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Review

Influence of Dental Implant Surface Modifications on Osseointegration and Biofilm Attachment

by
Wen Han
1,2,†,
Shuobo Fang
1,2,†,
Qun Zhong
1,2,* and
Shengcai Qi
1,2,*
1
Department of Prosthodontics, Shanghai Stomatological Hospital & School of Stomatology, Fudan University, Shanghai 200001, China
2
Shanghai Key Laboratory of Craniomaxillofacial Development and Diseases, Fudan University, Shanghai 200001, China
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this study.
Coatings 2022, 12(11), 1654; https://doi.org/10.3390/coatings12111654
Submission received: 13 September 2022 / Revised: 9 October 2022 / Accepted: 17 October 2022 / Published: 31 October 2022
(This article belongs to the Special Issue Antibacterial Coating in Biomedical Applications)
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Abstract

:
Dental implants have been widely applied in partially and fully edentulous patients and have shown predictable clinical outcomes, but there are still many cases of implant failures, such as osseointegration failure and peri-implant inflammation. To improve the success rate of implants, especially in improving osseointegration and antibacterial performance, various methods of implant surface modification have been applied. Surface modification methods covered include sandblasting with large-grit corundum and acid etched (SLA), plasma spraying, plasma immersion ion implantation (PIII), sputter-deposition, selective laser melting (SLM), anodic oxidation, microarc oxidation, sol-gel coating, alkaline heat treatment (AH) and Layer-by-Layer (LBL) self-assembly. This review comprehensively summarizes the influence of each method on osseointegration and biofilm attachment. The mechanical, chemical and biological disadvantages of these methods are involved. Besides, the mechanisms behind such techniques as increasing surface roughness to expand superficial area and enhance the adhesion of osteoblastic cells are discussed.

1. Introduction

Dental implant restoration has been widely applied in patients with missing teeth because of its good success rate and treatment effect [1]. By the year 2023, the global dental implant market will be growing smoothly and is predicted to reach about $13.01 billion [2]. Although dental implants have achieved a high success rate, there are still numerous complications that can lead to implant failure, such as failed osseointegration and peri-implantitis [3]. Osseointegration is the key to implant success, which is a direct contact between bone and the implant surface [4], while many factors can affect implant osseointegration, including incidences of mechanical and biological complications, which accelerate alveolar bone loss [5]. Because of the lack of periodontal membrane and blood vessels around the implant, inflammation is more likely to occur [6]. Peri-implantitis is a bacterial infectious disease, and Andrea Butera et al. reviewed that a progression from healthy state to peri-implantitis caused changes in microbiota composition [7]. Peri-implantitis accelerates alveolar bone resorption and is the capital cause of implant failure [8]. The prevalence of peri-implantitis and peri-implant mucositis can be as high as 56% and 80% [9]. Philipp Sahrmann et al. systematically compared microbial types of peri-implantitis periodontitis and healthy implants, finding that Actinomyces spp., Por and Rothia spp., phyromonas spp. were all discovered in three conditions, but the complex host-biofilm interaction was nuclear [10]. Therefore, maintaining excellent osseointegration, elucidating the etiology of inflammation and reducing peri-implant inflammation are particularly important for implant success.
Numerous brands are active in the global market. Among these brands, the material of the implant is mainly composed of titanium, titanium alloy and zirconia. Due to its excellent biocompatibility, titanium is the most frequently used in the dental implant field [11]. However, when the bone mass is insufficient and a narrow implant needs to be used, the strength of the pure titanium implant is not adequate, and the implant is prone to breakage [12]. To improve the mechanical strength and wear resistance of narrow-diameter implants, various elements are loaded to create titanium alloy implants, such as titanium–6aluminium–4vanadium (Ti–6Al–4V), titanium–zirconium (TiZr) [13,14]. Currently, zirconia has received widespread attention due to its white appearance, good mechanical properties and excellent biocompatibility [15,16]. However, some processing is still needed to improve the ability of osseointegration [17].
Dentists have exerted extensive modifications on the implant surface to enhance its biocompatibility [18]. The surface modification of these implants aims to either raise the implant osseointegration capacity or to improve the implant antibacterial effect. The most widespread implant surface treatment technologies used to obtain bioactivity in commercial implants are sandblasting with large-grit corundum and acid etched (SLA), plasma spraying, plasma immersion ion implantation (PIII), sputter-deposition, selective laser melting (SLM), anodic oxidation, microarc oxidation, sol-gel coating, alkaline heat treatment (AH) and electrodeposition (Table 1). These treatment techniques change the implant surface morphology and chemical composition, greatly improving the properties of the implant, which have been demonstrated to achieve a better osseointegration and antibacterial effect [19,20].
In this review, we collated the current surface treatment techniques of implants, and revealed the effect of different techniques on osseointegration or antibacterial effect. The numbers of relevant literature published annually are displayed in Table 2. We look forward to drawing on the benefits of different surface treatment techniques to provide innovative ideas for designing implants.

