Revolutionizing the Denture Process
A simple and accurate digital technique
By Lou Graham, DDS, and Craig Nelson, CDT
With the launch of its digital denture solution, Heraeus Kulzer found itself in a special position. Very few companies had digital offerings for removable prosthetics. Although technology and the industry are changing rapidly, the basic principles remain constant. One fact remains: The final denture is only as good as the records provided.
The Pala® Digital Denture System is designed around a unique set of impression trays that serve a dual purpose: 1) taking final impressions; and 2) functioning as base plates for vertical dimension (VD) and centric relation (CR) on the first visit. Once the impressions and records are taken, the patient is dismissed until the second appointment when he or she is presented with a printed preview (ie, try-in) of how the final denture will appear. The final denture is delivered for the third appointment.
A 70-year-old male presented with an existing upper denture requiring replacement due to loss of retention and substantial wear. The patient had complex mandibular issues with no lower molars present and substantial carious issues on multiple remaining teeth. His immediate concern was to have a new upper denture made and resolve his lower issues soon thereafter. Upon examination it was noted that his remaining teeth would not alter the eventual digital occlusal design of his new maxillary appliance and equally a new denture could be constructed with an enhanced smile and proper articulation.
The first step was tray selection, which is critical to success. A tray was selected that was closest to a final denture that would fit the edentulous ridge without overextending the vestibule. A common mistake is choosing a tray that overextends the vestibule (Figure 1 and Figure 2).
Many clinicians ask why the tray has no handle. The purpose is so the tray may be seated perpendicular to the ridge. With a handle, the tray is often seated anteriorly or posteriorly, rendering the base plate function of the tray unusable. The notch in the anterior part of the tray where it seems a handle would go is for scanning and can be removed if the impression will have better accuracy without it.
The next step was to assure the tray fit the ridge. The tray can be modified with heat to a custom fit.
Then, a two-step process was used for taking the upper and lower impressions. The tray was filled with a heavy-body material (Flexitime® Fast & Scan Heavy Tray, Heraeus Kulzer) and seated, and border-molding procedures were performed. The process was then continued with a light-body material (Flexitime Fast & Scan Medium Flow, Heraeus Kulzer) and border-molding procedures (Figure 3 and Figure 4).
After the impressions were made, the VD and CR could be taken.
To determine the VD, the pin-tracer and screw were utilized. The screw/pin was adjusted to transfer the VD as measured by the jaw gage to the record. The VD was evaluated by using the existing denture against the dentate lower. A measurement was recorded to set the pin in the gothic arch tracer in the next step (this should be before the setting of the pin). VD is set (Figure 5 and Figure 6).
Centric relation was achieved with the simple and extremely accurate gothic arch tracing method. A strike plate was on the upper tray. A Pala tracer was positioned on that plate by removing the back and exposing the adhesive side of the Pala tracer, and then applying it to the strike plate. The tray was placed back in the patient’s mouth with the lower tray in position, and the patient was asked to move his lower jaw backward and forward in protrusive movements. At the same time, a small amount of pressure was applied against the strike plate. A line was recorded.
Next, the patient was asked to move the mandible in a right lateral movement and repeat a few times, and then do the same on the left side. A distinct intersection was made on the strike plate. That intersection was the position where the joint was in centric relation. A small dimple was made at the intersection with a bur to aid the patient into centric when the bite was used to record the position (Figure 7). After the centric was in position, bite registration material was extruded to record the patient’s proper bite (Figure 8).
Once all the records were created and measurements taken, the impression was sent to a Pala Digital Laboratory Partner. Upon receipt, the laboratory scanned the bite and impression. The file of the now-digital impression was sent to the Heraeus Kulzer Pala Design Center to create 3D renderings of the denture and print a try-in. Once the try-in was approved, the final denture was created (Figure 9 through Figure 11).
Lou Graham, DDS, is a private practitioner in Chicago, IL.Craig Nelson, AAS, CDT, is Senior Technical Manager of Scientific and Clinical Affairs for Heraeus Kulzer.