The World's Longest Functioning Implant: A Verified Case Report Open Access

Inevitable repercussion of edentulism is resorption of alveolar bone that in turn results in adverse functional and esthetic consequences, often diminishing the quality of life of the afflicted.¹  The number of totally edentulous individuals and the imperative need for their complete rehabilitation has been largely disconcerting over the years.²  The predicament of severe bone resorption resulting in extreme alveolar atrophy, categorized as Cawood and Howell Class V or VI, may not be amenable by endosteal implant rehabilitation.^3–6 

As an alternate treatment, use of custom made, subperiosteal implants (circumferential/tripodal) had been considered as a viable clinical ingenuity in the 1940s. In its simplest form, a subperiosteal implant is a custom-made frame of metal, placed as an overlay on the cortical bone.^7–10  Vitallium, titanium, and titanium alloys that are approved by the American Society of Testing and Materials have been suggested to be the most optimal materials for fabrication of these implants, possibly because of resistance to corrosion, insolubility in body fluids, tissue tolerance, and stability of material even after the casting procedure.^6,11–13  Histological literature reports suggest that these implants are not osseointegrated and show connective tissue collagen fibers as a support system.^7,12  A consensus statement by a panel of 9 diplomates of the American Board of Oral Implantology/Implant Dentistry in 1997 stated that subperiosteal implants are fibro-integrated and they function best in this state.⁶ 

Subperiosteal implants were rebuffed in the past due to associated complications, typically comprising of implant exposure, inflammation, infection, fistula formation, dysesthesia, laceration of mandibular nerve, and even implant mobility.^9,14,15  Numerous authors had also suggested removal of these implants in situations where complications were present persistently. The declination of support to this implant therapy was further amplified when it was observed that severe atrophy of bone was observed upon the removal of this implant, which precluded any subsequent implant rehabilitation without any preceding bone augmentation.^14,15 

These implants have not been as popular as endosseous implants, as the literature supporting this treatment modality is not as robust, and is limited to clinical reports or prospective, single-arm studies. Moreover, outcomes for the subperiosteal implants have been variously documented in the past, and these inconsistencies have added to clinicians' apprehension. Added to this, globally, the implant education/training programs have been deficient in disseminating the information related to this treatment modality. As a consequence, many clinicians do not risk to venture in executing this treatment option.

Although low long-term survival rate and increased rate of failure of these implants has been documented, this treatment has been suggested to enable function in cases where dentures are found to be less than satisfactory and where grafting or endosseous implant procedures are not feasible.^8,16–27 

Notably, use of subperiosteal implants in the mandibular atrophic arch has been the departure to the numerous caveats mentioned for these implants in the literature. In fact, the highest success rates (within the varied subperiosteal implants) have been documented for mandibular subperiosteal implants when the opposing anatogonist arch is treated by mucosal borne complete denture.^28,29  A prospective study of 40 years' follow-up in 41 participants also suggests that implants developed later in the chronological evolution of this treatment modality were found to be superior to those placed earlier.¹⁸  The recent renaissance of this treatment modality is an antithesis to the repudiation received by it in the past. This has been attributed to enhanced radiographic methodology and digital workflow with CAD (computer-aided design) designing and 3D printing, thus rendering enhanced precision to the treatment modality.^5,30–32 