2. Sandblasting and Acid Etching Methodologies

Sandblasting and acid etching technology is considered a safe and reliable method for implant surface treating [21]. Titanium implants are made by large grit sandblasting with 0.25–0.5 mm corundum particles [22], and subsequently, HCl/H2SO4 acid-etching at high temperatures [23]. Such technology is also applied to titanium alloy implants [24]. Han et al. explored that titanium alloys and pure titanium treated with SLA had similar surface structures [25]. Zhan et al. found that the Ti alloy treated by SLA had an effect on osteogenesis that was superior to pure titanium [26]. Sandblasting and acid etching technology can also change the surface structure of zirconia, which improves osseointegration. HF was the most effective acid etching agent, but concentration should be 5% to avoid damage to zirconia mechanical mechanisms [27]. Studies have shown that the rougher the surface, the more bacteria adhere [28]. However, compared with titanium, SLA treated zirconia reduced the thickness of the plaque biofilm [29].

3. Plasma Spraying

Plasma spraying is a thermal spraying coating process that utilizes a high energy heat source to melt and spray powder onto a prepared surface to produce a high-quality coating. Benefits of this method are thermal insulation, preventing wear and tear, and protection from corrosion. Powders applied in dental implant surface modifications mainly cover titanium, hydroxyapatite and various silicates.
The titanium plasma spraying (TPS) technique is a well-documented surface modification method [30,31]. Titanium particles are sprayed onto the implant surface and form a porosity between 30 μm and 50 μm [32]. The average roughness of the surface is around 7 μm, which enlarges the contact area between implant and bone. Experimental studies directly observed a higher percentage of direct bone-implant contact when compared with smooth titanium implants, and demonstrated significantly higher removal torques [33]. Chappuis et al. [34] reported in a prospective study an 89.5% survival rate of titanium plasma sprayed implants after 20 years of function in partially edentulous cases. Becker et al. [30] reported in a retrospective study with 12–23 year follow-up that the long-term survival rate of implants with a TPS surface was 88.03%. Peri-implantitis was up to 9.7% in the remaining implants. Particles of titanium were observed in the bone adjacent to these implants [35], while the adverse effects of these particles have not been universally recognized and only considered as a potential risk [31]. It was found that the healing period for TPS surface implants could be cut in half to 6 weeks by using implants with an SLA surface, and no clinical difference was observed between these two types [36]. Nowadays, there is a consensus on the advantages of using implants treated with other surface modification methods rather than TPS [37].
Hydroxyapatite (HA) is another widely used coating material in the field of implant surface modification. HA exists in the physiological environment and is an important component of the bone matrix [38]. The structure of HA is crystallographically similar to that of bone mineral, which is not only bioactive but also osteoconductive, non-toxic and non-immunogenic [39,40]. An HA coating can be prepared by various processes [41,42,43,44,45,46], among which plasma spraying is the most common technology because of its high deposition rate and low cost. When HA is deposited onto Ti-6Al-4V, a relatively high bond strength could be obtained under high temperature by forming CaTiO3 acting as a bond layer [39]. However, plasma spraying also brings about several drawbacks. First, the thermal expansion coefficients of HA are larger than that of titanium-based alloys [47]. As a result, high residual stress would be kept between HA and the substrate, and gradually reduce the HA coating’s adhesion to the substrate. Poor adhesion may cause film delamination and do harm to