Trends and future perspectives of 3D printing in prosthodontics

Abstract

The three-dimensional (3D) printing technology has led to transformative shift in prosthodontics. This review summarizes the evolution, processing techniques, materials, integration of digital plan, challenges, clinical applications and future directions of 3D printing in prosthodontics. It appraises from the launch of 3D printing to its current applications in prosthodontics. The convergence of printing technology with digital dentistry has facilitated the creation of accurate, customized prostheses, redefining treatment planning, design, and manufacturing processes. The progression of this technology is from generating models to prosthesis like-fixed dental prosthesis (FDP), implants, and splints. Additionally, it exhibits more wide capabilities. The exploration of materials for 3D printing provides various options like polymers, ceramics, metals, and hybrids, each with distinctive properties that are applicable to different clinical scenarios. The combination of 3D-printing technology and digital workflow simplifies the processes of data transfer, computer-aided design (CAD) design to fabrication, decreasing errors and chairside time. The clinical benefits include enhanced accuracy, comfort, conservative lab procedures, and economics. Challenges in the technology involve significant aspects like initial investment, material availability, and skill requirements. Future trends emphasize on research for improved materials, bioprinting integration, artificial intelligence (AI) application, regularization efforts to ensure safe and common use of the technology. 3D printing offers promise in prosthodontics, addressing challenges through research. The material improvements will promote its broader adoption and revolutionize the future of dental rehabilitation.

Introduction

In recent years, the employment of three-dimensional (3D)-printing technology has created a significant revolution in the field of prosthodontics.¹ The innovation has transformed traditional approaches in prosthodontics and that changed the outlook of oral rehabilitation. The convergence of 3D printing with digital dentistry has created a new era of precision, customization, and efficiency in prosthodontics.² Customized prostheses with unique oral anatomies of individual patients can be produced with the cutting-edge additive manufacturing techniques.^{3, 4, 5}

3D-printing technology redefines the prosthesis fabricating procedures and also enhances patient care. Accurate digital impressions, use of computer-aided design (CAD) software, layer fabrication aids in constructing of prosthesis with the highest accuracy and improved patient-care.^{6, 7, 8} This review aims to explore into the intricate aspects of 3D printing in prosthodontics, exploring its applications, material advancements, integration with digital workflow, clinical benefits, limitations, and future developments. The review comprehends its impact, potentials, and implications for the future of prosthodontic rehabilitation.

History

The science fiction stories of Murray Leinster and Raymond Jones proposed the concept of 3D printing in 1940s and 1950s. The thoughts underwent various processes and developments.⁹ The early steps of 3D-printing technology can be tracked back to a metal printing device patented by Johannes F Gottwald in 1970's and with further significant developments occurred in 1980's. The inventions on additive manufacturing by Alain Le Méhauté, Olivier de Witte, Jean Claude André, Hideo Kodama and Bill Masters were vital and the emergence of stereolithography by Charles Hull was a major breakthrough in 3D-printing technology. In the 1990s, the use of 3D-printing technology increasingly expanded from industrial sectors into the medical field, including dentistry. The utility of 3D printing in dentistry, particularly in prosthodontics, started to gain traction in the late 1990s and early 2000s.⁵ By the mid-2000s, developments in material science and computer-aided design/computer-aided manufacturing (CAD/CAM) technology augmented the capabilities of the technology.¹⁰ Researchers continue to explore new materials, techniques to improve the mechanical properties, biocompatibility, and esthetics of 3D-printed dental prostheses.

Types of 3D-printing technologies

3D-printing technologies are of many types. These technologies vary on the needs, printable materials, accuracy levels, and speed. Each type has significant advantage and disadvantages over others. Table 1 provides a brief summary of various types used for 3D-printing technology.^{11, 12, 13, 14, 15} More popular among them are fused deposition modeling (FDM), selective laser sintering (SLM) and Vat polymerization. FDM is one of the most commonly used 3D printing methods. Thermoplastic material is extruded and deposited layer by layer to fabricate prosthesis. The affordability and wide material compatibility make it popular among other techniques. It lacks intricate detail found in other methods due to visible layer lines. Vat polymerization involves curing liquid resin layer by layer to create objects. This method uses a Vat or reservoir containing liquid photopolymer resin that hardens when exposed to light. There are two primary subtypes: stereolithography (SLA) and digital light processing (DLP). SLA uses a focused ultra violet (UV) laser to trace and solidify specific patterns on the liquid resin, solidifying it layer by layer. SLA printers are known for their high precision and surface finish, making them suitable for detailed models and prototypes. DLP utilizes a digital light projector to flash and cure entire layer of the resin simultaneously. This method can offer faster print compared to traditional SLA due to its ability to cure entire layers at once. Vat polymerization technologies, such as SLA and DLP, are valued for their ability to create intricate designs with high resolution and smooth surfaces.^5,8,11

Table 1.

