The management of postbleaching cervical resorption

Present status and future directions - Managing discoloured teeth

Managing tooth discolouration involves a range of different protocols for clinicians and patients in order to achieve an aesthetic result. There is an increasing public awareness in the appearance of their teeth and management of tooth discolouration may be inter-disciplinary and involve both vital and nonvital teeth. Vital teeth can be easily treated with low concentration hydrogen peroxide products safely and effectively using an external approach and trays. For endodontically treated teeth, the walking bleach technique with hydrogen releasing peroxide products is popular. However, there is an association with external cervical root resorption with higher concentrations of hydrogen peroxide of 30%-35%. There are also regulatory considerations for the use of hydrogen peroxide in certain jurisdictions internationally. Prosthodontic treatments are more invasive and involve loss of tooth structure as well as a life cycle of further treatment in the future. This narrative review is based on searches on PubMed and the Cochrane library. Bleaching endodontically treated teeth can be considered a safe and effective protocol in the management of discoloured teeth. However, the association between bleaching and resorption remains unclear although there is likely to be a relation to prior trauma. It is prudent to avoid thermocatalytic approaches and to use a base/sealer to cover the root filling. An awareness expectations of patients and multidisciplinary treatment considerations is important in achieving the aesthetic result for the patient. It is likely that there will be an increasing demand for aesthetic whitening treatments. Bleaching of teeth has also become increasingly regulated although there are international differences in the use and concentration of bleaching agents.

The association of external cervical resorption with modern internal bleaching protocols: what is the current evidence?

Internal bleaching is an effective and minimally invasive way of bleaching non-vital teeth. A commonly cited risk associated with it is external cervical resorption (ECR), which is a potentially significant complication that could result in loss of the tooth. This is an important point of discussion with a patient during the consent process. Legally, patients are required to be made aware of material risks to which they would be likely to attach significance, such as the loss of a tooth. The risk of ECR is therefore a key component in the patient's decision-making process as they weigh it against the perceived benefits. Over the last ten years, both clinical and legal reasons have resulted in a number of changes in the materials and protocols used for internal bleaching. This leads to the question of what the current quality of evidence is regarding the association of ECR following internal bleaching with modern protocols. Other restorative options for discoloured teeth, such as veneers or crowns, involve the irreversible removal of tooth tissue and these may be chosen by patients over internal bleaching based on out-of-date evidence.

pH-changes during intracoronal bleaching: an in vivo study

OBJECTIVES

This study aimed to measure pH changes during 14 days intracoronal bleaching with hydrogen peroxide/sodium perborate and carbamide peroxide/sodium perborate.

MATERIALS AND METHODS

Twenty patients presenting endodontically treated central maxillary incisors with color alterations were divided in two groups (n = 10): Group CP + SP: 37% carbamide peroxide + sodium perborate paste; Group HP + SP: 30% hydrogen peroxide + sodium perborate paste. The pH values were measured using a digital microprocessor at different times: Baseline, 2, 7 and 14 days. Data were analyzed with two-way ANOVA followed by Tukey's test (α = 0.05).

RESULTS

ANOVA showed p < 0.00 which indicated significant difference between the groups. The mean values (± sd) and the results of the Tukey´s test were: HP + SP/14 days-7.98 (±0.58)a; HP + SP/7 days-8.59 (±0.18)b; HP + SP/2 days- 8.83 (±0.32)bc; HP + SP/Baseline-8.83 (±0.01)bc; CP + SP/ Baseline-8.89 (±0.01)bc; CP + SP/14 days-9.11 (±0.58)cd; CP + SP/7 days-9.54 (±0.16)de; CP + SP/2 days-9.66 (±0.08) de. The group HP + SP resulted in significantly lower pH values compared with group CP + SP.

CONCLUSION

It can be concluded that both associations showed alkaline pH values; however, there was significant reduction in the pH values of the 30% hydrogen peroxide associated with sodium perborate after 14 days.

