For years, the severely atrophic edentulous alveolar ridge has posed significant challenges when it comes to dental prosthetic rehabilitation. Considering that many of these severely atrophic edentulous jaw cases are elderly medically compromised patients, the need for complex and protracted treatment means that many of these patients may never benefit from a fixed dental prosthesis that would improve their quality of life.
Currently, dental rehabilitation of the severely atrophic maxilla and mandible involves complex surgical procedures including jaw osteotomies, alveolar ridge distraction, complex bone grafts, sinus lifts, barrier membranes and even zygomaticus implants that rely on skilful surgery (1). The biggest drawback is often the long-drawn-out months between the start of treatment and the final prosthesis placement (1-3).
Dentistry and Oral & Maxillofacial Surgery have been the major beneficiaries of digital technologies. Computer aided design and computer aided manufacturing (CAD-CAM) tools have led to some remarkable advances in surgery of the jaws (4). The aim of this article is to present 3 clinical cases of how CAD-CAM technology with 3-D metal printing capabilities have facilitated the development of a new version of a subperiosteal jaw implant that requires no bone preparation and has the potential for the immediate placement of prosthetic teeth in severely atrophic jaws.
A 69yo lady presented to the author with ill-fitting dentures that were poorly supported by severely atrophic edentulous ridges in both the maxilla and mandible (Fig.1). The patient had been totally edentulous for over 40 years and she had been to see multiple dental practitioners who advised her that conventional dental implants were impossible without complex adjunctive bone grafting and osteotomy procedures.
The challenge for the author was to provide the patient with a simple and predictable solution that eliminated the need for complex bone related procedures to prepare the jaws to accommodate prosthetic teeth. Using CAD-CAM technology, a customized subperiosteal titanium frame was designed with numerous parallel transmucosal abutments upon which a fixed dental prosthesis could be attached (Fig.2).
Using cone beam Dicom CT scans of the patient’s edentulous alveolar ridge, the author, with the help of biomedical engineers at OMX Solutions (www.omx-solutions.com), designed a perforated titanium baseplate that was accurately contoured to the underlying bony anatomy of the edentulous alveolar ridge, with flanges that extended about 1-2cm on all sides from the crest of the resorbed alveolar ridge. In the maxilla, four conical transmucosal abutments projected about 10mm perpendicular from the ridge of the baseplate and were evenly spaced and perfectly parallel to each other to help simplify the design of the dental prosthesis. In the atrophic mandible, there were only two transmucosal abutments because the dental prosthesis was designed to be partly tissue borne, like an overdenture, so as not to place undue forces on the body of the pencil thin atrophic mandible, and also to avoid the mental nerve that sat
exposed on the crest of the alveolar ridge. Once the final design was approved by the author, the maxillary and mandibular subperiosteal jaw implants were 3-D printed using powdered titanium that was fused by intense laser beams, one layer at a time (3). The implants were cleaned and prepared for sterilization.
The patient was placed under general anaesthesia using naso-endotracheal intubation. The underlying maxillary alveolar bone was exposed via a crestal incision extending from the 15 to the 25 sites. Palatal and labial dissection was undertaken to expose about 10-15mm of bone on each side of the razor thin alveolar crest. The nasopalatine neurovascular bundle was preserved. Vertical relieving incisions were made in the midline and labial aspect of 15 and 25 sites to prevent tearing of the labial and buccal mucosae.
The customized maxillary subperiosteal jaw implant was carefully placed and positioned directly on the alveolar bone ridge and secured with 10 randomly placed self-drilling titanium alloy micro-screws (1.7mm wide x 5mm long). The remaining holes in the baseplate were left empty to encourage bone growth and osseointegration of the subperiosteal jaw implant to the alveolus. A crestal incision was similarly made in the mandible extending from 33 to 43 as the baseplate was much smaller than the maxillary implant so that surgical exposure of the mental nerve was avoided. The mandibular base plate was secured with 8 self-tapping micro-screws (1.7mm x 5mm) that were randomly placed around the multitude of holes in the baseplate. The mucosa was repaired with interrupted catgut sutures leaving the transmucosal abutments protruding through into the mouth (Fig.3). The maxillary dental prosthesis was directly attached to the 4 abutments with internal screws (Fig.4), while it was decided to delay the installation of the mandibular prosthesis for a few weeks. The whole procedure took a little over 1 hr to complete. Postoperative recovery was uneventful.
