The Essence of the Internal Staining Technique: Application and Fabrication

Naoto Yuasa, RDT1

ne of the most difficult tasks in dentistry is to ENAMEL AND DENTIN reproduce the esthetic characteristics of natu- Oral teeth using ceramic restorations. The in- Natural tooth color depends on two dental structures: troduction of the internal live staining technique in the enamel and dentin. Enamel is both highly translucent 1980s revolutionized the fabrication of highly esthetic and opalescent as a result of the hydroxyapatite crys- ceramic restorations due to its ease of use and reliabil- tals that compose enamel rods. These features must ity. This article discusses the application of the internal be reproduced to create natural-looking restorations. live staining technique in anterior ceramic crown res- Opalescence leads to the appearance of blue or or- torations. 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- 1Otani Dental Clinic, Tokyo, Japan. ing in translucency and high value. The light reflection within dentin varies drastically in different areas. The Correspondence to: Naoto Yuasa, Otani Dental Clinic, 2-3-2-1F apex is highly translucent compared to the coronal Shitaya, Taito-Ku, Tokyo, Japan 110-0004. Email: naotoyuasa0114@ gmail.com dentin, which yields high light reflection. Published originally in the Japanese QDT (2009;34[November]: The precise anatomical structure of the tooth de- 133–151). pends on the combination of enamel and dentin. The

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1a 1b

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.

gingival area has a thin enamel layer and thick dentin For this reason, ceramic modifiers or internal staining layer; therefore, the shade is primarily generated by techniques become important tools to build natural the dentin. In other words, the gingival third is the best characteristics in a porcelain restoration. area to view the shade of dentin by itself. The middle Natural three-dimensional color reproduction can third has relatively thick enamel and dentin layers, be achieved using ceramic modifiers; however, these creating a well-blended shade. The incisal third has a are technique sensitive since they must be fired before thick enamel layer and a very thin or nonexistent den- the final shade is visible. It is very difficult to reproduce tin layer. Thus, this area shows a pure enamel color and the subtle and delicate colors of a natural tooth using translucency, except at the mamelons. only ceramic modifiers. It is important to understand this correlation be- Single central incisor crowns are the most challeng- tween the thicknesses of the enamel and dentin struc- ing restorations because there is no room for error dur- tures that build natural tooth color. When porcelain ing shade matching. For such procedures, the internal restorations are fabricated, porcelain layering must live staining technique is the method of choice. The mimic this relationship to appear truly natural. 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 INTERNAL STAINING be carried out with the understanding that internal live staining will be used to provide minor shade correc- During shade taking, commercial shade guides are tion. In other words, the porcelain should be layered to rarely able to match the natural tooth shade exactly. provide a proper base for internal live staining.

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2a 2b

2c 2d

3a 3b

4a 4b 4c

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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 5a 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- 5b 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. 6a 6b

6c 6d

DILUTION POWDER This procedure can be difficult depending on the liquid used to mix the stains (eg, IS liquid, Noritake) because Internal staining of ceramic restorations allows for bet- of powder shift during application and drying. Special ter shade matching and a more lifelike appearance. attention must be paid when using White, Mamelon The Noritake Internal Stain Kit (Noritake Dental Sup- Orange, or Incisal Blue stains. These stains are opaque ply, Osaka, Japan) was specially developed for this and have high color peak emission and thus can easily purpose, offering high color emission and color stabil- become uneven during application. ity even after firing. To produce a more natural result, The Noritake Internal Stain Kit has an interesting the staining layer must be thin and evenly distributed. porcelain dilution powder called Bright. When Bright

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7a 7b 7c

8a 8b

9 10

dilution powder is mixed with internal stains, the final celain mixing. Since the Bright dilution powder has a color becomes more vibrant and the mixed porcelain coefficient of thermal expansion similar to that of the more stable and easy to apply (Figs 5 and 6). This di- body porcelain, cracks should not be a problem even lution powder is used mainly for characterization of if a thicker layer is fired. In other words, the Bright dilu- mamelons, white bands, crack lines, dark zones, and tion powder makes it possible to control value not only opalescent blue. This powder also allows the techni- by modifying the stain value, but also by altering the cian to control the value (Figs 7 to 10). thickness of the powder layer. The consistency of the staining layer can be con- trolled by altering the amount of IS liquid during por-

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Fig 11 In some cases, the natural tooth possesses similar Fig 12 The natural teeth appear to have higher translu- shade layer construction as the shade guide. 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.

