Prevention and Management of Discolored Tooth Preparations

One possible complication when performing esthetic dentistry is the staining of a tooth preparation underneath a ceramic crown. The discoloration of the tooth may appear through the ceramic restoration, leading to an unfavorable esthetic outcome. Two possible causes of tooth discoloration include discoloration of a tooth preparation following endodontic treatment or following contamination with ferric sulfate hemostatic agent.

Tooth discoloration following endodontic treatment

The various materials used during the course of endodontic treatment, such as intra-canal irrigants, medicaments, endodontic fillings materials and cements, all possess the ability to stain the tooth structure under the right conditions. Sodium hypochlorite, a very commonly used irrigant has been shown to cause staining when used with other irrigating agents, most notably chlorhexidine (CHX). When used with CHX (gel or solution), the interaction results in the formation of a dark brown precipitate, which stains dentin and is also carcinogenic.^1,2 Sodium hypochlorite also reacts with MTAD, which is a mixture of a tetracycline, an acid (commonly citric acid), and a detergent (causing brown and red-purple to yellow stains) or citric acid (causing white precipitate).¹ When EDTA is mixed with sodium hypochlorite there is no precipitate, however, when it is mixed with CHX, a cloudy blue hue is formed (Fig. 1). Various measures can be taken to prevent staining, such as incorporating a thorough rinse between each agent. Saline, sterile water, absolute alcohol, and sodium ascorbate have all been suggested as potential rinsing agents.¹

Fig. 1

Intra-canal medicaments lead to staining if left in the pulp chamber for longer than required. Leadermix and triple antibiotic paste, the two most used medicaments, both contain tetracyclines and cause grey-brown and blueish-grey stains respectively.¹ Both grey and white MTA have been shown to stain the tooth structure grey if they contain bismuth oxide as their radiopacifier. However, there are some brands of MTA-based materials which have shown a lower incidence of staining, such as Biodentine (Septodont) and Endosequence Root Repair Material (Brasseler).³ Other medicaments that cause staining include formocresol and iodoform-based products.¹

Gutta-percha is the most often used core filling material and causes a light pink discoloration. Of the different cements used in root canals, most cause a grey (AH-26, Sealapex, Kerr pulp canal sealer) or orange-pink (Grossman zinc oxide and eugenol, Tubli-Seal, Roth’s 801) stain.¹ Use of metallic materials such as pins, posts, and amalgam in post-endodontic therapy can also cause staining. It’s important to note that all these intra-canal agents cause staining only if left in the pulp chamber or in any portion of the tooth coronal to the gingival margin. The best way to avoid staining is to ensure that no material is left coronal to the root canals during treatment and immediate and thorough removal of them if it does.¹

The most commonly seen discoloration, however, is the one seen with improper access cavity preparation which leaves behind remnants of the pulp tissue, especially in the pulp horns. The red blood cells in this tissue break down into hemosiderin or hematin which release iron. This iron reacts with hydrogen sulfide to form ferric sulfide, which is a black precipitate and leads to grey discoloration of the tooth structure.¹

Staining caused by endodontic procedures may be treated with internal bleaching (Figs. 2-4) either prior tooth preparation, following tooth preparation, or in place of tooth preparation.

Fig. 2

Fig. 3

Fig. 4

Tooth discoloration following ferric sulfate hemostatic agent

Tooth discoloration may also occur following exposure to ferric sulfate containing hemostatic agent. The explanation for this discoloration is that dentinal tubules may be exposed by contact with acidic ferric sulfate or phosphoric acid. Ferric ions are then embedded in dentinal tubules from further exposure with the ferric sulfate hemostatic agent. The ferric ions are reduced to a black-colored, insoluble ferric sulfide following a reaction with anaerobic bacteria in saliva.^4,5 Clinically, this staining may occur during a crown preparation procedure if the dentin is etched with phosphoric acid prior to bonding a build-up. The tooth is then exposed to ferric sulfate hemostatic agent prior to taking an impression. Finally, the tooth comes into contact with anaerobic bacteria if there is microleakage underneath the temporary crown.

In order to further test this hypothesis, an experiment was performed in our laboratory in which extracted teeth were exposed to phosphoric acid, ferric sulfate hemostatic agent, and then saliva. After 5 days of storage, a thick black precipitate was formed on the tooth. Then several methods were tested to prevent the formation of the stain or remove the stain once it was formed.

In order to prevent the stain, alternative hemostatic agents may be used. In our experiment, an aluminum chloride hemostatic agent (Tissue Goo, Clinicians Choice) was used instead of ferric sulfate and no discoloration was formed. It is also possible to clean the tooth after exposure to ferric sulfate. In our study, teeth were rinsed with either a 2% chlorhexidine solution (Consepsis, Ultradent) or a 10% EDTA solution (Detail, Clinician’s Choice) for 30 seconds after exposure to ferric sulfate. No precipitate was formed on these teeth.

In order to remove the stain, the teeth may be either rinsed with sodium hypochlorite or hydrogen peroxide. These solutions will quickly remove all stain. It is also possible to perform intra-oral sandblasting of the tooth with alumina particles. In our study, the teeth were cleaned with these methods and then returned to saliva. For the teeth that were cleaned with sodium hypochlorite or hydrogen peroxide, a small amount of staining returned after several days in the saliva. No staining returned for the teeth that were sandblasted.

