An alternative hybrid

March 21, 2012

Dentistry by Dr. David Lovit. Restoring large, fixed implants is among the most challenging and time-consuming processes for lab technicians, in that most design choices are often left up to the technician with little or no guidance from the prescribing dentist.

Dentistry by Dr. David Lovit.

Restoring large, fixed implants is among the most challenging and time-consuming processes for lab technicians, in that most design choices are often left up to the technician with little or no guidance from the prescribing dentist.

Consequently, many labs choose not to take on these cases. This article describes a particular case and outlines suggestions for successful completion of the process.

To begin, choosing a framework design requires creativity and planning as well as patient specific information because of the many existing options. For example, we can use CAD/CAM to design and mill individual abutments or a framework from titanium or zirconia; we can wax and cast the framework from our own dental alloy; or we can create screw-retained frameworks, allowing us to bake the porcelain directly onto the substructure. Hybrid bridges are yet another option, accomplished by milling a bar and processing acrylic dentures onto the bar. Lastly, we can create screw-retained frames with cemented individual crowns.

The case presented in this article was fraught with some unique challenges. The patient did not want plastic denture teeth, so the typical hybrid denture was not an option. The dentist did not like the idea of baking porcelain directly onto the framework, as it would make it very difficult to repair if something were to fracture in the future.

As the lab technician, I wanted to make an indirect provisional (Figs. A-C) to verify function and esthetics and allow the patient to wear it for a while before beginning the final restoration. This extra step would ensure the patient was satisfied not only with the esthetics of the bridge, but would also be able to tolerate the new bite. Lastly, I wanted to find a way to use full-contoured IPS e.max Press (Ivoclar Vivadent) so that a wax injection could be employed. This would ensure easy duplication of the contours created for the provisional. The problem with this choice was trying to find a way to mask the metal framework to allow for the translucent e.max material.

The solution came from a friend and fellow CDT, Greg Martin, who suggested the use of light cured composite over the metal framework.

01 Incorporating adequate support and retention (Fig. D), the metal substructure was cast, finished and etched with GC Metal Primer II (Fig. E).

02 I then covered it with GC GRADIA Gum and dentin composite material (Figs. F, G). Because this material is completely light cured, I was able to layer the entire framework without firing it in a porcelain furnace. This eliminated the risk of distortion. While the primer creates a strong bond between the metal and the composite, it is still important to incorporate plenty of support and mechanical retention. On this frame, we had no more than 1 mm of unsupported composite. The many shades and levels of opacity available in the GRADIA Gum kit allow for the creation of life-like tissue with a minimal amount of material.

03 After contouring the preps (Fig. H), I modified my matrix to fit over the new framework, injected wax directly onto the preps, and pressed with IPS e.max Press (Figs. I, J).

04 The pressings were contoured, stained and glazed using GC Lustre Paste from GC America (Fig. K).

05 After some minor shade modifications, the framework was screwed in, and the crowns were cemented down (Figs. L-N).

The patient was very pleased with the results. The doctor also was pleased with the design, as it allowed for easy repairs if necessary. If something were to fracture in the future, he could simply remove the individual crown and take an impression. We would then treat it as a typical single-unit case.

The positive results of this complex but not unusual case reflect intersections between patients, professionals and technology. Lab technicians draw on training, experience and communication to create sustainable, effective, patient-specific designs. This large fixed implant case was successful largely because all involved parties communicated about needs and available options to mutually create a design and develop a plan before any lab work began.