133 QDT 2011

One of the most difficult tasks in dentistry is to reproduce the esthetic characteristics of natu-ral teeth using ceramic restorations. The in-

troduction of the internal live staining technique in the 1980s revolutionized the fabrication of highly esthetic ceramic restorations due to its ease of use and reliabil-ity. This article discusses the application of the internal live staining technique in anterior ceramic crown res-torations.

ENAMEL AND DENTINNatural tooth color depends on two dental structures: enamel and dentin. Enamel is both highly translucent and opalescent as a result of the hydroxyapatite crys-tals that compose enamel rods. These features must be reproduced to create natural-looking restorations. Opalescence leads to the appearance of blue or or-ange enamel shades, depending on how the light in-teracts with the enamel.

Dentin comprises inorganic and organic compo-nents. The inorganic portion consists of hydroxyapatite crystals, which promote intense light scattering result-ing in translucency and high value. The light reflection within dentin varies drastically in different areas. The apex is highly translucent compared to the coronal dentin, which yields high light reflection.

The precise anatomical structure of the tooth de-pends on the combination of enamel and dentin. The

1Otani Dental Clinic, Tokyo, Japan.

Correspondence to: Naoto Yuasa, Otani Dental Clinic, 2-3-2-1F Shitaya, Taito-Ku, Tokyo, Japan 110-0004. Email: naotoyuasa0114@gmail.com

Published originally in the Japanese QDT (2009;34[November]:133–151).

The Essence of the Internal Staining Technique: Application and Fabrication

Naoto Yuasa, RDT1

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gingival area has a thin enamel layer and thick dentin layer; therefore, the shade is primarily generated by the dentin. In other words, the gingival third is the best area to view the shade of dentin by itself. The middle third has relatively thick enamel and dentin layers, creating a well-blended shade. The incisal third has a thick enamel layer and a very thin or nonexistent den-tin layer. Thus, this area shows a pure enamel color and translucency, except at the mamelons.

It is important to understand this correlation be-tween the thicknesses of the enamel and dentin struc-tures that build natural tooth color. When porcelain restorations are fabricated, porcelain layering must mimic this relationship to appear truly natural.

INTERNAL STAININGDuring shade taking, commercial shade guides are rarely able to match the natural tooth shade exactly.

For this reason, ceramic modifiers or internal staining techniques become important tools to build natural characteristics in a porcelain restoration.

Natural three-dimensional color reproduction can be achieved using ceramic modifiers; however, these are technique sensitive since they must be fired before the final shade is visible. It is very difficult to reproduce the subtle and delicate colors of a natural tooth using only ceramic modifiers.

Single central incisor crowns are the most challeng-ing restorations because there is no room for error dur-ing shade matching. For such procedures, the internal live staining technique is the method of choice. The use of specific ceramic modifiers or internal staining is dependent on the case (Figs 1 to 4). Enamel, mam-elon, and translucent porcelain are built to create a mix of translucency and value. The layering process should be carried out with the understanding that internal live staining will be used to provide minor shade correc-tion. In other words, the porcelain should be layered to provide a proper base for internal live staining.

Figs 1a and 1b Porcelain crown samples fabricated using internal live staining (Super porcelain AAA, Noritake Dental Supply).

Figs 2a to 2d With the proper base porcelain, the internal staining technique allows for accurate reproduction of the natural teeth.

Figs 3a and 3b Subtle color variations in multiple-teeth restorations can be achieved by controlling the shade of internal staining: (a) zirconia fixed dental prosthesis spanning the maxillary incisors; (b) porcelain-fused-to-metal prosthesis spanning the maxillary incisors and right canine.

Figs 4a to 4c Characterization of a posterior restoration using internal and external staining.

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DILUTION POWDERInternal staining of ceramic restorations allows for bet-ter shade matching and a more lifelike appearance. The Noritake Internal Stain Kit (Noritake Dental Sup-ply, Osaka, Japan) was specially developed for this purpose, offering high color emission and color stabil-ity even after firing. To produce a more natural result, the staining layer must be thin and evenly distributed.

This procedure can be difficult depending on the liquid used to mix the stains (eg, IS liquid, Noritake) because of powder shift during application and drying. Special attention must be paid when using White, Mamelon Orange, or Incisal Blue stains. These stains are opaque and have high color peak emission and thus can easily become uneven during application.

