Practical Applications: Improving Darkened Anterior Peri-implant Tissue Color with Zirconia Custom Implant Abutments

One of the formidable challenges in implant dentistry is creating a gingival margin that resembles the appearance of the cementoenamel junction of a natural tooth. This can be difficult when placing titanium implant fixtures and titanium abutments because the metal substrates have color characteristics and light reflectivity properties that can compromise the appearance of the peri-implant gingiva. The portion of the abutment that is below the crown margin but is above the implant interface may be visible through the tissue. This phenomenon, known as show-through, can gray the marginal area of the crown. Any appearance of tissue discoloration may affect a patient’s satisfaction and acceptance of the final restorative result.^1-3 This esthetic challenge has been part of dentistry since porcelain-fused-to-metal restorations were first used in the esthetic zone,^4-6 and has continued to be an esthetic compromise when metallic implant parts are used there as well.

Mucosa thickness has been reported to be a crucial factor in hiding, or showing, the discoloration caused by different restorative materials. Show-through is most noted where the gingiva overlying the abutment is thin and transparent.⁶ When nonprecious alloys are used as abutment or crown substrates, their corrosion products may add to the appearance of tissue discoloration.⁷

One commonly used method to mitigate the poor appearance of discolored peri-implant tissue is to alter the metallic color by bonding colored porcelain to the abutment. Then, the final crown is made over a colored infrastructure where the abutment is no longer gray. According to one study, gingival esthetics can be improved by coloring the abutment neck with light pink porcelain.⁸

Recently, zirconia has been used as a crown infrastructure⁹ and an implant abutment material.¹⁰ Many studies have demonstrated that zirconia can meet and exceed known human occlusal forces.^11-18 One study analyzed anterior zirconia, titanium, and aluminous porcelain test abutments that were artificially aged, and found that the median fracture resistance of the zirconia abutments was 443.6> N. This load is very near the high end of human occlusal forces, indicating that zirconia has the potential to withstand the physiologic occlusal forces applied in the anterior region.¹⁴ Another strength test pre-aged the test specimens (zirconia crowns and implant abutments) and showed that when used as a dental material, zirconia fractures high enough to withstand maximum human occlusal loads.¹⁵ After processing, a zirconia abutment becomes white in color. When it is combined with an all-ceramic crown, this color does not show through the overlying tissues.

Computer-aided design/computer-aided manufacture (CAD/CAM) technology has made it possible to create duplicate abutments, whereby two precisely shaped abutments of similar, or dissimilar, materials can be fabricated from the same computer file.¹⁹ A crown that is fabricated for one of these abutments will fit the other, despite any material differences (Figure 1).

Although zirconia abutments are sufficiently strong for intraoral use^11-18 and can eliminate the appearance of tissue discoloration, their fabrication cost is higher than cast metal or CAD/CAM-milled titanium abutments, and they are not readily available for every commercial implant system.

This article describes two cases where a zirconia abutment was substituted for an existing titanium abutment (both made from the same CAD/CAM file). In each case, different esthetic results were obtained when the same all-porcelain crown was placed on a titanium abutment and on a zirconia abutment.

A 27-year-old woman presented for a premolar implant restoration in site No. 5. The natural tooth had been lost 2 years previously. The patient had worn a provisional removable partial denture for 2 years before implantation of the edentulous site.

A 4.3 mm x 13 mm implant (Replace® Select, Nobel Biocare USA, LLC, Yorba Linda, CA) was surgically placed into site No. 5 and exposed 5 months later. After the Stage 2 coping impression, a custom abutment (Atlantis Gemini+® Abutment, Atlantis® Components, Inc, Cambridge, MA) was designed and milled out of titanium (Figure 2). A provisional healing restoration was installed for tissue sculpting and worn for 2 months before final crown placement.

The final, all-ceramic crown (LavaTM, 3M ESPE, St. Paul, MN) was fitted over the titanium abutment (Figure 3A and Figure 3B). Show-through created a dark gray gingival margin. Because of this discolored tissue appearance, a second abutment (Atlantis® Abutment in ZirconiaTM, Atlantis® Components, Inc) was fabricated out of zirconia, using the original CAD/ CAM file. Then, the titanium abutment was removed and the zirconia abutment was placed (Figure 4). The original all ceramic crown was reseated over the replacement abutment, resulting in an esthetically acceptable gingival margin. No show-through was evident, creating a more natural appearance (Figure 5A and Figure 5B).

A 60-year-old woman required extraction of tooth No. 9. Radiographic examination revealed severe internal resorption. Immediately after extraction, a 4.7 mm x 13 mm implant (Tapered Screw-Vent® Zimmer Dental, Carlsbad, CA) was placed in the extraction site with a surrounding bone graft (Puros® Dermis Allograft, Zimmer Dental). A tissue-level implant impression was made before covering the surgical site with a membrane (BioMend® Membrane, Zimmer Dental).

The following day, a CAD/CAM-designed and fabricated titanium healing abutment (Atlantis Gemini+ Abutment) and a provisional restoration (IntegrityTM Temporary Crown and Bridge Material, DENTSPLY Caulk, Milford, DE) were placed (Figure 6). The tissue above the provisional restoration appeared dark because of healing abutment show-through. To create an esthetic final restoration, the titanium healing abutment was replaced with the final zirconia abutment (Atlantis Abutment in Zirconia) fabricated from the same CAD/CAM file (Figure 7). An all-ceramic crown (LavaTM, 3M ESPE) was constructed and placed (Figure 8). Although this case shows a more subtle color change of gingival margin than Case 1 exhibits, a more natural-appearing margin is seen with the zirconia abutment than was seen with the healing abutment.

Comparisons of Figure 3A with Figure 5A, and Figure 6 with Figure 8, reveal the significant improvement in the appearance of the gingival tissue obtained when a zirconia abutment replaces a titanium one. This improvement in appearance results when the abutment material exerts minimal color influence over the peri-implant tissue’s natural color. These clinical results reflect the findings of previous cases where zirconia abutments were placed in esthetic regions.^16-18

Esthetic excellence in anterior implant restorations necessitates precision color matching of the replacement crown, optimum tissue shape, and natural tissue color. Often, esthetic failure is caused, not by the crown itself, but by the shape and color of the tissue at the gingival margin. When a crown’s color is a near match to its neighboring teeth and the tissue contours closely mimic the neighboring tissue heights, esthetic failure still may result if the tissue color appears unnatural. Therefore, the authors recommend placing zirconia abutments when patients present with a high smile line or the gingival tissue can be seen with the lip line at rest.

Using CAD/CAM technology to fabricate a duplicate zirconia abutment simplifies the clinician’s ability to replace a metallic abutment that is discoloring the tissue’s appearance with a more esthetic zirconia one. Further, this technique can eliminate potential remakes of an esthetically acceptable crown.

Successful esthetic anterior single-crown restorations result when the crown color matches the neighboring teeth, the peri-implant tissue contours simulate the gingiva around the crown, and the peri-implant tissue appears its natural color. One method to retain the natural color of the peri-implant tissue is to place zirconia abutments rather than metal-based abutments. The zirconia’s white color imparts no dark hues to the peri-implant tissues, so a natural tissue color appears at the gingival margin. CAD/CAM technology easily allows clinicians to replace an existing metal abutment with a zirconia one, without creating a new crown.

Special thanks to Fabian Gallon of FG Laboratory, Medford, Massachusetts, for the creative all-ceramic crowns.

Dr. Kerstein is a consultant for Atlantis® Components, Inc.

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