Effect of acidity of in-office bleaching gels on tooth sensitivity and whitening: a two-center double-blind randomized clinical trial

OBJECTIVES

The study aimed to compare the tooth sensitivity (TS) and bleaching efficacy of two hydrogen peroxide gels with different pHs (acid pH [Pola Office, SDI] and the neutral pH [Pola Office+, SDI]) used for in-office bleaching.

MATERIALS AND METHODS

Fifty-four patients from Brazil and Chile, with right superior incisor darker than A2, were selected for this double-blind, split-mouth randomized trial. Teeth were bleached in two sessions, with 1-week interval. Each session had three applications of 8 min each, according to the manufacturer's instructions. The color changes were evaluated by subjective (Vita Classical and Vita Bleachedguide) and objective (Easy shade spectrophotometer) methods. Participants recorded TS with 0-10 visual analog scale. Color change in shade guide units (SGU) and ΔE was analyzed by Student's t test (α = 0.05). The absolute risk and intensity of TS were evaluated by McNemar's test and Wilcoxon-paired test, respectively (α = 0.05).

RESULTS

All groups achieved the same level of whitening after 30 days of clinical evaluation. The use of a neutral in-office bleaching gel significantly decreases the absolute risk of TS (28%, 95% CI 18-41) and intensity of TS when compared to the acid bleaching gel (absolute risk of 50%, 95% CI 37-63).

CONCLUSION

The use of a neutral in-office bleaching agent gel produced the same whitening degree than an acid bleaching gel but with reduced risk and intensity of tooth sensitivity.

CLINICAL SIGNIFICANCE

Clinicians should opt to use in-office bleaching with a neutral gel than an acid product because the former causes a significant lower risk and intensity of tooth sensitivity.

Effect of Bleaching on Microhardness of Esthetic Restorative Materials

High-concentration carbamide peroxide containing home bleaching may cause a varying influence on the microhardness of esthetic restorative materials.

The effect of home-bleaching application on the color and translucency of five resin composites

OBJECTIVES

The aim of this study was to investigate the effect of home bleaching agents on the color and translucency of resin composites.

METHODS

Thirty disc shaped specimens (1mm thick) were fabricated from each resin composite (Reflexions, Grandio, Gradia Direct, Clearfil Majesty Esthetic, Ceram-X Mono) and divided into 3 subgroups as carbamide peroxide (CP, Opalescence 10% PF), hydrogen peroxide (HP, 10% Opalescence Treswhite Supreme) and control group (n=10). Baseline CIE L*a*b* color coordinates were measured with spectrophotometer and translucency parameters (TP) were calculated. CP and HP groups were treated with bleaching agents according to manufacturers' instructions and control group was stored in distilled water (DW) for 14 days. Color and translucency measurements were repeated and color differences were calculated, ΔE values>3.3 were considered as clinically unacceptable.

RESULTS

Clinically unacceptable color change was detected for all resin composites exposed to bleaching agents and there was significant color difference between the control group and bleached specimens (P<0.05). However no significant color difference was found between CP and HP groups. Intragroup comparison revealed that Ceram-X Mono showed the highest color change but there was no significant difference among the other tested materials for both CP and HP groups. Intergroup comparison of TP values of CP, HP and control groups at the end of 14th day revealed that there was no statistical significant translucency difference among the groups.

CONCLUSIONS

Application of CP and HP resulted in clinically unacceptable color change for all resin composites. Translucencies of the resin composites were not affected by bleaching procedure.

CLINICAL SIGNIFICANCE

The results of this in vitro study suggest that patients should be informed regarding a potential color change of existing resin composite restorations with the use of home bleaching agents.

Hydrogen Peroxide Might Bleach Natural Dentin by Oxidizing Phosphoprotein

Recent studies suggested that bleaching agents may whiten teeth by oxidizing the fluorescent materials, which are the proteins located in the organic-inorganic interface. Therefore, we postulated that fluorescence of dentin came from dentin phosphoprotein (DPP) and that bleaching agents might bleach dentin by oxidizing DPP. Fifty-six specimens were randomly divided into 4 groups and exposed to distilled water, hydrogen peroxide (HP), ethylenediamine tetraacetic acid disodium salt (EDTA), and acetic acid for 24 h. After measuring the organic and inorganic components, fluorescence, and color characteristics of dentin before and after exposure, we found that when DPP was removed from dentin by EDTA, fluorescent intensity declined proportionally with the reduction in Raman relative intensity, and dentin was whitened considerably, with an Δ E value 6 times higher than that of the distilled water group. On the contrary, due to the incapability of acetic acid to dissolve DPP during decalcification, fluorescent intensity values and tooth color remained nearly unchanged after exposure to acetic acid. Dentin exposed to neutral HP showed no obvious morphologic and organic/inorganic component changes except for the destruction of DPP. Similarly, dramatically decreased fluorescent intensity and lightened color were found in the HP group. Moreover, DPP solution of the HP group exhibited decreased ultraviolet absorbance, especially between 250 and 300 nm, which arose from aromatic amino acids. The results indicated that DPP was responsible for the fluorescent properties of dentin and that HP might bleach dentin by the oxidization of aromatic amino acids in DPP. These findings are of great significance in promoting our further understanding of the mechanism of tooth bleaching and the fluorescent property of normal dentin.

