. [17] investigated this host-directed approach using CeO₂ nanoparticles with SOD- and CAT-like activities and hydroxyl-radical scavenging capacity. CeO₂ reduced lipopolysaccharide (LPS)-induced intracellular ROS in macrophages, suppressed interleukin 1β (IL-1β ), tumor necrosis factor α (TNF-α ), and inducible nitric oxide synthase expression, attenuated mitogen-activated protein kinase – nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling, and activated the nuclear factor erythroid 2-related factor 2 (NRF2) – heme oxygenase 1 antioxidant pathway. Local gingival administration in ligature-induced rat periodontitis reduced inflammatory responses, osteoclast activity, and alveolar bone loss. The therapeutic effect in this study was therefore achieved primarily by regulating the host oxidative-inflammatory environment rather than through direct bacterial killing [17].

Li et al. [40] developed an Au@CeO₂ yolk–shell nanozyme loaded with dimethyl fumarate (DMF) to target oxidative stress, mitochondrial dysfunction, and immune dysregulation in periodontitis. Photothermal activation of the Au core enhanced the antioxidant enzyme-mimetic activity of CeO₂ and promoted DMF release. The CeO₂ shell showed SOD-, CAT-, and glutathione peroxidase-like activities, while DMF activated NRF2, suppressed NLR family pyrin domain containing 3 signaling, restored mitochondrial homeostasis in periodontal ligament cells, and shifted macrophages away from an M1-associated inflammatory phenotype toward an M2-associated reparative state. In ligature-induced rat periodontitis, Au@CeO₂ -DMF with photothermal treatment reduced inflammation and osteoclast activity, preserved alveolar bone, and increased osteogenic markers. The system combined catalytic redox regulation with pharmacological immunomodulation and tissue-repair mechanisms [40].

Ren et al. [35] addressed the opposing redox requirements of periodontal treatment by physically separating antimicrobial and host-protective functions. Their antibacterial module consisted of hyaluronic acid-coated single-atom cerium nanozymes (Ce-N-C@HA). Degradation of the HA coating by bacterial hyaluronidase exposed POD-like catalytic sites and enabled localized •OH generation within the periodontal pocket. A second module combined ultrasmall CeO₂ nanoparticles with Lactobacillus reuteri-derived extracellular vesicles (CeO₂ -EV) for delivery to subgingival host tissue, where SOD- and CAT-like activities reduced oxidative stress, restored mitochondrial function, and favored M2-associated macrophage polarization. In ligature-induced mouse periodontitis, combined administration reduced Porphyromonas gingivalis burden, inflammation, and osteoclast activity while improving alveolar bone and collagen restoration more effectively than either module alone. Spatial separation allowed ROS generation to be directed toward the infectious compartment and ROS scavenging toward neighboring host tissue [35].

Jin et al. [30] took a different approach by optimizing ceria morphology rather than increasing system complexity. Ceria nanospheres, nanorods, nanocubes, and nano-octahedra were compared systematically. Nanorods had the largest specific surface area and abundant surface defects and oxygen vacancies, together with enhanced SOD- and CAT-like activity and ROS-scavenging capacity. The higher activity of the nanorods therefore likely reflects the combined contributions of accessible surface area, exposed facets, and defect chemistry; surface-area-normalized measurements would help distinguish increased catalytic surface availability from changes in intrinsic surface reactivity. These particles suppressed LPS-induced oxidative stress and inflammatory responses, favored a reparative macrophage phenotype, and preserved osteogenic differentiation of periodontal ligament stem cells under inflammatory conditions. Incorporated into an injectable thermosensitive poloxamer hydrogel, the nanorods reduced alveolar bone loss, clinical attachment loss, and IL-1β infiltration in rat periodontitis, with efficacy comparable to Periocline. The treatment suppressed the cluster of differentiation 14 (CD14)/toll-like receptor 4 (TLR4)/NF-κB axis and activated NRF2-mediated antioxidant defenses. These results indicate that optimization of morphology and surface redox characteristics can substantially alter therapeutic performance even without adding further functional components [30].