A patient presented for ceramic crowns on her central incisors. During the impression appointment, ferric sulfate hemostatic agent was applied to the tissue. Two weeks following the impression, the patient returned with a dark stain on her teeth that could be seen under her crowns. The provisional crowns were removed to reveal staining of her tooth preparations cervical to the build-up. The stain was removed by applying sodium hypochlorite for 1 minute. The permanent ceramic crowns were then delivered.

Fig. 5

Fig. 6

Fig. 7

Fig. 8

Restorative materials to minimize effects of tooth discoloration- Conclusion

If a tooth preparation is permanently discolored, its esthetic management is best accomplished through proper restorative material selection. The two common strategies for the management of the discolored preparation are to block out the discoloration on the tooth or block out the discoloration with the crown material.

Blocking out the discoloration on the tooth may be accomplished through the use of opaquers, which are light-cured resin-based materials. Examples include Clearfil ST Opaquer (Kuraray), Embrace Opaquer (Pulpdent), and Creative Color Opaquer (Cosmedent). Also there are pink shade opaquers which are high value and also add warmth.

The other option for blocking out discolored tooth preparation is to use crown material that will mask the underlying discoloration of the tooth. A study by Bacchi determined that a 1.8mm thick porcelain fused to zirconia restoration is more effective for blocking out discolored teeth (or implant abutments) than 1.8mm thick lithium disilicate or translucent (5Y) zirconia. The study also reported that the use of an opaque cement had very little effect on masking a discolored preparation.⁶

A study in our laboratory was conducted to examine the translucency parameter (Table 1) of several ceramic materials (lithium disilicate, 3Y zirconia and 4Y zirconia) at different thickness (0.5mm, 0.8mm, 1mm, 1.2mm, 1.5mm, 1.8mm, 2mm) in order to predict their ability to mask discolored tooth preparations (Fig. 9). The study determined that lithium disilicate at 1.5mm thickness had similar translucency as 4Y zirconia at 1.2mm thickness and 3Y zirconia at 1mm thickness. Clinically, this implies that a lithium disilicate restoration would need to be considerably thicker than a zirconia restoration in order to block a discolored tooth preparation.

Table 1

	Lithium disilicate	4Y zirconia	3Y zirconia
0.5mm	15.65	9.88	8.92
0.8mm	12.28	8.31	7.52
1mm	9.93	7.59	6.64
1.2mm	9.13	6.88	5.98
1.5mm	6.73	5.93	5.13
1.8mm	5.70	4.79	4.09
2mm	5.38	4.29	3.57

Fig. 9

Oral Health welcomes this original article.

Special thank you to the Alpha Omega Foundation for their generous contribution to this project.

References

1. Ahmed HM, Abbott PV. Discolouration potential of endodontic procedures and materials: a review. Int Endod J. 2012 Oct;45(10):883-97. doi: 10.1111/j.1365-2591.2012.02071.x. Epub 2012 May 23. PMID: 22621247.
2. Marchesan MA, Pasternak Júnior B, Afonso MM, Sousa-Neto MD, Paschoalato C. Chemical analysis of the flocculate formed by the association of sodium hypochlorite and chlorhexidine. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2007 May;103(5):e103-5. doi: 10.1016/j.tripleo.2006.11.008. Epub 2007 Feb 20. PMID: 17317234.
3. Mozynska J, Metlerski M, Lipski M, Nowicka A. Tooth Discoloration Induced by Different Calcium Silicate-based Cements: A Systematic Review of In Vitro Studies. J Endod. 2017 Oct;43(10):1593-1601. doi: 10.1016/j.joen.2017.04.002. Epub 2017 Aug 30. PMID: 28864217.
4. Reid JS, Beeley JA, MacDonald DG. Investigations into black extrinsic tooth stain. J Dent Res. 1977 Aug;56(8):895-9. doi: 10.1177/00220345770560081001. PMID: 270488.
5. Conrad HJ, Holtan JR. Internalized discoloration of dentin under porcelain crowns: a clinical report. J Prosthet Dent. 2009 Mar;101(3):153-7. doi: 10.1016/S0022-3913(09)00025-0. PMID: 1923156
6. Bacchi A, Boccardi S, Alessandretti R, Pereira GKR. Substrate masking ability of bilayer and monolithic ceramics used for complete crowns and the effect of association with an opaque resin-based luting agent. J Prosthodont Res. 2019 Jul;63(3):321-326. doi: 10.1016/j.jpor.2019.01.005. Epub 2019 Feb 10. PMID: 30755361.

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About the Authors

Bushra Nizami BDS, MS is a first year International Dentistry student at UAB School of Dentistry.

Hannah Bloom is an incoming dental student at UAB School of Dentistry.

Nate Lawson is the Director of the Division of Biomaterials and the Program Director of the Biomaterials Residency Program at UAB School of Dentistry.

Robert Le is a General and Cosmetic Dentist practicing in Folsom, California.

Dr Ronald Goldstein is a clinical professor of restorative sciences at the Dental College of Georgia, Augusta University.