Enamel Mineral Content Changes After Bleaching With High and Low Hydrogen Peroxide Concentrations: Colorimetric Spectrophotometry and Total Reflection X-ray Fluorescence Analyses

The purpose of this study was to evaluate the calcium (Ca) and phosphorous (P) content in enamel bleached with high and low concentrations of hydrogen peroxide (HP) using Total Reflection X-Ray Fluorescence (TXRF) and colorimetric spectrophotometry (SPEC). Forty-eight sound human third molars were used. Their roots were embedded in polystyrene resin and immersed for seven days in an artificial saliva solution. Then they were distributed into six groups to receive the bleaching treatments. The agents of high HP concentration (for in-office use) evaluated were Whiteness HP Maxx/FGM (35% HP), Whiteness HP Blue/FGM (35% HP, 2% calcium gluconate), Pola Office+/SDI (37.5% HP, 5% potassium nitrate), and Opalescence Boost/Ultradent (38% HP, 1.1% ion fluoride, 3% potassium nitrate); these agents were applied to enamel in three sessions. The agents of low HP concentration (for home use) evaluated were Pola Day/SDI (9.5% HP) and White Class 10%/FGM (10% HP, potassium nitrate, calcium, fluoride), and these agents were applied for 14 days. Enamel microbiopsies were evaluated by TXRF and SPEC analysis before the bleaching treatment (baseline), during the treatment, and 14 days after the end of the treatment. For TXRF, the Kruskal-Wallis test showed that Ca and P were not influenced by agent (p>0.05). For SPEC, Pola Office+, Opalescence Boost, Pola Day, and White Class 10% caused a decrease of Ca over time; there was a significant decrease of P over time to Pola Office+ and White Class 10%. The Spearman test showed no correlation between the Ca (p=0.987; r²=-0.020) and P (p=0.728, r²=0.038) obtained by SPEC and TXRF. For TXRF and SPEC, changes in Ca and P during bleaching occurred independently of the HP concentration used.

Evaluation of the genotoxic potential of different delivery methods of at-home bleaching gels: a single-blind, randomized clinical trial

OBJECTIVE

This single-blind, parallel, randomized clinical trial evaluated the genotoxic potential and effectiveness of 10% hydrogen peroxide (HP) in patients submitted to at-home bleaching.

MATERIALS AND METHODS

Sixty young volunteers with maxillary incisors equal to or darker than M1.5 were included in the study. Patients were submitted to bleaching for 14 days (30 min/day) with one of the three 10% HP treatments: the bleaching agent was delivered in a bleaching tray (White Class, FGM), whitening strips (White Strips, Oral-b), or in prefilled disposable trays (Opalescence Go, Ultradent). The color change was evaluated with the Vita Bleachedguide, and the micronucleus test of exfoliative oral mucosa was carried out, starting from a count of 1000 cells, at the baseline, immediately after and 30 days after the end of the treatment. The micronucleus data were evaluated with the Kruskal-Wallis and Wilcoxon tests and color change with the two-way ANOVA test and the Tukey test (α = 0.05).

RESULTS

Significant whitening was observed for all groups after 14 days (p = 0.001) and was maintained after 30 days, with no difference between groups (p = 0.42). The micronucleus count did not indicate genotoxic potential in any of the groups studied (p = 0.32), irrespective of the time intervals (p = 0.62).

CONCLUSION

No genotoxic effects of 10% HP were observed in patients submitted to at-home bleaching systems (30 min/day for 14 days), even 30 days after the end of treatment.

CLINICAL SIGNIFICANCE

It is safe to use different systems to deliver 10% HP during at-home bleaching according to the manufacturers' recommendations, with no risk of genotoxic effects applied.

Effect of antioxidant treatment on the shear bond strength of composite resin to bleached enamel

INTRODUCTION

This study examined the antioxidant treatment on the shear bond strength of composite resin to enamel after bleaching with two different bleaching systems.

MATERIALS AND METHODS

Seventy flat enamel surfaces were prepared from freshly extracted human molars using a low speed diamond saw. Then the specimens were divided into seven random groups (n = 10) to apply different procedures; namely, bleaching with White Smile and bonding with composite resin (G1), bleaching with White Smile, treatment with ascorbic acid and bonding with composite resin (G2), bleaching with White Smile, immersing in artificial saliva for 2 weeks and bonding with composite resin (G3), bleaching with Opalesence and bonding with composite resin (G4), bleaching with Opalesence, treatment with ascorbic acid and bonding with composite resin (G5) and bleaching with Opalesence, immersing in artificial saliva for 2 weeks and bonding with composite resin (G6). Another group was used as a control group. Shear bond test was performed on all specimens and data were analyzed using one way ANOVA and Bonferroni's test (p < 0.05).

