Additively Fabricated Permanent Crown Materials: An Overview of Literature and Update

Abstract

Background/Objectives: With advancements in technology, three-dimensional (3D) printing has become widely used, offering many advantages. Recently, 3D printing has been utilized for the fabrication of permanent crowns. However, there is still a need for more information regarding the technology, materials, and factors that may affect the properties of 3D-printed permanent crowns. Methods: This review was conducted to collect and assess information regarding the performance of 3D printing technology for permanent crown fabrication. An electronic search was performed using various search engines (Scopus, PubMed, Google Scholar) up to December 2024, yielding 123 articles. After screening, 24 articles that specifically investigated 3D-printed crowns were included. Results: Based on the findings, two categories of materials for 3D-printed permanent crowns were identified: ceramic-based and resin-based. Among the technologies used, digital light processing (DLP) was the most common, reported in 11 studies, followed by stereolithography (SLA) in 7 studies, and lithography-based ceramic manufacturing (LCM) in 4 studies. Conclusions: Ceramic-based crowns demonstrated higher performance compared to resin-based crowns. However, resin-based crowns were found to be clinically acceptable. Ceramic-based crowns are recommended for permanent crown fabrication, while resin-based crowns require further investigation to address the limitations of the materials and technologies used.

1. Introduction

In the last few years, dentistry has seen considerable technological breakthroughs, with digital technologies transforming different parts of dental practice [1]. Among these advancements, three-dimensional (3D) printing has emerged as a transformative technology, opening up new options for manufacturing dental prostheses, especially those constructed of ceramic-based and resin-based materials [2]. Dental crowns have long been essential to restorative dentistry, protecting, strengthening, and improving the appearance of damaged or compromised teeth [3]. Traditionally, dental crown production has relied on labor-intensive techniques such as impression-taking, model-making, and manual craftsmanship [3]. Dental restorations are produced through three primary methods: conventional techniques, subtractive manufacturing (milling), and additive manufacturing (3D printing) [4]. Traditional techniques, including lost-wax casting, heat-pressed ceramics, and hand-layered porcelain, are labor-intensive and include several stages, such as wax pattern creation, investment, casting, and sintering [4]. These techniques yield superior restorations, but they are labor-intensive, reliant on the operator’s skill, and susceptible to dimensional mistakes [5]. CNC milling, a subtractive manufacturing technique, established a digital workflow that markedly enhanced precision, consistency, and productivity [6]. Milling employs pre-sintered zirconia or resin blocks, which are shaped with high-speed burs. Due to the dense microstructure of the milled material [7], this technology has shown high accuracy (trueness ~10–50 µm) and better mechanical properties. Nevertheless, milling produces considerable material waste, tool degradation, and constraints in geometric intricacy [8]. Additive manufacturing (3D printing) constructs restorations incrementally, facilitating intricate designs, optimal material utilization, and mass customization [9].

While computer-aided design and computer-aided manufacturing (CAD/CAM) technologies have significantly improved the efficiency and precision of dental crown fabrication in recent decades [10], additive manufacturing is emerging as another tool that offers further opportunities for customization and material efficiency [11]. However, these technologies also present challenges, including the need for specialized software, proprietary systems limited to specific manufacturers, and material constraints such as the handling of zirconia-based ceramics. New advancements in dental crowns provide improved accuracy, personalization, and efficiency compared to older procedures [12].

Three-dimensional printing, also known as additive manufacturing, is the process of making 3D items layer by layer using digital models. Dentistry frequently uses this technology to create dental prostheses like crowns, bridges, and dentures [2], as well as surgical guides and orthodontic appliances [11]. The process starts with digital scanning of the patient’s oral cavity, followed by the use of computer-aided design (CAD) software to design the crown. The digital model is subsequently transformed into a physical object utilizing various 3D printing technologies, such as stereolithography (SLA), digital light processing (DLP), and selective laser sintering [12,13].

