The milled tooth for long-lasting full and partial dentures

I had the opportunity to challenge myself, as well as the digital technology. An implant-supported full class 1 denture in the upper jaw was to be manufactured using the most recent 3shape software (3shape A/S, Copenhagen, Denmark) and polychromatic composite disk VITA VIONIC DENT DISC multiColor (VITA Zahnfabrik, Bad Säckingen, Germany), which has recently arrived on the market, for the subtractive manufacturing of denture teeth. The interaction of traditional experience with new technology inspired me to once again break new ground, and to challenge the status quo and my own professional complacency when treating complex implant cases.

The patient came to the practice because he needed a new restoration in the edentulous upper jaw. Since the patient did not like the fit, the foreign body sensation or the functionality of a conventional denture, implant insertion had been suggested in advance, to which the patient consented. The new full denture was to be stabilized on top of four implants with Novaloc abutments (Straumann, Freiburg, Germany). In the treatment plan, we decided to manufacture the full denture using the digital workflow. The goal was to show whether the digital denture could be manufactured more easily, and whether a similar or even better fit could be achieved after integration, compared with conventional full dentures. Of particular interest here was the integration itself, as well as whether the abutments had to be integrated into the denture base in the treatment chair or in the laboratory.

1. The palate portion was to be freely designed.
2. The base from the VITA VIONIC BASE DISC HI should not be additionally reinforced.
3. The angulation of the implants should not be corrected. This decision was made because of the flexible angulation compensation with the different Novaloc Locators. They make it possible to compensate for the leverage provided by the extended free end. At the same time, the the strain on the implants was reduced despite the unfavorable positioning while chewing. A prosthetic correction of the angulation would only increase and strengthen the leverage effect. A trouble-free, occlusal freedom in centric was also essential in order to provide even more compensation for the load stress.
4. The focus was on making the occlusal morphology of the teeth functional within the patient‘s chewing cycles, while at the same time transferring the freedom of movement concept to the VITAPAN LINGOFORM posterior teeth. The VITA VIONIC DIGITAL VIGO denture tooth library, available in the 3shape software, is based on the design of the VITA VIONIC VIGO prefabricated teeth, which are in turn based on the design of the VITAPAN EXCELL anterior teeth and the VITAPAN LINGOFORM posterior teeth. Their basic functional principle was automatically transferred to the patient‘s occlusion. Note: The VITA VIONIC DENT DISC multiColor is made from the same VITA MRP (Microfiller Reinforced Polymermatrix) composite formulation as the premium teeth VITAPAN EXCELL and VITAPAN LINGOFORM.
5. Treatment continued with intraoral scans of the lower dental arch and the alveolar ridge in the upper jaw. Note: The updated version of 3shape software (3Shape Dental System 2022) includes an option for the prosthetic implant components used in this treatment. Once the scans and registration were uploaded, the design of the denture began. VITA VIONIC VIGO O45 and 22L were the teeth selected. The posterior contacts were adjusted and confirmed in order to implement freedom in centric.
6. The dental arch and denture base were manufactured subtractively and fixed using VITA VIONIC BOND.
7. Due to the virtual integration of the Novaloc Locators in the software and the high milling precision, the matrices clicked into the denture base after subtractive manufacturing. To ensure a secure bond, the matrices were also integrated into the denture base using DTK adhesive (Bredent, Senden, Bavaria).

