Repair of a Non-Retentive Crown Over a Press-Fit Implant Placed 30 Years Prior

Dental implant treatment is a predictable therapy for single or multiple teeth replacements for partially or fully edentulous rehabilitation. Treatment outcomes with implant-supported restorations have been shown to be highly successful in establishing long-term esthetics and function.^1,2 As dental implants survive for longer periods of time, it can be challenging to maintain the implant prosthesis due a variety of reasons, including discontinuation of the implant system, lack of compatible components, and/or missing records. When unavailable parts for the original implant prosthesis require replacement, an approach must be taken that is minimally invasive, relatively straightforward, and affordable and which can result in long-term success.

Press-fit implants were popular in the 1980s and 1990s due to the primary stability they offered.³ This was due largely to their rough surface, which was either titanium plasma-sprayed or hydroxyapatite-coated.^3,4 The press-fit implant design is usually a unibody one, which helps to prevent peri-implant soft-tissue recession because there are no repeated changes of the implant-abutment interface. The absence of a microgap and abutment complications due to the unibody design offers distinct advantages. Studies have shown that surface-coated unibody implant fixtures performed well long term.^5,6

This article describes the case of a patient who presented to the New York University Department of Periodontology and Implant Dentistry with a press-fit implant that was placed 30 years prior. Although the implant was well-integrated, the patient complained about the crown frequently dislodging. Due to the unavailability of compatible components, and faced with the option of implant removal, a decision was made to fabricate a custom cement-retained crown over the press-fit implant. The purpose of this case report is to demonstrate the step-by-step procedure used to address the management of a non-retentive cement-retained prosthesis over a one-piece press-fit implant and abutment.

Clinical data in this case report was obtained from the Implant Database (ID) at the New York University College of Dentistry (NYUCD). This data set was extracted as de-identified information from the routine treatment of patients at the Ashman Department of Periodontology and Implant Dentistry at NYUCD. The ID was certified by the Office of Quality Assurance at NYUCD. This study is in compliance with Health Insurance Portability and Accountability Act (HIPAA) requirements and approved by the University Committee on Articles involving Human Subjects.

A 70-year-old female patient presented to the Ashman Department of Periodontology and Implant Dentistry at NYUCD. The patient's chief complaint was a loose, frequently dislodging crown on her mandibular right second premolar implant. Upon clinical examination, it was found that the mandibular right second premolar site was restored with a press-fit implant that had been placed more than 30 years prior with a one-piece press-fit custom abutment. The implant (3.6 mm x 15 mm) was well-integrated in bone with no signs of infection or peri-implant bone loss (Figure 1). Clinically, however, the abutment presented with a clinical height less than that required for ideal retention of a crown (Figure 2 and Figure 3).

A decision was made to not remove the implant because of the risk of bone fracture and bone loss, but instead to increase the abutment height to enhance retention. A full-thickness flap was reflected, the press-fit abutment was prepared using a 1957 FG metal carbide cutter (Brasseler USA, brasselerusa.com) with a high-speed handpiece, and the marginal soft tissue was apically repositioned to increase the abutment height thereby improving retention for a cement-retained crown (Figure 4 through Figure 6). An anti-rotational groove was also made on the abutment using the same design carbide bur with a high-speed handpiece (Figure 7). A closed tray impression was taken and sent to the laboratory to fabricate a new custom cement-retained crown.

Following crown cementation using luting cement (Durelon^™, 3M Oral Care, 3m.com), the patient was pleased with the functional and esthetic results (Figure 8 through Figure 11). The new custom crown was more stable and more esthetic than the one with which the patient presented.

Press-fit endosseous implant systems were prevalent in the 1980s and 1990s because of the enhanced primary stability they offered. These implants were available in a cylindrical shape with apical vents that facilitated bone ingrowth, thereby enhancing mechanical retention.³ Prior to this period all implant systems were machine milled and did not have a relatively smooth surface, which, according to the literature, did not promote osseointegration.⁷ The press-fit implant systems with rough surfaces were one of the earlier systems introduced. They were either titanium plasma-sprayed or hydroxyapatite-coated,³ with which several clinical and animal studies reported favorable osseointegration. In the present case report the patient presented with a press-fit implant that had been placed 30 years prior. Radiographic evaluation showed no signs of peri-implantitis, marginal bone loss, or failed osseointegration.

