The Effect of Carbamide-Peroxide Gel on the Shear Bond Strength of a Microfil Resin to Bovine Enamel K.C. TITLEY, C.D. TORNECK1, and N.D. RUSE2 Department of Pediatric Dentistry, 'Department of Endodontics, and 2Centre for Biomaterials, Faculty ofDentistry, University of Toronto, 124 Edward Street, Toronto, Ontario, Canada M5G 1G6
Cylinders of a visible-light-cured microfil resin were formed on, and bonded to, the flattened labial enamel surfaces of young bovine incisor teeth which had previously been subjected to four different treatments: (1) immersion in 10% carbamide-peroxide gel, pH 4.7, for three h; (2) immersion in 10% carbamide-peroxide gel, pH 4.7, for six h; (3) immersion in 10% carbamide-peroxide gel, pH 7.2, for three h; and (4) immersion in 10% carbamide-peroxide gel, pH 7.2, for six h. For each experimental group, a control group ofresin-bonded to saline-immersed teeth was prepared. In addition, two groups, prepared according to treatment 4, were leached in distilled water for one and seven d, respectively, prior to resin application. Specimens were stored in distilled water at 370C for seven d prior to shear-bond-strength testing. A total of 90 teeth was tested. Statistical analysis of the results indicated that there was a highly significant reduction in the shear bond strength to carbamideperoxide-treated enamel as compared with that to saline-treated enamel. The effects of duration of peroxide treatment and pH, as well as the interaction term, were not statistically significant. Leaching of the peroxide-treated enamel in water for either one or seven d prior to resin application restored the adhesiveness of the enamel. Scanning electron microscopic examination of randomly selected, fractured test specimens indicated that the peroxideinduced reduction in enamel adhesiveness was related to alterations in both attachment-surface area at the resin-enamel interface and resin quality. J Dent Res 71(1):20-24, January, 1992
Introduction. The use of peroxide-based self-applied tooth-whitening agents has increased substantially in the past few years, despite many unanswered questions that attend their use. Thus, little is known about their biological and physical effects, particularly with respect to their local and systemic toxicity, their mutagenic potential, their influence on oral and gastro-intestinal flora, their effects on hard and soft oral tissues, and their effects on dental restorative materials. Previous investigations (Titleyet al., 1988; Torneck et al., 1990, 1991) have identified a substantial reduction in bond strengths to enamel shortly after its exposure to concentrated aqueous solutions of hydrogen-peroxide. The purpose of this investigation was to determine whether similar sequelae attended the use of 10% carbamide-peroxide, the less concentrated organic-based peroxide, which is the primary active ingredient used in most tooth-whitening products used in the home.
Materials and methods. A commercially available generic 10% carbamide-peroxide (CP) gel (Kirkwood Pharm., Houston, TX), having a pH of 4.7, was obtained and stored in a dark place at room temperature. So that the effect Received for publication April 29, 1991 Accepted for publication August 22, 1991 This investigation was supported in part by an MRC grant and by the Dean's Fund for Research, Faculty of Dentistry, University of Toronto.
of CP could be tested at both an acidic and a neutral pH, sodium hydroxide was added to the as-received solution, for adjustment of its pH to 7.2. Normal saline (S) solution (0.9% sodium chloride; Travenol Canada, Inc.) was used as the control reagent. A commercially available etching gel (ScotchBond Etching Gel, 3M Canada Inc.), containing 37% phosphoric acid, was used as the etching agent (E). A commercially-available visible-light-cured microfil restorative resin, Silux Plus (3M Canada Inc.), was used as the test resin. A visible-light-cured dental adhesive, ScotchBond 2 (3M Canada Inc.), was used to mediate the bond between the resin and enamel. Incisors were obtained from young cattle killed at a local abattoir. Only young animals having no more than four erupted permanent incisors were selected. The teeth were transported, in cold water, to the laboratory, where they were cleaned and decoronated with a band saw. The coronal pulp was removed with a dental explorer, and the crowns were washed in water. The teeth were then stored in water in a tightly sealed container at 40C until required, a period not exceeding six months. To ensure that the teeth could be held in a stable position when placed in a brass jig (Ruse, 1988; Titleyet al., 1988) for shear testing, the mesial and distal surfaces of each bovine incisor were ground parallel to one another with 180-grit silicon carbide (SiC) grinding paper on a water-irrigated grinding wheel. Immediatelybefore use, a central portion of the labial enamel surface was ground flat with 600-grit SiC grinding paper on a