Discoloration of anterior teeth is a cosmetic problem that often requires corrective measures. Although restorative methods such as crowns and laminates are available, discoloration can often be successfully corrected by bleaching.
Bleaching procedures are more conservative than other restorative methods, relatively simple to perform, and less expensive. They can be carried out intracoronally in non-vital teeth or extracoronally in vital teeth. The successful outcome of bleaching depends mainly on the cause of the discoloration, correct diagnosis of the problem, and proper selection of bleaching technique.
CAUSES OF TOOTH DISCOLOURATION
Tooth discoloration occurs during or after enamel and dentin formation and may be due to patient-related (natural) or dentist-related (iatrogenic) causes. Patient-related discolorations may be superficial or incorporated into tooth structure. Dentist-related discolorations are usually preventable and should be avoided.
(1) Pulp Necrosis
Bacterial, mechanical or chemical irritation to the pulp may result in tissue necrosis and release of tissue disintegration by-products. These compounds may penetrate tubules and discolor the surrounding dentin. The degree of discoloration is directly related to how long, the pulp has been necrotic. The longer the discoloration compounds are present in the pulp chamber, the deeper is the penetration into the dentinal tubules and the greater is the discoloration.
(2) Intrapulpal Hemorrhage
Due to Intrapulpal hemorrhage followed by traumatic injury to a tooth, blood disintegration products, mainly irons sulfides, are introduced into the tubules and discolor the surrounding dentin. If the pulp becomes necrotic, the discoloration persists and usually becomes more severe with time. This type of discoloration is also time dependent.
(3) Dentin Hypercalcification
Excessive formation of irregular dentin in the pulp chamber and the canal walls may occur following certain traumatic injuries. In such cases a temporary disruption of blood supply occurs, followed by destruction of odontoblasts. These are replaced by undifferentiated mesenchymal cells that rapidly form irregular dentin on the walls of the pulp lumen. As a result the translucency of the crowns of such teeth gradually decreases and may give rise to a yellowish or yellow-brown discoloration.
In elderly patients, color changes in the crown occur physiologically as a result of excessive dentin apposition, thinning of the enamel, and optical changes. Food and beverages also have a cumulative discoloration effect, which becomes more pronounced in the elderly patient because of the inevitable cracking and other changes on the enamel surface of the tooth and in the underlying dentin.
(5) Tooth Formation Defects
(I) Developmental defects. Discoloration may result from developmental defects during enamel and dentin formation.
Defects in enamel formation: Defects in enamel formation are either hypocalcific or hypoplastic. Enamel hypo calcification is a distinct brownish or whitish area, commonly found on the facial aspect of affected crowns. The enamel is well formed with an intact surface. Both the whitish and the brownish spots are amenable to enamel micro-abrasion technique, with good results.
Enamel hypoplasia differs from hypocalcification in that the enamel is defective and porous. This condition may be hereditary (as in amelogenesis imperfecta) or a result of environmental factors. In the hereditary type, both deciduous and permanent dentition is involved. Defects caused by environmental factors, such as infections, tumors, or trauma involving one or several teeth, can be detected in both types of dentition. Presumably during enamel formation the matrix is altered and does not mineralize properly. The defective enamel is porous and readily discoloured by materials in the oral cavity.
Systemic conditions: Various systemic conditions may cause massive lysis of erythrocytes. If this occurs in the pulp at an early age, blood disintegration products may he incorporated into and discolor the forming dentin.
High fever during tooth formation may result in cbronologic hypoplasia, a temporary disruption in enamel formation that gives rise to a banding type of surface discoloration. Porphyria, a metabolic disease, may also cause red or brownish discoloration of deciduous and permanent teeth. Thalassemia and sickle cell anemia may cause intrinsic blue, brown, or green discolorations.
(ii) Drug-related defects. Administration or ingestion of certain drugs during the tooth formation period may cause severe discoloration both in enamel and dentin.