RESULTS

Bond strengths of bleached specimens were significantly lower than those of non-bleached specimens. No statistical difference was found in bond strength between the bleached and non-bleached groups when the antioxidant treatment was carried out.

CONCLUSION

Ten per cent ascorbic acid treatment was found to be an effective method to reverse the compromised bond strength.

Effects of different bleaching methods on shear bond strengths of orthodontic brackets

OBJECTIVE

To evaluate the effects of different bleaching methods on the shear bond strength (SBS) of orthodontic brackets.

MATERIALS AND METHODS

Forty-five freshly extracted premolars were randomly divided into three groups (n = 15 per group). In group I, bleaching was performed with the office bleaching method. In group II, bleaching was performed with the home bleaching method. Group III served as the control. Orthodontic brackets were bonded with a light cure composite resin and cured with an LED light. After bonding, the SBS of the brackets were tested with a Universal testing machine.

RESULTS

Analysis of variance indicated a significant difference between groups (P < .001). The highest values for SBS were measured in group III (20.99 ± 2.32 MPa). The SBS was significantly lower in groups I and II than in group III (P < .001). The lowest values for SBS were measured in group II (6.42 ± 0.81 MPa). SBS was significantly higher in group I than in group II (P < .001).

CONCLUSIONS

Both of the bleaching methods significantly affected the SBS of orthodontic brackets on human enamel. Bleaching with the home bleaching method affected SBS more adversely than did bleaching with the office bleaching method.

Do mouthwashes with and without bleaching agents degrade the force of elastomeric chains?

OBJECTIVE

To evaluate, in vitro, the effect of mouthwashes with and without bleaching agents on the force of elastomeric chains.

MATERIALS AND METHODS

A total of 108 elastomeric chain specimens was divided into six groups (n = 18 in each group). Two test groups were exposed to two types of commonly used mouthwashes (Plax and Listerine), and two groups were exposed to mouthwashes containing bleaching agent (Plax Whitening and Listerine Whitening). Immersion in the solutions was performed twice a day for 60 seconds. One group of control specimens remained immersed in artificial saliva throughout the entire experimental period, and the other control specimens were exposed to distilled water. Force measurements were performed at six time intervals (initial, 1 day, 7 days, 14 days, 21 days, and 28 days).

RESULTS

No statistically significant differences were found between the groups in the initial period (P > .05). Statistically significant differences were found between the control group and the Plax, Plax Whitening, and Listerine groups at the time intervals of 7, 14, and 21 days. In the initial period, the force was statistically significantly higher than it was in any of the other experimental periods (P < .05). The control group with distilled water and the test group with Plax Whitening maintained the most force during the experimental period.

CONCLUSION

The presence of bleaching agent has no influence on the force degradation of elastomeric chains.

Anti-calculus and whitening toothpastes

In terms of novel formulations, there seems to have been a shift in emphasis from anti-caries/anti-gingivitis to anti-calculus/whitening toothpastes in recent years. The anti-calculus and whitening effects of toothpastes are to some extent based on the same active ingredients: compounds of high affinity for tooth mineral. Due to this affinity, crystal growth may be hindered (anti-calculus) and chromophores be displaced (whitening). Besides these common ingredients, both types of toothpaste may contain agents specifically aimed at each condition. Clinical studies have shown that these active ingredients can be successfully formulated in fluoride toothpastes to give significant reductions in supragingival calculus and stain formation and facilitate their removal. Some of the ingredients are formulated in toothpastes that additionally contain anti-plaque and anti-gingivitis ingredients, making these toothpastes (together with the fluoride) truly multi-functional. The development of these products is not straightforward because of interaction between formulation components and because the active ingredients must maintain their beneficial characteristics during the shelf life of the paste. Neither a therapeutic benefit (in terms of less gingivitis or less caries) nor a societal benefit (in terms of less treatment demand) has been demonstrated as a result of the anti-calculus and whitening effects of toothpastes.

Effect of in-office bleaching agents on the color changes of stained ceromers and direct composite resins

PURPOSE

To evaluate the effect of two in-office bleaching agents on the color changes of two ceromers (Ceramage and Adoro SR) and one direct composite resin (Gradia Direct Anterior) after staining by tea and coffee.

MATERIALS AND METHODS

Twenty-four disk-shaped specimens were fabricated for each resin material and randomly divided into three groups (n = 8). The specimens were immersed in tea, coffee or deionized water, respectively, for 7 days. Each group was then equally divided into two sub-groups (n = 4), which were subjected to two in-office bleaching agents (BEYOND and Opalescence Boost), respectively. The color of the specimens was measured by a spectrophotometer at baseline, after staining and after bleaching. The color differences (ΔE values) between baseline and after treatments were calculated.

