0099-2399/91/1705-0230/$03.00/0 JOURNAL OF ENDODONTICS Copyright 9 1991 by The American Association of Endodontists
Printed in U.S.A.
VOL, 17, NO. 5, MAY 1991
Effect of Cementum Defects on Radicular Penetration of 30% H202 during Intracoronal Bleaching Ilan Rotstein, CD, Yarom Torek, DMD, and Rivka Misgav, MSc
M A T E R I A L S AND M E T H O D S
Bleaching pulpless teeth with 30% hydrogen peroxide has been reported to cause external cervical root resorption. It has been hypothesized that H202 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.
Fresh, intact uniradicular premolars, extracted for orthodontic reasons from young adults, were placed in saline and the soft tissue covering the root surface was removed with a gauze soaked with 2.5% sodium hypochlorite. The teeth were subjected to stereomicroscopic examination of the radicular cementum and the cementoenamel junction (CEJ). Thirtysix teeth without apparent cementum defects or dentin exposures at the CEJ were used for this study. Thirty teeth were assigned to the experimental group and six teeth served as controls. Root canal treatment was performed in each tooth and included biomechanical preparation followed by obturation using the lateral condensation technique of gutta-percha and AH-26 root canal sealer (De Trey Denstply, Zurich, Switzerland). The gutta-percha filling was removed 3 m m short of the CEJ level using hot pluggers. The CEJ reference points were either on the buccal or the lingual side. Remnants of gutta-percha and sealer were removed from the access cavity with a cotton pellet soaked with chloroform and a 28m m round carbide bur, rotated at a slow speed. This was followed by thorough rinsing of the pulp chamber with bidistilled water. The teeth were divided into three groups: The first group consisted of 30 teeth without any cementum defects (group A), the second group consisted of 20 teeth in which artificial defects were created at the CEJ (group B), and the third group consisted of 10 teeth in which artificial defects were created at the middle third of the root (group C). Twenty teeth from group A were chosen at random to form group B and the remaining 10 teeth were designated as group C. Thus, results could be obtained for the same teeth before and after the presence of the defects. In each tooth in group B, the cementum covering the CEJ was removed at four different points--mesial, distal, buccal, and lingual, leaving the dentin tubules in those areas exposed. This was done with a round carbide bur mounted on a slow-speed handpiece to simulate defects or irregularities along the CEJ line. In group C similar defects were created at a level 4-ram below the coronal terminal level of the gutta-percha obturation. Each tooth was mounted in a 2- • 4-cm laminate of boxing wax (Kerr Brand, Emeryville, CA) so that on one side the crown and the access cavity and on the other side the root and the CEJ were exposed. The wax laminates were adapted at a level of 1-mm above the mesial or distal line of the CEJ. In order to achieve a hermetic coronal seal the circumferential union line between the boxing wax and the enamel was sealed with sticky wax and a double layer of varnish. The outer root
A serious complication of intracoronal bleaching with 30% hydrogen peroxide is the development of external cervical root resorption (1-9). In these reports hydrogen peroxide solution was used either solely or in combination with sodium perborate. It has been hypothesized that bleaching agents, such as hydrogen peroxide, could penetrate through patent dentin tubules to initiate an inflammatory reaction followed by bacterial invasion and root resorption (1-2, 4). Fuss et al. (10) examined the diffusion capacity of bleaching materials through human dentin. In their study, a walking bleach paste composed of Superoxol and sodium perborate was introduced into the root canal space and the change of pH was recorded in the medium surrounding the root. They concluded that bleaching materials could diffuse readily through dentin (10). The purpose of this study was to examine the influence of different cementum defects and their location on the radicular penetration ability of 30% hydrogen peroxide during thermocatalytic bleaching.
