Comparing Three Abutment Types With a Zirconia Crown in the Aesthetic Zone: A Case Report

Success in implant dentistry has evolved beyond mere osseointegration.1 The focus is now also being placed on the aesthetic results of both the final restoration and the surrounding soft tissues. In the last decade, there has also been an emphasis in simplifying clinical procedures. To help accomplish this, a variety of stock abutments have been introduced that make implant restoration more efficient and less costly. Although the use of prefabricated abutments can be highly successful, less than ideal implant placement and soft tissue architecture problems can limit their application.
In situations where stock abutments cannot establish proper margin definition, antirotation, and/or develop the necessary emergence profile, custom cast abutments are required. The authors were unable to find in the literature any direct clinical comparisons between restorations supported by custom and prefabricated abutments. The purpose of this article is to present an anecdotal direct comparison of the aesthetic results of 2 different types of prefabricated abutments and one custom cast abutment. Each abutment was used to support a zirconia crown in the replacement of the same maxillary left lateral incisor in the same patient.


Figure 1. Clinical appearance of tooth No. 10 prior to treatment.

Figure 2. Preoperative radiograph showed severe caries.

Figure 3. Following atraumatic extraction interdental papillae are intact.

Figure 4. Examination of the extracted root indicated the shape and volume of the extraction socket.

CASE REPORT

A70-year-old white male was found to have tooth No. 10 with advanced caries involving the root surface below the crestal bone level (Figures 1 and 2). After discussing the findings and the treatment plan options with the patient, he agreed to replace tooth No. 10 with an implant-supported crown.
Profound local anesthesia was accomplished using approximately 7.2 cc 2% lidocaine with 1:100,000 epinephrine. A circumferential incision was made using a No. 15 scalpel blade and the tooth was removed using periotomes and forceps. Care was taken not to traumatize the interdental papillae (Figure 3). The extracted tooth indicated the shape and volume of the extraction site (Figure 4). The extraction site was thoroughly curetted and the integrity of the buccal plate of bone was evaluated and found to be good.

Figure 5. Occlusal view of implant at time of placement showing the internal connection.

Figure 6. Buccal view of implant site with flared healing abutment in place.

Figure 7. Occlusal view of implant site 3 months after healing. (Note soft-tissue health.)

Figure 8. Radiographic view of implant with flared healing abutment.

An implant osteotomy was prepared toward the palatal side of the extraction socket and a regular diameter (4.0 x 13 mm) dental implant (PrimaConnex [Keystone Dental]) was placed (Figure 5). This implant had a macro-micro textured surface, a 1-mm machined smooth collar around the prosthetic table, a medialized microgap, and an internal prosthetic connection. A particulate calcified bone allograft (Puros Allograft [Tutogen Medical]) was placed into the spaces between the dental implant and the socket walls. A flared healing abutment with a 6-mm flare contour and a 5-mm cuff height was immediately placed on the implant (PrimaConnex) (Figure 6). Sutures were not required. An interim removable partial denture was delivered after being adjusted to avoid contact with the healing abutment and adjacent soft tissues.
Approximately 3 months after implant placement, the site was found to be healing well with a natural soft-tissue profile including well-formed interdental papillae (Figure 7). Radiographic evaluation found no pathology and interimplant bone levels were above the implant prosthetic tables (Figure 8). At this point, the patient was referred back to the prosthodontist for restoration of the implant.
A closed tray impression was taken using flared contoured impression posts (Prima-Connex). The matching contours of the impression post and flared healing abutment guaranteed the support of the surrounding soft tissue2 and allowed its accurate reproduction on the master model. An impression and an occlusal registration were made. The impression post was connected to an implant analog before being replaced in the impression.

Figure 9. From left to right: custom UCLA, prefabricated contoured, and cylindrical abutments (buccal view).

Figure 10. From left to right: UCLA, prefabricated contoured, and cylindrical abutments (lingual view).

In the laboratory, a soft tissue master model was fabricated. Three different abutments were used next (Figure 9 and 10). The first was a custom abutment (UCLA; Prima-Connex [Keystone Dental]) for which detailed design instructions were sent to the dental laboratory technicians. This abutment was customized with a high noble alloy and sandblasted to provide ideal margin placement, retention, emergence contours, angulation, height, and parallelism. Second, a prefabricated 15° angled titanium abutment (Esthetic Contour Ti abutment; Prima-Connex, [Keystone Dental]) was used “as is.” This polished abutment is gold-colored to give a warmer and more natural appearance to the surrounding gingiva. It also has scalloped margins to minimize the need for intraoral preparation and deliver superior aesthetics. Finally, a prefabricated cylindrical titanium abutment designed primarily for direct intraoral impressions, with plastic “snap-on” components, (Quick-Abutment; PrimaConnex [Keystone Dental]) was used. This abutment has a cylindrical shape with a flat wall to provide it with antirotation properties. All of its margins are on the same horizontal plane (ie, they are flat).
Ceramic zirconia crowns with an A3 shade (VITA Classical shade guide [Ivoclar Vident]) were fabricated for each abutment. In the case of the UCLA abutment and the prefabricated angled abutment, duplicate dies were made. These were scanned to make zirconia cores (Lava [3M ESPE]) that were of the appropriate base shade. For the prefabricated cylindrical abutment, a premade zirconia-locking coping that can be directly layered with compatible porcelain was used (Quick-Abutment Ceramic Coping; PrimaConnex [Keystone Dental]). This coping is white and its color cannot be modified. All the zirconia substructures were then veneered utilizing the same shades of compatible veneering porcelains to achieve the final desired shade of A3.