Three-dimensional printing in dentistry has various advantages over traditional approaches. For starters, it enables the exact manufacturing of dental crowns with complex geometries that would be difficult or impossible to create using traditional methods [14]. This precision leads to better-fitting crowns, which can enhance patient comfort and lessen the need for dental modifications. Furthermore, 3D printing is typically faster and more efficient than traditional manufacturing procedures, allowing dentists to perform same-day crowns in some circumstances [15]. New technologies have led to the suggestion of innovative materials for 3D-printed crown fabrication, which fall into two categories: ceramic-based and resin-based. Dental materials used in crown fabrication are categorized according to worldwide criteria to guarantee quality and safety. Ceramic crowns are chiefly governed by ISO 6872, which delineates the standards for dental ceramics, encompassing their strength and translucency [16]. ISO 10477 describes the mechanical and physical properties of polymer-based materials used in both permanent and temporary restorations [7]. This is where resin-based crowns fit in. These categories establish defined criteria for assessing the appropriateness of 3D-printed items for clinical use.

Ceramic crowns are composed of advanced ceramic materials; these crowns have become increasingly popular in restorative dentistry [17]. Ceramic crowns offer exceptional esthetic benefits, closely mimicking the natural appearance of teeth through their remarkable translucency and color-matching capabilities [18]. Their biocompatibility is a significant advantage, with minimal risk of allergic reactions and excellent tissue tolerance [19]. Clinically, these crowns allow for more conservative tooth preparation, preserving more of the natural tooth structure compared to traditional alternatives [20]. Despite their numerous benefits, ceramic crowns present several challenges. The primary concern is their higher cost, which can be substantially pricier than traditional crown materials [21]. Mechanical limitations include a greater propensity for chipping or fracturing, particularly in areas of high occlusal stress [22,23].

Polymer-based crowns are dental restorative devices fabricated from advanced synthetic materials, offering an alternative approach to traditional crown fabrication [24,25]. These crowns utilize high-performance polymeric materials designed to address specific clinical challenges in dental crowns. Their lightweight nature and reduced weight compared to ceramic or metal crowns provide improved patient comfort and reduced stress on the underlying tooth structure [26]. However, their mechanical properties are generally inferior to ceramic or metal-based alternatives, with reduced hardness and wear resistance [23]. Long-term durability remains a concern, as polymeric materials may demonstrate higher susceptibility to degradation, discoloration, and dimensional changes under oral environmental conditions [27].

The use of 3D printing to produce definitive crowns has also been linked to higher patient satisfaction. Patients appreciate the ability to swiftly generate custom-fitted crowns that match the color and feel of their natural teeth [14]. Furthermore, the flexibility of 3D printing allows for simple alterations and modifications, ensuring that the final crown suits each patient’s individual requirements [28].

As 3D printing technologies improve, several critical features must be thoroughly investigated to determine their suitability for clinical use [29]. These include the precision and fit of 3D-printed crowns, their mechanical qualities and longevity, surface characteristics and esthetic outcomes, and overall clinical performance [30]. Furthermore, factors such as manufacturing efficiency, cost implications, and the complexity of integrating these technologies into dental practices play a crucial role in their widespread adoption [31]. However, using 3D printing technology in dental crown production presents some obstacles [32].

This literature review provides a thorough review of the present state of 3D printing technologies for ceramic-based and polymer-based crown materials and fabrications. By evaluating recent studies and breakthroughs in this sector, we want to better understand the possible benefits, limitations, and future possibilities of these technologies. This review will look at various topics, including the accuracy and fit of 3D-printed crowns, their mechanical qualities, clinical performance, and manufacturing issues.

2. Materials and Methods

2.1. Search Strategy

A comprehensive literature search was conducted using the following electronic databases: PubMed/MEDLINE, Scopus, Web of Science, and Google Scholar. The search was limited to articles published in English from January 2014 to December 2024 to focus on the most recent developments in the 3D printing field. The search terms used included combinations of keywords such as “3D printing”, “dentistry”, “ceramic-based crowns”, “resin-based crowns”, “additive manufacturing”, “dental crowns”, “definitive crowns”, and “Milling”.

