Subperiosteal implants have experienced fluctuating popularity since their inception. Initially introduced in the mid-20th century, they were overshadowed by the development and success of endosteal implants, which are now the standard in dental implantology. Modern subperiosteal implants are typically custom-made using computer-aided design and computer-aided manufacturing technologies, which ensure a precise fit to the patient’s bone anatomy. A meta-analysis was conducted to evaluate the success rates, complications, and patient satisfaction associated with subperiosteal implants. Studies were selected based on predefined inclusion criteria, focusing on clinical trials and observational studies that reported on the long-term outcomes of subperiosteal implants.
Key points
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Historical subperiosteal implants are not comparable to newest generation patient-specific implants.
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Rigid fixation for framework-to-bone contact. Prosthodontic concept is a key, that is, removable modular overdenture should be aimed for.
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Main maxillary indication is compensation of the otherwise unmanageable pseudo-class III relationship for dental rehabilitation.
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Bone requisites are less critical, soft tissue is a key, that is, separation of anatomic subunits is required.
Introduction
Historically, the concept of subperiosteal implants for dental rehabilitation, which began in the 1940s, developed alongside endosseous dental implants as an alternative option for dental rehabilitation. Over the past 40 years, the use of subperiosteal implants has largely declined, even as modern dental implant technologies, such as zygomatic fixtures, have advanced significantly. , Subperiosteal implants were primarily used for addressing the edentulous jaw, with a higher frequency of use in the mandible compared with the maxilla, according to the literature. For example, Benjamin reported a total of 914 subperiosteal implants, with 60% in the mandible and 40% in the maxilla. Similarly, Obwegeser documented a total of 31 subperiosteal implants, with 74.2% in the mandible and 25.8% in the maxilla. However, this concept was revitalized with new technological advancements: game-changing ideas have redefined the concept of subperiosteal implants, incorporating computer-aided design/computer-aided manufacturing (CAD/CAM), prosthodontic backward planning, combined concept establishment with microvascular soft and hard tissue reconstruction in postablative cases, selective laser melting (SLM) technology, and rigid fixation far from the transition of the pillars through the soft tissues. , All these advancements support the idea of effective functional separation of compromised anatomic units.
Alternatively to conventional dental implant treatment, subperiosteal implants use a completely different approach that involves moving away from using multiple standard components and instead planning the positions of the posts as if they were part of a single-piece dental implant-abutment unit. This unified planning strategy results in a one-piece, patient-specific subperiosteal implant that encompasses the final design based on an ideal prosthodontic backward-driven planning workflow. This approach ensures even and perfectly aligned posts, and today is able to meet the precision requirements of dental technicians. No additional biological processes are necessary to achieve the long-term, correctly osseointegrated position of the originally planned dental implant. On the contrary, patient-specific subperiosteal implants inherently encompass this form of integration from the outset. Rigid fixation through multiple, multi-vector screw insertions can be applied with this technique and ensures a nonrestricted, primarily loadable situation. The evolution of new-generation subperiosteal implants around 2015 marked a significant advancement in dental implantology. ,
Despite this evolution in implant technology, skepticism persists among many surgeons regarding the efficacy of subperiosteal implants, including those developed using CAD/CAM technology. This skepticism often stems from historical issues associated with failed procedures. However, recent progress has led to the development of patient-specific subperiosteal implants, offering a range of design variations. These variations encompass several critical factors: the number of posts, design type (one-piece or two-piece) for full jaw rehabilitation, the extent of metal coverage, fixation degree, screw hole placement, and the use of locking screws. Moreover, considerations about the framework’s extension beyond the posts, the surrounding metal volume, and the type of suprastructure—whether removable with a modular overdenture or fixed—play crucial roles. Modern technology facilitates finite element method (FEM) analysis for each patient-specific subperiosteal implant to ensure that biomechanical needs are effectively addressed.