Zhang et al. [37] developed a molybdenum nitride nanozyme (Mo₅N₆ ) combining POD-, OXD-, and CAT-like activities. The Mo–N coordination framework supported H₂O₂ activation and ROS production while retaining CAT-like decomposition of excess H₂O₂ . In the presence of a low H₂O₂ concentration, Mo₅N₆ disrupted mature P. gingivalis and Fusobacterium nucleatum biofilms without the oxidative damage associated with high-dose H₂O₂ treatment. In ligature-induced periodontitis, treatment reduced subgingival bacterial burden, inflammatory infiltration, osteoclast activity, and alveolar bone loss and improved periodontal soft-tissue repair. 16S rDNA profiling showed partial restoration of subgingival microbial diversity and community composition toward a healthy state, suggesting that the effect extended beyond direct bactericidal activity [37].

Manganese-containing nanozymes provide an alternative to ceria for antioxidant treatment. Zhang et al. [41] developed a ligand-modulated manganese ferrite nanozyme hydrogel (MFZ@PG), in which zwitterionic dopamine sulfonate-modified manganese ferrite nanoparticles were incorporated into an injectable polyvinyl alcohol/gelatin/borax hydrogel. The manganese ferrite displayed SOD- and CAT-like activities with broad ROS-scavenging capacity, and the catechol-containing ligand further increased antioxidant performance. MFZ@PG reduced H₂O₂ -induced oxidative stress and restored osteoblast viability, migration, and osteogenic differentiation in vitro. In ligature-induced rat periodontitis, treatment improved alveolar bone parameters and collagen deposition, increased runt-related transcription factor 2 expression, and reduced oxidative stress and osteoclast activity. Transcriptomic and molecular analyses implicated a Z-DNA binding protein 1 (ZBP1)/ β -catenin positive-feedback loop in recovery of osteogenic function. The study therefore linked redox regulation to restoration of regenerative capacity rather than inflammation suppression alone [41].

Periodontitis and peri-implantitis share dysbiotic biofilms, persistent inflammation, and progressive destruction of supporting tissues [64]. Peri-implantitis differs in that the biofilm develops on a non-shedding biomaterial surface [65]. Rough fixture topography promotes persistent attachment and maturation and makes surface decontamination difficult [66]. Nanozyme approaches for peri-implantitis have therefore included physical disruption and detachment of implant-associated biofilms in addition to antimicrobial catalysis. MnO₂ is particularly suited to this application because CAT-like H₂O₂ decomposition generates O₂ that can both modify anaerobic conditions and, when sufficiently rapid and localized, generate bubbles capable of physically disturbing the biofilm.

Lee et al. [19] exploited this reaction for decontamination of confined dental implant microstructures. Porous diatoms decorated with MnO₂ nanosheets served as self-powered microbubblers (SMs) that catalytically decomposed H₂O₂ and generated O₂ microbubbles. Bubble-driven propulsion allowed the rigid particles to enter implant microgaps while simultaneously oxygenating the local environment and mechanically disrupting biofilms. In P. gingivalis biofilms formed within implant internal spaces, SM/H₂O₂ treatment removed both bacterial residues and the EPS matrix. Conventional antiseptic treatment reduced bacterial viability but left substantial attached biofilm structures. The system was also tested against multispecies biofilms collected from peri-implantitis-affected patient implants and freshly extracted contaminated implants and produced near-complete decontamination of internal microstructures. Biofilm removal restored implant – abutment reverse torque toward control values and reduced bacterial leakage, indicating that physical decontamination also affected implant function [19]. Although this study did not directly evaluate treatment of peri-implant tissue inflammation or bone loss, it demonstrates a catalytic strategy for eliminating peri-implantitis-associated biofilm reservoirs within otherwise difficult-to-access implant structures.

These peri-implant studies broaden the role of nanozyme catalysis from bacterial killing to manipulation of biofilm architecture and the implant-associated microenvironment. MnO₂ based systems are a clear example: H₂O₂ decomposition can be used both to produce oxygen and to generate mechanical forces within complex surface features and fixture–abutment microgaps. Current evidence, however, remains largely based on in vitro and ex vivo models. Dependence on exogenous H₂O₂ , exposure of peri-implant tissues to particles and oxidants, long-term material safety, and the effects of repeated treatment on implant surfaces and the peri-implant microbiome require further study.

