The Inherited Case: Why Laboratories Should Celebrate
Embrace the challenge to change a life
William “Butch” Houghton
In the laboratory industry, the phrase "inheriting a case" almost always has a negative connotation. Many technicians view these types of cases as needing to fix someone else's failures. But, that may not be the situation, even though the new laboratory was not part of the original treatment planning. While the new technicians may not have the knowledge or experience levels of the original clinical, surgical, and laboratory teams, they do have the benefit of hindsight, know of any changes in the patient's oral health, and are aware of advancements in materials and techniques. Therefore laboratories in this position should not complain about the prospect of facing such a case, but embrace the challenge; after all, the purpose of the laboratory industry is to ultimately serve patients by providing them with long-term restorations. To better understand this point, read the following story of one such inherited case.
The author's laboratory was presented the case of a Class II patient needing a new approach to their maxillary all-on-4, denture-opposing, full-porcelain occlusion. The restoration was a full-arch wraparound acrylic denture on a milled titanium bar supported by immediate-load implants. This prosthesis had been in use for 3-and-a-half years, requiring frequent repairs about every 3 to 4 months. Naturally, the patient's quality of life was being affected.
During the initial planning stages, the new dentist noted the patient's history of bruxism. The presence or severity of the patient's parafunctional habits may not have been known or considered when planning the original prosthesis. Therein lies the "gift" of the inherited case. The restorative team now had the benefit of hindsight from the failings of the previous appliance and new patient information, coupled with the knowledge of occlusion, to make this redesign a success. The primary challenge was then to create a new restoration that would hold up to the patient's occlusal forces.
Because this case had a history of failures, the author's first step was to ask for a tracing of the patient's occlusion and jaw function. This information was used to program and mount the articulator to account for any eccentric movements as closely as possible (Figure 1 and Figure 2). As a Class II, the patient's jaw relation had created an excessive anterior-posterior overjet. This made the lower dentition a perfect wedge to apply heavy lateral forces to the maxillary denture teeth and acrylic. In the technician's opinion, this was one of the main causes of the previous fractures. Upon discussing this with the provider and patient, the laboratory presented its recommendation for metal occlusion.
With everyone in agreement, the author proceeded to complete a maxillary set-up for try-in. During the first try-in appointment, he identified an error with the first tracing. This required a new tracing and adjustments to be made to the mountings, articulator, and denture set-up. The dentist requested the addition of group function, and the laboratory finalized the set-up and treatment plan.
Having a clear picture of the end goal, the author now had the task of executing the restorative team's plan and reached out to the Prism Design Center at Preat Corporation. Prism frames are made from titanium that is 3D printed rather than milled. Because of this, the technician could work with Preat's lead design technician and engineer qualities into the bar design that could not be achieved through traditional milling. Note the anterior pins, Pearl surface finish (Preat Corporation), and "windows" going through the middle of the framework, as shown in Figure 5, Figure 7, and Figure 8.
The next step was to wax in central contacts with green inlay wax (Figure 3), allowing the establishment of desired central stops and short excursive surfaces. The purpose of using the green inlay wax is to provide a visual distinction in the digital scan, as well as a means of communication with the Prism Design Center. The occlusals of the molars were outlined in ink for communication purposes as well. The framework was designed and sent back to the author's laboratory and the dentist via a 3D PDF for review, adjustments, and final approval. The author also requested the addition of Preat's signature Pearl surface, which provides maximum mechanical acrylic retention and a polished intaglio (Figure 4).
The framework was opaqued using a metal primer, pink Sea-Bond (Combe Incorporated), and GRADIA DIRECT A2 (GC America Inc.), being careful not to fill in the Pearl retentive surface (Figure 5). The teeth were transferred to the framework using stone matrices and the wax-up was completed (Figure 6). Because the framework was a solid unit with all-metal occlusion, the author needed to adopt more traditional methods of processing. This started with the framework "windows," a design feature that allowed the denture base resin to fully reach the finish lines during packing (Figure 7 and Figure 8). He also opted to use a "bank" flasking technique, where the teeth and framework are invested in only one-half of the denture flask. Utility wax was used to create vents near the finish lines to further aid in the flow of the resin when packing.
Next, the denture was boiled out, and the mold was cleaned and prepared to pack. Due to the intricacy of the design and viscosity of the acrylic separator, the latter would coagulate in some of the crevices, leading to minor voids. The denture was processed using Original-shade Lucitone 199 acrylic (Dentsply Sirona) and trial-packed with a pneumatic press. This was done multiple times at 2,000 psi until only a minimal amount of resin was extruded. The denture base was cured in accordance with the manufacturer's directions. After processing, the case was equilibrated, finished, and polished, and minor final adjustments were made upon delivery (Figure 9 and Figure 10).
The patient has now had their new denture for several months and is very happy with their improved quality of life. "Inherited" cases like these should motivate technicians to better their knowledge and hone the skills of their craft. Laboratories have a responsibility to their patients in providing the best level of care possible. A successful outcome for each patient is certainly reason to celebrate.
Disclaimer: The statements and opinions contained in the preceding material are not of the editors, publisher, or the Editorial Board of Inside Dental Technology.
About the Author
William "Butch" Houghton is the owner of Houghton Dental Laboratory in Atascadero, California.