Animal studies by Block et al indicated that bone formation and maturation occurred at a faster rate on hydroxyapatite-coated surfaces than on non-coated ones.⁸ Meffert et al showed that hydroxyapatite-coated implants were covered with a thick, dense layer of lamellar bone on most of the surfaces. No evidence of resorption of hydroxyapatite was evident in any area of the implant. In fact, coronal growth of bone appeared on the hydroxyapatite surface with new gingival fibers inserting perpendicularly into newly formed bone.⁹ In another clinical study, Kent et al discussed implant survival based on the criteria of bone loss for hydroxyapatite-coated cylindrical implants placed into the posterior mandible. They concluded that when hydroxyapatite-coated implants longer than 8 mm were placed in compact bone, the success rate was as high as 94.45% for up to 10 years, especially in the presence of adequate keratinized mucosa around the implant and the absence of plaque.¹⁰ The implant fixture for the patient in the present case was 15 mm long and had a rough surface. There also was an adequate amount of keratinized tissue present around the implant. Implant osseointegration and long-term survival were not problems with the case presented.

Many patients and clinicians prefer cement-retained restorations, as esthetics, improper fixture angulations, passively fitting restorations, and occlusal stability issues can be more easily managed with a cement-retained restoration than with a screw-retained one.¹¹ In patients with less interocclusal space, however, screw-retained restorations are generally preferred since there may not be enough vertical space to fabricate an adequate retentive abutment.^12,13 The patient in the present report presented with a decreased interocclusal space; therefore, a screw-retained restoration would have been a better choice for her. But since she presented with a one-piece implant with an abutment designed to receive a cement-retained prosthesis, replacement of the abutment alone was not an option. Because the implant system was discontinued, meaning no compatible parts were available, preserving the implant and placing a cement-retained restoration would be a challenge. Explantation and placing a new implant at the site was an option; however, with the press-fit implant being well-osseointegrated and 15 mm in length, removing it would have required extensive and aggressive bone removal. This could have predisposed the patient to lose the buccal/lingual cortical plates and complicated any future implant placement.

Considering the risks and keeping the patient's well-being in mind, it was decided to restore the existing implant instead. An apically positioned flap was performed to gain abutment height, thereby addressing the retention problem.^14,15 The abutment was then prepared using a metal carbide cutter with a high-speed handpiece. An anti-rotation feature was also added to the abutment by creating a vertical groove in line with the long axis of the tooth using a carbide bur. This groove was intended to provide resistance against non-axial forces acting on the future crown.

An alternative approach to replacing the discontinued implant system that required prosthetic replacement was utilized for this patient. The retention of the one-piece cementable abutment was addressed. The required critical height¹⁴ for the abutment was achieved by repositioning the soft tissue apically and repreparing the abutment. A vertical groove was also placed on the abutment wall for the purpose of resisting non-axial movements of the prosthesis. At the 2-year follow-up, the patient reported with the implant and crown in stable condition and was satisfied with the functional and esthetic outcome of the treatment.

The authors declare no conflict of interest.

Reem A. Alghamdi, DDS, MSc, Pros. Cert.
Department of Restorative and Prosthetic Dental Sciences, College of Dentistry, King Saud bin Abdulaziz University for Health Sciences, National Guard Health Affairs, Riyadh, Kingdom of Saudi Arabia; King Abdullah International Medical Research Center, National Guard Health Affairs, Riyadh, Kingdom of Saudi Arabia; Fellow, Royal College of Dentists of Canada; Fellow and Diplomate, International Congress of Oral Implantologists

Vatsal Jaipuria, BDS, MDS
Resident, Advanced Program for International Dentists in Implant Dentistry, Ashman Department of Periodontology and Implant Dentistry, New York University College of Dentistry, New York, New York

Leonor Limao Oliveira, DDS
Resident, Advanced Program for International Dentists in Implant Dentistry, Ashman Department of Periodontology and Implant Dentistry, New York University College of Dentistry, New York, New York

Stuart J. Froum, DDS
Clinical Adjunct Professor and Director of Clinical Research, Ashman Department of Periodontology and Implant Dentistry, New York University College of Dentistry, New York, New York; Private Practice, New York, New York

Sang-Choon Cho, DDS, MSc
Clinical Associate Professor and Director of Advanced Program for International Dentists in Implant Dentistry, Ashman Department of Periodontology and Implant Dentistry, New York University College of Dentistry, New York, New York

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