Multifunctional Bioceramic Coatings for Dental Implants: Advances in Antibacterial Activity, Corrosion Resistance and Osseointegration with Clinical Perspectives and a Focus on Zirconia-Based Systems

Abstract

Background/Objectives: Titanium alloy Ti₆Al₄V remains the gold standard in dental implantology due to its excellent mechanical properties, corrosion resistance, and biocompatibility. However, implant-associated infections and insufficient osseointegration continue to represent major clinical challenges, mainly related to bacterial biofilm formation and suboptimal surface–tissue interactions. Biofilm formation refers to the adhesion, accumulation, and growth of microbial communities embedded within a self-produced extracellular polymeric matrix on implant surfaces, which contributes to bacterial persistence and resistance to host defense mechanisms. This review aims to critically evaluate recent advances in multifunctional bioceramic coatings for dental implants, with a particular focus on zirconia (ZrO₂)-based systems and their antibacterial mechanisms. Methods: A structured literature analysis was conducted using major scientific databases including PubMed, Scopus, and Web of Science, focusing mainly on studies published between 2015 and 2025 related to CaP, Ag, and ZrO₂-based coatings for dental implants. The review examines their physicochemical properties, antibacterial strategies, ion release behavior, and biological responses, including osteogenic activity and biofilm inhibition. Particular attention is given to hybrid systems integrating multiple functional phases. Results: CaP coatings exhibit excellent osteoconductivity and promote early osseointegration but show limited intrinsic antibacterial activity. Ag-based coatings provide strong broad-spectrum antimicrobial effects through controlled Ag⁺ ion release, although concerns regarding cytotoxicity and dose-dependent responses remain. ZrO₂ coatings significantly enhance corrosion resistance and surface stability, while their antibacterial performance can be improved through nanostructuring, laser surface modification, and ionic doping. Hybrid Ag–CaP–ZrO₂ coatings demonstrate improved antibacterial activity, enhanced corrosion resistance, and better regulation of ion release kinetics and osteogenic response compared with single-component coating systems. Conclusions: Multifunctional bioceramic coatings represent a promising strategy for improving the performance of dental implants and addressing the dual challenge of infection control and tissue integration. However, challenges remain regarding long-term stability, controlled ion release, and limited clinical validation. Future research should focus on the development of smart, stimuli-responsive coatings and standardized evaluation protocols to facilitate clinical translation.

1. Introduction

Titanium and its alloys, particularly Ti₆Al₄V, remain the gold standard in dental implantology due to their favorable combination of mechanical properties, corrosion resistance, and well-established biocompatibility [1,2,3,4,5]. Despite this success, implant failure remains a significant clinical challenge, often associated with insufficient osseointegration and the development of peri-implant infections related to biofilm formation [6,7,8,9,10,11]. Microbial colonization of the implant surface, followed by biofilm maturation, promotes local dysbiosis (microbial imbalance of the oral microbiota), persistent inflammation of peri-implant tissues, and ultimately bone loss, compromising the long-term stability of the implant [6,7,8,11]. Recent studies have further demonstrated that implant surface properties, such as topography, surface energy, wettability, and chemical composition, play a critical role in modulating bacterial adhesion, cellular response, and the quality of the tissue implant interface [6,7,8,9,12,13,14,15]. Despite extensive research efforts, achieving a simultaneous optimization of antibacterial performance and long-term biocompatibility remains a major challenge.

To overcome these limitations, an increasing number of studies have focused on the development of multifunctional surface coatings capable of simultaneously improving bioactivity, corrosion resistance, and antibacterial performance of dental implants [12,13,16,17,18,19]. Current strategies rely on a combination of physical, chemical, and biological modifications, including nano- and microstructural engineering, bioactive coatings, and the incorporation of antimicrobial agents [12,13,16,17,18,19,20]. In the present review, the term ‘bioceramic coatings’ refers to bioactive or biocompatible ceramic-based coatings, particularly calcium phosphate and zirconia-based systems, developed to enhance the biological, antibacterial, and physicochemical performance of titanium dental implants [16,21,22]. Among the most extensively studied materials, CaP-based coatings occupy a central position due to their chemical similarity to the mineral phase of bone and their ability to stimulate osteoconduction and osseointegration [16,21,22]. However, CaP alone generally exhibits limited intrinsic antibacterial activity, which justifies its combination with antimicrobial agents or other ceramic phases [16,21,22,23].

