July 8, 2016
by Robert A. Lowe, DDS
Both chairside and laboratory digital technologies in dentistry are rapidly changing the way crown and bridge restorations are being fabricated for our patients. Traditional indirect techniques have always presented an opportunity to introduce inaccuracies into the fabrication process. Some of these potential errors include: 1) incorrect water-powder ratios of the dental stone, 2) hygroscopic expansion of the dental stone, 3) inaccurate identification of margins and die trimming, 4) distorted master impressions, 5) poor quality impressions that fail to provide the entire restorative margin and/or emergence profile of the preparations, 6) unstable impression trays. The potential steps where error can be introduced are too numerous to mention.
However, many clinicians seek “short-cut techniques” that decrease treatment time without thinking about the problems that may be introduced. Given the potential for inaccuracy, it is a pleasant surprise that indirect restorations with 30-50μ margins can be fabricated at all. Digital chairside and laboratory technologies streamline the steps, increasing the accuracy of the restoration. This ultimately leads to increased practice productivity; better fitting prostheses, reduced delivery times, and fewer appointments. Chairside scanning devices accurately capture digital images that CAD software converts to files that are used by milling devices to create models, frameworks, and completed restorations. These digital restorations often fit more accurately than those made by traditional methods even with the most stringent clinical techniques.
In this case report, two materials are demonstrated that incorporate digital workflow accuracy: porcelain-fused-to-metal and fully contoured zirconia. The objective is to create uncompromising functional and aesthetic restorations that are indistinguishable from one another regardless of which materials and fabrication techniques were used.
Zirconia, while increasing in popularity due to excellent durability and lower laboratory costs, can be very opaque and unaesthetic. Accordingly, zirconia is mainly relegated for full coverage use on first or second molars where gold was used in the past. Gold is durable, but cost-prohibitive.
SLM Captek: The Digital Porcelain-to-Metal Crown
Today, high strength ceramic crowns, such as lithium disilicate (E.max: Ivoclar Vivadent) are considered by many to be the overall material of choice, both aesthetically and structurally, for crown and bridge prosthetics. However, it is important to consider porcelain-fused-to-metal as an excellent restorative option for many indirect clinical situations. Captek, by Argen, is a composite metal-restorative material, both aesthetic and biocompatible, that has been used successfully for many years. Captek’s unique properties make it much more resistant to plaque accumulation than natural tooth surfaces, an important feature for patients who are more susceptible to periodontal disease or for those who “don’t know which end of the toothbrush has the bristles”. 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. 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.
The Captek restorative system has had several clinical advantages over conventional porcelain-to-metal and all ceramic materials. According to the manufacturer, two attributes that are very important to overall clinical success are:
1) Excellent retention of the luting cement to the internal surface of the coping material. The micromechanically retentive internal surface of the Captek coping offers 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 with deeper margins where isolation for 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 (75%) 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 sub-gingival margin placement, in areas of the mouth where control of moisture and fluid contamination may make using hydrophobic resin luting agents a challenge, an aesthetic and “bioprotective” material such as Captek is highly desirable.1-4
An Esthetic Full-Contoured Zirconia Material
As zirconia full-coverage restorations, particularly in the posterior regions increase in popularity, one of their challenges has been competing with the aesthetic quality of lithium disilicate and feldspathic porcelain crowns. The durability of zirconia is extremely good: it was first introduced as an economical alternative to cast gold posterior full coverage. Early zirconia materials were extremely opaque and lacked the natural vitality of traditional porcelains, making their aesthetic properties rather poor. ArgenZ (Argen Corporation), is a transitionally shaded aesthetic zirconia material that features a high degree of translucency for a beautiful, natural looking, full coverage restoration. The gingival color blends and transitions into the more translucent incisal or occlusal portion of the crown, ArgenZ Esthetic crowns absorb 100% of the shading liquid throughout the unit, assuring that there are no white or opaque areas on the surface of the restoration. This material is also milled from CAD files, making the fit and accuracy precise and consistent.
