Effect of direct peroxide bleach application to bovine dentin on flexural strength and modulus in vitro

Effect of Bleaching Treatments on the Mechanical Properties of the Dentin Matrix and on Collagen Biodegradation by Endogenous Protease

This study evaluated the mechanical properties of demineralized dentin matrix submitted to different bleaching treatments, as well as the changes in mass and collagen biodegradation brought about by endogenous protease. Dentin collagen matrices were prepared to receive the following treatments (n=12): no bleaching treatment (C-control), 10% carbamide peroxide (CP-Opalescence PF, Ultradent, South Jordan, UT, USA) 10%/8 hours/ day/14 days, and 40% hydrogen peroxide (HP-Opalescence Boost, Ultradent), 40 minutes per session/3 sessions. The dentin matrices were evaluated for elastic modulus and mass before and after treatments and ultimate tensile strength after treatments. The solution collected during storage was evaluated for hydroxyproline release. There was no statistically significant difference between CP and C in terms of the elastic modulus (p=0.3697) or mass variation (p=0.1333). Dentin beams treated with HP and C presented significant mass loss after the first session (p=0.0003). HP treatment led to complete degradation of collagen matrices after the second bleaching session. After the second session, CP showed higher hydroxyproline concentration than C (p<0.0001). Ultimate tensile strength was lower for CP than C (p=0.0097). CP did not affect the elastic modulus or the dentin collagen matrix mass but did promote hydroxyproline release by endogenous protease and reduce the ultimate tensile strength. HP significantly affected the mechanical properties of dentin and promoted complete degradation of the demineralized dentin collagen matrix.

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.

Evaluating the Effect of Different Intra-Orifice Barriers and Various Bleaching Agents on the Fracture Resistance of Teeth After the Walking Bleach Procedure: An In Vitro Study

Objective This study aimed to evaluate the effect of three different commercially available intra-orifice barriers and bleaching agents on root canal-treated teeth. Materials and methods Forty-five freshly extracted single-rooted incisors, canine, and premolars were collected and stored in 10% formalin. Root canal procedures were performed on the extracted teeth and these were classified into three groups and three subgroups (n=5). Group 1: resin-modified glass ionomer cement (RMGIC); placed at the level of cemento-enamel junction (CEJ) and cured for 20 seconds. Group 2: Biodentin^TM (Septodont Ltd., Saint Maur des Fausse´s, France); powder and liquid were mixed according to the manufacturer's instructions and placed at the level of CEJ, and waited for 15 minutes to set. Group 3: bulk-fill composite; placed at the level of CEJ. Group A was treated with 35% carbamide peroxide (Ultradent Opalescence 35% PF regular). Group B was bleached with 35% hydrogen peroxide (Pola Office). Group C, which was the control group, was treated with distilled water. The bleaching procedure was repeated once every seven days for a period of three weeks. After bleaching, every sample was sectioned 2 mm above the level of CEJ to remove the crown. Auniversal testing machine (UTM) was used for the evaluation of the fracture resistance of teeth. Data were analyzed for significance by using analysis of variance (ANOVA) and further pair-wise comparison was performed by pos-hoc analysis. The level of significance was set at p<0.05 Results There was a significant difference between the fracture resistance of the three materials when bleached using distilled water (p<0.05). The fracture resistance of Group 3 was significantly greater than that of Group 2 and Group 1 (p<0.05). The difference in the fracture resistance between Group 1 and Group 2 was nonsignificant (p>0.05). Conclusion Walking bleach performed via bleaching agents 35% carbamide peroxide and 35% hydrogen peroxide leads to a reduction in the fracture resistance of endodontically treated teeth; 35% hydrogen peroxide causes more fracture resistance reduction than carbamide peroxide of the same concentration. The presence of intra-orifice barriers leads to greater fracture resistance and reinforcement of endodontically treated teeth that undergo the walking bleach procedure. Bulk-fill composite can be used as an intra-orifice barrier with good fracture resistance.