water-irrigated grinding wheel. Ten groups of specimens, six experimental and four control, were prepared for shear-bond-strength testing according to the protocol presented in Table 1. In each group, the teeth were placed, with the flattened labial enamel surfaces down, into a Petri dish which was lined with two pieces of#1 filter paper. Depending upon whether the group was designated as control or experimental, the Petri dish was filled with 20 mL of saline or 20 mL of carbamide-peroxide, respectively. The immersed teeth were stored at 370C for either three or six h. The samples of two experimental groups (IX and X in Table 1) were further leached in distilled water at 370C for one and seven d, respectively. After storage in the test and control solutions (groups IVIII) and after being leached in distilled water (groups IX and X), the teeth were washedwith running distilledwater for60 s and driedwith compressed air for 30 s. Etching gel was applied to the flattened portion ofthe labial enamel for a period of60 s. Each tooth was then washedwith distilled water for 30 s and dried with compressed air for 15 s. The bonding resin was applied in a thin layer to the etched enamel surface and light-cured (COE-Lite Model 4000, Imperial Chemical Industries PLC, Cheshire, England) for 20 s, in accordance with the manufacturer's instructions. The tooth was then placed in a mounting jig (Ruse, 1988; Titley et al., 1988), and the lid-carrying a clear silicone diaphragm lined with a gelatine cylinder, cut from a #4 gelatine capsule-was placed over the flattened area of the labial surface. Silux Plus resin was packed into the lined diaphragm and light-cured for 60 s, in accordance with the manufacturer's instructions for the thickness of resin used. The lid and the diaphragm were carefully removed after initial resin curing, and the resin was lightcured for an additional 40 s. This produced resin cylinders with a constant-contact area of 14 mm2 between the resin and the enamel. The tooth, with its attached resin cylinder, was stored in distilled water at 37°C for seven d prior to being tested. For the shear-bond-strength tests, the samples were placed in the
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ADHESION TO BLECHED ENAMEL
V61. 71 IV. 1
21
Fig 1+A) Portion of enamel suirface of a three hour aline treated specimen. Tangentially fractured filled resin is present at the pe iphery (left, The central areas eonsist of exposed and bondmng- esinrcovLerd enan prsms and islets and rides o dsidual flled resin (arw) (B Higher power xicrograph of islet of resin dheren o the enamel surfa e
IABLE 2 SHEAR BOND STRENGTHS, MEANS, AND SIANDARD DEVIATIONS, IN MPa
TABLE I
SAMPLE PREPARATION PROCEDURES
Steps
Group
Leach (d
lime (h
I
10
3
CP (4.7)
II
10
3
S
III
10
6
IV
10
6
V
10
3
VI
10
3
CP (4.7) S CP (7.2) S
VII
10
6
VIll Ix
10
6
5
6
1
x
5
6
7
CP 72) S
n = no. of samples/group. CP =
carbamide-peroxide;
Duratior of Car~bamide Peroxide Exposure (h
Solutior (pH)
n
CP (7*2) CP (7.2)
Ireatrent CP pH 4.I
13.8
S
21.3 ± 2.8
20.4 + 24
CP pH 7.2
15.2 ± 3.8
13.7 ± 3.6
S
21.5 + 3.1
21.0
CPpH 7.2, 1 d HO
not available
24,6 ± 4.0
CP pH 7-2,7 d H2O
not available
18.1± 4.6
CP S
6
3
carbamide
peroxide; S
2.4
saine;
sane.
Downloaded from jdr.sagepub.com at Bobst Library, New York University on June 6, 2015 For personal use only. No other uses without permission.
14.7
2.9
+
4.4
stored in water at 37
22
J Dent Res January 1992
TI7MY et al.
Fig 2 A Enamel surface ofsix hour CFtreat4d specnun (pH 47). Periphery ofthe linrder hseisprest in the lower left. TVe central areas consist of expoed ard bording resm-coved enamel pr sm d islet ofresiduali ed resin (arr). (B) Higher pover photomicrograph of le of resin adherent to th enamel surface. Ite resi appear granular ad p us bracs 'G that the resin cylinder was ahlwa aned at 900 t the vertical plane. Theji was placed on the platen of a Universal testing machine (Iistron, Model TT.CM, Canton, MA) and positioned so that the shearing blade came into contact vith the resin cylinder at he enamel-resin interface, A 500 kg reversible load cell wa used at a fu-scale readingof 100kg. The testing machine was set with a chart speed of 100 mmhmin and a crossbeand speed of 5 inim/n Phe specimens were tested to failure and the results record in MPa The results of the shear bond strength tests were subectad to a 2 x 4 general fctorial design analysis of variance (GFDANOVA) A modi fled (Bonferroni) t test was used for between-group comparisons. One to from each group was selected at random and prepared for scanning electron microscopic (SEM) examination The teeti were mounted on SEM stubs to present the labia surfaces for examination, coated with 15 nm of gold in a Polaron E5100 SEM coating unit, and examined with a Hitachi S-2500 SEM. Photomi crographs were taken of each specimen at magnification of x50,
x530O ad xC2000. areas specific interest were examined and photographed at higher magnifications.