3. Salivary gland dysfunction and xerostomia

Xerostomia refers to the subjective sensation of oral dryness, and most commonly arises from hyposalivation, an objective reduction in salivary flow. Reduced salivary secretion increases the risk of dental caries, oral infection, and mucosal injury while impairing mastication, swallowing, and speech [67,68]. Sjögren’s disease is a chronic autoimmune disorder and an important cause of salivary gland dysfunction that can lead to xerostomia [69]. Persistent immune-cell infiltration and inflammation within the glands are accompanied by increased ROS accumulation and impaired antioxidant defense. Sustained oxidative stress can damage acinar and ductal epithelial cells and may further amplify inflammatory responses, progressively compromising salivary secretion.

Current treatment for Sjögren’s disease-associated xerostomia is largely symptomatic. Artificial saliva provides temporary moisture, while pilocarpine and cevimeline stimulate residual gland function. Approaches that directly restore redox balance within injured glands remain limited. Antioxidant nanozymes capable of sustained ROS scavenging have therefore been investigated as a means of protecting glandular tissue and preserving function.

Tao et al. [18] developed a salivary gland-targeted cerium oxide nanozyme system (Ce@gPEI) for hyposalivation-associated xerostomia. CeO₂ nanozymes were encapsulated within a polyethyleneimine (PEI)-poly(lactic-co-glycolic acid) copolymer-based carrier whose surface-exposed PEI segments promoted preferential accumulation in the submandibular gland through interactions associated with muscarinic M3 receptors. The ceria component showed SOD- and CAT-like activities and hydroxyl-radical scavenging capacity. In macrophages, treatment reduced oxidative stress and proinflammatory cytokines while increasing interleukin 10. Systemic administration to non-obese diabetic (NOD) mice with spontaneous salivary gland dysfunction restored salivary flow, reduced glandular hypertrophy and inflammatory infiltration, and improved acinar morphology. Aquaporin 5 (AQP5) and amylase 1 increased, whereas IL-1β and TNF-α decreased in the submandibular gland. Transcriptomic and immune-cell analyses also indicated modulation of TNF-, interleukin 17 (IL-17)-, and B-cell-associated responses together with increases in M2 macrophage and regulatory T-cell (Treg) populations. The therapeutic effect therefore involved both restoration of redox balance and changes in the local immune environment [18].

A subsequent strategy focused on local rather than systemic delivery to address rapid clearance within the oral cavity. Fang et al. [24] developed a mucoadhesive CeO₂ nanozyme microsphere system (adCe-MS) for Sjögren’s disease-associated xerostomia. CeO₂ nanoparticles were encapsulated in sodium alginate microspheres and coated with an adhesive hydrogel layer to prolong retention on wet oral mucosa and provide sustained release. The particles showed SOD- and CAT-like activities together with hydroxyl-radical scavenging capacity, reduced intracellular ROS, and suppressed TNF-α and interleukin 6 (IL-6) in macrophages. The microspheres degraded gradually over approximately 7 days in a collagenase-containing environment and released CeO₂ over this period, while the adhesive coating maintained attachment under wet and mechanically dynamic conditions. In NOD/LtJ mice with Sjögren-like xerostomia, local adCe-MS treatment increased salivary secretion, reduced inflammatory infiltration and structural injury in the submandibular gland, restored AQP5 expression, and normalized abnormal mucin 1 expression. Treg populations increased, M1 macrophages decreased, and circulating anti-Ro/anti-La autoantibodies and inflammatory cytokines were reduced. Transcriptomic analysis showed suppression of IL-17-, TNF-, chemokine-, and other inflammatory pathways together with increased expression of genes involved in salivary secretion and tissue repair. In this system, mucoadhesive retention extended local exposure to an antioxidant nanozyme and was associated with sustained immunoregulatory and functional effects [24].

The two studies use different delivery routes to achieve sustained antioxidant effects in the salivary gland environment. Both associate ceria-mediated ROS scavenging with reduced glandular inflammation and recovery of salivary secretion, rather than providing symptomatic moisture replacement alone. The mucoadhesive approach additionally addresses rapid oral clearance through prolonged local retention and sustained CeO₂ release. Evidence remains largely limited to Sjögren-like mouse models, however. Long-term nanozyme retention, chronic safety, delivery efficiency to deeper glandular tissue, and the relative contribution of the nanozyme and carrier have not yet been resolved.