In this context, the incorporation of metallic ions, particularly Ag, has attracted considerable attention due to its broad-spectrum antibacterial activity and its ability to reduce biofilm formation on implant surfaces [17,24,25,26]. Emerging evidence suggests that silver-based or hybrid coatings can enhance antibacterial efficacy while maintaining acceptable cytocompatibility, provided that ion release kinetics are carefully controlled [24,26]. In parallel, more complex systems combining nanoparticles, porous structures, and functional matrices have emerged as promising approaches to balance anti-infective activity and favorable tissue response [3,17,24,25].

Furthermore, ZrO₂ has gained increasing interest in dental implantology due to its high chemical stability, hardness, corrosion resistance, aesthetic properties, and favorable interaction with soft tissues [5,27,28]. Beyond its passive protective role, recent investigations indicate that zirconia-based surfaces can exhibit enhanced biological and antibacterial properties when appropriately engineered, for instance through nanostructuring, laser surface modification, or ionic doping with elements such as Ga or Zn [27,28,29,30]. These modifications help reduce bacterial adhesion, limit biofilm formation, and improve cellular response, thereby paving the way for more biologically and microbiologically efficient implant surfaces [27,28,29,30,31].

Consequently, hybrid approaches combining Ag–CaP–ZrO₂ have emerged as one of the most promising strategies for designing multifunctional dental implants capable of simultaneously providing electrochemical protection, enhanced bioactivity, and long-lasting antibacterial activity [18,22,25,29,30]. These systems aim to achieve a complementary balance between antibacterial efficacy, osteogenic potential, and physicochemical stability. However, despite encouraging in vitro and preclinical results, clinical translation remains limited due to heterogeneity in experimental protocols, variability in deposition techniques, challenges in controlling long-term ion release, and the lack of long-term clinical studies [7,13,17,26,30].

In this context, a structured literature search was conducted following PRISMA-inspired guidelines to improve methodological transparency and minimize potential selection bias. The bibliographic search was performed using PubMed, Scopus, and Web of Science databases and primarily included peer-reviewed articles published between 2015 and 2025 related to multifunctional bioceramic coatings for dental implant applications. The search strategy combined specific keywords and Boolean operators, including “dental implants”, “Ti₆Al₄V”, “calcium phosphate coatings”, “hydroxyapatite coatings”, “silver nanoparticles”, “Ag-based coatings”, “zirconia coatings”, “ZrO₂ coatings”, “antibacterial activity”, “biofilm inhibition”, “corrosion resistance”, and “osseointegration”. Article selection was based on title, abstract, and full-text screening according to predefined inclusion and exclusion criteria. Included studies focused on CaP, Ag, ZrO₂, or hybrid multifunctional coatings applied to titanium dental implants, particularly those evaluating antibacterial activity, bioactivity, corrosion resistance, osseointegration, ion release behavior, and related physicochemical or biological properties. Duplicate records, non-English publications, editorials, conference abstracts, studies unrelated to dental implantology or Ti₆Al₄V substrates, and studies lacking relevant biological or physicochemical evaluation were excluded. Although the present work is a narrative review rather than a full systematic review, the literature selection process was structured according to PRISMA-inspired recommendations in order to improve reproducibility, methodological rigor, and scientific reliability.

2. Comparative Analysis of Bioceramic Coatings

2.1. Calcium Phosphate (CaP) Coatings

CaP-based coatings are among the most extensively studied approaches for improving the biological performance of titanium dental implants due to their strong chemical and crystallographic similarity to the mineral phase of bone, primarily hydroxyapatite (HA) [32,33,34]. Hydroxyapatite (HA) possesses a hexagonal crystal structure that closely resembles the mineral phase of natural bone, contributing to its excellent bioactivity and osteoconductive properties. This similarity confers remarkable bioactivity, promoting protein adsorption, cell adhesion, and the activation of osteogenic signaling pathways [23,35,36].

From a biological perspective, CaP coatings play a critical role in modulating cell–material interactions [37,38]. They promote the adhesion, proliferation, and differentiation of osteoblasts, notably by enhancing the expression of osteogenic markers such as alkaline phosphatase (ALP), RUNX2, and osteocalcin. Furthermore, the partial dissolution of CaP in physiological environments leads to the release of Ca²⁺ and PO₄³⁻ ions, which actively contribute to bone mineralization and the formation of a direct chemical bond between the implant and the surrounding bone tissue [32,33,34,39,40,41].