Effect of Different Intraorifice Barriers and Bleaching Agents on the Fracture Resistance of Endodontically Treated Anterior Teeth

INTRODUCTION

Intraorifice barriers (IOBs) are usually used before internal bleaching for coronal sealing and the prevention of cervical resorption. The aim of this study was to investigate the effect of different IOBs on the fracture resistance (FR) of endodontically treated anterior teeth bleached with various bleaching agents (BAs).

METHODS

After performing root canal treatment for 72 extracted bovine upper incisors, the coronal 3 mm of gutta-percha was removed, and samples were classified into 3 based on the type of IOB: calcium-enriched mixture, mineral trioxide aggregate, and resin-modified glass ionomer. After applying IOBs, samples of each group were subdivided into 4 based on the BA: carbamide peroxide 45% (CP), hydrogen peroxide 35% (HP), sodium perborate (PB), and distilled water as the control. At the end of bleaching, the access cavities were restored with composite resin. The FR was measured with a universal testing machine at a crosshead speed of 5 mm/min. The data were analyzed using 2-way analysis of variance and least significant difference post hoc tests (P < .05).

RESULTS

The effect of BAs on the FR was significant (P < .05); however, the effect of the IOB and the interactive effect of these variables were not significant (P > .05). The FR in the HP and PB groups was significantly different from the control (P < .05) but that of CP was not significantly different from the control (P > .05).

CONCLUSIONS

Mineral trioxide aggregate and calcium-enriched mixture act similarly to resin-modified glass ionomer as an IOB. CP, unlike HP and PB, did not significantly decrease the FR.

The effects of fractional CO2 laser, Nano-hydroxyapatite and MI paste on mechanical properties of bovine enamel after bleaching

Background

This study investigated the effect of post bleaching treatments to the change of enamel elastic modulus and microhardness after dental bleaching in- vitro.

Material and Methods

Fifty bovine incisor slab were randomly assigned into five groups (n=10). The samples were bleached for three times; 20 minutes each time, by 40% hydrogen peroxide. Next it was applied fractional CO2 laser for two minutes, Nano- hydroxy apatite (N-HA) and MI-paste for 7 days and 2 minutes per day. The sound enamel and bleached teeth without post treatment remained as control groups. The elastic modulus and microhardness were measured at three times; 24 hours, 1 and 2 months. Data were statistically analyzed by two-way analysis of variance with 95% confidence level.

Results

Different methods of enamel treatment caused a significant increase in elastic modulus compared to bleached group (P<0.05). Modulus was significantly increased in 1 and 2 months (P<0/001: bleach, P= 0/015: laser, P= 0/008: NHA, P=0/010: MI paste) but there were no significantly difference between 1 and 2 months (P>0.05). There was any significance difference for hardness among treated and control groups, but hardness increased significantly by increasing storage time (P<0.05).

Conclusions

The use of the protective tested agents can be useful in clinical practice to reduce negative changes of enamel surface after whitening procedures.

Key words:Bleaching enamel, CO2 laser, MI pastes, Nano-hydroxy apatite, Microhardness, Elastic modulus.

Effect of peroxide bleaching on the biaxial flexural strength and modulus of bovine dentin

Objective:

This study evaluated the effects of carbamide peroxide and hydrogen peroxide on the biaxial flexural strength and flexural modulus of bovine dentin.

Materials and Methods:

Thirty coronal dentin disks (0.5 mm thick × 6.0 mm diameter) were prepared from bovine teeth. The disks were randomly divided into three groups (n=10): A control group (unbleached), a group bleached with 10% carbamide peroxide (8 h at 37°C), and a group bleached with 38% hydrogen peroxide (three 10 min applications at 37°C). The specimens were tested in a biaxial flexural apparatus held in a universal testing machine at 1.27 mm/min until failure occurred, and the biaxial mechanical properties were calculated. For each test parameter, the data were statistically analyzed by Fisher's PLSD test (predetermined α = 0.05).

Results:

The group bleached with 38% hydrogen peroxide demonstrated significantly lower flexural strength than the unbleached control group. Hydrogen peroxide treatment resulted in a significantly lower flexural modulus compared with the control group and with carbamide peroxide bleaching.

