Quick reference/description
Indications
Materials/instruments
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Alginate impression material
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3D scanners (intraoral and extraoral)
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Rubber-based impression materials
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Designing equipment (with or without physical sculptor)
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Laser-sintering equipment
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3D printing equipment
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Milling equipment
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Polyether ether ketone
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Ultaire aryl ketone polymer
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Acetyl copolymer
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Polyethylene terephthalate
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Polymethylmethacrylate
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Polyamide
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Finishing burs
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Barrels of ceramic and corn
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Electropolishing device
Procedure
Fabrication technique | Materials | Brand name | Manufacturers |
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Direct milling | Polyether ether ketone | PEEK-Optima LT1 | Juvora Ltd., Lancashire, UK |
CORTiTEC medical PEEK | Imes-icore GmbH, Eiterfeld, Germany | ||
Ultaire AKP (aryl ketone polymer) | Dentivera | Solvay Dental 360, Alpharetta, GA, USA | |
Acetyl polymer | Zirlux acetal | Zirlux, Milville, NY, USA | |
Polyethylene terephthalate | Estheshot Bright disk | Nissin Ltd., Japan | |
Polymethylmethacrylate (PMMA) | PMMA | Nissin Ltd., Japan | |
3D Printing | Polyamide nylon | Valplast denture base filaments | Afrona, Brooklyn, NY, USA |
Step | Equipment | Manufacturer |
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Scanning | Intraoral 3D scanners | |
Cadent iTero | Align Technology, San Jose, CA, USA | |
CEREC Omnicam | Dentsply Sirona, York, PA, USA | |
TRIOS | 3Shape, Copenhagen, Denmark | |
Extraoral 3D scanners | ||
DS20 optical scanner | Reinshaw, UK | |
7Series | Dental Wings, Montreal, Canada | |
inEos X5 | Dentsply Sirona, York, PA, USA | |
E3 | 3Shape, Copenhagen, Denmark | |
Designing | Without physical sculptor | |
3Shape CAD points | 3Shape, Copenhagen, Denmark | |
Partial Framework CAD | exocad GmbH, Darmstadt, Germany | |
DWOS Partial Frameworks | Dental Wings, Montreal, QC, Canada | |
SilaPart CAD | SilaDent, Golsar, Germany | |
Digistell CAD | C4W-Digilea, Montpellier, France | |
ModelCast | imes-icore GmbH, Eiterfeld, Germany | |
InLab CAD | Dentsply Sirona, York, PA, USA | |
With physical sculptor | ||
Geomatic® Touch™ X | 3D SYSTEMS, SC, USA | |
Production | Direct metal production | |
Laser sintering | ||
AM 250 | Reinshaw, UK | |
PM100 Dental & PM100T | Phenix, Riom, France | |
Farsoon FS121M | LSS GmbH, Holzwickede, Germany | |
M1 cusing laser | Concept Laser GmbH, Lichtenfels, Germany | |
EOSINT M270 | EOS, Munich, Germany | |
Repeated laser sintering and milling | ||
LUMEX advance-25 | Matsuura, Tokyo, Japan | |
Indirect production | ||
3D printing | ||
Varseo S | Imes-icore GmbH, Eiterfeld, Germany | |
Asiga PICO2 HD | BEGO, Bremen, Germany | |
ProJet™ DP 3000 | Whipmix, Louisville, KY, USA | |
Form 3B | Formlabs Inc., Somerville, MA, USA | |
Milling | ||
Organical Desktop S8 | R + K Organical CAD/CAM GmbH, Berlin, Germany |
Acquisition
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Alginate impression material is used to make primary impressions that are then poured into diagnostic casts.
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Careful case evaluation is performed from the diagnostic cast, and a design for the PRDP is planned. Simultaneously, planning of abutment teeth preparations is also done. The abutment teeth are prepared as per the PRDP design.
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After tooth preparation, intraoral or extraoral scanning of the patient’s arches is performed. Intraoral scanning is performed with an intraoral scanner, thereby, eliminating the requirement of a physical impression. This includes several scans of both arches requiring about 3–17 min. The scans are then joined by the software resulting in a full-mouth image. Intraoral scanning is particularly effective in Kennedy class III cases; however, it does not capture the physiologic extension of the mucosa in Kennedy class I and II cases.
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Alternatively, rubber-based impression materials are used to make final impressions, which are then scanned directly with an extraoral digital scanner or made into master casts and then scanned. In general, bench top scanning of the cast models achieves comparable accuracy regardless of the type of dental stone used.
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Extraoral scanning of either the impressions or the stone-model scans can both provide adequate precision, although, digitalized alginate impressions present considerably better dimensional accuracy than stone models, and the precision of scanned impressions can be further improved using scannable elastomeric impressions materials.