In terms of osseointegration, numerous studies have demonstrated that CaP-coated surfaces enable faster and more stable bone integration compared to unmodified Ti surfaces. This improvement is attributed not only to the intrinsic bioactivity of CaP but also to its ability to modulate key surface properties, such as roughness, wettability and surface energy, which directly influence cellular and tissue responses [16,21,22].

However, despite these advantages, CaP coatings exhibit limited intrinsic antibacterial activity, which represents a major drawback in the oral environment characterized by complex polymicrobial biofilms [42]. This limitation increases the risk of early bacterial colonization and peri-implant infection.

To address this issue, various functionalization strategies have been developed. The incorporation of antibacterial metallic ions, such as Ag, Zn, or Cu, into the CaP matrix represents one of the most effective approaches. These ions can be introduced either through ionic substitution within the crystal lattice or via the deposition of nanoparticles on the surface. Their controlled release enables the inhibition of bacterial adhesion, disruption of microbial cell membranes, and reduction in biofilm formation, while preserving the bioactive properties of CaP [8,43,44].

In addition, recent advances have highlighted the importance of nano- and microstructuring of CaP coatings. Nanostructured and nanoporous surfaces significantly increase the specific surface area, thereby enhancing protein adsorption and cell–material interactions. These architectures also enable controlled ion diffusion and may indirectly contribute to reducing bacterial adhesion [42]. The morphological characteristics of different CaP phases are illustrated in Figure 1 [11,14,15].

Another critical aspect concerns the mechanical stability and adhesion of the coating to the metallic substrate. CaP coatings, particularly those deposited by plasma spraying, may present a risk of delamination under mechanical loading or in physiological environments. To improve their stability, several deposition techniques have been developed, including electrodeposition, sol–gel processes and biomimetic approaches, which provide better cohesion and a more stable interface with the Ti₆Al₄V substrate [16,21,22]. To summarize the key physicochemical and biological properties of CaP coatings,

Table 1. Physicochemical and biological properties of CaP coatings for dental implants.

Parameter	Description	Biological/Clinical Impact	Limitations	References
Chemical similarity	Mimics natural bone mineral (hydroxyapatite)	Promotes bioactivity and bone bonding	—	[32,33,34]
Osteogenic properties	Enhances ALP, RUNX2, osteocalcin expression	Accelerates osseointegration	—	[32,33,34]
Ion release behavior	Release of Ca2+ and PO43− ions	Stimulates bone mineralization and remodeling	Excessive dissolution may occur	[32,33,34]
Surface properties	Tunable roughness and wettability	Improves cell adhesion and proliferation	—	[16,21,22]
Antibacterial activity	Intrinsically low	—	Susceptible to biofilm formation	[42]
Ion doping capability	Incorporation of Ag, Zn, Cu ions	Provides antibacterial functionality	Cytotoxicity risk if uncontrolled	[8,43,44]
Micro/nanostructure	Porous or nanostructured surfaces	Enhances protein adsorption and cell response	Complex fabrication processes	[42]
Mechanical stability	Depends on deposition technique	Influences coating durability	Risk of delamination (plasma spray)	[16,21,22]

presents their main advantages, limitations, and functional characteristics.

Overall, CaP coatings exhibit excellent bioactivity and osteogenic potential; however, their limited antibacterial performance and potential mechanical instability remain key challenges.

Finally, current research is increasingly focused on the development of multifunctional CaP-based coatings integrating bioactive, antibacterial, and even therapeutic properties. In this context, CaP is often used as a matrix in hybrid systems, particularly in combination with Ag or ZrO₂, in order to achieve an optimal balance between osseointegration and infection prevention [16,21,22].

2.2. Ag-Based Coatings

Ag is widely recognized as one of the most effective antimicrobial agents used in biomedical applications due to its broad-spectrum antibacterial activity against both Gram-positive and Gram-negative bacteria, particularly Staphylococcus aureus and Escherichia coli [45,46,47,48]. In the context of dental implants, silver-based coatings have been extensively investigated for their ability to prevent biofilm formation and reduce the risk of peri-implant infections [49].

The antibacterial mechanism of silver is primarily based on the release of Ag⁺ ions, which interact with bacterial cellular components at multiple levels. Ag⁺ ions can disrupt the integrity of the bacterial cell membrane, increasing its permeability and leading to leakage of intracellular contents. They can also bind to proteins containing thiol groups, thereby inhibiting essential enzymatic functions involved in bacterial metabolism. In addition, silver ions can interact with bacterial DNA, impairing replication and ultimately leading to cell death [45,46,47,48]. Furthermore, silver nanoparticles (AgNPs) have been reported to induce the generation of reactive oxygen species (ROS), thereby enhancing their bactericidal effect.

