Research Progress on the Preparation Process and Material Structure of 3D ‐ Printed Dental Implants and Their Clinical Applications

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Introduction
Oral problems are a growing concern in today's society.A healthy mouth not only promotes good eating habits but also affects a person's appearance [1].Prosthetic restoration of missing teeth can be achieved by means of cemented dentures, removable dentures, and dental implants, with dental implants being the most desirable restorative method.In 1969, Brånemark et al. [2] first proposed the concept of osseointegration by summarizing the good results obtained from implant trials in male canines, and since the concept of osseointegration was proposed, the development of dental implants has had a relatively clear direction.
Currently, dental implants continue to gain attention in dentistry [3].Simply, dental implants consist of the implant body and its supporting superstructure (crown and abutment), also known as an artificial tooth root, made of artificial material and surgically implanted into the jawbone in the area of the missing tooth.Dental implants provide an effective solution for restoring chewing function, offering superior strength and stability compared to other traditional restoration materials.In addition, implants can greatly beautify the patient's appearance, are more convenient in daily life than traditional dentures, protect the remaining natural teeth, prevent bone loss, and restore facial bone structure.It is important to understand that dental implants provide a restoration that is very similar in function, structure, and aesthetics to a natural tooth, and the structural comparison between a healthy tooth and a dental implant is shown in Figure 1.In recent years, attention has been drawn to the rise of 3D printing technology, which is capable of creating complex 3D structures directly from computational models, a feature that has led to the search for alternatives to the traditional mechanical fabrication of dental implants [4].The processes used for 3D printing of implants are numerous [5].The most used 3D printing technology processes are stereolithography (SLA), selective laser sintering (SLS), fused deposition molding (FDM), etc., and the principles and methods of the various processes are not the same.Relying on 3D printing technology, various types of implants already exist, with different implant structures, combination methods, and materials used.For example, many investigations and clinical studies have identified titanium as a biomaterial for oral rehabilitation, along with other materials such as zirconia, polyether ether ketone, and carbon nanotubes [6].
Successful implant placement is the result of a combination of factors, and although implantology is rapidly evolving and many surgical protocols are being improved, there are several potential complications that can compromise the stability of dental implants.Studies have proposed that a large part of early implant failure is due to bacterial infection, but of course, this undesirable outcome is the result of a number of cofactors [7,8].
Osseointegration, which pertains to oral implants, is a fundamental component of modern reconstructive dentistry [9].Osseointegration was originally defined as direct contact between vital bone and weight-bearing implants observed at the histological level [10].Insua et al. [11] presented an update on the molecular mechanisms occurring during osseointegration, focusing on the relevance of osteoblasts and immune cells in the process of bone maintenance.However, the biology and metabolism of peri-implant bone healing and its impact on bone loss at the peri-implant margin has been less well studied.
In this review, we examine the latest developments in clinically 3D-printed dental implants and whether they can be more effectively personalized to treat complex clinical problems.We highlight process methods, surface modifications, new types of dental implant, and advances in the clinical treatment and prognosis of dental implants with 3D printing technology to provide ideas for further research.

Selective Laser Melting
Selective laser melting (SLM) is an advanced 3D printing technique that uses a high-power laser to fuse metallic powders layer by layer.This process allows for the production of precise dental implant structures, overcoming the challenges associated with manufacturing metal parts [12].The processing flow of SLM technology is illustrated in Figure 2 [13].Commonly, materials like titanium and its alloys are employed in SLM-based dental implants due to their biocompatibility and resistance to corrosion.For instance, Qin et al. [14] conducted a study demonstrating the successful fabrication of titanium dental implants using SLM technology, resulting in a precise fit and osseointegration.The study emphasized the significance of optimizing laser parameters and powder characteristics to achieve the desired implant properties.One major advantage of SLM is its ability to create personalized implant designs based on individual patient anatomy.By utilizing patient-specific 3D imaging data, SLM can manufacture implants with customized geometries, improving the overall success rate and patient satisfaction [15].SLM has attracted significant attention in dental implantology due to its capability to produce complex geometries with excellent biocompatibility and mechanical properties [16].However, SLM also faces challenges.For instance, the high cost of SLM machines and materials may hinder its widespread adoption in some dental practices.Additionally, post-processing steps may be necessary to enhance the surface finish and eliminate residual stresses, thereby adding complexity to the manufacturing process [17].

