0099-2399/92/1806-0290/$03.00/0 JOURNAL OF ENDODONTICS Copyright © 1992 by The American Association of Endodontists

Printed in U.S.A. VOL. 18, NO. 6, JUNE 1992

Effect of Bleaching Agents on Inorganic Components of Human Dentin and Cementum Ilan Rotstein, CD, Zachi Lehr, and Itzhak Gedalia, PhD

Hydrogen peroxide used for bleaching has occasionally been associated with the development of external root resorption (2-9). This pathological condition was reported in clinical cases (2-7) as well as in experimental animal studies (8, 9). The exact mechanism of bleaching-induced root resorption has not been fully established. It has been suggested that the pathogenic mechanism involves diffusion of the hydrogen peroxide through the radicular dentin (2, 4, 10, 11). Cementum defects, mainly at the cementoenamel junction, significantly increase the radicular penetration of hydrogen peroxide (11). The defects may occur either physiologically (12) or as a result of pathological conditions affecting the integrity of the cementum layer (13, 14). Another hypothesis suggests that bleaching agents cause denaturation of the dentin which may then act as a foreign body and be susceptible to resorption (3). Data concerning the side effects of bleaching on the tooth structures is rather limited. It has been demonstrated that 35% hydrogen peroxide may cause morphological and structural changes in both dentin and enamel (15, 16). The changes are time dependent and affected by pretreatment with acid etchants. However, the exact chemical changes in the hard dental tissues caused by the different bleaching materials remain unestablished. The purpose of this study was to examine the effect of different bleaching agents on the solubility and percentage of inorganic components of human dentin and cementum.

The effect of bleaching agents on the inorganic composition of human dentin and cementum was examined. Intact teeth were crushed, pulverized, and separated to dentin and cementum powders. The pulverized tissues were exposed to treatments with 30% H202, 3% H202, 2% sodium perborate in 30% H202, 2% sodium perborate in 3% H202, and 2% sodium perborate in bidistilled water for periods of 15 rain and 1, 24, and 72 h. The degree of dissolution and the percentage of inorganic material for both dentin and cementum were measured. Thirty percent H202 and 2% sodium perborate in 30% H202 treatments significantly increased the solubility of dentin and cementum. The degree of dissolutions and the percentage of inorganic material remaining in the undissolved dentin and cementum increased with time progression. The greatest increase occurred with 30% H202 and 2% sodium perborate in 30% H202 after 24- and 72-h treatments. It is concluded that 30% hydrogen peroxide treatment may cause alteration in the chemical structure of the dentin and cementum making them more susceptible to degradation.

Discoloration of permanent anterior teeth is an esthetic problem. It may result from intracoronal hemorrhage, endodontic treatment, systemic diseases, or from the use of restorative materials or drugs (1). Improving the appearance of discolored teeth by bleaching may offer advantages over full coverage if a satisfactory shade can be achieved. The most commonly used intracoronal oxidizing bleaching agents are 30 to 35% aqueous solutions of hydrogen peroxide and sodium perborate. These materials have been used either separately or in combination. The most popular bleaching techniques include the thermocatalytic method and walking bleach. In the thermocatalytic technique a heat source is used to activate the bleaching agent placed in the pulp chamber to release nascent oxygen. In the walking bleach technique a paste of sodium perborate, mixed with either hydrogen peroxide or with another solvent, is placed in the pulp chamber and sealed for 3 to 7 days. Such techniques are repeated until a satisfactory tooth shade is obtained.

MATERIALS AND METHODS

Material Preparation Intact permanent teeth were collected from patients attending the oral surgery department. After mechanical cleaning, the teeth were crushed and pulverized to a powder of 100 mesh. The separation of the dentin and cementum was carried out according to the method of Brekhus and Amstrong (17) which is based on differences in the specific gravity. Thirty-milligram aliquots, each of pulverized dentin and cementum, were immersed in 10 ml of either 30% H202 (Hadassah Pharmaceutics, Jerusalem, Israel), 3% HzO2, 2% sodium perborate (BDH Chemicals Ltd., Poole, England) in 30% H_~O2, 2% sodium perborate in 3% H202, 2% sodium perborate in bidistilled water, or bidistilled water (control). The 2% concentration of sodium perborate was used since it 290

Effect of Bleaching A g e n t

Vol. 18, No. 6, June 1 9 9 2

following treatment with either 30% H202 or 2% sodium perborate in 30% H202 for the duration of the experiment. Cementum treated with 2% sodium perborate in 30% H202 was more soluble than dentin from the initial time period (15 min) until completion of the experiment (72 h). The higher solubility of this cementum treated was not statistically significant from the cementum treated with 30% Ha0: alone. The difference in solubility of cementum and dentin treated with 30% H202 and 2% sodium perborate in 30% H202 was significantly higher (p < 0.05) than that treated with 3% H202, 2% sodium perborate in 3% H202, 2% sodium perborate in bidistilled water, or bidistilled water alone (control). The results of the measurement of the percentage of inorganic material of dentin and cementum following treatment with the different bleaching agents are summarized in Tables I and 2. The initial percentage of inorganic material of the cementum was lower than that of the dentin. An increase in the percentage of inorganic material remaining after treatment took place for both dentin and cementum with time progression for each experimental treatment. The greatest increase occurred with 30% H20_, and 2% sodium perborate in 30% H202 after 24- and 72-h treatments. The increase in the percentage of inorganic material for each bleaching treatment and duration was greater in the cementum. However, after 24- and 72-h treatment with 30% H202 or 2% sodium perborate in 30% H202 no difference in the percentage of inorganic material between the dentin and cementum was evident. No change in the percentage of inorganic material took place in the control samples.

enabled a complete dissolution of the crystals in each of the solvents used. The exposure of the dentin and cementum powders to each of the bleaching agents was performed for either 15 rain, 1 h, 24 h, or 72 h at room temperature. These time periods were selected to simulate clinical conditions.

Determination of Solubility The degree of dissolution of the dentin and cementum powders was determined by analysis of calcium in the filtrates of the bleaching solution to which the dentin and cementum were exposed. This analysis was carried out using an atomic absorption spectrophotometer (Perkin-Elmer 403; Perkin-E1mer Corp., Norwalk, CT).

Determination of Inorganic Material (Residual Ash) Ashing of the inorganic material following each treatment was carried out with 5 mg of each tissue in a muffle oven at 600°C for 12 h. The samples were weighed before and after the ashing process in order to determine the percentage of inorganic material. Statistical analysis was carried out using the Mann-Whitney U test. RESULTS The results of the solubility measurements of dentin and cementum are shown in Figs. 1 and 2. The increased solubility of cementum and dentin during the entire experimental period with 3% H202 was not significantly higher than that of either 2% sodium perborate in 3% H202, 2% sodium perborate in bidistilled water, or the control. The solubility of both dentin and cementum increased in a similar fashion

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DISCUSSION From our results it is evident that the bleaching agents caused a reduction of the organic components of both dentin and cementum, thus increasing the percentage of inorganic material. The greatest increases took place for the 30% H202

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Effect of bleaching agents on inorganic components of human dentin and cementum.

The effect of bleaching agents on the inorganic composition of human dentin and cementum was examined. Intact teeth were crushed, pulverized, and sepa...
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