Despite this remarkable antibacterial efficacy, the use of silver in implant coatings presents significant challenges. The main issue lies in controlling the release kinetics of Ag⁺ ions. Excessive ion release may induce cytotoxic effects on host cells, particularly osteoblasts, thereby compromising biocompatibility and osseointegration [50]. Conversely, insufficient ion release may reduce antibacterial effectiveness, allowing bacterial persistence and biofilm formation. Therefore, achieving an optimal balance between antibacterial activity and cytocompatibility remains a critical challenge.

To overcome these limitations, several strategies have been developed to optimize silver delivery. The incorporation of Ag into ceramic matrices such as CaP or ZrO₂ enables modulation of ion release and improves coating stability [20,51,52,53,54]. These composite systems help minimize burst release effects while ensuring sustained antimicrobial activity.

Moreover, the use of AgNPs has attracted increasing interest due to their high specific surface area and enhanced interaction with bacterial cells [46,55].

Coatings incorporating AgNPs exhibit improved antibacterial performance even at low concentrations [56,57], thereby reducing the risk of cytotoxicity. However, their long-term stability, potential aggregation, and behavior in biological environments remain important challenges requiring further investigation [46,55,57].

A schematic illustration summarizing the morphology, surface distribution, and antibacterial mechanisms of silver nanoparticles on implant surfaces is presented in Figure 2.

Another aspect to consider is the aesthetic impact of silver, particularly in dental implantology. The presence of Ag may lead to discoloration of implant surfaces or surrounding tissues, which represents a potential limitation in esthetically sensitive areas.

Overall, silver-based coatings offer powerful antibacterial properties; however, their clinical applicability strongly depends on precise control of ion release, long-term stability, and cytocompatibility. Therefore, hybrid approaches combining Ag with bioactive materials such as CaP or ZrO₂ represent particularly promising strategies for the development of multifunctional implant surfaces [20,51,52]. The main properties, antibacterial mechanisms, and limitations of Ag-based coatings are summarized in

Table 2. Antibacterial mechanisms, advantages, and limitations of Ag-based coatings for dental implants.

Parameter	Description	Biological/Clinical Impact	Limitations	References
Antibacterial spectrum	Effective against Gram-positive and Gram-negative bacteria	Reduces peri-implant infections	—	[45,46,47]
Ion release (Ag+)	Release of silver ions	Disrupts bacterial membrane and metabolism	Requires controlled release	[45,46,47]
Mechanism of action	Membrane damage, protein denaturation, DNA interaction, ROS generation	Strong bactericidal effect	Potential cytotoxicity	[45,46,47]
AgNPs	High surface area and reactivity	Enhanced antibacterial efficiency at low doses	Stability concerns	[45,46,47]
Cytocompatibility	Dose-dependent effect	Safe at controlled concentrations	Toxic at high concentrations	[50]
Composite coatings	Ag combined with CaP or ZrO2	Controlled ion release and improved balance	Complex fabrication	[20,51,52]

.

2.3. ZrO₂-Based Coatings

ZrO₂-based coatings have attracted increasing interest in dental implantology due to their excellent physicochemical properties, including high chemical stability, superior corrosion resistance, high hardness, and remarkable biocompatibility [5,27,28,31,58,59,60]. As a surface layer, ZrO₂ acts as an effective protective barrier, limiting the electrochemical degradation of the Ti₆Al₄V substrate in the oral environment, which is characterized by pH fluctuations and the presence of aggressive ionic species [59,61].

Beyond its passive protective role, ZrO₂-based surfaces also exhibit promising biological properties, particularly in terms of interactions with both soft and hard tissues [62,63]. Recent studies have demonstrated that ZrO₂ promotes gingival fibroblast adhesion and reduces local inflammation, thereby contributing to improved peri-implant tissue integration [5,27,28,64,65,66]. In addition, its white color provides a significant aesthetic advantage over metallic surfaces, especially in anterior regions.

However, pure ZrO₂ exhibits limited intrinsic antibacterial activity, which represents a major limitation for preventing peri-implant infections. Consequently, advanced surface modification strategies are required to enhance its antibacterial performance. Among these, surface nanostructuring (e.g., nanotubes, nanopillars, and hierarchical architectures) plays a crucial role in reducing bacterial adhesion by modulating surface roughness, wettability and surface energy [5,67,68,69,70,71]. These nanostructured surfaces can also exert mechanical bactericidal effects by physically disrupting bacterial membranes [70,72]. The incorporation of Ag promotes the formation of dispersed surface particles, whereas the addition of ZrO₂ leads to a denser and more homogeneous coating morphology, as illustrated in Figure 3.