4. Oral ulcers

Oral ulceration can arise from diverse causes, including local trauma, recurrent aphthous stomatitis, systemic immune-mediated inflammatory disorders such as Behçet disease, and mucosal injury associated with chemotherapy or head-and-neck radiotherapy [70,71]. These lesions are often painful and can interfere with speech, mastication, and swallowing [70]. Although isolated ulcers are generally self-limiting, recurrent, immune-mediated, or treatment-induced lesions may cause persistent pain and dysphagia, with consequent effects on nutritional intake and quality of life [71,72]. Despite differences in etiology, oral ulcerative lesions commonly involve disruption of the epithelial barrier and a local inflammatory response. Oxidative stress can further contribute to mucosal injury and is particularly well established in therapy-induced oral mucositis, where early ROS generation amplifies inflammatory signaling and subsequent tissue damage [4]. This involvement of oxidative stress provides a rationale for antioxidant nanozymes aimed at limiting excessive ROS and regulating the injured mucosal microenvironment.

Addressing localized oxidative inflammation alongside the risk of secondary bacterial infection is a primary challenge in managing oral ulcers. Exploring dual-action therapeutics for mucosal lesions, Gu et al. [73] developed a Vitamin B₂ -modified iron oxide nanozyme (VB₂ -IONzyme). Vitamin B₂ functionalization enhanced the SOD-like activity of the iron oxide nanoparticles while retaining POD- and CAT-like activities. In vitro, VB₂ -IONzyme showed pH-dependent catalytic behavior, with POD-like ROS generation favored under acidic conditions and CAT-like H₂O₂ decomposition under near-neutral conditions. The nanozyme reduced H₂O₂ -induced oxidative stress in oral keratinocytes and also inhibited bacterial species including S. mutans and Staphylococcus aureus. In a murine acetic acid-induced tongue ulcer model, topical treatment accelerated re-epithelialization, reduced inflammatory cell infiltration, and decreased local interferon gamma (IFN- γ ) and IL-6 levels [73]. These findings demonstrate that surface functionalization can modify the catalytic balance of iron oxide nanozymes and enable simultaneous antioxidant and antibacterial effects in oral ulcer treatment.

Beyond catalytic efficiency, ensuring adequate localized retention and minimizing the required dosage of conventional anti-inflammatory drugs are critical factors for effective oral ulcer therapy. To overcome the rapid fluid clearance characteristic of the oral cavity, Lee et al. [25] developed a biodegradable microneedle patch incorporating a metabolized elastin-complexed ceria nanozyme (mEl-Ce) and triamcinolone acetonide (TA) for oral ulcer treatment. The mEl-Ce nanoparticles showed higher SOD- and CAT-like activities than polyethylene glycol-coated ceria and reduced intracellular oxidative stress while modulating macrophage responses through NRF2-associated pathways. The metabolized elastin component enhanced interaction with extracellular matrix components, contributing to local retention and proangiogenic responses. In the patch, mEl-Ce was incorporated into a rapidly dissolving tip layer for early ROS scavenging, whereas TA was loaded into a slower-degrading base layer for sustained release. In a recurrent large-diameter murine tongue ulcer model, the patch accelerated wound closure and re-epithelialization and increased vascularization compared with a commercial TA patch, despite containing a lower steroid dose [25]. These results demonstrate that ceria-mediated redox regulation can be combined with local retention and sustained corticosteroid delivery within an oral-adapted microneedle platform.

Spatially controlling redox regulation and minimizing the systemic exposure of nanomaterials are significant clinical challenges in topical oral therapies. To address these issues through physical compartmentalization, Kim et al. [26] developed a dual-layered Janus oral patch (DL-JPatch) incorporating CeO₂ nanoparticles and TA for oral ulcer treatment. The tissue-facing layer consisted of gallic acid-conjugated chitosan containing TA, whereas the outward-facing layer immobilized CeO₂ nanoparticles within a genipin-crosslinked chitosan network. This asymmetric structure provided adhesion to wet oral mucosa while reducing nonspecific adhesion to surrounding tissues and improving resistance to salivary shear. The outer layer also acted as a physical barrier against bacterial penetration. Immobilization of CeO₂ within the crosslinked matrix reduced particle aggregation and maintained radical-scavenging activity while limiting nanoparticle release. In a chemically induced murine oral ulcer model, DL-JPatch accelerated wound closure and re-epithelialization and reduced NF-κB-associated inflammatory signaling, CD11b + inflammatory cell infiltration, and 4-hydroxynonenal-positive oxidative damage compared with conventional TA gel. Repeated administration resulted in no detectable cerium accumulation in the examined major organs under the tested conditions [26]. These findings demonstrate that CeO₂ -mediated redox regulation can be combined with corticosteroid delivery, mucosal retention, and nanoparticle confinement within a Janus patch platform.

