Effect of hydrogen peroxide and sodium perborate on biomechanical properties of human dentin

Drug-induced disorders of teeth

It is essential that every health care professional who is involved with the prescription or recommendation of drugs be fully aware of any resultant disorders that may arise as a side-effect. A range of drugs can affect the teeth. In this review article, drugs that have the potential to induce changes in teeth have been classified as those leading to tooth discoloration (intrinsic and extrinsic), physical damage to tooth structure (enamel, dentin, and cementum), and alteration in tooth sensitivity.

Effect of direct peroxide bleach application to bovine dentin on flexural strength and modulus in vitro

OBJECTIVES

The objective of this study was to determine the effects of carbamide peroxide (CP) and hydrogen peroxide (HP) bleaching on the flexural strength (FS) and flexural modulus (FM) of dentin.

METHODS

2x2x20mm bovine dentin specimens were immersed in the bleaching agents to simulate overnight (10 or 15% CP, 6h daily, 2 weeks), exaggerated overnight (10% CP, 6h/day, 5 days/week, 2 months), daytime (6.5 or 7.5% HP, 1h daily, 3 weeks) and in-office (35% HP, 1h/day, 2 days/week, 3 weeks) treatment protocols. Distilled water (DW) and a placebo gel acted as control immersion materials. After immersion, the specimens were rinsed and stored in DW. Mechanical testing was performed 24h after the last treatment using an Instron Universal Testing Machine with a crosshead speed of 0.75 mm/min. The results were analyzed by ANOVA and Tukey's tests (p<0.05).

RESULTS

There were significant reductions in the FS and FM of dentin after 2-week and 2-month exposures to CP. There were no significant differences in the FS or the FM of the dentin among the HP treatment and control groups.

CONCLUSIONS

Direct in vitro application of CP bleaches caused significant decreases in dentin FS and FM. Similar decreases were not observed among the HP-treated dentin groups, which were exposed to shorter treatment times. Further research is needed to determine the effect of CP and HP on dentin in vivo.

Effect of bleaching agents on bonding to pulp chamber dentine

AIM

To determine the effect of intracoronal bleaching agents on adhesion of bonding agents to pulp chamber dentine.

METHODOLOGY

Forty extracted human maxillary anterior teeth were randomly divided into four groups of 10 teeth each. Bleaching agents were sealed in pulp chambers for 7 days, as in clinical use. Group 1 (control): distilled water, group 2: 35% hydrogen peroxide, group 3: sodium perborate mixed with water, and group 4: sodium perborate mixed with 35% hydrogen peroxide. Teeth were stored in saline at 37 degrees C for 7 days. After the bleaching agent was removed, teeth were leached in water for a further 7 days prior to bonding. The crown was cut vertically from mesial to distal and the labial pulp chamber dentine was prepared for bonding with Clearfil SE-Bond and filled with resin composite (Clearfil AP-X). The bonded specimens were kept moist at 37 degrees C for 24 h. Microtensile bond strengths were determined using a universal testing machine. Additional teeth were prepared using the same bleaching procedures to investigate the scanning electron microscopic appearance of the dentine surface.

RESULTS

Mean values (+/-SD) of microtensile bond strength for the experimental groups were: group 1: 5.29 +/- 2.21 MPa, group 2: 5.99 +/- 1.51 MPa, group 3: 9.17 +/- 1.65 MPa and group 4: 3.99 +/- 1.31 MPa. Dentine treated with sodium perborate in water (group 3) had significantly higher mean bond strength when compared with the other three groups (P < 0.05, Tukey's test). Mean bond strength was lowest when dentine was treated with sodium perborate plus hydrogen peroxide (group 4).

CONCLUSIONS

In terms of subsequent bond strength during restoration, sodium perborate mixed with distilled water appears to be the best intracoronal bleaching agent.

Effect of hydrogen peroxide on intertubular dentine

OBJECTIVES

To evaluate the effect of 30% hydrogen peroxide on the surface changes and nanomechanical properties of intertubular dentine.

METHODS

Five freshly extracted human premolars were sectioned and two specimens were obtained from each tooth. Atomic force microscopy (AFM) images of dentine were taken. Baseline hardness and Young's modulus of intertubular dentine were determined using nanoindentation testing and recorded. The specimens were then treated with either 0.5 ml of Hank's balanced salt solution (control group) or 30% hydrogen peroxide at 24 degrees C for 24 h. AFM imaging and determination of hardness and Young's modulus of intertubular dentine were then repeated. The images were compared and statistical analyses of hardness and Young's modulus were carried out using paired sample t-tests.