230
Vol. 17, No. 5, May 1991
Radicular Penetration of H202
surfaces of the teeth, including the apical foramina, were sealed with wax, leaving the coronal one third and the CEJ exposed. In group C the area of the defects was devoid of wax. The prepared teeth mounted in the wax laminates were placed in plastic assay tubes containing 1.75 ml of bidistilled water with their entire root, including the CEJ, submerged in the solution (Fig. 1). Prior to the experiment a 0 reading on all of the samples was performed to exclude the possibility of the presence of H202 in the experimental system. The teeth were then placed in an incubator for a period of 20 rain at 37~ to simulate body temperature. Twenty microliters of 30% H202 (8.8 M) were pipetted into each access cavity of the experimental teeth. Twenty microliters were used since it was found to be the quantity able to saturate a small cotton pellet. An additional two teeth in each group served as controls in which normal saline was pipetted into the access cavity instead of H202. A test for the coronal seal of the wax and varnish was also performed by placing the same amount of H2Oz on the circumferential line. This test proved the seal efficient since no H20_~ penetration was detected. The teeth were subjected to 15 cycles of 1 rain of thermocatalytic bleaching using a 1000-W heat lamp from a distance of 50 cm. The interval between each heating cycle was 30 s. Aliquots of 0.5 ml from the solution surrounding each root were placed in a test tube containing 0.5 ml ofbidistilled water to reach a total volume of 1 ml. Quantification of the H202 was performed according to the technique used by Thurman et al. (l 1). The samples are added to ferrous ammonium chloride. If hydrogen peroxide is present, a ferric ion results and upon the addition of potassium thiocyanate a ferrithiocyanate complex is formed which absorbs light at the wavelength of 480 nm. The amount of H202 in the samples tested is determined by comparing them with a standard curve generated by known amounts of H202. A standard curve for the 30% H202 used for the experiment was established, and the samples from each tooth tested were read in a spectrophotometer and compared with the standard curve. Each sample was taken in duplicate and the whole experiment repeated three times on the same teeth. The reagents' readings served as a negative control while the
reading of pure 20 ul of 30% H202 in 1.75 ml of bidistilled water served as a positive control. The statistical analysis comparing group A with groups B and C was done using the Wilcoxon matched-pairs signed rank test. The analysis between group B and group C was done using the Mann-Wittney U test.
RESULTS The results are summarized (Table 1) and the comparison of the median penetration percentage between the different groups is represented by a bar graph (Fig. 2). Hydrogen peroxide penetration was found in all of the groups tested. The median penetration of group A (no defect) was 0.009% equivalent to 10 nmol. The median penetration of group B (CEJ defect) was 0.031% equivalent to 31.5 nmol. In group C (mid-root defect) the median penetration was 0.030% equivalent to 30.5 nmol. Group B yielded the highest scores. The top limit of its interquartal range was 0.155% and the maximum H202 penetration measured was 82.11%. The statistical analysis revealed that teeth with artificial cementum defects at the CEJ were significantly more permeable to H202 than those without defects (p < 0.01). Teeth with artificial mid-root defects were more permeable than those without defects (p < 0.025). In this case, the difference between these two groups was less significant, indicating only a trend for the effect of mid-root defects on radicular permeability. No statistically significant difference was found between teeth with CEJ defects and those with mid-root defects.
DISCUSSION Dentin permeability and cementum integrity play a key role in determining radicular penetration of 30% H202. The goal of the clinician is to increase the dentin permeability in A - NO DEFECT 8 C.E J DEFECT C 9 MID-ROOT DEFECT N=20
~, HzOz
H20z
a UJ
HzOz
231
Z
N=IO
0.03
0.02
s CEJ
CEJ
CEJ
Gutlo Percha
Gullo Per cho
Percho
Buffer
Buffer
A
Gufto
0.01
Buffe
B
C
FIG 1. A diagram of the experimental models used in the three groups tested. Group !, teeth without defects; group B, teeth with defects at the CEJ; and group C, teeth with defects at the midroot level.
A
B
C
F~G2. Comparison of the median radicular penetration of 30% hydrogen peroxide in the three groups tested.
