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

0099-2399/92/1803-0114/$03.00/0 JOURNAL OF ENDODONTICS Copyright © 1992 by The American Association of Endodontists

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VOL. 18, NO. 3, MARCH1992

Effect of Different Protective Base Materials on Hydrogen Peroxide Leakage during Intracoronal Bleaching In Vitro Ilan Rotstein, CD, Daniel Zyskind, DMD, Israel Lewinstein, DMD, PhD, and Nathan Bamberger, DMD

require complex treatment and occasionally tooth extraction (2, 4-8). The exact mechanism of bleaching-induced root resorption is not yet fully understood. It has been established experimentally that hydrogen peroxide may leak from the pulp chamber to the outer radicular medium via dentin tubules, particularly in the presence of cementum defects (10, 11). Once reaching the periodontal tissues hydrogen peroxide may initiate a local inflammatory reaction followed by root resorption (12, 13). Several authors have suggested that a protective base layer should be placed over the root canal obturation prior to bleaching in order to prevent the seepage of hydrogen peroxide from the pulp chamber to the extraradicular tissues (14-16). However, no criteria have been established concerning either the type of base to be used or its thickness. The purpose of this study was to examine the preventive effect of a protective base placed over the root canal obturation on the radicular penetration of hydrogen peroxide during intracoronal bleaching and to compare the efficacy of different materials used for such purposes.

External root resorption may develop following intracoronal bleaching with hydrogen peroxide. The preventive effect of different base materials on the radicular penetration of HaO2 during intracoronal bleaching was assessed. Seventy-two bovine teeth and 20 human teeth were bleached with 30% H202. The bovine teeth were divided into four groups and the root canals filled with either IRM, zinc oxideeugenol, composite resin, or glass ionomer. The radicular HaOa 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 H2Oa penetration with a base thickness of 2 mm. When the base thickness was reduced to 1 mm, several teeth showed H2Oa penetration; however, there was no significant difference among the materials tested. When the base thickness was reduced to 0.5 mm, the HaO2 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 H2Oa 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 HaO2 hazards.

MATERIALS AND METHODS Bovine Teeth

Seventy-two freshly extracted mandibular bovine incisors of a similar size were used. Remnants of soft tissue covering the roots were removed, endodontic access cavities prepared, and the pulp tissue of each tooth extirpated. The roots were horizontally sliced 4 m m below the cementoenamel junction (CEJ) line with a carborundum disc, and their apical segments removed. The remaining coronal root canal segments were enlarged to a standard size using a #023 round carbide bur rotated at a slow speed. The teeth were divided into four groups, each consisting of 15 experimental teeth and 3 controls. The radicular cementum and the CEJ were sealed with sticky wax and a double layer of varnish. A 3-mm layer of each of the tested base materials was sealed in the root canal and leveled 1 mm below the CEJ (Fig. 1). The following materials were used: intermediate restorative material (IRM), type III (Caulk Denstply, Milford, DE), zinc oxide-eugenol (ZOE) (Merck, Darmstadt, Germany), Durafill VS composite (Kulzer & Co, Wehrheim,

An undesirable complication of intracoronal bleaching using hydrogen peroxide as the oxidizing agent is the development of external cervical root resorption (1-9). This condition may 114

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Human Teeth

H202

--Wax

Material

FIG 1. A schematic illustration of the experimental model demonstrating a bovine tooth filled with a 3-mm layer of base material. The base layer was reduced in each stage of the experiment by either 1 mm or 0.5 mm.