Results The results of the shear bond strength tests are summarized in Tahi 2. Th GFDANOVA of the results (groups IX and X not included) Table 3, showed that there was a statistically significant difference (p < 0.01) due to sample treatment. The modified (Bonferroni) t test showed that the difference lay between the S and the CP groups (p < 0.01). There were no statistically significant difrences due to tine of exposure three h vs. six h) or pH (4.7 vs. 7.2). The interaction term was also not statistically significant. All the examined specimens displayed a tangential pattern of failure in which there were various degrees of exposed enamel prisms resin-covered enamel, and randomly dispersed islets of
TABLE 3 Source of Variation
Treatment Time Interaction Within group
RESULTS OF THE 2 x 4 GEDANOVA STATISHCAL ANALYSIS Mean Squares Sum of Sqares Degrees of Freedom 3 1070.8 356.9 5.9 5.9 18.6
3
6.2
1161.4
95
12.2
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0.49
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71 No. 1 1 BLEACHED ENAME2L23 Vol.VADHESION
glycerol base (Miller 1989) Carbamide-peroxide (H N.CO.NH2 H 0 ) is urea containing 34% hydrogen-peroxide (Martindale, 1989). ThuS, whenbroken down, these 10% products have the potential to release 3.4% hydrogen-peroxide for tooth bleaching. The break down reportedly occurs more readily at a low pH than at a higher pH. Products currently on the market have a pH range of fom 4.0 to 7.5. Two CP pH 1eveIs 4.7 and 7.2, were selected for use in our investigation to determine whether enamel adhesiveness would be differently affected by the use of an acidic or a neutral product The recommended time ofCP application is variable, and, in the absence of professional guidance in the self applied products, itis potentially unlimited Most of the products are gels which are applied to the teeth on a nightly basis in a pre- or customfbriicated bleaching tray. In anticipaton that the average period of contact in such circumstances is between five and six h per night, two peroxideexposure times ofthree and six h were selected in this investigation as being representative of possible night time periods. The shear, rather than the tensile, mode of testing was selected for this study, because it was considered that it would more accurately reflect the types of fores generated on veneer restorations in the mouth. Statistical analysis of the data showed that exposure of the enamel to 10% CP for a period of three or six h resulted in a statistically signify cant reduction in the bond strength ofSilux resin to bovine enamel. T education however, was s~ubtaantay less when compared with the results of similar tests where concentrated (35%) aqueous hydrogen-peroxide was used (Titleyet a., 198 ). Since OP glycerol products are more viscous than the aqueous form of hydrogen-peroxide, the leaching of P-treated enamel in water was undertaken to determine whether its adhesiveness could be restored. The results showed that leaching CPtreated teeth in water for at Fig 3-Prto of enamel surfac of sixhou CP treated specimen (pH least one day resulted in shear bond-strength values at least equal T2). Displayed enamnl, adherent bonding resin, and sewvral islets of to those of the control samples The reduction in the adhesiveness of the CPreated cnamel can residual filled resin marrow There i evdcncc of bubble formation in the bonding resin. be explained on the basis of the resin/peroxide interaction that occurs at the rcsin-enamel interfae. SEM examination of CP treated samples revealed the presence of a granular. more porous adherent filled-resin. Significant differences were noted in the appearing resin at he cylinder base. In one of the examined appearances of the residual resin on S compared with CPtreated specimens there was also evidence ofbubbling in the bonding resin specimens. All of the filled-resin islets in the former specimens still adhering to the enamel surface. These occurrences were not as appeared solid in consistency and fragmented at the fractured widespread or as marked as those that were seen in our previous surfaces (Figs. IA and 1B), while in some of the latter specimens the studies, where concentrated (35%) aqueous hydrogen-peroxide was islets appeared granular and porous (Figs 2A and 2B). In one ofthe used(Titleyetal., 1988Tornecketal., 1990,1991). Theymaybedue six-hour CP specimens, the bonding resin, still adherent to the to gaseous ubbing, which could be the result of oxidizing reactions enamel surface, had