TABLE 1. Radicular penetration of 30% hydrogen peroxide during thermocatalytic bleaching Group
No. of Teeth
Median (%)
Interquartal Range (%)
Minimum (%)
No defect CEJ Defect Mid-root defect
30 20 10
0,009 0,031 0.030
0.007-0.011 0.009-0.155 0.006-0.038
0.001 0.002 0.002
Maximum (%) 0,091 82.11 0,049
232
Rotstein et al.
order to facilitate the bleaching procedure and achieve better esthetic results. However, this may lead to more diffusion of bleaching agents to the outer surrounding tissues. In our study, artificial defects were created in different locations on the root surface to simulate situations where the radicular dentin is found devoid of cementum. Similar radicular defects may be present in human teeth due to morphological or pathological reasons. Traditional studies suggested that in 10% of teeth the cementum and enamel do not meet at the CEJ, thus leaving exposed dentin tubules. However, recent studies, using improved microscopy techniques, have indicated that the cementum-enamel relationship at the CEJ may vary among different groups of teeth in the same person and even in the same tooth itself( 12, 13). General distribution analysis of the CEJ relationships revealed that dentin exposure occurred in 18% of all cases (12). Anterior teeth presented with 25% of dentin exposures at the CEJ (12). Schroeder and Scherle (13) found that the four aspects of the same tooth may have different CEJ characteristics with dentin exposure on one side of the tooth while the other sides are fully covered with cementum. According to these authors, dentin exposure occurred more on the buccal and the distal sides. These reports suggest that the CEJ area could often be devoid of cementum in healthy teeth. Pathological conditions, including iatrogenic factors, may also cause cementum defects. Cementum and dentin resorption were reported to occur following surgical procedures and during periodontal wound healing (14, 15). Small mechanical injuries to the gingivae or to the cervical periodontal ligament could cause similar pathosis (16). Orthodontic forces, especially those applied during rapid maxillary expansion, were also associated with root resorption (17). This resorption occurs mainly on the cervical and middle thirds of the root surfaces. To this date, there are no reports indicating that these conditions act as predisposing factors for bleaching related root resorption. However, it can be speculated that in such cases a higher leakage of bleaching agents may occur. In our experimental model, teeth with defects at the CEJ were significantly more permeable to 30% hydrogen peroxide than teeth without any defects. The level of significance was as high as p = 0.0018. In clinical conditions, where such defects at the CEJ could be present, hydrogen peroxide may diffuse readily from the pulp chamber to the periodontal tissues surrounding the root. Teeth with defects at the midroot were also more permeable to hydrogen peroxide than teeth without defects, but with a lesser degree of significance. This can be explained in several ways: (a) The group of 10 teeth was too small to reach definite statistical conclusions. (b) The mid-root defects are relatively distant from the site of application of the hydrogen peroxide which reduces the amount of the solution reaching the outer surface of the root. (c) The gutta-percha filling serves as a partial barrier which prevents some of the bleaching solution from reaching the site of the defects. (d) The radicular dentin is more permeable in the cervical third than in the middle and apical thirds. This may offer an explanation why hydrogen peroxide may diffuse more readily through dentin of the cervical third of the root and the CEJ. Moreover, when groups B and C were compared, no significant difference was found between them. This further indicates the trend of group C to yield more hydrogen peroxide penetration than group A. As a result, it may be concluded that the gutta-percha filling does not possess the
Journal of Endodontics