The Noritake Internal Stain Kit has an interesting porcelain dilution powder called Bright. When Bright

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Figs 5a and 5b White porcelain is diluted with Bright powder and applied. The luster porcelain is then applied and fired. Ratio between White porcelain and Bright powder (from left to right): White only, 1:2, 1:5, 1:10, 1:20, Bright only, no stain. (Samples fabricated with Noritake Cerabien ZR.)

Figs 6a to 6d Bright dilution powder can be added when complex char-acterizations such as mamelons or different translucencies are needed.

Figs 7a to 7c Mamelon character-ization. The color concentration is adjusted by adding Bright powder and a small amount of IS liquid into a Mamelon Orange + White base porcelain mixture. This will reproduce translucent mamelons. For more transparent mamelon characteriza-tion, Mamelon Orange 2 and slightly more Bright are thinly and carefully applied for staining.

Figs 8a and 8b A White + Bright mixture is thinly applied on the entire surface to produce enamel white-ness.

Fig 9 Fast drying can be performed in front of the furnace to provide uni-form staining without any running.

Fig 10 Final restoration.

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dilution powder is mixed with internal stains, the final color becomes more vibrant and the mixed porcelain more stable and easy to apply (Figs 5 and 6). This di-lution powder is used mainly for characterization of mamelons, white bands, crack lines, dark zones, and opalescent blue. This powder also allows the techni-cian to control the value (Figs 7 to 10).

The consistency of the staining layer can be con-trolled by altering the amount of IS liquid during por-

celain mixing. Since the Bright dilution powder has a coefficient of thermal expansion similar to that of the body porcelain, cracks should not be a problem even if a thicker layer is fired. In other words, the Bright dilu-tion powder makes it possible to control value not only by modifying the stain value, but also by altering the thickness of the powder layer.

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SELECTION OF BODY PORCELAINWhat is the most important factor to match the color of a porcelain restoration to the natural teeth? Color consists of three elements: value, chroma, and hue. The human eye is more sensitive to value than it is to chroma and hue. For example, when a patient with one ceramic crown (eg, a maxillary central incisor) is observed from a distance, we might recognize differ-ences in value, but differences in hue and chroma will be more challenging to identify. Dentin is the primary determinant of a tooth’s value. This means that for a ceramic crown, the primary determinant of value is the body porcelain.

The application of internal staining produces one of the following effects:

1. Decrease in value, depending on the stain color, type, and amount applied. (In some cases, the ap-plication of a nontranslucent layer can increase the value.)

2. Increase in chroma (except when achromatic or clear stains are used).

3. Formation of an opaque layer.

Stains with different translucencies are used to pro-duce different dental characterizations. An opaque stain

can be used to create enamel cracks and mamelons. If the purpose of internal staining is to adjust the color of a crown, a thick layer of opaque porcelain may be applied. The degree of translucency and opacity of the porcelain will change depending on the stain used. A thick layer of opaque stain applied on top of dentin porcelain will affect the overall translucency. As the dentin porcelain becomes more opaque, light cannot be transmitted to the inner layers, thus compromising the translucency. To avoid this problem, the internal stain should be mini-mized or applied in different layers.

The primary criterion for selecting body porcelain should be the highest value of the dentin. As previous-ly mentioned, the gingival region of the tooth offers the best view of the dentin shade. However, healthy gingival tissues reflect a reddish color onto the gingival third that may interfere with shade selection. Thus, the dentin shade must be observed at the middle-coronal portion of the gingival third. Dentin often presents the highest value at this region. Further, a whitish and rela-tively high value can be observed for enamel at this location. Therefore, the coronal portion of the gingival third should become the base area to determine the shade of the body porcelain.

The highest value of the dentin in this area is then matched with the closest body porcelain shade. Next, minor modifications or adjustments are performed

Fig 11 In some cases, the natural tooth possesses similar shade layer construction as the shade guide.

Fig 12 The natural teeth appear to have higher translu-cency and lower value compared to those of the shade tabs. However, only the enamel has high translucency. The cervical dentin has almost the same value as the shade guide’s body area.

