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

An in vitro comparative evaluation of intraorifice barriers and bleaching agents on the fracture resistance of the endodontically treated anterior teeth

Aim

This study aimed to evaluate and compare the impact of different bleaching agents on the fracture resistance of endodontically treated teeth when using either GC Fuji type 2 glass ionomer cement (GIC) or Shofu Glass Ionomer RX EASE as intraorifice barriers (IOB).

Materials and Methods

A total of 80 single-rooted human maxillary central incisors were prepared and obturated. Three millimeters of gutta-percha was then removed from the orifice. The specimens were divided into two primary groups based on the type of IOB material used: GC Fuji type 2 GIC and Shofu Glass Ionomer RX EASE (n = 40). Each group was further divided into four subgroups based on the bleaching agent used: Carbamide peroxide (CP) 37%, sodium perborate (SP), hydrogen peroxide (HP) 35%, and distilled water used as the control (n = 10). The teeth were subjected to fracture resistance testing.

Results

The study found that the order of root fracture resistance was control > CP > SP > HP. There was no statistically significant difference in fracture resistance between GC Fuji type 2 GIC and Shofu Glass Ionomer RX EASE when used as IOB materials.

Conclusion

The study concluded that the choice of bleaching agent significantly affects the fracture resistance of endodontically treated teeth. It was observed that fracture resistance is lowest with HP, followed by SP and CP. Both GC Fuji type 2 Glass Ionomer and Shofu Glass Ionomer RX EASE are effective as IOB.

Effect of Tooth Bleach on Dentin Fatigue Resistance in Situ

BACKGROUND

Negative effects of bleaching on dentin have previously been reported in vitro.

OBJECTIVE

The purpose of this study was to determine the effect of carbamide peroxide bleaching on dentin fatigue resistance using a clinically relevant in situ model.

METHODS AND MATERIALS

Following research ethics board approval, 60 human teeth requiring extraction were collected. Sterilized human dentin specimens were cut (1.2x1.2x10 mm) and secured into customized bleaching trays to be used by study participants. Participants were randomly assigned to either bleach (10% carbamide peroxide, n=23) or control (gel without bleach, n=26) treatment groups. Treatment was applied to the bleaching trays and worn overnight by participants for 14 days. After treatment completion, dentin specimens were removed from the bleaching trays and subjected to fatigue testing (10 N, 3 mm/s, 2x105 cycles) while submerged in artificial saliva. Kaplan-Meier survival analysis was conducted to compare the number of cycles to failure during fatigue testing in both groups. A log rank test was run to determine if there were differences in the survival distribution between the two groups (α<0.05).

RESULTS

The median number of cycles to failure was 352 ± 202 and 760 ± 644 for the bleach and control groups, respectively. The survival distributions for the two groups were significantly different (p=0.020). Dentin fatigue resistance was significantly lower in the bleach group compared to the control.

CONCLUSIONS

Direct bleaching of human dentin using an at-home tray bleaching protocol in situ reduced dentin fatigue resistance. This has implications for tooth fracture risk and longevity.

Comparison of MTA, CEM Cement, and Biodentine as Coronal Plug during Internal Bleaching: An In Vitro Study

BACKGROUND

Internal bleaching is a choice of treatment in discolored endodontically treated teeth. Cervical root resorption is one of the important complications of this treatment. A suggested procedure to prevent this type of resorption is using a coronal barrier under the bleaching materials. The aim of the study was to compare the microleakage of mineral trioxide aggregate (MTA), calcium-enriched mixture (CEM) cement, and Biodentine.

MATERIALS AND METHODS

In this in vitro study, a total of 60 single canal incisors were included. They were randomly divided into three experimental groups (n = 16), one positive control group (n = 6), and one negative control group (n = 6). Coronal portion of the canals in the experimental groups was sealed with 3 mm of MTA, CEM cement, or Biodentine as a coronal barrier. After 3 days, specimens were bleached. A fresh Enterococcus faecalis suspension was added to the samples. The culture tubes were observed for 45 days, and the daily turbidity was recorded. Statistical analysis was accomplished by the Kaplan-Meier test and SPSS 22.

RESULTS

All positive samples showed turbidity, whereas none of the negative samples allowed bacterial leakage. Results showed no significant difference between MTA, CEM cement, and Biodentine groups. (P value = 0.304, 0.695, and 0.217). The bacterial microleakage for the two groups also did not show significant differences.

CONCLUSIONS

CEM cement and Biodentine showed promising results as coronal plug, and clinical studies are needed to test these materials with MTA for avoiding microleakage in internal bleaching treatment.

Potential Advantages of Peroxoborates and Their Ester Adducts Over Hydrogen Peroxide as Therapeutic Agents in Oral Healthcare Products: Chemical/Biochemical Reactivity Considerations In Vitro, Ex Vivo And In Vivo

Peroxides present in oral healthcare products generally exert favourable protective activities against the development and progression of tooth decay, plaque, gingivitis, and halitosis, etc. However, despite the high level of research focus on hydrogen and carbamide peroxides as therapeutically active (and tooth-whitening) agents, to date the use of alternative chemical forms of peroxides such as peroxoborates for these purposes has received only scant attention. Intriguingly, peroxoborate and its esters with polyols, such as glycerol, have a very diverse chemistry/biochemistry in aqueous solution, for which there is an increasing amount of evidence that it remains distinctive from that of hydrogen peroxide; such properties include self-associative and hydrolytic equilibria, and their abilities to participate in electrophile- or nucleophile-scavenging, metal ion-complexing, redox and free radical reactions, for example. Therefore, the purpose of this detailed commentary is to evaluate both differences and similarities between the molecular/biomolecular reactivities of peroxoborate species and hydrogen peroxide in vitro, ex-vivo and in vivo. It encompasses brief sectional accounts regarding the molecular heterogeneity of peroxoborates, the release of bioactive agents therefrom, and their oxidative attack on oral cavity biomolecules (the nucleophilic or electrophilic character of these oxidations are discussed). Further areas explored are the abilities of borates and peroxoborates to enhance the solubility of iron ions in aqueous solution, their involvements in free radical biochemistry (particularly the complexation of oxygen radical-promoting transition metal ions by, and antioxidant properties of, peroxoborate-polyol ester adducts), and the specific inhibition of protease enzymes. Further aspects focus on the tooth-whitening, oral malodor neutralizing, and potential mutagenic and genotoxic properties of peroxoborates, along with possible mechanisms for these processes. The abilities of peroxoborates, and peroxides in general, to modulate the activities of inflammatory mediators and vitamins, antioxidant or otherwise, are also explored.