Electron Beam Melting
Electron beam melting (EBM) is an advanced 3D printing technique that shows great promise in the field of dental implant fabrication.This innovative technology uses a high-power electron beam to selectively melt and fuse metallic powder particles layer by layer, resulting in the precise manufacturing of complex dental implant structures [18].Figure 3 illustrates the EBM process [18].EBM is commonly employed to produce dental implants using biocompatible materials like titanium and its alloys.One of EBM's significant advantages is its ability to create implants with excellent mechanical properties and biocompatibility.The implants manufactured through EBM exhibit high strength, corrosion resistance, and osseointegration potential, making them ideal for long-term implantation [19].The customization potential of EBM is also noteworthy.By utilizing patient-specific 3D imaging data, dental professionals can tailor implant designs to match individual anatomical requirements.This personalized approach enhances the fit, stability, and overall success rate of dental implants [20].Moreover, EBM allows for the fabrication of lattice structures within the implant.These lattice structures not only reduce the implant's weight but also promote bone ingrowth, facilitating faster healing and osseointegration [21].Several studies have demonstrated the successful application of EBM in dental implantology.For instance, Li et al. [22] conducted a study utilizing EBM-fabricated titanium dental implants.The results showed the EBM implants not only diminished stress shielding but also demonstrated suitable osteoconductive properties.While EBM offers significant advantages, it is crucial to consider certain challenges.The equipment and materials required for EBM can be relatively expensive, which may limit its widespread adoption in smaller dental practices.Additionally, post-processing steps may be necessary to remove residual stresses and achieve the desired surface finish [23].

Selective Laser Sintering
Selective laser sintering (SLS) is a highly anticipated 3D printing technology that uses a high-power laser to selectively sinter metal powder particles layer by layer.This achieves the bonding of high-melting-point metals and ceramics [24].The process is illustrated in Figure 4 [24].Compared to other technologies, parts produced through laser sintering have several advantages, including good performance, fast production speed, a wide range of materials, and low cost.In the field of oral implants, SLS commonly employs biocompatible materials such as titanium and its alloys.Implants made using this method have shown excellent stability and osteogenic activity [25].Furthermore, SLS technology's high precision and chromatographic resolution enable the fabrication of microstructures.This is crucial in simulating the shape and function of natural teeth, which helps to enhance patients' oral comfort and chewing effectiveness.Patients not only receive natural-looking implants but also benefit from an improved oral experience.We have summarized the current research on these three process methods in Table 1.

References
Osteogenesis of 3D-Printed porous Ti-6Al-4V implant with different pore sizes.SLM SLM was able to fabricate porous Ti6Al4V implants with proper mechanical properties analogous to human bone.[26] Micro/nano topography of selective laser melting titanium inhibits osteoclastogenesis via mediation of macrophage polarization.

SLM
Both in vivo and in vitro studies revealed that the SLA-and SAH-treated SLM-Ti implants significantly inhibited peri-implant osteoclast activity. [27] Micro-/nano-topography of selective laser melting titanium enhances adhesion and proliferation.

SLM
Creating appropriate micro-/nano-topographies affected cell behavior and increased the stability of the SLM-Ti. [28] Osteoinduction of porous Ti implants with a channel structure fabricated by selective laser melting.

SLM
The RP-based SLM technique was very effective for investigating the influence of pore size on osteoinduction. [29] A biomimetic hierarchical structure on selective laser melting titanium with enhanced hydrophobic surface.

SLM
The SLM-Ti had a superhydrophilic surface, and the contact angles quickly reduced to zero upon complete wetting. [30] Improved osseointegration of 3D-printed Ti-6Al-4V implants with a micro/nano surface topography.

EBM
After acid etching and anodic oxidation, the hydrophilicity and bioactivity of EBM-Ti were improved. [31] Osteoconductivity of bioactive Ti-6Al-4V implants with lattice-shaped interconnected large pores fabricated by electron beam melting.
EBM EBM-Ti with NaOH, CaCl2, heating, and water treatment, with lattice-like pores, with superior mechanical properties and biological activity. [32] Electron beam-melted, free-form-fabricated EBM Compared with machined Ti, EBM-Ti implants [33] titanium alloy implants: Material surface characterization and early bone response in rabbits.
had higher surface roughness, thicker surface oxides, and better osteogenic activity.Mechanical properties of selective laser sintering pure titanium and Ti-6Al-4V, and its anisotropy.

