Metal–Ceramic implant-supported fixed dental prostheses: the gold standard for the completely edentulous patient. A case report

Case report

A 62-year-old female patient, with complete edentulism, who had worn dentures for more than 20 years, requested a fixed prosthetic solution (Figure 1). Clinical examination showed edentulous alveolar ridges, covered by healthy gingiva, without signs of infection, inflammation, or presence of residual dental roots. Imaging studies revealed moderate bone resorption in height and width in both jaws from the anterior to the premolar region. The molar area showed severe resorption, with maxillary sinus floor pneumatization and close proximity of the inferior dental canal to the edentulous ridge. According to the clinical and imaging findings, the ridges were classified following the guidelines proposed by Cawood and Howell, as class IV ridges and bimaxillary complete edentulism.

The proposed treatment plan included six Zimmer-Biomet Inc (USA) dental implants for each jaw with left maxillary sinus floor augmentation and immediate implant placement. This would be followed by rehabilitation with metal–ceramic implant-supported hybrid prostheses, with gingival tissue characterization to obtain proper labial support. In the upper jaw, under local anaesthesia, a bone expansion technique with osteotomes was performed for placement of a Tapered Screw-Vent Implant System (Zimmer Biomet Dental Inc) in UR3-UR5-UR6, and maxillary sinus floor augmentation was conducted in UL6 to place implants in UL3-UL5-UL6 (Figure 2). In a second session, implants were placed in the lower jaw from LR5 to LL5.

Six months after clinical and radiographic checks, and after confirming adequate osseo-integration, the restorative phase began (Figure 3). An open-tray technique with impression copings was used. Copings were splinted with pattern resin and the impression was cast in type IV plaster. On the working cast, record bases with wax rims were made for a jaw registration to determine vertical dimension, position, size of the teeth, smile line, profile, and facial fullness of the patient (Figure 4a). Once these aspects were determined, the cast was sent to the laboratory to prepare the abutments and design the structures. A first test for the verification jig of the working casts, the abutments, and the structures in polymethylmethacrylate (PMMA) was tried in the patient to check the precision of the position of the implants in the plaster model and parallelism of the definitive abutments (Figure 4b). The super structures were cast in Cr-Co, and a second try-in was carried out to verify accuracy (Figure 5). In the laboratory, ceramic layering was performed for the dental area with pink ceramic for the characterization of the gingiva. The final try-in of the prostheses was completed to check occlusion, the result was approved by the patient and she gave her consent for placing the screwed cement bridge. The objective of restoring function and self-esteem to the patient was achieved (Figure 6). Additionally, instructions were given about the special care of the prostheses, and review was indicated every 6 months.

Discussion

The presence of a metal superstructure, in this case, the Cr-Co alloy, reduces prosthetic complications associated with fractures and it creates ideal support for the ceramic material. The presence of a metal occlusal surface can improve wear resistance and help maintain the vertical dimension; however, the appearance can be compromised. The inclusion of CAD/CAM technology has allowed the use of aesthetic restorative materials, such as zirconia, for fixed implant-supported prostheses, with some success.¹⁴

Although the aesthetic result is one of the main factors to be considered in these cases, the survival of the dental prosthesis and implants with few complications, whether a fixed metal–ceramic or all-ceramic prosthesis is used, remains important for clinicians. A 2018 systematic review by Pjetursson et al¹⁵ reported on the survival rate and complications for zirconia-based and metal–ceramic implant-supported single crowns (SCs). The meta-analysis revealed a 98.3% 5-year survival rate for metal–ceramic implant-supported SCs compared to 97.6% for zirconia implant-supported SCs. For the metal restorations, 86.7% experienced no technical or biological complications, while 83.8% of the zirconia restorations met this objective. The incidence of chipping was similar between the two materials; however, a greater number of failures due to fracture were reported in the zirconia restorations (2.1% versus 0.2% for the metal–ceramic implant-supported SCs). The clinical case presented by the authors was a metal–ceramic implant-supported fixed dental prostheses. There were no complications in a 2-year follow-up and no fractures.

A systematic review by Sailer et al¹⁶ evaluated the survival rate and complications of zirconia–ceramic and/or monolithic zirconia implant-supported FDPs versus metal–ceramic FDPs. The study reported a higher number of cases treated with metal–ceramic FDPs (n = 932) compared to zirconia-ceramic FDPs (n = 175), which suggests that clinicians had a preference for metal–ceramic implant-supported restorations to rehabilitate completely edentulous patients. The survival rates of metal–ceramic implant-supported FDPs was 98.7% versus 93% for zirconia implant-supported FDPs) and there was a low incidence of fractures and chipping was reported (11.6% versus 50% for zirconia implant-supported FDPs).¹⁶ All of which make metal–ceramic restorations the gold standard for implant-supported fixed prostheses, especially in cases of multiple implants in bimaxillary edentulous patients. ^17–19

Ceramic chipping in zirconia prostheses is the most frequently described complication.²⁰ Larsson et al²¹ reported rates of more than 50% for this complication in implant-supported prostheses, despite advances in the quality of zirconia and prosthetic fabrication techniques.

Currently, there is insufficient evidence in the literature to support the use of metal-free materials for implant-supported fixed prostheses over traditional materials. Poggio et al²² recommended selecting the restorative material based on clinical experience and the individual needs and preferences of each patient. The authors of this report support this view and advocate the use of a metal–ceramic superstructure for full arch fixed-implant bridges.

Conclusions

The success of the rehabilitation in edentulous patients in whom the placement of dental implants is considered will depend on many factors, such as the experience of the team, the quantity and quality of the maxillary bone, and the material to be used in the prosthetic restoration. Since Brånemark's original design of the removable fixed prosthesis over implants, there have been many changes. The Brånemark prosthesis consisted of a gold alloy framework attached to implant copings. The teeth of the acrylic resin prosthesis were placed on the framework and secured with acrylic resin. The main drawbacks to this type of restoration were the distal extension fractures due to the extensive cantilever. In the case reported here, the authors designed the ceramic bridge implant with the hybrid technique, in which the ceramic prosthesis is cemented onto the titanium superstructure with resinous cement, and subsequently screwed onto the implants, thus allowing occlusal access to remove the prosthesis. Additionally, the cement settles passively and does not invade the peri-implant mucosa. The authors suggest that the gold standard construction for a full arch implant-supported fixed prostheses would use metal–ceramic.