X-ray diffraction (XRD) analysis reported in the literature plays an important role in characterizing multifunctional coating systems by identifying crystalline phases, evaluating phase stability, and assessing coating crystallinity. In CaP-based systems, XRD commonly confirms the presence of hydroxyapatite, β-TCP, or other calcium phosphate phases depending on the deposition conditions. In Ag-containing coatings, additional diffraction peaks associated with metallic Ag or Ag-containing phases may be observed, while ZrO₂-based coatings may exhibit tetragonal or monoclinic zirconia structures depending on processing parameters and thermal treatment. These structural characteristics may influence coating stability, ion release behavior, and overall biological and antibacterial performance [16,21,73,74].

In addition, ionic doping of ZrO₂ with elements such as Ag, Zn, Cu, Ga, or Ce has demonstrated promising antibacterial performance. These ions can be released in a controlled manner and interact with bacterial cells by disrupting their metabolism and membrane integrity [28,29,75,76,77,78]. Notably, Ga can interfere with bacterial iron metabolism, while Zn contributes not only to antibacterial activity but also to osteogenic stimulation, highlighting the multifunctional potential of doped ZrO₂ systems.

Recent advances have also highlighted the role of laser-functionalized surfaces and ZrO₂–bioactive glass hybrid coatings in simultaneously enhancing bioactivity and antibacterial performance. These approaches enable the formation of super hydrophilic surfaces, which promote protein adsorption and cell adhesion while reducing bacterial attachment [5,27,28,29,30,79].

Furthermore, the combination of ZrO₂ with CaP represents a particularly promising strategy. CaP provides high bioactivity and promotes osseointegration, while ZrO₂ ensures mechanical stability and chemical durability of the coating. This complementary interaction enables the design of coatings with optimized biological and physicochemical performance [5,21,22,28,29]. The main physicochemical, biological, and antibacterial properties of ZrO₂-based coatings are summarized in

Table 3. Physicochemical, biological and antibacterial properties of ZrO₂-based coatings for dental implants.

Parameter	Description	Biological/Clinical Impact	Limitations	References
Corrosion resistance	High chemical stability in oral environment	Protects Ti6Al4V substrate	—	[61]
Biocompatibility	Favorable interaction with soft and hard tissues	Improved tissue integration	Limited bioactivity alone	[5,27,28]
Aesthetic property	White color	Suitable for anterior implants	—	[5]
Antibacterial activity	Intrinsically low	—	Requires modification	[5,27,28]
Surface nanostructuring	Nanotubes, nanopillars, rough surfaces	Reduces bacterial adhesion	Complex fabrication	[64,67]
Ion doping	Ag, Zn, Cu, Ga, Ce incorporation	Enhances antibacterial activity	Risk of cytotoxicity	[28,29,75,76,77,78]
Hybrid coatings	Combination with CaP or bioactive glass	Improves bioactivity + stability	Multi-step processing	[5,21,22,28,29]
Laser surface modification	Creates micro/nano-textures	Enhances osseointegration	Requires optimization	[27,28,29,30]

.

Overall, ZrO₂-based coatings offer excellent corrosion resistance, biocompatibility, and aesthetic properties; however, their antibacterial performance requires additional functionalization through nanostructuring, ionic doping, or hybridization strategies.

Finally, the antibacterial mechanisms associated with modified ZrO₂ surfaces involve multiple synergistic effects, including changes in wettability, reduction in bacterial adhesion, controlled release of antimicrobial ions, and, in some cases, the generation of ROS [69,80,81]. These synergistic mechanisms contribute to improving both antibacterial performance and the overall biological response of implant surfaces.

The crystalline structure and phase composition of CaP and ZrO₂-based coatings may also influence their antibacterial and physicochemical behavior. Parameters such as crystallinity, grain size, surface defects, and phase stability can affect ion diffusion, surface reactivity, wettability, and bacterial adhesion. In ZrO₂-based systems, phase organization and surface modifications may additionally influence local electrochemical interactions and ROS generation. Therefore, the antimicrobial performance of multifunctional coatings depends not only on their chemical composition but also on their crystalline and microstructural characteristics [42,69,72,74].