RESULTS

The AFM images showed recession of the intertubular dentine surface post-bleaching. For the control group, there was no significant change in hardness (p=0.124) and Young's modulus (p=0.438) of intertubular dentine. However, a significant decrease in hardness (p=0.002) and Young's modulus (p=0.001) of intertubular dentine was observed for the experimental group.

CONCLUSIONS

Exposure to 30% hydrogen peroxide for 24 h caused surface changes to intertubular dentine and significantly decreased the hardness and Young's modulus of intertubular dentine.

Effect of EDTA and citric acid solutions on the microhardness and the roughness of human root canal dentin

The purpose of this study was to evaluate the effect of citric acid and EDTA solutions on the microhardness and the roughness of human root canal dentin. Forty-five human teeth sectioned longitudinally were used. Specimens were randomly divided into three groups of 30 teeth each and were treated as follows: (a) one molar (19%) citric acid (C6H8O7) for 150 s followed by 5.25% NaOCl; (b) 17% EDTA for 150 s and rinsed with 5.25% NaOCl; (c) rinsed with distilled water and served as control. Three groups were then divided into two subgroups of 15 specimens each. The specimens, in first subgroup were subjected to Vicker's testing whereas the second subgroup underwent surface roughness testing. The results were analyzed using one-way ANOVA and Tukey tests. Significant differences were observed in microhardness among the test groups, citric acid group being the least hard (p 0.05). Also, citric acid significantly increased surface roughness.

Effect of pH Modified EDTA Solution to the Properties of Dentin

The purpose of this study was to evaluate the influence of smear layer removal with 3% EDTA solution (pH of 9.0) on the dentin in terms of the permeability of root canal disinfectants into the dentin, wetting by endodontic sealer, and adhesive strength of the sealer. Three types of disinfectant (formalin cresol, phenol, and calcium hydroxide) and 4 types of endodontic sealers (included eugenol, non-eugenol, polycarboxylic acid, and resin) were used. The contact angle between endodontic sealer solution and dentin decreased in the 3% EDTA group but increased in the 15% EDTA. The adhesive strength of endodontic sealer to dentin increased in the EDTA groups for all types of sealers. The permeability of root canal disinfectants increased to similar degrees in the 3% and the 15% EDTA groups. In comparing these properties, we propose that the 3% EDTA is more useful for clinical applications.

Effect of Sodium Hypochlorite on Dentin Microhardness

This study was designed to evaluate the effect on root dentin microhardness of 2.5% and 6% sodium hypochlorite solutions for various irrigation periods. Forty-two bovine roots were divided into seven groups. The control group was irrigated with saline. The experimental samples were continuously irrigated with 2.5% or 6% NaOCl for 5, 10, or 20 min. Microhardness was measured at depths of 500 mum, 1000 mum, and 1500 mum from the lumen. A decrease in microhardness was found at 500 mum between the control and samples irrigated with 6% NaOCl and 2.5% NaOCl (p = 0.352, p = 0.084 respectively) at all irrigation periods. There also was a significant difference in groups irrigated for 10 or 20 min (p = 0.001, p < 0.001 respectively). At all distances, the decrease in microhardness was more marked after irrigation with 6% NaOCl than 2.5% NaOCl.

Evaluation of the Effect of Endodontic Irrigation Solutions on the Microhardness and the Roughness of Root Canal Dentin