Effects of 16% Carbamide Peroxide Bleaching on the Surface Properties of Glazed Glassy Matrix Ceramics

Objective

To determine the influence of the home bleaching agent, Opalescence PF, on the surface roughness and microhardness of glazed glassy matrix CAD-CAM ceramics. Materials and Methods. The 28 sintered leucite- and lithium disilicate-reinforced ceramic specimens (IPS Empress CAD and IPS e.max CAD) were divided into control and bleached groups. The home bleaching agent was applied to specimens of bleached groups for 7 days. The surface roughness and microhardness of all specimens were measured. A scanning electron microscope was used to evaluate the surface properties. The data were statistically analyzed by two-way ANOVA.

Results

The control e.max CAD showed the lowest surface roughness values. For both Empress and e.max CAD, surface roughness was significantly higher for the bleached group (p < 0.05). No significant differences in microhardness were observed.

Conclusions

According to our study, patients should be careful when using home bleaching agents because whitening agents can affect the mechanical properties of full ceramic restorations like e.max CAD and Empress CAD. Ceramic polishing may be required in clinical situations where ceramic restorations are accidentally exposed to bleaching gels.

Influence of Intracanal Irrigants on Coronal Fracture Resistance of Endodontically Treated and Bleached Teeth: An In vitro Study

Background:

Irrigation has a key role in the success of endodontic treatment. Intracanal irrigant solutions have adverse effects on the physical properties of dentin.

Aim:

The present study aimed to evaluate the effect of different irrigation protocols on coronal fracture resistance of endodontically treated teeth undergoing bleaching treatment.

Design and Materials and Methods:

Access cavities were prepared in 120 maxillary premolars which were divided into two groups (n = 60) – Group A: nonbleached, Group B: bleached (B). Each group was subdivided into five subgroups based on irrigation protocol (n = 12); G1: normal saline (NS), G2: 2.5% sodium hypochlorite (NaOCl), G3: 10% citric acid (CA), G4: 17% ethylene diamine tetra acetic acid, and G5: NaOCl plus CA. In Group B, the teeth were bleached using 38% hydrogen peroxide and 20% carbamide peroxide gels as in-office and at-home bleaching techniques for 3 weeks. All the teeth were restored with composite resin, thermocycled, and incubated for 24 h. The specimens underwent fracture resistance tests. Data were analyzed with ANOVA, Tukey honestly significant difference test, t-test, and Chi-squared test (α =0.05).

Results:

T-test showed significant differences between each two corresponding subgroups (P < 0.0001). In Group A, NS demonstrated significantly higher fracture resistance compared to others; however, minimum fracture resistance recorded in G2. In Group B, the maximum fracture resistance was recorded in G1, with the minimum being recorded in G5. Samples irrigated with NaOCl and NaOCl plus CA exhibited significantly lower fracture resistance compared to NS subgroup (P < 0.05).

Conclusions:

Within the limitations of this study, it can be concluded that the irrigation protocol used during endodontic treatment with/without bleaching can affect the coronal fracture resistance.

The effect of protocol for disinfection of extracted teeth recommended by center for disease control (CDC) on microhardness of enamel and dentin

Background

According to the guideline of the United States center for disease control (CDC), the extracted teeth should be sterilized by autoclaving or storage in 10% formalin before using for educational or research purposes. The objective of this study was to evaluate the effect of this protocol on microhardness of dentin and enamel.

Material and Methods

Thirty extracted single-root teeth were used in this study. The crowns were resected, and the roots were longitudinally sectioned into two halves. The Vickers microhardness (VHN) of specimens was measured on polished canal dentin and buccal enamel surfaces. The crowns were randomly divided into three groups (n=10). Group 1 and 2 were sterilized using autoclave and formalin, respectively while group 3 (control) was stored in synthetic tissue fluid. The root halves were also randomly divided into 3 groups (n=20) which were treated as mentioned above for crown samples. Following sterilization, VHN of samples was measured again. ANOVA and paired samples t-tests were used to analyze the data.

Results

Autoclaving caused a significant reduction in microhardness of dentin (P <0.001, 12.04% decreases in VHN). However, there were no significant differences for before and after sterilization within other groups.

Conclusions

Based on the results of this study, the CDC protocol is recommended in studies related to enamel microhardness. However, Autoclaving is not an appropriate sterilization method in studies related to dentin microhardness. In these studies, two-week immersion in 10% formalin is recommended.

Key words:Autoclave, CDC, extracted teeth, formalin, microhardness, sterilization.

Efficacy of cold light bleaching using different bleaching times and their effects on human enamel

This study investigated the efficacy of cold light bleaching using different bleaching times and the effects thereof on tooth enamel. Before and after bleaching, stained tooth specimens were subjected to visual and instrumental colorimetric assessments using Vita Shade Guide and spectrophotometric shade matching. Enamel surface alterations were examined using scanning electron microscopy (SEM) to analyze surface morphology, surface microhardness (SMH) measurement to determine changes in mechanical properties, and X-ray diffraction (XRD) to characterize post-bleaching enamel composition. Cold light bleaching successfully improved tooth color, with optimal efficacy when bleaching time was beyond 10 min. Significant differences in surface morphology were observed among the different bleaching times, but no significant differences were observed for enamel composition and surface microhardness among the different bleaching times. Results of this study revealed an association between the bleaching time of cold light bleaching and its whitening efficacy. Together with the results on enamel surface changes, this study provided positive evidence to support cold light bleaching as an in-office bleaching treatment.