There was minimal pain and swelling in the first few days and 10 days later the mandibular prosthesis was fitted as an overdenture while the maxillary denture remained completely fixed to the maxillary subperiosteal implant. The patient continues to do well aesthetically and functionally with her fixed maxillary prosthesis and removeable mandibular overdenture at the 36 month follow-up period.
A 48yo female was referred to the author with failing bridgework replacing the missing 12,13,14 and 15. The patient had an iliac crest bone graft and 4 dental implant fixtures placed 15 years previously following a motor vehicle accident where she lost not only the 12,13,14 and 15, but also a substantial amount of alveolar bone. The 4 failed dental implant fixtures and the associated bone graft were removed, and the patient was left with only basal bone in the right maxilla that was left to heal for 3 months (Fig. 5). The option of further bone grafting was discussed with the patient. However, she was concerned about the protracted treatment timelines. She was then given the option of a 3D printed titanium subperiosteal frame with immediate teeth on the clear understanding there were no long-term data on this new device.
As in case 1, a cone beam Dicom CT scan was taken of the edentulous right maxillary ridge and surrounding bone and 3D images were made of the defect upon which a custom titanium perforated baseplate was designed with 2 parallel transmucosal abutments that were placed with the aid of the existing partial denture. The acrylic teeth on the partial denture were used to help guide the position and direction of the abutments. The custom titanium frame was 3D printed and given to the prosthodontist who constructed a 4-unit bridge. Once the bridge was completed a date was set for the surgery.
Under general anaesthesia, the edentulous alveolar basal bone in the 12,13,14 and 15 edentulous sites of the right maxilla was surgically exposed and the custom titanium frame was placed and secured to the bone with 8 titanium
(1.7mm wide x 5mm long) self-drilling micro-screws. The frame was covered with surrounding mucoperiosteum which was sutured so that only the 2 abutments remained exposed in the oral cavity. The prosthodontist then fitted the 4 unit bridge which he screwed directly to the frame. The patient woke up from her general anaesthesia with teeth attached and was discharged from hospital the same day. A follow-up of 18 months showed the frame and prosthesis are functional and stable (Fig. 6).
A 62yo female was referred to the author with a severely atrophic maxilla for a custom subperiosteal implant to stabilize her very loose full maxillary dentures which she found impossible to retain without copious denture adhesives. There was insufficient alveolar bone in the edentulous maxilla to place conventional implants without major bone grafting procedures which the patient had declined. She eventually opted for the custom made maxillary subperiosteal implant that was modified to reduce the amount of metal coverage over the alveolar crest to eliminate the mucosal dehiscence which plagued earlier versions of the subperiosteal frame.
Through a crestal incision, the mucosa was reflected to expose the underlying alveolar bone and the custom subperiosteal implant was positioned onto the bone which was easy because it was custom made to closely adapt to the local anatomy. The frame was then secured with numerous self-drilling bone screws and the overlying mucosa closed with 3/0 vicryl sutures. The acrylic maxillary bridge was secured to the 4 transmucosal abutments with internal screws and the patient was discharged 2 hours later with antibiotics, antiseptic mouth rinse and analgesics. The surgical installation took around 40 minutes under general anaesthesia.
A week later, the acrylic bridge was removed to check and clean the underlying mucosal incision and around the abutments (Fig 7). The acrylic bridge was adjusted then re-inserted. Six months later the patient returned to have a permanent ceramic bridge constructed on a metal bar which was used to replace the interim acrylic bridge (Fig.8). A year later she was very pleased with her teeth and reported good aesthetic and function outcomes.
Dentistry and Maxillofacial Surgery have been early adopters of digital tools. Its benefits have been wide ranging from planning jaw osteotomies to crown and bridgework design and construction (4). The purpose of this article is to introduce a 21st century version of the subperiosteal jaw implant that is custom designed on a digital platform and 3D printed in titanium for patients who have insufficient alveolar bone for conventional dental implant supported prosthesis. The idea of the subperiosteal jaw implant is not new (5- 7). In fact, the first subperiosteal frames were conceived in the 1940’s by Dahl (8) but eventually fell out of favour when the osseointegrated endosseous screw implants became the gold standard for fixed prosthetic treatment in the 1980’s (6,7,9,10).