CLINICAL SIGNIFICANCE

The association of hydrogen peroxide and carbamide peroxide with sodium perborate paste presented alkaline characteristics during the 14-day evaluated period. Thus, regarding pH changes, both associations can be considered safe as intracoronal bleaching agents.

Effect of different protective base materials on hydrogen peroxide leakage during intracoronal bleaching in vitro

External root resorption may develop following intracoronal bleaching with hydrogen peroxide. The preventive effect of different base materials on the radicular penetration of H2O2 during intracoronal bleaching was assessed. Seventy-two bovine teeth and 20 human teeth were bleached with 30% H2O2. The bovine teeth were divided into four groups and the root canals filled with either IRM, zinc oxide-eugenol, composite resin, or glass ionomer. The radicular H2O2 penetration of each group at different layer thickness was compared. The experiment with the human teeth was performed in three stages. In the first stage no protective base was used. In the second stage IRM was placed to the cementoenamel junction level. In the third stage the IRM layer was removed 0.5 mm below the cementoenamel junction. None of the materials tested in the bovine teeth showed H2O2 penetration with a base thickness of 2 mm. When the base thickness was reduced to 1 mm, several teeth showed H2O2 penetration; however, there was no significant difference among the materials tested. When the base thickness was reduced to 0.5 mm, the H2O2 penetration in each group increased. A statistical difference was found between the composite and the glass ionomer (p < 0.05). The results for the human teeth showed that IRM layer placed at the cementoenamel junction level significantly reduced the radicular H2O2 penetration as compared with teeth where the IRM was either placed 0.5 mm below the cementoenamel junction or not placed at all (p < 0.01). It is therefore recommended that a protective base be placed to the cementoenamel junction level before intracoronal bleaching to prevent possible H2O2 hazards.

Nonvital tooth bleaching: a review of the literature and clinical procedures

Tooth discoloration varies in etiology, appearance, localization, severity, and adhesion to tooth structure. It can be defined as being extrinsic or intrinsic on the basis of localization and etiology. In this review of the literature, various causes of tooth discoloration, different bleaching materials, and their applications to endodontically treated teeth have been described. In the walking bleach technique the root filling should be completed first, and a cervical seal must be established. The bleaching agent should be changed every 3-7 days. The thermocatalytic technique involves placement of a bleaching agent in the pulp chamber followed by heat application. At the end of each visit the bleaching agent is left in the tooth so that it can function as a walking bleach until the next visit. External bleaching of endodontically treated teeth with an in-office technique requires a high concentration gel. It might be a supplement to the walking bleach technique, if the results are not satisfactory after 3-4 visits. These treatments require a bonded temporary filling or a bonded resin composite to seal the access cavity. There is a deficiency of evidence-based science in the literature that addresses the prognosis of bleached nonvital teeth. Therefore, it is important to always be aware of the possible complications and risks that are associated with the different bleaching techniques.

Hydrogen peroxide tooth-whitening (bleaching) products: review of adverse effects and safety issues

Hydrogen peroxide in the form of carbamide peroxide is widely used for tooth whitening (bleaching), both in professionally- and in self-administered products. Adverse effects have become evident. Cervical root resorption is a possible consequence of internal bleaching and is more frequently observed in teeth treated with the thermo-catalytic procedure. Tooth sensitivity is experienced in 15-78% of patients undergoing external tooth bleaching. However, clinical studies addressing other adverse effects are lacking. Direct contact with hydrogen peroxide induces genotoxic effects in bacteria and cultured epithelial cells, but the effect is reduced or totally abolished in the presence of metabolising enzymes. Several carcinogenesis studies, including the hamster cheek pouch model, indicate that hydrogen peroxide (H(2)O(2)) might possibly act as a promoter. Until further clinical research is concluded to address the question of possible carcinogenicity, it is recommended that: tooth-bleaching products using concentrated H(2)O(2) should not be used without gingival protection; that H(2)O(2) containing products should be avoided in patients with damaged or diseased soft tissues. For nightguard vital bleaching, minimal amounts of low dose H(2)O(2) (including in the form of carbamide peroxide) are preferred, thereby avoiding prolonged and concentrated exposures.