RESULTS

Statistical analysis indicated that the staining solution had significant influence on the color change of resin composites tested (p < 0.001). The discolorations of resin composites were perceptible after immersing in tea or coffee solutions (ΔE>2.0). There was no statistically significant difference between BEYOND and Opalescence Boost in stains removal from discolored resins (p = 0.550). The color changes in ΔE value between baseline and after bleaching were less than 2.0 for all resin composite groups.

CONCLUSIONS

Tea solution produces severe discoloration of three resin composites tested. The two in-office bleaching agents can effectively remove the stains from two ceromers and one direct composite resin tested in this study.

Antioxidant agents and their effects on shear bond strength of bleached enamel

AIM

The goal of this study was to fnd a method to eliminate bond strength reduction after vital bleaching.

MATERIALS AND METHODS

Sixty fat surfaces of enamel central human incisors were prepared by diamond disks. In the frst group, the samples immediately bonded to the tooth after bleaching. For the second group, the bleached samples were treated by sodium ascorbate for 1 hours. In the third and fourth groups the treatment was down using a new antioxidant agent for 1 hour and 15 minutes respectively. For the ffth group no bleaching was done. Cylindrical composite resin (Z 100) with a Single Bond adhesive system was bonded to the enamel with a special metal mold. After thermocycling, the samples were loaded at a crosshead speed of 0.5 mm/min. The mode of failures was inspected by the Dino Lite microscope and the microstructure of the debonding surfaces was observed by SEM. Considering normal data, statistical analysis was conducted by ANOVA and Tukey tests (p = 0.05).

RESULTS

The fourth group had maximum (21.82), while the frst group had the least (9.0971) shear bond strength. The ANOVA test showed a signifcant difference among the fve groups (p = 0.0002). There was not any signifcant statistical difference between the three types of debonding (p = 0.165).

CONCLUSION

The usage of sodium ascorbate or sodium ascorbate with detergent after vital bleaching are effective methods for reducing the damaging effects of bleaching agents on the shear bond strength of composite resin restoration to enamel. CLINICAL SIGNIFCANCE: Using antioxidants is necessary post bleaching and before resin bonding.

Effect of Various Bleaching Agents on the Surface Composition and Bond Strength of a Calcium Silicate-based Cement

This study aimed to evaluate the morphological and elemental changes that occur on the surface of calcium silicate-based cement (CSC) and to analyze the bond strength of composite resin to CSC after application of various bleaching agents. One hundred twenty-five CSC blocks (Biodentine) were prepared and randomly divided into five groups according to the bleaching agent applied over the material surface (n=25): SP-DW (sodium perborate-distilled water mixture), SP-HP (sodium perborate-3% hydrogen peroxide [H₂O₂] mixture), CP (37% carbamide peroxide gel), HP (35% H₂O₂ gel), and a control group (no bleaching agent). After 1 week, scanning electron microscopy provided an analysis of the surface morphology and elemental composition for 10 specimens from each group. Composite resin was placed at the center of each cement surface in the remaining specimens (n=15). A universal testing machine determined shear bond strength (SBS) and fracture patterns were identified with a dental operating microscope. Data were analyzed using one-way analysis of variance and Tukey HSD tests. The cement surface in the CP and HP groups presented changes in structure and elemental distribution compared with the remaining groups. The former groups exhibited a decrease in the calcium level and an increase in the silicon level and presented significantly fewer SBS values than the remaining groups ( p<0.05). Most failures were adhesive in the CP and HP groups, while they were predominantly cohesive in the remaining groups. The bleaching agents with higher concentration induced deterioration of the cement surface and negatively affected the bond strength of the composite resin to CSC. The use of CSC is recommended as a cervical barrier when intracoronal bleaching is performed with a mixture of sodium perborate with water or 3% H₂O₂.

The Effect of 3% Phosphate Ascorbyl Gel on Bond Strength of Composite Resin to Enamel treated with 35% Hydrogen Peroxide

OBJECTIVE

To evaluate the effect of 3% phosphate ascorbyl gel (PA) in different times onto the microshear bond strength of composite resin (CR) to bovine enamel treated with 35% hydrogen peroxide (HP).

MATERIALS AND METHODS

Thirty enamel blocks of bovine incisors were made and divided into 5 groups (n = 6) with three specimens per group (n = 18), according to treatment: G1= No bleaching + CR; G2 = HP + CR after 15d; G3 = HP + CR after 24 hours; G4 = HP + PA (15 min) + CR after 24 hours; G5 = HP + PA (2 hours) + CR after 24 hours. The resin cylinders were made by Tygon matrices. Microshear bond strength test was performed using universal testing machine with a 50N load at a speed of 0.5 mm/min. Fracture modes were assessed by a stereomicroscope 40 ×. Microshear bond strength values were submitted to the analysis of variance (ANOVA) one-way and Tukey test (p < 0.05).

RESULTS

G1 had significant results when compared to G3 and G5 (p < 0.01). However, G2, G3, G4 and G5 have showed no significant differences among groups (p > 0.05). Failure modes were categorized into adhesive (90%) and mixed (10%).

