Quality Aesthetics in the Digital Age of Crown and Bridge

INTRODUCTION
The advent of digital technologies in dentistry is rapidly changing the way crown and bridge restorations are being fabricated for our patients. Traditional indirect techniques present the opportunity to introduce a lot of errors into fabrication. Some of them include (1) water-powder rations of the dental stone, (2) hygroscopic expansion of the dental stone, (3) inaccurate identification and trimming of the dies, (4) distorted master impressions, (5) poor quality impressions that don’t provide the restorative margin and emergence profile of the preparations, (6) unstable impression trays, and the list goes on! With so many chances to introduce error, along with the fact that many clinicians are always interested in faster techniques that may “short cut” a procedure (creating the possibility to introduce even more error), it’s a wonder that indirect restorations can be fabricated with 30 to 50 μm margins at all!

Chairside and laboratory technologies are now in place that streamline the steps on both sides and increase the accuracy. This ultimately leads to better fitting prostheses, reduced delivery times, and better productivity. Chairside scanning devices can accurately capture digital images that CAD software can convert to files that can be used by milling devices to create model work, prosthetic frameworks, and completed restorations. In many cases, these digitally produced restorations are more accurate than those made using traditional methods with superior clinical technique.

Figure 1. The patient presented with old PFM restorations on teeth Nos. 30 and 31. Recurrent decay and facial abfraction necessitated replacement.	Figure 2. After removal of the old restorations, deep excavated areas and recurrent decay can be seen. Areas that have been excavated close to the pulp were built up with bioactive foundation restorations (ACTIVA Restorative [Pulpdent]) prior to taking the master impression.
Figure 3. The preparations after removal of decay, bioactive build-up placement (ACTIVA Restorative), and preparation refinement.	Figure 4. An SLM Captek P (Argen) coping prior to the addition of the Captek G layer. Note the minute capillary spaces in the coping into which the Captek G penetrates, reinforcing the coping with 97% gold inside and out.

This case report will be a comparison of digital restorative systems. It will showcase 2 different materials that incorporate the accuracy of the digital workflow to create side-by-side posterior indirect restorations with excellent functional and aesthetic results.

MATERIALS BACKGROUND
SLM Captek: The Digital PFM
Today, all-ceramic crowns are considered by many to be the overall material of choice, both aesthetically and functionally, for crown and bridge prosthetics. However, it is important not to exclude the use of PFMs as a good restorative option for many indirect clinical situations. Captek (Argen) is a composite metal restorative material that has been used successfully for many years and has been shown to be both aesthetic and biocompatible. Selective Laser Melting (SLM) is a digitally driven process by which Captek copings are now produced to a level of marginal accuracy superior to those copings fabricated by previous methods. Some of the advantages of SLM Captek include (1) extremely accurate substructures, (2) increased strength, and (3) the biocompatibility and aesthetic benefits of traditional Captek with added strength and accuracy of fit.

According to the manufacturer, Captek as a restorative system has several clinical advantages over conventional PFM and all-ceramic materials. Two attributes that are very important to clinical success are (1) excellent retention of the luting cement to the internal Captek surface. The micromechanically retentive internal surface of the Captek coping gives the clinician the capability to bond or conventionally cement the restoration, thus making the system useful in clinical situations with aesthetic margins (at the gingival crest or slightly below), or in situations with deeper margins where isolation for use of resin cements is not possible. And, (2) studies have shown less bacterial accumulation around Captek margins that extend to the restorative margin edge. Seventy-five percent less bacterial accumulation was found around Captek composite gold margins when compared to adjacent natural enamel surfaces. When aesthetic and restorative needs require equigingival or subgingival margin placement, in areas of the mouth where control of moisture and fluid contamination may make using resins a challenge, a material like Captek that is both aesthetic and “bioprotective” is highly desirable.^1-4

Figure 5. The same coping shown in Figure 4 after the Captek G layer was fired onto it in the porcelain furnace.	Figure 6. The milled zirconia (ArgenZ Esthetic [Argen]) crown and SLM Captek on the master model as the ceramist layers the porcelain on the SLM Captek coping.
Figure 7. The finished restorations on the master model as the ceramist compares the finished shades to a standardized VITA shade tab.	Figure 8. The completed ArgenZ and SLM Captek restorations.

ArgenZ Esthetic Zirconia
As the number of zirconia full-coverage restorations continues to rise, particularly in the posterior regions, one of the challenges for this material has been to compete with the level of aesthetic quality found with lithium disilicate and felspathic porcelain. While the durability of this material is extremely good, being first introduced as an economical alternative to cast gold for posterior full-coverage restorations, the aesthetic quality was not so good. These early zirconium materials were extremely opaque and lacked the vitality of traditional porcelains. ArgenZ (Argen), a transitionally shaded aesthetic zirconia material, exhibits a high degree of translucency for beautiful, natural looking full-coverage restorations. The gingival color blends and transitions beautifully into a more translucent incisal or occlusal portion of the crown, ArgenZ Esthetic crowns absorb 100% of the shading liquid throughout the unit, ensuring that there are no white or opaque areas on the surface of the restoration. This material is also milled from CAD files, so the fit and accuracy of the restoration is precise and consistent.