2.4. Ag–CaP–ZrO₂ Composite Coatings

Hybrid coatings incorporating Ag, CaP and ZrO₂ represent one of the most advanced and promising strategies for the development of multifunctional implant surfaces. These composite systems are designed to simultaneously address the main clinical requirements in dental implantology, namely infection prevention, enhancement of osseointegration, and long-term physicochemical stability of implants. From a functional perspective, these coatings rely on a synergistic interaction between their constituent components. Silver provides broad-spectrum antibacterial activity through the controlled release of Ag⁺ ions, which are capable of disrupting bacterial membranes, inhibiting enzymatic activity, and interfering with microbial DNA. Calcium phosphate acts as a bioactive phase, promoting cell adhesion and osteoblastic differentiation by mimicking the mineral composition of bone, thereby accelerating osseointegration. In parallel, ZrO₂ serves as a stable matrix, enhancing corrosion resistance, mechanical strength, and structural integrity of the coating [21,73,74,82].

Beyond this complementarity, recent studies have demonstrated that the integration of these three phases within hierarchical nanocomposite structures enables fine-tuning of interfacial properties and functional performance. In particular, the presence of ZrO₂ contributes to stabilizing the CaP matrix and modulating the diffusion of Ag⁺ ions, thereby reducing burst release effects responsible for cytotoxicity while maintaining prolonged antibacterial activity [83,84,85]. This controlled ion release behavior is critical for achieving an optimal balance between antimicrobial efficacy and biocompatibility.

However, the multifunctional behavior of Ag–CaP–ZrO₂ coatings should not be interpreted as a simple additive combination of the individual properties of each component. In complex hybrid systems, interfacial reactions between phases, oxidation phenomena, phase instability, and modifications in ion release kinetics may significantly alter the expected biological and antibacterial performance. For example, the incorporation of Ag within CaP or ZrO₂ matrices may modify Ag⁺ diffusion behavior and local electrochemical interactions, thereby influencing both antibacterial efficacy and cytocompatibility. Similarly, phase distribution, coating architecture, and long-term physicochemical stability under physiological conditions may affect coating durability and functional performance. Therefore, the overall multifunctional response of these systems results from complex synergistic and competitive interactions that require careful optimization and long-term evaluation [53,72,74].

It is also important to distinguish between the different architectures used in multifunctional coating systems, as their structural organization strongly influences their biological and physicochemical behavior. Ion-doped coatings generally involve the incorporation of antibacterial ions within a single matrix, allowing controlled ion release while preserving the original coating structure. In contrast, composite coatings combine multiple phases within the same layer, leading to more complex interfacial interactions and multifunctional responses. Multilayer systems consist of successive functional layers designed to separately optimize properties such as corrosion resistance, bioactivity, and antibacterial performance. Consequently, antibacterial efficacy, ion diffusion behavior, mechanical stability, and long-term durability may vary considerably depending on the coating architecture and fabrication strategy [53,72,74].

From an electrochemical standpoint, Ag–CaP–ZrO₂ coatings significantly enhance the corrosion resistance of Ti₆Al₄V, owing to the barrier effect of ZrO₂ combined with the compactness and bioactivity of CaP. In addition, modifications in surface topography and wettability induced by these coatings contribute to reducing initial bacterial adhesion, thereby limiting biofilm formation [73].

From a biological perspective, these hybrid systems promote more favorable cell–material interactions. Several studies have reported enhanced osteoblast adhesion and proliferation, as well as upregulation of osteogenic markers, suggesting improved osseointegration potential. At the same time, the combined antibacterial effect significantly reduces microbial colonization, contributing to the prevention of peri-implant infections.

Despite these promising results, several challenges remain. The complexity of fabrication processes, precise control over phase distribution, and reproducibility of coating properties represent major limitations. Furthermore, interfacial instability and long-term durability of multiphase coatings remain insufficiently investigated. In addition, most available studies are still limited to in vitro or preclinical models, and long-term clinical data remain scarce.

Overall, Ag–CaP–ZrO₂ composite coatings represent a highly promising approach for next-generation dental implants, enabling the integration of sustained antibacterial activity, enhanced bioactivity, and improved physicochemical stability. However, their successful clinical translation will require further optimization of fabrication techniques, standardization of evaluation protocols, and validation through long-term in vivo and clinical studies.

Table 4. Comparative analysis of CaP, Ag, ZrO₂ and Ag–CaP–ZrO₂ coatings for dental implant applications.