The purpose of this study was to evaluate the effect of 0.2% chlorhexidine gluconate on the microhardness and roughness of root canal dentin compared with widely used irrigation solutions. Ninety, mandibular, anterior teeth extracted for periodontal reasons were used. The crowns of the teeth were removed at the CEJ. The roots were separated longitudinally into two segments, embedded in acrylic resin, and polished. A total of 180 specimens were divided into 6 groups of 30 teeth at random according to the irrigation solution used: group 1: 5.25% NaOCl for 15 min; group 2: 2.5% NaOCl for 15 min; group 3: 3% H2O2 for 15 min; group 4: 17% EDTA for 15 min; group 5: 0.2% chlorhexidine gluconate for 15 min; and group 6: distilled water (control). Each group was then divided into 2 subgroups of 15 specimens: groups 1a, 2a, 3a, 4a, 5a, and 6a were submitted to Vickers microhardness indentation tests; groups 1b, 2b, 3b, 4b, 5b, and 6b were used for determination of the roughness of root dentin. The data were recorded as Vickers numbers and Ra, microm for roughness test. The results were analyzed statistically by using one-way ANOVA and Tukey tests. The results indicated that all the irrigation solutions except chlorhexidine significantly decreased microhardness of root canal dentin (p < 0.05); 3% H2O2 and 0.2% chlorhexidine gluconate had no effect on roughness of the root canal dentin (p > 0.05). Although there are many other factors for irrigation solution preference, according to the results of this study, 0.2% chlorhexidine gluconate seems to be an appropriate endodontic irrigation solutions because of its harmless effect on the microhardness and roughness of root canal dentin.

Effect of bleaching on restorative materials and restorations—a systematic review

OBJECTIVE

Internal and external bleaching procedures utilizing 3-35% hydrogen peroxide solutions or hydrogen peroxide releasing agents, such as carbamide peroxide or sodium perborate, can be used for whitening of teeth. The purpose of the review article was to summarize and discuss the available information concerning the effects of peroxide releasing bleaching agents on dental restorative materials and restorations.

SOURCES

Information from all original scientific full papers or reviews listed in PubMed or ISI Web of Science (search term: bleaching AND (composite OR amalgam OR glass ionomer OR compomer OR resin OR alloy) were included in the review.

DATA

Existing literature reveals that bleaching therapies may have a negative effect on physical properties, marginal integrity, enamel and dentin bond strength, and color of restorative materials as investigated in numerous in vitro studies. However, there are no reports in literature indicating that bleaching may exert a negative impact on existing restorations requiring renewal of the restorations under clinical conditions.

CONCLUSION

Bleaching may exert a negative influence on restorations and restorative materials. Advice is provided based on the current literature to minimize the impact of bleaching therapies on restorative materials and restorations.

Effect of different peroxide bleaching regimens and subsequent fluoridation on the hardness of human enamel and dentin

STATEMENT OF PROBLEM

Bleaching of teeth by "in-office" or "home" bleaching techniques are popular methods of whitening teeth. However, bleaching may reduce the surface hardness of enamel and dentin.

PURPOSE

The purpose of this study was to evaluate (1) the effect of different concentrations of 2 "in-office bleaching" and 2 "home bleaching" agents applied for different time periods on the hardness of enamel and dentin and (2) the effect of subsequent immersion in a low-concentration fluoride solution on the hardness of bleached enamel and dentin.

MATERIAL AND METHODS

The enamel and dentin of 12 extracted intact human molar teeth were sectioned lengthwise, ground, polished, embedded in acrylic resin and divided into 4 groups each (n=12). An area of approximately 5 x 5 mm of enamel and dentin tested for Knoop hardness number (KHN; kg/mm 2 ) at a load of 100 g for 20 seconds (baseline). The specimens were stored in distilled water for 1 hour and the microhardness testing repeated as a control group. The groups were bleached as follows: Group OX and Group OQ were bleached "in office" with Opalescence Xtra (35% hydrogen peroxide) and Opalescence Quick (35% carbamide peroxide), respectively, for 5, 15, or 35 minutes and retested for KHN at the end of each time period. "Home bleaching" products Opalescence F (15% carbamide peroxide) and Opalescence (10% carbamide peroxide) were applied in 14-hour applications at 24-hour intervals to Groups OF and O, respectively, which were then tested for KHN. Specimens were immersed in 0.05% fluoride solution (Meridol) for 5 minutes and retested for KHN. The hardness values were analyzed by 2-way ANOVA and Scheffe post hoc test (alpha=.05). Comparisons of KHN between each time and the baseline measurement for each group were of interest.

RESULTS

Significant decreases in KHN of enamel and dentin were found after bleaching for all test groups, dependent on the accumulated bleaching time. Group OX showed a 25% KHN reduction for enamel and 22% for dentin after 35 minutes bleaching (P < .0001). Group OQ showed a 13% KHN reduction (P < .0001) for enamel and 10% for dentin after 35 minutes (P < .005). Group OF showed a KHN reduction of 14% for enamel (P < .05) and 9% for dentin (P < .0001) after 14 hours bleaching, and Group O showed an 18% reduction in enamel (P < .0001) and 13% in dentin (P < .0001) for the same period. Fluoridation completely restored the softened dental tissues.