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.

In vitro assessment of dentinal permeability after the use of ultrasonic-activated irrigants in the pulp chamber before internal dental bleaching

This in vitro study aimed to assess dentin permeability quantitatively after the use of different irrigants into the pulp chamber, with or without ultrasonic activation, before the application of an internal bleaching agent. Thirty maxillary anterior teeth, treated endodontically, were randomly assigned to six groups, according to the irrigant used: group I, distilled water; group II, 17% EDTA; group III, 1% sodium hypochlorite; for groups IV, V, and VI, respectively, the same solutions were used, but were ultrasonicated. In groups I, II, and III, the irrigant that filled the pulp chamber was left undisturbed for 15 s and was then aspirated; in groups IV, V, and IV, the irrigants were placed into the pulp chamber, ultrasonic-activated for 15 s, and were then aspirated. This sequence was repeated three times for all groups. Afterwards, for all groups, the pulp chamber was dried, filled with a bleaching agent, and sealed with glass ionomer cement. At each change of the whitening agent, these procedures were repeated. Then, the temporary restorations were removed, access cavities were cleaned, and teeth were immersed in a 10% copper sulfate aqueous solution, submitted to vacuum and immersed in a 1% rubianic acid alcohol solution. Copper ion penetration was revealed by the rubianic acid. After staining, roots were removed at the cemento-enamel junction (CEJ) and sectioned in a mesiodistal direction starting from the cervical plug level. The sections were thinned, observed under an optical microscope, the images were digitized, and copper ion penetration was measured in each section using a specific software. Means and SD were: group I, 2.41 (+/-1.45); group II, 5.22 (+/-1.79); group III, 8.32 (+/-2.55); group IV, 3.73 (+/-0.89); group V, 14.83 (+/-4.99); and group VI, 10.51 (+/-2.65). Statistical analysis using two-way anova and Tukey test showed that, regardless of the irrigant, ultrasonication increased dentinal permeability (P < 0.01). Comparing the overall effectiveness of the tested solutions, EDTA yielded the greatest increase in dentinal permeability (P < 0.01). Based on these results, it may be concluded that use of ultrasonic-activated irrigants in the pulp chamber, before the accomplishment of internal dental bleaching procedures, may result in a remarkable increase of dentin permeability, which may enhance the efficiency of the whitening agent.

Sealing evaluation of the cervical base in intracoronal bleaching

Discoloration of non-vital teeth is an esthetic deficiency frequently requiring bleaching treatment. The purpose of this study was to evaluate in vitro the cervical base efficacy in order to prevent or to minimize the leakage along the root canal filling and into the dentinal tubules. Thirty-eight extracted single-root human teeth were used, which were biomechanically prepared, filled, and divided into three experimental groups: G1, a cervical base was applied (3 mm of thickness) below the cemento-enamel junction, with resin-modified glass-ionomer cement (Vitremer); G2, the base was done with glass-ionomer cement (Vidrion R); and G3 (Control), did not receive any material as base. A mixture of sodium perborate and hydrogen peroxide 30% was placed inside the pulp chamber for 3 days, and the access opening was sealed with Cimpat. This procedure was repeated thrice. Soon after this, a paste of calcium hydroxide was inserted into the pulp chamber for 14 days. All teeth were covered with two layers of sticky wax, except the access opening, and immersed in blue India Ink for 5 days. The results did not show statistically significant differences between the three groups concerning the leakage inside the dentinal tubules. Regarding the apical direction, a statistical difference (ANOVA P < 0.05) was observed among the experimental group G1 and control group G3. No statistically significant difference was observed between G2 and G3 groups. Therefore, the placement of a cervical base before internal bleaching procedures is still recommended.

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.