This article aims to shed light on the realm of subperiosteal implants, delineating the disparities between historical methodologies and designs while identifying crucial parameters essential for the successful reinvigoration of this technology. A focus will be placed on distinguishing between CAD/CAM and non-CAD/CAM subperiosteal implants, illustrating the evolution in design and technology. However, even within the CAD/CAM category, some designs have yet to achieve consistent clinical success. The meta-analysis will include the historical type of subperiosteal implants, which lacked rigid fixation to the bone recipient site, as well as the new generation of implants. Furthermore, it seeks to elucidate the integration of modern 3-dimensional (3D) planning and digital manufacturing technologies into this revitalization process. Even within the latest endeavors to refine the strategy for integrating patient-specific subperiosteal implants into advanced implant dentistry as a line extension, significant disparities persist. These differences warrant investigation through a meta-analysis of current patient-specific designs and manufacturing techniques in this area. In addition, 4 clinical cases will exemplify the evolution of modern subperiosteal implants in addressing complex dental rehabilitation scenarios.
Method
To identify eligible studies assessing the long-term survival of subperiosteal implants, a comprehensive search was conducted in the MEDLINE database using the following combinations of keywords.
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“Survival” AND “dental” AND “subperiosteal implants” ( n = 25); 8 studies fulfilled the criteria.
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“Long-term” AND “dental” AND “subperiosteal implants” ( n = 40); 20 studies fulfilled the criteria.
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“Survival” AND “dental” AND “CAD/CAM” AND “subperiosteal implants” ( n = 2); 0 studies fulfilled the criteria.
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“Long-term survival” AND “dental” AND “subperiosteal implants” ( n = 4); 2 studies fulfilled the criteria.
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“CAD/CAM” AND “dental” AND “subperiosteal implants” ( n = 26); 15 studies fulfilled the criteria.
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“Customized” AND “dental” AND “subperiosteal implants” ( n = 44); 25 studies fulfilled the criteria.
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“Patient specific” AND “dental” AND “subperiosteal implants” ( n = 27); 20 studies fulfilled the criteria.
The identified papers were evaluated based on whether they referred to the historical type of subperiosteal implants or modern CAD/CAM subperiosteal implants. Historical subperiosteal implants were designed either with the use of direct impression or based on 3D data with consecutive model fabrication, without adequate fixation to the bony recipient site. Modern CAD/CAM subperiosteal implants, with the first publications starting in 2017, were also included in the evaluation.
In addition to long-term survival and success, the following technical aspects were analyzed for both types of implants: Implant material, implant design (including the extent of the footplate and metal struts, such as extensions to the buccal, alveolar, or oral side, and whether the implant is a single piece or 2 pieces for full arch rehabilitation), connection to the bone (number, size, and length of screws), number of posts, and type of suprastructure (fixed, ie, screw retained or cemented vs removable, ie, bar retained or telescoping).
This comprehensive approach ensured a thorough assessment of the available literature on subperiosteal implants.
Results
The 7 different search term groups were evaluated, resulting in the selection of 168 publications. After initial screening, 78 papers were excluded due to insufficient information concerning the investigated terms. The remaining publications were pooled, and duplicates were removed, resulting in a final count of 57 publications that matched the search terms. Each paper was then assessed for its scientific contribution.
A further 9 papers were excluded due to their lack of scientific impact on the search terms. Twelve papers provided insights into the long-term success of historical subperiosteal implants, while only 1 paper offered some insights into the long-term success of CAD/CAM screw-fixated subperiosteal implants. Thirty-six papers focused on technical information related to the implant’s design and manufacturing, fixation techniques, and prosthodontic suprastructure. Of these, 30 papers referred to the new generation of CAD/CAM subperiosteal implants, whereas 6 papers referred to the historical style of nonrigidly fixated subperiosteal implants.
Currently, there is no valid long-term study (20 years) on the new generation of CAD/CAM subperiosteal implants. The first 10-year results are expected soon.
Historical subperiosteal implants
Schou and colleagues described a 41-year follow-up on a mandibular subperiosteal implant, which was eventually removed after several complications and significant resorption. This implant, typically a 3-post design, was never fixated or screw-retained to the bone, giving it a “floating” appearance radiographically. They also reviewed 9 papers with case series of mandibular subperiosteal implants ( n = 690), with partially defined evaluation methods. Extracted cumulative 5-year implant survival rates from 7 papers were around 92%, and 10-year rates from 6 papers ranged around 82% (67%–96%).