Parameter	CaP	Ag	ZrO2	Ag–CaP–ZrO2 (Composite)	References
Main function	Bioactivity	Antibacterial agent	Protective/stability layer	Multifunctional (bioactive + antibacterial + protective)	[14,29,30,31,36,48,49]
Antibacterial activity	Low	High (broad-spectrum)	Low (requires modification)	High (cooperative effect)	[26,29,30,31,40,48]
Bioactivity	Excellent (osteoconductive)	Limited	Moderate	Excellent	[14,15,20,48]
Osseointegration	Promotes early bone integration	May impair at high doses	Good soft tissue response	Enhanced osseointegration	[14,17,37,48]
Corrosion resistance	Moderate	Limited	Excellent	Excellent	[36,48]
Mechanical stability	Moderate (risk of delamination)	Depends on incorporation	High	High	[11,48,49]
Ion release behavior	Ca2+, PO43− release	Ag+ release	Minimal	Controlled multi-ion release	[23,24,25,50,51,52]
Cytocompatibility	High	Dose-dependent	High	Optimized (controlled release)	[32,48]
Surface properties	Tunable roughness and porosity	Enhanced reactivity	Stable surface	Tailored multifunctional surface	[26,48]
Fabrication complexity	Moderate	Moderate	Moderate	High	[11,33,34,35,48]
Clinical maturity	Clinically used	Limited (controlled use)	Increasing interest	Experimental/emerging	[7,22,48]

summarizes the main physicochemical, biological, and antibacterial characteristics of CaP, Ag, ZrO₂ and Ag–CaP–ZrO₂ composite coatings.

The multifunctional mechanisms and synergistic effects of Ag–CaP–ZrO₂ composite coatings are schematically illustrated in Figure 4.

These mechanisms are supported by experimentally reported observations in the literature, including controlled Ag⁺ ion release, reduced bacterial adhesion, enhanced corrosion resistance, and improved osteoblastic response associated with multifunctional Ag–CaP–ZrO₂ coatings [73,74,83].

At the molecular level, the antibacterial performance of multifunctional coatings is strongly influenced by ion release behavior and coating microstructure. Metal ions such as Ag⁺, Zn²⁺, Cu²⁺, and Ga³⁺ can interfere with bacterial membrane integrity, protein activity, enzymatic pathways, and microbial DNA replication. In addition, oxide-based surfaces and nanostructured architectures may promote reactive oxygen species (ROS) generation and modify local electrochemical interactions, thereby contributing to bacterial inactivation. Parameters such as coating porosity, crystallinity, grain size, and ion diffusion kinetics further regulate the accessibility and sustained release of antibacterial species, ultimately influencing biofilm inhibition and long-term antimicrobial efficacy [42,43,46,69,72,74].

3. Clinical Perspectives and Limitations

Multifunctional bioceramic coatings, particularly hybrid systems based on Ag–CaP–ZrO₂, have demonstrated promising performance in numerous in vitro and preclinical studies, especially in terms of antibacterial activity, bioactivity, and corrosion resistance. However, their translation into clinical practice remains limited and represents a major challenge in dental implantology. One of the primary limitations lies in the relevance of the experimental models used. Most studies rely on simplified conditions, including mono-species bacterial cultures such as Staphylococcus aureus or Escherichia coli, which do not accurately reflect the complexity of the oral microbiome or the dynamic interactions of polymicrobial biofilms under real clinical conditions [86]. In addition, these models often fail to account for host immune responses, salivary factors, pH fluctuations, and mechanical loading conditions characteristic of the oral environment.

Another critical challenge concerns the long-term durability of antibacterial properties. The effectiveness of silver-based coatings strongly depends on the controlled release of Ag⁺ ions. Rapid ion release may induce cytotoxic effects toward host cells, particularly osteoblasts, whereas insufficient release may allow bacterial persistence and biofilm formation. Furthermore, potential bacterial adaptation or tolerance to modified surfaces may compromise long-term antimicrobial efficacy [50,87,88].

The physicochemical and mechanical stability of coatings also represents a major concern. In the oral environment, implants are subjected to complex conditions, including cyclic mechanical loading, temperature variations, pH fluctuations, and exposure to salivary enzymes. These factors may lead to progressive degradation of coatings, partial dissolution of bioactive phases, or delamination of surface layers, ultimately compromising their integrity and long-term performance [89].

In multifunctional hybrid coatings, long-term interfacial stability represents an additional challenge due to the coexistence of multiple phases with different physicochemical properties. Differences in thermal expansion behavior, ion diffusion, and local electrochemical activity may progressively induce interfacial stress, microstructural degradation, or partial delamination under physiological conditions. Furthermore, the reproducibility of multifunctional coating architectures remains difficult to achieve at an industrial scale because small variations in fabrication parameters may significantly affect coating composition, phase distribution, and functional performance. These limitations highlight the need for standardized fabrication protocols and long-term in vivo evaluation before routine clinical implementation [53,72,83,89,90].