SLS
The SLS process with Ti-6Al-4V powder had great performance for the fabrication of dental prostheses. [34] In vitro and vivo comparisons of the porous Ti-6Al-4V alloys fabricated by the selective laser melting technique and sintering technique.

SLS
Microstructure and mechanical properties of the SLS porous Ti-6Al-4V were more similar to the cancellous bone, without obvious stress shielding. [35] 3D laser-printed porous Ti-6Al-4V dental implants for compromised bone support.SLS In micro-CT analysis, new bone formation and osseointegration within the SLS-ITRI implants were observed. [36]

Physical Modification
Sandblasting, plasma treatment, and laser modification are commonly used physical techniques for modifying implant surfaces [37].
Sandblasting involves using compressed air to spray particles of blast material, such as steel grit or emery, onto the implant surface to alter its roughness [38].Gil et al. demonstrated that sandblasting increases the contact area between the implant and surrounding bone tissue, promoting the adhesion and proliferation of osteoblasts and improving the implant's ability to integrate with the bone [39].Additionally, sandblasting is often combined with acid etching to remove any residual blast material [40][41][42][43].In a retrospective clinical study, Buser et al. [44] evaluated the outcomes of 511 SLA (sandblasted, large grit, acid-etched) implants in 303 partially edentulous patients over a 10-year period.The authors reported a success rate of 97.0% and a 10-year implant survival rate of 98.8%.The incidence of peri-implantitis was as low as 1.8%.
Plasma treatment can involve both spraying and implantation [45].Plasma spraying uses a plasma arc generated by ionized inert gases as a heat source to melt or semi-melt materials such as ceramics, alloys, or metals, which are then sprayed onto the pre-treated implant surface to form a firmly adhered coating [46].Hydroxyapatite (HA) coatings, commonly used in clinical practice, are created by spraying HA particles onto the implant surface at high temperatures and then rapidly cooling them [47][48][49][50].Lu et al. [51] demonstrated that a tantalum-doped HA-coated implant, created through plasma spraying, not only had improved roughness and wettability but also promoted osteogenesis and differentiation of bone marrow mesenchymal stem cells.Plasma implantation involves injecting ion beams directly into the implant, causing changes in its surface composition, structure, and properties [52,53].Jin et al. [54] used ion implantation to inject Zn and Ag ions into titanium, forming a Zn/Ag film that greatly enhanced the osteogenic activity and antibacterial ability of the material.Wan et al. [55] injected Cu and Ag ions into titanium alloy separately, and the modified samples exhibited good antibacterial properties against Escherichia coli and Staphylococcus aureus.
Laser modification is a technique that has gained notable attention in recent years.This method employs laser micromachining to create precise nano-and micro-scale features on implant surfaces.Implants with collar surfaces treated through laser micromachining to produce nano-channels have demonstrated improved integration and stability [56,57].The advantages of laser modification of implants are extensively documented, including enhanced osseointegration, improved mechanical interlocking between the implant and bone, and decreased bacterial adhesion [58,59].A study by Koodaryan R et al. [60] showed that laser microtexturing of the dental implant collar significantly improved crestal bone levels and peri-implant health.Botos et al. [61] found that the application of laser-microtextured grooves to the implant collar resulted in shallower probing depths and less peri-implant crestal bone loss than that seen around implants with ma-chined collars.These findings indicate that implants with laser-modified surfaces exhibit a superior peri-implant tissue response, thereby contributing to the long-term success and stability of the implants [62].

