Prosthetic Resolution of Peri-Implant Mucositis: Promoting Soft-Tissue Health Through Proper Restorative Design

David E. Azar, DDS

With the advent of successful osseointegration^1,2 the use of dental implants to restore the compromised dentition has become widespread. With that has come the emergence of a new classification of dental pathology, namely “peri-implant disease” (PID). Much attention is now being given to this pathological entity in the literature, particularly in regard to its prevalence, the need to recognize the phenomenon, and the need to develop proper therapeutic approaches and modalities for its treatment.³ Most reports focus on tissue-centered treatment modalities, including oral hygiene instruction and patient motivation, mechanical debridement, antiseptics, adjunctive administration of local and/or systemic antibiotics, and access flap surgery with or without bone regeneration.

Peri-implant disease has been broken down into two distinct entities: peri-implant mucositis (PIM) and peri-implantitis (PI). These can be considered analogous, though not identical, to gingivitis and periodontitis in the natural dentition, respectively. PIM is an inflammatory process affecting only the soft tissues surrounding a dental implant and its restorative components, ie, abutment and prosthesis. PI is defined as an inflammatory process that has extended beyond the surrounding mucosa to the underlying bone and has resulted in pathologic bone loss around the implant fixture itself.⁴

As with any disease process it is important to identify the disease’s etiology before deciding upon the appropriate corrective therapies. Various etiologies—some similar to those affecting natural teeth—have been associated with PIM and PI. First and foremost is dental plaque. Bacterial plaque has long been recognized as the primary causative agent in periodontal disease and is, likewise, just as relevant to peri-implant disease. Lack of proper patient-centered plaque control regimens and regular professional maintenance can lead to PIM just as the same can lead to gingivitis. PI, while impacted by plaque as well, can be significantly exacerbated by mechanical factors such as lack of adequate hard- and soft-tissue support, excessive occlusal loading, and retention of luting agents beyond the crown–implant interface.^5,6

The case report presented will examine one other factor that may play a role in peri-implant disease, namely improper restorative design, and the therapeutic benefits of modifying the morphology of existing restorative components in a case of chronic PIM. Before discussing the impact of restorative design, two basic concepts of current implant management will be reviewed: transmucosal abutment topography and cement versus screw retention.

Implant Management

Abutment Topography

In the past, abutments were traditionally prepared with a wide convex shape in an attempt to mimic the coronal third of a natural tooth. This design placed excessive pressure on the transmucosal soft tissue. The result was the crestal bone loss that has customarily been seen after implant loading. This, however, was long considered within acceptable functional limits.

More recently, the desire for not only functionally successful implant-supported restorations but also long-term esthetically successful results has driven the search for approaches that prevent such bone loss and the unesthetic gingival recession that often accompanies it. It has been recognized that the transmucosal submergence profile of an implant abutment can play a decisive role in the long-term stability of the bone and soft tissue surrounding the neck of an implant fixture. Rompen et al demonstrated the benefits of an under-contoured, concave submergence profile in the stability of soft tissue around implants, hypothesizing that “the curved profile allows for increased length of the soft tissue-to-implant interface, meaning that a biological seal of 3 mm can be obtained despite a shorter crown-to-implant distance” and that “after maturation of the soft tissues, a type of ring-like seal is created that could stabilize the connective tissue adhesion and, to some degree, functionally mimic the effect of Sharpey’s fibers attaching to teeth.”⁷

Cement Vs. Screw Retention

The choice of either cement- or screw-retained fixed implant-supported restorations has long been an issue of debate. Current thinking leaves the choice to the clinician. Both options have been shown to have advantages and disadvantages, and when executed properly both have been shown to have little effect on implant survival.⁸

One significant disadvantage of cement-retained restorations is the potential for excess residual cement beyond the crown–implant interface. This has been shown to be a significant etiological agent in PID,⁹ which can be totally eliminated with screw-retained restorations.

Disadvantages of screw-retained restorations are “screw loosening” and compromised esthetics. Screw loosening is often related to either improper occlusal load or inadequate torque at the time of abutment placement. Both of these problems can be easily remedied. Because of unavoidable angled implant orientation, screw retention is not always an option as the screw-access hole will exit the restoration in an esthetically critical area. In some cases a lingual screw may be utilized; otherwise, a cement-retained restoration must be employed. Occlusal access holes can be adequately masked with bonded materials such as opaque composites or custom fabricated inlays made from the same materials as the definitive restoration.

Case Presentation

A 71-year-old woman in good general health presented to the author’s general dental practice for a second opinion approximately 16 months after receiving treatment to replace her maxillary right first and second premolars and first molar (teeth Nos. 3 through 5) with an implant-supported fixed partial denture (FPD). Her chief complaint was bleeding, swelling, and extreme tenderness in the gums around her implant-supported fixed bridge. Implants had been placed in the first premolar (narrow platform) and first molar (wide platform) sites in early 2009. After 6 months, titanium abutments were placed and a cement-retained three-unit FPD was inserted with temporary cement. The patient reported that immediately after the restoration had been placed “it never felt right,” and though she returned repeatedly to the treating dentist the problem was not resolved and worsened as time passed. Once the temporary cement had completely washed out and the FPD was dislodged, the patient refused to have it recemented and she was able to remove and replace it at random. When she presented to the treating dentist with the aforementioned symptoms he referred her to an experienced periodontist who recommended corrective soft-tissue surgery. The patient was not convinced that this was appropriate, as the problem had started shortly after insertion of the prosthesis, and she desired to get another opinion. (Note: The author was not informed as to the periodontist’s rationale for performing surgery.)