CONCLUSION

The use of 3% phosphate ascorbyl gel for 15 minutes was able to improve bond strength of composite resin to bleached bovine enamel, but when 3% phosphate ascorbyl gel was applied during 40 minutes it negatively interfered in the adhesion of the resin to bleached bovine enamel.

Effect of three different mouthrinses on microleakage of composite resin restorations with two adhesive systems after bleaching with 10% carbamide peroxide

AIM

The aim was to evaluate the effects of Oral-B (OB), Listerine (LN) and Rembrandt Plus (RM) mouthrinses on microleakage of composite resin restorations bonded with two adhesive systems after bleaching with 10% carbamide peroxide.

MATERIALS AND METHODS

A total of 60 Cl V cavities were prepared on human premolars. The occlusal and gingival margins were placed 1 mm occlusal to and apical to CEJ respectively. The teeth were randomly divided into two groups based on the adhesive system used: Excite (EX) and Clearfil SE Bond (CSE) groups. After composite resin restoration of cavities, thermocycling and bleaching with 10% carbamide peroxide for 2 hours daily for 14 days, the teeth in each adhesive group were further subdivided into three subgroups and were immersed for 12 hours in the three OB, RM and LN mouthrinses. The teeth were then placed in 2% basic fuschin for 24 hours. After dissecting the teeth, microleakage was evaluated under a stereomicroscope at 16×. Data was analyzed with multifactor ANOVA and Bonferroni test at p < 0.05.

RESULTS

Microleakage with EX was significantly higher than that with CSE (p = 0.009). Microleakage at gingival margins was significantly higher than that at occlusal margins (p = 0.15). Microleakage with OB was higher than that with LN (p = 0.02). However, there were no significant differences in microleakage between LN and RM (p = 1) and between RM and OB (p = 0.15). In addition, with the EX adhesive system, microleakage with OB was higher than that with LN and RM (p = 0.02).

CONCLUSION

In the present study, microleakage of composite resin restorations was influenced by the type of the adhesive system, mouthrinse type and the location of the cavity margin.

CLINICAL SIGNIFICANCE

Use of some mouthrinses, such as OB after bleaching can increase postrestoration microleakage of resin composite restorations bonded with etch-and-rinse adhesive systems.

Influence of two different methods of delivering fluoride on bond strength and degree of conversion of an adhesive after bleaching

PURPOSE

To evaluate the influence of fluoride delivery and restoration time point on the microshear bond strength (mSBS) and degree of conversion (DC) values of an adhesive applied on bleached enamel.

MATERIALS AND METHODS

Fifty-four enamel specimens were submitted to bleaching and divided into 3 groups of n = 18: group HP: 35% hydrogen peroxide (HP); group HPF: HP + 1.23% sodium fluoride application (F); group PF: 38% HP with F. A control group of n = 6 was neither bleached nor fluoridated. Subsequently, each group except the control was subdivided into 3 subgroups (n = 6) to be restored immediately, or at 7 or 14 days. Tygon tubes were filled with composite resin and placed on enamel surfaces, then the mSBS test was performed. The DC of the interface was observed with Raman spectroscopy. The data were submitted to two-way ANOVA and Tukey's and Dunnet's post-hoc test (α = 0.05).

RESULTS

The mSBS results showed higher values for groups HP and HPF at 14 days compared with immediate and 7 days (p < 0.05). Lower DC values were obtained in the immediately restored groups HP and HPF, which were significantly different from 7 and 14 days (p < 0.05). mSBS and DC for group PF was similar at all restoration time points and to the control group (p > 0.05).

CONCLUSION

Only the use of a fluoridated in-office bleaching agent (Opalescence Boost PF) proved to be effective for immediately reversing the side effects of low mSBS and DC values when in-office bleaching is used.

Effect of Dentin Pretreatment on Bond Strength Stability of Self-etching and Etch-and-Rinse Adhesives to Intracoronally Bleached Dentin

PURPOSE

To evaluate the effect of chlorhexidine or glutaraldehyde pretreatment on the bonding stability of selfetching and etch-and-rinse adhesives to bleached dentin.

MATERIALS AND METHODS

The occlusal surface of 80 third molars was abraded to expose a flat mid-dentin surface, which was then subjected to a bleaching procedure using 20% hydrogen peroxide and sodium perborate for 14 days. Afterwards, the specimens were kept in distilled water, followed by application of either a three-step etchand- rinse (Adper Scotchbond Multi-Purpose Plus, SBMP) or a two-step self-etching (Clearfil SE Bond, CSE) adhesive system. For each approach, the bleached dentin was treated with chlorhexidine or glutaraldehyde, or left untreated, prior to the adhesive procedure. Unbleached dentin was used as a control. Composite cylinders were built up over the adhesive-covered dentin followed by parallel sectioning of specimens to obtain 1-mm slices. The slices were trimmed to obtain hourglass-shaped specimens with approximately 1.0 mm2 of bonding interface. Half of the specimens were subjected to microtensile bond strength (μTBS) testing after 24 h, while the other half were stored in distilled water for 3 months prior to the μTBS test. The mode of failure was analyzed using optical microscopy.

