Doing It White
Posted Nov 06, 2012 in Technical
The growing popularity of vital bleaching is creating new shade-matching challenges for the dental team because many patients are whitening their teeth to shades that are brighter and whiter than conventional shade guides. In addition to this expanded shade spectrum of uncommonly light shades, technicians have to contend with the unique optical qualities found in bleached dentition while working with a limited number of commercial shade tabs and restorative materials. (See Figures 1, 2 and 3.)
Bleaching presents a number of variables that can make accurate shade matching somewhat of a moving target:
Unpredictability of the reaction. Bleaching does not occur in a linear fashion. The amount of color change obtained in the initial applications is usually greater than in the subsequent ones and varies from patient to patient.
Patient behavior. If the patient continues bleaching after the final shade has been taken, his teeth will continue to lighten and the bleached teeth won't match the restoration.
Etiology of the discoloration. Stains caused by extrinsic organic pigments such as coffee, chocolate, red wine or tobacco are more readily bleached out than intrinsic discoloration such as tetracycline staining and fluorosis.1, 2 Some teeth will not respond to beaching, and can only be whitened with crowns and veneers. It is beneficial for any technician involved in the case planning process to understand the etiology of tooth discolorations, since this analysis will influence the treatment plan between a chemical whitening treatment and a restorative solution (see Figure 4).3
The rebound effect. Bleached teeth are usually brighter during treatment, and take up to three weeks to "rebound" to a more stable shade. This phenomenon is most pronounced in the first four to six days.
The relapse factor. In general, bleached teeth tend to slowly relapse toward their pre-whitened state, but this can be controlled by occasional re-treatments. However, if the patient continues tooth-staining diets or habits, this relapse factor is accelerated while the shade of the restoration remains unchanged.
Since all of these variables hinder the shade-matching process, there are some important guidelines that the dental team should follow when restoring a patient who has whitened his teeth. First, the final shade should be taken at least five days—and at best three weeks—after the last bleaching treatment, especially for single anterior restorations.
Secondly, the patient needs to realize the ramifications of continuous bleaching. For instance, many patients don't understand the relapse factor or the fact that bleaching agents only affect their natural dentition, not their restorations. This should be explained to the patient so he can complete his bleaching treatment well before the restorative phase. To avoid remakes, it's prudent to have the patient sign a custom shade form approving the shade selection and acknowledging that he has been informed about the effects of future bleaching.4
Because of the subjective perception of tooth colors, ideally the technician fabricating the restoration should take the shade. In addition, the final shade should be documented with photographs at the shade-taking appointment. Use a high quality 35mm or digital camera and the closest commercial and/or custom-made shade guides.
There are a limited number of commercial shade guides and shade ranges of the restorative materials that can mimic the unnaturally low chroma and high value of bleached teeth. Therefore, the technician needs a complete armamentarium of shade-taking tools, including:
Commercial shade guides. Several manufacturers have developed a limited number of bleached shade tabs, including Ivoclar Vivadent's "Bleached Shades" 010 through 040, Dentsply Ceramco®'s A-0 and B-0; and Vident's OM-1 through 0M-3. These tabs are higher in value and/or lower in chroma than any shade tab in the industry-standard Vita-Lumin® or Vita Classic® shade guides. However, wider ranges of these bright shade guides and restorative materials are still needed (see Figure 5).
-Fired tabs of all the different incisal porcelains at the technician's disposal, especially the lightest ones.
-1.0-mm-thick tabs of pressed-ceramic ingots, also in the lighter shades.
-Cured tabs of composite resins used in the laboratory, including the lightest dentin and enamel shades. These custom tabs are used to complement a shade selection or alone if no pre-fabricated shade tab matches closely enough.
The technician should examine the existing teeth or photographs to determine the chroma and translucency of the different layers and their effect on the overall value of the shade. For instance, teeth with translucent enamel will require a totally different ceramic buildup than those with bright, milky enamel, even if they both match the same shade tab. Since value is the most critical and elusive dimension of dental color and is greatly affected by dental bleaching, the precise control of brightness and opacity of the layering is of paramount importance to an acceptable shade match.
If the dentist or technician foresee unusual difficulties with a particular case, they should consider the fabrication of a sample restoration for color purposes only. For example, if the patient needs an eight-unit bridge, the technician can fabricate a single unit to check the color. The dentist can try it in, take photos, suggest any needed modifications and return the sample to the laboratory. The time and expense involved are well worth it because the dental team can avoid misunderstandings and costly remakes. For single anterior teeth, the technician should always consider presenting the restoration to the dentist and the patient as a sample until it is accepted (see Figure 6).
When appropriate, it is beneficial to treat all teeth in the esthetic zone so as to displace the shade-match distally. For example, the technician can greatly simplify a difficult matching situation by recommending that the treatment plan of six maxillary anterior veneers be augmented to include the bicuspids. An imperfect match between the second bicuspids and the first molars will be less objectionable than one between the canines and bicuspids (see Figures 7 and 8).
Fabricating the "bright" restoration
Following are various techniques for matching different types of restorations to bleached dentition.
Porcelain veneers: Porcelain veneers are often prescribed to lighten severely discolored teeth in combination with bleaching.5 They can mask deep discolorations such as tetracycline staining that did not respond to bleaching and simultaneously change the length and form of the teeth. The bleaching process is a topical reaction that affects the outer layer of the tooth the most. Consequently, the treated enamel may have brightened considerably while the dentinal substrate exposed during preparation usually changes minimally. The case then becomes an exercise in matching extreme color changes to which all pertinent rules must be applied. A thicker porcelain veneer is indicated to obtain a certain degree of vitality, so a deeper preparation is usually necessary. Unless the teeth are in lingual version, a minimum of 0.7mm is required to allow for a masking layer, followed by the dentin and incisal powders (see Figure 9).