Nanozyme-based approaches for oral ulceration have expanded from multifunctional nanoparticles designed for direct redox regulation to oral-adapted systems that combine antioxidant catalysis with pharmacological treatment and local delivery. Early iron oxide nanozymes showed that surface modification could enhance ROS-scavenging activity while retaining antibacterial function. More recent ceria-based systems have focused on challenges specific to the oral cavity, including lesion retention, coordinated corticosteroid delivery, and confinement of nanoparticles to the treatment site. These studies indicate that antioxidant activity alone is unlikely to determine therapeutic efficacy. Sustained local redox regulation, resistance to salivary clearance, and limited exposure of surrounding tissues are also important design considerations. Current evidence, however, remains largely limited to chemically induced rodent ulcer models, and efficacy in recurrent aphthous stomatitis, therapy-induced oral mucositis, and immune-mediated ulcerative diseases remains to be established.

Challenges and Future Perspectives

Nanozyme research for oral diseases has progressed from catalytic antimicrobial treatment toward approaches that also regulate host redox homeostasis and use localized delivery systems. High catalytic activity or favorable efficacy in preclinical models, however, does not by itself establish clinical utility. Substrate availability, salivary dilution and clearance, the complexity of the oral microbial community, and repeated nanomaterial exposure can all alter therapeutic performance. Catalytic activity therefore needs to be evaluated under conditions that more closely reproduce the intended oral environment.

1. Dependence on exogenous H₂O₂

Several nanozyme systems discussed in this review require an external source of H₂O₂ to achieve therapeutic activity. This applies both to POD-like antimicrobial systems that convert H₂O₂ into reactive oxidizing species and to CAT-like systems that use H₂O₂ decomposition to generate oxygen or microbubbles. Endogenous H₂O₂ concentrations and spatial distributions in the oral cavity are limited and variable. Exogenously delivered H₂O₂ is also diluted by saliva and consumed through reactions with biomolecules and microbial enzymes. Repeated exposure may additionally affect healthy tissues and commensal microorganisms.

Reducing dependence on exogenous H₂O₂ is therefore an important design objective, although complete elimination of H₂O₂ is not necessary for every application. OXD-like catalysis and in situ H₂O₂ generation by glucose OXD can provide alternative routes to oxidative reactions. Light- or ultrasound-activated systems may also decrease the amount of externally supplied oxidant, depending on the catalytic mechanism. Bacterial enzyme-responsive activation does not remove the need for H₂O₂ but can restrict catalytic activity more closely to diseased sites. These alternatives introduce their own constraints, including dependence on oxygen or other substrates, additional acidification, and the requirement for external equipment. The relevant criterion is whether sufficient catalytic flux can be generated at the lesion while limiting oxidant exposure in surrounding healthy tissue.

2. Material bias and function/composition relationships

Material selection in oral nanozyme studies has tended to follow therapeutic function. Fe-, Cu-, Mn-, and Mo-based materials are frequently used for catalytic antimicrobial therapy, whereas CeO₂ predominates in host-directed ROS-scavenging studies. The latter reflects the combination of antioxidant activities provided by Ce³⁺ /Ce⁴⁺ redox cycling and surface oxygen vacancies.

Broader material diversity is one route forward, but changes in composition are not the only means of improving catalytic activity. Manganese ferrite provides an antioxidant composition distinct from ceria, while morphology-engineered CeO₂ shows that catalytic performance can also be modified by controlling particle shape, surface area, and defect structure. Comparison of composition, structure, catalytic activity, and therapeutic outcome will be more informative than material composition alone.

3. Delivery, retention, and lesion-selective activation

Nanozymes must reach the lesion, remain there long enough to act, and retain their intended catalytic function during that period. These requirements are particularly difficult in the oral cavity because salivary flow, mastication, and swallowing continually remove locally applied materials.