SELECTION OF BODY PORCELAIN can be used to create enamel cracks and mamelons. If the purpose of internal staining is to adjust the color of a What is the most important factor to match the color crown, a thick layer of opaque porcelain may be applied. of a porcelain restoration to the natural teeth? Color The degree of translucency and opacity of the porcelain consists of three elements: value, chroma, and hue. will change depending on the stain used. A thick layer The human eye is more sensitive to value than it is to of opaque stain applied on top of dentin porcelain will chroma and hue. For example, when a patient with affect the overall translucency. As the dentin porcelain one ceramic crown (eg, a maxillary central incisor) is becomes more opaque, light cannot be transmitted to observed from a distance, we might recognize differ- the inner layers, thus compromising the translucency. ences in value, but differences in hue and chroma will To avoid this problem, the internal stain should be mini- be more challenging to identify. Dentin is the primary mized or applied in different layers. determinant of a tooth’s value. This means that for a The primary criterion for selecting body porcelain ceramic crown, the primary determinant of value is the should be the highest value of the dentin. As previous- body porcelain. ly mentioned, the gingival region of the tooth offers The application of internal staining produces one of the best view of the dentin shade. However, healthy the following effects: gingival tissues reflect a reddish color onto the gingival third that may interfere with shade selection. Thus, the 1. Decrease in value, depending on the stain color, dentin shade must be observed at the middle-coronal type, and amount applied. (In some cases, the ap- portion of the gingival third. Dentin often presents the plication of a nontranslucent layer can increase the highest value at this region. Further, a whitish and rela- value.) tively high value can be observed for enamel at this 2. Increase in chroma (except when achromatic or clear location. Therefore, the coronal portion of the gingival stains are used). third should become the base area to determine the 3. Formation of an opaque layer. shade of the body porcelain. The highest value of the dentin in this area is then Stains with different translucencies are used to pro- matched with the closest body porcelain shade. Next, duce different dental characterizations. An opaque stain minor modifications or adjustments are performed

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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.

13

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. 14 15

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.

16 17

using the internal staining technique to produce the and a slightly reddish hue (pink-orange). In this situa- correct value, hue, and chroma. For example, if the tion, if A2 body porcelain was selected and hue and natural tooth shade is A3 (Vita Shade Guide, Vident, chroma adjustments were made with internal staining, Brea, CA, USA) in value, hue, and chroma, then A2 can the overall value may turn out lower than A3. Instead, be chosen for the body porcelain, followed by minor an NP1.5 (Noritake) or A1 shade can be used as a base adjustments using internal staining. Another example even though the value is low. Note that this concept is of how the body porcelain can be modified is when only applicable if the natural tooth matches the shade the natural tooth has a value close to A3, high chroma, guide (Figs 11 to 17).

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18a 18b 18c

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.

19a 19b

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

If the natural tooth dentin has a higher value than room for layering. This method allows for modification that of the porcelain shade guide (Figs 18 and 19), the of the value by adjusting the chroma via the quantity value of the restoration can be adjusted by selecting a of opaque body porcelain. Opaque body porcelain lower number of body porcelain, without changing the should be applied in thick layers, whereas the body composition of the layers. For this reason, if the dentin porcelain layer should be thin. Opaque body and body shade value is high, the body shade can be close to porcelain can be applied as a mixture in one layer or white, and then most of the color adjustment will be selectively applied in different layers (Figs 20 and 21). done with internal staining. Since the thickness of the opaque body porcelain When internal staining is used, translucent layers increases the value (compared to body porcelain), the built on one plane will become more translucent, which author builds opaque body porcelain with a relative- may result in metamerism. To avoid this, the structure ly high value, then makes adjustments using internal of porcelain layers needs to be reevaluated. The au- staining after firing. thor has found that the value should be adjusted us- Significant differences can be found between all- ing opaque body porcelain unless there is not enough ceramic and porcelain-fused-to-metal crowns in terms

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20a 20b

20c 20d

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.

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

21a 21b

of value. The challenge of fabricating metal-ceramic opaque body porcelain reflection needs to be con- crowns is adjusting the value that results from the re- trolled and adjusted. Any color adjustments must be flection of high-value opaque body porcelain. Con- performed on a case-by-case basis since so many fac- versely, all-ceramic restorations limit light reflection tors influence the final result, including the thickness because of the translucency of the coping; therefore, and type of body or opaque body porcelain, type of

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22a 22b 22c

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.

