Use of Overdenture Implants in the Management of a Failed Long-term Transosteal Implant Prosthesis

For patients who are completely edentulous, implant-retained overdentures offer a number of functional, psychosocial, and anatomic advantages over traditional dentures and eliminate many of the problems associated with them.¹ Ample evidence in the literature favors the implant overdenture in the mandible as the first choice of treatment.^2-4 However, implant designs and treatment protocols have evolved along with available scientific knowledge, and many patients will require revision of their previous treatments as complications arise over time. Advances in implant alloys have improved strength characteristics, surface treatments have been optimized to increase bone-to-implant contact and improve osseointegration, and components have been better designed for prosthetic connection. In addition, more conservative surgical and prosthetic procedures have accompanied these advances.

In the following case report, a patient presented with a loose mandibular overdenture due to technical complications related to her transosteal implant and associated bar, which were now beyond repair. Limited available bone volume was a constraint, and removal of the existing implant or performance of invasive grafting procedures were aggressive treatment options with unwarranted risks for this elderly woman. A decision was made to use implants of narrow diameter and suitable length that would fit within the limited bone volume and between and lingual to the remaining nonusable transosseous and endosseous pins. Ultimately, individual overdenture attachments were used to achieve denture retention for the patient, as nonsplinted removable attachment systems have become widely accepted due to clinical simplicity, relative lower costs, and research supporting superior clinical peri-implant hygiene.⁵

An 81-year-old Caucasian woman presented to the clinic for evaluation of her complete mandibular implant-retained overdenture, which had become unstable and for which there were no available prosthetic replacement parts. The cast bar, which was attached to the two fastener abutments of her transosteal dental implant, had become inoperative due to a fractured transosseous pin.

A review of the patient's medical history revealed she was an ex-smoker who had quit in 1979. The patient reported having total joint replacements in both knees and her orthopedic surgeon wanted her to take antibiotic prophylactic medications before having dental work done. Hypertension, high cholesterol, arthritis, kidney problems, and recent hospitalizations also were reported, along with pain management for her lower back and a neck injury. The patient was classified as American Society of Anesthesiologists (ASA) 3.

The dental history showed that the patient was long-standing fully edentulous with a conventional maxillary complete denture and mandibular overdenture since the mid-1980s. The mandibular transosteal implant was placed in 1984 and maintained in function until 2009 when the patient experienced a high fracture of the left transosseous pin (Figure 1). The surgeon performed an alveoloplasty to expose a portion of the remaining transmucosal pin. A new fastener was placed and a new overdenture bar was fabricated.

Five years later new fasteners and a new bar were needed again due to excessive wear and lack of prosthesis retention. In 2016, the patient was referred to the University of North Carolina School of Dentistry Dental Faculty Practice to provide her with a stable prosthetic solution following the fracture of the right transosseous pin below the alveolar crest, which had finally rendered the transosteal implant completely unusable.

Radiographic evaluation and oral examination revealed that an attempt to remove the fractured transosteal mandibular implant would be an invasive procedure and could put the patient at risk for mandibular fracture due to extremely limited bone volume. Other previously performed resolutions for nonfunctional mandibular bone plate staple implants have included the use of iliac crest bone grafts under general anesthesia, lateral repositioning of the inferior alveolar nerve, and a fixed restoration supported by endosseous dental implants.^6-9

A conservative treatment plan based on clinical findings and cone-beam computed tomography (CBCT) 3-dimensional (3D) volumetric imaging was proposed to the patient who consented to the treatment. It included the placement of three narrow-diameter (<3 mm diameter) LOCATOR^® Overdenture Implants (LODI) (Zest Dental Solutions, zestdent.com) lingual to the existing fractured transosteal mandibular implant and the use of three LOCATOR abutments to retain the existing mandibular implant-retained overdenture (Figure 2). The LODI system includes a tapered contemporary implant composed of titanium alloy, with a self-tapping thread design and microroughened surface (Ra 1.2 to 1.5). A removable LOCATOR abutment, LOCATOR housing, and retentive inserts are also included in the system.

Mindful to maintain keratinized gingiva, the clinician made a mid-crestal incision and elevated a full-thickness mucoperiosteal flap to expose the alveolar crest and the two fractured transosseous pins of the existing transosteal mandibular implant (Figure 3). The right pin was fractured below bone level. There was also a significant circumferential crater defect around the fractured left transosseous pin with the remaining pin protruding 3 mm above the bone level. This pin was reduced below the bone height using rotary instrumentation and then smoothed. Copious irrigation was utilized to aid in the removal of any surgical debris.

The three implant sites were prepared using copious irrigation and the manufacturer-recommended drilling sequence to a depth of 10 mm and a diameter of 2.1 mm. While no prefabricated surgical guide was used, the implant-planning CBCT images, existing denture, and visible broken transosseous pins, along with the drill stops and guide pins included in the implant system, were all used as references and to guide the surgery to ensure that the planned depth and appropriate angulations were achieved (Figure 4). Three 2.4 mm x 10 mm LODI implants were inserted into the sites with an application torque of 45 Ncm and all were found to have excellent primary stability (Figure 5).

