Results - Discussion - References.
The results of the six bleaching preparations are shown in Table 3. A comparison of the bleaching success rate of the groups at each interval is provided in Figures 1 and 2. Successful bleaching was accomplished when the treated tooth had gained its original or a lighter shade.
No colour changes were noted in the control teeth. No statistically significant differences occurred between the treatment groups. Significant differences occurred between the bleaching times (P < 0.01).
Table 3. The number of specimen by degree of shade change for each group at days 7, 14 and 21.Discussion.
Figure 1. Percentage of successfully bleached teeth in water groups at days 7, 14 and 21.
Figure 2. Percentage of successfully bleached teeth in HP groups at days 7, 14 and 21.
In this study, the effect of three different types of sodium perborate mixed with water or hydrogen peroxide on intracoronal bleaching was determined in artificially discoloured human teeth. This method was used because it simulates the most common cause of tooth discolouration. When the pulp is injured, blood extravasation from ruptured vessels may invade the pulp chamber and erythrocytes can penetrate the dentinal tubules. The erythrocytes undergo haemolysis and liberate haemoglobin, which releases iron. The iron is combined with hydrogen sulphide to form iron sulphide, a black compound that gives the tooth its dark discolouration (Grossman 1978).
Caution must be exercised when applying the results of this in vitro study to clinical conditions. The following factors should be taken into consideration; first, tooth discoloration caused by blood decomposition is usually easier to remove than that caused by other factors; the discolouration produced in this study was a result of pure erythrocytic decomposition. Clinically, necrotic pulp tissue and bacterial by-products may also contribute to the discolouration process. Therefore, the present results may not be applied to all types of tooth discolouration. Secondly, bleaching is more likely to be successful in recently stained teeth than in these with a long standing discolouration (Brown 1965). The discolouration produced in this study occurred over 18 days. In other studies using similar techniques this period was shorter and did not exceed 1 week (Ho & Goering 1989, Warren et al. 1990).
Although the three types of sodium perborate are available, the tetrahydrate type is used commonly in walking bleaching techniques (Rotstein et al. 1991). Weiger et al. (1994) also used three different types of sodium perborate and showed that, although the monohydrate had the highest content of active oxygen, there was no significant difference between them.
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