ability to completely prevent the bleaching agent from penetrating further down the root. It is therefore recommended that the root canal filling always be protected with an isolating cement base while performing intracoronal bleaching with 30% hydrogen peroxide. Interesting results were found in the group of teeth without any defects (group A). This groups also showed some penetration of hydrogen peroxide; however the quantity was practically insignificant. In our experiment we used 20 ~1 of H202 which is the minimum amount that could be used clinically. However, in clinical conditions in which larger quantities of bleaching agent are usually applied, the potential of significant H202 penetration may exist. Several procedures during tooth preparation for the study could have an effect of hydrogen peroxide penetration. The use of sodium hypochlorite for the removal of the soft tissue from the root surface could have altered the cementum properties, although microscopic examination revealed no apparent radicular defects. The use of chloroform for the removal of residues of AH-26 sealer from the coronal access cavity could have the potential for disrupting the gutta-percha-sealer seal at the coronal level of the obturation. However, only minimal amounts of chloroform were used and they were immediately eliminated by water irrigation as in clinical practice. The exact mechanisms of bleaching-related root resorption is not yet fully understood. Several etiological mechanisms have been offered to explain this phenomenon (1-2, 4). Lado et al. (2) claimed that the bleaching agents may cause dentin denaturation at the CEJ if a defect between the enamel and the cementum is present. The denatured dentin may act as a foreign body and be attacked by elements from the periodontal tissues. At present, no experimental data exist to further support this theory. Harrington and Natkin (1) hypothosized that hydrogen peroxide used for bleaching could diffuse through patent dentinal tubules into the cervical periodontal ligament to initiate an inflammatory resorptive process. Cvek and Lindvall (4) suggested that after the seepage of hydrogen peroxide and its initial irritating effect on the periodontium, bacteria may colonize the empty tubules causing inflammation in the surrounding tissues as well as progressive root resorption. The bacteria may originate from the gingival crevice or the pulp chamber. Our findings support the hypothesis proposed by Harrington and Natkin (1) and further developed by Cvek and Lindvall (4). We believe that the initial insult to the periodontium by hydrogen peroxide can cause necrosis of the periodontal membrane or impair the normal function of this tissue. Correlation between the presence of necrotic periodontal membrane and root resorption was demonstrated by Lindskog et al. (18) in monkey's teeth. It was also demonstrated that hydrogen peroxide and other oxygen radicals are capable of causing cellular and tissue destruction (19, 20). Ramp et al. (19) found that small amounts of H202 inhibited glucose metabolism and collagen synthesis in vitro and decreased bone weight and alkaline phosphatase activity. Multiple exposures to H202 were more damaging than a single exposure (19). Ginsburg et al. (20) reported that membrane-active agents can bind to the surface of endothelial cells and enhance their susceptibility to killing by H20_~. These membrane-active agents which are capable of synergizing with H~O2 include cationic proteins, cationic polyamino acids, lysophosphatides,
Vol. 17, No. 5, May 1991
Radicular Penetration of H202
and enzymes which are capable of degrading membrane phospholipids (20). 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. We wish to extend our gratitude to Dr. Uzi Rudolfson and Dr. Lucille Rotstein for their help in obtaining the tooth material for this study and to Dr. Isaac Ginsburg for his valued suggestions. Dr. Ilan Rotstein is a lecturer, Department of Endodontics, The Hebrew University and Hadassah Faculty of Dental Medicine, Jerusalem, Israel. Dr. Yarom Torek is affiliated with the Department of Conservative Dentistry, The Hebrew University and Hadassah Faculty of Dental Medicine. Mrs. Rivka Misgav is affiliated with the Department of Oral Biology, The Hebrew University and Hadassah Faculty of Dental Medicine.
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.