Fracture resistance of endodontically-treated teeth submitted to bleaching treatment with hydrogen peroxide and titanium dioxide nanoparticles photoactivated by LED-laser

Objective: The aim of this study was evaluate the fracture resistance of endodontically-treated teeth after bleaching treatment using 15% hydrogen peroxide plus titanium dioxide nanoparticles (15HPTiO2) photoactivated by LED-laser, in comparison with protocols using 35% hydrogen peroxide (35HP), 37% carbamide peroxide (37CP) or sodium perborate (SP). Material and method: After endodontic treatment, fifty bovine extracted incisors were divided into five groups (n = 10): G1- without bleaching; G2- 35HP; G3- 37CP; G4- 15HPTiO2 photoactivated by LED-laser and G5- SP. In G2 and G4, the bleaching protocol was applied in 4 sessions, with a 7 day interval between each session. In G3 and G5, the materials were kept in the pulp chamber for 21 days, but replaced every 7 days. After 21 days, the crowns were subjected to compressive load at a cross head speed of 0.5 mm/min, applied at 135° to the long axis of the root using an eletromechanical testing machine, until fracture. The data were submitted to ANOVA and Tukey tests (p = 0.05). Result: The bleaching treatment in endodontically-treated teeth with 15HP plus TiO2 nanoparticles and photoactivated by LED-laser caused reduction of the fracture resistance similarly provided by 35HP, 37CP or SP (p>0.05). All bleaching treatments reduced the fracture resistance compared to unbleached teeth (p<0.05). Conclusion: All bleaching protocols reduced the fracture resistance of endodontically-treated teeth, but there were no differences between each other.

Fracture resistance of teeth submitted to several internal bleaching protocols

AIM

The aim of this study was to evaluate the fracture resistance of teeth submitted to several internal bleaching protocols using 35% hydrogen peroxide (35HP), 37% carbamide peroxide (37CP), 15% hydrogen peroxide with titanium dioxide nanoparticles (15HPTiO2) photoactivated by LED-laser or sodium perborate (SP).

MATERIALS AND METHODS

After endodontic treatment, fifty bovine extracted teeth were divided into five groups (n = 10): G1-unbleached; G2-35HP; G3-37CP; G4-15HPTiO2 photoactivated by LED-laser and G5-SP. In the G2 and G4, the bleaching protocol was applied in 4 sessions, with 7 days intervals between each session. In the G3 and G5, the materials were kept in the pulp teeth for 21 days, but replaced every 7 days. After 21 days, the teeth were subjected to compressive load at a cross head speed of 0.5 mm/min, applied at 135° to the long axis of the root using an eletromechanical testing machine, until teeth fracture. The data were submitted to ANOVA and Tukey tests (α = 5%).

RESULTS

The 35HP, 37CP, 15HPTiO2 and SP showed similar fracture resistance teeth reduction (p > 0.05). All bleaching treatments reduced the fracture resistance compared to unbleached teeth (p < 0.05).

CONCLUSION

All bleaching protocols reduced the fracture resistance of endodontically-treated teeth, but there were no differences between each other.

CLINICAL SIGNIFICANCE

There are several internal bleaching protocols using hydrogen peroxide in different concentrations and activation methods. This study evaluated its effects on fracture resistance in endodontically-treated teeth.

Effect of Sodium Ascorbate on Dentin Bonding After Two Bleaching Techniques

The purpose of this study was to analyze the influence of 10% sodium ascorbate (SA) on the hybrid layer, resin tag length, and bond strength to dentin after bleaching. Six groups were tested: G C, control; G SA, sodium ascorbate (SA) + restoration; G CP, bleaching with carbamide peroxide (CP) + restoration; G CP+SA, bleaching with CP + SA+ restoration; G HP, bleaching with 35% hydrogen peroxide (HP) + restoration; and G HP+SA, HP + SA + restoration. After dental bleaching, the dentin was exposed and the antioxidant solution was applied to groups G SA, G CP+SA, and G HP+SA, before bonding procedures. The teeth were sectioned in the mesiodistal direction. One section was decalcified, and the specimens were embedded in paraffin and sectioned in the longitudinal direction with a thickness of 6 μm. Fifteen slices of each specimen were selected according to a systematic sample of slices with an interval proportional to the total number of slices obtained for each tooth. The specimens were stained using the Brown & Brenn method, and an optic microscope was used to analyze the hybrid layer thickness and resin tag length. The remaining tooth segment was sectioned into stick-shaped specimens and used for microtensile bond strength testing (0.5 mm/min). Statistical analysis was performed using two-way analysis of variance and Fisher test. The results for hybrid layer + tag formation (in micrometers) were G C, 13.27 Aa; G SA, 11.85 Ba; G CP, 6.84 Bb; G CP+SA, 9.02 Ab; G HP, 7.28 Bb; and G HP+SA, 9.22 Ab; bond strength results (in MPa) were G C, 49.5 Aa; G SA, 51.7 Aa; G CP, 37.16 Bb; G CP+SA, 47.69 Aa; G HP, 32.39 Ab; and G HP+SA, 39.67 Ab. Tooth bleaching with CP or HP impairs the formation of the hybrid layer and resin tags and reduces the microtensile bond strength. Statistically, the use of SA significantly increases the hybrid layer thickness and resin tag length. The microtensile bond strength values for carbamide peroxide increased, but the microtensile bond strength for hydrogen peroxide was not affected.