a bubbled appearance (Fig. 3). due to the entrapment of peroxide in the subsurface layer of the enamel. The entrapment of the peroxide probably took place via transportationalong interpnsmatic spaces (Borggrevenet at., 1977; Discussion. Bowles and Ugwuneri, 1987) and it was not affected by thc brief Bovine teeth have been used in a number of our investigations for rinsing and drying to which the samples were exposed affer being comparison of the bond strength ofa restoraive material tobleaed bleached. Elimination ofthe entrapped peroxide can be achieved by and unbleached enamel surfaces. When stored, handled, and leaching in water, as evidenced by the results of is and previous prepared in a prescribed manner, they yielded bond strengths that, investigations rorneck et al., 1991). It is also of particular interest while not the same, were comparable with those obtained with that, once the entrapped peroxde is eliminated, the result is an human teeth (Nakamichi, 1982; Nakamichi et at., 1983. Other enamel surface which may show increased adhesiveness. This studies have shown that the bond strength of a resin to enamel was increase is probably caused by the reduction in surface and subsur significantly compromised when the resin was applied to an enamel face contaminants, which in turn results in more efctive etching surface which had previously been bleached with concentrated and resin penetration. The results obtained in our investigation could, in part, dem(35%) aqeous hydrogen-peroxide (Titleyetal., 1988; Iornecket al. onstrate he effect on the enamelresin bond strength that might be 1990, 1991). Tooth bleaching with concentrated aqueous hydrogen-peroxide expected if a resin is placed on an enamel surface immediately is a procedure which is generally done, as a dental clinical proce bowing removal of a bleaching tray and a brief syringe-washing dure, on a controlled basis over a limited period of time Weinman et and airwdrying of a tooth. The results, however, do not provide an at., 1987) Home bleaching products for tooth lightening have answer to whether the reduction in enamel adhesiveness brought recently been introduced into the professional and consumer mar* about by exposure to CP products is clinically significant. It may ket. The active ingredient in many of these products is carbamide- well be that the reduced enamel-resin bond strength s still sufficient peroxide, in a concentration of 10%, incorporated nto an anhydrous to resist the forces that may or could bpe generaed against a resin or Downloaded from jdr.sagepub.com at Bobst Library, New York University on June 6, 2015 For personal use only. No other uses without permission.
24
J Dent Res January 1992
TITLEY et al.
porcelain veneer during normal oral function. Until further data are available, however, we recommend, as in our previous studies, that restorative procedures encompassing acid etching be delayed at least 24 h following any bleaching procedures that are peroxidebased. REFERENCES BORGGREVEN, J.M.P.; VAN DIJK, J.W.E.; and DRIESSENS, F.C.M. (1977): A Quantitative Radiochemical Study of Ionic and Molecular Transport in Bovine Dental Enamel, Arch Oral Biol 22:467-472. BOWLES, W.H. and UGWUNERI, Z. (1987): Pulp Chamber Penetration by Hydrogen Peroxide Following Vital Bleaching Procedures, J Endodont 13:375-377. FEINMAN,R.A.; GOLDSTEIN, R.E.; andGARBER, D.A. (1987): Bleaching Teeth, Chicago: Quintessence Pub. Co. MARTINDALE, W. (1989): Martindale: The Extra Pharmacopoeia,
J.E.F. Reynolds, Ed., London: Pharmaceutical Press, pp. 1627. MILLER, M.B., Ed. (1989): Reality, Houston, TX: Reality Pub. Co., Vol. 3, pp. 110-118. NAKAMICHI, I. (1982): Adhesion of Various Dental Restorative Materials to Human and Bovine Teeth, Koku-Byo-Gattkaish 49:31-39. NAKAMICHI, I.; IWAKU, M.; and FUSAYAMA, T. (1983): Bovine Teeth as Possible Substitutes in the Adhesion Test, JDent Res 62:1076-1081. RUSE, N.D. (1988): Studies on Bonding to Teeth, PhD Thesis, University of Toronto. TITLEY, K; TORNECK, C.D.; SMITH, D.C.; and ADIBFAR, A. (1988): Adhesion of Composite Resin to Bleached and Unbleached Bovine Enamel, JDent Res 67:1523-1528. TORNECK, C.D.; TITLEY, K; SMITH, D.C.; and ADIBFAR, A. (1990): The Influence of Time of Hydrogen Peroxide Exposure on the Adhesion of Composite Resin to Bleached Bovine Enamel, JEndodont 16:123-128. TORNECK, C.D.; TITLEY, K; SMITH, D.C.; and ADIBFAR, A. (1991): The Influence of Leaching on the Adhesion of Light-cured Composite Resin to Bleached Bovine Enamel, JEndodont 17:156-160.
