Advancements in digital technologies over the past decade have revolutionized dentistry, particularly with the integration of digital workflows in removable partial dentures (RPDs). Key innovations include digital data capture and computer-aided design and manufacturing, which enhance patient comfort, streamline workflows, and reduce treatment time and costs. Initially embraced by fixed restorations, these technologies are now transforming RPDs, previously reliant on analog methods. The collaboration between dentists, laboratory technologists, and patients is essential for selecting optimal materials and achieving successful RPD treatments.
Key points
- •
Introduction of digital technologies has seen the rise of novel materials and fabrication techniques for removable partial dentures (RPDs).
- •
A critical factor in successful RPD treatment lies in the meticulous selection of materials for the framework, clasps, and denture base.
- •
Each step of digital workflows of RPD treatment will be outlined and compared with the conventional analog approach.
Introduction
Removable partial dentures (RPDs) serve as an essential treatment modality for restoring missing teeth either as an interim or a definitive treatment option for patients who either are not eligible for tooth or implant-supported fixed prostheses or cannot afford them. Since their inception, RPDs have had little in the way of change in both technique and material of fabrication. However, in recent years, the introduction of scanning, digital design, milling, printing technologies, and dental implants have seen the rise of novel materials and fabrication techniques for RPDs.
The restoration of partially edentulous arches remains a cornerstone of prosthodontic therapy. RPDs offer a cost-effective and versatile solution for patients missing their teeth. A critical factor in successful RPD treatment lies in the meticulous selection of materials for the framework, clasps, and denture base. Each material boasts unique properties, necessitating a collaborative approach between the dentist, the laboratory technologist, and the patient to determine the optimal choice.
The past decade has witnessed a revolution in dentistry fueled by advancements in digital technologies. Streamlined workflows, shorter appointments, and enhanced patient comfort are just a few of the tangible benefits. At the heart of this transformation lies the digital capture of data (scanning), computer-aided design (CAD), and computer-aided manufacturing (CAM) of dental prostheses. This not only minimizes errors but also reduces overall treatment time and cost. While fixed restorations were early adopters of these advancements, removable prostheses remained largely reliant on traditional analog methods. Fortunately, recent innovations are opening doors for a seamless integration of digital workflows into RPD treatment. This section will explore how digital workflows can be seamlessly integrated into RPD treatment, outlining each step compared with the conventional analog approach.
Diagnostic records
The traditional diagnostic workflow for RPDs involves a series of physical processes: capturing impressions of the dentition and edentulous ridges, registering occlusal contacts, and transferring maxillo-mandibular relationships using a facebow and inter-occlusal records. Thankfully, the digital revolution has ushered in a wave of effective digital alternatives that streamline the diagnostic phase, enhance patient comfort, and boost clinical efficiency.
At the heart of this digital transformation lies intraoral scanning. The intraoral scanners have undergone a remarkable metamorphosis since their early iterations as powder-coated image capture tools. Today, they leverage video capture and advanced artificial intelligence algorithms to facilitate a more accurate and efficient scanning experience. A 3-dimensional (3D) cast for an RPD can be acquired in 3 ways: either by directly scanning the patient’s mouth using an intraoral scanner, by scanning a traditionally made impression using a desktop scanner, or by scanning a traditionally made cast using a desktop scanner.
However, intraoral scanners have limitations when encountering the complexities of RPDs. They excel at capturing static, hard tissues like teeth, but soft tissues that move can pose a challenge. Treatments dominated by nonmovable tooth structures, like Kennedy Class III or IV RPDs, present minimal difficulties during scanning. However, for treatments with extensive edentulous spans or extension bases (Kennedy Class I or II RPDs), the scanner encounters the challenge of capturing the involved soft tissues, which tend to move and distort the scan. To mitigate this movement, dental professionals use techniques like cheek retraction and constant tension on the tongue and lips while scanning. Additionally, minimizing the number of scans taken on such areas is crucial, as each scan carries the risk of capturing the soft tissue in a slightly different position, potentially leading to discontinuities or inaccuracies in the final scan data. Maintaining a dry scanning environment is also paramount to avoid reflection and refraction that can compromise scan accuracy.
Diagnostic maxillo-mandibular relations are a critical component of RPD treatment planning, but this can be complicated by the multiple missing teeth often present in such treatments. Traditionally, a minimum of 3 occlusal stops are required to hand articulate analog casts on an articulator, a device that simulates jaw movements. However, patients requiring RPDs frequently lack these crucial stops. The analog workflow might involve obtaining physical casts, and fabricating record bases, followed by a separate appointment for interocclusal records, causing inconvenience for the patient.
Fortunately, intraoral scanners offer a distinct advantage. Even with just one remaining occlusal contact, jaw relation records can be captured accurately. For patients requiring positioning in centric relation (CR), record bases can be fabricated and scanned together with the teeth in CR position. Alternatively, an anterior deprogramming device (Lucia jig) or a leaf gauge can be used to stabilize the patient during the virtual capturing of CR.
The conventional facebow transfer, a process used to relate the dental arches to the patient’s cranium, can also be replaced with a digital alternative. A complete-face photograph, with the patient looking directly at a camera, can be aligned within the dental design software. The patient’s intraoral scan is aligned with the photo, enabling visualization of a digital smile design. Many software programs now boast sophisticated virtual articulators that can be overlaid on this merged photo. Some programs even allow input of additional condylar information, such as horizontal condylar inclination, if such records are available from other diagnostic methods.