Effect of internal bleaching agents on dentinal permeability of non-vital teeth: quantitative assessment

The aim of this in vitro study was to assess quantitatively dentin permeability of pulpless teeth after intracoronal bleaching therapy with three different agents. Twenty-four maxillary central incisors were randomly assigned to four groups according to the bleaching agent used: I--non-bleached control; II--37% carbamide peroxide; III--sodium perborate/20% hydrogen peroxide paste; IV--27% carbamide peroxide. After standard access and root-canal preparation the access opening, biomechanical preparation and root-canal filling, a cervical glass ionomer plug was prepared and intracoronal bleaching procedures were carried out in a standardized fashion. The access cavities were opened and the teeth were externally sealed and immersed in a 10% copper sulfate aqueous solution for 30 min, in vacuum for the first 5 min. Then, samples were removed, dried with absorbing paper and immersed in a 1% rubianic acid alcohol solution, for the same above-mentioned period in solution and in vacuum. Copper ion penetration was indicated by the rubianic acid staining. Mean values and SD for the experimental groups were: I--7.88% (+/-1.33), II--16.94% (+/-5.72); III--11.45% (+/-3.90) and IV--8.98% (+/-4.19). Data were submitted to one-way anova. The results showed that the 37% carbamide peroxide provided the highest increase in dentin permeability, followed by sodium perborate with 20% hydrogen peroxide. The 27% carbamide peroxide provided the lowest results and showed statistical similarity to the control group. On basis of these findings, it may be concluded that, among the tested intracoronal bleaching agents, 37% carbamide peroxide presented an optimized overall performance in increasing dentinal permeability.

Calcium hydroxide pastes: classification and clinical indications

REVIEW ARTICLE: Calcium hydroxide has been used in endodontology for many years. The aim of this paper is to review the various formulations of calcium hydroxide that have been described, with specific reference to the vehicle used to carry the compound. The requirements for a vehicle are described, and ex vivo and in vivo studies reviewed. Vehicles can be classified into aqueous, viscous and oily, the clinical properties of calcium hydroxide changing depending on the vehicle. The review also describes the use of various active components that have been added to calcium hydroxide, including antimicrobial and anti-inflammatory agents. This review will help clinicians to make informed judgements about which formulations of calcium hydroxide should be used for specific endodontic procedures.

A new approach in restorative treatment of external root resorption. A case report

This case report describes the treatment of an external root resorption with extensive loss of tooth structure and bone at the labial surface of an upper left central incisor. The area of bone loss and root resorption was surgically exposed and an impression was taken using curing silicone. An individual ceramic insert was fabricated, allowing endodontic retreatment through an artificial root canal. The insert was incorporated using a dentin bonding system and a dual curing luting composite. Following endodontic retreatment and internal bleaching, a ceramic veneer was bonded to the tooth to obtain good esthetics and to improve stability. Twenty months after surgical treatment no further root resorption could be detected radiographically. A shallow residual pocket but no bleeding on probing was found.

[Replantation of avulsed immature permanent teeth. Results in 39 cases after an average of 2.5 years]

The aim of this investigation was a critical assessment of the short- and medium-term results of replantation of immature, avulsed permanent teeth. Thirty-nine teeth were investigated after 2.5 years on average. Only 7 teeth (18%) had been replanted within 5 min after avulsion. Sixteen teeth (41%) showed revascularisation or ingrowth of alveolar bone into the pulp. Twenty-two teeth (56%) showed signs of ankylosis, 6 (15%) had been exfoliated or extracted. Seventeen teeth (77% of the ankylotic ones) exhibited an alveolar growth arrest of 1.5 mm per 10 cm body growth. By planimetric assessment, the yearly loss of root dentin by replacement resorption was about 15%. The appearance was compromised in 11 cases (33%) by severe discoloration. In spite of intense therapeutic effort and partial success, the results must be classified as unsatisfactory. In avulsions of immature permanent teeth, replantation therefore has to be considered an intermediate solution. Since the main reason for a failure is extended extra-oral unphysiologic storage, replantation by lay helpers immediately after the accident should be propagated as a first-aid treatment to improve the situation of the replanted tooth. In addition, more attention should be paid to preserving teeth in tissue cultures before replantation.