The LOCATOR abutments for these implants are available in two sizes: 2.5 mm and 4 mm cuff heights. The 2.5 mm cuff height abutments were selected as initial healing abutments and screwed on the implants with an application torque of 30 Ncm (Figure 6). Autogenous bone collected during the osteotomy preparations was then compressed into the osseous crater defect around the remaining portion of the left pin (Figure 7). The surgical site was sutured closed, and the denture was relieved at the implant abutment sites and relined using a soft material (COE-SOFT^™, GC America, gcamerica.com) to enable the patient to wear the lower denture without applying direct loading forces on the implants during the healing period.

After implant placement and 10 weeks of osseointegration, the 2.5 mm cuff height abutments were removed and replaced by 4 mm cuff height abutments (Figure 8). This was done to create additional clearance for the abutment retentive housings.

The patient's existing denture was relined and converted to accept the new implants and LOCATOR abutments as follows: A definitive impression using the patient's existing mandibular denture was made, and a laboratory hard reline was completed leaving enough relief at the abutment sites for passive intraoral seating. Next, the denture attachment housings were placed on the abutments (Figure 9) and picked-up in the denture intraorally through the use of attachment processing material (CHAIRSIDE^®, Zest Dental Solutions). The black processing inserts included in the LODI system were removed and replaced with the red extra-light-retention extended-range inserts (Figure 10).

A post-insertion visit was scheduled at which adequate retention and patient comfort were observed. Additionally, the patient's dexterous ability enabled her to properly place and remove the overdenture. Because the patient was fully edentulous with no implants in the maxilla, and she was able to remove her conventional complete maxillary denture along with her mandibular overdenture at night, there was no need to fabricate an acrylic nightguard appliance to protect the implants and abutments from opposing forces.

The patient presented with a nonfunctional mandibular transosteal implant and requesting a solution to restore stability and retention to her mandibular overdenture. The elderly woman had been completely edentulous for more than 30 years, and severely resorbed residual alveolar ridges were observed in both the maxilla and mandible. Opposing her treatment arch was a conventional complete maxillary denture.

When treatment revision is necessary due to failure of existing treatments, it is prudent for the clinician to consider the cause(s) of the breakage and, thus, how to better manage these contributing factors in the revision treatment. In the present case, heavy occlusal forces of opposing teeth or implants were not of concern, nor were strong masticatory muscles or parafunctional habits, as the patient did not show excessive wear on her existing prostheses, had indiscernible muscle tone, was of small stature, and removed both her upper denture and lower overdenture at night.

Two transosseous pins in the 30-year-old implant were supporting the overdenture. After more than 20 years in function the first pin fracture occurred, then 7 years later the second pin fracture ensued. These 2.75-mm-diameter pins were constructed of commercially pure titanium, which was the standard dental implant material at the time of their insertion. Many modern-day dental implants, including the three LODI implants used in this case, are constructed of a titanium alloy that has increased strength characteristics.¹⁰

Alternative treatment plans are important to consider when revision treatments are required. In this case the removal of the existing transosteal implant device would have had potential serious risks associated with mandibular jaw fracture. If significant bone augmentation was desired and block grafting techniques considered, this patient lacked adequate bone for ramus block harvest without risk of mandibular jaw fracture. If the iliac crest was used as a donor site, a significant increase in morbidity would ensue. Neurovascular bundle repositioning was another treatment alternative that could have been employed.⁶ All of these surgical alternatives, however, would significantly increase the length of treatment time to achieve the patient's goal of restored denture retention and stability.

The patient's desire for quick overdenture stability and retention was met through placement of three narrow-diameter implants made of a titanium alloy within the available bone volume of the mandible without the need for extensive bone grafting procedures or removal of the existing implanted appliance. This modality also offered the least invasive surgical intervention with the fewest associated risks. Amato and Polara supported this approach in 2015 when they identified the use of narrow-diameter implants as a simplified treatment for challenging cases such as those in which severe bone atrophy was present.¹¹ The changeable abutments on this two-piece implant will allow for replacement of the LOCATOR abutment in the future if necessary. Having various retention inserts will allow for their replacement and alterations so that resistance can be optimized to suit the patient's dexterous ability as she continues to mature. The choice of using individual retentive abutments rather than employing a splinted bar procedure offers the patient improved access for hygiene and an overall simplified treatment solution.

An implant-retained mandibular overdenture was successfully stabilized in an anatomically challenging case where bone volume was limited and the existing transosteal implant was fractured and unable to be reused. The use of LODI implants with legacy LOCATOR abutments to support the existing implant-retained overdenture proved to be an ideal treatment option to rehabilitate this patient's mandible with a conservative, stable, and favorable treatment outcome.

While the short-term results of this case are promising, no long-term (>5 years) clinical studies have been completed on the LODI narrow-diameter (2.4 mm) implants regarding biologic or technical complications. Long-term concerns in the present case include the possibility of abutment wear (the two-piece system allows for future replacement of abutments), the need for prosthetic relines or denture replacement, and biological or fracture complications of the new implant(s).

Dr. Prudenti has received honoraria from Zest Dental Solutions.

Anthony P. Prudenti, DDS, MS
Adjunct Professor, University of North Carolina, School of Dentistry, Department of Restorative Sciences, Division of Prosthodontics, Chapel Hill, North Carolina; Private Practice, Long Island, New York

Glenn J. Reside, DMD, MS
Associate Professor, University of North Carolina, School of Dentistry, Department of Oral and Maxillofacial Surgery, Chapel Hill, North Carolina

Matthew Hopfensperger, DDS, MS
Assistant Professor, University of North Carolina, School of Dentistry, Department of Restorative Sciences, Division of Prosthodontics, Chapel Hill, North Carolina