Q&A with IDT Symposium Speakers

At the IDT International Digital Denture Symposium last month, attendees were offered the opportunity to send questions via text message for the presenters. Below are those questions, along with the presenters’ responses.

Audience Question: For Dr. Johnson, can you please review what all happens at each appointment for your workflow to deliver dentures in two appointments?

Andrew Johnson, DDS, MDS, CDT, FACP: If basic information can be gathered at the first interaction (ie, the consultation), that patient can depart with a decision to make about initiating treatment, and the provider can sit on that data until a reasonable commitment to treatment has been made on the part of the patient. A printed wax try-in can be generated using that initial information and utilized clinically for establishing esthetics, function, phonetics, etc (just like a regular wax try-in, with all the customary modifiability/flexibility) and combined with master impressions in printed custom trays and whatever bite recording methods the provider prefers (ie, chin point guidance, bi-manual manipulation, gothic arch, etc). That becomes the singular recording step that gathers all necessary information to digitize and begin the final digital denture fabrication through whichever software/hardware/materials means you choose. The next and final appointment is denture delivery as usual.

Audience Question: For Dr. Lo Russo, how do you scan for muscle attachment and movable vestibular depth?

Lucio Lo Russo, DDS, PhD: I do not scan for them. They are not relevant to mucostatic impressions like intraoral scans.

Audience Question: For Dr. Lo Russo, how do you retract/maintain static tissue position during your intraoral scan?

Audience Question: For Dr. Lo Russo, how do you keep the vestibule from moving when scanning? Do you use cheek retractors?

Lo Russo: I use two mirrors as retractors: one for me and the other for my nurse.

Audience Question: For Dr. Lo Russo, how portable is the IOS you use? Can I take it to a remote location to use, such as a hospital environment with a laptop and WiFi?

Lo Russo: 3Shape TRIOS, the intraoral scanner I use to make scans of edentulous arches, is portable. You can take it wherever you want with ease. It can be used with a laptop, and there is a WiFi version available.

Audience Question: For Dr. Lo Russo, what would you say regarding the cross-arch distortion with intraoral scanning?

Lo Russo: The scanning strategy is the key point. As shown in the presentation and already published, when using the suggested scanned strategy for edentulous arches, the measured global mean 3D difference when compared with conventional impression is 30 microns for the upper jaw and 20 microns for the lower jaw, which means that the potential distortion, if any, is within this range of magnitude.

Audience Question: For Mr. Versteeg, how many digital dentures have you completed via direct intraoral scanning?

Germen Versteeg: I have done around 60 cases for full dentures/immediate dentures and around 100 cases for partial/RPD with intraoral scans.

Audience Question: For Dr. Bendayan, are there any considerations of bone and CT scans in regard to the design of the denture? Do you merge images?

Alexander Bendayan, DDS, CAGS, FICD: The foundation for complete denture design in regard to tooth placement remains the same: incisive papilla, retromolar path, buccal shelf, hard and soft palates, plane of occlusion, interpupillary line, and ridge-to-lip measurement, among others. In order to correlate the design of the denture to a CT, fiduciary markers are needed. This is more common in dentures that are to be made and where these markers are bonded to then obtain a CBCT and correlate the digital images.

Currently we continue to look for ways to integrate face scans, smile design, and CBCT to create a virtual patient. The market has different software companies that develop solutions for bits and pieces, together with a struggle to open the workflow. It is possible and is in process but not in a single platform yet.

Audience Question: For Dr. Bendayan, with all the new resin materials, have you done any types of biocompatibility tests? Are these new materials toxic to the patient?

Bendayan: During my presentation, I informed the audience that more research is needed, including biofilm adhesion, repairs, and long-term clinical follow-ups. The resins used for this workflow do not differ in chemical components from conventional dentures; therefore, we should not expect a different outcome. 