osseointegration in long-term clinical loading. Second, HA plasma sprayed under some conditions may transform to other phase composition, which causes the HA particles to be released into the intermediate space and result in the inflammation of surrounding tissue. In short-term studies in vivo, HA-coated titanium often exhibit faster osseointegration than noncoated titanium; however, bone resorption occurred in some HA-coated implants during the first 12 weeks [48]. In long-term studies in vivo, there was no difference between the HA-coated group and the noncoated group. Wheeler [49] drew a similar conclusion in a multicenter study that HA-coated implants showed good clinical effect in the early stage, but problems would accumulate with time. At eight years, cumulative survival rates of two commercially available HA-coated implants were 79.5% and 79.2%. It has been suggested by investigators [50,51,52] that such implants were more susceptible to peri-implantitis. Peri-implantitis is generated by polymicrobial etiology and results in persistent bone loss and implantation failure. A systematic review reported that bone-to-implant contact surface of bioactive surfaces such as HA or calcium phosphate were better performing than SLA or similar surfaces [53]. Currently, HA-coated implants are more common in the hip implant field [54].
In order to enhance antibacterial activity, there are various antibiotics incorporated with calcium phosphates; for example, cephalothin [54], amoxicillin [55], gentamicin [56,57,58], tobramycin [55], tetracycline [59,60], flomoxef sodium [61], streptomycin [62], ibuprofen [63], aspirin [64], etc. However, organic compounds cannot be incorporated with coatings in the plasma spraying technique due to the extremely high processing temperature, and the half-value period release rate is too short to maintain the capability of anti-bacteria. Besides, antibiotic-releasing implants have the limitations of a narrow antimicrobial spectrum and antibiotic resistance [65], bringing a greater risk of dysbacteriosis.
Another attractive attempt is introducing antibacterial ions and nanoparticles (NPs) of metal elements onto implant coatings. Silver ion is well known for its antibacterial properties, which is toxic for bacteria and fungi by interfering the synthesis of the cell wall, damaging the cell membrane and inhibiting the synthesis of proteins and nucleic acids [39]. Silver is the least toxic for humans among the elements, having an antibacterial effect put to use in water filters. Beneficially, Ag+ binds to the HA by displacing calcium ions. However, Fielding et al. [66] observed poorer cell morphology and more cell death of the Ag-HA coatings group than the control group, indicating its cytotoxic effects. In order to decrease or eliminate negative effects, SrO was added to the Ag–HA coatings. Some companies have developed silver coatings on medical devices, but practitioners still raise concerns about argyria and allergies. Ashley et al. [67] incorporated biologically relevant metallic oxides of ZnO, SiO2 and Ag2O within a plasma sprayed hydroxyapatite coating and showed both improved implant osseointegration and mitigate infections. Qi et al. [68] reported that the plasma-sprayed cerium oxide-incorporated calcium phosphate coating in dental implants showed strong antimicrobial activity on E. faecalis, with good biocompatibility.
Since Ti6Al4V coated with plasma-sprayed HA shows poor bonding strength, other materials or techniques are tried as well. CaSiO3 ceramics are coated as another attempt by investigators on Ti6Al4V. Research results showed enhanced bonding strength of the plasma-sprayed CaSiO3 coating compared to HA. However, the chemical stability of CaSiO3 coatings is poor, and the long-term stability after implantation is questionable. Wu et al. [69] found that Ti6Al4V coated with novel CaTiSiO5 sphere ceramics using the plasma spraying method possessed excellent bonding strength, chemical stability and cellular bioactivity.

