Solving a Shade Dilemma

More Translucent All-Ceramics: Esthetic Challenges and Solutions

It is well understood that the more translucent a restorative material is, the more esthetic it will be, and the more it will be able to mimic the desirable characteristics of natural teeth as long as the color of the tooth is acceptable.¹ However, a restorative material with higher translucency will allow a dark underlying color to show through, adversely affecting the final restoration. Conversely, a more opaque restorative material may be better at masking a dark tooth or substrate but may lack the esthetic qualities desired for anterior teeth unless it can be successfully layered with a more translucent ceramic.^2,3 Therefore, when faced with the clinical situation of restoring a dark anterior tooth (or teeth), it is desirable to either improve the color of the tooth or to somehow mask it.

Endodontically-treated discolored teeth, tetracycline-stained teeth, metal post-and-cores, and titanium abutments are some examples of clinical situations that present a challenge in achieving acceptable esthetics with translucent restorative materials. Internal and external bleaching, replacing metal posts (when possible) and titanium abutments with dentin-shade materials, and placing tints and composites are some of the options for improving the underlying color. Using layered core restorations (ie, porcelain-fused-to-metal, -gold, or -zirconia) can also be used for masking dark teeth and substructures, sometimes with underlying composites or tints in an attempt to idealize the stump shade. While internal bleaching of endodontically-treated discolored teeth can be successful in improving the color of a dark tooth, the likelihood of relapse could adversely affect the shade of a more translucent all-ceramic restoration. The same would hold true for external bleaching of tetracycline-stained teeth where long-term results are also unpredictable.⁴ However, if the shade of the prepared tooth (stump) can be improved satisfactorily with opaque composites and tints, it will be more color-stable in the long term and would not require the ceramist to mask it with the restoration. In cases where enough room exists without having to sacrifice healthy tooth structure, the ceramist can successfully mask a dark substrate or discolored tooth with a layered restoration if necessary, as long as the core (coping) material chosen is opaque enough and adequately thick for the task at hand.^2,3 It is important that the restorative dentist and the dental laboratory technician fully and properly communicate with one another to determine which option offers the best chance for clinical success.

Case Presentation

Diagnosis and Treatment Plan

A 36-year-old man presented with a complaint about a discolored right central incisor (tooth No. 8) (Figure 1 and Figure 2). According to the patient, this tooth had undergone root canal therapy several years prior and had progressively become darker. The clinical examination revealed that the access opening still had a temporary filling in place that, most likely, had contributed to the extreme discoloration over time. In addition, it was noted that the maxillary anterior teeth (teeth Nos. 5 through 12) had significant lingual erosion (Figure 3). Most of the enamel had been eroded from lingual surfaces, resulting in shorter anterior teeth, a slight open bite, and a reverse smile line (Figure 4). The characteristic wear pattern was indicative of intrinsic erosion caused by regurgitated stomach acids. Upon gentle questioning, the patient confirmed the diagnosis but stated that he had not had the problem for several years. (The scope of this article does not allow for a discussion of acid erosion, but suffice it to say that the long-term prognosis of both direct and indirect restorations is good for these types of cases when the source of acid can be prevented or eliminated.) Restorative options were presented to the patient and the agreed upon treatment plan was to prepare for, and place, porcelain veneer crowns on teeth Nos. 5 through 12. These would improve the color match of the central incisor (tooth No. 8) to the other teeth, restore the eroded lingual surfaces of teeth Nos. 5 through 12, and optimize his overall esthetics and function.

The endodontically-treated discolored central incisor presented the biggest esthetic challenge in this case. As stated earlier, there are two options when treating discolored teeth: improve the color or mask it with the restoration. Even though internal bleaching with a walking bleach technique would most likely be successful in improving the color of the tooth in this case, it would also have a high probability for relapse that could result in a darkening or “shade shift” of a more translucent overlying all-ceramic restoration with time. Instead of bleaching, the author elected to improve the underlying color as much as possible with composite resin, and then to mask it with a definitive restoration.

Preparation Appointment

The temporary filling material was removed from tooth No. 8 and the access opening was thoroughly cleansed and filled with a shade A20 nanohybrid composite (Beautifil II, Shofu Dental, www.shofu.com). Teeth Nos. 5 through 12 were prepared with 0.5-mm facial reduction, and little-to-no lingual reduction with a 360° equigingival chamfer margin placed in enamel. Additionally, the facial surface of tooth No. 8 was reduced slightly more and a shade A20 nanohybrid composite (Beautifil II) was bonded on in an attempt to further improve the color (Figure 5). After the preparations were completed, digital photographs were taken with the appropriate foundation shade tabs. Although there was some improvement in the color noted, the preparation shade for tooth No. 8 was ND8, compared to ND1 for the other teeth (Figure 6). In addition to photographs of the prepared teeth, the additional information sent to the lab team included a preoperative series of photographs, a full-arch maxillary polyether impression (Impregum™ Soft, 3M, www.3m.com), a vinyl polysiloxane (VPS) bite registration (Vanilla Bite, DenMat, www.denmat.com), a stick bite, an opposing-arch mandibular model, the length of the centrals, a digital photographic series, an impression of the provisionals (fabricated with Tuff-Temp™ Plus Shade B1, Pulpdent, www.pulpdent.com) (Figure 7), and a written prescription detailing the goals of treatment.