Benjamin reported on 914 subperiosteal implants (40% maxillary, 60% mandibular) with a success rate of 98% to 100% after 6 years, with no fixation applied between the framework and the recipient site. The modifications reported included 3D imaging and hydroxyapatite coating.
Bloomquist reported a high failure rate in a series of 19 subperiosteal implants after a minimum of 4.5 years. He found that 26% failed and 63% had at least one infection around a post. Complications often arose due to the lack of implant-to-bone fixation.
Golec reported a 95.7% to 98% survival rate for 560 subperiosteal implants (273 maxillary, 287 mandibular) with hydroxyapatite coating, observed up to 7 years postinsertion. No implant-to-bone fixation was provided apart from the fitted design.
Kurtzman and Swartz concluded from a single case observed over 40 years that subperiosteal implants could be a viable long-term treatment option for severely atrophied mandibles. No implant-to-bone fixation was provided apart from the fitted design.
Maeglin reviewed 24 patients (5 maxillary, 19 mandibular) treated between 1954 and 1959, with only 25% achieving successful integration and functionality after 9 to 12 years postinsertion. No implant-to-bone fixation was provided apart from the fitted design. Among the successful cases, only patients who received one-piece implants for full-arch mandibular dental rehabilitation had positive outcomes, whereas all partial implants failed.
Moore and Hansen studied 39 patients with mandibular subperiosteal implants, where 14 patients had implants for over 10 years and 12 patients between 5 and 10 years. Thirty-eight patients showed no evidence of inflammation or implant mobility, and all 39 patients reported satisfaction and functional stability.
Obwegeser reported on 31 subperiosteal implants (8 maxillary, 23 mandibular), noting that one-third of the patients experienced complications within the first year. No implant-to-bone fixation was provided apart from the fitted design; only Spiessl was criticized because he used screws to achieve functional stability for his “funktionsstabile Implantatprothese.” However, Obwegeser openly doubted the need for rigid fixation of the footplate in the subperiosteal design, instead focusing on complications related to the biological interface problem at the transition zone where the posts pass through the mucosa. He viewed this problem as similar to that of endosseous dental implants.
Schmidt observed bone resorption below the implant saddle in partial subperiosteal implants in 14 patients. No implant-to-bone fixation was provided apart from the fitted design.
Yanase and colleagues reported a 79% survival rate for subperiosteal implants 10 years after placement ( n = 63) and 60% after 15 years ( n = 34). No implant-to-bone fixation was provided apart from the fitted design.
For all long-term reports on historical subperiosteal implants, neither rigid nor minimal fixation was applied, apart from the custom fit of the footplate underside to the bony recipient site. This lack of adequate fixation did not meet basic requirements for rigid hardware fixation to bone.
Technical aspects
Golec and Krauser and Schou and colleagues described the historical design of full-arch dental rehabilitation using patient-specific one-piece subperiosteal implants. These implants typically featured extensive frameworks that covered the entire alveolar region and extended to both the buccal and oral sides. The designs showed minimal screw fixation, with a screw-to-post ratio of less than 1, despite the use of CAD/CAM-generated jaw models. Additionally, unilateral implant designs were promoted in combination with fixed partial dentures; in these cases, mechanical retention was achieved solely through the implant-to-bone design, without relying on additional screws. Linkow and colleagues and Nordquist and Naisbitt similarly advocated such design features in full-arch dental rehabilitation. Furthermore, Leake and colleagues highlighted the importance of the interface between posts and adjacent soft tissues, emphasizing that the posts should not be positioned too far buccally, as this could negatively interfere with the function of the vertical anatomic unit of the cheek.