4. Metal Ions Implantation

Many metal elements such as silver, cerium, copper and zinc are loaded into implants to obtain a good antibacterial effect. Silver has a multi-stage antibacterial function with a broad-spectrum antibacterial character [70]. The antibacterial mechanism of silver mainly includes silver ion release [71], reactive oxygen species free radical production, oxidative stress occurrence, etc. Li et al. incorporated Ag nanoparticles (NPs) into TiO2 nanotubes prepared on the SLA Ti surface, showing strong “release bactericidal” activity in the early phase that gradually changed to the “contact bactericidal” ability [72]. GAO deposited a titanium-silver coating on the Ti surface by magnetron sputtering, and then formed a TiO2 nanotube structure carrying nano-silver oxide by anodizing. This unique structure allowed the release of silver ions to be controlled, thus exhibiting an effective antibacterial effect without cytotoxicity. The nanotube array containing silver oxide had long-term effective antibacterial ability, and can still effectively exterminate E. coli and Staphylococcus aureus after soaking for 28 days, with a bacteriostatic rate of 97%. At the same time, the surface also showed good cytocompatibility, which can promote the spreading, proliferation and differentiation of osteoblasts [71].
Zinc is an essential trace element that plays a vital role in growth. The affinity of nano zinc oxide with bacteria is stronger than that of ordinary zinc oxide, thereby improving the antibacterial efficiency. The antibacterial mechanism of nano-zinc oxide particles is mainly divided into four aspects: (1) the release of high concentrations of free zinc ions destroys the bacterial membrane and intracellular proteins [73]; (2) the nano-zinc oxide particles interact with the bacterial membrane, causing bacterial surface damage [74]; (3) nano zinc oxide particles induce the generation of reactive oxygen species (ROS) in vivo, eventually leading to bacterial death [75]. When applied to the surface of dental implants, nano-zinc oxide coatings promote bone growth and improve the biocompatibility, bone conductivity and antibacterial properties of implants [76] Abdulkareem et al. prepared nano-zinc oxide, nano-hydroxyapatite (HA) and composite coatings on the surface of titanium sheets by current-driven atomization. The experimental results show that the antibacterial rate of nano-zinc oxide coating and nano-zinc oxide-nano HA composite coating surface is higher than that of the nano-HA-coated titanium surface [77]. Yao et al. found that zinc-coated titanium dioxide nanotubes constructed by electrochemical deposition had a strong inhibitory effect on Staphylococcus aureus [78].
In recent years, the antioxidant capacity of cerium oxide (CeO2) has been demonstrated, and Ce4+/Ce3+ ions are able to accept or lose electrons according to the environment, which gives cerium oxide biological antioxidant properties, allowing it to catalyze the decomposition of excess ROS in living organisms [79]. Li et al. coat different shapes of nano-CeO2 onto Ti surfaces to improve antibacterial and anti-inflammatory properties [80]. Zhao et al. composited cerium oxide with titanium dioxide to prepare coating materials, which have certain anti-infection and self-cleaning functions [81].
Copper is an essential trace element with strong antibacterial properties. Copper ions can inhibit bacterial DNA activity and the synthesis of related enzymes, interfering with bacterial metabolism. Copper nanoparticles (CuNPs) incorporated into Ti implant can release copper ions to inhibit bacterial activity [82]. Rosenbaum et al. synthesized nano-copper particles on the surface of TiO2 nanotubes via pulse electrodeposition method, which greatly inhibited the activity of E. coli and Staphylococcus aureus [83]. Valdez–Salas et al. have demonstrated that TiO2 nanotubes can reduce the initial adhesion of Gram-negative and positive bacteria.

5. Sputter-Deposition

Sputtering deposition belongs to physical vapor deposition technologies, which means there is no chemical reaction during this process (Figure 1). It is an electronic process in which inert gas ions, usually argon ions, acquire kinetic energy under the control of the electric field and bombard the sputtering target in a vacuum chamber. The sputtered target atom moves from the sputtering material to the substrate to form the target coating.
There are several sputter techniques, including magnetron sputtering, diode sputtering, radiofrequent or direct current sputtering, ion-beam sputtering and reactive sputtering. The benefits of this method are good durability, convenient cleaning, high quality and environmentally friendly. The sputtering targets vary in size and materials. Common sputtering targets are composed of pure metal, pure ceramic or alloy. This approach produces thin coatings of 0.05 to 5 micrometers.
Jansen et al. [44] produced ceramic coatings on implant materials without any sign of adverse tissue reaction. Xu et al. [84] reported calcium phosphate-based composite bioactive films on Ti6Al4V orthopedic alloy with radiofrequent magnetron concurrent sputtering of Hydroxyapatite and Ti. In vitro cell culturing tests suggest that the Ca–P–Ti films show great biocompatibility.
Titanium and its alloy need to be used in complex mechanical and biological environments.There are still poor wear resistance, fatigue life, poor biological viability and corrosion resistance to be further improved in the orthopaedic field. Nitride coating (TiN, ZrN, TiAlN, etc.) and diamond-like (DLC) coating can reduce the surface friction coefficient of titanium alloy and improve its wear resistance and corrosion resistance. Yang et al. [85] prepared TiAlN coatings with different Al concentrations on Ti6Al4V substrate via reactive magnetron sputtering. Due to the good combination of high hardness and toughness, the corrosion properties are significantly improved. Yi et al. [86] prepared a series of multilayered gradient TiAlN coatings on a Ti6Al4V substrate using closed field unbalanced magnetron sputter ion plating process. The hardness, Young’s modulus and wear resistance were also found to be improved.