Various types of 3D-printing technology.^{11, 12, 13, 14, 15, 16}

Technology	Technique	Advantages	Disadvantages
Fused deposition modeling (FDM)	Uses melted thermoplastic materials to build layer by layer.	•Economical, •versatile materials, •easy to use.	•Lesser resolution, •noticeable layer lines, •restricted with intricate designs.
Stereolithography (SLA)	UV light polymerizes liquid resin layer by layer.	•Superior precision, •smooth finish, •can print complex details.	•Costly equipment, •limited materials, •post-processing mandatory.
Selective laser sintering (SLS)	Laser blends powdered materials into solid layers.	•Multi- material choices, •can print intricate geometries.	•Expensive, •uneven surface finish, •Powder handling.
Digital light processing (DLP)	Instantaneous curing of resin layer through Projector (DLP)	•Rapid printing, •economical, •superior resolution.	•Limited materials, •low precision than SLA, •post-processing required.
Binder jetting	Binds layers of powder material with a binding agent.	•Fast process, •multiple materials, •cost-effective for prototypes.	•Lower resolution, •brittle parts, •post-processing required.
Material jetting	Jets and polymerizes ingredients in droplet form layer by layer.	•Diverse material options, color prints, superior accuracy.	•Costly •slower than other methods, •reduced scalability.
Electron beam melting (EBM)	Electron beam softens and fuses metal powders.	•Robust metal printing, •marginal material waste.	•Narrow choice of material, •costly equipment, •complex procedure.
Direct energy deposition (DED)	Dissolves and deposits material from a nozzle or powder bed.	•Fast, •appropriate for large parts.	•Higher surface roughness, •limited accuracy, •Expensive equipments.
Laminated object manufacturing (LOM)	Layers and bonds sheets of material.	•economical, •suitable for large models, •diverse materials can be used	•Inferior resolution •post-curing required •can't print for intricate details.
Continuous liquid interface production (CLIP)	Uses UV light and oxygen to polymerize resin.	•Fast, •good finish,	•Restricted to specific resins, •Initial investment is expensive, •rarely used.
VAT polymerization (SLA and DLP)	Cures liquid resin in a vat layer by layer.	•Superior precision •detailed models •superior finish.	•Limited materials, •post-curing needed •relatively expensive.

There are variations in the precision obtained through different technologies. Each technique is associated with specific layer thickness. SLA has a thickness of 25 μm, inkjet prints at 12 μm, and FDM approximately 127 μm.¹⁰ However these methods have assured replication at nano-scale fabrication. The accuracy can be of concern in some of the prosthetic applications like implant components. Though technically it provides greater assurance. The literature data display a vertical gap of 11 μm for the implant abutment in 3D-printing technology. Additionally, the technology demonstrates errors of 0.4 mm for implant guides and satisfactory accuracy (0.1–0.4 mm error range) for the wax patterns of maxillofacial prosthesis. The recent advancements in Direct metal laser sintering (DMLS) technology have limited validated studies on the internal and marginal fit accuracy. While the techniques display capacity for various prostheses, further research and standardization in methods are required to ensure consistent accuracy for clinical use.^5,10,11

Applications

The employment of 3D printing has revolutionized various aspects in prosthodontics, offering a wide array of applications that enhance precision, customization, and efficiency. An overview of the diverse applications of 3D printing in prosthodontics include diagnostic models, implant guides, customized implants, custom trays, crowns, fixed dental prosthesis (FDP), removal partial denture (RPD) patterns using various materials like ceramics, resins, and metals.^{12, 13, 14}

3D applications enable easy fabrication of FDP. The software facilitates the precise design of these prostheses based on digital scans, ensuring an accurate fit and natural appearance. Initial investment in CAD/CAM systems can be high, and requires adequate training to optimize its use. Additionally, there are limitations in the use for some materials in fabrication of FDP.^16,17

Conventional complete dentures require multiple appointments and adjustments. The dentures can be fabricated through various digital modeling softwares. The technology offers better fit, comfort, and aesthetics.^18,19 The narrow choices of materials and concerns on biocompatibility can influence the durability and longevity of printed dentures. Additionally, the maintenance and calibration of 3D printers are essential for their precision.

