Advances in Dental Implants: A Review of In Vitro and In Vivo Testing with Nanoparticle Coatings

Abstract

Since tooth loss is a common problem in humans and is widespread worldwide, dental implants are an effective and optimal alternative to solve this problem. Thus, it is necessary to develop implants with improved surfaces that favor the osseointegration of the implant into the surrounding tissues and promote cell adhesion and proliferation while also preventing and inhibiting peri-implant infections that can lead to implant failure. In this regard, this review aims to provide new insights into nanotechnology and the use of nanoparticles in creating new coatings, the new trends for enhancing dental implant surfaces, and the current technologies used for this purpose. Although in vitro and in vivo tests attest to the possible use of the nanomaterials described in this review, further tests are needed to establish the optimal concentrations to be safe for clinical trials.

1. Introduction

Tooth loss remains a major challenge worldwide, as the rate of patients losing teeth altogether is on the rise. Through their loss, the functionality and esthetics of the oral cavity are impaired, causing discomfort for patients. In this regard, teeth have a major impact on people’s wellness, and it is important to maintain their health and longevity. Apart from aesthetics, teeth health is essential to maintaining the quality of patient’s lives, as teeth greatly impact speech, smiling, chewing, and social communication [1,2,3,4].

According to the World Health Organization (WHO) and their Global Oral Health Status Report from 2022 [5], it is estimated that oral diseases affect around 3.5 billion people worldwide, 2 billion people worldwide are suffering from caries of permanent teeth, and 514 million children are suffering from caries of primary teeth. At this point, frequent oral health diseases that represent a serious problem to public health include dental caries, periodontal disease, tooth loss, xerostomia, and oral precancerous and cancerous diseases [2]. Dental caries are the most known chronic infectious disease in dental hard tissue [6]. Cavities are biofilm-associated diseases caused by dental plaque accumulation on the teeth surfaces, in general, produced by cariogenic bacteria (e.g., Streptococcus mutans, Rothia spp., Actinomyces spp., Lactobacillus spp., Bifidobacterium spp., Selenomonas sputigena) and fungi (e.g., Candida albicans), which accumulate and form biofilm on the tooth surface. In general, Streptococcus mutans plays a key role in this process [7,8,9]. The formation of cavities involves the presence of sugars, which are further metabolized and transformed into acids that gradually lead to demineralization of teeth structure over time, with host factors (e.g., saliva) favoring the development of cavities in the oral cavity [6,8].

On the other hand, periodontal disease represents an inflammatory condition characterized by the progressive destruction of the periodontal complex’s soft and hard tissue; untreated, it can lead to loosened tooth cavities and tooth loss [10,11,12]. Based on WHO’s statements [5], 19% of global adults are diagnosed with severe periodontal disease. Untreated dental cavities and periodontal disease can cause edentulism, a severe condition characterized by teeth loss, and it can affect general health because of the absence of proper chewing and speech [13].

Replacing the missing teeth requires a strategy based on the patient’s overall condition, number of missing teeth, hard and soft tissue structure, and developmental stage [14]. The first option to solve this problem is using dentures bonded to the surrounding tissues or healthy teeth [3]. Therefore, dental implants represent a great alternative and a common practice in dentistry to solve the problem of tooth loss. In this way, dental implants have become a popular choice for replacing missing teeth or entire dentitions, and they have the potential to enhance people’s life standards [15]. Dental implants are mainly manufactured of titanium or other biocompatible materials. The implant is introduced into the alveolar bone, where it gets anchored because of the osseointegration process [16]. Osseointegration represents a complex process resulting from the structural and functional interaction of the implant and bone tissue [16,17]. However, various complications can occur after the implantation, such as infections, poor osseointegration, and other side effects that may result in dental implant failure [18,19]. These issues can be influenced by factors like age, sex, smoking, maxillary implant place, systemic diseases, quantity and quality of bone, oral hygiene and maintenance, and implant surface [20].

Numerous studies in this field are leading to an advanced and performant implant that can be affordable to needy patients. In this regard, researchers modified and improved the dental implants, making the surgical procedure easier, and developed characteristics for the implant that should be safe to use, resistant esthetically, and functionally similar to the natural tooth [18]. Implants should also have the following features: osseointegration, bone regeneration, antibacterial activity, and biocompatibility [21]. Hence, based on their biocompatibility, implant materials can be classified as bioinert, biotolerant, and bioactive, and based on their composition, they can be classified as metal and metal alloys (e.g., titanium, iron, cobalt-chromium, copper, and tantalum), natural polymers (e.g., collagen, chitosan, cellulose, bone morphogenic proteins, and demineralized bone matrix), and ceramics (e.g., alumina, zirconia, hydroxyapatite, and calcium phosphate) [18,21,22]. Biotolerant materials (e.g., cobalt–chromium alloys, stainless steel) can increase osteogenesis in the bone because of the implant’s irritating effect in the interaction area, leading to encapsulation in a layer of soft fibrous tissue that isolates the implant from the bone. However, this aspect may be important for the implants’ long-term stability as the integration process may be hindered. Bioinert materials (e.g., alumina, zirconia, tantalum, and titanium and its alloys) can induce contact osteogenesis when they are used in adequate mechanical conditions. These materials tend to be well integrated with bone because of the material’s chemically inert surfaces (bonding without causing chemical effects) to the enclosing tissues and body fluids. Their chemically inert surfaces can limit their ability to improve bone regeneration around the contact surface. Meanwhile, bioactive implants produce chemical interactions with bone and allow it to deposit on the implant surface [21,23]. Yet, such properties can be modified by adjusting implant composition or surface modifications, which is a strategy to improve implant performance, properties, and longevity. Additionally, these materials can be used to develop an artificial tooth, and each can be used to produce separate components that make up the complex construction of a dental implant (Figure 1) (implant, abutment, crown) [18,21]. Therewith, implants can be divided into several categories depending on the number of pieces used in the fabrication of the implant (one-piece implant and two-piece implant), the method of implantation (one-staged method and two-staged method), and the density (hollow implants and solid implants) [18].

In a one-piece implant, the implant body and the abutment are manufactured as a single piece, while in a two-piece implant, the implant body and abutment are connected with a screw. Both implants gave a high survival rate (4–6 years) [24], but both have advantages and disadvantages. The use of a one-piece implant can lead to avoiding screw loosening and fast rehabilitation with a reduced operating time. Likewise, one-piece implants do not damage surrounding tissues and lead to better use of space limitations [18,25]. Instead, in two-piece implants, bone mass loss can occur because of the space between the implant and the blunt, resulting in inflammation [26].

In recent years, research has been leading to the evolution of implant design to improve dental implants. Aspects such as shape (e.g., cylindrical or conical), implant diameter and length, thread pitch, and depth are important for biomechanical fixation and interaction with bone tissue. The implant design can also determine the integration of the implant with the bone tissue, and among the methods to improve the implant surface is porosity (e.g., tantalum-based implant with a porous surface that mimics the topography of the bone tissue surface) [22,27,28]. A similar topography of the implant’s surface can enhance the osseointegration process. This represents a key factor in the success rate of the implant and the implant’s interaction with bone tissue. However, weak osseointegration leads to micro-mobility and implant loss [29]. The implant’s features (such as physicochemical properties) and the recipient site bone determine the interaction between the implant interface and bone that contributes to the success or failure of osseointegration [27]. In this regard, a strategy to improve these interactions is represented by surface modifications that can change implants’ physical, chemical, and pharmacological properties and improve the physiological environment responses for the osseointegration of dental implants [30]. For example, surface properties such as hydrophobicity and hydrophilicity provide a better interaction among the surface, biological fluids, and cells. Thus, this ensures better wettability, which can generate a large surface area of adhesion [22,27,28,30].