233
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. Thurman RG, Ley HG, Scholz R. Hepatic microsomal ethanol oxidation. Eur J Biochem 1972;25:420-30. 12. Muller CJF, Van Wyk CW. The amelo-cemental junction. J Dent Assoc S Africa 1984;39:799-803. 13. Schroeder HE, Scherle WF. Cemento-enamel junction--revisited. J Periodont Res 1988;23:53-9. 14. Magnusson I, Claffey N, Bogle G, Garrett S, Egelberg J. Root resorption following periodontal flap procedures in monkeys. J Periodont Res 1985;20:7985. 15. Karring T, Nyman S, Lindhe J, Sirirat M. Potentials for root resorption during periodontal wound healing. J Clin Periodonto11984;11:41-52. 16. Satoshi N, Yoichiro K. Root resorption caused by mechanical injury of the periodontal soft tissues in rats. J Periodont Res 1987;22:390-5. 17. Langford SR. Root resorption extremes resulting from clinical RME. Am J Orthod 1982;81:371-7. 18. Lindskog S, Pierce AM, Blomlof L. The role of the necrotic periodontal membrane in cementum resorption and ankylosis. Endod Dent Traumatol 1985;1:96-101. 19. Ramp WK, Arnold RR, Russell JE, Yancey JM. Hydrogen peroxide inhibits glucose metabolism and collagen synthesis in bone. J Periodontol 1987;58:340-4. 20. Ginsburg I, Gibbs DF, Schuger L, Johnson KJ, Ryan US, Ward PA, Varani J. Vascular endothelial cell killing by combinations of membrane-active agents and hydrogen peroxide. Free Radic Biol Med 1989;7:369-76.
Printed in U.S.A.
VOL, 17, NO. 5, MAY 1991
Effect of Cementum Defects on Radicular Penetration of 30% H202 during Intracoronal Bleaching Ilan Rotstein, CD, Yarom Torek, DMD, and Rivka Misgav, MSc
M A T E R I A L S AND M E T H O D S
Bleaching pulpless teeth with 30% hydrogen peroxide has been reported to cause external cervical root resorption. It has been hypothesized that H202 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.
Fresh, intact uniradicular premolars, extracted for orthodontic reasons from young adults, were placed in saline and the soft tissue covering the root surface was removed with a gauze soaked with 2.5% sodium hypochlorite. The teeth were subjected to stereomicroscopic examination of the radicular cementum and the cementoenamel junction (CEJ). Thirtysix teeth without apparent cementum defects or dentin exposures at the CEJ were used for this study. Thirty teeth were assigned to the experimental group and six teeth served as controls. Root canal treatment was performed in each tooth and included biomechanical preparation followed by obturation using the lateral condensation technique of gutta-percha and AH-26 root canal sealer (De Trey Denstply, Zurich, Switzerland). The gutta-percha filling was removed 3 m m short of the CEJ level using hot pluggers. The CEJ reference points were either on the buccal or the lingual side. Remnants of gutta-percha and sealer were removed from the access cavity with a cotton pellet soaked with chloroform and a 28m m round carbide bur, rotated at a slow speed. This was followed by thorough rinsing of the pulp chamber with bidistilled water. The teeth were divided into three groups: The first group consisted of 30 teeth without any cementum defects (group A), the second group consisted of 20 teeth in which artificial defects were created at the CEJ (group B), and the third group consisted of 10 teeth in which artificial defects were created at the middle third of the root (group C). Twenty teeth from group A were chosen at random to form group B and the remaining 10 teeth were designated as group C. Thus, results could be obtained for the same teeth before and after the presence of the defects. In each tooth in group B, the cementum covering the CEJ was removed at four different points--mesial, distal, buccal, and lingual, leaving the dentin tubules in those areas exposed. This was done with a round carbide bur mounted on a slow-speed handpiece to simulate defects or irregularities along the CEJ line. In group C similar defects were created at a level 4-ram below the coronal terminal level of the gutta-percha obturation. Each tooth was mounted in a 2- • 4-cm laminate of boxing wax (Kerr Brand, Emeryville, CA) so that on one side the crown and the access cavity and on the other side the root and the CEJ were exposed. The wax laminates were adapted at a level of 1-mm above the mesial or distal line of the CEJ. In order to achieve a hermetic coronal seal the circumferential union line between the boxing wax and the enamel was sealed with sticky wax and a double layer of varnish. The outer root
A serious complication of intracoronal bleaching with 30% hydrogen peroxide is the development of external cervical root resorption (1-9). In these reports hydrogen peroxide solution was used either solely or in combination with sodium perborate. It has been hypothesized that bleaching agents, such as hydrogen peroxide, could penetrate through patent dentin tubules to initiate an inflammatory reaction followed by bacterial invasion and root resorption (1-2, 4). Fuss et al. (10) examined the diffusion capacity of bleaching materials through human dentin. In their study, a walking bleach paste composed of Superoxol and sodium perborate was introduced into the root canal space and the change of pH was recorded in the medium surrounding the root. They concluded that bleaching materials could diffuse readily through dentin (10). The purpose of this study was to examine the influence of different cementum defects and their location on the radicular penetration ability of 30% hydrogen peroxide during thermocatalytic bleaching.