Ceramic crowns: For ceramic crowns, value and translucency are inversely related: as a general rule, an increase in translucency lowers the overall value, while an increase in opacity of the outer layers raises the value. Bright, translucent teeth need a brighter opaque or dentin. This can be accomplished by adding white and neutral modifiers to the opaque, opaceous dentin and dentin layers.
Bright teeth with a milky, less translucent enamel are best built with whiter opalescent enamels. Adding white modifiers to the enamel can lead to a chalky-looking restoration. If the enamel is very white, incorporate a thin layer of translucent porcelain between the body and incisal to add depth.
Multimedia cases: Matching a porcelain veneer and porcelain jacket to bleached teeth is a difficult scenario. The technician should first equalize the color of the underlying layers by baking an opaceous dentin on the jacket that is the same shade as the preparation of the veneer. Make sure the facial space for porcelain is the same as the thickness of the veneer. Then, build up the jacket with the same layering as the laminate. When matching a porcelain jacket to a ceramo-metal crown and bleached teeth, opaque the platinum foil or refractory die directly with the same opaque as the PFM.
Aluminous core jackets: The core of all Procera® crowns is the same shade—approximately equivalent to a Vita Classic® A2. When fabricating a restoration with a very light shade, the opaque layer required to mask the core can make the restoration appear lifeless if space is limited. To solve this problem, additional preparation space should be provided. Otherwise, consider a different type of restoration. For example, In-Ceram® copings are also alumina-based, comparable in strength and the cores can be fabricated in light shades.
Pressed ceramic jackets: Pressed-ceramic crowns cannot be opaqued internally so ingot selection is critical to control the influence of the color of the preparation. It is best to select an ingot that is a shade lighter and brighter than the desired shade (see Figure 10). Verify that the preparation will be masked by filling the crown with a composite resin of the same shade as the prepared tooth. If the resulting shade is too bright, it can be adjusted by staining the pressed ceramic before the incisal buildup.
Ceramo-metal crowns: If the technician is using a ceramic system that doesn't include bleached shade powders, use these techniques as a starting point:
The color of the opaque layer is critical to obtain bright shades that are lifelike. To noticeably lighten the opaque layer, opaque pastes and powders require a substantial amount of white opaque modifier. For example, to match an Ivoclar Chromascop® Bleached Shade 030, the technician might need to add one-part white modifier to one-part B-1 shade opaque paste.
To lighten a two-part opaque system consisting of a universal base paste and a shaded second layer, the ceramist needs to first lighten the base paste or it will greatly influence the overall shade. For example, to achieve a Ceramco A-0 shade, the base layer would consist of three-parts white opaque modifier to one-part universal base paste.
Some manufacturers provide porcelains intended to match "lighter-than-B1" bleached shades. But to achieve the intended shade, the technician may still find it necessary to modify these opaque powders or pastes as suggested above. Here more than ever, the use of opaceous dentin is vital to conceal the outline of the bright opaqued coping. Opaceous dentins and dentins can be modified with white, neutral and chroma modifiers.
At this point, the ceramist should carefully analyze the teeth being matched, try to determine the specific translucency of the different layers and add the modifiers accordingly. In general, white modifiers increase value and decrease chroma and translucency. Neutral modifiers maintain value while decreasing chroma. Chroma modifiers increase color saturation, and should be used sparingly. The right amount of all three can create very light shades that are translucent, not chalky.
Determining the optical qualities of the teeth's enamel is easier if pre-fired enamel tabs are used for shade taking, but the technician can also evaluate the optical properties using quality slides or photographs. For very light shades, even the lightest enamels—such as those labeled "Light", "57", or "White"—may be too gray against the bright dentin (see Figure 11). However, the use of white modifiers in the surface layers can give the crown a dead appearance. A better choice is to use the newer "opal" enamels, which tend to be bright yet still translucent.
Despite the multiple systems available, using indirect resin crowns for anterior restorations is still rare. The shades of the resins are pre-formulated and cannot be easily modified either extrinsically or by blending different pastes. In addition, the surface luster of the finished crowns is generally short-lived. Technicians should share these concerns with the clinician and recommend a ceramic alternative to ensure a more accurate shade match.
If the technician decides to use an indirect resin, material selection, layering and use of pre-cured resin tabs at the shade-taking appointment are critical. For complex shades, consider building the crown with a lighter dentin and a lighter enamel, keeping it slightly under-contoured. Then place colored resin modifiers as needed to adjust the chroma. Emphasize the lobes, translucency and incisal characterizations, cure and finish with enamel. If adjustments are necessary, the crown can be cut back and re-layered in the same way (see Figures 12A&B).
Experienced technicians are also keenly aware that virtually all resins change color between their uncured and cured states, and usually become slightly more translucent and lower in value once polymerized. Sample restorations and experimenting with layering techniques and shades can be very helpful for matching shade-critical resin restorations (for more information, see Nine Bright Ideas for Shade-Matching Success on page 14).
An expanded shade spectrum
Bleached shades are here to stay. With a better understanding, a little experimentation and a dash of ingenuity, technicians can expand their skills to effectively address the expanded prosthetic shade spectrum created by vital bleaching. By working together with the clinical team and dental manufacturers, technicians can successfully address the new challenges of bleached shades and make these bright restorations another part of their artistic repertoire.
About the Author:Charles Moreno, CDT, MDT, is the owner of Excel Dental Studios in Encino, CA. He is an Accredited Member of the American Academy of Cosmetic Dentistry (AACD) and currently serves on the Board of Directors of the AACD. Moreno is on the editorial review board of several dental publications and also teaches and lectures on esthetic dentistry, dental photography and laboratory technology. He can be reached for comment at firstname.lastname@example.org
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