Custom Fabricated Subperiosteal Implants for Sectional Rehabilitation of Severely Atrophic Maxillae: A Technical Note

Innovation

In recent years, subperiosteal implants have garnered renewed interest. In 2017, Mommaerts introduced a new generation of custom manufactured implants, which take advantage of CAD/CAM technology and laser melting.¹ These advances allow for the production of custom-made implants based on computed tomography (CT) scans and diagnostic wax-ups, eliminating the need for direct bone impressions.² The design of these implants has undergone significant evolution, informed by stress-shielding simulations and finite element analysis (FEA), with the goal of achieving rigid fixation and optimal distribution of masticatory forces on the maxillary resistance pillars.² ³

As a result, several reports over recent years have documented successful full-arch rehabilitation of severely atrophic maxillae using these implants. The outcomes have been promising, demonstrating an implant survival rate exceeding 95% in the short to medium term.⁴–⁸ One key advantage of these rehabilitations lies in enabling immediate loading for cases of severe bone atrophy without requiring preimplant regenerative surgery.

However, the literature on sectional rehabilitations of the atrophic maxilla with subperiosteal implants remains scarce. To date, there is insufficient evidence supporting the efficacy of subperiosteal implants in such cases, as most of the research focuses on full-arch rehabilitations.⁹

Sectional rehabilitations of the maxilla, though, are frequently requested by patients who do not require treatment of the anterior maxillary sectors or the extraction of the first or molars. In these situations, graftless techniques such as pterygoid or zygomatic implants may not be technically feasible due to the constraints imposed by the anatomical structures of the maxilla.¹⁰ The implant’s emergence in these graftless techniques is often limited by the anatomy of the region.¹¹ In such cases, custom manufactured subperiosteal implants may represent the only graftless alternative to avoid bone regeneration procedures.

For this reason, at the Maxillofacial Surgery Unit of the University of Sassari (Sassari, Italy), rehabilitation with custom-made subperiosteal implants is offered to all patients with Cawood and Howell class V and VI posterior maxillary atrophy who specifically request a graftless, immediate-loading solution, having declined bone regeneration procedures and traditional delayed implant protocols.

As previously described,⁷ ¹²–¹⁴ all patients undergoing this type of rehabilitation are subjected to cone beam computed tomography (CBCT) of both the maxilla and mandible, with scans featuring a slice thickness of 0.1 to 0.3 mm and covering a wide field of view, including the entire maxilla and cheekbones. The scans are conducted using a radiological template embedded with radiopaque markers, developed based on prosthetic planning. Digital impressions of the dental arches and the radiological template used during the CBCT are also obtained. The Digital Imaging and Communications in Medicine files (DICOM) and stereolithographic (STL) files are then sent to B&B Dental (B&B Dental, San Pietro in Casale, Italy), the company responsible for fabricating the implant.

The CBCT DICOM files are processed using B&B Dental’s GS software (B&B Dental, San Pietro in Casale, Italy) to create a 3-dimensional (3D) reconstruction of the bone structure, refined to remove scatter and other artifacts. The STL files of the dental arches and diagnostic wax-up are integrated with the 3D jaw model. The consolidated 3D files are imported into Meshmixer software (Autodesk, San Rafael, CA) for designing the implant, following the surgeon’s guidance.

While our protocol does not include FEA, the implant design used is based on extensive FEA research previously conducted on the upper maxilla. These studies have demonstrated the efficacy of specific designs in optimizing load distribution and minimizing stress at the bone-implant interface, particularly under oblique and lateral forces.³ ⁴ ¹⁵

In addition, the angulation of the abutments is determined through prosthetic planning to align with the functional occlusion. This approach ensures that the abutments align with the long axis of the prosthetic crowns, minimizing stress concentrations and promoting even force distribution across the implant framework.³ ⁴ ¹⁵

Each implant features 2 arms with osteosynthesis screw holes—one on the nasomaxillary pillar and the other on the maxillomalar pillar, extending to the anterior face of the zygomatic arch. Screw placement is based on bone thickness, with a minimum of 2 holes per arm. The implants are equipped with integrated multiunit abutments, designed to sit deeper in the alveolar crest slots to reduce basal bone resorption beneath the abutments. The length and orientation of the abutments are customized to align with the diagnostic wax-up and gingival thickness derived from the scans of the dental arches.