Freedom in centric: Freedom in centric is defined as a “flat area” in the central fossa in which the antagonist cusps have 0.5 to 1 mm of eccentric freedom of movement upon contact, unaffected by tooth inclination. All natural teeth work according to this concept, but very few denture teeth have it integrated. Why is freedom in centric important? This concept is important because denture teeth are not innervated. This means that a patient cannot feel when the teeth are in occlusion or if they are almost in occlusion. It is important to note that there is food between the teeth during chewing and it is not possible to create perfect centric contact with each individual chewing cycle, as is possible in the articulator during the manufacture of dentures. And then there is also the fact that full dentures are supported by mucous membranes. When considering these two aspects, it is actually inconceivable that a patient with full dentures can always return precisely to centricity. For the same reason, the natural dentition – even if we can feel our teeth during the chewing process - cannot achieve precise centricity after each chewing cycle. This is also the main cause of instability and tension within the denture. Why was freedom in centric important for the success of this treatment? Due to the distribution of the implant abutments, a free occlusal concept without interference was important for preventing a leverage effect. A prefabricated tooth with a locked centric would not allow this compensation to achieve a good denture fit and the desired function. This applies in the present case, especially with regard to the pronounced free end distal from the area of the implant support. For this reason, the patient needs a flexible and adjustable occlusal design.

As already described, special attention was paid to the locators because the matrices were integrated into the denture base in the laboratory and not at the patient‘s chair. As a result, we had to check whether the dimensional transfer of the implant position into the software, in conjunction with the precise subtractive manufacturing, would make it unnecessary to integrate the matrices on the patient chairside. Bonding in the laboratory can reduce chair time by 1.5 to 2 hours. That is much more comfortable for the patient because less work needs to be performed inside the mouth. However, the matrices can also be fixed in the laboratory with an accurate model and a careful, precise conventional procedure. Subtractive manufacturing of the base and bonding of the matrices in the laboratory was effective and accurate in this case. Due to the complex implant distribution, a precise relationship between implant head and matrix was a must, especially in this clinical situation.

• Analog or digitally manufactured denture teeth that are designed with occlusal freedom provide stability, flexibility and adaptability to the patient‘s chewing cycle. The occlusal design can be modified in the production of tooth material with the VITA VIONIC DENT DISC multiColor to obtain the desired reliability and function.
• Hitting and sliding on the main cusps is the main cause of these well-known denture problems.
• This treatment plan demonstrates the challenges of dealing with one‘s own professional complacency, and the digital workflow for the production of implant-supported dentures.
• The VITA VIONIC DENT DISC multiColor enabled an easyto- implement and time-saving workflow that created a high-quality denture.

As denture professionals, we have to create this form of care specifically for each patient and not expect them to simply adapt to their new dentures. In order to achieve this, denture teeth that are adaptable must be used. On the other hand, self-reflection is important to prevent complacency and to allow an adaptation of the skills needed for the specific requirements of the patient case. Freedom in centric is the possibility of moving within the centric contact and therefore not to be blocked in a bite. This concept allows for flexible occlusal adjustment to the patient‘s needs, but has only been integrated into a few prosthetic tooth designs available to us. In this case, the successful treatment can be attributed to precisely this freedom, which is contained in the VITA tooth library and in the subtractively manufactured dental arch from the VITA VIONIC DENT DISC multiColor. If we want to be superheroes for our patients, we need to think outside the box when it comes to complete dentures. Digital workflow manufacturing is another viable “tool in your arsenal” to provide your patients with consistent, highquality removable dentures. It matters what type of teeth you use for traditional or digital manufacturing. Find out about the freedom in centric of the VITAPAN LINGOFORM posterior tooth set and the VITA VIONIC DIGITAL VIGO denture tooth library with the VITA VIONIC DENT DISC multiColor. Freedom is great!

The author is grateful to his patients, VITA Zahnfabrik, Aurum Lab Calgary and, especially, Jason Atwood.

When fabricating combination prosthetics, it was common practice to make basal and occlusal modifications to prefabricated teeth. Every tooth had to be handled individually and adapted to the framework structure. The next logical step was to fabricate the dental material on frameworks individually using a single CAD/CAM-supported mould. The VITA VIONIC DENT DISC multiColor comes from a company whose knowledge of prefabricated teeth has grown historically for 100 years and is part of the company's DNA and name: VITA Zahnfabrik. The multichromatic disc made of the proven VITA MRP (microfiller reinforced polymer matrix) composite formulation now offers the well-known quality and esthetics of VITA premium teeth for combination prosthetics, which are created using the design software to perfectly fit the patient. In the following interview, Lukas Wichnalek and Arbnor Saraci (both of Zahntechnik Wichnalek – HIGHFIELD DESIGN, Augsburg, Germany) report on their successful use of the disc.

