Intrinsic staining of teeth is caused by the presence of pigment within the enamel or dentine and can be divided into two types: pre- and post-eruptive intrinsic staining. [Addy & Moran, 1995]
Intrinsic staining due
Pre-eruptive staining occurs while the tooth is still developing. The most common cause is excessive fluoride intake during tooth development. Taking tetracycline medication can also cause the developing tooth to become discoloured, as this antibiotic interacts with the calcium hydroxyapatite crystals of the tooth enamel. [Nathoo, 1997]
Post-eruptive staining occurs once the tooth is fully developed. It may be caused by trauma to the tooth, resulting in hemorrhage of the dental pulp and the entry of blood into the dentinal tubules. Dental procedures may also lead to tooth discolouration as a result of incomplete cleaning or closure of the pulp chamber following root canal therapy. [Nathoo, 1997]
The fact that some extrinsic stains can become internalised through enamel defects or cracks or as a result of dentine becoming exposed is yet another cause of tooth discolouration. [Nathoo, 1997] Internalised discolouration is the incorporation of extrinsic stain within the tooth substance following dental development. It occurs in enamel defects and in the porous surface of exposed dentine. The routes by which pigments may become internalised are [Watts and Addy, 2000; Thylstrup and Ferjerskov, 1995]:
Intrinsic staining due
The basic tooth colour is changed by the very existence of the defects – influencing light transmission through dentine and enamel. Another mechanism causing changes in tooth colour is the penetration of extrinsic stains into the enamel because of increased enamel porosity, or because of the presence of enamel defects (fluorosis, enamel hypoplasia or hypocalcification, etc.). Alternatively, dentine defects such as dentinogenesis imperfecta or exposed dentine due to enamel loss can facilitate the penetration of chromagens into dentine directly, probably by the tubule system.
a. Tooth wear and gingival recession. Tooth wear is due to erosion, abrasion or attrition which causes progressive loss of enamel and dentine. Dentine colour becomes more apparent as the enamel becomes thinner, and the penetration of chromagens in the body of the tooth is increased. The internalisation of extrinsic stains can also be facilitated by loss of enamel or enamel cracks due to trauma. Gingival recession, exposing areas of unprotected dentine, also increases the potential for the uptake of chromagens into the tooth.
b. Restorative material. The colour of teeth can be affected by some of the materials used in restorative dentistry. For instance, dentine can be stained by pigments contained in eugenol and phenolic compounds used during root canal therapy. Darkening of the root dentine can be caused by polyantibiotic pastes used as root canal medications. The removal of a long-standing amalgam restoration often reveals a dark grey to black colour of dentine, shown in electromicroscopic studies to be caused by the migration of tin into the tubules.