—Patients with tooth hypersensitivity should not have their teeth bleached because of the risk of postoperative sensitivity.
—When bleaching nonvital teeth, root resorptions may occur. Since the teeth are prepared internally, crown fractures are also possible.
—No restorations should be bonded directly after bleaching because the bonding ability of the adhesive material is greatly reduced. A period of approximately two weeks should elapse before any resorations are bonded.
—The patient should be informed that the bleaching result will decrease with time and it may be necessary to do a supplementary bleaching (after approximately one year). This change in color has several causes (coffee, red wine, fruit juices, soft drinks, and other drinks with low pH-values, smoking, etc.). As long as these external factors are present, the teeth will become darker.
53 Chemistry of the bleaching process
When bleaching teeth, oxidation reactions take place. After a certain amount of bleaching time, the enamel surface is saturated with the bleaching agent. When this happens, the bleaching process must be stopped, because otherwise the enamel could be damaged.
(Adapted from Adept Report)
Despite these potential risks, bleaching of vital and nonvital teeth is the most conservative therapy available in dentistry.
Which Discolorations Can Be Bleached?
Tetracycline Discoloration
The first tetracycline compound was purified in 1948, and the first tetracycline-induced tooth discoloration was described in 1956. Only some of the tetracycline accumulates in the enamel, while a much larger proportion accumulates in dentin (Brown 1974). After light-induced oxidation, a red quinone compound forms (4-a, 12-a anhydro-4-oxo-4-dimethyl-amino-tetracycline). Different bleaching agents can reduce this dye.
Tetracycline discolorations can be brownish, grayish, or bluish. They usually occur bilaterally and can involve several teeth in both upper and lower jaws. If the anterior baby teeth are involved, the tetracycline discoloration was induced some time between the fourth month of pregnancy and the ninth month after birth. However, if the permanent front teeth are discolored, the tetracycline medication most likely occurred between the third month after birth up to the seventh year of age.
The strength of the discoloration depends on duration and quantity of the tetracycline application. The type of color change depends on the type of the tetracycline derivate. Gray-brown discolorations are due to Aureomycin (Haywood and Heymann 1994). Yellow discolorations are due to Ledermycin, Terramycin, or Achromycin (Bailey and Christen 1968). Yellowish evenly discolored teeth can be successfully bleached (Bevelander 1961).
54 Causes and therapy of tooth discoloration
The best results with bleaching are achieved with color changes caused by the aging process, light fluoroses, and tetracycline discolorations of Category 1. All other discolorations should be treated using restorative methods.
The three categories of tetracycline discolorations are:
Category 1:
Slight (yellow, brown, or gray) discolorations that extend evenly over the whole tooth. They can usually be removed after three to five bleaching treatments in-office or through a 4-week bleaching treatment at home.
Category 2:
A strong, but even discoloration that can normally be removed after five to seven in-office bleachings, or after four to six weeks of treatment with the home bleaching method.
Category 3:
Strong discolorations using horizontal strips. This requires veneers or even crowns.
Fluorosis
Dental fluorosis can be induced between the second trimester of pregnancy and the ninth year of age, i.e., during tooth development when fluoride uptake is in excess of 1 ppm in the drinking water. (The fluoride level of the drinking water should be checked before fluoride medication is prescribed.) The degree of tooth discoloration—which varies from slightly chalky to strong yellow-brown spots due to precipital accumulations (secondary) after the eruption of the teeth—correlates directly with the fluoride uptake. The discolorations are restricted to the enamel (true enamel formation defects or hypoplasia); they are usually found bilaterally and in both jaws.
Bleaching is only successful when the enamel discolorations are superficial. A combination of micro abrasion and bleaching (two to four bleaching treatments), followed by facets or reconstruction of the enamel with microfilled composite is the treatment of choice. Alternatively, veneers can be made.
White Spot Lesions
These discolorations are innate or acquired during enamel formation and result from incomplete mineralization, due to a trauma, high fluoride exposure, genetic disposition, or illness. Acquired white spots are incipient carious lesions caused by plaque. They are often found around orthodontic brackets. The cause of innate acquired white spots must be removed first. That means that good oral hygiene must be established and low bacteria (caries) activity must be achieved.
Color Changes Due to Aging
Teeth become darker with age. Thus, a youthful tooth color of, for example, A1, becomes A2, A3, and A4 with age. This is a natural process which is enhanced by the presence of certain components in spicy food, alcoholic beverages, cigarette smoke or tobacco. Color changes caused by aging are ideal for bleaching.
55 Types of discolorations
A Mild tetracycline discoloration (bleaching time: three months).
B Mild tetracycline discoloration.
C Strong tetracycline discoloration (bleaching time: six months).
D Fluorosis with brown color changes.
E White spot discolorations after orthodontic treatment.
F Nonvital tooth.
Courtesy of Van B. Hoywood
Bleaching Vital Teeth
Prerequisites and Pretreatment
Radiographs must be available and the question of tooth vitality must be clarified. Existing restorations must be tight to avoid H2O2 reaching the dentin and the proximity of the pulp.
Acid treatment: The enamel of single, strongly discolored teeth can be locally etched with phosphoric acid. This improves the penetration of the bleaching agent and accelerates and reinforces the bleaching process. A general etching of enamel is not recommended. The result can be a rough enamel surface which later changes color more quickly.
In principle, tooth color should be determined before each treatment. Many patients wish to have snow-white teeth. Those beyond A1 tooth colors are also marked as “Hollywood toilet white.” One should not strive for such a goal. A tooth color change of about two shades is more realistic. Usually it is possible to reduce a tooth color of A3.5 to A2. The bleaching treatment should not proceed after Al color has been achieved, because an uncontrolled, long bleaching treatment can damage the tooth structures.