The Evolution of Dental Materials in Implant-Retained Fixed Prostheses

At that time, patient perceptions of implant-retained fixed prostheses were dictated by the idea of the perfect "Hollywood smile": the straighter and whiter, the better. This ideal led most laboratory technicians and dentists to develop standardized, rather than customized, restorations for their patients to meet this demand.

Current prosthodontic and laboratory procedures have evolved significantly from what was done in previous years. Screw-retained prostheses are now the first choice over cemented restorations due to the biological advantages of avoiding the use of cement intraorally and being able to retrieve the restorations easily. Materials have also shifted from metal-ceramic restorations to all-ceramic restorations made of either lithium disilicate or zirconia materials.

Dento-alveolar structures can be replaced predictably with pink porcelain or pink resin compounds. Developing harmony between the prosthesis and soft tissue requires knowledge of the anatomical morphology of the dento-gingival complex. First, the incisal edge position needs to be determined along esthetic and functional principles, followed by overall shape and color selection. A dynamic relationship between overall tooth morphology and lip position will yield what the patient will traditionally show whenever they open their mouths: white. A functional lip position assessment will also provide valuable information to determine the display of gingival structures: pink.

The restoration of the dento-gingival structures opened a whole new avenue of collaboration among the restorative dentist/prosthodontist, implant surgeon, and laboratory technician. Along with these technical advances has come a shift in the patient perception of esthetics. Dentists and technicians are starting to see that now most patients want teeth that are more age-appropriate and customized to their specific situation. The following case report shows how materials, prosthetic approaches, and patient perceptions have evolved over the last 5 to 15 years.

A 64-year-old white male came for a prosthodontic consult to explore the possibility of redoing his artificial-looking anterior implant bridge. He claimed that his teeth did not look fitting for his age anymore; they were too white. The current bridge was made in 2014, but his first version was done in 2004. The custom abutments made for that original restoration in 2004 were kept and used to support the 2014 bridge. He also wondered if a new bridge would give him more lip support.

Extraoral examination showed that the temporomandibular joint was within normal limits for this brachycephalic patient with a low Frankfort mandibular plane angle. He exhibited a moderate smile line with minimal incisor display at rest. An intraoral examination revealed a bilateral Class II canine occlusion as well as short mandibular and maxillary posterior crowns. Overall, his full-mouth reconstruction was in good repair (Figure 1 through Figure 3).

The area in question was the anterior implant-retained maxillary bridge, which had been made with the "Hollywood" standard in mind. The patient pointed out that the provisional restoration had been done following the initial bridge, so he had not had a real chance to evaluate the final shape and length of his teeth prior to delivery. That's why the final restoration had been sent back to the laboratory multiple times prior to cementation.

The patient's expectations were attainable through his collaboration with the prosthodontist and the laboratory technician. The following prosthetic modifications were made in order to improve form, characterization, and lip support:

• adding pink porcelain on the cervical aspect of the implant-fixed dental prosthesis
instead of on the root form;

• changing the abutment system to provide an improved emergence profile and to provide the foundation for a screw-retained prosthesis;

• improving line angles, changing tooth shape to square-looking teeth, increasing length, and opening incisal embrasures and contacts to give the illusion of individual crowns; and

• using layered zirconia for the final restoration instead of metal-ceramic restorations.

The restorative team explained all of the potential changes to the patient and took impressions and photographs. This helped the team determine esthetic parameters, and make such changes as adding pink wax on the root areas to improve the clinical crowns' height-to-width proportions and provide lip support (Figure 4). Using mounted casts, the team presented the plan to the patient for approval, and he agreed to the course of treatment.

Then the team removed the existing fixed partial denture for teeth Nos. 7 through 10, including the custom abutments on implants Nos. 7, 10, and 12, in addition to crowns on teeth Nos. 5, 6, and 11, and the crown on implant No. 12 (Figure 5). They took an implant-level impression and added indirect provisionals to the natural teeth and implants using a matrix from the diagnostic wax-up (Figure 6 and Figure 7). The provisionals were modified on several occasions until the patient was satisfied with the upgraded features. Phonetics and esthetics were evaluated in detail.

Next, the team used the master cast and an impression of the existing provisionals to create a new set of temporary crowns with improvements. In the master, they also used angled abutments to correct the implant angulation and used screw-retained cylinders to make the new set of provisionals. For the fabrication of the final set of provisionals, the team chose to duplicate the usual anaxdent flask (anaxdent North America; anaxdentusa.com) to process, injecting VITA VM^®CC (VITA North America; vitanorthamerica.com) to layer the tissue aspect with anaxgum Paste and anaxgum Flow (anaxdent North America). Adjustments were made, texture was added, strong line angles and square features were achieved, and gingival embrasures were opened slightly to allow flossing between the implants (Figure 8). The patient granted approval after
2 months of use (Figure 9 and Figure 10).

At that point, the team made the final impressions at the abutment level for teeth Nos. 7 and 10 and at the implant level for No. 12, transferring the tissue contours from the approved provisionals to the master cast. They used an anaxdent silicone flasking system for this purpose.

The fabrication of the final restoration consisted of a zirconia frame (Prettau^®, Zirkonzahn; zirkonzahn.com) with lingual monolithic and facial layers using a high-fusing ceramic (VITA VM^®9, VITA North America) (Figure 11 and Figure 12).

Finally, the prostheses were ready for delivery. Crowns on the natural teeth were cemented with PANAVIA cement (Kuraray America; kuraraydental.com). The implant-retained bridge with Nos. 7 through 10 was screw-retained, and teflon tape and composite were used to seal the lingual access holes. Implant No. 12 used a custom titanium abutment with a screw-cementable crown (Figure 13 through Figure 18). Oral hygiene instructions, a floss threader, a water flosser, and an occlusal night guard with anterior guidance were also provided to the patient with delivery of the final prostheses.

Materials and patient preferences have evolved significantly in the last two decades. Customization of form and function in esthetic cases has become the gold standard. Whether the restoration is done using traditional or digital methods, the outcome has to meet each patient's expectations as well as the current esthetic preference for a customized smile. Upon treating this patient, the restorative team realized that their prostheses should always be retrievable to make it easy to upgrade esthetics or repair/replace components as the patients get older. Screw retention is the ideal prosthetic retention choice for the patients who want their teeth to age along with them.

Despite zirconia's rigidity, it has been the material of choice of many top clinicians and laboratory technicians for the last 5 to 6 years. The material has improved immensely. In addition to its inherently fracture-resistant properties, zirconia can now be used for highly esthetic cases needing pink ceramics or translucency. Nonetheless, not all zirconia is created equal. As the market is now inundated with so many different brands and types, restorative teams should be careful to select a reputable brand with a long track record.

Sergio Ortegon, DDS, MS
Board Certified Prosthodontist
Private Practice
Houston, TX

Victor E. Castro, CDT
Founder and President
Studio-280
Houston, TX