RESULTS

For the SBMP protocol, the highest μTBS was achieved with glutaraldehyde-treated dentin, and the same μTBS values were maintained after 3 months of storage. For the CSE protocol, the highest μTBS was obtained with chlorhexidine-treated dentin.

CONCLUSION

Glutaraldehyde and chlorhexidine pretreatment should be considered to improve the μTBS of adhesives to bleached dentin, while the pretreatment effect was adhesive dependent.

Evaluation of the effect of a home bleaching agent on surface characteristics of indirect esthetic restorative materials--part II microhardness

BACKGROUND

The exponential usage of esthetic restorative materials is beholden to society needs and desires. Interaction between the bleaching agents and the esthetic restorative materials is of critical importance.

AIM

This in vitro study has been conducted to evaluate the effect of a home bleaching agent, carbamide peroxide (CP) 38%, on the microhardness of the fiber reinforced composite (FRC), overglazed, autoglazed, or polished porcelain specimens.

MATERIALS AND METHODS

For overglazed, autoglazed, polished ceramics and also FRC cylindrical specimens (n = 20 per group) were prepared. The specimens were stored in distilled water at 37°C for 48 hours prior to testing. Six samples from each group were selected randomly as negative controls which were stored in distilled water at 37°C that was changed daily. CP 38% was applied on the test specimens for 15 minutes, twice a day for 14 days. By using Knoop-microhardness tester microhardness testing for baseline, control and test specimens was conducted. Data were statistically analyzed using paired t-test, Mann-Whitney test, and Kruskal-Wallis test.

RESULTS

Home bleaching significantly decreased the surface microhardness of all the test samples (p < 0.05), whereas the control groups did not show statistically significant changes after 2 weeks. The polished porcelain and polished composite specimens showed the most significant change in microhard-ness after bleaching process (p < 0.05).

CONCLUSION

Although the type of surface preparation affects the susceptibility of the porcelain surface to the bleaching agent, no special preparation can preclude such adverse effects.

CLINICAL SIGNIFICANCE

The contact of home bleaching agents with esthetic restorative materials is unavoidable. Therefore protecting these restorations from bleaching agents and reglazing or at least polishing the restorations after bleaching is recommended.

Evaluation of the effect of a home-bleaching agent on the surface characteristics of indirect esthetic restorative materials: part I--roughness

BACKGROUND

Pressing esthetic demands of good looking make people undergo bleaching procedures. However, the effect of bleaching agents on esthetic restorative materials with different surface preparations has been poorly studied.

AIM

The aim of this study was to examine the effect of a homebleaching agent (carbamide peroxide: CP 38%) on the surface roughness of the polished fiber reinforced composite (FRC), overglazed, autoglazed, or polished ceramic samples.

MATERIALS AND METHODS

Twenty standardized cylindrical specimens were made of each of the following groups: over-glazed, autoglazed, polished porcelain and also FRC. The test specimens exposed to the CP 38%, 15 minutes, twice a day for 2 weeks according to the manufacturer's recommendation. Six samples from each group were selected randomly to form negative controls. Surface roughness measurements (Ra, micrometer) for baseline, test and control specimens were performed by use of a profilometer. Paired t-test, Mann-Whitney test, and Kruskal-Wallis test were used for statistical analyses.

RESULTS

The data showed that bleaching with CP 38% significantly increased the surface roughness of all the test samples (p < 0.05). The type of surface preparation caused significant differences between the susceptibility of porcelain subgroups to bleaching (p < 0.05). The polished porcelain specimens showed the highest changes after bleaching.

CONCLUSION

CP 38% significantly increases the surface roughness of the porcelains and FRC. The type of surface condition affects the amenability of the porcelain surface to the bleaching agent. Glazed porcelains were more resistant to roughness than the polished porcelains and also the composite.

CLINICAL SIGNIFICANCE

Roughening of porcelain and FRC occur following bleaching procedure. No special surface preparation of indirect esthetic restorative materials can completely preserve these materials from adverse effects of bleaching agents.

pH-changes during intracoronal bleaching: an in vivo study

OBJECTIVES

This study aimed to measure pH changes during 14 days intracoronal bleaching with hydrogen peroxide/sodium perborate and carbamide peroxide/sodium perborate.

MATERIALS AND METHODS

Twenty patients presenting endodontically treated central maxillary incisors with color alterations were divided in two groups (n = 10): Group CP + SP: 37% carbamide peroxide + sodium perborate paste; Group HP + SP: 30% hydrogen peroxide + sodium perborate paste. The pH values were measured using a digital microprocessor at different times: Baseline, 2, 7 and 14 days. Data were analyzed with two-way ANOVA followed by Tukey's test (α = 0.05).

