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Over the years, the use of zirconium oxide in implant-supported prosthetic rehabilitations has evolved from crowns and small bridges to complete rehabilitations. Consequently, the challenge of using this material in large implant-supported rehabilitations is achieving optimal passivity to ensure the durability of the structure, as these have high rigidity and do not tolerate torsion well.
Currently, instead of monolithic zirconia complete prostheses on titanium interfaces, the design of hybrid structures composed of a primary and a customized secondary structure with different materials is preferred. This approach provides greater passivity to the zirconia while maintaining aesthetics in the final rehabilitation. Innovative solutions enable high-quality, extensive implant rehabilitations with optimal fit, durability, and high aesthetic demands using 100% digital protocols, based on three key concepts: prosthetically guided planning, simple immediate provisionalization, and predictable final restoration.
In these cases, the significant difficulty lies in, on one hand, achieving correct passivity of the structures to the implants and, on the other hand, correctly distributing occlusal loads so that the masticatory forces are supported by the metal reinforcement structure. This is challenging because the distribution of implants in the edentulous patient is not always ideal due to bone resorption accompanying edentulism. Achieving a good location for the primary structure will help ensure the durability of the zirconium oxide superstructure and the long-term maintenance of the rehabilitation in the mouth.
Keywords: digital rehabilitations, metal-zirconia, new concepts and protocols.
A 60-year-old male patient with functional wear, a smoker with good oral hygiene, with hypertension, a history of a mild myocardial infarction a few months ago, and ASA II risk. He visits the clinic due to the failure of the previous tooth-supported rehabilitation he had for over 15 years, where, due to lack of posterior support and overloading from bruxism, some abutment teeth that supported the prosthesis fractured.
After a thorough clinical examination, and given the patient's expression of being unable to tolerate a removable prosthesis, a fixed full-arch implant rehabilitation was proposed.
Although the implants would be placed manually and not using a guided surgery splint, their distribution was prosthetically guided using the 3Shape Implant Studio software. Six Biomimetic Iceberg CC.I implants were planned in positions 12, 14, and 16 in the upper left quadrant and 22, 24, and 26 in the right quadrant.
The surgical phase began with the placement of the posterior implants on both sides of the upper jaw: Biomimetic Iceberg CC.I 4.0x10, 4.5x8.5, and 4.5x10 in positions 14, 16, and 26, respectively. However, due to insufficient primary stability, the placement of the anterior implants was postponed for a subsequent appointment, and the initially planned immediate loading was discarded. The fact that the patient initially presented with posterior edentulism facilitated decision-making, assuming the risk that the remaining anterior teeth might fail during the healing time of these initial implants.
Sixteen weeks after the first surgery, the implant in position 26 failed asymptomatically.
Taking advantage of the second surgery to place the anterior implants, two Biomimetic Iceberg CC.I 3.5x11.5 implants were placed in positions 22 and 24. A new implant was placed in position 26, slightly distal to the previous location but in accordance with the initial prosthetic plan. After the surgery, immediate provisional loading was performed on transepithelial abutments of the anterior implants along with those placed in the first surgery, excluding the implant in position 26.
After the appropriate healing time following surgery, the provisional prosthesis was removed for the first time, revealing the failure of two implants in the second quadrant (22 and 24). Besides being a smoker, the patient suffered a second heart attack during the implant healing months; the first one occurred before the first surgery.
The failed implants were extracted and replaced with two more in the same positions (22 and 24), and an additional implant was placed in position 21, given the favorable healing in that area and to avoid an excessively long and curved prosthetic section in the anterior sector. The implants were connected to the initial provisional prosthesis, and the necessary osseointegration time was awaited, keeping the patient with a fixed screw-retained prosthesis.
After many surgical problems, the necessary stability was finally achieved to begin the definitive prosthetic phase.
Digital impressions were taken with the Trios intraoral scanner (3Shape) to create a full-volume plastic (PMMA) trial based on the provisional design from the first phase, which had to be modified several times. Once the new PMMA provisional was verified, the primary titanium structure was designed.
A primary structure was designed in grade V titanium, a biocompatible material with optimal biological behavior for good tissue maintenance. The titanium structure was machined, as were the implant connections, maintaining a fully polished finish on the basal area. Once the metal structure design was validated, the secondary zirconia structure with an anatomical design and smoother profiles was designed.
The primary structure acts as a customized interface, while the secondary structure compensates for weaker areas with its design, resulting in a more homogeneous final hybrid prosthesis and accommodating minor misalignments and micromovements between the metal and the cement.
About six months after implant placement, gingival recession was detected at implant 14. Initially, a graft was considered, but since the patient had a low smile line and did not want more surgeries, the intervention was postponed and kept under observation.
Finally, twelve months after the placement of the last implants, the definitive screw-retained prosthesis was placed.
Correct planning and good selection of components that form part of the implant treatment are crucial for the overall success of the treatment.
In this patient, the geometry of the Biomimetic Iceberg implants allows for distancing the prosthetic connection from the bone-implant junction, and the transmucosal zone of the neck with a convergent profile favors soft tissue sealing, maintaining good peri-implant tissue levels, an essential condition for the long-term success of the treatment.
The conical connection of the Iceberg implant allows for better force distribution, avoiding stress concentration at the screw level and the coronal zone of the implant, as extensively demonstrated in the literature. The placement of intermediate transepithelial abutments in a multiple prosthesis takes advantage of the biomechanical behavior of the conical implant, facilitating the placement and adjustment of large rehabilitations.
The new design of two-part hybrid superstructures allows for restoring large zirconia works with less risk of fracture. This cement-retained screw prosthesis, which yields good results in unitary or partial rehabilitations, is transferred to full arches, where the risk of fracture increases due to the difficulty of achieving perfect passivity. In this case, due to the difficulty of sector-wise rehabilitation, we had to perform a full-arch single-piece rehabilitation. Both for technical advantages and patient comfort, the entire digital workflow was used, simplifying the laboratory procedure by reproducing the digital design with the final material.
Currently, digital workflows and new materials like zirconium oxide (aesthetic, functional, resistant, and biologically very stable) allow for screw-retained large rehabilitations on implants thanks to new designs like superstructures.
These innovative and functional solutions enable the fabrication of high-quality dental rehabilitations with perfect fit, great durability, and high aesthetic demand.4o