Roughness can improve cell adhesion and better integration into bone tissue, while wettability can help the surface retain biological fluids. This contributes to improved cell–implant interactions [30]. In addition, changes in roughness can shorten healing time, favor osseointegration, and are preferable for areas with poor bone quality. Thus, it has been observed that the failure rate of implants with surface roughness modification has significantly decreased. However, a major disadvantage of the method is the possibility of biofilm adhesion, which may increase the susceptibility of implants to peri-implant damage [30].

Another way to improve the surface of implants is to coat them. Coating methods can be considered a conventional surface treatment strategy for dental implants and can improve characteristics such as biocompatibility and mechanical properties, avoiding implant failure in this way. However, some limitations may lead to poor uniformity and adhesion of the coating. Coatings can be made with bioceramics; calcium-, phosphate-, and hydroxyapatite-magnesium; and carbon- and nitrogen-based materials that can mimic bone characteristics and enhance the osseointegration of the implant, osteoblast proliferation, and implant bioactivity. Thus, coatings can provide the implant with properties such as significantly better biocompatibility, corrosion resistance, and superior mechanical properties. Organic coatings made of polymers, such as chitosan, collagen, PEG (polyethylene glycol), and PLGA (poly(lactic-co-glycolic acid)), and bone stimulatory factors enhance bone density. Using organic coatings on implant surfaces produces proper healing [29,30,31,32]. However, the coatings can be improved using several nanoparticles like silver (AgNPs), titanium dioxide (TiO₂) nanohydroxyapatite (HAp), cubic zirconia, pectins, carbon nanotubes, and ultra-nanocrystalline diamond, using physical and chemical methods to be added on the implant surface [33]. The coatings can be deposited using physical deposition methods (e.g., plasma spray technology, plasma immersion ion implantation, laser cladding), chemical methods (e.g., thermal oxidation, anodic oxidation, acid etching and etching, hydrothermal treatment, micro-arc oxidation), but also by biological methods (e.g., layer-by-layer self-assembly) [33,34].

This review acknowledges areas of ongoing discussion about dental implant coatings. It points out the need for further research to consolidate their role and importance in the dentistry field and clinical practice to improve patient’s quality of life and to discover new strategies and opportunities. In this regard, papers published in English between 2014 and 2024 (e.g., reviews, in vitro and in vivo studies) were selected and analyzed in this review to provide a perspective on the evolution of ongoing research in the field of nanotechnology for dental implant coatings. The information was retrieved from scientific databases such as Google Scholar, PubMed, MDPI, Science Direct, Scopus, Web of Science, SpringerLink, and Wiley Online Library, using a variety of combinations among the following keywords: “dental implants”, “implant coatings”, “inorganic coatings”, “surface modification”, “nanoparticles”, “nanotechnology-based dental implant coatings”, “implant osseointegration”, “antimicrobial activity”, “in vitro study”, and “in vivo study”.

2. Nanoparticles in Dental Implant Coatings

2.1. Types of Nanoparticles and Their Mechanism of Action

Nanomaterials are defined as materials that measure on the nanoscale or encompass in their structure nanoscale structures, and they consist of nanocomposites, nanoparticles, nanocoatings, and more, and have started to be increasingly used in the stomatology field [35,36]. Applications such as dental diagnostics, preventive dentistry, dental materials, prosthodontics, endodontics, implantology, and regenerative dentistry are interested in nano-engineering dentistry. Nanomaterials provide implants with new and complex features such as stimulating cellular bioactivity, leading implicitly to implant integration, improved antimicrobial effect, and controlled drug release [3,36].

A main challenge for dentistry is the development of resistant materials to cope with the oral cavity environment [37]. Moreover, the immune system can act against dental implants, eventually causing their failure. Even though the immune responses to non-degradable alloy implants are well-known, there is still debate and ongoing research regarding immune responses against degradable alloy implants [38]. However, there is a consensus that the biodegradation of dental implants due to immune system interactions can compromise their longevity and effectiveness. Important focus points to mitigate these unwanted outcomes include careful implant material selection, implant surface modifications, and implementation of techniques that minimize harmful particle release. In particular, nano-engineered implant surfaces have been tackled for their ability to enhance integration with bone and reduce immune-mediated degradation [23,39,40,41,42]. Through such approaches, the risk of implant biodegradation influenced by the immune system can be significantly reduced, leading to improved outcomes for patients.

Therefore, nanoparticles have started to be studied in this direction due to their physicochemical and biological properties, such as high specific surface area, small size, solubility, surface chemical reactivity, high surface stability, thermal conductivity, and biocompatibility with bone tissue [37]. Despite these properties, studies need to continue, as some nanoparticles may have limitations, such as toxicity by provoking inflammation response and irreversible damage to cells because of oxidative stress production, and can influence basic cellular processes [43]. Given the limitations of dental implants, including peri-implant inflammation, bone loss, or limited osseointegration, researchers are trying to develop new strategies to improve implant longevity and reduce the side effects postimplantation. In this regard, research interest is growing in designing dental implants with enhanced features that can provide bioactive properties that can elicit an increased biological response, boosting the success of the implant without problems and failures [16,37].

Thus, nanoparticles are being studied to produce methods to improve implant surfaces. The modifications they can bring can improve the antimicrobial effect and the integration of the implant into soft tissue and bone [16,42]. Additionally, surface nanocoatings (e.g., nanodiamonds, titanium dioxide, or silver nanoparticles) can enhance implants’ mechanical properties [44]. It was observed that nanoparticles can improve corrosion resistance, leading to prolonged implant life [45]. Additionally, nanoparticle sizes can influence their antimicrobial effects. It was demonstrated that nanoparticles with sizes below 10 nm have an increased effect compared to larger-sized particles [46]. However, nanoparticles promote cellular signaling mechanisms, while those with porous or core-shell structures can act as drug delivery systems for antibacterial or immunomodulatory drugs, attenuating inflammation and inhibiting bacterial growth [45]. In the following subsections, nanoparticles that are used to modify implant surfaces will be presented.

2.1.1. Inorganic Nanoparticles

Silver

Silver nanoparticles (AgNPs) are among the most widely used particle types in nanocomposites and in mixtures for dental implants and dental applications due to their antimicrobial effects against bacteria, fungi, viruses, and anticaries. They can also be used for the treatment of oral cancer. It has also been shown that the antimicrobial effect of silver nanoparticles depends on their size, shape, concentration, and colloidal state and is associated with the release of cationic silver and its oxidative potential. AgNPs’ efficacity increases at dimensions under 50 nm, especially between 10–15 nm, because they become more stable and can easily penetrate the cell membrane, increase cell permeability, and produce cellular death. The AgNPs’ shape affects their physicochemical properties and determines the interaction of the nanoparticles with microorganisms. Then, it was demonstrated that the truncated triangular shape of AgNPs has a higher antimicrobial effect than spherical and rod-shaped nanoparticles. At the same time, AgNPs, at low concentrations, can act against methicillin-resistant Staphylococcus aureus (MRSA) strains and other bacteria. It has also been observed that Gram-negative strains are much more susceptible than Gram-positive ones [36,47,48,49,50].