Conclusion:

Exposure of dentin to hydrogen peroxide significantly reduced both the flexural strength and the flexural modulus compared with the no-treatment control, whereas exposure to carbamide peroxide did not significantly affect either parameter.

Tooth-bleaching procedures and their controversial effects: A literature review

AIM

This review article will help clinicians improve their understanding of the history of bleaching procedures, bleaching types, components, mechanisms, and their effects on soft tissue, tooth structures, resin composite, and bonding.

METHODS

The controversial issues about bleaching procedures and their effects are reviewed. Additionally, the consequences of pre- and post-bleaching on the bonding potential of composite resin restorations to tooth structure are discussed.

CONCLUSION

The overall goal of the paper is to help reduce risks for patients.

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.

Effect of CPP-ACP Application on Flexural Strength of Bleached Enamel and Dentin Complex

In the absence of saliva, flexural strength of the bovine enamel-dentin complex decreases after in vitro simulation of both at-home and in-office bleaching procedures. Application of Casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) subsequent to both bleaching regimens could compensate for this decrease.

Ex-vivo evaluation of the intrapulpal temperature variation and fracture strength in teeth subjected to different external bleaching protocols

This study evaluated the influence of bleaching protocols on intrapulpal temperature and fracture strength of the bleached teeth. Ninety maxillary incisors were assigned to 9 groups (n=10): G1: 35% carbamide peroxide (35% CP), G2: 38% hydrogen peroxide (38% HP), G3: halogen light, G4: LED-laser, G5: 35% CP + halogen light, G6: 38% HP + halogen light, G7: 35% CP + LED-laser, G8: 38% HP + LED-laser, and G9: no treatment (control). Pulp space was widened, a thermocouple was introduced through the apex up to the pulp chamber and the temperature was recorded (°C). The fracture strength (kN) was determined using an Instron machine. Data were analyzed by ANOVA and Tukey's test (p<0.05). The halogen light alone (1.10 ± 0.24) (G3) and associated with 38% HP (1.15 ± 0.30) (G6) produced the highest temperature increase, statistically different (p<0.05) from the other groups. G1 (0.15 ± 0.06) and G6 (0.19 ± 0.07) produced the lowest values, statistically different (p<0.05) from G5 (0.65 ± 0.49). The bleaching protocols increased the temperature, but no increment exceeded the critical value of 5.6°C. Neither 35% CP nor 38% HP or the light sources alone altered the fracture strength of the teeth.

Effects of in-office and at-home bleaching on human enamel and dentin: an in vitro application of Fourier transform infrared study

In-office and at-home bleaching techniques are widely used methods for the whitening of teeth. However, the safety of these techniques has not been clarified yet. The aim of the current study is to investigate the in-office- and at-home-bleaching-induced structural and quantitative changes in human enamel and dentin at the molecular level, under in vitro conditions. The Fourier transform mid-infrared (mid-FT-IR) spectroscopic technique was used to monitor bleaching-induced structural changes. Band frequency and intensity values of major absorptions such as amide A, amide I, phosphate (PO(4)), and carbonate (CO(3)(-2)) bands, for treatment groups and control, were measured and compared. The results revealed that both procedures have negligible effects on dentin constituents. In office-bleached enamel, in addition to demineralization, a decrease in protein and polysaccharide concentrations, mineral-to-protein ratio, and the strength of hydrogen bonds around NH groups, as well as a change in protein secondary structure were observed. The protein structure changed from beta-sheet to random coil, which is an indication of protein denaturation. However, no significant variations were observed for at-home bleached enamel. The control, at-home, and in-office bleached enamel samples were differentiated with a high accuracy using cluster analysis based on FT-IR data. This study revealed that office bleaching caused deleterious alterations in the composition and structure of enamel that significantly affected the crystallinity and mineralization of the tissue. Therefore, at-home bleaching seems to be much safer than in-office bleaching in terms of molecular variations.

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.

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.

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.