Manually adjusting denture teeth to a model casting framework is tedious work that does not allow for true precision. There is a fair amount of guesswork involved as it is ground out until it fits, and often more of the basal tooth is sacrificed than would have been necessary. With the digital workflow, innovative materials for removable partial dentures, which now enable custom-fit prosthetic components based on the lock-and-key principle, have been introduced. These only need to be bonded together using modern adhesive systems. This means that high-precision production technology is replacing the guesswork of manual grinding. In the following, Norbert Wichnalek, Lukas Wichnalek, Patricia Strimb and Arbnor Saraci (all Zahntechnik Wichnalek – HIGHFIELD.DESIGN, Augsburg, Germany) show how the polychromatic VITA VIONIC DENT DISC multiColor is now being used to create precision-fit premium teeth in a digital workflow, and discuss the advantages this offers.

What are the reasons why digital full dentures are becoming more and more established in the Netherlands?

We offer a dental technology service with our milling center. We have noticed that more and more practitioners are able to design their own complete dentures in CAD software, but are not equipped to manufacture them with CAD/CAM support. And that's where we come in. Of course, the lack of specialist staff is also a key reason for the rise in digital full dentures. Automation means that the milling unit can also work independently overnight. There have been great leaps in development in terms of quality, so we have decided that our clients should benefit from this too.

Where do you see decisive differences, perhaps also advantages and disadvantages, between analog and digital fabrication of removable full dentures?

I don't think the time factor is even that decisive. If someone has a lot of total prosthetic experience, they may even be a little faster than the digital workflow if they move quickly. But if they've had a bad weekend, for example, the result on a Monday morning may not be as successful as usual. In the digital workflow, the quality will always be the same. Regardless of the human element, two millimeters will remain two millimeers. The setups are always reproducible. For me, this is the decisive reason as to why I produce complete dentures in the digital workflow.

Who are your customers and how have they accepted digital full dentures? Are there price differences between analog and digital fabrication?

We generally do not make analog prosthetics. We have focused on producing digital full dentures with VITA VIONIC VIGO. We then only have to bond the ready-to-use premium teeth into the base with VITA VIONIC BOND. This enables us to offer better quality than other milling centers that mill the teeth from unfilled PMMA, for example. Our clients are mainly denturists who can't use CAD/CAM. So once I'm a denturist, I'll become my own client (laughs). I then order the complete dentures from my own company.

Is there a price difference between analog and digital full dentures, and if so, how big is it?

When we started producing CAD/CAM-supported full dentures around six years ago, the material components were still a little too expensive compared to analog production. However, we have observed that the material prices for digital full dentures have become lower and lower over time, making it more and more economically attractive. The classic wax set-up is probably a little cheaper in terms of materials, but the time required is significantly higher in most cases. The bottom line is that digital full dentures are now comparable in price to analog full dentures. 

What experience have you had with the VIONIC DENT DISC multiColor so far? For which removable restorations do you mill your teeth yourself?

The VITA VIONIC DENT DISC multiColor has closed a gap in our portfolio. The composite disc is a real advantage, especially when space is limited. With a very low vertical bite height, the material gives us the functional leeway we need. We will also use it for immediate dentures. It offers high-end quality in the subtractive fabrication of dental material, as the composite formulation is the same as with all other VITA premium teeth. It can therefore be assumed that the quality is better than that of conventional, unfilled PMMA blanks. I am very pleased that VITA VIONIC DENT DISC multiColor is available.

How do you assess the development of additive manufacturing in removable full denture prosthetics? Are you planning to work with this technology?

3D printing is certainly the future of full denture prosthetics. Even as a milling center, we cannot close our eyes to it. It is cheaper and will probably also be faster. A single-colored denture base can already be printed easily today. This does not yet apply to robust teeth with a color gradient and translucency in the right places. Sustainability is now also a major issue in dentistry and dental technology. Only the material that is really needed is used as an additive. This is much better for the environment than milling from a blank and throwing away the leftovers.