CASE REPORT
Diagnosis and Treatment Planning
A patient presented with 2 adjacent posterior PFM crowns on teeth Nos. 30 and 31. Severe abfraction was observed on the root surfaces apical to the crown margins of both of these 15-plus-year-old restorations (Figure 1). The patient’s broad smile and these dark areas had been an aesthetic issue for a long time. The treatment plan was to include replacing these 2 old restorations.

The question is, what material should be used? With the amount of gingival recession and bone loss present in this 46-year-old patient, a few clinical issues needed to be considered.

First, a material that is “periodontally friendly” like Captek immediately comes to mind, due to a decreased potential for bacterial accumulation, as mentioned above. Margin position will be determined in part by the previous restoration and any recurrent decay that may be present. In this case, the lingual margin of the original crown on tooth No. 30 was deep subgingivally (at more than 50% of the gingival crevice depth). Captek composite metal margins in these deep subgingival areas would help keep bacteria and plaque accumulation to a minimum.

Figure 9. An intaglio view of the 2 restorations, comparing the zirconia and SLM Captek inner surfaces. Note the Captek gold lingual collar on tooth No. 30 that was extended into the subgingival areas to help control plaque accumulation.	Figure 10. A lingual view of the restorations on the master models in occlusion.
Figure 11. The restorations were tried in on the preparations.	Figure 12. A lingual view at try-in to show the difference in margin construction due to the depth of the restorative margin. A subgingival margin was used in Captek due to the “anti-plaque” effect afforded by the polished gold surface. The zirconium crown was designed with equicrevicular margins that will be more easily maintained by proper home care.

Secondly, in posterior areas, where both compressive and tensile strength to resist occlusal forces is often required, as well as precision of fit, a milled zirconia restoration is becoming the “go-to” material of choice, as long as margin position is not too far subgingival. Because of the digital workflow and lower cost of production, milled zirconia crowns are replacing more costly full-gold restorations. Since all the margins of the crown to be placed on tooth No. 31 would be equicrevicular, or slightly supracrevicular, a milled zirconia restoration was a good choice for this tooth. The aesthetic dilemma is this: Can these 2 restorations, side by side, be fabricated so that they will be indistinguishable from one another?

Clinical Protocol
The old PFM crowns were removed and the preparations examined (Figure 2). After removal of recurrent decay, the excavated areas of the preparations were built up with a bioactive restorative material (ACTIVA Restorative [Pulpdent]) (Figure 3). A diode laser (Picasso [AMD LASERS]) was used to remove excess tissue in the retromolar area distal to the second molar. Master impressions were taken and sent to the dental laboratory team for fabrication of an SLM Captek restoration on tooth No. 30 and a full-contoured zirconium restoration (ArgenZ) on tooth No. 31. The impression was poured and then digitally scanned.

Figure 13. The restorations in occlusion at the try-in.	Figure 14. The restorations after checking the occlusion with articulating paper (prior to cementation).
Figure 15. The luting cement (Ceramir Crown & Bridge [Doxa Dental]) was mixed and placed into each restoration.	Figure 16. A facial view of the crowns luted in place prior to cement cleanup. The crowns were placed and held in place for one minute. Next, a cotton roll was placed on each side of the mandibular arch, then the patient was asked to close and maintain pressure for an additional 2 minutes.
Figure 17. At the 3-minute mark, an explorer was used to remove the excess cement while in a “rubbery” phase. Once the majority of the cement was removed, the restorations were held in place from the occlusal aspect, and a piezo scaler (Ultrawave [Ultradent Products]) with a thin tip was used around the margins to remove any last bits of cement.	Figure 18. Occlusion was rechecked after cementation. A good dispersion of “B” (holding) contacts of approximately equal size and intensity are seen in red on both natural and restored teeth.

Figure 19. A 3-month postoperative view of the completed ArgenZ and SLM Captek restorations from a facial view. These 2 different materials were chosen due to the periodontal benefits of Captek (tooth No. 30) and the strength of full-coverage zirconia (tooth No. 31), without aesthetic compromise.

