Minimally Invasive Protocol to Maximize Aesthetics

INTRODUCTION
Patients’ simple desires for a better smile have taken clinicians, dental technicians, and material scientists on a complex search for restorative materials that have excellent optical and physical properties. While no one material is recommended for every prosthetic situation, certain new materials, such as lithium disilicate, can be used successfully in a broad array of applications.^1-3
Lithium disilicate was first introduced in 1998 by Ivoclar Vivadent. Since 2005, the strength of lithium disilicate was increased as a result of an improved fabrication protocol.⁴ This material is now available as either IPS e.max Press (Ivoclar Vivadent), which is heat pressed from an ingot; or IPS e.max CAD (Ivoclar Vivadent), which is processed from a preformed block via a CAD/CAM milling unit. Although both materials have nearly identical compositions, IPS e.max Press may provide a slight advantage over IPS e.max CAD in certain limited situations.⁵
The advantages of these materials compared to feldspathic porcelain or leucite-based all-ceramics include greater flexural strength, marginal integrity, and fracture resistance.^6,7 Additionally, pressed or CAD monolithic lithium disilicate restorations can be fabricated with the entire restoration composed of one material. In contrast, materials such as alumina or leucite are generally used for copings, which are then overlaid with porcelain, creating a laminated (layered) restoration. The junction between the porcelain and coping is an area that can be associated with reduced flexural strength and fracture resistance.⁸ Although the layered porcelain can fracture off at this interface without damaging the underlying coping, replacement of the entire restoration often becomes necessary.
Additionally, monolithic restorations require less aggressive tooth reduction when compared to layered ceramic systems, because there is no need to provide clearance for the both the thickness required by a coping along with an additional porcelain layer(s). This could directly impact postpreparation sensitivity, particularly if full-coverage restorations on vital teeth are required. If desired, monolithic restorations can be selectively “cut back” and then effect/tint porcelains can be added for aesthetic enhancement.
Many practitioners utilize monolithic or laminated (porcelain layered over a zirconia core) zirconia restorations for similar applications. Zirconia is touted due to its high strength.^9,10 Although zirconia has greater physical properties than lithium disilicate, there have been historical issues with porcelain fracturing off the zirconia core in layered restorations.^11,12 Monolithic zirconia restorations have also been shown to be less translucent than lithium disilicate, which could impact an aesthetic outcome.¹³
The following case demonstrates the use of lithium disilicate veneers to enhance a patient’s smile utilizing a minimally invasive preparation. Additionally, aesthetic considerations in regard to shade and ingot selection of the restorations will be discussed.

CASE REPORT
Diagnosis and Treatment Planning
A 27-year-old female presented with a chief complaint of, “I don’t like the way my smile looks.” Further discussion revealed that the patient was concerned with the appearance of teeth Nos. 7 and 10 (Figures 1 and 2). These teeth were peg-shaped and palatally inclined. In addition, open contacts were also noted on the mesial and distal surfaces of both teeth. No clinical or radiographic caries were present, and the patient exhibited good periodontal health.

Due to the palatal position of the crowns of these teeth, coupled with the open contacts, treatment was ideally suited for minimally-prepared veneers. Indeed, the patient presented with teeth that were already essentially “prepped.” It was decided that because of its excellent optical and physical properties, pressed lithium disilicate (IPS e.max Press) would be selected for the veneers.

Clinical Protocol
Local anesthesia was administered. Next, a No. 00 nonimpregnated retraction cord (Ultrapack [Ultradent Products]) was placed into the sulci of teeth Nos. 7 and 10. Tooth preparation consisted of placing a minimal gingival finish line (0.3 mm) to establish an emergence profile, and then roughening the facial surfaces to enhance bonding (Figure 3).^14,15
The preparation shade (stump shade) of the restoration was noted to be Vita A2.5, with a desired final shade outcome of A2. Due to the positioning of Nos. 7 and 10 and their underlying color, an A2 Low Translucency (LT) ingot was selected for these veneers.

Figure 2. Radiographs demonstrating open contacts between the lateral incisors and adjacent teeth.	Figure 3. Final preparations of teeth Nos. 7 and 10.
Figure 4. Facial view of temporary bis-acryl veneers.	Figure 5. Magnified view of solid model demonstrating minimal preparation on No. 7. Note the minimal (0.3 mm) yet definite gingival margin.

Figure 6. A self-etching ceramic primer (Interface [Apex Dental Materials]) and a multisituational bonding system (Surpass [Apex Dental Materials]) were used to prepare the teeth and veneers for bonding with a colorless resin cement (NX3 Clear [Kerr]).

Figure 8. Demonstration of the differing translucency among High Transluency, Low Translucency, Medium Opacity, and High Opacity ingots at identical thicknesses.