Effect of Sodium Ascorbate on Resin Bonding to Sodium Perborate–bleached Dentin

This was an in vitro study to evaluate the effect of sodium ascorbate on the microshear bond strength (MSBS) of resin composite to sodium perborate–bleached dentin. Molar dentin sections were divided into six groups: 1) control, 2) sodium perborate (SP) bleach and immediate bonding, 3) SP and 30 second sodium ascorbate (SA); 4) SP and 1 minute SA; 5) SP and 2 minute SA; and 6) SP and 7 day delay before bonding. They were further divided into two-step self-etching (Clearfil SE Bond) or all-in-one self-etching (Xeno IV) adhesive systems. Resin composite microtubes were bonded according to dentin location—center, pulp horn, and peripheral positions—and an MSBS test was carried out. Failure mode was determined using light microscopy and scanning electron microscopy. There were no significant differences between the treatment types/groups. MSBSs were significantly higher for two-step self-etching adhesive compared with all-in-one self-etching adhesive (p=0.028). For the all-in-one adhesive, MSBSs at the center and pulp horn positions were significantly lower than the peripheral positions (p&lt;0.001). All-in-one groups had significantly more adhesive failures than two-step adhesive groups (p=0.015). The odds of adhesive failure were higher at the pulp horn position than the peripheral position (p=0.004). Sodium perborate bleaching of dentin had no effect on MSBS or mode of failure for either two-step or all-in-one self-etching adhesives; therefore, the effect of sodium ascorbate was negligible. The two-step adhesive groups demonstrated the highest MSBS, and the all-in-one groups, when bonded to center and pulp horn dentin, exhibited the lowest MSBS.

Effect of 10% and 15% carbamide peroxide on fracture toughness of human dentin in situ

PURPOSE

Although damage to the structural integrity of the tooth is not usually considered a significant problem associated with tooth bleaching, there have been some reported negative effects of bleaching on dental hard tissues in vitro. More studies are needed to determine whether the observed in vitro effects have practical clinical implications regarding tooth structural durability.

OBJECTIVES

This in situ study evaluated the effect of 10% and 15% carbamide peroxide (CP) dental bleach, applied using conventional whitening trays by participants at home, on the fracture toughness of dentin.

METHODS

Ninety-one adult volunteers were recruited (n ≈ 30/group). Compact fracture toughness specimens (approximately 4.5 × 4.6 × 1.7 mm) were prepared from the coronal dentin of recently extracted human molars and gamma-radiated. One specimen was fitted into a prepared slot, adjacent to a maxillary premolar, within a custom-made bleaching tray that was made for each adult participant. The participants were instructed to wear the tray containing the dentin specimen with placebo, 10% CP, or 15% CP treatment gel overnight for 14 nights and to store it in artificial saliva when not in use. Pre-bleach and post-bleach tooth color and tooth sensitivity were also evaluated using ranked shade tab values and visual analogue scales (VASs), respectively. Within 24-48 hours after the last bleach session, the dentin specimens were tested for fracture toughness using tensile loading at 10 mm/min. Analysis of variance, Kruskal-Wallis, χ (2) , Tukey's, and Mann-Whitney U tests were used for statistical analysis. The level of significance was set at p<0.05 for all tests, except for the Mann-Whitney U tests, which used a Bonferroni correction for post hoc analyses of the nonparametric data (p<0.017). Results : The placebo, 10% CP, and 15% CP groups contained 30, 31, and 30 participants, respectively. Mean fracture toughness (+ standard deviation) for the placebo, 10% CP, and 15% CP groups were 2.3 ± 0.9, 2.2 ± 0.7, and 2.0 ± 0.5 MPa*m(1/2) respectively. There were no significant differences in mean fracture toughness results among the groups (p=0.241). The tooth sensitivity VAS scores indicated a significantly greater incidence (p=0.000) and degree of tooth sensitivity (p=0.049 for VAS change and p=0.003 for max VAS) in the bleach groups than in the placebo group. The color change results showed generally greater color change in the bleach groups than in the placebo group (p=0.008 for shade guide determination and p=0.000 for colorimeter determination).

CONCLUSIONS

There were no significant differences in in situ dentin fracture toughness results among the groups. The results of this study provide some reassurance that dentin is not overtly weakened by the bleaching protocol used in this study. However, the lack of a statistically significant difference cannot be used to state that there is no effect of bleach on dentin fracture toughness.

Changes in the stiffness of demineralized dentin following application of tooth whitening agents

OBJECTIVE

The purpose of this study was to evaluate the effect of the bleaching agents on the elastic modulus of bovine demineralized dentin matrix (EMDM).

MATERIALS AND METHODS

Eighty-five slices were obtained from 17 bovine teeth. The slices were divided randomly into five experimental groups (n = 17): unbleached control group (CG), 4% hydrogen peroxide (HP4), 4% hydrogen peroxide + 0.05% Ca (HP4 + Ca), 7.5% hydrogen peroxide + ACP (HP7.5) and 10% carbamide peroxide (CP10). The HP4, HP4 + Ca and CP10 groups were treated with the bleaching agents for 8 h/day (14 days), while the samples of HP7.5 group were exposed to bleaching agent for 30 min twice a day (14 days). The CG was kept in 100% humidity. After bleaching treatments, the enamel of the samples was removed and 85 dentin beams (0.5 × 1.7 × 7.0 mm) were prepared. Afterwards, the beams were immersed in 10% phosphoric acid solution (5 h) and rinsed with water (10 min). The beams were tested after 24 h, 7 and 14 days of storage in distilled water, using three-point bend method. Data were statistically analyzed using ANOVA and Fisher's test.

RESULTS

All bleaching treatments reduced the EMDM. After 14 days post-bleaching, the EMDM increased for HP4 and HP4+Ca groups.