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Cylinders of a visible-light-cured microfil resin were formed on, and bonded to, the flattened labial enamel surfaces of young bovine incisor teeth which had previously been subjected to four different treatments: (1) immersion in 10% carbamide-peroxide gel, pH 4.7, for three h; (2) immersion in 10% carbamide-peroxide gel, pH 4.7, for six h; (3) immersion in 10% carbamide-peroxide gel, pH 7.2, for three h; and (4) immersion in 10% carbamide-peroxide gel, pH 7.2, for six h. For each experimental group, a control group ofresin-bonded to saline-immersed teeth was prepared. In addition, two groups, prepared according to treatment 4, were leached in distilled water for one and seven d, respectively, prior to resin application. Specimens were stored in distilled water at 370C for seven d prior to shear-bond-strength testing. A total of 90 teeth was tested. Statistical analysis of the results indicated that there was a highly significant reduction in the shear bond strength to carbamideperoxide-treated enamel as compared with that to saline-treated enamel. The effects of duration of peroxide treatment and pH, as well as the interaction term, were not statistically significant. Leaching of the peroxide-treated enamel in water for either one or seven d prior to resin application restored the adhesiveness of the enamel. Scanning electron microscopic examination of randomly selected, fractured test specimens indicated that the peroxideinduced reduction in enamel adhesiveness was related to alterations in both attachment-surface area at the resin-enamel interface and resin quality. J Dent Res 71(1):20-24, January, 1992
Introduction. The use of peroxide-based self-applied tooth-whitening agents has increased substantially in the past few years, despite many unanswered questions that attend their use. Thus, little is known about their biological and physical effects, particularly with respect to their local and systemic toxicity, their mutagenic potential, their influence on oral and gastro-intestinal flora, their effects on hard and soft oral tissues, and their effects on dental restorative materials. Previous investigations (Titleyet al., 1988; Torneck et al., 1990, 1991) have identified a substantial reduction in bond strengths to enamel shortly after its exposure to concentrated aqueous solutions of hydrogen-peroxide. The purpose of this investigation was to determine whether similar sequelae attended the use of 10% carbamide-peroxide, the less concentrated organic-based peroxide, which is the primary active ingredient used in most tooth-whitening products used in the home.
Materials and methods. A commercially available generic 10% carbamide-peroxide (CP) gel (Kirkwood Pharm., Houston, TX), having a pH of 4.7, was obtained and stored in a dark place at room temperature. So that the effect Received for publication April 29, 1991 Accepted for publication August 22, 1991 This investigation was supported in part by an MRC grant and by the Dean's Fund for Research, Faculty of Dentistry, University of Toronto.
of CP could be tested at both an acidic and a neutral pH, sodium hydroxide was added to the as-received solution, for adjustment of its pH to 7.2. Normal saline (S) solution (0.9% sodium chloride; Travenol Canada, Inc.) was used as the control reagent. A commercially available etching gel (ScotchBond Etching Gel, 3M Canada Inc.), containing 37% phosphoric acid, was used as the etching agent (E). A commercially-available visible-light-cured microfil restorative resin, Silux Plus (3M Canada Inc.), was used as the test resin. A visible-light-cured dental adhesive, ScotchBond 2 (3M Canada Inc.), was used to mediate the bond between the resin and enamel. Incisors were obtained from young cattle killed at a local abattoir. Only young animals having no more than four erupted permanent incisors were selected. The teeth were transported, in cold water, to the laboratory, where they were cleaned and decoronated with a band saw. The coronal pulp was removed with a dental explorer, and the crowns were washed in water. The teeth were then stored in water in a tightly sealed container at 40C until required, a period not exceeding six months. To ensure that the teeth could be held in a stable position when placed in a brass jig (Ruse, 1988; Titleyet al., 1988) for shear testing, the mesial and distal surfaces of each bovine incisor were ground parallel to one another with 180-grit silicon carbide (SiC) grinding paper on a water-irrigated grinding wheel. Immediatelybefore use, a central portion of the labial enamel surface was ground flat with 600-grit SiC grinding paper on a water-irrigated grinding wheel. Ten groups of specimens, six experimental and four control, were prepared for shear-bond-strength testing according to the protocol presented in Table 1. In each