Regarding implant success, objective documentation has been cited variously in the literature over the decades. The Harvard consensus conference in Boston, convened by Dr. Paul Schnitman and Dr. Leonard Shulman, appraised the 4 commonly used implants in practice at that time, including subperiosteal implants. According to the consensus, a dental implant should provide functional service for 5 years in 75% of the cases to be considered successful. Due to lack of watertight studies and statistically weak support, the consensus statement appended a warning for interpretation of survival for all subperiosteal implants, except for the mandibular subperiosteal implant opposing a complete denture. The consensus statement further stated the guidelines for subperiosteal implants, suggesting their use be reserved in mature adult patients (between 50 to 70 years), when conventional methods are found to be less successful, and in those patients in whom general and oral health is acceptable.^11,33  In 1986, Dr. Albrektson created 5 objective criteria for defining success of osseointegrated implants.⁹  This widely popular minimum criteria is, however, restricted to osseointegrated implants and cannot be applied to plate/blade form implants and subperiosteal implants, as these implants have a fibrous integration.^6,7,10,12  In 1988, the National Institutes of Health initiated a consensus conference and several recommendations were made for endosteal and subperiosteal implants. Although this consensus is archived and due to cumulative nature of the scientific literature, much caution is warranted against the consensus report. Yet the underscoring fact that this consensus demonstrates is that the “functional success of implants should include the ability to support fixed or removable prostheses in the absence of discomfort, the presence of satisfactory esthetics, and clinical and radiographic evidence of tissue health.”³⁴ 

Regrettably, an unrealistic expectation of success of any treatment, including implants, makes a patient or clinician overlook the complex, multidimensional aspects affecting the outcome of that treatment.³⁵  Success criteria cannot be unanimously adopted for all implant systems, as each system is distinct from another in design and geometry as well as properties of implant biomaterial.^9,36–39  Moreover, the surgical technique, status of implant host site, healing phase, prosthetic design and loading, and maintenance of tissue health are some of the numerous factors underscoring the outcome of treatment. What can be understood by the success criteria established by numerous authors worldwide is that specific parameters for implant functioning have been laid down for a minimum period of service. A departure from those criteria then deems the modality “a failure.” Adding another facet to outcome assessment of subperiosteal implants is the fact that the U.S. Food and Drug Administration does not regulate these implants, as these are custom-made devices. Thus, it can be summed up that the outcome measures with subperiosteal implants are considerably dependent on surgical, prosthetic, and laboratory procedures together with impeccable execution of hygiene and recare follow-up.^9,11,36–39  While scrutinizing the outcome of treatment of implants, survival statistics is a measure of the ability of the implant to serve its intended purpose. Concurrently, the ultimate metrics of any implant treatment outcome, including subperiosteal implants, are patient-centric perceptions. Accomplishment of satisfactory function, esthetics, and phonetics, together with long-term stability, associated low levels of complications during placement, healing, and follow-up can be considered as defining objectives of a satisfactory implant treatment.^40,41 

This current case report presents a documentation of a subperiosteal implant that was placed in 1958 by the late Dr. Leonard Linkow in his private office in New York. Dr. Linkow, after his graduation in 1952 from New York University, spent time with Dr. Gustav Dahl and his contemporaries, Dr. Aaron Gershkoff and Dr. Norman Goldberg, who were responsible for the founding of the American Academy of Implant Dentistry. From an evolutionary point of view the first mandibular subperiosteal implant was placed by a Swedish dentist, Dr. Dahl in 1942. Dr. Gershkoff and Dr. Goldberg were impressed by the concept and brought the idea of these implants to the United States.^8,16  The forthcoming narrative is exclusively based on personal communication with the operating author, Dr. Linkow. Dr. Linkow had an express desire to highlight the benefits of alternate modalities in dental implant treatment. The purpose of this report is to emphasize the successful use of a subperiosteal implant as a treatment modality in an atrophic mandible, one that has survived over 56 years.

A 29-year-old female patient reported with an unstable mandibular complete denture. A mandibular denture with better stability, especially during function, was requested by the patient. On clinical examination the patient presented with complete edentulism. The mandibular arch was atrophic. The patient was using maxillary and mandibular complete dentures. The maxillary denture was satisfactory on clinical examination and from the patient's perspective as well. The mandibular denture showed reduced stability on clinical examination and less than satisfactory performance. The patient did not have any underlying systemic disorder at the time of presentation.