Internal bleaching: long-term outcomes and complications

Internal bleaching with a 30 percent hydrogen peroxide solution is aesthetically very successful in the short term; however, in the long term, the success rate falls below 50 percent. This procedure is associated with a risk of external root resorption, documented both clinically and experimentally. The etiology of resorption and the effects of 30 percent hydrogen peroxide on dental tissues suggest that this chemical should be avoided. Internal bleaching is possible using sodium perborate mixed with water. The aesthetic outcome is still acceptable and the potential for resorption may be minimized.

Role of cementoenamel junction on the radicular penetration of 30% hydrogen peroxide during intracoronal bleaching in vitro

Intracoronal bleaching of nonvital, teeth with 30% hydrogen peroxide is occasionally associated with external cervical root resorption. The exact mechanism by which bleaching induced root resorption occurs is not yet fully understood. The relationship of cementum to the enamel at the cementoenamel junction may have clinical significance. Seventeen single rooted human mandibular premolars extracted atraumatically for orthodontic reasons were used. The radicular hydrogen peroxide penetration in each tooth was measured in vitro by an indirect colorimetric method. Thereafter, the teeth were examined with a scanning electron microscope to determine the type of the cementoenamel junction. It was found that the radicular penetration of 30% hydrogen peroxide was related to the type of cementoenamel junction.

Radicular penetration of hydrogen peroxide during intra-coronal bleaching with various forms of sodium perborate

The development of external cervical root resorption following internal bleaching of discoloured pulpless teeth is associated with the use of hydrogen peroxide. The aim of the study was to determine radicular penetration of hydrogen peroxide following intracoronal bleaching with various forms of sodium perborate. 63 extracted human incisors were root filled and stained artificially. Standardized cementum defects were created on the mesial and distal aspects of the root directly below the cemento-enamel junction (CEJ). Using the walking bleach technique all teeth were bleached for a 6-day period, with replacement of the bleaching paste after days 1 and 3. Sodium perborate monohydrate (MH), trihydrate (TRH) or tetrahydrate (TH) was mixed with H2O2 or H2O and subsequently placed intracoronally 1 mm below the labial CEJ. The teeth were divided into six groups: I. MH + H2O2(30%) (n = 12); II. TRH + H2O2(30%) (n = 12); III. TH + H2O2(30%) (n = 12); IV. TH + H2O (n = 12); V. TH + H2O, gel (n = 12); VI. no bleaching paste (n = 3). At baseline and at days 1, 3 and 6 the amount of H2O2 taken up from the surrounding medium of each root was indirectly recorded and calculated as p.p.m. Almost all teeth of the experimental groups showed leakage of hydrogen peroxide compared to those of the control group. The radicular penetration of hydrogen peroxide was significantly higher in teeth of groups I and III than in those of groups IV and V (P < or = 0.001). In conclusion, the amount of hydrogen peroxide leakage depends, among other factors, on the form of sodium perborate used.(ABSTRACT TRUNCATED AT 250 WORDS)

A method to determine the location and shape of an intracoronal bleach barrier

The external cervical root resorption associated with intracoronal bleaching of pulpless teeth can be a devastating lesion. It often cannot be repaired. To prevent this problem, increasing attention has been focused on placing a barrier between the pulp chamber and the endodontic filling material. The objective of this article is to propose a method for determining the location and shape of an intracoronal bleach barrier.