A polyether (Impregum/Permadyne [3M ESPE]) full-arch impression and vinyl polysiloxane bite registration (Blu-Mousse [Parkell]) were taken. The teeth were then temporized (Figure 4) with a bis-acryl-based material (Luxatemp Ultra [DMG America]) using a preformed stent made from a diagnostic wax-up. Photographs, models, final impressions, bite registration and a det;ailed prescription were sent to the dental laboratory team.
Ten days later, the temporaries were removed and the teeth were cleaned with medium grit plain pumice. Figure 5 demonstrates a magnified view of the minimal gingival finish line for the veneers on the solid working model. The restorations were treated with a self-etching ceramic primer (Interface [Apex Dental Materials]). A bonding agent (Surpass [Apex Dental Materials]) (Figure 6) was then applied to both the teeth and the veneers as per manufacturer’s instructions. A colorless light-cured resin cement (NX3 Clear [Kerr]) was utilized to bond the veneers into place. The final results are shown in Figure 7.

DISCUSSION
The physical advantages of lithium disilicate have been well documented. This case demonstrates the use of this material to provide an aesthetic result.
A critical aspect of this case involved the selection of the appropriate shade and type of ingot to be used. When selecting the appropriate ingot for pressed restorations, the shade of the preparation, aka the stump shade, must be considered. If the desired shade of the final restoration is close to the stump shade, then an LT or Value ingot could be chosen. If the restorations were only to replace tooth enamel, such as in the case of a thin veneer, a High Translucency (HT) or Opal ingot may be used. A more opacious ingot is required when a more dramatic color change is desired, especially where a darker stump shade is present. In these situations, a Medium Opacity (MO) or High Opacity (HO) ingot should be selected.
The Table provides recommendations for ingot selection, while Figure 8 demonstrates the differing translucencies of the HT, LT, MO, and HO ingots at an identical thickness.
In this case, an LT ingot was selected. This was due to the initial positioning of the teeth, the need to impart some increased chroma (intensity of color) to the restorations, and the fact that the stump shade was close to the final desired shade. An HT or Opal ingot would not have provided the appropriate chroma needed for the restorations, and might have caused the final restorations to appear too gray.^16,17

CLOSING Comments
The decision making and techniques utilized in this case demonstrate that lithium disilicate restorations, when indicated, can be used with aesthetic advantage. In addition, the functional and aesthetic advantages of this all-ceramic material have been well documented.

References

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3. Marquardt P, Strub JR. Survival rates of IPS Empress 2 all-ceramic crowns and fixed partial dentures: results of a 5-year prospective clinical study. Quintessence Int. 2006;37:253-259.
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7. Baig MR, Tan KB, Nicholls JI. Evaluation of the marginal fit of a zirconia ceramic computer-aided machined (CAM) crown system. J Prosthet Dent. 2010;104:216-227.
8. Kelly JR, Rungruanganunt P, Hunter B, et al. Development of a clinically validated bulk failure test for ceramic crowns. J Prosthet Dent. 2010;104:228-238.
9. Tinschert J, Natt G, Mautsch W, et al. Fracture resistance of lithium disilicate-, alumina-, and zirconia-based three-unit fixed partial dentures: a laboratory study. Int J Prosthodont. 2001;14:231-238.
10. Komine F, Blatz MB, Matsumura H. Current status of zirconia-based fixed restorations. J Oral Sci. 2010;52:531-539.
11. Guess PC, Zavanelli RA, Silva NR, et al. Monolithic CAD/CAM lithium disilicate versus veneered Y-TZP crowns: comparison of failure modes and reliability after fatigue. Int J Prosthodont. 2010;23:434-442.
12. Fischer J, Stawarczyk B, Sailer I, et al. Shear bond strength between veneering ceramics and ceria-stabilized zirconia/alumina. J Prosthet Dent. 2010;103:267-274.
13. Baldissara P, Llukacej A, Ciocca L, et al. Translucency of zirconia copings made with different CAD/CAM systems. J Prosthet Dent. 2010;104:6-12.
14. Perdigão J, Gomes G, Duarte S Jr, et al. Enamel bond strengths of pairs of adhesives from the same manufacturer. Oper Dent. 2005;30:492-499.
15. Loguercio AD, Moura SK, Pellizzaro A, et al. Durability of enamel bonding using two-step self-etch systems on ground and unground enamel. Oper Dent. 2008;33:79-88.
16. Jarad FD, Moss BW, Youngson CC, et al. The effect of enamel porcelain thickness on color and the ability of a shade guide to prescribe chroma. Dent Mater. 2007;23:454-460.
17. Corciolani G, Vichi A, Louca C, et al. Influence of layering thickness on the color parameters of a ceramic system. Dent Mater. 2010;26:737-742.

Dr. Volker graduated from the Columbia University School of Dental and Oral Surgery. He is the chairman of the New Dentist Committee and a member of the Continuing Education Committee for the New York State AGD. Additionally, he is a clinical attending at the Coler-Goldwater Specialty Hospital and Nursing Facility on Roosevelt Island, and is in private practice in New York. He can be reached at volkerdds@gmail.com.

Disclosure: Dr. Volker reports no disclosures.

Mr. Kim, a Certified Dental Technician, is the founder and chief ceramist at ACE Art Dental Lab in New York. He lectures to dentists and dental laboratory technicians on ceramic topics and other laboratory technologies. Mr. Kim can be reached at aceartdentallabny@gmail.com.

Disclosure: Mr. Kim reports no disclosures.