CONCLUSIONS

The use of bleaching agents promoted a decrease in EMDM, which indicates that the bleaching treatment interacts with the dentin organic matrix. The EMDM measurement for the specimens of the 7.5% hydrogen peroxide group that were immersed in water at 14 days post-bleaching did not recover the EMDM values when compared to the control group.

Fracture resistance of endodontically-treated teeth: effect of combination bleaching and an antioxidant

This in vitro study assessed the fracture resistance of endodontically-treated teeth undergoing combination bleaching with 38% and 9.5% hydrogen peroxide gels as in-office and at-home bleaching techniques, respectively. In addition, the effect of an antioxidizing agent, sodium ascorbate, was investigated.

METHODS AND MATERIALS

Sixty maxillary premolars were endodontically-treated, received a glass ionomer barrier as a mechanical seal and were embedded in acrylic resin up to the cemento-enamel junction. The specimens were divided into four groups (n = 15) as follows: G I: no bleaching, access cavity restored with resin composite (negative control); G II: bleached for three weeks daily using 9.5% hydrogen peroxide for two hours and three sessions of in-office bleaching using 38% hydrogen peroxide every seven days, then restored (positive control); G III: bleached similar to G II and restored after one week; G IV: bleached similar to G II, along with the use of an antioxidizing agent for 24 hours, then restored. In each in-office and at-home bleaching session, the whitening gels were applied to the buccal surface of the tooth and placed inside the pulp chamber (inside/outside bleaching technique). Finally, the specimens underwent fracture resistance testing; the data were analyzed using ANOVA and Scheffé's test (alpha = 0.05).

RESULTS

Significant differences were observed among the study groups (p < 0.05). Groups I and II demonstrated the highest and lowest fracture resistance, respectively. The samples that were not bleached (Group I) and the 10% sodium ascorbate gel group (Group IV) demonstrated significantly higher fracture resistance than the positive control group (p < 0.05). No significant differences were found between Groups III and II (p > 0.05).

CONCLUSION

Within the limitations of the current study, it can be concluded that the fracture resistance of endodontically-treated teeth decreases after combination bleaching. The use of sodium ascorbate can reverse decreased fracture resistance.

Evaluation of the effect of maleic acid and ethylenediaminetetraacetic acid on the microhardness and surface roughness of human root canal dentin

INTRODUCTION

The aim of this in vitro study was to evaluate the effect of 7% maleic acid and 17% EDTA solutions on the microhardness and the surface roughness of human root canal dentin.

METHODS

Forty-five extracted human maxillary central incisors were sectioned longitudinally into a total of 90 segments, were embedded in auto polymerizing acrylic resin, and were grounded flat with silicon carbide abrasive papers. Based on the test solutions used, samples were divided randomly into three groups: (1) the EDTA group, 1 mL of 17% EDTA for 1 minute (n = 30), (2) the maleic acid group, 1 mL of 7% maleic acid for 1 minute (n = 30), and (3) the control group, 1 mL of 0.9% saline for 1 minute (n = 30). Every group was then divided into two subgroups of 15 specimens each. In group 1a, 2a, and 3a, specimens were used to determine the microhardness of the root canal dentine in the coronal, middle, and apical third using Vicker's hardness tester. In groups 1b, 2b, and 3b, specimens were used for the determination of surface roughness of the root canal dentine using a roughness tester (Surtronic, Leicester, England). The data were statistically analyzed using the Kruskall Wallis and Mann Whitney U tests.

RESULTS

There was no significant difference between EDTA and maleic acid in the reduction of microhardness. The increase in roughness was significantly greater with maleic acid when compared with EDTA.

CONCLUSION

Maleic acid reduced the microhardness of root dentin similar to EDTA but increased the surface roughness significantly more than EDTA.

Fracture resistance and failure pattern of teeth submitted to internal bleaching with 37% carbamide peroxide, with application of different restorative procedures

Objective.

This study investigated the compressive fracture strength and failure pattern in premolars submitted to endodontic treatment and internal bleaching with 37% carbamide peroxide for 21 days, with application of different restorative procedures.

Material and methods.

Six groups were employed (n = 10): 1) non-bleached teeth and pulp chamber sealed with IRM; 2) bleached teeth and pulp chamber sealed with IRM; 3) bleached teeth and pulp chamber filled with light cured composite resin; 4) bleached teeth, root canals prepared at 10mm, filling of the root canal and pulp chamber with IRM; 5) bleached teeth, root canals prepared at 10mm, luting of prefabricated metallic post with zinc phosphate and pulp chamber sealed with composite resin; 6) bleached teeth, root canals prepared at 10mm, luting of glass fiber post with resin cement and pulp chamber sealed with composite resin. After 24-hour storage in distilled water, the specimens were submitted to compressive fracture strength testing in a universal testing machine.

Results.

The following values were found: Group 1 – 56.23kgf; Group 2 – 48.96kgf; Group 3 – 53.99kgf; Group 4 – 45.72kgf; Group 5 – 54.22kgf; Group 6 – 60.12kgf. The analysis of variance did not reveal statistically significant difference between groups (p<0.05), suggesting that internal bleaching with 37% carbamide peroxide did not weaken the dental tissues. The largest number of unfavorable fractures was observed for Groups 2 (50%), 4 (40%), and 5 (30%). Group 6 exhibited the most favorable failure pattern.

Conclusions.

The results suggest that internal bleaching with 37% carbamide peroxide did not significantly weaken the teeth. Among the bleached teeth, those with temporary IRM restorations or metallic posts demonstrated the most unfavorable fracture pattern, whereas the most favorable fracture pattern occurred in teeth restored with composite resin and glass fiber posts.

An evaluation of the effect of non-setting calcium hydroxide on human dentine: a pilot study

AIM

To evaluate the effect of non-setting calcium hydroxide (NSCH) on the hardness and elastic modulus of dentine from extracted permanent premolar human teeth.