Intracanal isolating barriers as they relate to bleaching

Four restorative materials were evaluated for effectiveness as intracanal isolating barriers to prevent leakage of bleaching agents into the coronal part of the root canal. Fifty-five teeth were stained in vitro, instrumented, and filled with gutta-percha. In the experimental groups, gutta-percha was removed 2 mm apical to the labial cementoenamel junction, and an intracanal isolating barrier (zinc oxide-eugenol, IRM, Ketac-Cem, or Scotchbond Multipurpose) was placed even with the facial and proximal cementoenamel junction areas in a sloped manner. All were bleached with a thermocatalytic and walking bleach technique until the crown was one shade lighter than the original shade. The roots were then examined for the occurrence of bleaching. The results indicate that none of the materials used was a totally effective intracanal isolating barrier. Although a significant difference was found when IRM was compared with Ketac-Cem or Scotchbond Multipurpose (p < 0.05), all restorative materials evaluated showed a high incidence of leakage as demonstrated by bleached roots. There was no significant difference between zinc oxide-eugenol and IRM.

Effect of various types of sodium perborate on the pH of bleaching agents

Time-dependent changes in the pH value of various types of sodium perborate solutions used as bleaching agents were evaluated. Sodium perborate-monohydrate (MH), sodium perborate-trihydrate (TRH), and sodium perborate-tetrahydrate are available. Each perborate was mixed with 10%, 15%, or 30% fresh hydrogen peroxide or with bidistilled water in a powder to liquid ratio of 2 g:1 ml, respectively. The pH values were recorded at baseline and after 1h, 1 day, 3 days, and 7 days, respectively. At baseline the pH values of MH, TRH, and tetrahydrate in conjunction with 30% H2O2 were 8.7, 7.0, and 7.5, respectively. The pH increased significantly with decreasing concentrations of H2O2. For TRH, MH, and tetrahydrate mixed with bidistilled water more alkaline values were measured at baseline and after 1 h. Due to solidification of the samples, the pH could not be determined for MH starting day 1 and for TRH starting day 3. In conclusion, the pH of bleaching pastes depends on the content of water of crystallization in sodium perborate, H2O2 concentration, and time of measurement. The bulk of the mixtures recorded reached alkaline pH values of 10 to 11. It is recommended that the pH of the mixture being used be checked to avoid potential postbleaching root resorption.

Prognosis of intracoronal bleaching with sodium perborate preparation in vitro: 1-year study

Bleaching materials containing hydrogen peroxide have been used for treating discolored nonvital teeth but their use was occasionally associated with external root resorption. In a previous study it was found that the immediate results of bleaching teeth in vitro were equal for sodium perborate mixed with either water or hydrogen peroxide. The purpose of this study was to compare the bleaching prognosis of sodium perborate mixed with water or hydrogen peroxide over a 1-yr period. Extracted human teeth with intact crowns were discolored with human erythrocytes and bleached by sodium perborate mixed with either 30% hydrogen peroxide (group A), 3% hydrogen peroxide (group B), or water (group C). The bleaching materials were placed in the pulp chambers of the discolored teeth and sealed with IRM. They were replaced with fresh preparations after 3 and 7 days. After 14 days the coronal access cavities were sealed with composite resin and the teeth photographed with a color slide film under standardized conditions. The teeth were stored in artificial saliva for 1 yr and photographed after 3, 6, and 12 months. Two separate evaluators ranked the teeth by comparing them with the shades before and after bleaching. The bleaching success rates of the tested groups at each time interval were compared and analyzed statistically. It was found that after 1 yr all of the teeth in groups A and C maintained their shades. In 20% of the teeth in group B there was color regression. Statistically, these differences were not significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of bleaching time and temperature on the radicular penetration of hydrogen peroxide

Extracted human premolars were treated endodontically and bleached intracoronally. The teeth were bleached with 30% hydrogen peroxide for periods of 5, 20, 40 and 60 min at temperatures of 24 degrees C, 37 degrees C and 47 degrees C. A correlation for both bleaching time and temperature and the radicular penetration of hydrogen peroxide was found. No penetration was found after 5 min bleaching at any of the temperatures tested. Prolonging the bleaching time after 5 min increased the hydrogen peroxide penetration at each of the temperatures tested. A rise in the bleaching temperature also increased the hydrogen peroxide penetration although not significantly for all tested periods. It is therefore suggested to minimize the bleaching time and temperature when hydrogen peroxide is used as the oxidizing agent. Bleaching should be limited to separate 5-min periods rather than being performed over a long continuous period.