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The scanner generates a stereolithographic file (STL) of the master cast that is imported into the designing software ( Fig. 1).×
Manipulation
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Initially, a digital survey tool is used to automatically determine the path of insertion (Fig. 2). The software measures the depth of undercuts and the parallelism and rotates the cast three dimensionally to achieve the best tilt for the path of insertion. Based on these calculations, a survey line is automatically created. This digital step saves time in comparison to the conventional manual procedure.×
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After establishing the survey line, the undesirable undercuts are blocked digitally and the sites for the placement of the retentive clasp tips are determined (Fig. 3).×
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Thin layers of virtual wax are placed on relief areas, like the rugae.
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A sprue is designed for the casting process in indirect fabrication systems (3D printing and milling).
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Prior to submission of the completed design for additive technology systems (laser-sintering and 3D printing), special supports are added to the structure to hold the prosthesis (Fig. 10). The supports should have enough strength to stabilize the PRDP framework layers during production. During manufacturing, the supports prevent movement and dissipate heat away from the completed part of the framework.×
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The entire designing process requires about 30 min for each framework.
Fabrication
Direct metal production | Indirect metal production |
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Laser sintering and laser melting are used for direct metal production of PRDP | Stereolithography, and direct light processing and milling are used for indirect metal production of PRDP |
In these systems, the metal powder is laser sintered to create the framework (Fig. 11a) | A wax or resin framework pattern is printed or milled in these systems (Fig. 11b, c, d) |
A laser-sintering machine requires up to 12 h to fabricate 12 PRDPs in a single cycle | Following 3D-printing of a framework, multiple post-curing steps, like removing of wet resin residue through solvent immersion of the pattern and final curing in a UV oven for complete hardening and achieving structural integrity, are essential |
The printed PRDP is retrieved and sent for post-fabrication processing | |
For retrieval of the PRDP, it is subjected to heat treatment according to the manufacturer’s instructions and detached from the supporting base | |
If required, the resin pattern can be checked in the patient’s mouth before casting it conventionally using the lost-wax technique | |
The fit of the framework is assessed on the cast and adjusted (Fig. 12) |
Post-fabrication processing
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Finishing and polishing of the framework is performed in a series of steps. It is first finished using finishing burs followed by finishing under rotating barrels of ceramics and corns in sequence. Electropolishing is performed for final finishing of the frameworks (Fig. 11).
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The PRDP framework is evaluated for its fit and occlusion in the patient’s oral cavity. At this stage, several factors like maxillomandibular relationship and tooth shade and form are selected as for conventional PRDP.
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The framework is forwarded to the laboratory for manual teeth setting, final wax-up and acrylization.
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The final PRDP is checked in the patient’s mouth for fit, retention and occlusion. It is adjusted if necessary. Following adjustment, the PRDP is finished, polished, and delivered to the patient (Fig. 13).×××
Advantages of digital PRDPs
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Digital designing methods save time, as manual surveying and framework wax-up is not required.
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Direct metal production systems enhance productivity, while reducing the workflow and manufacturing costs. They also minimize maintenance costs of the machines.
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Digital PRDP production is environment friendly because of decreased wastage of wax, alloy, and investment materials. The residual uncured metal powder following laser sintering can be recycled and reused.
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Virtual designs can be saved to allow clinicians to provide patients with additional or replacement prostheses having the same or a modified design. Saving virtual designs also enables their sharing between dentists and technicians through email or over the internet.
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Digital PRDP production facilitates the workflow and improves the quality of the treatment. Digitalization of the production permits the use of optimized designs with enhanced mechanical properties that are customized for each patient.
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It allows the use of multiple different materials such as polymer-based materials to overcome the limitations of metal PRDPs.
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Use of intraoral scanning is beneficial in patients with specials needs or a severe gag reflex or in anxious patients. Its sectional scanning technique allows easy moisture control, and joining together of the images allows easy identification and correction of any impression defects or deficiencies.
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Clinical trials comparing digital PRDPs to conventional have shown that digital PRDPs present fewer complications and achieve higher patient satisfaction rates than conventional PRDPs, specially when it comes to the fitting and retention of the prosthesis.
Pitfalls and complications
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Only the metal framework can be fabricated using the laser-sintering technology, while tooth setup is performed manually as it cannot be done digitally.
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The initial cost of the machine for digital production of PRDP is high.
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Favorable production of digital PRDP has a steep learning curve and requires time.
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During the 3D-printing process of digital PRDP, special supports are required to hold the prosthesis that needs additional steps for planning these supports and removing them following fabrication.
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The layering nature of the process of 3D-printing results in a staircase effect that can be markedly decreased by reducing the thickness of the layer. But decreasing layer thickness can increase production time.
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The technique of producing digital PRDP cannot be utilized in all patients, as it is difficult to produce some special designs due to limitations of the available software and manufacturing methods.