The following is a description of how the SLM Captek coping is created: First, the Captek P layer (platinum/palladium) of the coping is manufactured through the SLM process. SLM is a process by which an extremely precise, high-powered laser builds the coping structure additively, layer by layer. Next, the Captek G (gold) layer is painted on the outer surface of the Captek P and is then fired in a porcelain furnace. Capillary action causes the gold to flow through the unit as well as coat it on the inside and outside, giving it a bright yellow color (Figures 4 and 5). Figure 6 shows the milled zirconia (ArgenZ Esthetic) crown and SLM Captek coping with porcelain layered upon its surface. Upon completion of the restorations by the ceramist, a shade tab is shown next to the 2 restorations to compare their color (Figure 7). The SLM Captek and ArgenZ restorations are virtually indistinguishable from one another (Figure 8). An intaglio view (Figure 9) and a lingual view (Figure 10) are shown. A polished Captek gold collar extends on the proximal and lingual surfaces of the crown for tooth No. 30 to take advantage of the “anti-plaque” effect of Captek. The internal surface of the ArgenZ crown (No. 31) shows the digital precision of the milling process, including the marginal detail.

The restorations were returned from the laboratory and tried in the mouth (Figures 11 and 12) to check marginal accuracy and proximal fit. Next, the occlusion was checked and verified with articulating paper (AccuFilm II [Parkell]) (Figures 13 and 14). For cementation, a calcium aluminate cement was chosen (Ceramir Crown and Bridge Cement [Doxa Dental]). The cement was mixed and placed into the crowns (Figure 15). Figure 16 shows the cement after about 3 minutes, just before cleanup was initiated with an explorer (or scaler). Ceramir Crown and Bridge cleans up extremely well as it is in a “rubber-like” phase at this time so that the excess will “peel off” very easily, including the proximal areas as well.

Ceramir is a biocompatible cement, with excellent retention to both zirconia and metal. It is used without the silane, metallic primers, or bonding resins. Also, one unique feature of this cement is that apatite crystals form on the surface of the cement in the presence of saliva, sealing any marginal discrepancy that may exist after cementation.^5-7 Calcium aluminate cements have been shown in a recent publication by Jefferies et al⁸ to seal artificial gap margins where resin, resin modified ionomers, and glass ionomer cements fail to do so.

Figure 17 shows the cement being peeled away from the facial surface of teeth Nos. 30 and 31. Figure 18 shows the occlusion after it is checked after cementation.

CLOSING COMMENTS
This case has demonstrated the use of a milled full-zirconia crown, and a digitally fabricated composite gold coping with stacked porcelain on adjacent teeth (Figure 19).

The takeaway? Different materials may be used on adjacent teeth to take advantage of their biocompatibility, or high strength to resist heavy occlusal forces, without any compromise in aesthetic quality. This allows the dentist to pick the appropriate substrate to maximize restorative longevity and health of the surrounding gingival tissues and teeth without worrying whether the individual restorations will be an aesthetic match.

Acknowledgement
The author would like to acknowledge the ceramic expertise of Vincent Devaud, CFC, MDT, of the Smile Design Center, Beverly Hills, Calif, for the beautiful restorations shown here.

References

1. Goodson JM, Shoher I, Imber S, et al. Reduced dental plaque accumulation on composite gold alloy margins. J Periodontal Res. 2001;36:252-259.
2. Knorr SD, Combe EC, Wolff LF, et al. The surface free energy of dental gold-based materials. Dent Mater. 2005;21:272-277.
3. Gottehrer NR. The periodontal crown: creating healthy tissue. Dent Today. 2009;28:121-123.
4. Lowe RA. Biologic restorative systems for predictability. Dent Today. 2014;33:134-139.
5. Engstrand J, Unosson E, Engqvist H. Hydroxyapatite formation on novel dental cement in human saliva. ISRN Dent. 2012;2012:624056.
6. Pameijer CH, Zmener O, Alvarez Serrano S, et al. Sealing properties of a calcium aluminate luting agent. Am J Dent. 2010;23:121-124.
7. Hermansson L, Lööf J, Jarmar T. Integration mechanisms towards hard tissue of Ca-aluminate based biomaterials. Key Eng Mater. 2009;396-398:183-186.
8. Jefferies SR, Fuller AE, Boston DW. Preliminary evidence that bioactive cements occlude artificial marginal gaps. J Esthet Restor Dent. 2015;27:155-166.

Dr. Lowe received his doctor of dental surgery degree, magna cum laude, from Loyola University School of Dentistry in 1982. He is a member of Catapult Elite Speakers’ Bureau and has Fellowships in the AGD, both the International and American Colleges of Dentists, Academy of Dentistry International, Pierre Fauchard Academy, International Academy of DentoFacial Aesthetics, and American Society for Dental Aesthetics. Throughout his career, he has authored and published several hundred articles in many phases of cosmetic and rehabilitative dentistry. He can be reached at (704) 450-3321 or boblowedds@aol.com.

Disclosure: Dr. Lowe reports no disclosures.