2.2. Inclusion and Exclusion Criteria

The inclusion criteria include original research (in vitro and clinical studies); reported 3D printing technologies for fabricating ceramic or resin-based crowns; studies evaluating the accuracy, fit, mechanical properties, or clinical performance of 3D-printed crowns; and full-text articles available in the English language only. Excluded studies were case reports, opinion articles, or conference abstracts; studies focusing solely on other dental applications of 3D printing (e.g., surgical guides, orthodontic appliances); and articles are not published in peer-reviewed journals or in English.

An initial search yielded 453 articles, from which 330 duplicates were removed. After screening 123 articles, 62 were excluded for being unrelated to permanent crowns. A total of 38 full-text articles were assessed for eligibility, leading to the exclusion of 14 studies due to irrelevance or unmet criteria. Ultimately, 24 full-text studies were included in this review (Figure 1).

2.3. Data Extraction

A standardized data extraction form was created in Excel to collect relevant information from each included study. The following data were extracted in Table S1

Study characteristics (authors, year of publication, study design).

3D printing technology used.

Material(s) studied (zirconia, dental resin-based, or both).

Outcome measures (e.g., accuracy, fit, mechanical properties, clinical performance).

Key findings.

Strengths and limitations of the study.

2.4. Data Synthesis

The extracted data were synthesized to provide a comprehensive overview of the current state of research on 3D-printed ceramic-based and resin-based crowns. The synthesis involved summarizing the key findings, comparing the results across studies, and identifying common themes and discrepancies. The findings were categorized into key themes: accuracy and fit, mechanical properties, clinical performance, surface characteristics and esthetics, manufacturing efficiency, and others. The results were synthesized within each theme to identify trends, consistencies, and discrepancies across studies.

3. Results

This review analyzed multiple studies on the application of 3D printing technologies for fabricating ceramic-based and resin-based dental crowns. The detailed characteristics of the included articles are presented in Table S1.

3.1. Printing Technologies

Approximately 11 out of 24 of the studies utilized DLP as the 3D printing technology, followed by SLA in 7 studies and lithography-based ceramic manufacturing (LCM) in 4 studies. The remaining studies reported using various other technologies: nanoparticle jetting (NPJ) in 1 study and inkjet printing in 1 study.

3.2. Crown Materials

A total of 15 studies used ceramic-based crown material, 7 studies used resin-based crown material, and 2 studies reported using both ceramic-based and resin-based crown materials.

3.3. Properties Investigated

The results from the selected studies can be categorized and discussed into several vital areas, including accuracy and fitness, mechanical properties, clinical performance, surface characteristics and esthetics, and manufacturing efficiency.

3.4. Accuracy and Fit

Several studies have evaluated the precision and fit of 3D-printed ceramic-based crowns. A study discovered that 3D-printed ceramic-based crowns had comparable trueness and a better fit than milled crowns [33]. Another study found that 3D-printed monolithic ceramic-based crowns had higher precision and better margin quality than conventional approaches [34]. This fits with what Revilla-León et al. found, which was that the fit of 3D-printed temporary dental crowns on the outside and inside was good enough for clinical use [35]. Different studies, like those by Refaie et al. and Lerner et al., which found bigger marginal gaps or lower trueness in 3D-printed crowns, show that there is still room for improvement [36,37]. According to a study, 3D-printed ceramic veneers were just as good at marginal adaptation (95 μm) and production accuracy (26 μm) as traditional methods [38].

For dental resin-based crowns, the authors discovered that ceramic-filled 3D-printed resin-based crowns fit and were just as accurate as traditionally made crowns, which suggests that they could be used in clinical settings [39]. Li et al. conducted a comparative analysis utilizing the 3D deviation and adaptation approach and discovered that SLAs with occlusal full-supporting structures demonstrated higher external 3D trueness and clinically acceptable performance than pillar supports [40].

The heterogeneity in results among research underscores the necessity for measuring methodology standardization, as underlined by Nawafleh et al. in their systematic review of crown margin measurements [41]. Future studies should concentrate on optimizing printing parameters and post-processing processes to ensure excellent accuracy and fitness.