A Comparison of Digital Restorative Technologies
A patient presented with two adjacent unattractive porcelain-to-metal crowns on teeth 46 and 47. A buccal preoperative view (Fig. 1) shows severe abfraction on the root surfaces with root discoloration apical to the crown margins of these 15+ year-old restorations. The patient has a broad smile and these dark areas have been an aesthetic issue for a long time. The treatment plan involved replacing these two restorations. The question is: which materials are optimal for this case?
FIGURE 1. A preoperative facial view of old PFM restorations on tooth numbers 46 and 47. Recurrent decay and facial abfraction have necessitated replacement of these restorations.
The gingival recession and bone loss in this 46-year-old patient suggest the following clinical considerations: The clinician must select 1) a material that is “periodontally friendly” such as Captek, (decreased potential for bacterial accumulation at the restorative-tooth interface). The position of the margin will be determined by the previous restoration and any recurrent decay. In this case, the original lingual margin of the crown on tooth 46 was deep subgingivally (>50% of the gingival crevice depth). Captek composite metal margins in these deep crevicular areas help to minimize bacterial and plaque accumulation. 2) In posterior areas both compressive and tensile strength to resist occlusal forces are required in addition to a precise fit. Thus, full contour zirconia restorations are becoming the “go to” material of choice, as long as margins are not too far subgingival. Full contour zirconia crowns, with an enhanced digital workflow and lower cost of production, are replacing more costly full gold crowns. The margins of the crown on tooth 47 will be equicrevicular, or slightly supracrevicular, and therefore a full contour zirconia restoration is a good choice.
The aesthetic dilemma: can these two restorations, made of different materials, seated side-by-side, be fabricated so that they will be indistinguishable from one another? First, the old PFM crowns were removed and the preparations examined (Fig. 2). After removal of recurrent decay, the excavated areas of the preparations were built up with a bioactive restorative material (Activa Restorative: Pulpdent Corporation) (Fig. 3). A diode laser (Picasso Lite: AMD Lasers) was used to remove excess tissue in the retromolar area distal to the second molar. Master impressions were made and sent to the laboratory for fabrication of an SLM Captek (Argen Corporation) restoration on tooth 46 and a full contour zirconium restoration (ArgenZ: Argen Corporation) on tooth 47. In this case, the master impression was poured and digitally scanned. Another option is a chairside scanning device to take an optical impression of the preparations. The digital files are then sent directly to the laboratory for model construction.
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 should be built up with bioactive foundation restorations prior to the making of the master impression.
FIGURE 3. The preparations are shown for tooth numbers 46 and 47 after removal of decay, bioactive build up placement, and preparation refinement.
The SLM Captek coping is created as follows: first, the Captek P layer (Platinum–Palladium) of the coping is manufactured through a process called Selective Laser Melting. SLM is a process by which an extremely precise, high-powered laser builds the coping structure in an additive process, layer by layer. Next, the Captek G (Gold) layer is painted on the outer surface of the Captek P coping, which is then fired in a porcelain oven. Capillary action causes the gold in the Captek G to flow through the coping, coating it inside and out, giving it a bright gold hue (Figs. 4 & 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 two restorations to compare their color and characteristics (Fig. 7). The SLM Captek and ArgenZ restorations are virtually indistinguishable from one another (Fig. 8). An intaglio view (Fig. 9) and a lingual view (Fig. 10) are shown. A polished SLM Captek gold collar extends on the proximal and lingual surfaces of the crown for tooth 46 to take advantage of the “anti-plaque” effect of SLM Captek. The internal surface of the ArgenZ crown on 47 shows the digital precision of the milling process, including the marginal detail. The restorations were tried in the mouth (Figs. 11 & 12) to check marginal accuracy and proximal fit. Next, occlusion was checked with articulating paper (Accufilm II: Parkell) (Figs. 13 & 14). Once occlusal accuracy was verified, the case was ready for cementation.