Chemical Modification
Chemical modification techniques for implants can be classified into two main categories: electrochemical modification, and acid-base solution treatment [63].
Anodic oxidation is a method that involves the formation of an oxide film on the implant surface through discharge oxidation [68].This oxide film can alter the implant's surface color, corrosion resistance, hardness, and other properties [69][70][71][72].It is worth noting that the anodic oxidation method is often used to create titanium dioxide nanotube arrays.These nanotubes have a hollow tubular structure, which provides a large specific surface area and high adsorption capacity, greatly improving the implant's bioactivity [73][74][75][76][77].In a retrospective study conducted by Wagenberg et al. [78], 312 anodic oxidized surface implants were analyzed among 1187 implants that were immediately placed after tooth extraction.Radiographic comparisons over 2-12 years (with an average of 7.4 years) revealed that these implants experienced significantly less mesial-distal bone loss (0.4 mm) compared to machined implants (0.6 mm) following the same immediate placement protocol.
Micro-arc oxidation (MAO) is a modification method that utilizes the transient high-temperature effect generated by arc light discharge to form an oxide film with a dense inner layer and porous outer layer on the implant surface.This technique is considered to be an upgrade to anodic oxidation technology [79].The micro/nano bioactive titanium coating formed through MAO modification promotes the adhesion of osteoblasts on the implant surface and enhances the osteogenic activity of the implant [80][81][82].Furthermore, MAO can be combined with other coating methods.Huang et al. [83] conducted a study investigating the surface morphology, chemical properties, and cellular interactions of coatings prepared through MAO and hydrothermal treatment.The in vitro and in vivo results indicated that the encapsulated implant exhibited enhanced protein adsorption, osteoblast activity, adhesion, and differentiation.Moreover, it facilitated early osseointegration, improved bioactivity, and enhanced osseointegration compared to implants with MAO alone.Hu et al. [84] combined ultrasound with MAO to create coatings on the surface of Ti-Cu alloys, which demonstrated strong long-term antimicrobial properties and were non-toxic.Electrophoretic deposition (EPD) is a modification method that deposits charged particles onto the surface of an implant using an electric field [85].EPD not only ensures a uniform coating but also controls the thickness of the coating [86].Common coatings applied using EPD include HA, graphene oxide (GO), and Ag [87][88][89][90].Juliadmi et al. [91] used EPD to deposit HA coatings of natural origin onto implant surfaces, resulting in good surface coverage and improved coating performance.EPD is also capable of coating more complex shapes.Nicoli et al. [92] utilized EPD technology to apply a novel semi-transparent coating on a 3D-printed Ti alloy mesh for guided alveolar bone regeneration.
In terms of acid and alkaline solution treatments, commonly used modifications are acid etching and alkaline heat treatment [93,94].
Acid etching is a common method that enhances the biocompatibility of implants [95].By immersing the metal implant in hydrofluoric, sulfuric, nitric, or mixed acid solutions, a chemical reaction occurs, resulting in increased surface roughness of the implant [96,97].Yan et al. [98] discovered that acid-etched Ti alloy implants did not significantly affect hydrophilicity, but they did promote macrophage adherence and polarization while reducing reactive oxygen species (ROS) levels.However, it is important to control the reaction time and conditions during acid etching treatment to prevent overreaction and damage to the implant surface [99].
Alkaline heat treatment is a modification method that involves immersing the metal implant in a strong alkaline solution for a certain period, followed by heat treatment at 300-800 °C to obtain a porous oxide layer [100].Nishio et al. [101] observed that alkaline heat treatment greatly increased the surface roughness of titanium, and that the resulting micrometer-sized porous structure provided nucleation sites for apatite deposition when immersed in a simulated body fluid.Zhang et al. [102] conducted continuous alkaline heat treatment, pre-calcification, and simulated body fluid immersion to obtain HA-coated porous titanium.Implanting porous titanium and HA-coated porous titanium into a tibial defect model in New Zealand white rabbits, it was found that the latter effectively reduced the fracture risk and enhanced bone healing.

Classification of the Implant Structure
First, according to the structure of the implant, there are three types of implant: one-stage implants, two-stage non-embedded implants, and two-stage embedded implants.Two-stage implants do not support the attachment of fixed screws, so the single-stage small-diameter implants are generally considered to be more robust than the two-stage implants [103].For the three types of implant, see Figure 5 below, and the advantages and disadvantages of the three implant types are compared in Table 2.

Planting patterns
The appropriate position is selected in the alveolar bone, the implant is placed in the hole, and the screw is closed; 7-10 days later the stitches are removed.
Non-invasive surgery (gum surgery): The implant is directly inserted into the alveolar bone and mounted on a healing abutment.The implant is directly or indirectly exposed in the mouth.
First surgery: To ensure that the bone tissue has a long enough time to heal, we place the implant in the alveolar bone and bury it completely under the soft tissue, without exposing it to the mouth.Second procedure: After the bone has healed, the abutment is attached to the implant, the gums are cut, and the abutment is connected to the implant using the implant's center screw.