As part of preparing a new product for regulatory (FDA, EU, etc) approval, standardized biocompatibility (cytotoxicity, sensitization, etc) testing is undertaken and the materials must be shown to be non-toxic.  

Audience Question: For Dr. Bendayan, with the new Lucitone material, will those dentures be considered “premium”? Would laboratories charge printed dentures as premium?

Bendayan: I would prefer you ask the question directly to Dentsply Sirona/Carbon. But it should be known that the final cost is determined by the dental laboratory, not Dentsply Sirona or Carbon. We would expect that because of the benefits of the new workflow to both the patient and dentist, the laboratories would position the product as premium. 

Audience Question: Can you tell me some do's and don’ts that you wish someone had told you when you started doing digital dentures?

Johnson: Do play up the efficiency, strength, biocompatibility, fit, and reproducibility, but do not play up the esthetics (at least at first). The biggest learning curve for me with digital dentures was the “wax try-in,” which is hardly that. While you can achieve a still-modifiable, human-looking wax try-in through pretty much all digital denture workflows, they usually require additional time and money to accomplish. If they don’t, then they typically are lacking in natural appearance and/or flexibility. A monolithic, monochromatic printed/milled try-in is valuable but hardly as much as the traditional try-in step we are all familiar with. If you value patient approval; if you value fine-tuning your setup directly; if you value custom impression trays, border molding, your own VDO/bite recording techniques; if you value your patient’s time; if you value your own time like I do, there is a way to do it all like you’re used to and get more out of it than ever before.

Versteeg: When you buy all the equipment, start transferring your whole workflow to digital, not only the impression trays.

Make a good choice for which partner/equipment you work with; support/back-up and service are key if you have to rely on this equipment. Also proper training is really important. Be assured that all the equipment and software you buy can work in an easy, validated total workflow so you don’t need to be an MIT guy to work with these products.

Start with a good proper calculation about what is going to change in your laboratory. You have a lot of extra time when you turn to a digital workflow so you need to fill this extra time with extra work. Maybe you are already a little tight on employees; that is the perfect situation in which to transition. Doing a good calculation gives you a good insight into your ROI and which choices to make.

Henk-Jan van den Heuvel: That wasn’t the case for me. I was educated very well because I performed beta tests for the manufacturer. But lots of people bought software and learned the hard way that it isn't simple to integrate every tooth library they want. So that means that you have to mill or print those teeth yourself, which has been problematic for some users.

Audience Question: If I have an intraoral scanner in my office, should I start scanning intraorally or is it easier to start with conventional primary impressions initially?

Johnson: It has been demonstrated many times (and beautifully so, at the recent IDDS) that soft tissues can be captured with IOS. Philosophically that may be the only way to achieve a true “mucostatic” impression, especially of displaceable tissues like traumatized maxillary anterior ridges, tuberosities, retromolar pads, etc. What you cannot capture are the “place-able” tissues like the vestibular roll and the potential spaces of the mylohyoid extension. In my opinion, if you are comfortable making final dentures from overextended alginates and either grinding back the subsequent denture flanges at delivery, or arbitrarily foreshortening the flange extensions/frenal notches, and you do great case selection, and you are particularly skilled with your scanner, then go for it. In my experience, the time I save in generating controlled, accurate, full-coverage anatomic surfaces for use in my CAD software by scanning impressions (for now) and the out-of-the-box fit of the intaglio surface and the peripheral flanges greatly outweighs the potential improvement in fit I may get with a no-contact tissue scan. Long story short, I scan my impressions with my IOS, but I have begun hybridized scanning (ie, scanning the easy areas in the mouth and picking up the rest from the impression by stitching together the inverted normal as a single-capture STL).