METHODS

30 freshly extracted single rooted human premolar teeth were decoronated and the roots then sectioned longitudinally into equal halves. In the experimental group a thin layer of NSCH was applied whilst the control group had no medicament. After 1, 3 and 6 months, nanoindentation was used to assess dentine hardness and the modulus of elasticity. Scanning Electron Microscopy (SEM) was used to visualize the depth of penetration of NSCH into the dentinal tubules.

RESULTS

SEM images showed that there were no structural changes in the dentine slabs that had NSCH application after 1, 3 or even 6 months. However, penetration of NSCH into the dentine tubules was seen at both 3 and 6 months with a significant reduction in the hardness of dentine observed at 3 (p<0.02) and 6 months (p<0.01). The modulus of elasticity was significantly lower (p<0.01) at 6 months.

CONCLUSION

It appears that there is a significant reduction in the hardness of dentine with increasing periods of calcium hydroxide application. Prolonged application of NSCH could have a detrimental effect on dentine, making the dentine more prone to fracture.

The use of atomic force microscopy in determining the stiffness and adhesion force of human dentin after exposure to bleaching agents

INTRODUCTION

Oxidant bleaching agents may induce several alterations on mineralized teeth tissues. Our aim is to study, at the ultrastructural level, mechanical modifications induced on dentin after exposure to different bleaching agents.

METHODS

Nanoindentation performed with atomic force microscopy was used to measure changes in dentin stiffness as well as the adhesion force between the tip and the tissue both in intertubular and peritubular dentin. For each specimen, dentin localization, and bleaching agent, 100 independent nanoindentations were performed. Carbamide peroxide (30%) and hydrogen peroxide (35%) were used as bleaching agents.

RESULTS

A significant reduction of both stiffness and adhesion force was found for both carbamide and hydrogen peroxide in peritubular and intertubular dentin.

CONCLUSIONS

The use of bleaching agents led to a significant reduction in dentin local (at the nanoscale) mechanical properties.

Coronal resistance to fracture of endodontically treated teeth submitted to light-activated bleaching

OBJECTIVES

The aim of this study was to assess the fracture resistance of endodontically treated teeth submitted to bleaching with 38% hydrogen peroxide activated by light-emitting diode (LED)-laser system.

METHODS

Fifty maxillary incisors were endodontically treated, received a zinc phosphate barrier and were embedded in acrylic resin until cemento-enamel junction. The specimens were distributed into five groups (n=10) according to the number of bleaching sessions: GI, no treatment (control); GII, one session; GIII, two sessions; GIV, three sessions and GV, four sessions. The whitening gel was applied to the buccal surface of the tooth and inside the pulp chamber for three times in each session, followed by LED-laser activation. Specimens were submitted to the fracture resistance test (kN) and data were submitted to the Tukey-Kramer multiple comparisons test.

RESULTS

No significant difference (p>0.05) was found between GI (0.71+/-0.30) and GII (0.65+/-0.13), which presented the highest strength values to fracture. Groups III (0.35+/-0.17), IV (0.23+/-0.13) and V (0.38+/-0.15) showed lower resistance to fracture (p<0.01) when compared to GI and GII.

CONCLUSIONS

The fracture resistance of endodontically treated teeth decreased after two sessions of bleaching with 38% hydrogen peroxide activated by LED-laser system.

Effects of direct and indirect bleach on dentin fracture toughness

There are concerns that tooth-whitening procedures irreversibly damage tooth structure. We investigated the hypothesis that dental bleaches significantly affect dentin structural integrity. The objective was to evaluate the effects of peroxide bleaches on dentin fracture toughness. Compact test specimens, composed of human dentin, were used (n = 10/group). Bleach (16% or 10% carbamide peroxide or 3% hydrogen peroxide) or control material, containing 0.1% sodium fluoride, was applied directly or indirectly to dentin through enamel (6 hrs/day) for 2 or 8 weeks. Fracture toughness results were analyzed by ANOVA and Fisher's LSD test (p < 0.05). There were significant decreases in mean fracture toughness after two- and eight-week direct (19-34% and 61-68%, respectively) and indirect (up to 17% and 37%, respectively) bleach application. The in vitro reduction in dentin fracture toughness caused by the application of peroxide bleaches was greater for the direct application method, longer application time, and higher bleach concentration.

Effects of hydrogen peroxide on human dentin structure

It has been hypothesized that hydrogen peroxide (H(2)O(2)) bleaching may cause destruction of dentin by a mechanism of protein oxidation. However, to our knowledge, there has been no direct chemical evidence to validate this viewpoint. To investigate the effects of H(2)O(2) on the structure of human dentin, we used Fourier transform infrared spectroscopy (FTIR) and attenuated total reflection (ATR) spectroscopy. Human intact dentin specimens were treated either with 30% H(2)O(2) or Hanks' balanced salt solution (HBSS). Significant differences were observed in ATR spectra parameters. Additionally, demineralized dentin specimens were also tested. They were completely dissolved in the H(2)O(2), but remained intact in the 0.1 N HCl and HBSS. The results suggested that H(2)O(2) attacked both the organic and mineral components of dentin. Destruction of the organic components was mainly because of the oxidizing ability of H(2)O(2), while changes in the mineral components were probably due to its acidity.

Effect of Carbamide Peroxide Treatments on the Metal-ion Release and Microstructure of Different Dental Amalgams

Carbamide peroxide bleaching releases metal-ions from dental amalgam.

Effect of Prolonged Direct and Indirect Peroxide Bleaching on Fracture Toughness of Human Dentin

STATEMENT OF THE PROBLEM

The effects of prolonged exposure to peroxide bleaching agents on dentin structural integrity are uncertain.