Underlying the antimicrobial effect (Figure 2) of AgNPs on pathogens is the interaction between silver ions (Ag⁺) and negatively charged molecules, such as phosphorus and sulfur, which are the main components of the cell membrane and DNA. Thus, they provoke damage to the cell membrane of bacteria cells, causing morphological changes. AgNPs continuously release Ag⁺, which penetrates the cell, causing the respiratory enzymes to be deactivated, reactive oxygen species (ROS) to be produced, and adenosine triphosphate (ATP) production is interrupted. ROS can denature DNA and affect its replication and then cell propagation. Ag⁺ can limit protein synthesis, causing denaturation of ribosomes in the cytoplasm. Also, AgNPs can produce the same effect by themselves because their nanosize allows them to penetrate the cell membrane, damage cellular organelles, and produce cell lysis [48,51,52,53,54].

AgNPs have been shown to have an enhanced antimicrobial effect when used together with antibiotics. Thus, AgNPs have been used to coat the titanium substrates of implants and have been shown to have a significant antimicrobial effect against relevant oral pathogens, including Staphylococcus spp. and Pseudomonas spp., at a lower concentration, and can prevent infiltration into the space between the implant and the abutment [47,48,49,55,56,57,58]. It has also been shown that AgNP-coated titanium implants do not produce a cytotoxic effect on osteoblast cells, promote bone mineralization, and form new bone tissue [42,59].

Gold

Gold nanoparticles (AuNPs) are used in the biomedical field due to their versatile properties, which are especially appealing because of their safety and chemical inertness. AuNPs are also advantageous because their shape, surface area, and size can be tailored according to targeted application. In addition, the antimicrobial properties of AuNPs can be potentiated by modifying their physicochemical characteristics by functionalization with different compounds (e.g., antioxidants, biological ligands, organic molecules, and dendrimers). In the dental field, AuNPs can be included in dental materials (e.g., titanium, polymethylmethacrylate, and resin composites) due to their antimicrobial effect on bacteria such as Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa [60,61,62,63,64]. It has been shown that AuNPs can interact with the cell membranes of pathogens and can denature them by altering the permeability of the cell membrane and interacting with nucleic acids. The presence of AuNPs can also lead to the chelation of magnesium ions, which is essential for membrane stability. Once they penetrate bacteria, AuNPs disrupt vital functions by the following processes: inhibition of enzyme activity by neutralizing bacterial plasmids, reducing the number of active plasmids, fragmentation of DNA and triggering cell death, and interfering with the synthesis of proteins essential for bacterial survival. At the same time, for an enhanced antimicrobial effect of antibiotics, AuNPs are used, facilitating the penetration into bacteria (e.g., AuNPs + vancomycin have been shown to affect resistant bacteria such as E. coli and S. aureus) [65]. These properties are attributed to these particles’ extremely small size, thus involving electrostatic interaction between Au atoms and microorganisms’ negatively charged cell membranes. Also, AuNPs can enhance the osteogenic process on osteoprogenitor cells after intracellular uptake. Furthermore, it was observed that AuNPs, with sizes of 30–50 nm, enhanced the differentiation of mesenchymal stem cells into osteoblasts [60,61,62,63].

Zinc Oxide

Zinc is an important trace element for the human body, found in bone, hard dental tissue, muscle, and skin tissues. Zinc oxide-based nanoparticles (ZnO-NPs) are also commonly used in various applications in different branches of dentistry (e.g., endodontics, regenerative dentistry, periodontology, cancer diagnosis, dental implantology, etc.) [66]. The use of these nanomaterials is preferred, as they have high biocompatibility, are nontoxic, have remarkable mechanical, chemical, and electrical properties, have a strong anti-corrosive effect, and can exert an increased antimicrobial effect on many Gram-positive and Gram-negative strains, as well as fungi, by generating ROS (e.g., H₂O₂, HO⁻) that affect lipids, proteins, and DNA of bacteria [67,68]. These properties are influenced by factors such as the size and shape of the nanoparticles and the presence of UV radiation. Thus, small particles can exert a high antimicrobial effect due to their large specific surface area. At the same time, their shape (e.g., spherical, acicular) determines the degree of penetration into the biofilm and the bacterial efficiency [69]. It has been observed that the use of UV radiation may lead to an enhanced antimicrobial effect due to increased ROS. In terms of this effect, ZnO-NPs can retard bacterial growth and denature the cell membrane by generating oxidative stress, which leads to the loss of structural integrity and impede the metabolic functions of pathogens by generating Zn²⁺ ions. Another effect that ZnO-NPs have on cells is to modify their negative surface charge, thus preventing them from attaching to substrates by interfering with the quorum sensing communication mechanism. It also inhibits the formation of extracellular polymeric substances that are necessary for biofilm formation [68,69]. It has been observed that ZnO-NPs can be used in the coating of dental implants, having bactericidal effects on strains isolated from the oral cavity but also improving osseointegration by promoting osteoblast cell proliferation at the implant [66].

Strontium

Strontium (Sr) is an important cation for bone and, at the same time, a material used in the fabrication of nanoparticles (SrNPs) that are used in controlled drug delivery, cancer treatment, chemosensors, and bioimaging. SrNPs have the potential to accelerate bone healing by inducing osteogenic and osteoinductive processes, making them an ideal candidate for use in implantology. SrNPs can increase replication, osteoblast cell differentiation, and bone matrix mineralization, while released Sr²⁺ ions can induce VEGF synthesis of osteoblasts. Sr may have an increased antimicrobial effect on peri-implantitis-causing bacteria, used alone or with other metal ions such as Ag [70,71,72].

Titanium Dioxide

In general, titanium and its alloys are used in implant manufacturing because of their excellent mechanical properties and their high biocompatibility. Naturally, Ti implants form a stable, protective oxide layer contributing to high corrosion resistance. This may contribute to a much better interaction with biological fluids and the surrounding tissues, such as bone tissue, where Ti implants can promote osseointegration [73,74]. Titanium dioxide-based coatings are widely used due to their ability to improve the surface properties of dental implants. Thus, these coatings are biocompatible, nontoxic, and promote osseointegration while protecting the implant from corrosion and biofilm formation [75,76,77]. The antimicrobial effect can be exerted on different microorganisms such as Gram-negative and Gram-positive bacteria, algae, fungi, protozoa, and viruses [77]. TiO₂-based coatings can stop the bacteria adhesion on the substrate surface by altering its surface free energy and increasing the electron donor surface energy [78,79]. On the other hand, TiO₂ tubular particles present a higher interest in implant coating because of their roughness and high surface area, which sustain osseointegration and a great cytocompatibility with osteoblast and bone marrow mesenchymal stem cells, impart a uniform, stable structure, and they can be used as drug delivery systems [75,76,77].