Germany), and Fuji II glass ionomer cement (GC Dental Industrial, Tokyo, Japan). Each tooth was mounted on a 2- x4-cm laminate of boxing wax (Kerr Brand, Emeryville, CA) which separated the tooth crown and the access cavity from the radicular segment. The circumferential union line between the wax laminate and the enamel was sealed with sticky wax and a double layer of varnish. After 48 h the prepared teeth were placed in plastic assay tubes containing 1.30 ml of bidistilled water and incubated for a period of 20 min at 37°C to simulate body temperature. Twenty microliters of 30% H202 (8.8 M) were pipetted into each access cavity and the teeth bleached for 60 min in a dry incubator at a temperature of 37°C. In the control teeth the same quantity of saline was used instead of H202. The quantification of the H202 penetration was measured using a specific H202 assay (17). Aliquots of 0.5 ml from the solution surrounding each root were taken in duplicate and placed in test tubes containing 0.5 ml of bidistilled water to reach a total volume of 1 mt. The samples were added to ferrous ammonium chloride. In the presence of H202 a ferric ion results and upon the addition of potassium thiocyanate a ferrithiocyanate complex is formed which absorbs light at 480 nm wavelength. The amount of H202 in the samples tested was determined by their comparison to a standard curve generated by known amounts of H202. The H202 penetration in each group was recorded and the bleaching treatment repeated three times. The base layer in each tooth was then reduced by 1 mm and the H202 penetration reassessed. Further reductions of 1 mm and 0.5 mm were performed leaving a final base layer of 0.5 ram. After each reduction stage the teeth were rebleached and the H202 penetration recorded. Statistical analysis comparing the different experimental groups was calculated using the Kruskal-Wallis one-way analysis of variance and Mann-Whitney U test. The comparison between the different thickness of the base layers in the same group was calculated using the Wilcoxon matched pairs signed rank test.

Fresh, intact single-rooted premolars, extracted for orthodontic reasons, were placed in saline and the soft tissue covering the root surface was gently removed with a gauze soaked with 2.5% sodium hypochlorite. The teeth were subjected to stereomicroscopic examination of the radicular cementum and the CEJ. Twenty teeth without apparent cementum defects or dentin exposures were used. Root canal preparation was performed in each tooth followed by lateral condensation of gutta-percha and AH26 sealer (De Trey Dentsply, Zurich, Switzerland). The gutta-percha filling was removed 3 mm below the CEJ using hot pluggers. In each tooth the cementum covering the CEJ was uniformly removed with a #008 round carbide bur, rotated at slow speed, in four points: mesial, distal, buccal, and lingual, leaving the dentin tubules in those areas exposed. The defects were then rinsed with bidistilled water. The teeth were mounted on a model for the detection of radicular penetration of hydrogen peroxide during intracoronal bleaching as previously described by Rotstein et al. (11). Briefly, each tooth was mounted on a 2- ×4-cm laminate of boxing wax. The wax laminates were adapted and sealed at a level of I mm above the proximal line of the CEJ. The outer root surface including the apical foramina was sealed with wax except for the coronal third and the CEJ. The prepared teeth were placed in plastic assay tubes containing 1.75 ml of bidistilled water with their entire root, including the CEJ, submerged in the solution. At this point, the teeth were placed in an incubator for a period of 20 min at 37°C. Twenty microliters of 30% H202 were then pipetted into each access cavity and the teeth bleached for 60 min in a dry incubator at a temperature of 37°C. The experiment was designed in three stages. In the first stage, no protective base was placed. In the second stage, a uniform layer of IRM, type II (Caulk Dentsply) was placed over the gutta-percha obturation of each tooth to the proximal level of the CEJ and was allowed to set for 48 h (Fig. 2). In the third stage, the IRM layer was removed 0.5 mm below the CEJ line. Bleaching was performed following each experimental stage and the radicular H202 penetration assessed. Quantification of H202 penetration was performed using the specific H202 assay as previously described. A statistical analysis comparing the different experimental stages was done using the Wilcoxon matched pairs signed rank test. RESULTS Bovine Teeth

The results for the bovine teeth are shown in Fig 3. When the base thickness exceeded 2 ram, no H202 penetration was found in any of the groups tested. With the base thickness of 1 mm, two teeth (13%) in the IRM group, one tooth (7%) in the ZOE group, none of the teeth in the composite group, and two teeth (13 %) in the glass ionomer (GI) group showed H202 penetration. When the base thickness was reduced to 0.5 mm, six teeth (40%) in the 1RM group, eight teeth (53%) in the ZOE group, four teeth (27%) in the composite group, and nine teeth (60%) in the GI group showed H202 penetration. No H202 was found in the controls at any of the experimental periods.

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Rotstein et al.