RESULTS

ANOVA showed p < 0.00 which indicated significant difference between the groups. The mean values (± sd) and the results of the Tukey´s test were: HP + SP/14 days-7.98 (±0.58)a; HP + SP/7 days-8.59 (±0.18)b; HP + SP/2 days- 8.83 (±0.32)bc; HP + SP/Baseline-8.83 (±0.01)bc; CP + SP/ Baseline-8.89 (±0.01)bc; CP + SP/14 days-9.11 (±0.58)cd; CP + SP/7 days-9.54 (±0.16)de; CP + SP/2 days-9.66 (±0.08) de. The group HP + SP resulted in significantly lower pH values compared with group CP + SP.

CONCLUSION

It can be concluded that both associations showed alkaline pH values; however, there was significant reduction in the pH values of the 30% hydrogen peroxide associated with sodium perborate after 14 days.

CLINICAL SIGNIFICANCE

The association of hydrogen peroxide and carbamide peroxide with sodium perborate paste presented alkaline characteristics during the 14-day evaluated period. Thus, regarding pH changes, both associations can be considered safe as intracoronal bleaching agents.

Accounting for measurement reliability to improve the quality of inference in dental microhardness research: a worked example

OBJECTIVES

Dental microhardness experiments are influenced by unobserved factors related to the varying tooth characteristics that affect measurement reproducibility. This paper explores the appropriate analytical tools for modeling different sources of unobserved variability to reduce the biases encountered and increase the validity of microhardness studies.

MATERIALS AND METHODS

The enamel microhardness of human third molars was measured by Vickers diamond. The effects of five bleaching agents-10, 16, and 30 % carbamide peroxide, and 25 and 38 % hydrogen peroxide-were examined, as well as the effect of artificial saliva and amorphous calcium phosphate. To account for both between- and within-tooth heterogeneity in evaluating treatment effects, the statistical analysis was performed in the mixed-effects framework, which also included the appropriate weighting procedure to adjust for confounding. The results were compared to those of the standard ANOVA model usually applied.

RESULTS

The weighted mixed-effects model produced the parameter estimates of different magnitude and significance than the standard ANOVA model. The results of the former model were more intuitive, with more precise estimates and better fit.

CONCLUSIONS

Confounding could seriously bias the study outcomes, highlighting the need for more robust statistical procedures in dental research that account for the measurement reliability. The presented framework is more flexible and informative than existing analytical techniques and may improve the quality of inference in dental research.

CLINICAL RELEVANCE

Reported results could be misleading if underlying heterogeneity of microhardness measurements is not taken into account. The confidence in treatment outcomes could be increased by applying the framework presented.

Color stability of enamel treated with different antioxidant agents following at-home bleaching with 10% hydrogen peroxide

OBJECTIVE

This study evaluated the color stability of enamel submitted to 10% hydrogen peroxide (HP) followed by antioxidants agents, and the pH and antioxidant activity (AA%) of these agents.

METHODOLOGY

Bovine enamel-dentin blocks were randomly distributed into groups (n=10/group): GNC (negative control: no treatment); GPC (positive control: bleaching only); TOC_10% (HP+10% α-tocopherol); GT_10% (HP+10% green tea extract); GS_5% (HP+5% grape seed extract); SA_10% (HP+10% sodium ascorbate); QUI_10% (HP+10% quinoa extract); and QC_1% (HP+1% quercetin). Color (ΔE00) and whiteness index (ΔWID) changes were analyzed using a digital spectrophotometer. The pH and AA% were determined using a pH meter and the DPPH method, respectively. Data were analyzed by ANOVA/Tukey's and Dunnett's tests (α=0.05).

RESULTS

At 14 days post-bleaching, GNC promoted the lowest ΔWID and ΔE00 (p<0.05), and no differences were found between GPC and the remaining groups submitted to the antioxidant agents (p>0.05). QC_1% and QUI_10% exhibited acidic pH levels (3.64 and 4.75, respectively), whereas TOC_10% and GS_5% exhibited alkaline pH (7.07 and 7.64, respectively). No differences in AA% were found between the agents (p>0.05), ranging from 92.6 to 97.6%.

CONCLUSION

The antioxidant agents did not interfere in bleached enamel color stability, showing satisfactory antioxidant activity. However, QUI and QC gels displayed acidic pH. Clinical significance: The antioxidants evaluated showed high AA% and no impact on post-bleaching color stability, suggesting that their capacity to recover bond strength demonstrated elsewhere would not compromise the esthetic efficacy of tooth bleaching. However, those with acidic pH should be used with caution due to potential enamel damage.

Effect of accelerated stability on the physical, chemical, and mechanical properties of experimental bleaching gels containing different bioadhesive polymers

OBJECTIVE

To evaluate the physical-chemical (weight, pH, quantification of hydrogen peroxide) and mechanical (texture profile and rheology tests) properties of the experimental bleaching gel based on the bioadhesive polymer Aristoflex® AVC, after accelerated stability testing.