Moreover, significant limitations remain regarding the reproducibility of fabrication processes and their scalability for industrial applications. Advanced deposition techniques (such as sol–gel, electrodeposition, and plasma spraying), although allowing precise control of surface properties, are often costly, sensitive to processing parameters and difficult to standardize, which hinders large-scale clinical implementation [90].

In addition, the lack of standardized experimental protocols represents a major obstacle to the comparison of results across studies. Variations in coating methods, testing conditions, bacterial strains, and evaluation criteria make it difficult to establish robust conclusions and slow down clinical validation of these technologies.

In this context, future research should focus on the development of “smart” or stimuli-responsive coatings capable of dynamically adapting to the biological environment. Systems with controlled or triggered release mechanisms (e.g., pH-responsive, enzyme-responsive, or mechanically activated systems) represent particularly promising strategies to optimize antibacterial efficacy while minimizing cytotoxic effects.

Recent advances in additive manufacturing have also stimulated growing interest in 3D-printed polymer- and composite-based materials for dental implant applications. These technologies allow the fabrication of patient-specific implants with complex architectures and controlled porosity, which may enhance tissue integration and biomechanical adaptation. In particular, polymer–ceramic composites incorporating bioactive phases such as hydroxyapatite or zirconia have shown promising biological performance. However, compared with Ti6Al4V implants modified by multifunctional bioceramic coatings, these systems may present limitations related to lower mechanical strength, long-term degradation behavior, wear resistance, and limited intrinsic antibacterial activity. Future research may explore the combination of additive manufacturing technologies with multifunctional antibacterial and bioactive coating strategies to develop next-generation implant systems with enhanced personalization and clinical performance [91].

Furthermore, the integration of multifunctional approaches combining antibacterial, immunomodulatory, and osteogenic properties may provide improved control of host–implant interactions. Finally, significant efforts should be directed toward the development of more representative biological models, including polymicrobial biofilms and relevant in vivo systems, as well as long-term clinical trials. The standardization of experimental protocols and rigorous evaluation of safety and efficacy will be essential for successful clinical translation [29,30].

4. Conclusions

Multifunctional bioceramic coatings applied to titanium dental implants represent a promising strategy for simultaneously improving corrosion resistance, bioactivity, and antibacterial performance of implant surfaces. This review highlights the complementary roles of CaP, Ag, and ZrO₂-based coatings, as well as the growing importance of hybrid systems in the development of next-generation dental implants.

CaP coatings are distinguished by their excellent bioactivity and their ability to promote early osseointegration, although their intrinsic antibacterial activity remains limited. In contrast, silver-based systems provide strong antimicrobial efficacy through the release of Ag⁺ ions but require precise control to avoid cytotoxic effects. ZrO₂ plays a crucial role as a stable matrix and protective barrier, significantly enhancing corrosion resistance and mechanical performance, while also serving as a versatile platform for advanced surface modifications.

In this context, hybrid Ag–CaP–ZrO₂ coatings emerge as a particularly effective approach to address the major challenges in dental implantology. By combining antibacterial activity, osteogenic potential, and physicochemical stability, these multifunctional systems enable synergistic effects and optimized control of ion release kinetics. These properties position hybrid coatings as strong candidates for improving long-term implant performance and reducing the risk of peri-implant infections.

Nevertheless, the clinical translation of these technologies remains dependent on overcoming several key challenges, including long-term coating stability, precise control of ion release behavior, and the standardization of experimental protocols. Furthermore, the widespread reliance on simplified biological models continues to limit the clinical relevance of current findings.

Future research should focus on the development of smart, stimuli-responsive implant surfaces capable of dynamically interacting with their biological environment. The integration of additional functionalities, such as immunomodulation and host–biofilm interaction control, may represent a major advancement in the design of next-generation coatings. Furthermore, well-designed in vivo studies and long-term clinical trials will be essential to validate the safety, efficacy, and durability of these systems.

In conclusion, ZrO₂-based coatings, particularly when combined with CaP and Ag, represent a strategic and highly promising direction for the development of multifunctional dental implants capable of meeting the complex biological, mechanical, and microbiological requirements of modern implantology. Their successful clinical translation will depend on continued advances in material design, process optimization, and rigorous clinical validation.