Hydroxyapatite

Some of the most important natural compounds that are part of the bone test are calcium carbonate and calcium phosphate, which are being intensively studied due to their increased biocompatibility with natural bone and tooth structure [80,81]. Hydroxyapatite (HAp) is an osteoconductive material that can accelerate bone healing by forming direct bonds with bone. In contrast to its usual form, nanohydroxyapatite is a biocompatible material, available in a variety of forms (e.g., mesoporous microspheres with hierarchical nanostructures, mesoporous rhomboids or hollow microspheres) [82], similar to inorganic bone structure, which can exhibit improved properties (e.g., increased solubility, high surface energy, improved biocompatibility, high specific surface area, excellent bioactivity), as well as high osseointegration. It excels in biomedical applications such as dental implantology, enabling much better fixation of the implant into the bone tissue. HAp can be used to coat implants made of stainless steel and titanium, helping to integrate them with the bone tissue and stimulate the formation of new bone tissue. It may also exhibit anti-inflammatory capacity by modulating monocytes and macrophages but may also inhibit the growth of Gram-negative and Gram-positive bacteria. HAp may exhibit enhanced properties, forming composites with either metal nanoparticles (e.g., ZnO-NPs) or chitosan to enhance osteoblasts’ antimicrobial effect, adhesion, and differentiation [80,81,83,84]. However, they also present disadvantages, such as high fragility and rapid aggregation [83,85].

2.1.2. Carbon-Based Nanoparticles

Researchers are showing an increased interest in the biological applications of carbon-based materials due to their extraordinary chemical and physical properties, which help them become an example of novel nanostructures with revolutionary potential in the medical field [86,87]. Thus, these materials are being investigated for a wide variety of dental applications [86].

Carbon Nanotubes

Carbon nanotubes (CNTs) are a type of carbon-based nanomaterial that has been studied as a coating material for dental implants. CNTs exhibit superior mechanical properties, are biocompatible, and can stimulate bone growth by modulating their surface with functional groups such as amino, phosphate, and carboxyl. CNTs also exert an antimicrobial effect through mechanisms such as cell lysis, and in this regard, they can prevent peri-implant infections by piercing the bacterial cell walls [87,88]. The microorganism’s cell wall and membrane may sustain significant structural damage as a result of CNTs. When pathogens are exposed to CNTs, they experience oxidative stress, which results in the breakdown of cell membranes and the discharge of intracellular materials. Furthermore, they can biologically separate cells from their surroundings, ultimately resulting in the generation of harmful compounds like reactive oxygen species and exposing the cell to oxidative stress, which eventually causes biological death. Determining the nanotubes’ length during interactions with the cell membrane is crucial. For instance, a shorter tube was shown to have greater bactericidal activity, whereas a shorter CNT showed less toxicity to the pathogens [87,88,89].

Nanodiamonds

Nanodiamonds (NDs) represent unique nanocarbon structures made by layered structures and sp²- and sp³-hybridized carbons. NDs are composed of carbon NPs with truncated octahedral architecture, with a 2–8 nm diameter, and can be used in various medical applications such as targeted drug delivery systems, tissue engineering, and gene therapy [90,91,92]. Diamond nanostructured coatings can increase wear resistance and prevent the leaking of metal ions from dental implants. Also, NDs are bioinert materials that have excellent properties, such as high biocompatibility, and can promote cell implant substrate interactions, such as adhesion, proliferation, and stimulation of osteoblast differentiation [93]. Ultrananocrystalline diamond coatings (UNCD) are nanostructured materials made of diamond crystals with a size ranging between 3 and 5 nm with good biocompatibility. Also, this material has high hardness and low coefficient of friction compared with other carbon-based coatings. This novel material can furnish superior electrochemical properties to implants. It was observed that UNCD has a high corrosion resistance at extreme pH conditions. Likewise, UNCD coatings present nanometric-sized structures that promote the interaction between the material and cells, favoring coated implant osseointegration [94,95]. Additional investigations are required to comprehend the biological compatibility of NDs in dentistry [92].

2.2. Advantages of Nanoparticles Used in Implant Coatings

The developing field of nanostructured implants is continuously growing and involves considerable enhancements in the medical and dental fields. In this regard, surface nanofeatures contribute to solving medical problems, such as microbial infections, and demand the discovery, evolution, and use of new biomaterials for better properties of dental implant design and surface engineering techniques such as nanoscale coating, patterning, functionalization, and molecular grafting [96]. From the previously analyzed data, nanoparticle-based inorganic, metallic, and carbon-based coatings lead to significant improvements in dental implant surfaces, increasing their biocompatibility and bone integration. In this respect, nanoparticle coatings can optimize the implant’s longevity and decrease risks related to postimplantation infections and corrosion [97]. In principle, metallic nanoparticles have an antimicrobial protective role, inhibiting biofilm formation and implant loss. However, the presented nanoparticles can also stimulate the formation of new bone tissue by adhesion, proliferation, and stimulation of osteoblast cells, and they can prevent implant corrosion under the conditions of an oral cavity environment [75].

Although they have many advantages, the nanoparticles mentioned above also have limitations that do not yet allow their use in clinical trials. Even though nanoparticles promote implant osseointegration and antimicrobial protection, there are still concerns about the toxicity they may cause. For example, depending on factors such as dimension and shape, they can be easily absorbed in the oral cavity, causing toxic damage to tissues and organs, and more importantly, can be transported across the blood–brain barrier and lead to neurotoxicity [98]. Moreover, nanoparticles are reported to cause toxicity in high concentrations, not only to brain tissue but also to other organs such as the liver, kidneys, and spleen [99,100,101].

Table 1. Comparison of nanoparticles used in dental coatings.