Merits
Strong function: Can restore tooth function, chewing function is better than traditional dentures.No grinding: Artificial root restoration, without grinding healthy teeth next to it.High comfort level: No foreign body sensation, and conducive to maintaining oral hygiene.
The implant soft tissue and bone tissue have the same healing time, which is more favorable for healing soft tissue.The implant and periodontal tissue heal well, with improved initial stability.The need for secondary surgery shortens the dental implant time and reduces secondary trauma to the oral cavity.The non-submersible implant has a higher joint plane and only one joint, thus providing a more favorable biological width and gingival margin height.
High stability: Higher implant stability due to adequate healing time between implant and bone tissue.Difficult to infection: The risk of infection is reduced because the implant is completely embedded under the soft tissue.Good bone integration: The closer bonding between the implant and the bone tissue is conducive to long-term stability.Good long-term results: The long-term results are usually better because the connection between the implant and the abutment is better.High success rate: Due to the above advantages, the success rate of two-stage embedded implants is usually higher.

Shortcomings
Long operation cycle: It usually takes 3 to 6 months between primary and secondary operations to facilitate the full integration of the implant and the alveolar bone.Postoperative discomfort: After the first phase of the surgery, the mouth may be swollen and painful.
As implants are directly exposed to the oral environment, they may be more susceptible to infection by the oral bacteria.During healing, the implant may be affected by the bite force, thus affecting its stability.
Two operations are required: Compared to a one-stage implant, the two-stage embedded implant requires two operations, increasing the risk and complexity of the procedure.Long healing time: Due to the need to wait for bone tissue and implant healing, the entire treatment process is longer, usually taking several months.Higher cost: The cost of two-stage embedded implants is usually higher due to the need for two surgeries and longer treatment times.

One-Stage Implants
The base and threaded parts of an implant are manufactured as one piece, which allows for simultaneous processing and eliminates the need for later assembly.The placement of the implant in the clinic only requires a single surgical procedure, which is relatively minor and minimizes the patient's response to the implant.After surgery, the abutment is exposed to the oral cavity through the gums.The abutment may experience external forces that cause micromotion, which can affect the integration of the implant with the bone [104].By performing only one operation for a short duration, the pain can be reduced.There is no need for additional surgery, resulting in less pain and shorter healing time for the patient.Overall, this treatment reduces the cost of treatment.Although this approach involves a staged procedure, there is still a microgap between the implant and the prosthetic abutment at the level of the bone crest [105].
However, because the abutment is directly exposed to the oral cavity, it is susceptible to external fluctuations that can influence the ability of the implant to fuse with the surrounding bone tissue within a specific time period.Ensuring successful implantation in a single operation can be challenging [106].Kawakita et al. used CT scans to examine the bone morphology around the first mandibular molars and maxillary incisors.They found that selecting an appropriate implant diameter and length based on the bone morphology helped improve the success rate of the implants.Based on 10 years of clinical experience with the prototype implant system developed in the mid-1980s by the ITI ® Dental Implant System (Straumann, Switzerland), three basic implant shapes are available: solid screw, cannulated screw, and hollow cylinder implants [107].These implants were evaluated not only for survival but also for their prospective success rates.Detailed analysis showed that solid screw implants had the best results compared to cannulated screw and hollow cylinder implants.When comparing implants of different lengths, the 12 mm long implants had the highest 8-year success rate [108].

Two-Stage Non-Embedded Implants
A two-stage non-embedded implant denture can complete the implantation in one operation, eliminating the need for a second operation to repair the upper part of the structure at the oral junction.This significantly reduces the entire treatment cycle [109].The denture is connected to healthy teeth through a dental bridge, which holds it to the alveolar bone.The stability of the denture depends on the condition of the surrounding teeth or other forms of support.Soft tissue healing occurs simultaneously with bone tissue healing, promoting the closure of the soft tissue.Compared to underwater implants, non-underwater implants have a higher abutment connection plane and only require one connection suture.This creates a more favorable biological width and height of the gingival margin, eliminating the need for two surgeries and reducing the treatment time.However, this implant approach requires high levels of oral hygiene to prevent plaque formation around the healing abutment during implant healing, which can cause inflammation in the peri-implant soft tissue [110].Additionally, this type of implant requires good dental conditions and may not be suitable for everyone.
Zhang et al. [111] summarized the success rate of non-embedded implant dentures.In addition to correct treatment design, good perioperative care measures are also crucial to ensure the success of the implant surgery and form a strong implant-bone interface.This provides a solid bone support system for future implant denture repairs and enables good chewing function.