6. Selective Laser Melting (SLM)

Selective laser melting (SLM) is a main technical approach applied in metal material additive manufacturing. In this technology, a laser is selected as the energy source, and the metal powder bed is scanned layer by layer according to the path planned in the 3D CAD slice model. The scanned metal powder is melted and solidified to achieve the effect of metallurgical combination, and finally the pre-designed metal parts are obtained. SLM technology overcomes the problem of manufacturing metal parts with complex shapes via traditional technology. Although many techniques have been used to improve the resistance of titanium and its alloys, SLM provides an opportunity to fabricate titanium and its alloys in a totally different way.
Bartolomeu et al. [87] compared the hardness and wear resistance of Ti6Al4V alloys fabricated by selective laser melting, hot pressing and conventional casting. The results showed that the best wear behavior were obtained for Ti6Al4V alloy produced by selective laser melting. Qin et al. [88] fabricated titanium alloy implants with a selective laser-melting process, followed by further nano-structuring with electrochemical anodization to form titania nanotubes (TNT) and subsequent bioactivation via HA coating. An in vitro study suggested these implants showed better osseointegration performances. Hu et al. [89] established a surface modification method for SLM implants to enhance its antibacterial efficacy. In this method, sandblasting, anodization and electrochemical deposition were applied to construct a novel composite nanostructure of nanophase calcium phosphate embedded in TiO2 nanotubes on microrough SLM titanium substrates. SLM titanium substrates showed antibacterial efficacy superior to TiO2 nanotubes samples and had no significance difference compared to mechanical polished samples.

7. Anodic Oxidation

Anodizing can prepare uniformly controllable nanotube structures on pure Ti [90]. Titanium dioxide nanotubes have more surface area, increased coarseness and enhanced hydrophilicity, playing an important role in promoting osseointegration [91], soft tissue closure [92] and antibacterial [93]. The hydrophilicity and roughness of TiO2 nanotubes are important factors affecting the initial adhesion of bacteria [94]. Valdez–Salas et al. have demonstrated that TiO2 nanotubes can reduce the initial adhesion of Gram-negative and positive bacteria [95]. TiO2 nanotubes are a photocatalyst that produces reactive oxygen species (ROS) under the catalytic action of ultraviolet light, destroying the cell membrane of bacteria under oxidative stress to achieve an antibacterial effect [96]. TiO2 nanotubes act as carriers to load antibiotics [97], metal nanoparticles [98] and antimicrobial peptides to synergistically exert antibacterial effects. TiO2 nanotubes have demonstrated good antimicrobial effects, and the application of combined antimicrobial agents has shown convincing antibacterial effects.

8. Micro-Arc Oxidation

The micro-arc oxidation (MAO) has been applied to implant surface modification [99], which can make the titanium surface grow a dense ceramic oxide film in situ [100]. As far as antibacterial is concerned, the MAO treatment can convert amorphous TiO2 into crystalline anatase TiO2 to reduce bacterial adhesion [101]. However, by changing the composition of the electrolyte, bioactive elements can be added to improve their biological properties [102], so researchers incorporated antibacterial elements into a Ti implant via MAO treatment. Masaya Shimabukuro’s review summarizes that Ag, Cu and Zn are incorporated respectively into the Ti surface by MAO, exhibiting long-term antibacterial property [103]. He et al. incorporated Ag and Sr simultaneously into TiO2 coatings through MAO, and the osteogenic and antibacterial capabilities are enhanced [104].