MATERIALS AND METHODS

A total of 300 syringes of bleaching gels were divided into 5 groups (n = 60): Whiteness Perfect® 10%-FGM (WP); carbamide peroxide 10% with aristoflex (CPa); carbamide peroxide 10% with Carbopol (CPc); aristoflex thickener (A); and Carbopol thickener (C). According to the following requirements and time, the accelerated stability test was performed: in an incubator at 40 °C and 75% humidity per 1, 3, and 6 months, and baseline (refrigerator at 5 °C and 25% humidity). The variables were analyzed following the statistical tests: Two-way ANOVA and Tukey's test were applied to pH; weight data were analyzed using a mixed model for repeated measurements over time and the Tukey-Kramer test; one-way ANOVA and Tukey's test analyzed the rheology test; generalized linear models were used to quantify the peroxide amount and texture profile data. A significance level of 5% was considered.

RESULTS

The experimental bleaches CPa and CPc had the highest pH values when compared to the others in 6 months. Thickeners A and C did not change the pH, weight, and active content over the accelerated stability times (p > 0.05). Furthermore, there was weight loss after 3 months of storage for CPa and CPc (p < 0.05). In the quantification of hydrogen peroxide, the WP group showed the highest values over time (p < 0.0001), only showing a significant loss after the 3rd month. Meanwhile, CPa and CPc showed a reduction in quantification from the 1st month.

CONCLUSIONS

Temperature and humidity directly influenced the active content and properties of bleaching gels. In addition, the presence of components regardless of thickeners, such as stabilizers, in the commercial gel allowed for greater stability over time.

CLINICAL RELEVANCE

The development of experimental bleaching gels for clinical use requires careful testing. Therefore, accelerated stability testing represents a valuable tool in the development and evaluation of cosmetic formulations.

Transenamel and Transdentinal Penetration of H2O2 in Restored Bovine Teeth

PURPOSE

To quantify hydrogen peroxide (H2O2) penetration into restored bovine teeth subjected to whitening treatment.

MATERIALS AND METHODS

Seventy-five enamel/dentin disks were divided into 5 groups (n = 15): intact disks (G1); cavity preparation only (G2); conventional adhesive system and composite resin (G3); resin-modified glass-ionomer cement (G4); and self-etching adhesive only (G5). After 24 h, the disks were placed into artificial pulp chambers containing an acetate buffer solution, and the first whitening session was performed using a 35% H2O2 (hydrogen peroxide) product. The disks were submitted to 10,000 thermal cycles and then stored for 1 year in deionized water. After this period, a second whitening session was performed. After each whitening procedure, the buffer solutions were analyzed for optical density in a spectrophotometer to assess the amount of H2O2 that had diffused. ANOVA and Tukey's test were used to compare the different groups and a Student's t-test was used to compare the different times (p ≤ 0.05).

RESULTS

Prior to aging, group 2 had the highest penetration of H2O2; the other groups showed similar, lower penetration. After thermocycling and aging, all groups showed a significant increase in H2O2 penetration. The greatest penetration of H2O2 into the pulp chamber was found in groups 2 and 5.

CONCLUSION

Aged restorations allowed greater H2O2 permeation through the tooth structure.

Effect of Salivary Flow on Bleached Enamel Roughness and Mineral Content: an In Situ and In Vitro Study

This study aimed to evaluate the effect of human saliva in vitro and salivary flow in situ on the roughness and mineral content of bleached enamel. Dental specimens were divided into five groups (n=15): not bleached (NB); bleached (35% hydrogen peroxide) and exposed to distilled water (DW); human saliva in vitro (IV); normal salivary flow in situ (NSF); and low salivary flow (LSF) in situ. Enamel roughness (Ra, Rz) and calcium/phosphorus contents were evaluated with laser profilometry and energy-dispersive spectroscopy, respectively, at baseline (T1), after bleaching (T2), and after seven days (T3). Salivary pH and buffer capacity were evaluated with colorimetric strips and salivary calcium and phosphorus with absorbance spectrophotometry. Data were analyzed with non-parametric tests and linear regression (α=0.05). After contact with saliva, Ra and Rz of LSF=DW>IV=NSF=NB was found. For DW and LSF, the roughness of T1<T2=T3 was found. For IV, T1<T3<T2; for NSF, T1=T3<T2. Enamel calcium/phosphorus content did not change with bleaching or with saliva contact (p≥0.05). Buffer capacity and calcium concentration did not differ between LSF and NSF. Phosphorus was higher, and pH was lower in LSF. Ra and Rz were, respectively, 0.14 and 1.95 lower with NSF than LSF. The conclusions were that NSF in situ and human saliva in vitro recovered original enamel roughness. The experimental conditions did not affect enamel mineral content. Recovery of bleached enamel roughness was higher in NSF when compared to LSF, regardless of salivary pH, calcium and phosphorus concentrations, and buffer capacity.