The original subperiosteal frames that were developed in the last century failed for a number of reasons. Poor choice of materials and the lack of direct screw fixation plagued the original frames. Even when screw fixation was introduced, the cobalt-chrome metal frame was not osteoinductive and the frames were far too large, which necessitated extremely large flaps that made the surgery difficult and cumbersome (7). The 2-stage process of taking direct impressions of the exposed bone, then having to re-expose the bone again a few weeks later to install the large cumbersome frames undoubtedly compromised the healing process and the patients’ decision not to proceed (9,11).
The availability of digital technology, including cone beam CT scans, has enabled the design of the subperiosteal frame to be customized in virtual space, eliminating the need for direct impressions. Metal 3D printing has also speeded up the manufacturing process that accurately mirrors the original design and helps reduce the cost of the medical device. Furthermore, the osseointegration capabilities of titanium means that the baseplate does not need a large footprint, so smaller areas of alveolar bone only need to be exposed to install the implant. Osseointegration is further enhanced by the roughened surface texture and multiple perforations in the baseplate which potentially results in secondary stability of the implant 6-8 weeks following implantation. While the 1.7mm diameter micro-screws provide the primary stability, the functional load is distributed not in the screws, but across the whole surface area of the baseplate that is closely adapted to the underlying alveolar bone anatomy. This not only enhances the overall stability of the device, but also allows direct and immediate functional loading with a dental prosthesis (Fig.2). The greatest advantage of this device is the potential for the direct attachment of the immediate dental prosthesis at the time of surgery (Fig. 4).
The limited bone exposure required, the ease of placement and the customized design of the subperiosteal jaw implant means that the implant is relatively quick and easy to surgically install as
there is no bone surgery preparation required, apart from insertion of the 1.7mm diameter micro-screws. The ease of installation of the custom device ensures that the procedure can also be undertaken in a Surgeon’s office setting under local anaesthesia and intravenous sedation. The advanced 3Matic software (Mimics – Materialize, Belgium) has made it possible for the rapid customization of each subperiosteal implant with accurate parallel positioning of each abutment that simplifies the construction of the dental prosthesis (Fig.4).
One of the major drawbacks with the early prototypes of this particular device was wound dehiscence and exposure of the underlying titanium baseplate. This was rectified with a major design change which left the alveolar ridge uncovered and reduced the amount of metal frame covering the underlying bone. This resulted in predictable healing of the overlying mucosa and with no further metal exposure at the base. Design changes to the abutments also evolved with time so that fewer abutments and conical shapes were preferred over the more numerous cylindrical abutments, the latter which made prosthesis engagement much more challenging. As more clinical experience is gained, ongoing design changes to the subperiosteal implant are being made by OMX Solutions to enhance the predictability and simplicity of the device.
It is hoped that the new CAD-CAM, 3-D printed subperiosteal jaw implant will provide a simple, accurate, reliable and cost-effective solution to the intractable challenges of full dental rehabilitation for atrophic jaws, so that bone augmentation procedures become unnecessary. Furthermore, the surgical procedure is relatively simple for experienced implant practitioners. It is anticipated this state of the art device may also find a role in the fixed restoration of normal edentulous ridges where patients seek the convenience of immediate prosthetic teeth without the need for further scans or impressions.
The new 3D printed and fully customized subperiosteal jaw implant provides a simple, accurate, rapid and cost-effective option for the intractable challenges of full dental rehabilitation for atrophic edentulous jaws, which not only avoids the need for bone augmentation, but also has the potential for immediate placement of prosthetic teeth.
The author would like to thank Dr Chris Hart and Dr Simon Watson, Specialist Prosthodontists, who were involved in the management of these cases. The contribution of biomedical engineers at OMX Solutions (www.omx-solutions. com) who helped design, develop and produce this device is also gratefully acknowledged.
Dr George Dimitroulis is a practicing Oral & Maxillofacial Surgeon and Managing Director of OMX Solutions Pty Ltd, (www. omx-solutions.com) a Melbourne based Medtech Company which developed and manufactured the devices described in this article that are collectively trademarked as the “OsseoframeTM”
The OsseoframeTM device has been approved for clinical use by the Australian Therapeutic Goods Administration (TGA) as a Class IIb implantable medical device (ARTG listing 286266).
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