3D applications play a vital role in the treatment planning and surgical positioning of dental implants. The technology aids in fabrications of precise surgical guides based on CT scans that assist in accurate positioning of implants.⁵ The technology enhances precision, decreases surgery time, and improves the success rate of the implants. However, methodological concerns or mistakes in planning may alter the accurate implant placement. Quality assurance and rechecking becomes mandatory in the design and construction of surgical guides for optimal outcomes.¹⁰

3D printing SLA aids in fabrication of lightweight prosthesis without compromising strength.¹⁹ The CAD software eases the design procedure, aids in adjustments and before printing, reduces the requirements for manual changes during clinical procedures. 3D printed RPD offers benefits in weight, fit, strength and durability of the material. However, integrating 3D technology into conventional laboratory workflows requires training and knowledge.²¹

Digital modelling and printing technology creates aesthetic facial prostheses in shorter time. Concerns still exist on definitive materials especially on biocompatibility, surface finish for fabrication of maxillofacial prosthesis compared to conventional materials.⁹

Digital models aid in fabrication of temporomandibular disorders (TMD) devices or splints in accordance with the patient requirements. Inadequate clinical research data are available on long-term effectiveness and standardized protocols are a clinical concern for the TMD devices. Extended printing applications involves the fabrication of aligners and other orthodontic devices. It is been widely used with huge success. The ongoing advancements in materials shall further improve the applications and transform the fabrication of various dental prosthesis.^{4, 5, 6}

Materials used for 3D printing technology

A diverse range of material including polymers, ceramics, metals, and hybrid material are utilized for 3D printing. Each material has distinct properties, strengths, limitations, and suitability for various clinical scenarios. Polymers like acrylonitrile butadiene styrene, polylactic acid, acrylates, methacrylate, and photopolymer resins are generally used for temporary crowns, models, and some denture components. Polymers offer high versatility, are economical, and can provide adequate aesthetics. They lack the strength and durability required for long-term restorations. Some polymers might also exhibit higher wear rates compared to other materials. It is commonly used for temporary prosthetics, prototypes, models, where long-term durability is not a primary concern. The concerns especially on biocompatibility and durability exists on various materials used. More clinical research data are required to substantiate their validity. Further research is required on the development of materials for their long term use.

Dental ceramic materials in 3D-printing technology face challenges with anisotropic shrinkage during sintering and display surface effects due to the fabrication process. Presently the use is limited primarily to tissue scaffolds rather than functional prostheses. However, the research and developments on the materials display more assurance.^10,16,17

Metals like cobalt-chromium and titanium alloys are utilized for printing dental implants and RPD frameworks due to their strength and biocompatibility.²⁰ These metals offer exceptional strength, durability, and corrosion resistance. They can be challenging to mill or polish. Additionally, their high density might lead to increased weight for larger restorations. They are more ideal for dental implants, RPD frameworks, and prostheses that require superior mechanical properties and long-term stability.²¹

Hybrid materials combine properties of different materials, such as polymers with ceramic fillers or composite materials. These materials can offer a balance between strength, aesthetics, and ease of processing. The properties and performance of hybrid materials may vary based on the specific composition.^{22, 23, 24} Hybrid materials can be suitable for various applications, providing a compromise between different material characteristics based on specific clinical needs.

Selecting the appropriate material for 3D-printed prosthodontic applications involves considering factors like mechanical properties, biocompatibility, aesthetics, wear resistance, and the specific requirements of each clinical case. Advances in material science continue to expand the range of available materials, offering clinicians and dental technicians more options to cater to diverse patient needs in prosthodontics.^10,21,23

Digital work flow integration

The integration of 3D printing into the digital workflow has transformed the entire process.