In your opinion, how will the technology and the job profile of dental technicians and denturists change in the future?

I think digitalization will become mainstream in the future. Materials will continue to improve and processes will become faster and more consistent. Digitalization will definitely prevail in the technical fabrication of dental restorations. VITA VIONIC VIGO and the VITA VIONIC DENT DISC multiColor are already helping us to produce functional and esthetic complete dentures in a digital workflow to give patients their teeth back and make them happy. As a dentist, however, you should always bear in mind that the option for analog treatment of patients will continue fort he forseeable future.

Since when did you start offering your customers digital, removable dentures? What was the decisive factor in including CAD/CAM fabricated removable dentures in your portfolio?

Urban Christen: To be honest, I have already worked with CAD/CAM-supported fabricated complete dentures since they were approved for patient care. That was 15 years ago now. The higher precision than with analog fabrication excited me from the very beginning, especially with regard to occlusion. The bite simply fits without distortion, and occlusal adjustments are no longer necessary. And the workflow is repeatable one-to-one.

Eelco van Wort: CAD/CAM-supported fabrication of complete dentures has been part of our milling center portfolio for about five years. Since VITA VIONIC can be used in open CAD/CAM systems, we are offering digital dentures to our customers. In the Netherlands, digital dentures have increased considerably due to a lack of technical personnel. On the material side, everything is now available to produce total prosthetics digitally in the desired quality.

Where do you see differences – advantages and disadvantages – between subtractive and additive production of removable dentures?

Urban Christen: Both methods are very, very precise. At the moment, the material quality is still slightly better with subtractive manufacturing. Soon, however, additive materials will come onto the market where there will no longer be any differences in quality. A milling unit is much more expensive to buy than a printer and is already completely occupied with a blank. The printer can be used for several bases at the same time, maintenance is inexpensive, and there is no instrument wear.

Eelco van Wort: I think 3D printing will be the future. As a milling center, we can’t close our eyes to that either. It is already cheaper and probably faster. The process is more sustainable because there is much less waste. In the future, this will be the manufacturing method for total prosthetics. The single-coloured denture bases are already easy to print. Teeth with shade and translucency gradient cannot yet be manufactured additively in the desired quality.

How quickly can the technology pay for itself in terms of removable prosthetics? What pays off faster, subtractive or additive manufacturing?

Urban Christen: Of course, a direct comparison depends on which milling unit is purchased. Generally speaking, it can be said that amortization takes longer when it is used solely for complete dentures. If crowns and bridges are also produced on the same machine, the payback is much faster. The printer pays for itself more quickly in comparison. It is also important to note that additive manufacturing is certainly more favourable in terms of running costs.

Eelco van Wort: I don’t really have a comparison. At the moment, we only work subtractively. As a milling center, we naturally use our milling units in such a way that they are always working to capacity. Then, such a machine can pay for itself more quickly. Purchasing an additional printer makes no sense in the current situation. In general, additive manufacturing is certainly more cost-effective, so we will also start printing at some point for sure.

Which CAD/CAM workflow did you choose in the end, and why is this, at the moment, the appropriate solution for you?

Urban Christen: To tell you the truth, I have just decided on both production methods (laughs). At the moment, I am using a subtractive approach for the denture base with the VITA VIONIC BASE DISC. For teeth, I use the preconditioned VITA VIONIC VIGO, which is simple and fast bonded into the alveoli of the denture base without any modifications. For immediate dentures, I use the VITA VIONIC VIGO with a printed base.

Eelco van Wort: We also use VITA VIONIC VIGO for teeth because you really only need to bond the precisely fitting teeth to the denture base without using a cold-curing PMMA. In cases of limited space, we will grind out the tooth material from VITA VIONIC DENT DISC multiColour in the future. Of course, as a classical milling center we actually manufacture the denture base only from the blank VITA VIONIC BASE DISC.