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Complete dentures have long been the most commonly used treatment option for completely edentulous patients.1,2 Their prevalence has increased worldwide with the rising demographic of older patients, who represent the primary users within the general population.
The clinical performance of a prosthesis depends largely on the mechanical properties of its materials. During function, dentures experience flexural stress, which generates internal strains. The most prevalent material for fabricating conventional complete removable denture prostheses is polymethyl methacrylate (PMMA). Despite its widespread use in this capacity, PMMA has several shortcomings, including high polymerization shrinkage, susceptibility to microbial colonization from the oral environment, lack of radiopacity, a proneness to allergic reactions due mainly to the monomer, degradation of mechanical properties over time, and low wear resistance in human saliva.1
Efficiency is crucial to optimizing workflows, and this is a key driver of digital dentistry. Computer-aided design/computer-aided manufacturing (CAD/CAM) technology has transformed manufacturing processes in dentistry. A remarkable benefit of this approach in prosthodontics is the ability to create complete dentures (CDs) in just two or three clinical appointments.
This article explores the current state of clinical workflows, materials, and manufacturing processes for digital dentures.
Manufacturing Techniques and Workflows
The digital fabrication process for removable dental prostheses begins with data collection; this involves scanning the maxilla, an impression, or a cast. Next, the record blocks and wax rims are scanned to transfer the clinical data to a computer to begin the designing phase. Lastly, the CAM process is then carried out through either an additive technique, commonly known as 3-dimensional (3D) printing, or a subtractive technique, referred to as milling.3,4
3D Printing Technique
One of the early attempts to manufacture digital dentures involved the integration of digital design with traditional methods. Over the past 20 years, 3D printing has emerged as a promising solution, primarily because of its ability to deliver faster restorations compared to those created by dental technicians. This technology could represent a potentially low-cost alternative for the manufacturing of CDs.
3D printing can be defined as a method for producing digitally designed objects by stacking materials in successive layers.3 The first 3D-printed denture was developed by Dentca in 2015.1 Additive techniques involve the direct photoactivation of a liquid resin into a desired shape, which could potentially provide better accuracy compared to subtractive methods. However, this approach may lead to polymerization shrinkage. In contrast, PMMA blocks used for milling are characterized by a high degree of polymerization and high fracture resistance; therefore, they enhance longevity.1,5
Two primary types of printing technology are used to fabricate 3D-printed CDs: digital light processing (DLP) and stereolithography (SLA). Both methods use a photopolymer resin available in various shades for denture bases and teeth. The 3D-printing process begins with the design of the denture, which is divided into two separate files: one for the pink denture base and another for the white denture teeth (Figure 1). These components must be printed independently, as only one color can be printed at a time. The printing process starts by mixing the resin according to the manufacturer’s instructions. The resin is subsequently poured into a tank for printing. Once both components are printed, the denture base and teeth must be cleaned of any unpolymerized resin by soaking them in an isopropyl alcohol bath.6
Following the cleaning process, the denture teeth need to be securely attached to the denture base using a denture base resin (Figure 2). The finished CD is then placed in a light box, where it is exposed to a specific temperature and light wavelength. In some workflows, only the denture base can be fabricated while conventional carded denture teeth are used. In such cases, each tooth is individually bonded to the denture base with specific bonding agents.
Polyjet technology is another printing method that facilitates the multimaterial jetting of photopolymers. This process enables the simultaneous printing of both the denture base and teeth. Like all denture processing techniques, these entities need to be post-processed to remove the supports, soaked in caustic soda solution, and polymerized while submerged in glycerol. Finally, the denture is polished and finished (Figure 3).7
The orientation of resin layers during 3D printing can significantly impact the mechanical properties and precision of the dentures. This is because of the additive nature of the layers, which can initiate crack propagation that could possibly lead to structural failures in the printed object. When a material is printed vertically, with the load applied perpendicular to the layer orientation, it exhibits higher compressive strength compared to a material printed horizontally. Additionally, the bond between layers is generally weaker than the bond within a single layer. This phenomenon can be attributed to the residual stresses and porosities that accumulate during ultraviolet polymerization and material shrinkage.8 In a study by Hada et al on the effect of printing direction on the accuracy of 3D-printed dentures using SLA technology, the highest trueness and precision and the most favorable surface adaptation occurred when the printing direction was 45 degrees (Figure 4).9
Other factors such as light intensity, layer count, the software used, shrinkage between layers, support structures, and post-processing can also affect the accuracy of printed dentures. Conversely, the subtractive method often yields more uniform objects with better accuracy, making it more appropriate for intraoral devices with high occlusal forces.10
CAD/CAM (Milling) Technique
The subtractive approach involves milling the denture base from a pre-polymerized resin blank, followed by the bonding of prefabricated or milled denture teeth to the base. Examples of these systems include the Florence TotalProx® Denture System (Zirkonzahn, zirkonzahn.com), Ivoclar Digital Denture (Ivoclar, ivoclar.com), Vita Vionic® (Vita Zahnfabrik, vita-zahnfabrik.com), and AvaDent® Digital Dentures with Bonded Teeth (AvaDent, avadent.com). Recently, innovative systems, such as AvaDent Digital Dentures XCL1 and XCL2, the Baltic Denture System (Merz Dental, merz-dental.de), and Ivotion® (Ivoclar), have been introduced that are capable of milling both the denture and teeth from a single blank.