New generation CAD/CAM subperiosteal implants
Onică and colleagues published longer-term clinical outcomes of 3D-printed subperiosteal titanium implants in 36 patients (61 patient-specific subperiosteal implants) with a 6-year follow-up. In full-arch cases for the maxilla, 2 separate implants were designed. Two to 3 posts were designed per hemi-arch. The screw length utilized ranged between 5.5 and 13 mm, and occasionally palatal screws were used; the total number of screws remains unclear. From the figures in the paper, the estimated ratio of screws to posts is around 2. The implants’ survival rate was 54.1%, and the success rate was 25%. Faster hardware exposure was observed in implants with 3 posts compared with those with 2 posts. The authors concluded that the long-term viability of subperiosteal implants remains questionable.
Anitua and colleagues reviewed the survival and complication rates of modern subperiosteal implants, identifying 13 relevant studies involving 227 patients with a mean follow-up time of 21.4 months. All implants were screw-retained, with posts for full-arch rehabilitation varying between 4 and 6. Detailed information on the number of screws per implant versus the ratio of screws per post is not derivable from this review. Nine papers addressed bone atrophy, while the remaining studies focused on postablative defects and one study on cleft-lip and palate-associated treatment with subperiosteal implants. The review suggested that one-piece subperiosteal implants provide the benefits of overdentures with the stability of rigidly anchored prostheses. However, the necessity for removable and hygienic definitive suprastructures was not adequately addressed, which is essential for elderly patients or those requiring third-party support.
Vaira and colleagues conducted a retrospective study on 36 patients with 72 patient-specific subperiosteal implants placed in 2 university hospitals, exclusively addressing edentulous patients in the maxilla for full-arch dental rehabilitation. The screw length around the piriform aperture varied between 4 and 6 mm, at the hard palate between 4 and 8 mm, whereas 10 to 14 mm long screws were used in the malar prominence region. Four (75%) to 8 posts were designed for the maxillary full-arch cases; all implants were limited to one quadrant only, meaning that a single implant design was not used for the edentulous maxilla. The ratio of screws to posts ranged from 1.38 to 3.5, with an average of 2.75. The implants had a 100% survival rate and a 90.3% success rate with a mean follow-up of 30.1 months. The study detailed the fixation method for the first provisional suprastructure but did not provide a detailed description of the final suprastructure design (removable or fixed).
Technical aspects
Elsawy and colleagues introduced polyetheretherketone (PEEK) subperiosteal implants for the maxilla, featuring an extended framework with 6 buccal screws and 4 palatal screws. At 12 months postoperatively, all implants survived; the longest follow-up in their case series ( n = 4) was 30 months. Similarly, Ayhan and colleagues investigated 3D-printed (SLM, titanium alloy) custom-made subperiosteal implants and found adaptation issues in 34.4% of patients. Problems included excessively high numbers of posts, insufficient fixation, and unnecessary bridging. The final prosthetic design, lacking an overdenture option, may also contribute to complications such as “chipping,” indicating a need for more effective removable prosthetic suprastructures. Their implant design was limited to hemi-arches in the maxilla, with additional extensions to the hard palate apart from the laterally oriented framework to the midface. An even more palatal-oriented design was proposed by Cerea and Dolcini for titanium subperiosteal implants ( n = 70), which reported a 95.68% implant survival rate after 2 years. Despite modern manufacturing techniques, they did not take advantage of a functionally stable reconstruction principle. Their design featured 4 posts per hemi-arch, with a screw-to-post ratio not exceeding 2.5. Furthermore, if a vertical line is drawn on an orthopantomogram perpendicular to the occlusal level, the extension of the framework hardly extends mesially to the most anterior post versus distally to the most posterior post. FEM analyses indicate that exceeding 4 posts in edentulous mandibles and maxillas may pose risks of complications, such as framework exposure or infection. This concept is improved by Herce-López and colleagues, who demonstrated the design evolution in full-arch maxillary rehabilitation from 2-piece implants to a 1-piece implant. However, additional features to provide a safer one-fit-only design, which were already available at that time, were not mentioned. These features include small basal extensions into the piriform aperture and more 3D geometry around the lateral midfacial buttress of the framework.