FIGURE 4. An SLM Captek P coping is shown prior to the addition of the Captek G layer. Note the minute capillary spaces in the coping into which the Captek G will penetrate reinforcing the coping with 97% gold inside and out.
FIGURE 5. The same coping in Figure 4 is shown after the Captek G layer is fired onto it in the porcelain furnace.
FIGURE 6. The milled zirconia (ArgenZ) crown and SLM Captek are shown on the master model as the ceramist layers the porcelain on the SLM Captek coping.
FIGURE 7. The finished restorations are seen 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 are shown. These restorations were fabricated by Mr. Vincent Devaud, CFC, MDT of the Smile Design Center, Beverly Hills, CA.
FIGURE 9. An intaglio view is shown of the two restorations comparing the zirconium and SLM Captek inner surfaces. Note the Captek gold lingual collar on tooth number 46 that will extend in to 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 are tried in on the preparations and shown from a facial view.
FIGURE 12. FIGURE 12. The try-in is shown from the lingual view to show the difference in margin construction due to the depth of the restorative margin. The subgingival margin is in Captek because of the “anti-plaque” effect afforded by the polished gold surface. The zirconium crown has equicrevicular margins that will be more easily maintained by proper homecare.
FIGURE 13. A facial view of the restorations at try-in in occlusion.
FIGURE 14. The restorations are shown after checking occlusion with articulating paper prior to cementation.
For cementation, Ceramir Crown and Bridge Cement (Doxa) was selected because of its excellent biocompatibility and for its excellent retention to both zirconia and Captek, without the use of silane, metallic primers, or bonding resins. Another 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 Jefferies, et al, in a recent publication, demonstrated that Calcium Aluminate cements seal artificial gap margins where resin, resin modified glass ionomer, and glass ionomer cements fail to do so.8 The cement was mixed and placed into the crowns (Fig.15). Figure 16 shows the cement after about three minutes, just before cleanup is initiated with an explorer or scaler. Ceramir Crown and Bridge cement cleans up quickly and easily, having a “rubber-like” consistency such that the excess cement “peels off”, including in the proximal areas of the restoration. Figure 17 shows the cement being peeled away from the facial surface of teeth 46 and 47. Figure 18 shows the occlusion checked after final cementation.
FIGURE 15. The luting cement (Ceramir Crown & Bridge: Doxa Dental) is mixed and placed into each restoration.
FIGURE 16. facial view shows the crowns luted in place prior to cement clean up. The crowns are placed then held in place for one minute. Next, a cotton roll is placed on each side of the mandibular arch and the patient is asked to close and maintain pressure for an additional two minutes.
FIGURE 17. At the three-minute mark, an explorer is used to remove the excess cement while in a “rubbery” phase. Once the majority of the cement is removed, the restorations are held in place from the occlusal aspect and a piezo scaler (Ultradent Corporation) with a thin tip is used around the margins to remove any last bits of cement.
FIGURE 18. Occlusion is 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 three-month postoperative view of the completed Argen Z and SLM Captek restorations from a facial view. The periodontal benefits of Captek on tooth number 46 and the strength of zirconium on tooth number 47 without aesthetic compromise.
The case demonstrated adjacent posterior restorations made of different substrates with different techniques – one a milled full contour zirconia crown, the other, a digitally produced composite gold coping (SLM Captek) with stacked porcelain. The final result clearly shows that different materials may be used on adjacent teeth to take advantage of their biocompatibility (Captek) or high strength to resist heavy occlusal forces (ArgenZ) 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 having to worry about an aesthetic match. OH
Dr. Robert A. Lowe has received Fellowships in AGD, ICD, ADI, ACD, IADFE, and ASDA. He is a diplomate on the American Board of Esthetic Dentistry and maintains a private practice in Charlotte, North Carolina. Dr. Lowe can be reached at firstname.lastname@example.org.
Oral Health welcomes this original article.
The author would like to acknowledge the ceramic expertise of Mr. Vincent Devaud, CFC, MDT of the Smile Design Center, Beverly Hills, CA for the aesthetic work done on this case.
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