9. Sol-Gel Coating

The sol-gel method is a wet chemical method for preparing various metal oxide materials at a relatively low temperature, including coatings, films, fibers and bulk parts which are difficult to melt using conventional processes. The ester compound or metal alkoxide is dissolved in organic solvent to form a uniform solution, and then other components are added to form a gel at a certain temperature. After drying, sintering and curing, gels form molecular and even nanostructured materials. Commonly used alkoxides are alkoxysilanes, aluminates, titanates and zirconates.
Sol-gel coating is a common technique applied to deposit HA films on implants in preclinical studies. The plasma spraying technique may affect the final properties of the coating due to its high temperature. The sol-gel coating is performed at a relatively low temperature and produces coatings with high purity and homogeneity [105,106]. This technique mainly covers two steps—sol and gel. First, calcium and phosphorus precursors combined with solvents composed of ethanol and water are mixed as raw materials [107], in which the molar ratio of Ca/P is controlled as close as possible to 1.67. The mixture is stirred at various temperatures, and the solvent is evaporated until a thicker sol is obtained [108]. Second, the produced HA sol is deposited on the Ti substrate with a dip coating or spin coating. The dip coating is commonly used in complex shapes, and the spin coating is suitable for flat surfaces [91]. However, many studies in vitro have demonstrated that the properties of pure HA are unsatisfying because of its low bonding strength and high dissolution rate (Figure 2).
Several strategies have been attempted to tackle these shortcomings, including optimizing the processing parameters, engineering of the interface and reinforcement of HA [108]. To promote the purity, crystallinity, stability, adhesion strength and biocompatibility of the coatings, several parameters including the chemical compositions of the precursors, pH value [110], sol preparation temperature and time [93], sol viscosity, sintering duration and temperature [111], and heating rate [112] are tested stringently and comprehensively. Another practical way to overcome these shortcomings is to create an intermediate layer between substrate and HA coating before the deposition of HA by sol-gel technique. Common intermediate layers include TiO2 interlayer produced by sol-gel or anodization, titanium boride interlayer and titanium nitride interlayer. These interlayers contribute to increase the bonding strength, slowing down the cooling rate, reducing the thermal decomposition of HA, and improving the crystallinity of the coatings. Studies of HA composites have also demonstrated its advantages in reinforcing HA coatings. HA-TiO2 composites increase bonding strength and hardness. HA-ZrO2 composites improve the interfacial shear strength between the substrate and coatings remarkably. HA-Fe3O4 composites promote the bioactivity by increasing the wettability. The introduction of multi-walled carbon nanotubes to sol-gel HA coating is proved the features of high biocompatibility and enhanced bonding strength.
Antibacterial activity is obtained by substituting the Ca2+ of HA with antibacterial ions such as Zn2+, Cu2+, Ag+ or substituting the OH- of HA with F- in sol-gel method. Zhang prepared a ZnHA/TiO2 coating on commercially pure Ti and found it inhibited the growth of Porphyromonas gingivalis significantly [113]. Batebi et al. developed a composite coating containing silver, fluoride and HA on Ti substrate using sol-gel method. It was found that antibacterial activity of coatings against Escherichia coli indicated a significant enhancement in the antibacterial property of Ag-FHA nanocomposite with an increasing of the amount of fluoride [114]. Bi et al. incorporated zinc ions and bismuth ions into HA lattice by substituting Ca2+ ions, and then prepared Zn-substituted hydroxyapatite/bismuth substituted hydroxyapatite (Zn-HA/Bi-HA) biphasic coatings with different proportions on titanium plates via sol-gel and dip coating processes. The biphasic Zn-HA/Bi-HA coatings promoted antimicrobial activity against Escherichia coli and Staphylococcus aureus compared with pure HA coatings [115]. Several private investigators have studied the production and mechanical properties of FHA [116,117]. In vitro studies indicate that the F-for OH- substitution enhances cell proliferation and reduces bacterial activity [118].

10. Alkaline Heat Treatment

Alkaline heat (AH)treatment refers to the use of a strong alkaline solution to form a rough surface on the surface of titanium under the action of high temperature, greatly increasing titanium surface activity [119]. Richard Bright et al. found that alkali treatment agents are different and have different effects: for Gram-negative pathogens, the NaOH surface was more effective, while for Gram-positive strains, the KOH surface was better [120]. Zhang et al. discovered the Ti-10Cu sample exhibiting good antibacterial properties via AH treatment [121].