Nanoparticle Type	Synthesis Methods	Advantages	Disadvantages	Refs.
AgNPs	Chemical methods: Chemical reduction Electrochemical Microemulsion Photoreduction Physical methods: Evaporation–condensation Laser ablation Gamma irradiation Lithography Biological methods: Bacteria Fungi Plant extract	High antimicrobial activity against bacteria, fungi, and viruses Antibiofilm Anti-inflammatory effect Osteoconductive activity	Ag+ ions released correspond with the toxicity of AgNPs At high concentrations, it can provoke neurotoxicity Might cause decreased mitochondrial activity in a variety of cell types Can trigger oxidative stress, DNA damage, and inflammation High tendency to accumulate in tissues	[98,102,103,104,105,106,107]
AuNPs	Chemical methods: Chemical reduction Sol-gel Turkevich Method Brust–Schiffrin method Electrochemical method Seeding growth method Physical methods: Laser ablation Ultrasonication Pyrolysis Nanolithography Biological methods: Bacteria Fungi Plant extract	Favorable antimicrobial effect Antioxidant and anti-inflammatory activities with less toxicity than other metal NPs Drug or gene delivery Enhancement of bone-related cell adhesion, proliferation, and differentiation	Long-term biocompatibility studies have not been performed Smaller NPs can accumulate in various organs, such as the liver, spleen, and brain Cytotoxicity and genotoxicity at a smaller size	[107,108,109,110]
ZnO-NPs	Chemical methods: Sol-gel method Chemical deposition Precipitation Solvothermal and hydrothermal methods Microwave-assisted synthesis Microemulsion Physical methods: Laser ablation Arc plasma Physical vapor deposition Ultrasonic irradiation Biological methods: Plant Microorganisms Algae	High antibacterial efficiency at low concentrations Antifungal effect Relatively low cost Enhance the mechanical strength of dental composites Improve implant osseointegration Enhance the osteoblast proliferation Prevent implants’ premature corrosion	Have deleterious effects on several key organs, including the lungs, kidneys, liver, CNS, reproductive system In animal models influenced fetal development Cause cell apoptosis, necrosis, genotoxic effects	[107,111,112,113,114]
HAp	Wet methods: Hydrothermal method Hydrolysis Mechanochemical method Precipitation Mechanochemical method Emulsion Sol-gel Dry methods: Solid state Mechanochemical High-temperature method: Combustion Pyrolysis Biological methods: Plant	Effective in the osseointegration of implants Favors absorption of proteins, adhesion, and proliferation of bone cells Enhance bone healing Enhance the bone–implant interfacial strength Considered harmless to the cell environment Similar chemical and crystallographic structures to those of the human bone Can immobilize proteins and growth factors	The particle size influences toxicity; smaller particles may damage some cells, while larger ones do not Some disadvantages include brittleness, low tensile strength, and fracture toughness Delamination of coating can produce marginal bone resorption and incompatibility with antibiotic incorporation	[42,115,116,117,118,119,120,121]
Carbon-based materials	Physical methods: Arc discharge Laser ablation Arc discharge method Chemical methods: Chemical vapor deposition technique Plasma-enhanced chemical vapor deposition Hydrothermal method	Toxicity can be reduced by chemical functionalization Can promote a suitable surface for bone growth Have tunable chemical, physical, and biological properties Enhance the growth of osteoblasts High antibacterial efficiency	Their toxicity is related to cellular uptake that is influenced by shape, size, and aspect ratio Their toxicity is related to impurities remaining during the synthesis or purification stage In high concentrations, they are toxic Produce inflammation High cost of production	[88,122,123,124,125,126]

summarizes these key aspects, facilitating a clearer understanding of their properties and risks as a dental coating.

In this respect, studies must continue addressing regulatory and safety concerns in dental coatings and the potential for long-term use. Research progress on nanoparticles in dental coatings is limited to in vitro and short-term in vivo studies, and some of them are presented in Section 4. Thus, further research is needed, leading to the emergence of clinical trials and enabling the use of NPs due to the numerous advantages mentioned.

3. Thin Coating Techniques for Nanoparticle Integration

3.1. Physical Vapor Deposition

Physical vapor deposition (PVD) (Figure 3) is a versatile and popular method for depositing thin films of materials on surfaces in a multitude of fields. It refers to the transfer of material at the atomic level under vacuum conditions, modifying the surface features of a substrate while not changing its biomechanical properties [127,128,129,130]. In this regard, the wanted material is transformed into the gaseous phase using laser energy, thermal energy, electron beam, highly energetic particles or ions, resistive heating, and so on [130]. This method can be utilized for implants made of metals and ceramics, significantly increasing their efficacy and quality. PVD-coated medical implants promote osseointegration, reduce wear and friction, boost corrosion resistance, and have antibacterial qualities, which lead to better patient outcomes, fewer problems, and overall higher quality of life for those who require implantable medical devices [127,128]. PVD processes can take the following steps: (i) evaporation or sputtering of target materials to produce a vapor phase; (ii) transportation of the evaporated material through an inert atmosphere to the substrate surface; (iii) supersaturation of the vapor phase to promote the condensation of metal nanoparticles, and (iv) deposition and consolidation of the nanocomposite as a coating on the substrate surface, followed by thermal treatment under an inert atmosphere to improve adhesion and structural stability [130,131,132].

PVD methods provide various advantages, including continually varying coating properties across the film. It also enables the deposition of alloy complexes, multilayer compositions, and specialized architecture. This adaptability has created, enhanced, and disseminated procedures for numerous processes [135]. For medical implants, PVD provides implant surface properties such as improved osseointegration, reduced friction and wear, increased corrosion resistance, and enhanced antimicrobial properties [127].

Sputtering deposition (SD) represents one of the most common PVD techniques used for dental implant coatings, thus obtaining a crystalline structure and a rough surface. For this technique, atoms or molecules of specific materials are released into a vacuum chamber and bombarded with high-energy ions, converting them into coating precursors. Film deposition is determined by several sputtering parameters, including material characteristics, sputtering power and time, gas flow rate, and operating pressure [96,136].

In a study conducted by Yongyi Xu et al. [137], the deposition of AgNPs on titanium surfaces using the magnetron sputtering deposition technique was investigated to evaluate the antimicrobial performance of these nanoparticles. Thus, this technology aided in the deposition of AgNP layers after the preparation of titanium surfaces by surface mechanical attrition treatment (SMAT), double acid etching, and alkaline heat treatment techniques to form a rough surface with micro and nano morphologies. It was observed that by deposition of AgNPs, aggregates are formed, which, by prolonging the sputtering time, form a uniform nano-Ag coating. By evaluating the antimicrobial potential, it was observed that the effects were promising without causing toxicity on osteoblast cells taken from mice. Thus, the newly formed surface exhibited excellent biocompatibility and improved antimicrobial properties, offering the possibility of developing a material that could revolutionize coatings for future implants. Another study conducted by Liao Juan et al. [138] explored the potential of AgNPs to coat titanium implants by sputtering deposition. Thus, the antimicrobial effect was evaluated, observing the efficacy of these nanoparticles to promote antimicrobial and anti-adhesive activities against strains such as S. aureus and E. coli, suggesting that AgNPs modified surfaces represent promising materials for creating implantable biomaterials.

Also, the techniques of macro-arc oxidation (MAO) and magnetron sputtering have been investigated by Luísa Fialho et al. [139] to coat tantalum (Ta)-based implant surfaces. The objective of the study was to obtain surfaces that mimic the morphology and chemical composition of bone tissue by obtaining porous layers of Ta₂O₅ containing calcium and phosphorus by the MAO technique, after which ZnNPs were deposited by the magnetron sputtering technique with or without a thin carbon layer to control the release of Zn²⁺ ions. Both coatings exhibited increased biocompatibility, promoted osteoblast cell adhesion and proliferation, and showed antimicrobial effects on S. aureus, but only the material without carbon film inhibited bacterial colonization.

This technique allows the production of thin films, presenting advantages such as rapid deposition, an optimal substrate heating temperature, and minimal impact on the film properties. It can also be used to deposit a wide range of materials. Also, the parameters can be easily controlled to obtain optimal particle sizes that deposit uniformly on the substrate due to the high energy atoms that favor the adhesion of the film to the substrate. At the same time, this technique is advantageous because it is possible to deposit on large, compact, and high-purity surfaces. Still, magnetron sputtering has certain drawbacks, such as plasma instability and the inability to carry out high-speed sputtering at low temperatures for strong magnetic materials due to magnetic flux constraints [140,141].