Two-Stage Embedded Implants
A two-stage embedded implant denture involves two separate surgeries to complete the implant placement [112].In the first stage, an artificial implant is fully embedded in the alveolar bone, and a healing period follows.In the second stage, an incision is made to expose the implant in the gums, and the final crown connector is repaired.This type of implant, with a strong structural implant integrated into the bone, provides stability similar to that of a natural root.The embedded implant is thus more stable and capable of supporting normal chewing and bite force.Additionally, this two-stage process separates the healing environment of the implant from the external environment, preventing bacterial attacks and reducing the risk of infection.It also allows for independent healing of the implant, without being affected by bite force.This promotes initial stability and minimizes the chances of osseointegration failure or retention of fibrous bone.However, it is important to note that the two-stage implant denture requires a second operation, resulting in a longer treatment time.Moreover, the second operation involves another incision of the soft tissue, which may potentially cause secondary damage to the soft tissue.

Classification of Implant Length
According to the classification of implant length, there are four categories: ultra-short, short, standard, and long (Table 3).Implants measuring 6 mm or less are classified as ultra-short, those measuring greater than 6 mm and less than 10 mm are classified as short, those measuring 10 mm or more but less than 13 mm are classified as standard, and those measuring 13 mm or more are classified as long [113].

Implant Diameter Classification
Implants are classified based on their diameter and can be categorized into four groups: ultra-narrow, narrow, standard, and wide (Table 4).Implants with a diameter of less than 3.0 mm are considered ultra-narrow, while those measuring 3.0 mm to 3.75 mm are classified as narrow.Implants less than 5 mm in diameter are considered standard, and those equal to or greater than 5 mm are classified as wide [113].[114].It has good biocompatibility and stability.ZrO (zirconia), on the other hand, is a ceramic material with excellent mechanical properties and chemical stability, often used for high-end dental and orthopedic implants.By combining PMMA and ZrO, a biomimetic nanocomposite material can be created, which fully exploits the advantages of both materials [115].This material inherits the biocompatibility and stability of PMMA while also possessing the high mechanical strength and chemical stability of ZrO.

Zirconia-Glass Ceramic Composite Material
The zirconia-glass ceramic composite is a combination of ZrO (Li2Si2O5) and a glass ceramic material (lithium silicate or lithium disilicate).This combination results in a material that combines the high strength, high hardness, and good biocompatibility of zirconia with the light transmittance and natural appearance of the glass phase [116].Compared to traditional total zirconia ceramic materials, this composite material provides a more natural appearance and better light transmission, making restored teeth more realistic.Additionally, this material is easier to process and repair, offering more flexibility and convenience.It has good biocompatibility and is widely used in dental restoration, such as creating tooth crowns and implant bridges.Its excellent performance ensures that restored teeth not only look realistic but also function effectively, meeting the daily needs of patients.
With the continuous development of materials science and oral clinical medicine, the application prospects for new dental implant materials will continue to expand.In the future, this material is expected to play an even greater role in improving the aesthetic effect of restorations, enhancing biocompatibility, and extending the service life.

Titanium Alloy Dental Implant Material
The use of titanium (Ti) alloy as a dental implant material offers numerous advantages due to its excellent performance.It not only prevents damage to healthy teeth but also protects the integrity of the surrounding teeth [117].Additionally, it restores the ability to chew in the area where a tooth is missing, allowing patients to eat and digest normally.Titanium implants can also serve as brackets, providing firmness to the teeth and simulating the pressure stimulation that real teeth provide.Moreover, they help maintain the stability and shape of the jawbone.Titanium has been the preferred material for dental implants for many years due to its favorable mechanical and biological properties, resulting in high clinical success rates.As surface development and temperature enhancement continue to progress, modifications are being made to improve the speed and degree of osseointegration, therefore enhancing the choices and outcomes of clinical treatment.Li et al. found that the tested titanium material exhibited reduced bacterial counts and reduced biofilm development compared to the control materials [118], Ti and PEEK.Furthermore, the experiment confirmed that the survival and success of a Ti implant in the implant area corresponded to those of an implant in natural bone.