Laboratory Fabrication

The all-ceramic restorative material chosen for the case was IPS e.max Press (Ivoclar Vivadent, www.ivoclarvivadent.com). This very esthetic, high-strength ceramic consists of 70% by volume needle-like lithium-disilicate crystals embedded in a glassy matrix. The size of the crystals (about 3 µm to 6 µm) and the interwoven crystalline structure contribute to the strength of the material (400 MPa), which possesses a refractory index that can be controlled to vary the translucency or opacity created, depending on the clinical situation.⁵ Furthermore, the glassy matrix can be etched with hydrofluoric acid and silanated for adhesive bonding, increasing retention, and the physical properties of the ceramic while decreasing the risk of microleakage. IPS e.max Press is available in multiple ingot selections (including the new medium translucency [MT] ingots) with varying translucencies and opacities, and, because of its combination of high strength and excellent optical properties, it is ideal for veneers, thin veneers (0.3 mm), inlays, onlays, partial crowns, and full-contour crowns.^5,6 For this case, the ceramist chose the Impulse Value 3 ingot (now called the MT ingot), which has an intermediate translucency and produces optimal esthetics, especially when doing a cutback and layering technique. The final shade (selected by the patient) was 1M1, so the restorations were cut back and layered with OE1 and BL incisal powders. After completion, they were placed on dies corresponding to the shade of the prepared teeth; ND1 for teeth Nos. 5 through 7 and 9 through 12; and ND8 for tooth No. 8, which still exhibited some show-through of the underlying darker color. Due to this minor show-through that persisted on the shaded die, the ceramist elected to fabricate a zirconia coping (for its masking ability) that had a foundation shade of ND1. It was then layered with the same layering ceramic as the other lithium-disilicate restorations (Figure 8 and Figure 9).

Delivery of the Final Restorations

At the cementation appointment, after the provisionals were removed, the teeth were cleaned with hydrogen peroxide and rinsed thoroughly. Next, the restorations were tried in using both water and a clear try-in paste. The fit was excellent, and an acceptable shade match was noted between the layered zirconia crown and the other more translucent restorations. The teeth were then isolated with a rubber dam in preparation for the adhesive bonding procedure (Figure 10). The intaglio surfaces of the definitive restorations were cleaned for 20 seconds with a universal cleaning paste (Ivoclean, Ivoclar Vivadent), rinsed, and air-dried. Next, silane (Bis-Silane™ Porcelain Primer, BISCO Dental, www.bisco.com) was applied to the internal surfaces for 60 seconds, and then dried with water- and oil-free air. After applying a 2% chlorhexidine gluconate solution (Cavity Cleanser™, Bisco) to the prepared tooth surfaces, the isolated teeth were then etched for 15 seconds with a 35% phosphoric-acid gel (Select HV® Etch, BISCO), rinsed, and lightly air-dried. Next, after applying two coats of a universal adhesive (All-Bond Universal, Bisco) for 10 seconds each, the teeth were dried to evaporate the solvent and then light-cured. This is an important step because this universal adhesive is hydrophilic when applying it, but becomes hydrophobic after light-curing. (Note: Because the film thickness of the adhesive is less than 10 µm, the cured adhesive will not interfere with the seat of an indirect restoration.) All of the restorations were seated simultaneously using the eCEMENT™ (Bisco) kit that contains both light- and dual-cure resin cement options. The restorations on teeth Nos. 5 through 7 and 9 through 12 were seated with the translucent light-cured cement and, after the excess cement was cleaned off with cotton rolls and brushes, the restorations were tacked at the gingival margin (Figure 11). Then, the crown on tooth No. 8 was seated using the dual-cure resin, chosen so that complete polymerization under the zirconia core would be ensured. After flossing interproximally to remove excess cement, all of the restorations were light-cured (Bluephase® 20i, Ivoclar Vivadent) for 40 seconds from both the facial and lingual directions. The rubber dam was removed and minor occlusal adjustments made, followed by a final polish with rubber points (Ceramisté, Shofu).

The final result achieved the goals of treatment, and importantly, the satisfaction and appreciation of the patient. In addition, successfully treating a challenging esthetic case was extremely rewarding for the entire dental and dental laboratory team (Figures 12 through 15).

Conclusion

It is well known that more translucent restorative materials are ideal for mimicking the desirable characteristics of natural teeth and achieving excellent esthetic results when the underlying color is ideal or within acceptable limits. However, translucent restorative materials lack the ability to disguise or mask dark underlying substructures and foundation shades such as metal post-and-cores, titanium implant abutments, and tetracycline- or endodontically-treated discolored teeth. In order to achieve acceptable esthetic results in such cases, it is important to improve the underlying color of the tooth, mask the discoloration with the restoration, or both. The case report presented herein demonstrates the use of composite resin to improve the color of an endodontically-treated, severely discolored tooth, along with a layered zirconia restoration to further mask any undesirable shade and to achieve a shade match to the surrounding ceramic restorations.

Acknowledgment

The author wishes to thank ceramist Gary Vaughn, CDT (Corr Dental Laboratory in Roseville, California), for the excellent laboratory work done for this patient.

Disclosure

The author has no relevant financial relationships to disclose.

About the Author

Thomas E. Dudney, DMD
Private Practice
Alabaster, Alabama