Versteeg: The easiest step into digital dentures is to start with impression scanning with a TRIOS or laboratory scanner. The next level is to use the intraoral scanner. You have to be skilled to use the intraoral scanner on edentulous ridges and you need to feel comfortable with it. Just practice and do a lot of cases; you will train yourself.

van den Heuvel: That’s a case of trial and error. In lots of cases, you can use the intraoral scanner, but it's not always possible for lowers—that's quite hard to do. There are no fixed references and the lingual bottom is continuously moving. To obtain a smooth workflow, you can also make an alginate impression when the intraoral scanner doesn't do the trick, then scan that alginate with the intraoral scanner; that way you are always able to send orders digitally to the laboratory and eliminate plaster models.

Audience Question: Why does every setup seem to have no second molars? Should I leave them off in dentures?

Johnson: That is a classic prosthodontic question which has an answer much older than any of the technologies we now use in contemporary denture fabrication. In my opinion, this is a question of space and support. Do we have enough room for two molars and two premolars before we run up the retromolar pad or into the tuberosity? Do we need the extra arch length area for any functional/esthetic purpose? Are we unnecessarily cantilevering occlusal surfaces behind posterior implant support? Do the terminal teeth of the decided arch form encroach on the neutral zone? To me it matters not whether the prosthesis is “digital,” these design concepts come from the century of denture philosophy that has lead us to this amazing point in professional history.

Versteeg: With 3Shape, you can choose to delete the second molar or the second premolar. Both choices are made based on the space there is to the retromolar path. If you are adding too many molars, you can have problems with biting on the cheeks and tongue. Furthermore, proglisma can occur; this is where the biting force on the last molar will push the lower denture forward.

van den Heuvel: You want to eliminate all forces that could force a denture to glide forward (proglisma), and you always want to put the biggest posterior tooth in the chewing center to obtain stability in occlusion and articulation. So that's why we often make a shortened arch, and research has proven there is no measurable difference in functionality. You can always put it on if you want, or leave it out of occlusion. As the teeth wear, they will become functional again, or they may even have a negative side effect when food is in between the upper and lower denture.

Audience Question: What if the patient is wearing old dentures in which they are fetching their jaw forward (unknowingly) to contact? Do you use the old set but put it in CJR for your scan, or keep the same bite? Wax try-ins? A few extra appointments before milling or printing?

Andrew Johnson: Most often I wait until my records step to make interarch position corrections, which I can do relatively simply by either noting it and compensating for subtle mandibular tooth alignment irregularities in my final denture or by melting/moving the lower try-in arch into more ideal occlusion relative to the mandibular trail base. If a case is a bit more exaggerated (ie, a class III tendency that has worn itself into full-blown underbite over 40 years), I do sometimes try to capture a bite nearer to centric relation on the outset just so I’m not so far off at try-in. And yes, sometimes the wildcard case does require an additional try-in step as you try to undo decades of wrong.

Versteeg: When a patient has a “false third-class bite,” then we always do a gothic arch tracing to check the RCP. Most times the third-class bite is forced by a too-low VOD. When you recover the perfect VOD, this also will help to recover the normal bite situation.

van den Heuvel: That totally depends on the situation, if a patient has been in a habitular bite for too long there can be lots of problems in acceptance if you put the bite back in centric relation. But normally the best way would be a gothic arch tracing, back in the most unforced, most retruded position. You can always build a gnathometer in a printed copy of the old dentures as well. Keep in mind that with a concept that contains "freedom of centric, "a patient will always use that freedom to glide off again. It would be way worse if you have a protruded bite registration and a locked occlusion.

Audience Question: The term “denturist” has a negative connotation in the US, but it is proudly displayed for the European speakers. Why is this?

Johnson: Professional politics and culture. I think that anytime you introduce change, the response is typically proportionate to the time and scale of the established status quo. I think there is a place for denturists for sure. However, we just have to ensure that patients also receive access to the additional levels of care (ie dental implants, alveoloplasty, airway analysis, cancer screening, etc). For the same reason I practice with an oral/maxillofacial surgeon that carries our diagnostics and treatment capabilities well beyond my own, I think that we should all work together in providing dentures in efficient, quality, complimentary ways.