11. Acid-Alkali Treatment

Acid-alkali treatment modifies the implant surface with a two-step method. The acid treatment produces microstructure pits and grooves on the titanium surface, while the alkali treatment produces nanoscale pits [122]. The combination of acid-alkali treatment is suggested to be beneficial to osseointegration [123]. It has been confirmed that bacteria prefer to adhere to rough Ti surfaces [124]. Zhong et al. found acid-alkali-treated porous Ti (AAPT) intensified bacterial adhesion more than nontreated porous Ti (NTPT); however, AAPT coated protein tended to prevent bacteria from adhering [125].

12. Layer-by-Layer Self-Assembly Technique

Layer-by-Layer (LBL) self-assembly is an approach in which an ultrathin film is developed on solid support by spontaneously alternating layer-by-layer deposition with the aid of weak interaction between each layer [126]. The LBL self-assembly process is as follows: the charged substrate is immersed in a solution consisting of oppositely charged polyelectrolytes and the first monolayer is formed by absorption. This step is followed by a cleaning step to remove the weakly bound or unbound species. In addition, this cleaning step prevents cross-contamination of oppositely charged polyelectrolytes. The substrate with the first monolayer is then immersed in another polyelectrolyte solution with an opposite charge, and a second monolayer is also formed by absorption. This process is repeated until the desired multilayer is formed [127,128]. It is a versatile technique that has been used in the surface modification of dental implants, energy storage, drug delivery, and tissue and cell engineering. This technique is simple and robust, while it is susceptible to the concentration and ionic strength of the polyelectrolyte solution, pH, temperature, assembly time, molecular weight, and size. Because the polyelectrolyte multilayers (PEMs) are formed under mild conditions, the biological activity of cytokines and small interfering RNA (siRNA) can be maintained. Targeted sustained release administration can be easily achieved by adding different substances or by adjusting the physical and chemical properties of the self-assembled materials [129]. The morphology of the resulting film can be controlled at the nanoscale to achieve the desired thickness, biocompatibility, and other properties.
To promote osteogenesis and osseointegration of titanium and its alloys, cytokines, DNA plasmid and siRNA are used as colloids in many studies. Hu et al. [130] incorporated a bioactive gelatin/chitosan pair multilayer structure with bone morphogenetic protein 2 (BMP2) and fibronectin onto a Ti6Al4V surface through a LBL assembly technique to mimic the extracellular microenvironment of bone. Huang et al. [131] constructed a chitosan/gelatin multilayer containing BMP2 and an anti-osteoporotic agent of calcitonin on the Ti6Al4V implants by LBL electrostatic assembly technique to improve the long-term survival rate of titanium implants in patients with osteoporosis. Jiang et al. [132] developed multilayer coatings composed of hyaluronic acid and liposome-DNA complex as a delivery vehicle for recombinant human BMP-2. Song et al. [133] built up a multilayered film of sodium hyaluronate and chitosan/siRNA on a smooth titanium surface via LBL approach. Several studies have applied the LBL method in surface modification of the titanium substrate with natural polymeric substances [134,135]. All of these studies show good biological effects, which indicate the application potential of this method.
The LBL technique is also applied to promote the antibacterial properties of Titanium by introducing nano-silver, antibiotics or antibiotic peptides. Zhong et al. [136] established a novel initial layer on Ti surfaces using phase-transited lysozyme, on which multilayer coatings can incorporate silver nanoparticles using chitosan and hyaluronic acid via LBL self-assembly technique. Lv et al. [137] constructed antibacterial multilayer coatings loaded with minocycline on the surface of Ti substrates using chitosan and alginate based on the LBL self-assembly technique. Pérez–Anes et al. [138] built up bioinspired titanium drug eluting platforms based on a poly-β-cyclodextrin−chitosan LBL self-assembly targeting infections.

13. Conclusions and Outlook

Different implant surface modifications have their own design significance. The modifications such as SLA, MAO, etc. increase surface roughness and improve hydrophilicity, which make implants more biocompatible and accelerate osseointegration. The implant surface is incorporated with metal ions or antimicrobial peptides and performs a resistance effect on bacteria. These modifications have achieved significant results, but long-term studies are still needed to verify the effect of these coatings. Though there have been various surfaces in markets and laboratories, and implant properties have been greatly enhanced, it is still necessary to continue improving modification methods, especially in obtaining faster osseointegration, reducing infection, and avoiding mechanical complications. Future research should focus on establishing innovative modification methods in the laboratory, comparing different surface implants in strict and long-term clinical trials.