Scanners capture accurate details of required oral structures either by direct (intra oral) or by indirect technique (lab scanners). These digital records are the foundation of digital workflow-designing, and fabrication of the prosthesis.¹⁵ The digital workflow combined with 3D-printing technology ensures high precision and accuracy. The streamlined digital workflow significantly decreases chairside time and the patient's clinical visits. The customized prostheses additionally improve patient satisfaction.^12,13

3D printing enables the creation of surgical guides and precise treatment planning for minimally invasive procedures, especially in implant dentistry. Accurate placement of implants with pre-surgical planning, minimizes invasiveness, reduces surgical time, and enhances the success rate of implant procedures.¹⁶

The integration of technology allows for the creation of physical models that patients can visualize and understand, enhancing their involvement in treatment decisions. Visual aids support in patient education by demonstrating the proposed treatment outcomes, leading to better-informed patients and improved treatment acceptance. The rapidly evolving nature of 3D-printing technology enables dental professionals to stay at the forefront of innovation, adopting new materials, techniques, and advancements for better patient care.^7,8

Challenges and future directions

Implementing the technology has brought in transformative developments, but it confronts several limitations for its universal acceptance. The initial investment overheads for the equipment are comparatively high making it a limitation in few dental practices. Limited availability of few materials for prosthodontic applications may restrict the use of the technology. Regulatory frameworks differ across regions causing difficulties in ensuring the fulfilment of global prosthodontic standards and regulations. The requirement for recognized guidelines for safety, quality assurance and production processes are vital for safeguarding patient safety.^5,6

Sufficient training and expertise are required for professionals to efficiently use the technology. The learning skill related with digital workflows, software, and machine operation may present challenges for professional to transit from conventional methods. Attaining ideal finish and aesthetics requires further post-processing procedures. Developments in these procedures are required to simplify the finishing process and achieve dependable results. Constant research is required to develop the 3D-printing technology in prosthodontics, with special focus on improving material properties, printing techniques, and evaluating on long-term clinical outcomes.^{10, 11, 12, 13, 14} Further studies are essential to evaluate the biocompatibility, mechanical properties, and durability of 3D-printed prostheses for various applications.

Emerging trends and future developments

Ongoing research aims to develop new materials with improved properties, including better strength, durability, aesthetics, and biocompatibility for diverse prosthodontic applications. The integration of bioprinting techniques with 3D printing may lead to the fabrication of bioactive materials and structures for tissue regeneration and custom-designed implants. Integration with AI and automation could enhance the efficiency of digital workflows, allowing for automated design optimization and predictive modeling. Efforts to establish standardized protocols, regulations, and quality control measures specific to 3D-printed dental prosthetics will drive the adoption and safe implementation of this technology.

3D printing holds immense promise in prosthodontics, addressing these challenges through research, standardization, improved materials, and enhanced accessibility will pave the way for its wider adoption and future advancements in the field.

Considerations for diverse use of technology^10,11,12,15

Various critical aspects are essential to apprehend and consider in 3D-printing technology in prosthodontics, they are:

• •Selecting the appropriate materials is fundamental in 3D printing. The materials have varying properties like strength, flexibility, durability, biocompatibility, and aesthetics. Choosing the suitable materials for intended application ensures optimum performance.
• •The layer height or resolution establishes the accuracy of the printed prosthesis. Finer layer resolution aid in superior details but it extends the printing time. The knowledge on optimizing layer resolution is important for attaining accuracy in prostheses.
• •Diverse printing technologies have distinct advantages and disadvantages. Knowledge on the proficiencies and limitations of the technology assists in selecting the suitable technique for prosthodontic applications.
• •Adequate training and knowledge in CAD software is essential for making precise digital models. CAD proficiencies aid in customization of prosthetic designs ensuring a perfect fit and functionality.
• •Proficiency in post-processing procedures that involves polishing, curing, staining, or glazing is essential to obtain the required surface finish. This is essential to warrant that the final prosthesis meets the optimum standards.
• •Knowledge and binding of regulatory standards related to 3D-printed medical devices, including prosthetics, is vital and essential. Observing the standard aids in quality, biocompatibility, patient safety, and legal adherence.
• •Estimating the cost-effectiveness of the printing technology is vital. The investments on machines, materials, and training should be matched on the reimbursement.

Conclusion

The ongoing research and inventions drive developments in 3D-printing technology for prosthodontics. It aids in producing improved materials, printers, and widen the applications in prosthodontics. Understanding the critical aspects are important for effective implementation, application, and development of technology in prosthodontics.

Disclosure of competing interest

The authors have none to declare.