Glass and Ceramic Materials
Glass and ceramic implant materials have good biocompatibility, bioreactivity, aesthetic effects, and bonding performance [119], and they are not easy to denature after sterilization, while also having strong compression strength, hardness, wear resistance, and stable chemical properties, but the materials are brittle and easy to fold.They can meet the patient's aesthetic and functional needs and are a worthwhile choice for restorative dentistry.In addition, they have rich sources, simple production processes, low cost, and their mechanical properties and process integrity also meet the clinical requirements.The temperature system and master phase of glass and ceramic dental materials were characterized by Wang et al. [120], who discussed how to determine the main phase of the glass and ceramic materials according to the performance requirements of the dental materials and use it to select the glass composition and the corresponding crystallization temperature system.Compared with metal and other alloy materials, their color is closer to that of natural teeth, and most of them have a guiding osteogenesis effect, which has been a hot spot in the development of biomaterials in recent years.

Different Structures of the Tooth Root
The design of the root profile of the implant directly affects the initial stability of the implant.This is determined by the shape of the portion of the implant placed approximately 3-5 mm above the alveolar socket.The design of the root profile, thread design, and self-tapping characteristics all contribute to this stability [121].
In a study by Zhong et al. [122], double-root 3D tomography, micro-computed tomography (micro-CT), and histological analysis of a 3D printed implant were conducted.It was found that the stability and bone remodeling around the fixation of the 3D-printed double-root implant were comparable.
Implants are made from a wide variety of materials.In Table 5, we have summarized the advantages and disadvantages of different types of implants.

Development of Dental Implant Surgery
Generally, prior to dental implant surgery, oral CT is required along with a routine oral examination to ensure the success of the procedure [123].In practice, the dental implant procedure is not complicated, but it does take some time.First, the dental implant can only be placed three months after the tooth extraction [1,124]; the procedure begins with anesthesia, and then the mucosa is incised on the gingiva of the missing tooth area, the alveolar bone is exposed, the implant socket is prepared, and the implant is placed.After the completion of the implant surgery, approximately three months of waiting is necessary to allow for osseointegration between the alveolar bone and the implant.Subsequently, a 3D model is created, and the most suitable simulated crown is calculated, which is then fitted onto the implant.
New 3D printing techniques have been rapidly advancing, and current surgical protocols are evolving quickly.Recent studies have demonstrated that piezoelectric surgery can minimize trauma and enhance postoperative healing more effectively than traditional drilling techniques.For instance, Maglione et al. [125] found that the ultrasonic piezoelectric approach yielded positive results in implant surgery when compared to the conventional technique.By comparing operative time and postoperative pain between the two methods (conventional drilling and ultrasonic implantation), they observed significant differences.In another study, Fujiwara et al. [126] experimentally compared the osseointegration level and marginal bone in implants using either conventional drilling or piezoelectric devices.They concluded that utilizing piezoelectric devices for implant placement is a safe procedure.
As digital technology continues to develop, personalized treatment is receiving more attention in dental implant surgery, and robot-assisted surgery may emerge as a new trend.Robotic surgery offers higher precision and stability, reducing the influence of human factors and enhancing the success rate of surgeries.

Postoperative Evaluation and Patient Expectations of Implants
Implant failures can be classified into early and late failures.Many risk factors for early implant failure listed in clinical studies are not systemic diseases, such as diabetes and hypertension, or bone-related factors, such as placement site, implant diameter, and length.Instead, they are related to bone augmentation, such as the technique and graft material used.Clauser et al. [127] conducted a systematic evaluation and meta-analysis, which found a significant association between bone enlargement procedures and early implant failure.Munakata et al. [128] summarized the factors related to early implant failure and concluded that various surgical choices of graft materials and appropriate surgical techniques can help prevent it.Late failure is mainly caused by bacterial infection.Other causes include excessive occlusal forces, poor plaque control, and overloading due to an insufficient number of implants or the effects of implant diameter and length [129][130][131].
Furthermore, implant dentistry is a relatively new field in oral healthcare, and patients often have limited experience or understanding before undergoing implant treatment.Yao et al. [132] conducted a study and found that many patients highlighted the high cost of implants in their postoperative evaluations.Many also expressed a desire for enhanced therapeutic function and improved aesthetics.McCrea et al. [133] designed a post-treatment questionnaire and conducted a statistical analysis, concluding that there was a direct relationship between patients' expectations of treatment outcomes and their satisfaction upon the completion of treatment.Significant relationships were found between appearance, comfort, and overall satisfaction, with p = 0.001.Moreover, a highly significant relationship was found between comfort level and the patient's overall experience, with p = 0.001.These studies suggest that the quality of communication between the patient and the healthcare provider plays a crucial role in determining patient satisfaction.Kashbour et al. [134] conducted face-to-face and telephone interviews with over 40 patients to explore their feelings and thoughts about dental implant surgery.They found that many patients are increasingly interested in implants as a solution for missing teeth; therefore, it is essential to establish a complete and accurate understanding of implants with patients.
The postoperative evaluation of dental implants has a significant impact on the further development of the field.Therefore, it is important to assess patient satisfaction with the treatment and identify areas for improvement in both the implant itself and the procedure.