Several studies on CAD/CAM dentures show high accuracy of the denture base adaptation and retention compared to conventional denture manufacturing, mainly because of the absence of polymerized shrinkage.4,11 Other advantages of CAD/CAM-produced dentures in relation to conventional dentures include high mechanical properties, reduced clinical time, less movement of artificial teeth, high patient satisfaction, and less biofilm formation.2,3,8,12-14 A systematic review by Wang and colleagues on the accuracy of digital CDs revealed a positive outcome in trueness and denture base adaptation that was similar to or better than conventionally fabricated CDs, thus supporting digital technology as an alternative to traditional manufacturing.10 Another study by Yoshidome et al showed that milled CD bases presented with excellent fitting accuracy, and SLA-printed CDs had a clinically acceptable fitting accuracy when compared to conventional dentures.15 Charoenphol and colleagues also found that milled dentures fit more accurately than 3D-printed dentures.16
Nevertheless, substrative systems also have several disadvantages. Teeth are usually monochromatic and unappealing. To overcome this shortcoming, some manufacturers have developed a unique layering system to produce polychromatic teeth, which enhances esthetics. Waste materials are also considered a detriment, as a considerable portion of the resin blank remains unused and is typically discarded during the milling process.16 The wearing of milling burs is another drawback. These issues are the main drivers to improve 3D printing technology. However, the mechanical and physical properties of materials used with 3D printing are still inferior compared to CAD/CAM technology materials, and 3D printing materials also still offer reduced retention and have compromised esthetics. The accuracy of impressions is also considered one of the drawbacks of digital dentures.5,12
Benefits and Challenges of Digital Dentures
Digital CDs offer several clinical advantages over their conventional counterparts, including time savings—which may reduce the possibility of mistakes—lower costs, pleasing clinical outcomes, reduced workload for technicians, and improved management of patient records. Nevertheless, numerous studies recommend conducting clinical trials to achieve reliable results.7
3D printing is considered to be a more sustainable technique than CAD/CAM milling, as these additive systems use less material and can create large, high-resolution models such as maxillofacial prostheses, and multiple dentures can be fabricated simultaneously. Furthermore, 3D printing is generally more cost-effective compared to CAD/CAM systems, because there is no need for a specialized laboratory, making digital CDs more accessible to individual dental practitioners.3
Regarding the number of appointments, the conventional workflow of dentures typically comprises five sessions: diagnostic impressions, master impressions, wax rim try-in, esthetic try-in, and complete denture placement. These steps are then followed by post-insertion adjustment sessions as required. With the digital workflow, many of the manual procedures are digitized, and appointments can include between two and four sessions based on the manufacturer’s system being used (Figure 5 through Figure 7).3,7
While these technologies help shorten treatment times and decrease the number of clinical appointments, they do require know-how for designing, printing, and finishing. Although this process can be performed chairside, it is often necessary to collaborate with a laboratory. The digital workflow undoubtedly saves time and enhances the clinician’s efficiency. Ultimately, the reduction in chairtime for clinicians and patients is among the most significant benefits of using digital CDs and 3D printing.