group, the teeth were placed, with the flattened labial enamel surfaces down, into a Petri dish which was lined with two pieces of#1 filter paper. Depending upon whether the group was designated as control or experimental, the Petri dish was filled with 20 mL of saline or 20 mL of carbamide-peroxide, respectively. The immersed teeth were stored at 370C for either three or six h. The samples of two experimental groups (IX and X in Table 1) were further leached in distilled water at 370C for one and seven d, respectively. After storage in the test and control solutions (groups IVIII) and after being leached in distilled water (groups IX and X), the teeth were washedwith running distilledwater for60 s and driedwith compressed air for 30 s. Etching gel was applied to the flattened portion ofthe labial enamel for a period of60 s. Each tooth was then washedwith distilled water for 30 s and dried with compressed air for 15 s. The bonding resin was applied in a thin layer to the etched enamel surface and light-cured (COE-Lite Model 4000, Imperial Chemical Industries PLC, Cheshire, England) for 20 s, in accordance with the manufacturer's instructions. The tooth was then placed in a mounting jig (Ruse, 1988; Titley et al., 1988), and the lid-carrying a clear silicone diaphragm lined with a gelatine cylinder, cut from a #4 gelatine capsule-was placed over the flattened area of the labial surface. Silux Plus resin was packed into the lined diaphragm and light-cured for 60 s, in accordance with the manufacturer's instructions for the thickness of resin used. The lid and the diaphragm were carefully removed after initial resin curing, and the resin was lightcured for an additional 40 s. This produced resin cylinders with a constant-contact area of 14 mm2 between the resin and the enamel. The tooth, with its attached resin cylinder, was stored in distilled water at 37°C for seven d prior to being tested. For the shear-bond-strength tests, the samples were placed in the
20 Downloaded from jdr.sagepub.com at Bobst Library, New York University on June 6, 2015 For personal use only. No other uses without permission.
ADHESION TO BLECHED ENAMEL
V61. 71 IV. 1
21
Fig 1+A) Portion of enamel suirface of a three hour aline treated specimen. Tangentially fractured filled resin is present at the pe iphery (left, The central areas eonsist of exposed and bondmng- esinrcovLerd enan prsms and islets and rides o dsidual flled resin (arw) (B Higher power xicrograph of islet of resin dheren o the enamel surfa e
IABLE 2 SHEAR BOND STRENGTHS, MEANS, AND SIANDARD DEVIATIONS, IN MPa
TABLE I
SAMPLE PREPARATION PROCEDURES
Steps
Group
Leach (d
lime (h
I
10
3
CP (4.7)
II
10
3
S
III
10
6
IV
10
6
V
10
3
VI
10
3
CP (4.7) S CP (7.2) S
VII
10
6
VIll Ix
10
6
5
6
1
x
5
6
7
CP 72) S
n = no. of samples/group. CP =
carbamide-peroxide;
Duratior of Car~bamide Peroxide Exposure (h
Solutior (pH)
n
CP (7*2) CP (7.2)
Ireatrent CP pH 4.I
13.8
S
21.3 ± 2.8
20.4 + 24
CP pH 7.2
15.2 ± 3.8
13.7 ± 3.6
S
21.5 + 3.1
21.0
CPpH 7.2, 1 d HO
not available
24,6 ± 4.0
CP pH 7-2,7 d H2O
not available
18.1± 4.6
CP S
6
3
carbamide
peroxide; S
2.4
saine;
sane.
Downloaded from jdr.sagepub.com at Bobst Library, New York University on June 6, 2015 For personal use only. No other uses without permission.
14.7
2.9
+
4.4
stored in water at 37
22
J Dent Res January 1992
TI7MY et al.
Fig 2 A Enamel surface ofsix hour CFtreat4d specnun (pH 47). Periphery ofthe linrder hseisprest in the lower left. TVe central areas consist of expoed ard bording resm-coved enamel pr sm d islet ofresiduali ed resin (arr). (B) Higher pover photomicrograph of le of resin adherent to th enamel surface. Ite resi appear granular ad p us bracs 'G that the resin cylinder was ahlwa aned at 900 t the vertical plane. Theji was placed on the platen of a Universal testing machine (Iistron, Model TT.CM, Canton, MA) and positioned so that the shearing blade came into contact vith the resin cylinder at he enamel-resin interface, A 500 kg reversible load cell wa used at a fu-scale readingof 100kg. The testing machine was set with a chart speed of 100 mmhmin and a crossbeand speed of 5 inim/n Phe specimens were tested to failure and the results record in MPa The results of the shear bond strength tests were subectad to a 2 x 4 general fctorial design analysis of variance (GFDANOVA) A modi fled (Bonferroni) t test was used for between-group comparisons. One to from each group was selected at random and prepared for scanning electron microscopic (SEM) examination The teeti were mounted on SEM stubs to present the labia surfaces for examination, coated with 15 nm of gold in a Polaron E5100 SEM coating unit, and examined with a Hitachi S-2500 SEM. Photomi crographs were taken of each specimen at magnification of x50,
x530O ad xC2000. areas specific interest were examined and photographed at higher magnifications.