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using the internal staining technique to produce the correct value, hue, and chroma. For example, if the natural tooth shade is A3 (Vita Shade Guide, Vident, Brea, CA, USA) in value, hue, and chroma, then A2 can be chosen for the body porcelain, followed by minor adjustments using internal staining. Another example of how the body porcelain can be modified is when the natural tooth has a value close to A3, high chroma,

and a slightly reddish hue (pink-orange). In this situa-tion, if A2 body porcelain was selected and hue and chroma adjustments were made with internal staining, the overall value may turn out lower than A3. Instead, an NP1.5 (Noritake) or A1 shade can be used as a base even though the value is low. Note that this concept is only applicable if the natural tooth matches the shade guide (Figs 11 to 17).

Fig 14 Dentin porcelain application. Base porcelain: NP1.5B + A2B. Internal stain: Salmon Pink + Mamelon Orange2 + A+.

Fig 15 After building up to the mid-enamel layer, enamel characterizations are applied with internal stain. The mamelon value appears to be lowered after applying a thicker layer of trans-parent porcelain.

Fig 16 Final porcelain-fused-to-metal restoration.

Fig 17 The restoration was fabricated with a construction of layers that can diffuse strong light reflection from the opaque layer.

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Fig 13 The natural tooth has a similar hue to the shade A group, with a similar pink-orange color and layer construc-tion as the shade tabs. Porcelain application in this case should not be complex if there is enough room for layering.

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If the natural tooth dentin has a higher value than that of the porcelain shade guide (Figs 18 and 19), the value of the restoration can be adjusted by selecting a lower number of body porcelain, without changing the composition of the layers. For this reason, if the dentin shade value is high, the body shade can be close to white, and then most of the color adjustment will be done with internal staining.

When internal staining is used, translucent layers built on one plane will become more translucent, which may result in metamerism. To avoid this, the structure of porcelain layers needs to be reevaluated. The au-thor has found that the value should be adjusted us-ing opaque body porcelain unless there is not enough

room for layering. This method allows for modification of the value by adjusting the chroma via the quantity of opaque body porcelain. Opaque body porcelain should be applied in thick layers, whereas the body porcelain layer should be thin. Opaque body and body porcelain can be applied as a mixture in one layer or selectively applied in different layers (Figs 20 and 21).

Since the thickness of the opaque body porcelain increases the value (compared to body porcelain), the author builds opaque body porcelain with a relative-ly high value, then makes adjustments using internal staining after firing.

Significant differences can be found between all-ceramic and porcelain-fused-to-metal crowns in terms

Figs 19a and 19b The natural tooth dentin has higher translucency than the shade guide’s body porcelain.

Figs 18a to 18c The dentin of the maxillary central incisor has high translucency and high value. Because the value and chroma are higher than those of the shade guide, the restoration’s dentin layer must be fabricated brighter. The canine has slightly higher translucency and value, whereas the maxillary lateral incisor has a similar shade to that of the shade guide.

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of value. The challenge of fabricating metal-ceramic crowns is adjusting the value that results from the re-flection of high-value opaque body porcelain. Con-versely, all-ceramic restorations limit light reflection because of the translucency of the coping; therefore,

opaque body porcelain reflection needs to be con-trolled and adjusted. Any color adjustments must be performed on a case-by-case basis since so many fac-tors influence the final result, including the thickness and type of body or opaque body porcelain, type of

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Figs 21a and 21b Harmony between the natural teeth and restoration was achieved by using a porcelain slightly more translucent than the shade guide.

Figs 20a to 20d After a zirconia coping was fabricated and the opaque body porcelain was fired, base color was adjusted with internal staining. Value control can be performed by building up a mixture of high-value opaque body and body porce-lain, followed by buildup of body porcelain as usual.

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coping, presence of masking, and value of the natural teeth and dentin.

In some cases, the dentin value is lower than that of the body porcelain shade guide (Fig 22). Dentin value and translucency must be evaluated thoroughly before selecting the base porcelain. Additionally, it is impor-tant to understand the layer construction of porcelain shade guides to properly build up the porcelain thick-ness (Fig 23).

COLOR REFLECTION FROM GINGIVAL TISSUES There are two important factors to address while matching the porcelain crown shade to that of the natural tooth: (1) color reflection from abutment teeth, and (2) color reflection from the gingiva. To better evaluate these so-called environmental factors, an en-vironmental mock-up must be fabricated and tried in.

