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New technology reduces the process and time necessary to achieve ideal fit for denture patients.
One of the most common complaints by dentists about dentures is that the fabrication and adjustment process takes a long time. However, new technology streamlines the denture process, reducing the number of appointments necessary to achieve an excellent fit and wear for patients.
Dr. Shirin Khoynezhad, prosthodontist and director of second-year pre-clinical dentistry at the University of Alabama (UAB) says the average timeline from seeing the patient for the first time till the time that they deliver a conventionally fabricated denture is about one month. Several appointments are required for conventional dentures.
Per FOR.org, the global nonprofit organization that advocates for science, education, and humanity in oral rehabilitation partnering with Nobel BioCare, the clinical objectives of a complete denture protocol are best met with a routine protocol. They recommend that the conventional timeline includes the following steps:1.
“In general, it is five or six visits with the conventional method,” Dr. Khoynezhad says.
Every step is essential for a proper prosthesis using the conventional method
Dr. Khoynezhad says you can bypass and combine the first two visits in some cases, using moldable trays and taking the final impression in the first session. In many cases, however, the dentist will first get a diagnostic impression to make the study cast.
“There are plenty of muscle attachments around the upper and lower ridges that activates when patient functions (easts, speak, etc.). So, capturing these muscles in action is very important using a custom tray so that the denture will be stable when patient functions with it,” Dr. Khoynezhad says.
Making conventional impressions takes up the first two visits in a traditional denture fabrication method, per Dr. Khoynezhad. However, most dental professionals and technicians agree impressions are critical appointments.
“We have to see the patient first to get the diagnostic impressions, and then fabricate the cast in stone. We study it and fabricate the custom tray over it so we can get the final impression,” Dr. Khoynezhad says. “So, the final impression is the second visit in the conventional method.”
On the second visit, after you fabricate that custom tray based on the diagnostic impressions, the doctor takes the master impression. From that impression, the clinician makes the master cast for the next step.
The third visit is getting bite registration and the vertical dimension. Finding the correct vertical dimension requires consideration of a few parameters.
“For conventional dentures, we make something that we call records base and wax rims over the master cast, and then we adjust it inside the patient's mouth to get the centric relation (CR). Also, we take the vertical dimension. We can open and close the jaw, but there should be somewhere in between where the teeth come together. So, we establish that in the patient’s mouth,” Dr. Khoynezhad says.
Also, in this appointment, the clinician establishes the lip supports. Dr. Khoynezhad says that when patients lose their teeth, the lips will be collapsed, so they build that back out and mark the midline, the smile line, and others. This data gives the clinician guidelines for when the patient is not there to setup teeth.
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The fourth visit is the try-in with the teeth set up in wax. The doctor is looking to see if the denture works in the patient’s mouth, if the midline is correct and the patient’s smile looks correct. If not, the clinician will adjust it.
“After everything is perfect, we send it out to the lab to process it,” Dr. Khoynezhad says. “The wax gets replaced with acrylic.”
The last visit is where the clinician delivers the denture after processing. There is another try-in to ensure the bite is the same as the wax try-in.
“A lot of times it's not, because acrylic shrinks and it moves the teeth a little bit. So, it’s very important to double check and adjust the teeth after processing,” Dr. Khoynezhad says.
Dr. Khoynezhad says sometimes clinical remounting is necessary. The dentist will get the bite registration again in the patient's mouth and the CR. It is then sent to the laboratory and adjust the teeth so that that they come together all at once in this centric relation.
“The process of the conventional denture is not ideal. There are limitations that we have with the materials,” she says. “However, both digital and computer-aided design and computer-aided manufacturing (CAD/CAM)processes have helped simplify all of those steps.”
Digital dentures reduce the steps and streamline the process
In addition to her position at UAB, Dr. Khoynezhad also lectures on denture materials and CAD/CAM dentures. With CAD/CAM fabrication for conventional dentures, there are only two or three appointments. Dr. Khoynezhad says the first appointment is where they get impressions.
“And at the second visit, you deliver the denture to the patient,” Dr. Khoynezhad says.
With CAD/CAM dentures, the study cast is unnecessary so you can skip the diagnostic impression taking. Instead, the clinician jumps to the custom-tray step of conventional dentures.
“There is a special tray that they put in the warm water, and they are moldable so we can mold them intraorally,” Dr. Khoynezhad says.
In that same initial appointment, the doctor gets a conventional final or master impression, as well as the CR Record, vertical dimension, and other measurements from the first three regular fabrication method appointments.
Today, the impressions are still traditional for a full conventional denture over digital impressions because of limitations of the scanning technology. It cannot yet capture the soft tissue and muscle attachments well enough for a system to fabricate a denture that fits.
Also, at this initial appointment, the doctor and patient can choose the teeth and the suitable teeth mold for the patient. Then, they send all of that data to the lab.
Dr. Khoynezhad says once you have the impressions, records and the related measurements, you ship them to the lab, which usually takes about a week. The lab scans in the impression, designs the prosthesis, and ships it back to you.
“Now, there is no teeth try-in with CAD/CAM. You can ask the company to send back the teeth to try- in the patient’s mouthto see if it works and then process it or finalize it,” she says.
The try-in denture from the CAD/CAM process has an acrylic base. However, it has sockets for the teeth that are set in wax so the teeth can adjust if necessary.
Some clinicians have the patients bring in foods they like to eat to test the denture. Dr. Khoynezhad says they give the patients chewing gum so they can chew with the denture. The wax is only in the sockets so the denture won’t fall apart when the patient chews.
“But in general, with the two-day process, we don’t do the try-in,” Dr. Khoynezhad says.
The lab makes the prosthesis based on the first appointment. At the next visit, the doctor has the actual denture for delivery and adjustment. Dr. Khoynezhad says that CAD/CAM dentures are more accurate than conventional dentures. Part of that has to do with how the acrylic is processed; the digital method does not have the volumetric changes that occur in a traditional process.
“Acrylics in CAD/CAM dentures are poured in either a disc or cylinders and they undergo shrinkage before they mill the denture out of it. The actual acrylic doesn't shrink after they mill the denture. There are fewer changes in the denture compared to the conventional methods. It's more accurate,” Dr. Khoynezhad says.
However, the CAD/CAM process doesn’t mean you don’t have to have the same skill level as you would with conventional dentures. The preparation for the lab requires precise measurement and accurate capture of the patient’s bite.
Getting the record is crucial, and that relies on the clinician’s expertise either conventionally or digitally.,” Dr. Khoynezhad says. “To find the correct spot that you want to re-establish your patient’s teeth is very important.”
1. “Complete Denture Clinical Protocol.” www.for.org Web. 13 March 2019. https://www.for.org/en/treat/treatment-guidelines/edentulous/treatment-procedures/removable-prosthetics/complete-dentures/complete-denture-clinical-protocol>.