230
Vol. 17, No. 5, May 1991
Radicular Penetration of H202
surfaces of the teeth, including the apical foramina, were sealed with wax, leaving the coronal one third and the CEJ exposed. In group C the area of the defects was devoid of wax. The prepared teeth mounted in the wax laminates were placed in plastic assay tubes containing 1.75 ml of bidistilled water with their entire root, including the CEJ, submerged in the solution (Fig. 1). Prior to the experiment a 0 reading on all of the samples was performed to exclude the possibility of the presence of H202 in the experimental system. The teeth were then placed in an incubator for a period of 20 rain at 37~ to simulate body temperature. Twenty microliters of 30% H202 (8.8 M) were pipetted into each access cavity of the experimental teeth. Twenty microliters were used since it was found to be the quantity able to saturate a small cotton pellet. An additional two teeth in each group served as controls in which normal saline was pipetted into the access cavity instead of H202. A test for the coronal seal of the wax and varnish was also performed by placing the same amount of H2Oz on the circumferential line. This test proved the seal efficient since no H20_~ penetration was detected. The teeth were subjected to 15 cycles of 1 rain of thermocatalytic bleaching using a 1000-W heat lamp from a distance of 50 cm. The interval between each heating cycle was 30 s. Aliquots of 0.5 ml from the solution surrounding each root were placed in a test tube containing 0.5 ml ofbidistilled water to reach a total volume of 1 ml. Quantification of the H202 was performed according to the technique used by Thurman et al. (l 1). The samples are added to ferrous ammonium chloride. If hydrogen peroxide is present, a ferric ion results and upon the addition of potassium thiocyanate a ferrithiocyanate complex is formed which absorbs light at the wavelength of 480 nm. The amount of H202 in the samples tested is determined by comparing them with a standard curve generated by known amounts of H202. A standard curve for the 30% H202 used for the experiment was established, and the samples from each tooth tested were read in a spectrophotometer and compared with the standard curve. Each sample was taken in duplicate and the whole experiment repeated three times on the same teeth. The reagents' readings served as a negative control while the
reading of pure 20 ul of 30% H202 in 1.75 ml of bidistilled water served as a positive control. The statistical analysis comparing group A with groups B and C was done using the Wilcoxon matched-pairs signed rank test. The analysis between group B and group C was done using the Mann-Wittney U test.
RESULTS The results are summarized (Table 1) and the comparison of the median penetration percentage between the different groups is represented by a bar graph (Fig. 2). Hydrogen peroxide penetration was found in all of the groups tested. The median penetration of group A (no defect) was 0.009% equivalent to 10 nmol. The median penetration of group B (CEJ defect) was 0.031% equivalent to 31.5 nmol. In group C (mid-root defect) the median penetration was 0.030% equivalent to 30.5 nmol. Group B yielded the highest scores. The top limit of its interquartal range was 0.155% and the maximum H202 penetration measured was 82.11%. The statistical analysis revealed that teeth with artificial cementum defects at the CEJ were significantly more permeable to H202 than those without defects (p < 0.01). Teeth with artificial mid-root defects were more permeable than those without defects (p < 0.025). In this case, the difference between these two groups was less significant, indicating only a trend for the effect of mid-root defects on radicular permeability. No statistically significant difference was found between teeth with CEJ defects and those with mid-root defects.
