Abstract
Severe bone atrophy jeopardizes the success of endosseous implants. This technical note aims to present the innovative concept of additively manufactured sub-periosteal jaw implants (AMSJIs). Digital datasets of the patient’s jaws and wax trial in occlusion are used to segment the bone and dental arches, for the design of a sub-periosteal frame and abutments in the optimal location related to the dental arch and for the design of the suprastructure. The implants and suprastructure are three-dimensionally (3D) printed in titanium alloy. The provisional denture is 3D-printed in polymer. AMSJIs offer an alternative approach for patients with extreme jaw bone atrophy. This report refers to the use of this technique for full maxillary rehabilitation, but partial defects in either jaw and extended post-resection defects may also be approached using the same technique. This customized, prosthesis-driven reverse-engineering approach avoids bone grafting and provides immediate functional restoration with one surgical session.
Up to 56% of patients with endosseous implant-retained prostheses develop peri-implantitis, leading to eventual fixture loss . Of the many causes of peri-implantitis, most are not clinically controllable . Maxillary bone loss, whether combined with implant loss or arising from disuse atrophy, poses a major challenge. Current solutions include all-on-4, when sufficient bone is present anterior to the maxillary sinuses ; ‘quad-zygoma’ or zygoma implants plus conventional oral implants in the alveolus ; and bone grafting with sinus floor augmentation and buccal onlay grafts and subsequent (redo) endosseous implantation . An alternative technique, described below, revisits a 70-year-old concept by applying modern computer-aided design and computer-aided manufacturing (CAD/CAM) technology.
Materials and methods
The dental practitioner chooses a double structure with overdenture or a screw-fixed hybrid bridge, depending on the inter-crestal space, phonetics, lip contour, and patient preference. A wax trial is fabricated, comprising a base plate with a wax bite rim and teeth of the desired colour, shape, and occlusion.
The patient brings the models of the lower dental arch and wax trial to the surgeon who checks the parameters for adequate positioning of the suprastructure in relation to the crest and the occlusal surfaces. The buccal, lingual, and occlusal surfaces of the wax trial model teeth are brushed with radiopaque silicone varnish (X-resin flow; Bredent GmbH and Co. KG, Senden, Germany). Alternatively, radiopaque artificial teeth are used (SR VivoTac and Posteriors; Ivoclar Vivadent, Schaan, Liechtenstein). Traditional or cone beam computed tomography (CT) of the maxillofacial complex is performed with the wax trial model in centric occlusion (maximum intercuspation). The lower dental arch model is scanned by high-resolution CT or optical scanning in the laboratory.
Bone and radiopaque tooth surfaces are segmented, and a surface tessellation language (STL) file is generated (e.g., with Geomagic Freeform Plus; 3DSystems, Rock Hill, SC, USA). The occluding lower dental arch is superimposed. Starting from the upper dental arch (rendered visible by the radiopaquer) that will house the connection screws, the sub-periosteal implant is designed as two segments upon which a customized, screw-retained temporary connecting bar fits. A three-dimensional (3D) print provisional prosthesis is designed. The sub-periosteal implant segment typically has three (sometimes four) abutments fixed to the main frame by four arms ( Fig. 1 ). The main frame generally has two extensions on the midfacial pillars, each of which receives three osteosynthesis screws. The interface between the flanges and the bony surface can be made porous (scaffolding) to encourage osseointegration.
The sub-periosteal implant and temporary bar ( Fig. 2 ) are additively manufactured in titanium grade 23 ELI (extra-low interstitial) (CADskills, Ghent, Belgium). The provisional prosthesis is additively manufactured in C&B MFH (microfilled hybrid) (NextDent, Soesterberg, the Netherlands).
With the patient under general or only local anaesthesia, a crestal incision is made 1 mm caudal to the mucogingival border, with relaxing incisions in the midline and behind the tuberosity ( Fig. 3 ). Sub-periosteal flap dissection is performed in the buccal and palate areas. The AMSJIs are fitted left and right; this may require tapping because of the tight fit.
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