A cobalt-chrome surgical guide is produced to facilitate the preparation of alveolar crest slots. On the palatal side, abutments are reinforced by a palatal connection with a screw hole, where the underlying bone allows it.

The 3D models of the bones, gums, prostheses, and implants are then reviewed in the B&B Dental GS software for final approval by the surgeon. Once approved, the implants are manufactured using grade V titanium and double laser melting technology (MYSINT100, Sisma, Piovene Rocchette, Italy). The implants undergo sintering at 840°C for 4 hours and 500°C for 2 hours to stabilize the titanium and remove porosity without altering dimensions. Abutments are milled with precision using a 5-axis milling machine (Datron D5, Datron, Milford, NH), and the internal threads of the multiunit abutments are crafted as needed.

To ensure cleanliness, the implants are thoroughly cleaned with DOWCLENE 1601 (Dow Chemicals Corporation, Midland, MI), an organic acid, and subsequently sterilized. Templates for crest preparation are fabricated from durable cobalt-chrome. In addition, a STL resin model of the maxilla is created using a 3D printer (Stratasys Objet 30, Stratasys, Eden Prairie, MN) and provided to the surgeon as a reference.

The surgery is carried out under local anesthesia supplemented with superficial intravenous sedation using diazepam. Local anesthesia is administered with articaine containing 1:100,000 adrenaline. Anesthesia of the upper front surgical field is achieved by blocking the infraorbital and zygomatic nerves through an extraoral approach. Intraoral anesthesia is applied to the upper vestibular fornix, with palatal anesthesia achieved by blocking the greater palatine and nasopalatine nerves.

A full-thickness mucosal incision is made along the alveolar crest with 2 releasing incisions at least 5 mm away from the most distal and mesial abutments. The incision is positioned 2 to 3 mm palatally to ensure sufficient keratinized gingiva could be repositioned on the vestibular side of the abutments. A full-thickness flap is raised on both the vestibular and palatal sides.

Initial dissection of the maxilla is limited to the alveolar crest to allow for the placement of the crestal preparation template. Slots for the abutment housing are prepared using the template, ensuring they reach the basal bone. If preparation extends to the sinus membrane, the membrane is carefully preserved or, if perforated, repaired using a porcine-derived collagen membrane (Geistlich Bio-Gide Perio, Geistlich Pharma AG, Wolhusen, Switzerland).

Further dissection is performed to expose the upper maxilla, identify and preserve the infraorbital nerve, and fully detach the nasomaxillary pillar and zygomatic buttress. If needed, the anterior insertions of the masseter muscle are released to facilitate this step. The subperiosteal implant is positioned and its fit verified. Rigid fixation is achieved using grade V titanium osteosynthesis screws (B&B Dental, San Pietro in Casale, Italy) with diameters of 2 mm. Screw lengths range from 10 to 14 mm for the zygomatic buttress, 4 to 6 mm for the nasomaxillary pillar, and 4 to 8 mm for the palate. If adequate torque cannot be achieved, a 2.3 mm diameter safety screw is used. At least 2 screws per pillar are placed to ensure adequate primary stability for immediate loading.

Once the implant is fixed, the structure is covered with resorbable membranes, cortical laminae, or, when feasible, Bichat’s fat pad is transposed to thicken the soft tissue over the vestibular aspect. The mucosal flap is passivated using periosteal releases and sutured.

Postoperatively, all patients are prescribed antibiotics (amoxicillin with clavulanic acid, 1 g twice daily for 6 days) and pain management medications. Immediate loading is performed in all cases using a fixed provisional prosthesis secured to the multiunit abutments. The definitive prosthesis is delivered 6 months postsurgery, after sufficient soft tissue conditioning. Patients are advised to maintain a soft diet for the first 15 days and to avoid hard foods until the final prosthesis was fitted.