The treatment plan was to rehabilitate the maxillary arch with mucosa borne complete denture and the mandibular arch with an overdenture retained by a circumferential subperiosteal implant. The treatment for placement of the mandibular subperiosteal implant was planned in 2 phases, with 2 weeks intervening between the 2 phases. In the first phase, primary surgery was done for making a bone level impression. In the second phase, secondary surgery was done for implant placement and attachment of the mandibular overdenture, retained by the telescopic abutment posts of the surgically placed subperiosteal implant.

Lack of distinct keratinization of the alveolar mucosa was observed in the mandibular arch. A continuous incision was made from retromolar pad of one side to the other, bisecting the attached mucosa, and flaps were reflected. The buccal posterior full-thickness flaps on each side were extended from distal to mental foramen until the ascending ramus, and the flaps were sutured to the cheek bilaterally to gain maximum accessibility. Labial full-thickness flap was also reflected between the mental foramina, and this flap was sutured to the mucosa of the lips. Partial-thickness flap was reflected superior to the mental foramen as well as lingual to the incision. The lingual flaps were drawn together by a cross-arch, purse-string suture to hold the lingually reflected flap and to provide space for the impression material to flow and record the ridge. Reflection of the buccal and labial flaps enabled identification of the mental foramen and neurovascular bundle, external oblique ridge, and the symphysis in anterior region. Reflection of the lingual flap enabled the visualization of the mylohyoid attachment and the periosteum superior to the genial tubercle.

A direct impression of the residual ridge was made in rubber base impression material in a custom tray previously fabricated from a preliminary, mucosal impression. Once set, the rubber base impression was carefully removed, taking care to free the material gently from periosteum over the neurovascular bundle. Maxilla-mandibular jaw relation record was made during surgery by using the custom impression tray. The patient was asked to close at the predetermined vertical dimension of occlusion at the tentative centric relation position. After recording the impression with jaw relation, the reflected flaps were coapted by using 3–0 silk interrupted sutures.

The working cast of the residual ridge was made out of the impression. This cast was used to design a subperiosteal implant. The implant was designed to extend as one unit, bilaterally across the ridge, up to the bone corresponding to the retromolar pad. The implant extended like a saddle or tabletop on the buccal and lingual walls of the anterior mandibular ridge. In the posterior mandibular region, the implant extended bucally, over the oblique ridge, from the crest of the ridge. Peripheral struts or the main bearing struts were placed, forming the outermost limit of the implant, while circumventing the undercuts, if any. These struts were located against the basal bone. Primary struts or pergingival struts, bearing the permucosal abutments, were made to extend across the ridge crest. Numerous secondary struts were used to incorporate strength and rigidity. It was ensured not to traverse the secondary struts across the ridge, to avoid them being crossed by the incision line. The parallel walled permucosal abutment posts were made contiguous with the respective pergingival or primary strut, and were positioned bilaterally in the second molar and canine region. The bucco/labio-lingual position as well as the height of the permucosal abutments was adjusted according to the space to be occupied by the prosthesis and the interocclusal space as determined by the jaw relation record. Screw access holes (delineated as small circles) were made on facial aspect of the implant in symphyseal region and on buccal oblique ridges to enable placement of the monocortical screw, in the event there was no primary fixation and adaptation of the framework to the ridge. The implant was cast in surgical Vitallium (chrome, cobalt, molybdenum) by the late Mr. Jack Wimmer from Park Dental Research, New York.

Mandibular overdenture prosthesis was fabricated. The tissue surface of the overdenture carried receptacles for the telescopic posts of the implant, such that a friction fit was attained between the denture and the abutment. The denture was reinforced by embedding a metal framework within the denture base. The overdenture was completely implant supported so as to prevent tissue contact or pressure that could have led to dehiscence of soft tissue and exposure of implant infrastructure.

The patient received the implant within 2 weeks of impression making. The implant was affixed directly on the bone, under the periosteum mechanically. The prosthesis was inserted at the same visit to provide immediate function.

The patient was satisfied with the outcome in terms of mandibular overdenture stability, esthetics, and phonetics throughout the course of follow-up. Immediate treatment outcome can be appreciated in Figure 1a–d.