Clinical examination revealed red, smooth (unstippled) mucosa on the buccal surface of the three-unit FPD (Figure 1). Removal of the FPD revealed erythematous, hypertrophic tissue around both abutments (Figure 2). Upon patient approval the abutments were unscrewed and the condition was found to continue along the transmucosal collar with spontaneous hemorrhage and ulceration of the mucosa surrounding the first premolar abutment (Figure 3).

The implants were deemed to be stable through tactile manipulation. Periapical radiographs confirmed almost 100% bone-to-implant contact along the mesial and distal aspects of both implants with only a slight gap at the mesial aspect of the neck of the premolar fixture, which did not extend to the first thread. A diagnosis of peri-implant mucositis was made.

Clinical and radiographic evaluation indicated that the molar abutment was moderately overcontoured and the premolar abutment was excessively overcontoured (Figure 4). Although the author recommended a 3-dimensional (3-D) cone-beam computed tomography (CBCT) scan to verify the condition of the bony support of the implants, the patient refused. The patient’s informed consent was given to proceed without the CBCT.

It was suggested to the patient that a provisional bridge with undercontoured abutments should be placed in order to test the author’s suspicions that the overcontoured abutments were adversely affecting gingival health. Since the existing restoration would not be affected and could easily be re-inserted if desired, the patient consented.

A vinylpolysiloxane (VPS) impression of the existing FPD in-situ was made to serve as a template for fabrication of the new provisional. A VPS open-tray transfer impression was taken and an analog soft-tissue model fabricated. The template impression and analog model were trimmed and synchronized to ensure complete seating. Undercontoured abutments were prepared and fitted to the analogs, and the screw-access holes were blocked out with wooden dowels (cut from cotton tip applicators) and, using the Nealon technique, the abutments were coated with self-curing acrylic. A mixture of the same self-curing acrylic was poured into the template impression and seated on the analog model with the abutments in place. The assembly was secured with elastic bands and cured in a pressure pot. Upon retrieval, the analogs were captured securely in the acrylic. The excess acrylic was trimmed, and passive fit was tested utilizing the “one-screw test.”^10,11 To do this, the provisional was placed and only the molar abutment screw was tightened with maximum finger pressure. A periapical radiograph was taken to verify complete seat of the premolar abutment (Figure 5). Once the passive fit was verified, final adjustments were made to the occlusion, and the ridge lap of the pontic was modified to a flat design to allow for ease of hygiene access. The provisional restoration was then polished and screwed into place with maximum finger torque (Figure 6). Cotton pellets were placed into the screw holes and the access holes were sealed with a silicone-based temporary material (Figure 7). The patient was scheduled for a 2-week follow-up.

At the 2-week follow-up visit the provisional restoration was removed to evaluate the soft-tissue condition. Complete resolution of the inflammation was noted (Figure 8 and Figure 9). The patient reported feeling comfortable for the first time since the original restoration had been inserted, and she was able to eat on the right side and had begun to exercise oral hygiene.

The provisional was replaced and the tissue allowed to mature for 6 more weeks. At that point a VPS open-tray transfer impression was made using the provisional restoration as the transfer medium in order to capture the morphology of the undercontoured abutments. A laboratory fabricated an acrylic verification jig, which was tried in and tested for passive fit with the one-screw test. Upon verification of passive fit, a screw-retained, all-zirconia superstructure was fabricated, mimicking the undercontoured design of the provisional abutments. The zirconia was tested for passive fit and returned to the lab for the application of porcelain and finishing. The occlusion was adjusted intraorally and tested with shim stock to ensure no premature contact of the implant-supported restoration. The final restoration was inserted with maximum finger torque, the access holes sealed as before (Figure 10 and Figure 11), and the patient scheduled for a 2-week follow-up observation.

At the follow-up visit the patient reported no discomfort or bleeding when performing oral hygiene. She stated that she was very satisfied with the outcome. The restoration was removed to check the gingival condition. The gingival collars were found to be healthy and displayed excellent adaption to the convex abutments (Figure 12). The restoration was torqued to the manufacturer’s recommendation, and the screw-access holes were sealed with a light-cured, condensable composite.

Conclusion

The increased use of osseointegrated dental implants to restore the compromised dentition over the past several decades has led to a new classification of oral pathology, namely peri-implant disease. Efforts to deal with this disease entity have prompted the search for an understanding of its processes, etiologies, and therapeutic treatments. The current case presentation has attempted to demonstrate an etiology—improper restorative design—that might easily be overlooked and to propose a treatment modality for its resolution. An awareness and understanding of the most current implant restorative guidelines should help to prevent peri-implant mucositis in the design of new cases and to treat PIM in existing cases where those guidelines may not have been followed.

ABOUT THE AUTHOR

David E. Azar, DDS
Private General Practice in Manhattan Financial District since 1984, New York, New York; Master Clinician in Implant Dentistry from Global Institute for Dental Education (gIDE)/UCLA, Los Angeles, California; Fellow, International Congress of Oral Implantologists; Member, Academy of Osseointegration

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