Versteeg: In a few countries in Europe, “denturist” is an official title. In Holland, almost all the dentures are made by denturists and not by dentists. This is because the denturist completed a 9-year education to fully specialize in dentures. So dentists will see denturists as an official part of the chain of specialists in intraoral care.

van den Heuvel: Denturists are well-educated people in some countries. It's also a protected title for a dental professional who has total independence in treating edentulous patients and partially dentate patients (after check-up by a dentist) and providing implant-supported removables. In Holland, it's a 4-year course of study done after the 5 years needed to become a dental technician, so in total it's 9 years. It's a paramedical study just like physiotherapists and optometrists. The key to success is that the same person who treats the patients is the same person who does the technical jobs too; that way the specific wishes of the patient are translated the best into the final product. In Holland, the denturists have a very high success rate and are trained in pharmacology, anatomy, and pathology as well. So yes, it's a very dedicated group of professionals in all the countries where the denturists are recognized by law and having jurisdiction—Switzerland, the Netherlands, Denmark, Austria, and Canada.

Audience Question: A chain is as strong as its weakest link. One issue for laboratories is frequently receiving poor impressions and inadequate records for complete dentures. What can be done to help private-practice, general dentists provide better records and impressions?

Johnson: This is a tough one. As we all know, the “standards” of many clinical dentists are in decline. Dental education standards are in decline. Laboratory technicians with solid foundational knowledge and digital savvy are exceedingly rare, and the corporatization/commoditization of the entire dental industry has it primed for either serious setback or significant disruption. I think that we may find that technology not only enhances our ability to accomplish tasks in our offices/laboratories but also to provide clinicians/technicians with faster ways to do better things. Case in point: What I tell university educators looking to integrate “digital” into their denture curriculums is to start with custom trays, designed on freely downloadable CAD software, produced on a hobby printer, using an intraoral scanner (of a mouth or a model). That way you can ensure that you’ve exposed them to digital scanning/designing/printing, and taught them something useful and simple that they are very likely to teach/delegate to their future staff members. The best part is that now you’ve given them a sensible reason to keep doing one of the first things they all give up on after they graduate—doing master impressions in custom trays—which I think can only help the impression quality problem we all see behind the curtain. It will help acclimate those dentists to more easily latching on to digitizing even more procedural steps from there.

Versteeg: The easiest way is to see if you can show the dentist how to use the old denture as an impression tray if the fit is proper enough, or you can choose to use this old denture to make a copy denture as a monoblock and print it. The big benefit of this is that the borders are mostly already a good length (if they are not too old); on the other hand, all the information for the new denture comes mostly from the old denture, so you are already pretty close to the key of the new denture. This gives the dentist a lot more information to work with.

van den Heuvel: That's a hard one. In my opinion, there is no difference in competence whether working analog or digital. In both workflows, you will need an honest and open relationship with the one who is treating patients to get to the best results, and hope for a healthy ability to reflect on the performance of yourself and your customers. If it is within your abilities (for example when you are a skilled denturist), help out your customers who are struggling to deliver quality. Sharing is caring. The key to success is to motivate each other to deliver the best quality possible.

Audience Question: Some of the printed materials have a specified/authorized time for intraoral use. Who is responsible for monitoring, managing, and complying with those FDA specifications, and how? What, in your opinion, is the best way to handle the issue?

Bendayan: Ultimately the dentists are responsible to prescribe and recommend materials or drugs according to FDA and ADA recommendations in order to care for their patients, follow best practices, and maintain a license to practice. Try-in materials are intended for try-in purposes only and should be used as such.

The FDA rarely makes recommendations. They are a Federal agency with full legal authority to enforce the laws published in Title 21 of the Federal Register. What that means is that manufacturers and end users (licensed dental professionals) are responsible for complying with the regulations.  If we don’t, then they can (and often will) do everything within their authority to force compliance.