The purpose of this paper is to review the available literature on three-dimensionally printed complete dentures in terms of novel biomaterials, fabrication techniques and workflow, clinical performance and patient satisfaction.
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A total of 126 titles were obtained from the electronic database, and the application of exclusion criteria resulted in the identification of 21 articles pertaining to printed technology for complete dentures. Current innovations and developments in digital dentistry have successfully led to the fabrication of removable dental prostheses using CAD/CAM technologies. Milled dentures have been studied more than 3D printed ones in the currently available literature. The limited number of clinical studies, mainly case reports, suggest current indications of 3D printing in denture fabrication process to be custom tray, record bases, trial, interim or immediate dentures but not definitive prostheses fabrication. Limitations include poor esthetics and retention, inability to balance occlusion and low printer resolution.
Despite the reduction in the incidence of edentulism in this generation cohort [1], the absolute number of edentulous patients is increasing due to the increase in life-expectancy [2,3,4]. Complete removable dental prostheses (CRDP) or complete dentures (CD) have been used to rehabilitate patients with complete edentulism for centuries [5]. Those prostheses meet the minimum social and physiological needs of the patients [6] and have not evolved significantly in recent years.
Contemporary advancements in digital dentistry have started to affect the fabrication of this treatment modality. Digital dentistry has revolutionized the practice of dentistry in many fields since its introduction in the 1980s [11]. In 1994, the first attempt of developing a computer-aided-designed/computer-aided-manufactured (CAD/CAM) system to fabricate a complete removable dental prosthesis emerged [12]. The launch of digital denture construction, however, was marked by Goodacre et al. in 2012 [13]. In this article, a prototype served as an example of the type of program that could be incorporated in the future fabrication of digital dentures. Today, an exponential increase in the number of materials available in the market for fabrication of digital CRDPs is attributed to the ongoing evolution and enhancement of digital technologies [14].
Additive manufacturing (AM), also known as 3-dimensional (3D) printing or rapid prototyping (RP), encompasses techniques that fabricate objects layer by layer. 3D printing, despite its relative recent introduction, has shown potential in many fields like engineering and medicine including dental medicine [17]. The available 3D printing systems for complete removable dental prostheses are FotoDenta denture (Dentamid, Germany) and Dentca 3D Printed Denture (Dentca, USA) [15].The limited resolution and reproducibility of the available printers along with their technical constraints have so far posed obstacles in such manufacturing methods of dental restorations [18, 19].
The emerging AM technology is modifying the clinical and laboratory processes of fabricating removable prostheses. The purpose of this paper is to review available literature on 3D printed complete dentures in terms of novel biomaterials, fabrication techniques and workflow, clinical performance, and patient satisfaction.
Contrary to that, another study evaluated the accuracy and surface resolution of denture bases fabricated by three methods: injection molding, milling, and rapid prototyping using surface matching software. The results comparing the fit accuracy between the cast and the maxillary complete denture base were evaluated on the second upper premolar and the second upper molar regions crossing the midpalatal suture, showing relatively high deformation in the conventional method due to polymerization shrinkage and internal stress. The mean value of discrepancies, however, was the lowest in the RP method, followed by that in the milling method and the injection molding method [23].
With 3D printing, the build direction (layer orientation) affects the mechanical properties of the dental restorative material [31]. This is due to the nature of incremental layers in additive manufacturing technology, which may initiate crack propagation and result in a structural failure of the printed material. In an in vitro study, layer orientation was found to affect the compressive strength of 3D-printed composite material. The material printed vertically with the load perpendicular to the layer orientation exhibits a higher compressive strength than a material printed horizontally [32]. Also, it is important to understand that the bond between the layers is weaker than that within the layer. This is explained by the amount of residual stresses and porosities that accumulate during UV polymerization and material shrinkage [33].
Initial reports describing the CAD/CAM fabrication of CRDPs less than a decade ago, demonstrated several advantages. The two systems that were commercially available first for fabrication of digital complete dentures were Avadent and Dentca [38, 39]. Avadent uses laser scanning and proprietary software to arrange the denture teeth and design the bases. Dentca, on the other hand, uses computer software to produce virtual maxillary and mandibular edentulous ridges, arrange the teeth, and form bases. The dentures in AvaDent are milled from prepolymeried pucks of resin while those of Dentca were initially fabricated with a conventional processing technique.
A significant goal of incorporating new technologies into the dental practice is to provide better treatment solutions for the patients. There are only a few clinical studies with small sample sizes either case reports or pilot prospective cohorts, mainly on milled digital dentures, The retention with milled complete denture bases from prepolymerized poly(methyl methacrylate) resin is significantly higher than that with conventional heat-polymerized denture bases [53]. Esthetics appears to be the limiting factor when evaluating the clinical outcomes of a two-appointment process for digital dentures [54, 55]. Generally, more adjustment appointments were necessary than indicated by the manufacturers [55, 56] while relining has been reported to be required in as much as 40% of the digital dentures [57].
An online survey sent to all of the 50 program directors of postdoctoral prosthodontics programs across the United States revealed that all program directors were aware of current trends in complete denture fabrication using CAD/CAM technology but only 10% or less of complete denture cases are currently processed using the CAD/CAM technology, at either the post- or predoctoral levels [65]. However, plans to add digital denture fabrication into their curricula within the next 1 to 4 years were stated in their responses.
Current innovations and developments in digital dentistry have successfully led to the fabrication of removable dental prostheses using CAD/CAM technologies. 3D printing has the potential to modernize and streamline the denture fabrication techniques, materials and workflows. Current limitations include elimination of try-in appointment without reliable virtual esthetic evaluation, lack of retention with printed polymers requiring reline for clinical acceptability, inability to balanced occlusion that may compromise denture stability or potentially affect bone resorption and long-term color instability that leads to esthetic deterioration. Presently recommended usages for 3D printed complete dentures are interim or immediate dentures as well as custom tray or record base fabrication for conventional workflows. Well-designed clinical studies are needed to scientifically prove the claimed advantages of this technology.
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