3.2. Chemical Vapor Deposition

Chemical vapor deposition (CVD) (Figure 4) represents a method that forms thin films or coatings on the substrate surface by a gas-phase process at a higher temperature by a chemical reaction occurring on/in the vicinity of the surface. The chemical gases are heated and converted into reactive species, which then react on the surface of the substrate to generate solid products. CVD techniques are classified as thermal and laser CVD [142,143,144,145]. Thus, CVD is an essential technology for implant surface modification due to its advantages, such as the easy handling of chemical reactions in the vapor phase to obtain precise, thin, uniform films that increase wear and corrosion resistance, implant durability, as well as its biocompatibility [145,146].

CVD and PVD differ in the procedures used; CVD simply uses chemical bonding to deposit the layer, whereas PVD uses physical forces. CVD employs mixed-source materials, whereas PVD employs pure-source materials. The precursor finally decomposes in CVD, leaving the desired source material layer in the substrate [96]. Implant coatings may involve the use of Hap, which aims to enhance the interaction between bone tissue and the implant by promoting bone cell growth and formation [145]. CVD has also been used by Rifai et al. [149] to obtain diamond coatings on titanium-based implants, which promoted cell proliferation and inhibited biofilm formation on implants. The nanocoating-based bioceramic CaP-O can be covered on Ti-based dental implants through the CVD technique. CaP-O bio-ceramic nanostructured coatings on metals promote bone connection, abrasion, bond resistance, and dissolution rate [22].

3.3. Sol-Gel Method

The sol-gel method represents a cost-effective approach that uses a solvent containing a chemically active component as a precursor, followed by hydrolysis and polycondensation reactions to form the sol at a low temperature [132,150,151]. The sol is gradually polymerized, forming a gel that is then dried and heated to form a layer. The sol-gel technique yields layers with consistent chemical and physical characteristics. A potential advantage for biomaterial applications is the capacity to construct nanoporous structures on implant surfaces for bioactivity control or transport of biologics and antibacterial agents, as well as the high purity and homogeneity of the coating [152,153]. The layers obtained by this process are determined by several factors that influence the sol-gel reaction, such as the nature of the catalyst, the starting material used to create the sol, temperature, thickness, pH, and others, and they can determine the rate of hydrolysis as well as the layer’s density. The sol-gel method can be used to create wear-resistant layers and generate nanocomposite layers of micron thickness. The gel obtained by this method has some limitations, such as susceptibility to cracking, time-consuming preparation, high raw material costs, and potential health and environmental risks [132,150,151]. Surface modification of implants to promote desired cell response and establish a chosen implant–tissue interface structure is a goal of modern implant design. Sol-gel-derived coatings are an appealing approach to reaching this goal. In this regard, sol-gel-formed calcium phosphate coatings have been shown to promote faster osseointegration rates on bone-interfacing orthopedic and dental implants, resulting in secure long-term implant-to-bone attachment [152]. For example, in this respect, sol-gel-deposited HAp coatings have been developed to improve osseointegration and reduce post-implant complications on titanium-based implant surfaces [153,154]. The sol-gel approach enables the production of nanoscale calcium phosphate deposits on implant surfaces. The sol can be applied to the substrate using a variety of processes, such as dip-coating, spin-coating, or spraying (Figure 5). The coating is applied in a gel state, and when dried, the precursor components create a thin layer [22,96].

3.4. Alkali Surface Treatment

Alkaline treatment of implant surfaces is a popular method for modifying dental implant surfaces using substances such as NaOH, forming a layer of sodium titanate on the implant surface and allowing the subsequent deposition of HAp. This method of forming dental coatings favors the formation of a robust substrate that promotes the formation of bone tissue around the titanium implants [96].

3.5. Acid Etching

Acid etching is a method used for the surface modification of implants and involves selective removal of material, thus forming roughness of the base material, being dependent on substrate type, microstructure, impurities, acid type, and exposure time. This technique can be used to form nanostructured surfaces of implants based on titanium and its alloys, tantalum, and cobalt–chromium–molybdenum alloys. It also leads to enhanced osseointegration of implants [96].

3.6. Anodization

Anodization is an electrochemical process by which nanostructures are formed on the surfaces of titanium-based implants to transform smooth surfaces into porous or nanotubular structures due to changes in parameters such as electrolyte composition, current, anode potential, and temperature. This process can enhance the interaction between the implant and bone tissue but also improves the adhesion of the bone tissue to the implant and its biomechanical properties [96].

3.7. Electrospinning

In recent years, electrospinning has grown in favor of a variety of biological applications due to its versatility. Electrospinning (Figure 6) is used to create nanofibers for various biomedical and dental applications, including tooth regeneration, wound healing, and caries prevention, by using electrostatic forces to obtain fibers with different dimensions and diameters [156,157,158,159]. Electrospinning utilizes a power source with a high voltage to create a significant potential difference between a grounded “collector” structure and a polymer solution or melt that is fed at a steady pace through an aperture, such as a blunt end needle. As the voltage increases, similar charges in the polymer fluid directly oppose surface tension, causing the typically spherical droplet at the aperture to expand into a conical shape. At a critical voltage, the attractive electrostatic attraction between the solution and the collector causes a jet of polymer solution to be blasted from the cone tip and onto the grounded collector surface [159].

Electrospun materials have unique features, such as a high surface area to volume ratio, increased cellular connections, and protein absorption, which facilitates binding sites for receptors. Electrospinning is an appealing approach for coating the implant surface with bioactive substances, being able to fabricate bioactive polymer nanofibers capable of the sustained release of therapeutic antimicrobial drugs and also hydroxyapatite-incorporated polymer nanofibers that can improve the osteointegration of titanium implants [157,158].

In a study carried out by Pierre Pouponneau et al. [162], they obtained a membrane by electrospinning based on poly-L-lactic-co-glycolic acid (PLGA) and poly(L-lactic-co-caprolactone) together with chlorhexidine diacetate (CHX) complexed with β-cyclodextrin (CD) to prevent the development of biofilm around the implant.

Another study by R. G. Shahi et al. [158] investigates the ability of tetracycline-loaded fibers to inhibit biofilm formation specific to periimplantitis pathogens (e.g., Porphyromonas gingivalis (Pg), Fusobacterium nucleatum (Fn), Prevotella intermedia (Pi), and Aggregatibacter actinomycetemcomitans (Aa)). Thus, the researchers used tetracycline hydrochloride (TCH) incorporated in solutions of polymer blends such as poly(lactic) acid (PLA), PCL, and gelatin (GEL) in distinct concentrations to obtain the following films: PLA:PCL/GEL, PLA:PCL/GEL-TCH-5 (5% TCH), PLA:PCL/GEL-TCH-10 (10% TCH), PLA:PC;/GEL-25 (25% TCH). Biofilm development was completely inhibited on fibers containing 10% or 25% TCH by weight. Fibers containing 5% TCH demonstrated full suppression of biofilm formation by Aa. Although increasing TCH concentration resulted in a considerable drop in CFU/mL, Pi was shown to be the most resistant microbe. Thus, it was discovered that tetracycline-containing fibers offer enormous potential as an antibacterial coating for dental implants.

Thus, electrospun fibers can lead to an advanced coating technique for dental implants due to their simplicity, scalability, and ability to mimic the natural extracellular tissue matrix. The fibers have the potential to influence the adhesion of cells to the substrate to lead to better implant integration, while the implant surface is more resistant to corrosion. At the same time, these fibers may exhibit increased antimicrobial potential, as they can be loaded with antimicrobial agents (e.g., vancomycin, AgNPs) [157]. However, studies are still needed to optimize and implement them in clinical trials.