Clinical Performance and Patient-Related Outcomes
Complete dentures can have a significant impact on oral health, affecting not only masticatory efficiency, phonetics, and esthetics but also denture-related issues, such as denture stomatitis, which refers to the inflammation of the mucosa beneath a removable prosthesis. It presents with a high prevalence, affecting between 15% to more than 70% of CD wearers. Several factors can contribute to the development of this condition. Some risk factors are associated with systemic and immune diseases or reduced salivary flow, while others are related specifically to the dentures, including trauma, poor denture hygiene, rough surfaces, and the presence of pores in the acrylic material. The colonization of Candida albicans has been identified as a significant risk for denture wearers developing denture stomatitis. An in vitro study examined the surface characteristics, biofilm formation, and mechanical resistance of resins in dentures made using CAD/CAM milling and 3D printing technologies. The findings showed that increased surface roughness significantly enhanced biofilm adhesion compared to smoother specimens. In particular, CAD/CAM-milled PMMA polymers demonstrated the lowest formation of C albicans biofilm and the highest flexural strength, whereas 3D-printed specimens displayed the lowest flexural strength and the highest surface roughness.14 Additionally, a study conducted by Al-Fouzan et al compared the adhesion of C albicans to the surfaces of CAD/CAM denture bases and conventional denture bases. The results revealed a significant difference, with C albicans demonstrating lower adherence to complete denture bases made with CAD/CAM technology compared to those made conventionally.17
When assessing retention and stability with digital dentures, several studies have shown better retention among CAD/CAM-fabricted dentures compared to conventionally fabricated ones,18 and others have confirmed that 3D-printed dentures are comparable to, or even superior to, conventional dentures with regard to retention.2 However, 3D-printed dentures made using digital impressions have shown inferior retention when compared to those created from conventional impressions and digitized casts.2 Faty et al reported that milled denture bases demonstrated significantly higher retention than printed and conventional denture bases with insignificant differences between the latter two. The authors attributed this to the minor dimensional changes of the pre-polymerized blocks in the subtractive manufacturing process.19 Other investigations showed that conventional CDs exhibited better retention than 3D-printed dentures, but no significant difference was found between conventional CDs and CAD/CAM CDs.4
Inconsistencies exist among different studies regarding patient-based outcomes, such as patient satisfaction, oral health–related quality of life, complications, and preferences. Patient satisfaction is a key outcome measure that evaluates the performance of a prosthesis from the patient’s perspective across several aspects, including retention, stability, esthetics, and phonetics. A meta-analysis by Avelino and colleagues revealed no significant difference between digital and conventional CDs with regard to patient-related outcome measures.4 Zandinejad et al showed improved retention and reduced production time with milled and printed CAD/CAM-fabricated CDs.18
While most studies have reported positive results in these areas of patient satisfaction, some have raised concerns, particularly regarding esthetics and phonetics with 3D-printed dentures. These issues might be due to the increase in the palatal thickness of approximately 2.5 mm to ensure resin strength. In the Yoshidome et al study, the authors also reported that phonetics was significantly better with conventional dentures than with 3D-printed dentures.15 Ohara found that conventional dentures outperformed digital dentures with regard to comfort, stability, phonetics, and overall satisfaction. Additionally, CAD/CAM dentures were found to provide a more suitable treatment option compared to 3D-printed dentures due to their better properties, including trueness, base adaptation, and strength.20 A systematic review by Zandinejad et al revealed that patient satisfaction regarding pronunciation was higher for conventional dentures than for complete digital dentures.18 However, internal adaptation and overall satisfaction were comparable between conventional and digital dentures. As for post-insertion maintenance, printed dentures have shown comparable results to conventional dentures in the short term.2
When clinicians evaluated denture quality, both types of digital CDs (CAD/CAM and 3D-printed) were deemed significantly better than conventional dentures in all evaluated parameters, with insignificant differences between CAD/CAM and 3D-printed.21 Other researchers have shown that the esthetics of 3D-printed dentures are inferior to those of conventional dentures.3 A systematic review on clinical outcomes of milled, 3D-printed, and conventional CDs revealed that both milled and 3D-printed versions performed better than conventional dentures in terms of retention, fewer appointments, patient comfort, and maintenance.18
Conclusion
The integration of digital technologies in the manufacturing of CDs has marked a significant paradigm shift in prosthodontics. Conventional manufacturing for CDs involves considerable effort from both the dentist and dental technician. Digital dentures, whether fabricated using additive or subtractive methods, offer promising advantages, particularly in terms of efficiency, reproducibility, clinical time reduction, and simplicity of procedures. Milled dentures demonstrate superior mechanical strength, surface properties, and lower biofilm adherence, while printed dentures are rapidly moving forward as materials improve and because of sustainable fabrication methods. Nonetheless, challenges with digital CDs still remain regarding esthetic quality, phonetic outcomes, and material limitations. As the technology continues to evolve, further research is necessary to establish standardized protocols and validate the effectiveness of digital dentures in the long-term. The future of removable prosthodontics is undeniably digital, yet for now this methodology should be approached with critical evaluation and an evidence-based perspective.
ABOUT THE AUTHORS
Macarena Rivera, DMD, MSc
Assistant Professor, Department of Prosthodontics, University of Chile, Santiago, Chile; Adjunct Professor, Department of Preventive and Restorative Sciences, University of Pennsylvania School of Dental Medicine, Philadelphia, Pennsylvania; Private Practice, Santiago, Chile
Sebastián Cifuentes, DMD, MSc
Clinical Instructor, Department of Prosthodontics, San Sebastián University, Concepción, Chile; Private Practice, Llay Llay, Chile
Markus B. Blatz, DMD, PhD
Professor of Restorative Dentistry, Chair, Department of Preventive and Restorative Sciences, and Assistant Dean, Digital Innovation and Professional Development, University of Pennsylvania, School of Dental Medicine, Philadelphia, Pennsylvania
Queries to the author regarding this course may be submitted to authorqueries@conexiant.com.
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