Results The results of the shear bond strength tests are summarized in Tahi 2. Th GFDANOVA of the results (groups IX and X not included) Table 3, showed that there was a statistically significant difference (p < 0.01) due to sample treatment. The modified (Bonferroni) t test showed that the difference lay between the S and the CP groups (p < 0.01). There were no statistically significant difrences due to tine of exposure three h vs. six h) or pH (4.7 vs. 7.2). The interaction term was also not statistically significant. All the examined specimens displayed a tangential pattern of failure in which there were various degrees of exposed enamel prisms resin-covered enamel, and randomly dispersed islets of
TABLE 3 Source of Variation
Treatment Time Interaction Within group
RESULTS OF THE 2 x 4 GEDANOVA STATISHCAL ANALYSIS Mean Squares Sum of Sqares Degrees of Freedom 3 1070.8 356.9 5.9 5.9 18.6
3
6.2
1161.4
95
12.2
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F 2919
0.49
0.51
71 No. 1 1 BLEACHED ENAME2L23 Vol.VADHESION
glycerol base (Miller 1989) Carbamide-peroxide (H N.CO.NH2 H 0 ) is urea containing 34% hydrogen-peroxide (Martindale, 1989). ThuS, whenbroken down, these 10% products have the potential to release 3.4% hydrogen-peroxide for tooth bleaching. The break down reportedly occurs more readily at a low pH than at a higher pH. Products currently on the market have a pH range of fom 4.0 to 7.5. Two CP pH 1eveIs 4.7 and 7.2, were selected for use in our investigation to determine whether enamel adhesiveness would be differently affected by the use of an acidic or a neutral product The recommended time ofCP application is variable, and, in the absence of professional guidance in the self applied products, itis potentially unlimited Most of the products are gels which are applied to the teeth on a nightly basis in a pre- or customfbriicated bleaching tray. In anticipaton that the average period of contact in such circumstances is between five and six h per night, two peroxideexposure times ofthree and six h were selected in this investigation as being representative of possible night time periods. The shear, rather than the tensile, mode of testing was selected for this study, because it was considered that it would more accurately reflect the types of fores generated on veneer restorations in the mouth. Statistical analysis of the data showed that exposure of the enamel to 10% CP for a period of three or six h resulted in a statistically signify cant reduction in the bond strength ofSilux resin to bovine enamel. T education however, was s~ubtaantay less when compared with the results of similar tests where concentrated (35%) aqueous hydrogen-peroxide was used (Titleyet a., 198 ). Since OP glycerol products are more viscous than the aqueous form of hydrogen-peroxide, the leaching of P-treated enamel in water was undertaken to determine whether its adhesiveness could be restored. The results showed that leaching CPtreated teeth in water for at Fig 3-Prto of enamel surfac of sixhou CP treated specimen (pH least one day resulted in shear bond-strength values at least equal T2). Displayed enamnl, adherent bonding resin, and sewvral islets of to those of the control samples The reduction in the adhesiveness of the CPreated cnamel can residual filled resin marrow There i evdcncc of bubble formation in the bonding resin. be explained on the basis of the resin/peroxide interaction that occurs at the rcsin-enamel interfae. SEM examination of CP treated samples revealed the presence of a granular. more porous adherent filled-resin. Significant differences were noted in the appearing resin at he cylinder base. In one of the examined appearances of the residual resin on S compared with CPtreated specimens there was also evidence ofbubbling in the bonding resin specimens. All of the filled-resin islets in the former specimens still adhering to the enamel surface. These occurrences were not as appeared solid in consistency and fragmented at the fractured widespread or as marked as those that were seen in our previous surfaces (Figs. IA and 1B), while in some of the latter specimens the studies, where concentrated (35%) aqueous hydrogen-peroxide was islets appeared granular and porous (Figs 2A and 2B). In one ofthe used(Titleyetal., 1988Tornecketal., 1990,1991). Theymaybedue six-hour CP specimens, the bonding resin, still adherent to the to gaseous ubbing, which could be the result of oxidizing reactions enamel surface, had a bubbled appearance (Fig. 3). due to the entrapment of peroxide in the subsurface layer of the enamel. The entrapment