3.8. Overview of Thin Coating Techniques for Nanoparticle Integration

Following the discussion in the previous subsections about each thin coating technique used to integrate nanoparticles into dental implant coatings, it is essential to compare these methods in terms of their key characteristics (e.g., layer thickness, deposition temperature, uniformity, cost, and complexity).

Table 2. Comparative table of thin coating techniques for nanoparticle integration.

Technique	Layer Thickness (µm)	Deposition Temperature (°C)	Uniformity	Cost	Process Complexity	Refs.
PVD	1–5	100–600	High precision	High costs	Complex	[163,164,165]
CVD	1–1000	800–1200	High precision	High costs	Complex	[166,167,168]
Sol-gel	<1	<100	Good precision	Low-cost	Simple	[169,170,171]
Electrospinning	<0.5	25–104	High precision	Low-cost	Simple	[172,173,174,175]

provides a clear comparison of layer thickness, uniformity, and cost, thus facilitating the choice of the optimal method that provides dental implants with their optimal properties. Hence, it can be seen that PVD, CVD, and electrospinning are high-precision techniques that can impart uniformity to coatings but involve high production costs and complex processes (in the case of PVD, CVD), and the easiest of them seems to be the sol-gel method. In this context, studies should continue to establish the optimal parameters for obtaining coatings for dental implants and subsequently choose the easiest method for their deposition.

4. In Vitro and In Vivo Testing of Nanoparticle-Coated Implants

The success rate of dental implants, osseointegration, and the prevention of post-implant infection are key challenges in developing dental implants that are improved over those on the market. Implant surfaces require modifications to prevent post-implant complications. In this regard, nanoparticle coatings have the potential to overcome these limitations, being able to stimulate osteogenesis and inhibit the appearance and development of bacterial biofilms. Thus,

Table 3. In Vitro and in vivo tests of nanoparticles as surface coatings of dental implants.

Testing Stages	Substrate	Material	Study aim	Observations	Ref.
In vitro	Titanium alloy (TiAl6V4) micro-implants	TiO2 and ZnO NPs	Evaluation of antimicrobial efficiency of TiO2 and ZnO nanoparticles (NPs) when used as a coating for orthodontic micro-implants	The 30 implants were divided into 3 groups according to the coating method and the materials used for coating, as follows: control group without coatings, TiO2-coated group by direct current (DC) spattering method, TiO2-ZnO-coated group by DC spattering method (TiO2), ZnO by vacuum laser. Antibacterial tests were performed on Staphylococcus aureus, Streptococcus mutans, and Porphyromonas gingivalis strains. This study demonstrated the importance of improving the surface of orthodontic microimplants by coating them with TiO2 and ZnO NPs to prevent biofilm formation.	[176]
In vitro/in vivo	Titanium disks	AuNPs	Evaluation of an osseointegrated titanium implant coated with gold nanoparticles to promote bone regeneration	The titanium implant surface was chemically treated with (3-Mercaptopropyl) trimethoxysilane (MPTMS) and an immobilized AuNP (Ti-AuNPs) layer on their surfaces by Au-S bonding. The in vitro results revealed that Ti-AuNPs improve osteogenic differentiation by increasing mRNA expression of osteogenic differentiation-specific genes in human adipose-derived stem cells (ADSCs). The in vivo data demonstrated that Ti-AuNPs had a considerable effect on osseous interface formation in New Zealand rabbit models. In vitro and in vivo experiments revealed that Ti-AuNPs can be used as osseo-integration-inducing dental implants to produce an osseous contact and maintain nascent bone development.	[61]
In vitro	Titanium disks	AgNPs	Determination of the antimicrobial potential efficacy of nanosilver-doped titanium biomaterials	The Tollens reaction was used to integrate silver nanoparticles into titanium disks across different periods. The antibacterial activity was further assessed using disk diffusion assays for microorganisms often recovered from the peri-implant biofilm: Streptococcus mutans, Streptococcus mitis, Streptococcus oralis, Streptococcus sanguis, Porphyromonas gingivalis, Staphylococcus aureus, and Escherichia coli. Cytotoxicity was assessed in vitro using a genuine human osteoblast cell culture. After 48 h of exposure, these surfaces were considerably hazardous to all of the bacteria tested. A concentration of 0.05 ppm was adequate to inhibit both Gram-positive and Gram-negative bacteria, with the latter being substantially more sensitive to silver ions. The nanosilver on the titanium gives an antibacterial action associated with the microorganisms involved in peri-implantitis. However, after the exposure of human osteoblasts to 0.1 ppm of silver ions, a significant decrease in cell viability was observed after 72 h.	[177]
In vitro	Titanium surfaces	HAp-NPs	Evaluation of the effects of coating titanium surfaces with HAp nanoparticles on cell behavior and osseointegration in vitro, comparing smooth-surfaced and HAp-activated implants	The test was carried out on two groups: the mach group, in which the titanium surface was mechanically machined without additional treatments, and the nano group, in which the titanium surface was coated with HAp-NPs. For surface testing, osteoblast cell culture (MC3T3-E1) was used to assess cell adhesion, viability, and differentiation. Osteoblast cells showed significantly higher viability on nano compared to mach surfaces. Cells in the nano group have a more stable adhesion, covering the surface evenly. The nano group showed more intense mineralization after 28 days of culture, indicated by denser calcium accumulation. Nanoscale HA-activated surfaces significantly stimulate the adhesion and differentiation of osteoblasts due to their increased roughness and favorable chemical composition.	[178]
In vitro	Ti cylindrical samples	Calcium-phosphate-based solution doped with AgNPs	Development of a functional coating on titanium (Ti) implants using a calcium-phosphate-based solution doped with AgNPs while evaluating the structural and chemical properties, biocompatibility, and antibacterial efficacy	AgNPs were synthesized with cubic morphology, and then electrolytic oxidation by mesh was performed using a solution containing the nanoparticles, nitrilotriacetic acid (NTA), and calcium–phosphate compounds. Cell adhesion and proliferation were performed on the U2OS cell line, while antibacterial assays were performed on the S. aureus strain. A porous surface with a silver-enriched ceramic layer was obtained. Cell adhesion and proliferation were significantly higher on AgNP-treated surfaces. AgNP-doped samples effectively inhibited bacterial adhesion and biofilm formation within 6 h. Combining silver and calcium phosphates created an environment favorable for osteogenic cell growth while providing antibacterial protection.	[179]
In vivo	Titanium alloy (TiAl6V4) implants	HAp and AgNPs	Examination of the osseointegration of AgNP-doped HAp coatings compared to conventional coatings using a rabbit experimental model	New Zealand white rabbits (12) each received two femur implants, one with conventional HAp and one with AgNPs-doped HAp. It was observed that the bone structure formed was similar between both implant types. The bone-to-implant contact was 52% for conventional HAp and 50.5% for HAp with AgNPs, with no statistically significant differences. AgNPs offer a potentially prolonged antimicrobial effect without interfering with bone formation.	[180]
In vitro/in vivo	Ti6Al4V ELI (Extra-low interstitial) alloy implants	TiO2-NTs	Exploration of enhanced osseointegration of nanostructured-modified titanium nanotube-coated and Simvastatin-loaded nanotube-coated dental implants	TiO2 nanotubes were created by electrochemical anodization and then loaded with Simvastatin using an ultrasonic immersion method. In vitro testing was performed on osteoblastic cell lines (MG-63) to assess cell viability, proliferation, and differentiation. In vivo testing was performed by using implants on rabbits for osseointegration using micro-CT analysis, histopathology, and torsion strength tests. In vitro tests demonstrated that at concentrations of 0.01 μM and 1 μM, the biocompatibility of the materials was very good, and they stimulated osteoblast differentiation. Also, bone mineralization was significantly better on drug-loaded surfaces compared to unloaded ones. In vivo tests showed that the coatings generated accelerated bone tissue development and great integration of implant coated and loaded with Simvastatin. Nanotubular surfaces showed improved cell adhesion and proliferation compared to smooth or acid-etched surfaces.	[181]
In vitro	Polyether ether ketone (PEEK) dental implant	Boron-doped nano-hydroxyapatites (B-nHAp)	Surface modification of PEEK implants with boron-doped nanostructured hydroxyapatite to improve implant bioactivity	The MTT study showed higher cell proliferation on PEEK implants treated with SPEEK sulfuric acid and SPEEK-B-nHAp compared to untreated PEEK. The cells attached better and formed a denser extracellular matrix on SPEEK-B-nHAp. ALP activity was significantly higher on SPEEK and SPEEK-B-nHAp.	[182]
In vitro/in vivo	Titanium implants	AgNPs and SrTiO3NPs	Development and evaluation of titanium implants with Ag and strontium titanate (SrTiO3) functional layers, highlighting their antibacterial and osteogenesis properties	Layered surfaces were obtained on titanium implants combining AgNPs and SrTiO3NPs to improve osseointegration and reduce the risk of peri-implant infections. Thus, sandwich layering improved the surface structure, combining micro- and nanometric structures. The SrTiO3 layer reduced the release of Ag ions by 30% and 15% on days 4 and 7, maintaining the antibacterial effects without affecting osteogenic cells. In vitro tests demonstrated improved osteoblast differentiation (increased ALP activity and mineralization). Antibacterial efficiency of approximately 93% against Staphylococcus aureus and 88% against Escherichia coli. In vivo tests of SrTiO3/Ag-layered implants showed significant increases in new bone formation compared to the control group.	[183]
In vitro	PEEK disks	Nano-dimensional zirconium phosphate (nZrP) and graphene oxide (GO)-based coating	Investigation of nano-dimensional zirconium phosphate (nZrP) and graphene oxide (GO)-based coatings of PEEK for the enhancement of hydrophilicity bioactivity, as well as antibacterial activity	nZrP/GO reduced the number of E. coli and S. aureus colonies 2-fold compared to untreated PEEK. Viability of MG-63 osteoblast and gingival fibroblast cells remained above 70% after 72 h, demonstrating the absence of cytotoxicity. After 28 days of immersion in SBF (Simulated body fluid), apatite crystals formed on the nZrP/GO surface, indicating bioactivity.	[184]
In vitro/in vivo	Zirconia implant	Nanoporous tantalum	Coating investigation of implant surfaces with a uniform layer of tantalum nanoporous to evaluate the surface topography, chemical composition of tantalum layer adhesion strength, hydrophilicity, and surface roughness, as well as the bioactivity and osseointegration of the TaNS layer	ZrO₂/TaNS showed significantly higher protein uptake, promoting enhanced cell adhesion. MC3T3-E1 osteoblast cells attached more rapidly and exhibited enhanced proliferation and differentiation on the surface covered with TaNS. The expression of osteogenic genes (RunX2, ALP, COL-1, OSX, OCN, OPG) was increased, indicating better osteogenic differentiation. Significantly greater bone formation around TaNS-coated implants was observed in animal models.	[185]