DISCUSSION Dentin permeability and cementum integrity play a key role in determining radicular penetration of 30% H202. The goal of the clinician is to increase the dentin permeability in A - NO DEFECT 8 C.E J DEFECT C 9 MID-ROOT DEFECT N=20
~, HzOz
H20z
a UJ
HzOz
231
Z
N=IO
0.03
0.02
s CEJ
CEJ
CEJ
Gutlo Percha
Gullo Per cho
Percho
Buffer
Buffer
A
Gufto
0.01
Buffe
B
C
FIG 1. A diagram of the experimental models used in the three groups tested. Group !, teeth without defects; group B, teeth with defects at the CEJ; and group C, teeth with defects at the midroot level.
A
B
C
F~G2. Comparison of the median radicular penetration of 30% hydrogen peroxide in the three groups tested.
TABLE 1. Radicular penetration of 30% hydrogen peroxide during thermocatalytic bleaching Group
No. of Teeth
Median (%)
Interquartal Range (%)
Minimum (%)
No defect CEJ Defect Mid-root defect
30 20 10
0,009 0,031 0.030
0.007-0.011 0.009-0.155 0.006-0.038
0.001 0.002 0.002
Maximum (%) 0,091 82.11 0,049
232
Rotstein et al.
order to facilitate the bleaching procedure and achieve better esthetic results. However, this may lead to more diffusion of bleaching agents to the outer surrounding tissues. In our study, artificial defects were created in different locations on the root surface to simulate situations where the radicular dentin is found devoid of cementum. Similar radicular defects may be present in human teeth due to morphological or pathological reasons. Traditional studies suggested that in 10% of teeth the cementum and enamel do not meet at the CEJ, thus leaving exposed dentin tubules. However, recent studies, using improved microscopy techniques, have indicated that the cementum-enamel relationship at the CEJ may vary among different groups of teeth in the same person and even in the same tooth itself( 12, 13). General distribution analysis of the CEJ relationships revealed that dentin exposure occurred in 18% of all cases (12). Anterior teeth presented with 25% of dentin exposures at the CEJ (12). Schroeder and Scherle (13) found that the four aspects of the same tooth may have different CEJ characteristics with dentin exposure on one side of the tooth while the other sides are fully covered with cementum. According to these authors, dentin exposure occurred more on the buccal and the distal sides. These reports suggest that the CEJ area could often be devoid of cementum in healthy teeth. Pathological conditions, including iatrogenic factors, may also cause cementum defects. Cementum and dentin resorption were reported to occur following surgical procedures and during periodontal wound healing (14, 15). Small mechanical injuries to the gingivae or to the cervical periodontal ligament could cause similar pathosis (16). Orthodontic forces, especially those applied during rapid maxillary expansion, were also associated with root resorption (17). This resorption occurs mainly on the cervical and middle thirds of the root surfaces. To this date, there are no reports indicating that these conditions act as predisposing factors for bleaching related root resorption. However, it can be speculated that in such cases a higher leakage of bleaching agents may occur. In our experimental model, teeth with defects at the CEJ were significantly more permeable to 30% hydrogen peroxide than teeth without any defects. The level of significance was as high as p = 0.0018. In clinical conditions, where such defects at the CEJ could be present, hydrogen peroxide may diffuse readily from the pulp chamber to the periodontal tissues surrounding the root. Teeth with defects at the midroot were also more permeable to hydrogen peroxide than teeth without defects, but with a lesser degree of significance. This can be explained in several ways: (a) The group of 10 teeth was too small to reach definite statistical conclusions. (b) The mid-root defects are relatively distant from the site of application of the hydrogen peroxide which reduces the amount of the solution reaching the outer surface of the root. (c) The gutta-percha filling serves as a partial barrier which prevents some of the bleaching solution from reaching the site of the defects. (d) The radicular dentin is more permeable in the cervical third than in the middle and apical thirds. This may offer an explanation why hydrogen peroxide may diffuse more readily through dentin of the cervical third of the root and the CEJ. Moreover, when groups B and C were compared, no significant difference was found between them. This further indicates the trend of group C to yield more hydrogen peroxide penetration than group A. As a result, it may be concluded that the gutta-percha filling does not possess the