Figs 23a to 23d If a study cast is made, a shade holding device can be fabricated. The device keeps the shade guide located on the same plane as the natural tooth. This ensures consistent photographic documentation and also eliminates the need for an assistant.

Figs 22a to 22c The natural tooth dentin has higher translucency and lower value than the shade guide. The most chal-lenging factor is controlling the color reflection from the opaque porcelain layer of the porcelain-fused-to-metal restoration.

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The use of mock-up abutments has been well ex-plored by other authors; therefore, this article will discuss the color reflection from gingival tissues. This color reflection can significantly influence the gingival porcelain shade. At the gingival margins, the shade of any natural teeth will be influenced by the gingival red hue. Porcelain crowns will also be affected if a translu-cent porcelain coping is fabricated (Fig 24).

The factors that influence the gingival shade in-clude the gingival color, gingival transparency, gingival architecture around the crown, abutment reduction, finishing line placement (intrasulcular or at the gingival level), anatomy of the gingival area around the crown, translucency of the crown, and cement shade/translu-cency. Of those many factors, the two most influential are abutment reduction and translucency of the crown.

If the margin of a porcelain crown is placed deeply subgingival, the final crown shade will be affected by the gingival color reflection. The degree of influence depends on the thickness and translucency of the por-celain margin. Conversely, if the porcelain margin is located at the gingival level, the final crown shade will not be affected by the gingival color reflection. This concept applies to both all-ceramic and porcelain-fused-to-metal crowns. The shade of the gingival area of the porcelain crown can be better matched by add-ing the right amount of reddish color.

CASE REPORTFigures 25 to 53 show a clinical case carried out us-ing the internal live staining technique. In this case,

the tooth enamel had a higher translucency compared to that of the shade guide. Whitish characterizations were observed all over the facial surface. This whitish characterization was consistent with horizontal growth.

The incisal enamel showed extremely high trans-lucency and a bluish hue. High opal effect porcelain would be needed to match the incisal enamel; unfor-tunately, there is no such porcelain on the market. It is practically impossible to match this kind of shade using only one porcelain color.

The incisal halo was clear with a high value. A per-fect color match with porcelain is difficult because of the differences in reflection ratio between enamel and dentin. Therefore, a porcelain translucent mixture must be selected and applied.

It is important to consider the differences between the shade guide and a natural tooth. Natural tooth enamel has a high translucency compared to that of the shade guide. The transparency of dentin is simi-lar to the body color of the shade guide. At the same time, there is a high value area compared to the shade guide in the middle third of the dentin. Natural tooth dentin has more color emission from the layer close to the enamel than from the inner dentin layer (which is comparable to the porcelain opaque layer). Therefore, lighter opaque body porcelain should be applied. Fol-lowing the usual body porcelain application, the over-all color must be adjusted with internal staining.

For the body porcelain selection, the cervical third of the dentin is close to B2 in value, while the chroma is slightly lower than B3 and the hue is B with a slightly pink and orange hue. The base body porcelain should have a higher value than B2, considering that B2 will be achieved after internal staining.

Figs 24a to 24c (a) In-Ceram Spinell coping (VITA Zahnfabrik, Bad Säckingen, Germany) crown on top of a colored abut-ment with water. (b) A variety of colored abutments. (c) Crown and waxed gingiva used to imitate the intraoral environment.

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CASE REPORT

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Figs 25a to 25f Intraoral views of the pretreatment situation.

Figs 26 and 27 Porcelain buildup on the unsectioned cast. AL1 glass-porcelain powder is applied and adjusted on the In-Ceram Alumina coping (VITA Zahnfabrik). A wash bake with M clear marginal porcelain is performed to stabilize Cerabien porcelain application. Since this case has a deep finishing line and enough space for porcelain application, coping color adjustment with internal staining is unnecessary.

Fig 28 OB White + OBA1 (1:1) is applied to the cervical half, while OBA1 is applied to the incisal half. It must be remembered that internal staining will affect the value.

Fig 29 After firing, translucency can be observed at the top of the coping. The translucency can be adjusted by inter-nal staining, reducing the need for opaque body porcelain.

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Figs 30 and 31 Color adjustment of the base of the crown with internal staining. Salmon Pink + Mamelon Orange 2 + B+ (3:1:3) is applied to the entire surface. Gray-tinted stain with Bright porcelain is applied to the incisal area of the coping. The value will be lowered when the body porcelain is fired. At that point, B2B + A1B (3:2) will be applied.