PURPOSE

To evaluate the effect of in vitro prolonged tooth bleaching on the fracture toughness (K(1C)) of human dentin.

MATERIALS AND METHODS

Dentin from recently extracted molar teeth was directly or indirectly treated to simulate a prolonged at-home (10% carbamide peroxide or 3% hydrogen peroxide, 6 hours/day, 5 days/week for 8 weeks) or in-office (30% hydrogen peroxide, 1 hour/week for 8 weeks) bleaching regimen (N=8/group). Placebo gel and distilled water acted as control materials. Compact tension test specimens (approximately 4.60 x 4.50 x 1.60 mm) were prepared from coronal dentin and tensile loading was applied at a rate of 10 mm/min 24 hours after the last bleaching session. Results were analyzed using analysis of variance and Tukey's test (p < 0.05). For direct bleach application, the treatment materials were applied onto dentin that was already prepared as compact tension specimens. For indirect bleach application, bleach was applied to the enamel of intact teeth prior to specimen preparation.

RESULTS

There was a significant decrease in dentin K(1C) after 8 weeks of direct bleach treatment (p < 0.05). There were no significant differences between the bleach and control groups after 8 weeks of indirect bleach treatment (p=0.19).

CONCLUSIONS

The in vitro fracture resistance of dentin was reduced after the prolonged use of bleach products that were applied directly to dentin.

CLINICAL SIGNIFICANCE

Caution should be considered when using bleach for prolonged treatment times in clinical cases where there is dentin exposure such as occlusal attrition or gingival recession.

Effect of Intracoronal Bleaching Agents on Dentin Microhardness

The purpose of this in vitro study was to compare the effect of intracoronal bleaching agents associated or unassociated with chlorhexidine gel on dentin microhardness. Sixty human maxillary incisor crowns were divided into six groups, and bleaching agents were sealed into the pulp chambers as follows: sodium perborate + water (SPW), sodium perborate + 2% chlorhexidine gel (SP + CHX), sodium perborate + 30% hydrogen peroxide solution (SP + HP), 37% carbamide peroxide gel (CP), 37% carbamide peroxide gel + 2% chlorhexidine gel (CP+CHX), and water (W). After the bleaching procedure, microhardness testing was carried out on the dentin surface at three different levels: inner, middle, and outer dentin. The greatest reduction in microhardness was observed for the SP + HP group. No differences were observed between the SPW and SP + CHX group. The 2% chlorhexidine gel did not adversely affect dentin microhardness when associated with the tested bleaching agents. CHX might be considered as an antimicrobial vehicle during intracoronal bleaching.

Influence of the endodontic treatment on mechanical properties of root dentin

This study evaluated the effect of endodontic treatment and storage time on the flexural and ultimate tensile strength of root dentin. Eighty bovine teeth were divided into endodontically treated (ET) and endodontically untreated (NT) teeth. The ET canals were instrumented and irrigated with sodium hypochlorite 1.0%. Roots were filled with gutta-percha and zinc-oxide/eugenol cement by the lateral condensation technique. Tests were performed as follows: t1, immediately; t2, 7 days; t3, 15 days; and t4, 30 days after extraction for NT groups or after extraction and endodontic treatment for ET groups (n= 0). Roots were axially cut into two halves, one half was used to obtain bars for performing the four-bending flexural test and the other half to obtain slices that were trimmed resulting in hourglass-shaped specimens for microtensile testing. Samples were submitted to the tests, and the data were statistically analyzed. Results indicated that endodontic treatment potentiated by time elapsed after endodontic treatment can affect the physical properties of dentin.

Micromorphology of enamel surface after vital tooth bleaching

The aim of the present study was to assess microroughness changes of enamel surfaces after bleaching procedures with 10% and 16% concentrations of carbamide peroxide by confocal laser scanning microscopy. Twenty caries-free incisors, extracted for periodontitis reasons, were sectioned into two halves of experimental and control specimens. The teeth were divided into two groups, and the experimental specimens were exposed to either 10% or 16% carbamide peroxide for 4 hours per 7 days. Measurements were made at three randomly selected 140 x 100 microm areas of 10 experimental and control specimens per group at the same crown level. Microroughness was measured in "total roughness" (Rt) and "average roughness" (Ra) descriptor values. The statistical analysis showed significantly higher microroughness according to Rt values and Ra values for both groups of carbamide peroxide exposed enamel surfaces.

In Vitro Assessment of a Gel Base Containing 2% Chlorhexidine as a Sodium Perborate’s Vehicle for Intracoronal Bleaching of Discolored Teeth

The purpose of this study was to assess a gel base containing 2% chlorhexidine (CHX) as a vehicle to be mixed with sodium perborate for intracoronal bleaching of discolored teeth, comparing its bleaching efficacy to sodium perborate mixed with other vehicles; 37% carbamide peroxide and 30% hydrogen peroxide. There were 110 fresh bovine incisors artificially stained using whole blood. The samples were divided into 11 groups and the intracoronal bleaching was performed using the "walking bleach technique". The bleaching agents were replaced three times at 7-day intervals. Using digital photos and a shade guide created for bovine teeth, the samples were evaluated at day 0, 7, 14, 21, and 28. On evaluation day, the photos were examined by three endodontists giving scores from 1 to 5 based on the shade guide created. Data were analyzed statistically by Kruskall-Wallis test. After 28 days, all evaluated teeth received scores that were statistically similar. Groups that used sodium perborate and a liquid vehicle bleached faster than those that used a gel based vehicle. The CHX gel allowed dissociation for the bleaching agent. The 2% CHX gel exhibited a good potential for use as a vehicle for sodium perborate or as a complement for carbamide peroxide.

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

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

Evaluation of the effect of EDTA, EDTAC and citric acid on the microhardness of root dentine

AIM

To evaluate the effect of citric acid, ethylenediaminetetraacetic acid (EDTA) and ethylenediaminetetraacetic acid plus Cetavlon (EDTAC) solutions on the microhardness of human root canal dentine.