of the peroxide probably took place via transportationalong interpnsmatic spaces (Borggrevenet at., 1977; Discussion. Bowles and Ugwuneri, 1987) and it was not affected by thc brief Bovine teeth have been used in a number of our investigations for rinsing and drying to which the samples were exposed affer being comparison of the bond strength ofa restoraive material tobleaed bleached. Elimination ofthe entrapped peroxide can be achieved by and unbleached enamel surfaces. When stored, handled, and leaching in water, as evidenced by the results of is and previous prepared in a prescribed manner, they yielded bond strengths that, investigations rorneck et al., 1991). It is also of particular interest while not the same, were comparable with those obtained with that, once the entrapped peroxde is eliminated, the result is an human teeth (Nakamichi, 1982; Nakamichi et at., 1983. Other enamel surface which may show increased adhesiveness. This studies have shown that the bond strength of a resin to enamel was increase is probably caused by the reduction in surface and subsur significantly compromised when the resin was applied to an enamel face contaminants, which in turn results in more efctive etching surface which had previously been bleached with concentrated and resin penetration. The results obtained in our investigation could, in part, dem(35%) aqeous hydrogen-peroxide (Titleyetal., 1988; Iornecket al. onstrate he effect on the enamelresin bond strength that might be 1990, 1991). Tooth bleaching with concentrated aqueous hydrogen-peroxide expected if a resin is placed on an enamel surface immediately is a procedure which is generally done, as a dental clinical proce bowing removal of a bleaching tray and a brief syringe-washing dure, on a controlled basis over a limited period of time Weinman et and airwdrying of a tooth. The results, however, do not provide an at., 1987) Home bleaching products for tooth lightening have answer to whether the reduction in enamel adhesiveness brought recently been introduced into the professional and consumer mar* about by exposure to CP products is clinically significant. It may ket. The active ingredient in many of these products is carbamide- well be that the reduced enamel-resin bond strength s still sufficient peroxide, in a concentration of 10%, incorporated nto an anhydrous to resist the forces that may or could bpe generaed against a resin or Downloaded from jdr.sagepub.com at Bobst Library, New York University on June 6, 2015 For personal use only. No other uses without permission.
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J Dent Res January 1992
TITLEY et al.
porcelain veneer during normal oral function. Until further data are available, however, we recommend, as in our previous studies, that restorative procedures encompassing acid etching be delayed at least 24 h following any bleaching procedures that are peroxidebased. REFERENCES BORGGREVEN, J.M.P.; VAN DIJK, J.W.E.; and DRIESSENS, F.C.M. (1977): A Quantitative Radiochemical Study of Ionic and Molecular Transport in Bovine Dental Enamel, Arch Oral Biol 22:467-472. BOWLES, W.H. and UGWUNERI, Z. (1987): Pulp Chamber Penetration by Hydrogen Peroxide Following Vital Bleaching Procedures, J Endodont 13:375-377. FEINMAN,R.A.; GOLDSTEIN, R.E.; andGARBER, D.A. (1987): Bleaching Teeth, Chicago: Quintessence Pub. Co. MARTINDALE, W. (1989): Martindale: The Extra Pharmacopoeia,
J.E.F. Reynolds, Ed., London: Pharmaceutical Press, pp. 1627. MILLER, M.B., Ed. (1989): Reality, Houston, TX: Reality Pub. Co., Vol. 3, pp. 110-118. NAKAMICHI, I. (1982): Adhesion of Various Dental Restorative Materials to Human and Bovine Teeth, Koku-Byo-Gattkaish 49:31-39. NAKAMICHI, I.; IWAKU, M.; and FUSAYAMA, T. (1983): Bovine Teeth as Possible Substitutes in the Adhesion Test, JDent Res 62:1076-1081. RUSE, N.D. (1988): Studies on Bonding to Teeth, PhD Thesis, University of Toronto. TITLEY, K; TORNECK, C.D.; SMITH, D.C.; and ADIBFAR, A. (1988): Adhesion of Composite Resin to Bleached and Unbleached Bovine Enamel, JDent Res 67:1523-1528. TORNECK, C.D.; TITLEY, K; SMITH, D.C.; and ADIBFAR, A. (1990): The Influence of Time of Hydrogen Peroxide Exposure on the Adhesion of Composite Resin to Bleached Bovine Enamel, JEndodont 16:123-128. TORNECK, C.D.; TITLEY, K; SMITH, D.C.; and ADIBFAR, A. (1991): The Influence of Leaching on the Adhesion of Light-cured Composite Resin to Bleached Bovine Enamel, JEndodont 17:156-160.
Downloaded from jdr.sagepub.com at Bobst Library, New York University on June 6, 2015 For personal use only. No other uses without permission.