Tetracycline: A common cause of discoloration is tetracycline ingestion in children. Tooth shades can be yellow, yellow-brown, brown, dark gray or blue, depending on the type of tetracycline, the dosage, duration of intake, and the patient’s age at the time of administration. Discoloration is usually bilateral, affecting multiple teeth in both arches.
Endemic fluorosis: Ingestion of excessive amounts of fluoride during tooth formation may produce a defect in mineralized structures, particularly in the enamel matrix, causing hypoplasia. The severity and degree of subsequent staining generally depends on the degree of hypoplasia and is directly related to the amount of fluoride ingested during odontogenesis. The teeth are not discolored on eruption, but their surface is porous and will gradually absorb colored chemicals present in the oral cavity. Discoloration is usually bilateral, affecting multiple teeth in both arches. It presents as various degrees of mild, intermittent white spotting, chalky or opaque areas, yellow or brown discoloration, and in severe cases surface pitting of the enamel.
Discolourations caused by various dental materials or unsuitable operating techniques should be always avoided. Some of these conditions may be very difficult to correct later by bleaching.
(1) Endodontically Related
Pulp tissue remnants. Tissue remaining in the pulp chamber disintegrates gradually and may cause discolouration. Pulp horns must always be included in the access cavity to ensure removal of pulpal remnants and to prevent retention of sealer at a later stage.
Intracanal medicaments. Several intracanal medicaments are liable to cause internal staining of the dentin. Phenolics or iodoform-based medicaments sealed in the root canal and chamber are in direct contact with dentin, sometimes for long periods, allowing penetration and oxidization.
Obturating materials. Incomplete removal of obturating materials from the pulp chamber on completion of treatment often results in dark staining. This is prevented by removing all material to a level just below the gingival margin. Primary offenders are sealer remnants, mainly those containing metaffic components.
(2) Restoration Related
The modes of tooth discoloration by amalgams and composites restorations are different.
Amalgams. Amalgams have severe effects on dentin due to dark-colored metallic components that can turn the dentin dark gray.
Sometimes the dark appearance of the crown is due to the amalgam restoration, which can be seen through the tooth structure. In such cases replacement of the amalgam with an aesthetic restoration usually corrects the problem.
Composites. Micro leakage of composites causes staining. Open margins may allow chemicals to enter between the restoration and the tooth structure and discolor the underlying dentin. These conditions are generally corrected by replacing the old composite restoration with a new well- healed one.
Pins and posts. Metal pins and prefabricated posts are sometimes used to reinforce a composite restoration in the anterior dentition. Discolouration from inappropriately placed pins and posts is due to metal that can be seen through the composite or tooth structure. In such cases removal of the metal and replacement of the composite restoration are indicated.
Bleaching materials are either oxidizing or reducing agents, but the former are generally used. Many different preparations are available today. Aqueous solutions of various concentrations of hydrogen peroxide, sodium perborate, and carbamide peroxide are commonly used.
Various concentrations of hydrogen peroxide are available, but 30% to 35% stabilized aqueous solutions are the most common.
Sodium perborate is an oxidizing agent available in a powdered’ form or as various commercial preparations. When fresh, it contains about 95% perborate, corresponding to 9.9% of the available oxygen. Sodium perborate is stable when dry but in the presence of acid, warn air, or water decomposes to form sodium metaborate, hydrogen peroxide, and nascent oxygen.
Sodium perborate is more easily controlled and safer than concentrated hydrogen peroxide solutions. Therefore, sodium perborate should be the material of choice in most intracoronal bleaching procedures.
Carbamide peroxide, also known as urea hydrogen peroxide, is available in the concentration range of 3% to 15%. Popular commercial preparations contain about 10% carbamide peroxide with a mean pH of 5 to 6.5. Solutions of 10% carbanfide peroxide breakdown into urea, ammonia, carbon dioxide, and approximately 3.5% hydrogen peroxide.
Bleaching preparations containing carbamide peroxide usually also include glycerin or propylene glycol, sodium stannate, phosphoric or citric acid, and flavor additives.