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Edentulous jaw atrophies are an evolutionary condition characterized by the loss of bone volume, which makes it difficult to place endosseous dental implants in a conventional way. This situation can be the result of various factors, such as tooth loss, periodontal disease, trauma, oncological surgeries, progressive bone resorption associated with Edentulism of long evolution, or natural bone resorption associated with aging. These can lead to significant functional, aesthetic and phoniatric deficits, with all the corresponding implications at a psychological level.
The only possible way to rehabilitate patients with severe atrophy (Cawood-Howell), characterized by bone crests of insufficient width and density, is to subject them to long and complicated bone regeneration procedures.
But thanks to new diagnostic imaging techniques and new 3D design and additive manufacturing systems (CAD-CAM), subperiosteal implants anchored in the jawbone are presented as a viable alternative for this type of atrophy. Offering optimal fit and stability as it is a customized implant, in addition to being a less invasive surgical technique that provides the patient with comfort and quality of life early after the procedure.
Case presentation
A 65-year-old female patient, completely edentulous and with no relevant medical history, with grade IV maxillary atrophy, came to the consultation with the intention to replace her upper removable complete denture with a fixed rehabilitation. She had a skeletal pseudoclass III due to anteroposterior atrophy of the upper jaw.
After a meticulous study and evaluation of the different treatment alternatives, the most suitable and predictable option was rehabilitation by means of a customized subperiosteal implant (ISP) with immediate screw-retained complete prosthesis.
In order to start the planning of the case, it is necessary as complementary tests, the radiological study of the patient's jaw, a positioning test in the mouth of the future final prosthesis and, if possible, some digital impressions of the soft tissues. With this information it is possible to design the structure of the ISP, plan the ideal fixation positions of the osteosynthesis screws and size and position the prosthetic connections based on the level of the patient's available soft tissues.
Using the double-scan technique, a CT scan of the patient was performed with the new prosthesis test placed in the mouth (in occlusion and correctly adjusted), with radiological markers (Composite®) in the positions where the connections of the structure were desired.
Tomographic slices must be between 0.4 and 0.8 mm thick and the exploration area must include the entire arch, the TMJ and the zygomatic arches in order to carry out the most precise study possible of the patient's facial symmetry and determine the most appropriate ISP fixation points based on bone availability, given that in most of these cases the atrophies are extreme.
And, on the other hand, a second CT scan of only the prosthesis, with the radiological markers in the same orientation.
The radiological files must be sent in original DICOM format in order to be able to perform the segmentation and thus generate the 3D model on which the ISP will be designed.
CT segmentation was performed using Materialise's Mimics Medical certified medical software.
Materialise's 3-Matic Medical certified software was used for the implant design.
The CSI was designed in two pieces, avoiding the premaxilla area where there is a greater risk of exposure of the implanted material and the nasopalatine canal. For its fixation, corticalized areas were sought in the bone buttresses where the osteosynthesis screws could be inserted.
In order to optimize the adaptation and settlement of the ISP in extreme maxillary atrophy, a protocol of guided osteotomies has been defined prior to implant placement. These "box"-shaped osteotomies allow the ISP to be fixed with greater stability and at the same time immerse the union between the implant and the connections in the alveolar bone, thus minimizing the risk of dehiscence in the soft tissues.
The cutting guides made of sintered Ti are fixed using osteosynthesis screws and these fixation points are also used for ISP fixation.
The design of all parts is summarized in a final report that must be reviewed and approved by the clinician before the fabrication of the different parts. This document also details the length and diameter of the fixation screws, as well as the planned positions.
The surgery was performed under local anesthesia and outpatient conscious sedation. A crestal incision was made from tuberosity to tuberosity with distal reliefs that allowed us to expose both nasal vestibules and malar buttresses using a full-thickness flap.
Following the surgical protocol, the titanium guide was carefully positioned on top of the bony ridge and checked for stability and passive seating before fixation to the bone using two osteosynthesis screws.
Guided bone osteotomies were performed according to plan using a Piezosurgery (Mectron®) with a 0.25 mm thick microsaw.
Once the osteotomies were created, the two pieces of the customized titanium implant were placed on the bone of each quadrant and once the passive fit and stability were verified, the distal screws were fixed in the zygomatic area.
Once all the screws were fixed, LPRF membranes were placed between the connections to improve the healing of soft tissue and bone. Suturing was carried out to achieve a good seal to protect the implant from exposure to the oral environment during the healing phase.
Once the ISP was fixed, scan abutments were placed and digital impressions were taken in the same session. These were sent to the prosthetic laboratory to make a provisional resin prosthesis on an internal metal reinforcement structure that was placed on the patient the following day.
It should be noted that since the implant and prosthesis had been planned virtually, the parallelism and distribution of the connections was ideal and the passivity of the prosthesis was optimal.
After 6 months, the provisional prosthesis was replaced by a micro-milled chrome-cobalt structure (Avinent Implant System) with an IPS Style ceramic finish (Ivoclar Vivadent) as a definitive prosthesis, at the same time as an occlusal splint was made to prevent the appearance of mechanical complications.
Conclusion
Subperiosteal implants can be a solution for permanently rehabilitating patients with extreme bone atrophy where bone regeneration techniques are difficult to predict.
The custom design of these implants allows for optimal positioning and parallelism of the prosthetic connections, which means a better distribution of occlusal forces, as well as allowing for immediate, predictable rehabilitation that is not dependent on the period of osseointegration.
Clinical experience with this type of implant has allowed the creation of a guided osteotomy protocol that allows the submersion of the unions between the ISP and the prosthetic connections, reducing the risk of dehiscence and perimplantitis.
