Mark D. Williamson, CDT
(IDT, Oct. 2020, Vol. 11, Issue 9)
As digital denture manufacturing becomes more mainstream and while different processes, techniques, and materials emerge, not all digital dentures are the same just as not all treatment plans are the same. When a dentist prescribes a digital denture case for the laboratory to complete, a detailed discussion is imminent between the two. Of course, this is preceded by a discussion between the treating dentist and the patient regarding expectations, finances, and commitment to treatment.
The design options available in digital denture manufacturing and their application are critical for successful and predictable treatment, not only for the patient but the entire restorative team. So, it is most important to know which option to choose based on the individual patient’s needs and expectations.
Full CAM digital dentures are typically categorized into two processes: additive (3D printing) and subtractive (milling). Some laboratories may choose to invest in one CAM process or the other, but a laboratory can provide the best results by using the best method based on each individual case, rather than being based on the only method the laboratory knows and uses. The investment a laboratory makes in their CAM digital dentures requires the design software, a 3D printer and/or a milling machine, and FDA-cleared materials.
3D printing, or additive manufacturing, is the process of making 3-dimensional solid objects from a digital file by fusing many thin layers of material on top of one another. There are multiple 3D printers available to meet the demands of laboratories of all sizes. All dental 3D printers can print denture teeth and denture bases from an STL file generated through the laboratory’s design software.
Milling, or subtractive manufacturing, is cutting- or hollowing-out a piece of dental material with a machine. A milling machine rotates a cutter to produce formed surfaces on a puck/disc or block. There are many milling systems available to laboratories today. Milling machines can produce denture teeth and denture bases from a PMMA disc/puck. Just like their 3D printing counterparts, milling machines process information from an STL file generated through the laboratory’s design software.
After determining the treatment plan for a patient, the digital denture team must choose the best fabrication option for the case. The following are different digital denture fabrication techniques and what determines their indication. Keep in mind that the treatment plan regulates the fabrication process and no single technique will meet the needs of every case.
Printed Denture Base with Printed Denture Teeth
First-generation print materials such as DENTCA Denture Teeth resin are appropriate for this option. This is an economical choice for the dentist and patient. It can be used for an immediate denture worn while healing from extractions, an option for an economical denture, or an alternative for a spare (backup) denture. The STL file can be archived for future or multiple reprint if needed. Printing the denture base and denture teeth allows the designer freedom to have full control of individual tooth design and the relation the teeth have to the ridge. This is most useful when the design requires the denture teeth to be intimately adapted against the residual ridge due to the lack of restorative space or any other type of tooth modification. (Fig. 1) Pre-manufactured, carded teeth make this option very difficult to produce.
Printed Denture Base with Milled PMMA Denture Teeth
When a long-term prosthesis is prescribed, this digital denture is a more permanent solution to finalize removable denture treatment. The milled PMMA teeth offer increased esthetics and higher strength. (Fig. 2) The esthetics of the teeth are enhanced by polychromatic layering designed with gradient translucency toward the incisal area in the puck that will eventually get milled to fabricate the teeth. When the denture tooth design requires an intimate adaptation to the residual ridge, the shape is virtually modified then manufactured accordingly. As previously mentioned, pre-manufactured, carded teeth are not best suited for this option.
Printed Denture Base with Pre-manufactured Carded Denture Teeth
An option where pre-manufactured, carded teeth are successful is when a permanent, final denture is prescribed and esthetics and strength of the denture takes priority. Dentsply Sirona has a unique approach to this option. The use of pre-manufactured, IPN 3D™ digital denture teeth combined with Lucitone Digital Print 3D™ denture resin is one of the most current digital denture products offering wear resistance to the denture teeth and denture base. The overall esthetics and strength are enhanced. The printed base has specially designed tooth sockets to cradle the denture teeth into position for permanent bonding. (Fig. 3)
This long-term digital denture option is superior to the first generation print materials and milled denture teeth. However, as mentioned above, this technique is not applicable to every case. The caveat is the need to design the denture base around the pre-manufactured teeth and print exclusively on a Carbon printer. Also, the ridge lap on carded teeth cannot be modified virtually, as opposed to what is typically done to carded denture teeth in conventionally produced dentures. While designing the denture, the designer has to have sufficient restorative space for the denture teeth to fit.
Milled Denture Base and Milled Teeth from PMMA
This esthetic option also offers premium strength for the teeth and the final digital denture base (Fig. 4). Not only is this type of denture an ideal selection for conventional use, having a milled PMMA denture base also makes it an excellent option for use as an all-on-X conversion prosthesis. The teeth and base are milled from a monolithic PMMA puck, producing superior strength by sharing the same chemical properties with the material used for the conversion. This eliminates the risk of denture tooth delamination and decreases the risk of fracture often experienced with conventional/analog conversion dentures during the patient’s healing phase.
Milled Denture Base and Tooth Material Combined in One Disc
Any true monolithic option is perfect for all-on-X conversion dentures. Different manufacturers offer two-toned 3D pucks that dramatically improve the integrity of an acrylic bridge after conversion. The entire conversion denture—teeth with base—is milled simultaneously without the need to bond multiple segments. (Fig. 5) The only drawback to this technique is that the puck must be positioned very accurately in order to eliminate an obvious transition line between the teeth and the base. If this is not done precisely, it can compromise the esthetics.
This unique option offers a permanent prosthesis when esthetics and strength are needed for both the teeth and base. Both Ivoclar Vivadent and AvaDent offer monolithically milled denture systems. Ivotion from Ivoclar offers a high-quality tooth and denture base material combined in a single bicolor puck with a unique shell geometry that defines the transition between the teeth and denture base. It should be noted that the Ivotion material and workflow can be used with only Ivoclar Vivadent milling systems, while AvaDent’s system is open.
In conclusion, when a dentist prescribes a digital denture, the laboratory has to consider the technique necessary to successfully meet the patients needs and expectations. Materials always play a role in every dental prosthesis to successfully withstand the biting forces they will endure from natural dental function. As dental material manufacturers progress to improve their offerings, the world of dental technology may someday have a one-size-fits-all digital denture solution. Until then, the choice is determined by the case.