Figure 11. Clinical view of UCLA abutment. Ideal abutment contours were achieved.

Figure 12. Clinical view of prefabricated contoured abutment. (Note its high-polish surface compared to the sandblasted UCLA abutment.)

Figure 13. Clinical view of prefabricated cylindrical abutment. (Note the nonanatomic contours.)

Figure 14. Intraoral view of the zirconia crown supported by UCLA abutment. The closest shade match was achieved with this crown.

Figure 15. Intraoral view zirconia crown supported by prefabricated contoured abutment. Crown has a subtly higher value than the adjacent teeth.

Figure 16. Intraoral view of zirconia crown supported by prefabricated cylindrical abutment. This crown had the highest value.

At the next appointment each abutment and crown were tried in and compared by the authors with the A3 shade tab. The patient was also given the opportunity to evaluate each restoration. In addition, intraoral photographs of each of the restorations were taken with fixed camera and flash settings, under color-corrected lighting. For this, the patient’s head position was maintained constant through the use of a special jig. In this way, the authors were able to evaluate the results directly and indirectly (Figures 11 to 16).

DISCUSSION

An implant restoration can only be as aesthetic as the surrounding soft- and hard-tissue architecture permits. To support the success of this case, a considerable amount of attention had to be paid to the surgical details. Reconstruction of lost osseous support and gingival contours in the aesthetic zone had been challenging.3-5 Therefore, preservation of the natural osseous and gingival architecture seemed to be most prudent.6,7
In order to preserve aesthetics, tooth No. 10 was removed as atraumatically as possible and the implant was immediately placed.6,8-10 The implant used had a medialized microgap to help minimize crestal bone loss associated with the establishment of biologic width and to maximize interproximal bone heights.10,11 Furthermore, care was taken to place the implant at least 1.5 mm from the adjacent teeth. As indicated by the classification developed by Salama, et al12 with this type of tooth-implant spacing, an interdental soft-tissue height of 4.5 mm could be expected.12
The implant was placed along the palatal aspect of the extraction socket with the long axis directed toward the cingulum of the crown.13 A particulate graft was placed in the spaces between the implant and the facial place of bone to encourage bone regeneration in these spaces.14 A flared contoured stock healing abutment was placed to begin the development of the emergence profile.15 Due to the patient’s thick biotype, it was expected that the buccal gingival margins would be relatively stable.16

Figure 17. Side-by-side comparison of UCLA (left), prefabricated contoured (center), and cylindrical abutment (right) with their respective crowns. The abutment margins and management of the screw access hole are more ideal in the UCLA abutment. Although the contours of the cylindrical abutment are nonanatomical, its crown still provided an adequate aesthetic result.

Figure 18. From left to right: Buccal view of UCLA, prefabricated contoured, and prefabricated cylindrical abutment supported zirconia crowns. Note longer emergence profile of the latter due to nonanatomical margins of the abutment.

Figure 19. From left to right: Intaglio view of UCLA, prefabricated contoured, and prefabricated cylindrical abutment supported zirconia crowns. Note the stark white color of the zirconia core of the latter.

Figure 20. The UCLA supported zirconia crown was deemed the most natural looking by both the patient and the authors.