3.5. Mechanical Properties

The mechanical integrity of 3D-printed crowns is crucial to their long-term clinical effectiveness. Several studies have focused on the mechanical qualities of 3D-printed crowns. A study discovered that both 3D-printed ceramic-based crowns and composite crowns had the right amount of fracture resistance. However, 3D-printed ceramic-based crowns were less reliable than milled ceramic-based crowns because they had flaws in the material [42]. This observation is reinforced by another study where two short-term clinical trials found no mechanical or biological complications with 3D-printed yttrium-stabilized tetragonal zirconia polycrystal (3Y-TZP) ceramic-based crowns [43]. A study discovered that milled ceramic-based crowns had stronger fracture resistance than 3D-printed crowns, but both groups produced clinically acceptable results [36]. This is consistent with a study that found the mechanical properties of 3D-printed dental ceramics were generally lower than those of conventionally produced ceramics [30]. When glued to ceramic-based abutments that are supported by implants, Zandinejad et al. found that there was no significant difference in how easily the crowns broke between those that were milled and those that were made with additive manufacturing [44,45].

The physical and mechanical properties of three-dimensionally printed crowns can be affected by the layer thickness, which can interfere with the choice of the 3D-printed resin-based solution for a desired clinical outcome [46]. Three-dimensionally printed materials may be suitable for long-term crowns, such as inlays, onlays, and laminate veneers, despite the observed decrease in mechanical properties after aging [47]. Another study also stated that 3D-printed composite resins have mechanical qualities comparable to commercially available composite resins [48]. It is possible that screw-retained, implant-supported crowns made from the tested definitive composite resin-based crowns could be good alternatives for premolar implant-supported crowns [49]. It was found that 3D-printed crowns were as true on the outside, inside, marginal area, and inside of the teeth’s biting surface as CAD-CAM crowns, which means they met the standards for trueness [50]. Researchers compared fracture strength and hardness, reporting that milled materials’ fracture strength increased with thickness, while 3D-printed materials’ fracture strength varied [51].

3.6. Clinical Performance

In a short-term pilot study, Kao et al. looked at 3D-printed zirconia crowns made with selective laser melting (SLM) for restoring back teeth [52]. Over a 24-week follow-up period, the study reported that 100% of the crowns received satisfactory grades based on the quality evaluation system of the Modified California Dental Association. The crowns demonstrated excellent marginal adaptation and no adverse periodontal effects, despite minor increases in plaque and gingival indices during the early weeks. Three-dimensionally printed resin-based crowns performed similarly clinically to stainless steel crowns in primary molar crowns, with better esthetics and patient satisfaction [14]. However, as emphasized by Alharbi et al., long-term clinical trials are still required to properly prove the efficacy of 3D-printed dental restorations [30]. Another one-year recall study reported on the clinical performance of 3D-printed dental restorations, indicating that while short-term results are promising, randomized controlled studies with longer follow-up periods are crucially needed [53].

3.7. Surface Characteristics and Esthetics

Çakmak et al. evaluated different polishing techniques and found that coffee thermal cycling affected the surface roughness and stainability of the materials [54]. They recommended considering the polishing technique and material type to optimize the esthetic dental crown. In terms of esthetics, researchers compared the color stability and translucency of 3D-printed crowns with those of conventionally constructed ceramic crowns [55]. Another study compared multiple printing technologies and materials, providing a comprehensive understanding of their performance and finding variations in surface roughness and color stability [56]. This fluctuation is comparable with the findings of Chavali et al., who discovered that the rough surface of 3D-printed dental materials can vary greatly depending on printing conditions and post-processing processes [57].

Raszewski et al. (2023) and Shishehian et al. (2023) both show how important it is to prepare the surface of 3D-printed dental restorations before they are used to keep their color [58,59]. Both studies found that unpolished surfaces were highly susceptible to discoloration when exposed to common staining agents, such as coffee, tea, and orange juice. Polished surfaces, on the other hand, exhibited significantly better resistance to staining, highlighting the importance of proper polishing and curing to ensure long-lasting esthetic outcomes in clinical applications. The influence of material type and thickness on fracture resistance was observed. Recommendations for clinical practice include considering the material properties and thickness when selecting materials for dental crowns to enhance durability [60]. In another study, they additively manufactured resin-based crowns and found them more susceptible to simulated brushing and coffee thermal cycling than other materials [61]. Future studies should focus on refining these characteristics to achieve consistent, high-quality surface finishes.