Arshad and colleagues described a case of edentulous upper jaw rehabilitation with a SLM printed 1-piece subperiosteal implant featuring 10 pillars and 10 screws, achieving a 1:1 ratio of fixation screws to implant posts. The resulting fixed prosthesis does not employ a coverdenture design. Bai and colleagues explored modern manufacturing methods such as CAD/CAM and SLM technology. However, their design recommendations, applicable to both animal models and human mandibles, often perpetuate historical errors from analog manufacturing techniques. Notably, their designs exhibit insufficient fixation, a concern also observed in Cohen and colleagues, where a large mesh-style framework was presented with only 4 screws for an implant with 3 pillars.
With modern CAD/CAM subperiosteal implants, there seems to be no consenus yet, what the final suprastructure design should be. Basavaraju and colleagues advocated a screw retained implant-bridge prosthesis as the final suprastructure for dental rehabilitation in a mucormycosis-related partial maxillectomy case.
Four patient case examples illustrating modern subperiosteal implants for dental rehabilitation, highlighting key design elements of both the implant and the suprastructure are conceptually significant. Patients number 2 and 4 demonstrate a master design proposal for the maxilla versus the mandible, that follows the principle of minimal amount of metal with a maximum of anchorage, including position aids as design elements and a sloped design at each ending of the framework extensions; minimal screw lengths of 7 mm are recommended, with a diameter of 1.5 for the maxilla and 2.0 for the mandible. The design of the metallic framework for modern subperiosteal implants should minimize the amount of metal near the posts. Ideally, the framework-footplate should extend only to the buccal side, avoiding coverage of the crestal and oral interpost distances with metallic bars. This approach ensures better adaptation to the bone structure and reduces potential interference with the surrounding soft tissues. The ratio of screws to posts should be around 5 to 6 per post; without any limitation above. Case no. 1 was one of the early cases implanted in 2015, where the current framework to abutment to suprastructure design was not yet evolved. The importance of the first provisional suprastructure design as well as the final suprastructure design is highlighted.
Case 1
Following 3 previously surgically treated squamous cell carcinomas in the left maxilla, a 55-year-old male patient presented with the wish for maxillary dental rehabilitation.
The first onset of a squamous cell carcinoma was diagnosed in the maxilla in region 28 in 2002, and another carcinoma was identified in the left maxilla in regions 23 to 25 in 2012. Both malignancies were surgically removed.
In 2014, a third squamous cell carcinoma was diagnosed in the left maxilla, necessitating a hemimaxillectomy. This extensive surgical procedure involved the removal of half of the maxilla to eradicate the cancer. The patient declined any microvascular procedure for postablative reconstruction. Instead, the resultant soft tissue defect was covered using a local flap technique, which involved repositioning adjacent tissue to cover and heal the surgical site. Notably, no adjuvant radiotherapy or chemotherapy was administered following these surgeries, which are sometimes employed to eliminate residual cancer cells and reduce the risk of recurrence. The patient expressed a strong desire for dental restoration with prosthetics, yet he declined both a bone reconstruction and a soft tissue augmentation using a free flap.
Given the patient’s preferences and his refusal of the aforementioned reconstructive options, a customized approach was necessary to achieve functional dental restoration. In 2015, a decision was made to utilize a subperiosteal patient-specific framework implant. This innovative solution involves creating a custom-designed implant that fits the unique anatomy of the patient’s maxilla. The framework implant provides the structural support needed for dental prosthetics, allowing for the placement of dental restorations despite the significant surgical alterations and the absence of traditional bone and soft tissue reconstruction. Twenty-two screws allowed for primarily rigid fixation (ratio of screws to posts: 22 to 3 = 7.33).
The prosthetic restoration was performed using a bar-supported, removable denture on 3 implant posts. Patients often express a preference for fixed dental prosthetics. However, the authors strongly recommend designing prosthetics on subperiosteal implants to be removable. This approach significantly enhances oral hygiene and allows for thorough tissue monitoring, which is crucial for tumor control.
The patient has been using this dental prosthesis for over 9 years without any issues. Eating is unrestricted, and the arch-shaped design of the bar ensures reliable oral hygiene, which can efficiently be managed by the patient himself. Additionally, the design of the denture saddles acts as a shield, minimizing mobility in the areas where the implant posts pass through. There is no mobility at all of the subperiosteal implants in relation to the midface ( Fig. 1 A–I).