shows the in vitro and in vivo results of coatings with clinical potential. The in vitro studies evaluate the behavior of nanocomposites in contact with cells and determine the osteoconductivity and biocompatibility of these materials, and in vivo tests evaluate their behavior in complete biological environments.

5. Emerging Trends and Future Directions

Dental implants are a necessity because they can restore functionality, esthetics, and health to patients suffering from tooth loss. Therefore, the development of implants with improved properties, low potential for adverse reactions, and a low failure rate is a subject intensively studied by researchers, and the interactions between the implant surface and the surrounding tissues may determine a biological response that may lead to acceptance or rejection of the implant. In this respect, dental implants have developed considerably due to the interdisciplinarity among surface chemistry, biomechanics, and manufacturing technologies [29,186,187,188].

At present, strategies for their improvement involve surface modification to achieve nano-, micro-, and macro-roughness to improve dental implant osseointegration. Thus, using coating materials, such as hydroxyapatite or calcium phosphates, to roughen surfaces shows a high success rate due to superior mechanical fixation and favorable surface-bone–tissue interactions. An emerging strategy to improve implant surfaces is the incorporation of nanotechnology in the development of new coatings so that the nanoscale roughness modification allows protein uptake and cell adhesion to be much easier. Also, nanotechnology may lead to biomimetic coatings containing calcium phosphates, antiresorptive drugs, growth factors, and biomolecules (collagen type 1, BMP-2) to facilitate bone healing. At the same time, obtaining hybrid coating is another new strategy to improve dental implants. Thus, coatings with superior antimicrobial properties can be obtained using antibiotics and nanoparticles with antimicrobial properties and by combining them with peptides with such properties. These hybrid coatings may also be developed to enhance osseointegration using materials such as hydroxyapatite, titanium dioxide nanoparticles, extracellular matrix proteins with ceramics, and incorporation of growth factors. Thus, the research aims to obtain complex coatings to prevent infection, promote osseointegration, and stimulate bone tissue regeneration [29,186,187,188].

6. Conclusions

To summarize, this review has discussed the advancements in dental implant technology, emphasizing the importance of nanostructured coatings in enhancing osseointegration, biocompatibility, and antimicrobial properties while mitigating complications such as peri-implant infections and biofilm formation. Recent studies have revealed the ability of various nanoparticles (e.g., silver, gold, zinc oxide, titanium dioxide, and carbon-based nanomaterials) to confer superior physicochemical and biological characteristics to implant surfaces. Precise nanoparticle deposition and uniform coating formation can be obtained through various methodologies, such as PVD, CVD, sol-gel techniques, anodization, and electrospinning.

Although the use of nanotechnology in obtaining coatings for dental implants is under research and development, studies are still needed to improve their biological, physical, and chemical properties. Indeed, nanostructured modifications of implant surfaces using nanoparticles can lead to increased biocompatibility, improved corrosion resistance, and good surface–bone–tissue interaction, and by adding nanocomposites with osteoinductive properties and antimicrobial potential, they can contribute to better tissue healing, improved implant integration, and thus reduce the chances of implant failure. However, further interdisciplinary studies and in-depth testing are needed to help overcome existing challenges before translating emerging solutions to widespread human use.

Therefore, combining nanotechnology, material science, and bioengineering has the potential to generate novel high-performance coatings that enable the manufacturing of next-generation dental implants with improved longevity and reduced failure rates, subsequently enhancing patients’ quality of life.