The patient's follow-up has been the longest one, from 1958 until 2016, as per the authors' knowledge. Periodic recare appointments by Dr. Linkow were done for clinical and radiographic evaluation as well as photographic records at various instances during this time (Figures 2–7).

When the patient presented in 1986 (28 years after the implant placement), mucositis was observed around the posterior most abutment on the left side. Radiographic finding suggested bone growth over the distal struts of the implant (as seen in Figure 2f). It is plausible that the flexion of the mandible caused periimplant force distribution in a manner that stimulated bone growth superior to the distal most implant, thus causing soft tissue inflamation in that region.¹⁰  To overcome this problem, the biomechnnical design of the prosthesis was modified (Figure 3). A detachable mesostructure bar was cemented on the abutment posts of the implant (Figure 3b). The bar carried 4 ball abutments and the overdenture carried the O-rings to engage into the ball abutments (Figure 3e). The inclusion of the ball abutments allowed for resilence of the prosthesis around the abutments and redistribution of peri-implant bone stress, thereby minimizing the deposition of bone superior to the implant. The revised prosthesis had Hardy's cutters to improve the masticatory efficiency.⁴² 

At the request of Dr. Linkow, the patient was seen in the office of Dr. Jack Piermatti, prosthodontist, Voorhees, New Jersey, for evaluation and follow-up. A complete examination was performed, photographs taken, and radiologic imaging was done. On examination, no oral pathology was noted with healthy gingival tissues present around all implant abutments. The complete overdenture prosthesis was performing satisfactorily according to the patient, was quite hygienic, and was very stable in the mouth.

The close adaptation of implant to the bone is appreciable even 52 years after the implant placement as can be seen in the cone beam computerized tomography (CBCT) taken in the year 2010 (Figure 6). Soft tissue beneath the bar and around the permucosal abutments maintained a healthy status, with absence of inflammation during the subsequent years of follow-up. The patient executed a meticulous oral hygiene protocol for the dentures, permucosal abutments, and bar, and the same can be contributory to health of the tissue during a large part of the observation. Satisfactory outcome was maintained during numerous follow-up visits (Figure 7). Regrettably, the patient was lost to follow-up in 2016 due to her demise. However, for the purpose of academia and research, the patient's family volunteered for retrieval of the implant after cremation, and donated the implant, together with the bar and the prosthesis that were removed prior to cremation (Figure 8).

Despite limited documentation, subperiosteal implants have shown promising outcomes, when chosen appropriately for specific indication. Substantial literature support exists for mandibular subperiosteal implants opposing maxillary complete dentures. The case narrated in this manuscript belongs to the aforementioned category. Numerous aspects that had contributed for a long-term successful outcome can be appraised in the case documented.

The subperiosteal implant, by virtue of its large surface, dissipates the forces to a large area of the bone, analogous to the snowshoe effect. It has been documented that close contact of the implant with underlying bone is a requisite for the success of these implants. This close contact was achieved in the early phase of treatment by the quality of impression of the underlying bone, which in turn depends on the careful yet thorough surgical reflection and atraumatic handling of soft tissues. The implant used the most vital and dense cortical structures of the basal bone for support, including the external oblique ridge, genial tubercle, mylohyoid ridge, and surface of symphysis.^5,16,43,44  It is to be noted that the authors always emphasize the contraindication of subperiosteal implants in the presence of alveolar bone and suggest that areas of low bone resorption (basal bone) should be capitalized for resting these implants.⁴  After the early phase, throughout the follow-up (Figure 6) this close adaptation was faithfully maintained.^1,16  This was probably due to consistent and well distributed force dissipation due to implant design and meticulous laboratory procedure. In reciprocation, this also helped to minimize introduction of noxious force vectors over the bone. The principles of retention, resistance, stability, support, and encirclement through circumferential design of the implant (biomechanics) are cardinal features that contributed to the long-term, successful outcome.