Different applications have addressed this problem in different ways. Cariogenic biofilm targeting has been achieved through interactions with bacterial surface components [33]. Injectable or thermoresponsive hydrogels improve retention within periodontal pockets [30]. Mucoadhesive microspheres provide sustained local delivery for xerostomia [24], and bacterial enzyme-responsive coatings can restrict exposure of catalytic sites to disease-associated conditions [35].

Retention time alone is not an adequate measure of delivery performance. Future studies should determine whether catalytic activity is preserved over the full residence period and define how nanozymes are subsequently degraded or cleared.

4. Limitations in preclinical evidence and standardization of catalytic activity

Much of the current evidence is derived from in vitro biofilm experiments and rodent disease models. Single-species biofilms are useful for mechanistic studies but do not reproduce the complexity of polymicrobial oral communities [74]. Ligature-induced periodontitis also differs from the slowly progressive, chronic course of human disease [75]. Clinically relevant preclinical evidence is particularly limited for peri-implantitis and Sjögren’s disease-associated xerostomia.

Comparison across studies is further complicated by differences in catalytic assays. Reporting apparent K_m and V_max alone is insufficient when particle concentration, surface area, pH, temperature, substrate concentration, and reaction time vary among experiments [76]. A more standardized framework should include particle concentration, mass-normalized activity and, when feasible, surface-area-normalized activity together with defined reaction conditions and quantitative measures of ROS production or scavenging.

5. Oral-specific safety considerations

A fraction of nanozymes applied in the oral cavity may be swallowed with saliva and enter the gastrointestinal tract. This is particularly relevant for chronic diseases that require repeated treatment. Safety assessment should therefore extend beyond acute cytotoxicity to biodistribution, degradation, clearance, systemic exposure, and possible effects on the gastrointestinal microbiome [77].

ROS-generating nanozymes do not inherently distinguish pathogenic microorganisms from commensal species. Antimicrobial studies should therefore assess community-level microbiome changes in addition to bactericidal efficacy. The opposite concern applies to antioxidant nanozymes. Excessive ROS scavenging could interfere with physiological redox signaling and normal antimicrobial defense [78]. The aim should be to reduce pathological oxidative stress without abolishing physiological ROS functions.

Peri-implant applications raise an additional material-specific issue. Repeated exposure to oxidants and catalytic particles may affect titanium surface chemistry, the passive oxide layer, or other aspects of implant surface integrity [79]. These parameters should be assessed alongside biofilm removal.

6. Clinical translation and manufacturing reproducibility

Nanozyme activity is sensitive to particle size, morphology, oxidation state, and surface defects [30]. Batch-to-batch differences in these properties may therefore produce corresponding variation in therapeutic performance. Clinical development will require quality-control criteria that maintain both critical material attributes and catalytic activity during scale-up [80].

Manufacturing and regulatory complexity also increases when nanozymes are incorporated into hydrogels, microspheres, coatings, or externally activated systems. The most active catalytic formulation is therefore not necessarily the most clinically practical one. Reproducible manufacturing, straightforward delivery, defined clearance pathways, and demonstrable advantages over existing treatment will be equally important.

Clinical translation of oral nanozymes will ultimately depend on whether catalytic activity can be reproduced under physiologically relevant conditions and delivered to the appropriate disease compartment. Reducing unnecessary dependence on externally supplied substrates, matching catalytic reactions to lesion microenvironments, and maintaining activity at the target site are central requirements. Standardized catalytic assays, more clinically representative disease models, long-term safety studies, and assessment of microbiome effects will also be needed before these materials can move beyond experimental catalytic platforms.

Conclusion

Nanozymes have been applied to oral diseases through different catalytic functions, ranging from ROS generation for biofilm disruption to ROS scavenging in inflamed or damaged tissues. Their therapeutic effect, however, cannot be determined by catalytic activity alone. The relevant reaction must remain effective under the pH, oxygen availability, substrate concentration, and biological conditions of the target lesion, and the material must remain at the site long enough to act. These requirements differ among dental caries, periodontal and peri-implant diseases, salivary gland dysfunction, and oral ulceration. Further development will require catalytic evaluation under physiologically relevant conditions, more representative preclinical models, and careful assessment of repeated oral exposure, microbiome effects, material clearance, and manufacturing reproducibility. Rather than maximizing catalytic activity as an isolated material property, oral nanozyme design should focus on achieving a reproducible catalytic function that is appropriate for the pathophysiology and microenvironment of the target disease.