Journal of Endodontics

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FiG 4. A graph representing the percentage of human teeth showing H202 penetration compared for the three experimental stages. Stage 1, no cement base; stage 2, IRM cement base placed at the CEJ level; and stage 3, IRM cement base placed 0.5 mm below the CEJ.

obturation and the pulp chamber, 18 teeth (90%) showed H202 penetration. When a layer of IRM cement was placed over the gutta-percha obturation at the CEJ level, only one tooth (5%) showed H202 penetration. Once the cement layer was reduced by 0.5 mm, four teeth (20%) showed H202 penetration. A significant difference was found between the teeth where the IRM cement was placed at the CEJ level and those where the IRM was placed 0.5 mm below the CEJ (p < 0.01). No difference was found between the teeth where the IRM was placed 0.5 mm below the CEJ and those without any cement base. DISCUSSION

1 turn MATERIAL

0.5 mm

THICKNESS

F~a 3. A graph representing the percentage of bovine teeth showing H202 penetration as related to the different base materials tested and their thickness.

Generally, when the base thickness was reduced from 1 mm to 0.5 mm a significant increase of H202 penetration was found for three materials: IRM (p < 0.05), ZOE (p < 0.05), and GI (p < 0.01). No significant difference was found in the composite group. A comparative analysis for the four different materials revealed no statistical difference at l-mm thickness. Composite material was found to be superior to the GI at 0.5 mm thickness (p < 0.05). No statistical difference was found between the other materials at 0.5-mm thickness. Human Teeth

The results for the human teeth are represented in Fig 4. When no protective base was placed between the root canal

It has been demonstrated that hydrogen peroxide may diffuse through radicular dentin during intracoronal bleaching to provoke inflammatory reaction and root resorption (1013). Cementum defects, mainly at the cementoenamel junction, significantly increase the extraradicular hydrogen peroxide seepage (11). These defects may be present in the anterior teeth of approximately 25% of the population (18). It is therefore important that in these cases the cemental defects be isolated from the bleaching agents placed into the pulp chamber. An effective intracoronal isolating base should be impermeable to the bleaching agents as well as esthetically acceptable. The results of this study indicate that all tested materials are equally effective in preventing the radicular HEO2 penetration when the thickness of the base layer exceeds 1 mm. In addition, the isolative effect of all of the materials improves as the base layer thickness increases. Since all four tested materials possess an esthetic light shade, any one of them may be used provided a sufficiently thick layer is applied. A statistical difference was found between the composite material and the glass ionomer cement at the 0.5 mm thickness. However, the ability to accurately determine such thin cement layers in a clinical situation is questionable. Each one of the tested materials presents several advantages and disadvantages. Thus their use before bleaching should be considered according to the restorative treatment plan and the operator's clinical convenience. Two of the materials used

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in this study contained zinc oxide-eugenol as their principal component. The zinc oxide-eugenol cements are probably the most effective materials known for minimizing microleakage (19). However, since the final restoration of anterior teeth is usually made of composite resin, the eugenol released from these cements may affect the resin polymerization process. The composite resin is a material known to suffer shrinkage following polymerization. However, in this study the composite resin proved to be excellent in preventing H202 penetration even when applied as a thin layer. It seems that this polymerization shrinkage is not significant when a thin layer of resin is used in the radicular orifices (20). Glass ionomer cement has the potential to form a chelative bonding to the tooth structure and therefore can be successfully used as a protective base before bleaching. This material, however, is very sensitive due to its complex setting reaction and therefore may suffer composition alterations during manipulation and setting time or when contacted with H202 molecules. The coronal level of the isolating base may compromise the bleaching effect, especially at the coronal cervical portion. It has been suggested that the protective base layer should be left 1 mm below the CEJ to prevent leakage of the bleaching agents and at the same time ensure effective bleaching (15). However, the results of the present study show that radicular penetration of H202 increased significantly when the cement base was placed 0.5 mm or more apically to the CEJ level. It seems that the thickness of the base layer and its relation to the CEJ in the root canal is more critical for the prevention of H202 penetration than the type of material to be used. Therefore, it is recommended that a thick intracoronal isolating base should always be used before bleaching and placed at the CEJ level. With regard to bleaching efficacy, it has been demonstrated that the gingival portion of the crown and root were effectively bleached when an IRM base was placed at the CEJ (16). When additional bleaching of the cervical area of the tooth is required it should be performed gradually, removing a small layer of the base material each visit and using milder bleaching agents. This study was supported by a grant from the Joining Research Fund of the Hebrew University-Hadassah Faculty of Dental Medicine, founded by the Alpha Omega Fraternity, and the Hadassah Medical Organization.