It has been stated that when designed properly, subperiosteal implants can remain in function successfully for considerable periods of time.⁴⁴  Selection of the material for fabrication of the implant in this case was base metal alloy, which has the advantage of low density. The struts were narrow in dimension, further reducing the weight of the prosthesis. Additionally, the design of the prosthesis was exclusively implant supported. The atrophic ridge was thus shielded from forces due to absolute lack of mucosal contact of the overdenture prosthesis design, thereby preventing the risk of dehiscence of soft tissue and implant exposure, particularly in the early phase of healing.¹⁶  Selection of location of 4 permucosal abutments, bilaterally, anterior as well as posterior to the mental foramen, helped to mitigate lateral forces. The absence of any parafunctional habits was also contributory for a favorable outcome by eliminating noxious forces.

The laboratory procedures ensured a superior fit of the implant infrastructure over the bone. The initial overdenture prosthesis was friction fit over the telescopic abutments. The active fit of the prosthesis may have induced force vectors that stimulated excessive bone growth over the distal struts of implant on the left side. The growth of the bone could have precipitated mucositis from violation of biologic width that was observed on the left distal most abutment. This was an observation made after 28 years of treatment. To address the problem, design of the prosthesis was modified by including some degree of prosthetic resilience. A mesostructure bar with 4 ball abutments was cemented on the abutment posts, and the overdenture with O-ring attachments was retained on this bar. This imparted the overdenture a prosthetic resilience, thereby diminishing the transfer of forces to the bar as well as to the implant, reducing the risk of excessive bone formation.^16,45,46  The design of the bar permitted oral hygiene practice, as a clearance of nearly 3 mm was present between the bar and the soft tissue. Additionally, regular periodic follow-ups further helped to mitigate inflammation of soft tissues due to imperceptible collection of debris. The overdenture design, particularly the occlusal morphology established by using Hardy's teeth, also helped to curtail the lateral shearing forces that can be detrimental to the already atrophic bone. The vertical chewing pattern with a metal inserts also ensured bolus penetration and effective masticatory efficiency.

The improvement of the patient's appearance, phonetics, efficiency, comfort, and overall outcome helped her lead a satisfactory quality of life for a long duration, bringing an end to the dental hardship. The patient had reported to find the overdenture more efficient and comfortable, possibly because the stresses of mastication were transferred through the abutment onto the mandibular bone, with no pressure on the underlying mucosa. This treatment was also more conservative, more cost effective, took considerably less time for completion, and offered a more predictable long-term outcome compared with the alternative methods of rehabilitation such as bone grafting or nerve repositioning.^1,47,48 

It has been well established that the pursuit for an ideal implant treatment protocol is endless. Numerous contributory factors including selection of the patient, knowledge of basic anatomic and physiologic principles, designing of the implant and superstructure, surgical execution, application of sound restorative principles, conscientious hygiene, and clockwork review re-care are the factors resulting in a successful outcome. The intense cooperation and coordination among the surgeon, restorative dentist, and laboratory technical staff, together with immaculate patient compliance, are required to optimize the results in such scenarios, as was seen in this case. It can be concluded by observations of this case report that the most dependable yardstick for any successful treatment is patient satisfaction, and by all means the treatment rendered to this patient successfully helped overcome the status of dental cripple to that of a dental cured individual, one with the longest survival and success ever documented in the history of any type of implant treatment. This was a clinical outcome achieved at a time when the experience in implant procedures was at outset, and technical support was embryonic. In times like today, with far greater technical support in CBCT, 3D printed models, laser printed titanium, and substantial surgical and prosthetic experience in implantology, the authors are convinced that subperiosteal implants, if planned meticulously, will achieve greater good in the future for cases that are otherwise considered challenging or impossible to treat.

The authors wish to acknowledge Dr. Aditi Nanda, Assistant Professor, All India Institute of Medical Sciences, New Delhi, for her contributions in preparing the manuscript, bibliography, and organization of the draft. There is no conflict of interest reported by the authors.

Dr. Leanard Linkow is now deceased.