Author Contributions

Literature search, writing—original draft preparation, W.H.; writing—review and editing, S.F.; manuscript correction, Q.Z.; Conceptualization, S.Q. All authors have read and agreed to the published version of the manuscript.

Funding

This review was funded by the Science and Technology Innovation Talent Training Program of Shanghai Stomatological Hospital (SSH-2022-KJCX-B05).

Acknowledgments

The authors would like to thank all references for their significant researches contributing to this manuscript.

Conflicts of Interest

The authors declare no conflict of interest.

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Coatings 12 01654 g001 550
Figure 1. A schematic illustration of sputter-deposition.
Figure 1. A schematic illustration of sputter-deposition.
Coatings 12 01654 g001
Coatings 12 01654 g002 550
Figure 2. The fundamental stages of sol-gel HAp preparation and deposition by dip and spin coating [109].
Figure 2. The fundamental stages of sol-gel HAp preparation and deposition by dip and spin coating [109].
Coatings 12 01654 g002
Table
Table 1. Implant surface modifications used in commercial implants.
Table 1. Implant surface modifications used in commercial implants.
Surface ModificationsImplant Brand
SLASLA Straumann® (Straumann Institute, Basel, Switzerland), Friadent Plus® (Dentsply Friadent, Mannheim, Germany), Promote® (Camlog, Basel, Switzerland), Ankylos® (Dentsply Friadent, Mannheim, Germany)
Anodic oxidationTiUnite® (Nobel Biocare, Gothenburg, Sweden)
Plasma sprayingBonefit® (Straumann Institute, Waldenburg, Switzerland), IMZ-TPS® (Dentsply Friadent, Mannhein, Germany), ITI-TPS® (Straumann Institute, Waldenburg, Germany), Steri-Oss-TPS® (Nobel Biocare, Yorba Linda, CA, USA)
Table
Table 2. The numbers of relevant literature published annually.
Table 2. The numbers of relevant literature published annually.
Surface ModificationsPublication Time (Year)Numbers
SLA20111
20122
20141
20151
20161
20192
20201
Plasma Spraying19761
19901
19921
19931
19944
19962
19971
19982
20001
20012
20021
20031
20051
20061
20081
20092
20103
20112
20121
20131
20142
20153
20161
20172
20192
20202
Metal ions implantation20091
20111
20121
20141
20153
20161
20171
20181
20194
Sputter-deposition20021
20041
20151
Selective laser melting20171
20183
Anodic oxidation20081
20151
20161
20172
20181
20193
Micro-arc oxidation20051
20061
20081
20151
20201
Sol-gel coating19951
19981
20051
20081
20122
20132
20141
20151
20161
20181
20191
20201
Alkaline heat treatment20152
20221
Acid-alkali treatment19981
20101
20141
Layer-by-Layer self-assembly technique20111
20122
20142
20153
20164
20171
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Han, W.; Fang, S.; Zhong, Q.; Qi, S. Influence of Dental Implant Surface Modifications on Osseointegration and Biofilm Attachment. Coatings 2022, 12, 1654. https://doi.org/10.3390/coatings12111654

AMA Style

Han W, Fang S, Zhong Q, Qi S. Influence of Dental Implant Surface Modifications on Osseointegration and Biofilm Attachment. Coatings. 2022; 12(11):1654. https://doi.org/10.3390/coatings12111654

Chicago/Turabian Style

Han, Wen, Shuobo Fang, Qun Zhong, and Shengcai Qi. 2022. "Influence of Dental Implant Surface Modifications on Osseointegration and Biofilm Attachment" Coatings 12, no. 11: 1654. https://doi.org/10.3390/coatings12111654

APA Style

Han, W., Fang, S., Zhong, Q., & Qi, S. (2022). Influence of Dental Implant Surface Modifications on Osseointegration and Biofilm Attachment. Coatings, 12(11), 1654. https://doi.org/10.3390/coatings12111654

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