Surveying and design
Traditionally, removable partial denture design has been a hurdle for dentists due to several factors. First, design philosophies often rely on subjective opinions rather than objective evidence, leading to inconsistencies and confusion, even among dental students. This often results in dentists deferring design to laboratory technicians, who may not possess the same level of knowledge and clinical expertise. Second, the traditional workflow involves manual surveying with tools like the Ney Surveyor to identify the path of insertion, survey lines, and undercut areas for clasps. Finally, once a design is finalized, it is typically drawn on paper or directly on the diagnostic cast.
Fortunately, the advent of digital dental technologies has ushered in a new era of streamlined and efficient RPD design. Many dental laboratories now use design software equipped with digital surveying tools ( Fig. 1 ). These tools analyze digital casts to identify undercuts and heights of contours, aiding in both the design and the fabrication of the RPD framework. However, these software systems are often expensive, not readily accessible to dentists in their practices, and not easy to learn and master.
Formerly, the only feasible way for dentists and laboratory technicians to survey a digital cast involved printing a physical copy and mounting it on a traditional surveyor. While feasible, this method introduced delays due to printing times and steps involved, disrupting the digital workflow. Fortunately, a new generation of diagnostic digital surveyors has emerged. These innovative tools allow direct surveying of patient scans, identifying the path of insertion, undercuts, and heights of contour directly from the intraoral scan data, eliminating the need for physical casts and saving valuable treatment and laboratory time ( Fig. 2 ).
Following the surveying process, digital RPD design software empowers dentists and laboratory technicians to create designs digitally. These programs offer 2 main design approaches: manual drawing for user-driven design and philosophy-specific automatic design algorithms. Automatic design algorithms generate design proposals based on preprogrammed design philosophies ( Fig. 3 ). It is crucial to remember that these algorithms function solely as design assistants, providing proposals that require final approval and potential customization by the laboratory technician and the dentist. The dentist ultimately bears the responsibility for fabricating an optimal prosthesis for the patient, while considering the complexities of the oral environment.
Once a design is generated, further customization is possible using free 3D model editing software. These tools allow laboratory technicians and dentists to directly mark specific areas on the 3D cast for potential mouth preparation, further enhancing communication and treatment planning.
Mouth preparations
Mouth preparations encompass adjustments made to the dentition prior to capturing the final impression. These modifications can include adjustments to the height of contour, creation of guide planes, rest seat preparations, and incorporation of existing fixed or surveyed restorations. Traditionally, any modification to the tooth structure would be completed following the established treatment plan.
However, the digital revolution has introduced an exciting opportunity to integrate “surveyed fixed restorations” into the digital workflow. Advancements in zirconia material science have led to the development of stronger iterations that can be milled directly from a digital design, eliminating the need for traditional surveying techniques ( Fig. 4 ). Following the milling process, it is recommended to print a 3D model including the tooth preparations, the milled surveyed crowns, and the surveyed abutments. This model is then mounted on a surveyor to meticulously verify the parallelism of all guide planes and the precise contours of these crowns ( Fig. 5 ).
While the long-term interaction between zirconia crowns and cast metal RPD frameworks requires further investigation, these restorations offer undeniable advantages. Zirconia boasts unmatched esthetics and strength compared with traditional metal-ceramic restorations, proving particularly beneficial for patients with high esthetic demands. By integrating surveyed fixed restorations into the digital workflow, laboratory technicians and dentists can achieve a more streamlined and potentially more precise restorative treatment.
Final impressions
Similar to the diagnostic impressions, final impressions can also be made using intraoral scanners. However, meticulous attention to detail is crucial during the scanning process. Particular emphasis should be placed on comprehensively capturing all rest seat preparations, guide planes, and the functional depth of the vestibule. The same meticulous protocols employed during diagnostic scans, to minimize soft tissue movement and the potential inaccuracies, remain paramount.
Furthermore, final impression accuracy is critical for successful RPD outcomes. The scan must encompass all major anatomic landmarks required for an RPD design ( Fig. 6 ). Constant and sustained retraction of the tongue and cheeks is essential to achieve an accurate soft tissue impression ( Fig. 7 ). However, in some challenging cases, complete capture of supporting soft tissues might be hindered. In such scenarios, an additional “corrected cast impression technique” ( Fig. 8 ) can be employed to complement the digital scan.
One of the most significant advantages of digital final impressions lies in the ability to verify real-time clearance for lingual rest seat preparations on the maxillary anterior teeth. Traditionally, this verification could only occur after the master casts were articulated, potentially causing treatment delays. Fortunately, intraoral scanners eliminate this wait time, allowing for immediate confirmation and any necessary adjustments during the scanning appointment.
Work authorization
Traditionally, work authorizations, and paper forms outlining specific instructions for RPD fabrication, have been the linchpin of communication between dentists and dental laboratories. These forms ensured quality assurance and quality control, protecting patients and dental professionals, and delineated responsibilities.
With the advent of digital technology, however, communication channels have undergone a significant transformation. Previously, the limitations in digital media and the cumbersome nature of sending all required information digitally hindered the widespread adoption of digital workflows for RPDs. However, the ability to capture all necessary components electronically has paved the way for a new era of streamlined communication through digital laboratory work authorizations.
Digital laboratory authorizations offer several compelling advantages over their paper counterparts. First, they eliminate the need for physical transportation of impressions, casts, and articulators, minimizing the risk of damage during transit. Second, they streamline the workflow by facilitating a completely digital exchange of information. Finally, they allow for easier archiving of digital data for future reference.
Despite these advantages, the core principles of proper work authorization remain equally important in the digital realm. Clear and concise instructions are essential for a successful collaboration between dentists and laboratories. Many contemporary laboratories now offer dedicated digital portals where dentists can submit work authorizations. These portals typically follow a user-friendly format, allowing dentists to input protected patient information, select the specific work request, provide written instructions, and upload relevant digital and photographic files ( Fig. 9 ).