3.8. Manufacturing Efficiency

Several studies have shown that 3D printing has the potential to reduce material waste compared to traditional milling technologies [12,62]. This conclusion is consistent with a comprehensive review by Dawood et al., who highlighted the potential of 3D printing to revolutionize dental manufacturing processes [2]. The increasing interest in 3D printing technologies highlights their significant potential in the future of implant dentistry [63]. These technologies offer benefits such as high material efficiency, the capability to create intricate geometric shapes, and the production of customized components from CAD files, making them a viable alternative for generating dental implants. Detailed cost–benefit evaluations are required to properly comprehend the economic ramifications of incorporating 3D printing technologies into dental practices [64].

3.9. Implications for Different Crown Materials

The review identifies unique patterns in ceramic-based and resin-based crowns. While 3D-printed ceramic-based crowns show potential, they still struggle to match the mechanical qualities of milled ceramic-based ones. This conclusion is congruent with the findings of Li et al., who highlighted the improved mechanical qualities of traditionally treated ceramic-based crowns [40]. In contrast, 3D-printed resin-based crowns, particularly for pediatric applications, perform similarly to or better than traditional options.

Kim et al. compared 3D-printed and conventional dental crowns clinically. They found that 3D-printed resin-based crowns performed similarly to traditional ones [65]. However, 3D-printed ceramic-based crowns showed lower fracture resistance in posterior areas compared to their conventional counterparts.

3.10. Technological Considerations

The research evaluated various 3D printing technologies, including stereolithography (SLA), digital light processing (DLP), and lithography-based ceramic manufacturing (LCM). According to Stansbury and Idacavage in their evaluation of 3D printing technologies for dental applications, the used technology appears to influence the end product’s qualities [66].

3.11. Comparative Studies and Clinical Performance

Comparative studies have demonstrated that ceramic-based and resin-based crowns made with 3D printing methods perform well in clinical settings. For example, 3D-printed ceramic-based crowns have been shown to have good marginal adaptation and fracture resistance, comparable to or better than milling crowns [52]. Similarly, 3D-printed resin-based crowns have produced favorable clinical results regarding fit, durability, and patient satisfaction [52]. However, obstacles still exist, particularly in improving the surface roughness and long-term performance of 3D-printed crowns [15]. Additionally, future studies are needed to test other important characteristics such as fatigue [67] and resistance to acidic drinks [68].

3.12. Study Limitations

Despite several investigations into innovative technologies for permanent prostheses, a limited amount of research has examined crown configuration. The limited number of included studies constitutes a constraint of this research, compounded by the diverse technologies and materials employed (resin-based and ceramic-based) throughout the included articles, as well as the variations in assessed attributes among the studies. This study possesses multiple shortcomings requiring acknowledgment. The scope of materials and printing settings analyzed was limited, potentially failing to encompass the full range of alternatives present in the field. Secondly, the absence of extensive clinical data limits our capacity to ascertain the longevity and efficacy of these crowns in practical settings. Future studies should address those shortcomings to furnish a more thorough assessment of 3D-printed dental crowns. Despite these encouraging results, additional study is required to comprehensively understand the long-term clinical efficacy of 3D-printed crowns. Future investigations should prioritize systematic reviews and meta-analyses to deliver a more thorough evaluation of 3D-printed permanent crown materials. Integrating standardized procedures, including systematic risk of bias evaluations and extended clinical trials, would improve the reliability of results. Moreover, broadening the scope to include more types of fabrication techniques, material compositions, and clinical performance outcomes will enhance the evidence base.

4. Conclusions

Three-dimensional printing technology has substantially revolutionized the field of dental crowns, particularly in the production of ceramic-based and resin-based crowns. These advances have several benefits, including increased accuracy, adaptability, and efficiency. While current research shows promising outcomes, further studies are required to enhance these technologies for broader clinical application. This literature review focuses on the potential of 3D printing to alter dental crown practices, paving the door for more effective and personalized patient treatment.