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.

23a 23b

23c 23d

coping, presence of masking, and value of the natural COLOR REFLECTION teeth and dentin. In some cases, the dentin value is lower than that of FROM GINGIVAL TISSUES the body porcelain shade guide (Fig 22). Dentin value There are two important factors to address while and translucency must be evaluated thoroughly before matching the porcelain crown shade to that of the selecting the base porcelain. Additionally, it is impor- natural tooth: (1) color reflection from abutment teeth, tant to understand the layer construction of porcelain and (2) color reflection from the gingiva. To better shade guides to properly build up the porcelain thick- evaluate these so-called environmental factors, an en- ness (Fig 23). vironmental mock-up must be fabricated and tried in.

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24a 24b 24c

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.

The use of mock-up abutments has been well ex- the tooth enamel had a higher translucency compared plored by other authors; therefore, this article will to that of the shade guide. Whitish characterizations discuss the color reflection from gingival tissues. This were observed all over the facial surface. This whitish color reflection can significantly influence the gingival characterization was consistent with horizontal growth. porcelain shade. At the gingival margins, the shade of The incisal enamel showed extremely high trans- any natural teeth will be influenced by the gingival red lucency and a bluish hue. High opal effect porcelain hue. Porcelain crowns will also be affected if a translu- would be needed to match the incisal enamel; unfor- cent porcelain coping is fabricated (Fig 24). tunately, there is no such porcelain on the market. It The factors that influence the gingival shade in- is practically impossible to match this kind of shade clude the gingival color, gingival transparency, gingival using only one porcelain color. architecture around the crown, abutment reduction, The incisal halo was clear with a high value. A per- finishing line placement (intrasulcular or at the gingival fect color match with porcelain is difficult because of level), anatomy of the gingival area around the crown, the differences in reflection ratio between enamel and translucency of the crown, and cement shade/translu- dentin. Therefore, a porcelain translucent mixture must cency. Of those many factors, the two most influential be selected and applied. are abutment reduction and translucency of the crown. It is important to consider the differences between If the margin of a porcelain crown is placed deeply the shade guide and a natural tooth. Natural tooth subgingival, the final crown shade will be affected by enamel has a high translucency compared to that of the gingival color reflection. The degree of influence the shade guide. The transparency of dentin is simi- depends on the thickness and translucency of the por- lar to the body color of the shade guide. At the same celain margin. Conversely, if the porcelain margin is time, there is a high value area compared to the shade located at the gingival level, the final crown shade will guide in the middle third of the dentin. Natural tooth not be affected by the gingival color reflection. This dentin has more color emission from the layer close to concept applies to both all-ceramic and porcelain- the enamel than from the inner dentin layer (which is fused-to-metal crowns. The shade of the gingival area comparable to the porcelain opaque layer). Therefore, of the porcelain crown can be better matched by add- lighter opaque body porcelain should be applied. Fol- ing the right amount of reddish color. 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 CASE REPORT is slightly lower than B3 and the hue is B with a slightly pink and orange hue. The base body porcelain should Figures 25 to 53 show a clinical case carried out us- have a higher value than B2, considering that B2 will ing the internal live staining technique. In this case, be achieved after internal staining.

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CASE REPORT

25a 25b 25c

25d 25e 25f

26 27

28 29

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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30 31

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.

32

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. 33a

33b 33c 33d

34 35

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36 37

38 39

40 41

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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42 43

44 45

46 47

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 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 48 Enamel (1:1) is applied to the interproximal area to cre- ate a bright and translucent crown outline.

49 50

51 52

Fig 51 The restoration following final shaping and polishing.

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

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53a 53b

Figs 53a to 53c Final result.

53c

CONCLUSIONS on tooth shade because light reflection influences col- or. Reproducing the anatomical features of the natural The internal live staining technique is easy to apply tooth is essential to providing esthetically harmonious and provides predictable results. The most important ceramic restorations. 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 ACKNOWLEDGMENTS tooth shade, reflection of gingival color, and color con- The author thanks Dr Tadao Kondo, Mr Tamotsu Sudo, and Mr Hi- trol with base porcelain prior to internal staining. Tooth toshi Aoshima (creator of the internal live staining technique) for surface texture and characterization have a great effect their guidance and instruction.

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