Mechanisms of Implant Osseointegration
The maxillofacial skeleton is a highly dynamic system that requires a delicate balance between bone resorption and bone formation.It is important to understand the complex interactions among dental implants, bone, and the immune system.Osseointegration, for example, is considered to be an immune process that can result in the formation of new bone on the surface of the implant.It is not simply a single bone response.The success of an osseointegrated implant largely depends on the process of bone formation and remodeling [135].
Biologically, the fate of the implant is determined by the interaction between bone cells, immune cells, and the implant surface.Luis et al. [136] proposed that dendritic cells and macrophages, which are immune sentinels in the peri-implant environment, play a crucial role in determining the longevity of the implant.Wang et al. [137] conducted a study on dental implant osseointegration and found that macrophages play a dual role in regulating the bone healing process and the immune response to implant placement.On the other hand, research has shown that an ion-treated implant can modulate pro-regenerative immune responses and optimize osseointegration.For example, high concentrations of magnesium (Mg) on the implant surface have been shown to reduce the secretion of pro-inflammatory cytokines such as TNF-α, IL-1b, IL-6, and PEG2 [138].
In recent years, several studies have suggested a connection between hypertension and periodontal tissue metabolism and disease.Saravi et al. [139] conducted a retrospective analysis comparing a group of patients taking β-blockers and renin-angiotensin system (RAS) inhibitors with a control group.The results showed that bone remodeling and osseointegration were enhanced in the group taking RAS inhibitors (Figure 6).Therefore, the use of anti-hypertensive medication may reduce the risk of dental implant failure due to enhanced bone remodeling.The mechanisms of oral osseointegration are complex and involve various cellular and molecular processes specific to the oral and maxillofacial structures [140].A study has also shown that porous titanium surfaces can recruit bone progenitor cells, which, when differentiated into osteoblasts, produce woven bone with the influence of bone morphogenetic proteins, vascular endothelial growth factor, and other specific osteoprotegerins [141].Recognizing this complexity is important for designing specialized implant structures and achieving successful therapeutic outcomes in implant placement and prevention of oral diseases.

Conclusions
This review offers a unique perspective on the use of 3D printing technology in designing innovative dental implants.It examines the potential future advancements in the clinical application of dental implants.It begins by providing an overview of the 3D printing workflow, with a particular focus on implant coating methods and the preparation of implants using various materials, such as metals and bioceramics.It also highlights the different implant configurations available.The subsequent section summarizes recent research on the clinical application of dental implants, covering surgical approaches, patient expectations, and osseointegration studies that push the boundaries of knowledge and technology.These findings can serve as a foundation for future studies, which can incorporate emerging technologies and employ the best techniques to create superior implants.This will undoubtedly drive rapid progress in dental implant research, leading to more precise clinical treatments in the near future.

Figure 1 .
Figure 1.Comparison of healthy tooth structure and dental implant structure.Natural teeth include natural crowns, gums, and fibrous bone; dental implants include artificial crowns, abutments, and the implant.Created through Adobe Photoshop (PS) CS 8.0 drawing software.

Figure 5 .
Figure 5. Implant modeling with three types of implant: one-stage implant, two-stage non-embedded implant, and two-stage embedded implant.Created through Adobe Photoshop (PS) CS 8.0 drawing software.

Figure 6 .
Figure 6.Illustration of the potential role of beta-blockers and RAS inhibitors in peri-implant bone remodeling processes.Created through Adobe Photoshop (PS) CS 8.0 drawing software.AP-1, ac-

Table 1 .
Studies on the different 3D printing methods.

Table 2 .
Comparison of the advantages and disadvantages of different implantation methods and their use.

Table 3 .
Proposed classification scheme for dental implants based on length.

Table 4 .
Proposed classification scheme for dental implants based on diameter.

Table 5 .
Advantages and disadvantages of different types of dental implant.