Fig 32 Porcelain cut back for dentin characterization.

Figs 33a to 33d Tx + LT0 + LT Natural (2:1:1) is applied to the palatal side to provide a more square shape.

Fig 34 The body porcelain is gradually thinned at the incisal region.

Fig 35 Mamelon 1 followed by E2 are applied selec-tively to adjust the value and translucency of the base porcelain, which is the foundation for mamelon charac-terization. E2 porcelain is gradually applied to provide slight translucency. Firing is then performed.

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Fig 36 Restoration after firing.

Fig 37 After minor adjustment firing, the built-up space should be checked carefully.

Fig 38 Surface treatment for internal staining with sandblasting is carried out, and the surface is wet with IS liquid. Dentin characterization with internal staining is completed. Firing shrinkage will occur; therefore, the restoration may need to be overbuilt to compensate for this effect. Cerabien has high firing shrinkage.

Fig 39 Salmon Pink + Mamelon Orange 2 + B+ (3:1:3) is applied to the entire surface to reproduce dentin shade. Mamelon Orange 2 + Bright is then applied on the mamelon to finish dentin characterization. It is important to make the mamelon extra long due to firing shrinkage.

Fig 40 Fabrication of the enamel middle layer provides a foundation for enamel characterization with internal stain-ing. Tx + LT0 is applied to the entire surface.

Fig 41 Tx is applied to the highly transparent areas of the incisal region and then fired.

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Fig 42 After firing, the space must be checked again, and then any adjustments can be performed.

Fig 43 After adjustment, there is space for one thin layer of internal staining and luster porcelain. The incisal area shows three-dimensional shrinkage.

Fig 44 The incisal area can be shaped from the palatal aspect to provide more transparency. Extra care must be taken not to lose mamelon characterization. The restoration is wet with IS liquid after sandblasting.

Fig 45 Enamel characterization. White + Bright porcelain is applied to the whitish zone. The incisal area of a natural tooth has high translucency with an opal effect. If the usual blue porcelain is applied to the palatal aspect, the incisal area will be less transparent due to the reflection of the staining surface. Thus, by applying external blue staining and a small amount of yellow porcelain diluted with Bright to the palatal aspect, the blue hue can finally show through to the facial aspect. This technique allows for translucency and the blue hue to coexist, better reproducing the natural tooth color.

Figs 46 and 47 White + Mamelon Orange 2 + Salmon Pink + Bright is applied to support the incisal halo, and White + Cervical 1 + Salmon Pink + Bright is applied and then fired once. If necessary, additional color adjustment can be performed and fired again.

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Fig 51 The restoration following final shaping and polishing.

Fig 52 Final restoration. External staining has been applied to reproduce surface characterization.

Fig 48 The author’s enamel sample tabs. Since normal sample tabs are too thick to analyze for transparency, 0.7-mm self-made tabs were fabricated. In the actual clinical cases, enamel porcelain can be built thinner; however, tabs thinner than 0.7 mm make it difficult to evaluate hue.

Fig 49 Enamel characterization phase. LT0, which has the highest transparency of the luster porcelains, is ap-plied to the entire surface.

Fig 50 E1 + Creamy Enamel (1:1) is applied to the mesial surface to provide white translucency. Incisal Au-reola + Mamelon 1 + Mamelon 2 (2:1:1) is applied for incisal halo characterization. Incisal Aureola + Creamy Enamel (1:1) is applied to the interproximal area to cre-ate a bright and translucent crown outline.

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CONCLUSIONSThe internal live staining technique is easy to apply and provides predictable results. The most important factors for success are an understanding of enamel and dentin layer structure as well as knowledge of por-celain color as influenced by internal staining. Other important factors to consider include the abutment tooth shade, reflection of gingival color, and color con-trol with base porcelain prior to internal staining. Tooth surface texture and characterization have a great effect

on tooth shade because light reflection influences col-or. Reproducing the anatomical features of the natural tooth is essential to providing esthetically harmonious ceramic restorations.

ACKNOWLEDGMENTSThe author thanks Dr Tadao Kondo, Mr Tamotsu Sudo, and Mr Hi-toshi Aoshima (creator of the internal live staining technique) for their guidance and instruction.

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Figs 53a to 53c Final result.

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