Journal of Endodontics
ability to completely prevent the bleaching agent from penetrating further down the root. It is therefore recommended that the root canal filling always be protected with an isolating cement base while performing intracoronal bleaching with 30% hydrogen peroxide. Interesting results were found in the group of teeth without any defects (group A). This groups also showed some penetration of hydrogen peroxide; however the quantity was practically insignificant. In our experiment we used 20 ~1 of H202 which is the minimum amount that could be used clinically. However, in clinical conditions in which larger quantities of bleaching agent are usually applied, the potential of significant H202 penetration may exist. Several procedures during tooth preparation for the study could have an effect of hydrogen peroxide penetration. The use of sodium hypochlorite for the removal of the soft tissue from the root surface could have altered the cementum properties, although microscopic examination revealed no apparent radicular defects. The use of chloroform for the removal of residues of AH-26 sealer from the coronal access cavity could have the potential for disrupting the gutta-percha-sealer seal at the coronal level of the obturation. However, only minimal amounts of chloroform were used and they were immediately eliminated by water irrigation as in clinical practice. The exact mechanisms of bleaching-related root resorption is not yet fully understood. Several etiological mechanisms have been offered to explain this phenomenon (1-2, 4). Lado et al. (2) claimed that the bleaching agents may cause dentin denaturation at the CEJ if a defect between the enamel and the cementum is present. The denatured dentin may act as a foreign body and be attacked by elements from the periodontal tissues. At present, no experimental data exist to further support this theory. Harrington and Natkin (1) hypothosized that hydrogen peroxide used for bleaching could diffuse through patent dentinal tubules into the cervical periodontal ligament to initiate an inflammatory resorptive process. Cvek and Lindvall (4) suggested that after the seepage of hydrogen peroxide and its initial irritating effect on the periodontium, bacteria may colonize the empty tubules causing inflammation in the surrounding tissues as well as progressive root resorption. The bacteria may originate from the gingival crevice or the pulp chamber. Our findings support the hypothesis proposed by Harrington and Natkin (1) and further developed by Cvek and Lindvall (4). We believe that the initial insult to the periodontium by hydrogen peroxide can cause necrosis of the periodontal membrane or impair the normal function of this tissue. Correlation between the presence of necrotic periodontal membrane and root resorption was demonstrated by Lindskog et al. (18) in monkey's teeth. It was also demonstrated that hydrogen peroxide and other oxygen radicals are capable of causing cellular and tissue destruction (19, 20). Ramp et al. (19) found that small amounts of H202 inhibited glucose metabolism and collagen synthesis in vitro and decreased bone weight and alkaline phosphatase activity. Multiple exposures to H202 were more damaging than a single exposure (19). Ginsburg et al. (20) reported that membrane-active agents can bind to the surface of endothelial cells and enhance their susceptibility to killing by H20_~. These membrane-active agents which are capable of synergizing with H~O2 include cationic proteins, cationic polyamino acids, lysophosphatides,
Vol. 17, No. 5, May 1991
Radicular Penetration of H202
and enzymes which are capable of degrading membrane phospholipids (20). 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. We wish to extend our gratitude to Dr. Uzi Rudolfson and Dr. Lucille Rotstein for their help in obtaining the tooth material for this study and to Dr. Isaac Ginsburg for his valued suggestions. Dr. Ilan Rotstein is a lecturer, Department of Endodontics, The Hebrew University and Hadassah Faculty of Dental Medicine, Jerusalem, Israel. Dr. Yarom Torek is affiliated with the Department of Conservative Dentistry, The Hebrew University and Hadassah Faculty of Dental Medicine. Mrs. Rivka Misgav is affiliated with the Department of Oral Biology, The Hebrew University and Hadassah Faculty of Dental Medicine.
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