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Dr. Rotstein is a lecturer, Department of Endodontics, Hebrew UniversityHadassah Faculty of Medicine, Jerusalem, Israel. Dr. Zyskind is a lecturer, Department of Restorative Dentistry, Hebrew University-Hadassah Faculty of Medicine. Dr. Lewinstein is a lecturer, Department of Restorative Dentistry and head, Laboratory of Dental Materials, Hebrew University-Hadassah Faculty of Medicine. Dr. Bamberger is in general practice. Address requests for reprints to Dr. Ilan Rotstein, Department of Endodontics, Hebrew University-Hadassah Faculty of Dental Medicine, P.O. Box 1172, Jerusalem 91010, Israel.

References 1. Harrington GW, Natkin E. External resorption associated with bleaching of pulpless teeth. J Endodon 1979;5:344-8. 2. Lado EA, Stanley HR, Weisman MI. Cervical resorption in bleached teeth. Oral Surg 1983;55:78-80. 3. Montgomery S. External cervical resorption after bleaching a pulpless tooth. Oral Surg 1984;57:203-6. 4. Cvek M, Lindvall AM. External root resorption following bleaching of pulpless teeth with oxygen peroxide. Endod Dent Traumato11985; 1:56-60. 5. Latcham NL. Postbleaching cervical resorption. J Endodon 1986;12:262-4. 6. Goon WWY, Cohen S, Borer RF. External cervical root resorption following bleaching. J Endodon 1986;12:414-8. 7. Friedman S, Rotstein I, Libfeld H, Stabholz A, Heling I. Incidence of external root resorption and esthetic results in 58 bleached pulpless teeth. Endod Dent Traumato11988;4:23-6. 8. Friedman S. Surgical-restorative treatment of bleaching related external root resorption. Endod Dent Traumato11989;5:63-7. 9. Gimlin DR, Schindler WG. The management of postbleaching cervical resorption. J Endodon 1990; 16:292-7. 10. Fuss Z, Szajkis S, Tagger M Tubular permeability to calcium hydroxide and to bleaching agents. J Endodon 1989; 15:362-4. 11. Rotstein I, Torek Y, Misgav R. Effect of cementum defects on radicular penetration of 30% H202 during intracoronal bleaching. J Endodon 1991 ;17:230-3. 12. Madison S, Walton R. Cervical root resorption following bleaching of endodontically treated teeth. J Endodon 1990; 16:570-4. 13. Rotstein I, Fdedman S, Mor C, Katznelson J, Sommer M, Bab I. Histological characterization of bleaching-induced external root resorption in dogs. J Endodon 1991 ;17:436-41. 14. Walton RE, Torabinejad M. Principles and practice of endodontics. Philadelphia: WB Saunders, 1989:390. 15. Ho S, Goerig AC. An in vitro comparison of different bleaching agents in the discolored tooth. J Endodon 1989; 15:106-11. 16. Warren MA, Wing M, Ingram TA. An in vitro comparison of bleaching agents on the crowns and roots of discolored teeth. J Endodon 1990;16: 463-7. 17. Thurman RG, Ley HG, Scholz R. Hepatic microsomal ethanol oxidation. Eur J Biochem 1972;25:420-30. 18. Muller CJF, Van Wyk CW. The amelo-cemental junction. J Dent Assoo S Africa 1984;39:799-803. 19. Philips RW. Skinner's science of dental materials. 7th ed. Philadelphia: WB Saunders, 1973:485. 20. Bausch JR, de Lange K, Davidson CL, Peters A, de Gee AJ. Clinical significance of polymerization shrinkage of composite resins. J Prosthet Dent 1982;48:59-62.