CONCLUSION

The "in-office" bleaching technique reduced the hardness significantly more than the "home" bleaching technique. Low-concentration fluoride mouth rinse (Meridol) restored the softened dental tissues.

Influence of post-bleaching time intervals on dentin bond strength

It has been reported that bond strength of resin to tooth structure can be reduced when the bonding procedure is carried out immediately after the bleaching treatment. This study evaluated the effect of bleaching of non-vital teeth bleaching on the shear bond strength (SBS) of composite resin/bovine dentin interface and the influence of delaying the bonding procedures for different time intervals following internal bleaching. According to a randomized block design, composite resin cylinders (Z100/Single bond - 3M) were bonded to the flattened dentin surface of two hundred and fifty-six teeth which had previously been subjected to four different treatments: SPH - sodium perborate + 30% hydrogen peroxide; SPW - sodium perborate + distilled water; CP - 37% carbamide peroxide; and CON - distilled water (control), each one followed by storage in artificial saliva for 0 (baseline), 7, 14, and 21 days after bleaching (n = 16). The bleaching agents in the pulp chambers were replaced every 7 days, over 4 weeks. The SBS test of the blocks was done using a universal testing machine. The ANOVA showed that there was no significant interaction between time and bleaching agents, and that the factor time was not statistically significant (p > 0.05). For the factor bleaching treatment, the Student's t-test showed that [CON = CP] > [SPW = SPH]. The bleaching of non-vital teeth affected the resin/dentin SBS values when sodium perborate mixed with 30% hydrogen peroxide or water was used, independently of the elapsed time following the bleaching treatment.

Tooth bleaching--a critical review of the biological aspects

Present tooth-bleaching techniques are based upon hydrogen peroxide as the active agent. It is applied directly, or produced in a chemical reaction from sodium perborate or carbamide peroxide. More than 90% immediate success has been reported for intracoronal bleaching of non-vital teeth, and in the period of 1-8 years' observation time, from 10 to 40% of the initially successfully treated teeth needed re-treatment. Cervical root resorption is a possible consequence of internal bleaching and is more frequently observed in teeth treated with the thermo-catalytic procedure. When the external tooth-bleaching technique is used, the first subjective change in tooth color may be observed after 2-4 nights of tooth bleaching, and more than 90% satisfactory results have been reported. Tooth sensitivity is a common side-effect of external tooth bleaching observed in 15%-78% of the patients, but clinical studies addressing the risk of other adverse effects are lacking. Direct contact with hydrogen peroxide induced genotoxic effects in bacteria and cultured cells, whereas the effect was reduced or abolished in the presence of metabolizing enzymes. Several tumor-promoting studies, including the hamster cheek pouch model, indicated that hydrogen peroxide might act as a promoter. Multiple exposures of hydrogen peroxide have resulted in localized effects on the gastric mucosa, decreased food consumption, reduced weight gain, and blood chemistry changes in mice and rats. Our risk assessment revealed that a sufficient safety level was not reached in certain clinical situations of external tooth bleaching, such as bleaching one tooth arch with 35% carbamide peroxide, using several applications per day of 22% carbamide peroxide, and bleaching both arches simultaneously with 22% carbamide peroxide. The recommendation is to avoid using concentrations higher than 10% carbamide peroxide when one performs external bleaching. We advocate a selective use of external tooth bleaching based on high ethical standards and professional judgment.

Review of the current status of tooth whitening with the walking bleach technique

Internal bleaching procedures such as the walking bleach technique can be used for whitening of discoloured root-filled teeth. The walking bleach technique is performed by application of a paste consisting of sodium perborate-(tetrahydrate) and distilled water (3% H2O2), respectively, in the pulp chamber. Following a critical review of the scientific literature, heating of the mixture is contra-indicated as the risk of external cervical resorption and the formation of chemical radicals is increased by application of heat. An intracoronal dressing using 30% H2O2 should not be used in order to reduce the risk of inducing cervical resorption. This review provides advice based on the current literature and discusses how the walking bleach technique can lead to successful whitening of non-vital root-filled teeth without the risks of side-effects.