Histological characterization of bleaching-induced external root resorption in dogs

External root resorption occasionally develops after intracoronal bleaching with hydrogen peroxide. In this study, an experimental model was established to study thermocatalytic bleaching-induced root resorption in dogs. Histological examination after 6 months revealed that 18% of the teeth had root resorption lesions. The lesions could be divided into three types. In type I, root excavations were associated with a dense inflammatory cell infiltrate. Type II lesions were characterized by granulation tissue formation. In type III, the lesions were filled with reparative cementum. The three types probably represent different phases of one process. Calcium hydroxide had no effect on the occurrence or type of resorption. The instability of hydrogen peroxide and the presence of inflammatory resorption lesions 6 months postoperatively suggest hydrogen peroxide-induced toxic radicals or denaturants as potential irritants.

In vitro efficacy of sodium perborate preparations used for intracoronal bleaching of discolored non-vital teeth

Bleaching materials containing 30% hydrogen peroxide have been used successfully for the treatment of discolored non-vital teeth. Intracoronal application of these materials was occasionally associated with the development of external root resorption. Extracted human teeth with intact crowns were discolored in vitro and bleached with three preparations of sodium perborate. These preparations included: sodium perborate with 30% hydrogen peroxide, sodium perborate with 3% hydrogen peroxide and sodium perborate with water. The bleaching materials were placed in the pulp chamber of the discolored teeth and sealed with IRM for 14 days. They were replaced with fresh preparations after 3 and 7 days. The coronal tooth shades were evaluated after 3, 7 and 14 days and a comparison of the bleaching success of the groups was made at each interval. It was found that after 14 days and three bleachings there was no significant difference in success between the groups. It is therefore recommended that sodium perborate be used in combination with water rather than with hydrogen peroxide to reduce the risk of post-bleaching external root resorption.

pH variation among materials used for intracoronal bleaching

Intracoronal bleaching of pulpless teeth with 30% hydrogen peroxide may result in external cervical root resorption. One of several suggested etiological factors associated with this complication is the pH of the bleaching materials. Because the available data on the pH values of bleaching materials were conflicting, it was the purpose of this study to measure the pH of the materials commonly used for bleaching pulpless teeth. The pH of different concentrations of sodium perborate and 30% hydrogen peroxide, alone or in combination, were measured for a period of 14 days. Sodium perborate was confirmed to be alkaline, whereas 30% hydrogen peroxide was acidic. The pH of the materials when mixed together gradually changed from acidic to alkaline as the concentration of sodium perborate was increased. A thick clinical consistency mixture of both materials was alkaline, and its alkalinity increased with time. These results do not support the theory relating bleaching-induced root resorption to an acidic pH of the bleaching pastes.

Effect of cementum defects on radicular penetration of 30% H2O2 during intracoronal bleaching

Bleaching pulpless teeth with 30% hydrogen peroxide has been reported to cause external cervical root resorption. It has been hypothesized that H2O2 penetrating through open dentin tubules can initiate an inflammatory reaction which could result in root resorption. Extracted human premolars were treated endodontically and bleached intracoronally using the thermocatalytic technique. The teeth were divided into three groups; one group with no cementum defects at the cementoenamel junction, one group with artificial cementum defects at the cementoenamel junction, and another group with artificial cementum defects at the middle third of the root. The radicular penetration of 30% hydrogen peroxide in the three groups was assessed directly and compared using an in vitro model. Radicular penetration of hydrogen peroxide was found in all of the groups tested. The penetration of hydrogen peroxide was significantly higher in teeth with cementum defects at the cementoenamel junction than in those without defects.