METHODOLOGY

Sixteen maxillary human canines were sectioned transversely at the cemento-enamel junction and the crowns were discarded. Subsequently, each root was embedded in an epoxy resin cylinder and their middle third sectioned horizontally into 4 mm thick slices. The samples were randomly divided into three groups according to the chelating agent employed, as follows (n = 6): group 1: EDTA 17%, group 2: EDTAC 17% and group 3: citric acid 10%. Dentine microhardness was then measured with a load of 50 g for 15 s. At the beginning of the experiment, reference microhardness values were obtained for samples without any etching (t = 0 min). The same samples were then exposed to 50 microL of the chelator solution for 1, 3 and 5 min. The Student's t-test (P < 0.05) was used to compare results for different times for each chelator and different chelators for each time.

RESULTS

Microhardness decreased with increasing time of application of chelating solutions. There were no significant (P > 0.05) differences between initial microhardness for the three groups as well as after 1 min of application of the substances. After 3 min, EDTA produced a significantly greater reduction in microhardness. However, there was no significant difference between EDTA and EDTAC after 5 min. Citric acid caused significantly less reduction in microhardness.

CONCLUSIONS

Overall, citric acid was least effective in reducing dentine hardness whilst EDTA had the strongest effect.

Bleaching Teeth Treated Endodontically: Long-Term Evaluation of a Case Series

The chromatic stability of nonvital discolored teeth, subjected to the combined intracoronal bleaching technique and to endodontic treatment, was evaluated at a distance of 16 yr (1989-2005). The series comprised 50 patients (age range 7-30 yr) selected from among those attending the Dental Clinic at "Federico II" University, Naples, between 1987 and 1989. After 16 yr, only 35 cases could be evaluated: in 22 of these cases (62.9%) the color had remained stable and was similar to that of adjacent teeth, indicating a successful outcome of the combined bleaching technique. There were 13 cases (37.1%) classified as failures because of marked color relapse. Radiology showed none of the cases re-examined to have undergone internal or external root resorption. These results confirm the validity of the combined intracoronal bleaching technique in terms of efficacy, rapid esthetic result, and safety.

Nanoindentation study of human premolars subjected to bleaching agent

Bleaching of teeth is gaining popularity due to cosmetic reasons. However, the effect it has on teeth is still largely unknown. This paper seeks to evaluate the effect of a bleaching agent, 30% hydrogen peroxide, on the nanomechanical properties of dentin and enamel using the nanoindentation technique. The Young's modulus and hardness obtained from nanoindentation before and after bleaching were compared. Five newly extracted human premolars were used. Nanoindentation was first done on the sliced enamel and dentin regions to determine their mechanical properties. One batch of samples was kept in Hank's balanced salt solution as control while the other was bleached in 30% hydrogen peroxide for 24h. The same number of nanoindentations was then done near the previously indented regions for both the control and bleached samples and the results compared. Using paired sample t-tests with alpha=0.05, it was found that there were no significant differences in both the Young's modulus and hardness of dentin and enamel kept in control. However, the mechanical properties of the bleached dentin were significantly decreased. For intertubular dentin, the mean hardness decreased by 29-55% and the mean Young's modulus decreased by 19-43%. For enamel, the mean hardness decreased by 13-32% while the mean Young's modulus decreased by 18-32%. The exact mechanism by which hydrogen peroxide affects the dentin and enamel has yet to be fully elucidated. However, it is observed to have an undermining effect on the nanomechanical properties of teeth.

Flexural Strength and Modulus Properties of Carbamide Peroxide?Treated Bovine Dentin

BACKGROUND

The effects of carbamide peroxide bleach on tooth structure are uncertain.

PURPOSE

The purpose of this study was to investigate the effects of direct or indirect carbamide peroxide application on dentin flexural strength and modulus in vitro.

MATERIALS AND METHODS

Dentin bars were machined from bovine incisors and treated with 10% carbamide peroxide for 6 h/d for 14 days. Four groups were created, with eight bars in each group: group 1-direct bleach application only; group 2-indirect bleach application only; group 3-direct bleach application followed by a 2-week storage in artificial saliva; group 4-direct bleach application followed by a 2-week storage in artificial saliva and daily topical fluoride treatments. The specimens' flexural strength and modulus were tested after 24 hours, and the results were compared with water controls using independent t-tests (p < .05).

RESULTS

Flexural strength results (in megapascals) for bleached versus control dentin (1=205+/-26 vs 215+/-14, 2=257+/-25 vs 261+/-14, 3=180+/-22 vs 193+/-36, 4=157+/-18 vs 184+/-11) were significantly lower in group 4 (p=.005). Modulus results (in gigapascals) for bleached versus control dentin (1=10.7+/-1.4 vs 12.2+/-0.6, 2=14.2+/-1.7 vs 14.4+/-1.6, 3=10.0+/-2.0 vs 10.9+/-1.3, 4=9.0+/-1.2 vs 11.1+/-1.0) were significantly lower in groups 1 and 4 (p=.013 and p=.003, respectively). There were no significant differences in strength and modulus results between the bleached and control dentin in groups 2 and 3. A direct application of carbamide peroxide to bovine dentin significantly decreased some dentin mechanical properties in vitro. An indirect application of carbamide peroxide to dentin did not significantly decrease dentin strength and stiffness.

CLINICAL SIGNIFICANCE

This in vitro study suggests that a bleaching treatment, when applied to the enamel of intact teeth, does not significantly affect the mechanical properties of the underlying dentin. However, when applied directly to dentin in clinical situations such as root exposure or occlusal attrition, the bleaching treatment may result in altered mechanical properties of dentin. The clinical consequences of this observation are, however, unknown.