In the author’s opinion, all 3 restorations delivered aesthetically pleasing results (Figure 17). While being similar, subtle differences between the abutments and crowns were evident. The contours of the UCLA abutment and prefabricated angled abutment were comparable. The custom UCLA abutment, however, provided a more ideal gingival profile with 1.5 mm and 1 mm subgingival margins on the buccal and interproximal surfaces respectively, and lingual margins located at the gingival crest. The prefabricated cylindrical abutment was nonana-tomical and had margins that were almost 2 mm below the gingival margin. This could present a problem with cement removal. In addition, its shorter height also gave concerns regarding its ability to provide adequate retention for the crown.
The emergence profiles of the crowns varied depending on the location of the margins of its abutment (Figures 18 and 19). The prefabricated cylindrical abutment had the deepest margins and therefore its zirconia crown had the longest emergence profile. The prefabricated angled abutment had scalloped margins that varied its proximity to the gingival margin. The emergence profile for its zirconia crown was shorter than the prefabricated cylindrical abutment, but its margins were deemed slightly too subgingival by the restorative team. The locations of the margins of the UCLA abutment (determined by the restorative dentist) paralleled most closely the contours of the gingival margins. Therefore, the emergence profile of its zirconia crown was the most ideal for both aesthetic reasons and cement-removal purposes.
The authors’ opinions coincided for both the direct and photographic comparisons. It seemed that the abutment type used might have affected the value of the zirconia crowns. In the authors’ opinion, when comparing the photographs side-by-side; the crowns supported by the prefabricated abutments seemed to be slightly higher in value than the crown supported by the UCLA abutment, with the crown supported by the prefabricated cylindrical abutment having the highest value. The latter could have been due to the stark white shade of the zirconia coping. If this were true, it would be an important consideration since it could pose a problem when a crown with a low value is desired.17 To compensate for this, a greater thickness of porcelain may be needed in order to attain the desired shade, and the laboratory technician should be made aware of this challenge. The additional room for greater porcelain thickness was not available in this case. Therefore, in instances such as this one, a high strength ceramic core imparts a degree of compromise when used in relatively dark restorations since it can prevent adequate aesthetic camouflage. Although zirconia was chosen as a restorative material, a PFM crown would have been a possible option to match the adjacent teeth due to the relatively lower shade value.
The authors agreed that the crown on the prefabricated angled abutment produced a better color match when compared to the prefabricated cylindrical abutment. However, its value was somewhat greater than the crown on the UCLA abutment and the neighboring dentition. It could be hypothesized that the highly polished surface of the contoured stock abutment generated greater light reflection than the dull surface of the UCLA abutment, resulting in the value mismatch. The UCLA abutment and its corresponding crown appeared to provide the best aesthetic match in the view of the patient and authors (Figure 20). It is worth mentioning that light reflection differs between all-ceramic and PFM restorations (such as the ones present on teeth Nos. 8 and 9), so one should exercise caution when making the kind of comparisons made here.
In terms of ease, speed, and cost of fabrication, the advantages of the prefabricated abutments are clear. Laboratory turnaround and expenses are greatly diminished when prefabricated components are used. This is especially true for the prefabricated cylindrical abutment. Its inexpensive premade ceramic coping eliminates the need for scanning to produce a ceramic core, further reducing the time and costs of crown fabrication.
Prefabricated abutments have an additional advantage in being able to be used as provisional and final abutments. Multiple connections and disconnections of implant components can increase the risk of gingival recession and aesthetic complications in thin biotypes and immediate load cases.18 Prefabri-cated abutments, however, are not adequate for all situations since average anatomic contours and limited customization can result in less than ideal emergence profiles.19

CONCLUSION

Zirconia crowns supported by custom UCLA, prefabricated 15° angled titanium, and prefabricated cylindrical titanium abutments can all deliver aesthetic results. The prefabricated cylindrical abutment was considered the most challenging to restore because of its nonanatomical margins and the inability to color the corresponding ceramic coping. Therefore, the authors believe this abutment seems better suited for the restoration of less aesthetically demanding sites. The prefabricated angled abutment provided adequate margin location and based on the comparison methods utilized here resulted in an improved zirconia crown shade match than the prefabricated cylindrical abutment.
The photographs and direct intraoral comparisons done by the authors appeared to show that the value of its crown was higher than that of the zirconia crown supported by the UCLA abutment and the surrounding dentition. The zirconia crown supported by the UCLA abutment appeared to achieve the best aesthetic integration in the view of both the patient and the authors.
While this report is clearly not a scientific evaluation, further investigation on the aesthetic effects of different abutments on zirconia crowns would appear worthwhile.


References
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Dr. Mahn is a periodontist in private practice in Manassas, Virginia. He graduated SUNY Stony Brook Dental School in 1990 and completed his periodontal residency at MCV School of Dentistry in 1992. He also completed a residency in Temporomandibular Disorders and Orofacial Pain at NYU College of Dentistry in 1996. His practice emphasizes perioplastic and dental implant treatments. He has several publications and lectures on these topics. He was listed in the Washingtonian's Best Dentists List in 2003. He can be reached at (703) 392-8844 or by e-mail at dmahn@cox.net.

Disclosure: Dr. Mahn reports no conflict of interest.

Dr. Polack obtained his specialty training in Prosthodontics and Master of Science degree from the University of Minnesota. He practices full-time in Gainesville, Virginia. He has published more than 30 abstracts and papers on prosthodontics and dental materials in various scientific journals and lectures nationally and internationally on those subjects. He can be reached at mpolack@comcast.net or (703) 753-8753.

Disclosure: Dr. Polack reports no conflict of interest.

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