Effect of Artificial Saliva Storage on Microhardness and Fracture Toughness of a Hydrothermal Glass-Ceramic

Purpose: This study evaluated the effect of artificial saliva storage on the hardness, crack length, and fracture toughness of a glazed, polished, and bleached hydrothermal low‐fusing glass‐ceramic (Duceram LFC). Materials and Methods: Forty ceramic discs were constructed. The discs were assigned to four groups (n = 10) according to their surface finish: Gp1—Autoglaze, Gp2—Autoglaze/ground/diamond‐polished, Gp3—Overglaze, Gp4—Overglaze/ground/diamond‐polished. Each group was further divided into two subgroups forming eight total subgroups (n = 5). Subgroup A was unbleached; Subgroup B was bleached. Testing was performed before and after 21 days of artificial saliva storage. Data were presented as means and standard deviation (SD). ANOVA was used, along with Duncan's post hoc test for pairwise comparison between the means when ANOVA test was found significant (p≤ 0.05). Results: Surface treatments such as glazing, polishing, and bleaching, saliva storage, and the interaction between these variables had a statistically significant effect on mean values of microhardness, crack length, and fracture toughness of the specimens. There was a statistically significant increase in microhardness and fracture toughness mean values, while crack length values decreased after saliva storage. Polished specimens recorded the smallest crack lengths and fracture toughness, and highest hardness values before and after saliva storage. No difference in fracture toughness values was evident between glazed and polished specimens. Mean crack lengths decreased after saliva storage in all the tested specimens. Hardness values increased after saliva storage. The autoglazed group showed significantly higher fracture toughness, lower crack length, and microhardness than the overglazed group. Conclusions: Surface finishing procedures and artificial saliva storage had a statistically significant effect on mean values of microhardness, crack length, and fracture toughness. This in vitro study suggests that fracture toughness of ceramics may be affected by different surface treatments such as glazing, polishing, bleaching, or a combination; however, in this study Duceram LFC proved its self‐healing property after 3‐week storage in artificial saliva.     

The effect of at-home bleaching on the microhardness of six esthetic restorative materials

BACKGROUND: The authors conducted an in vitro study to evaluate the effect of an at-home bleaching product on the microhardness of six restorative materials under different surface treatments. METHODS: Four resin-based composite materials (a hybrid, flowable, microhybrid and nanohybrid), an ormocer (organic modified ceramic) material and a ceramic material were bleached with 15 percent carbamide peroxide. The authors prepared two groups of samples (polished and unpolished) (n = 7) from each resin-based composite material and the ormocer. The authors polished all of the samples in the ceramic group. Two samples from each group served as negative controls. The authors measured the microhardness of the samples before bleaching, after eight hours and 56 hours of bleaching, and 24 hours and one month after the end of bleaching. RESULTS: The statistical analysis showed that the at-home bleaching technique did not have a statistically significant effect on the microhardness of any of the restorative materials tested (hybrid, P = .0679; flowable, P = .5088; microhybrid, P = .0601; nanohybrid, P = .6166; ormocer, P = .2154; ceramic, P = .9943). CONCLUSION: At-home bleaching with 15 percent carbamide peroxide did not cause any harmful changes to the microhardness of tooth-colored restorative materials. CLINICAL IMPLICATIONS: Clinicians do not need to replace resin-based composite, ormocer or ceramic restorations after at-home bleaching treatment when the restorations are in posterior teeth.     

The Effect of Bleaching Agents on the Surface Topography of Ceramometal Dental Alloys

Purpose: To study the effect of bleaching agents on the surface topography of ceramometal alloys. Materials and Methods: Three types of ceramometal alloys were used (gold, Ni‐Cr, Co‐Cr‐Ti), and two types of bleaching agents (an agent intended for home use, one intended for use in the dental office) were studied. Forty‐five specimens were constructed and divided according to the alloy type into three main groups, 15 specimens per group. Each group was further subdivided into three subgroups according to the type of bleaching agent used. The first subgroup (five specimens) was not subjected to any bleaching agent. The second and third subgroups were subjected to home and in‐office bleaching agents, respectively. Results: Au alloy showed the least surface roughness when subjected to either of the two bleaching agents. Ni‐Cr alloys showed the highest surface roughness for both the control and home bleached subgroups, and Co‐Cr‐Ti alloy showed the highest surface roughness in the in‐office bleached subgroup. No statistically significant difference was found between the control subgroup and the home‐bleached subgroup for either the Au alloy or the Co‐Cr‐Ti alloy. For the two alloys, both the control and home‐bleached subgroups were statistically different from the in‐office bleached subgroups. There was a statistically significant difference between the Ni‐Cr control subgroup and the other two bleached subgroups, while there was no difference between the two bleached subgroups. Results also showed that increasing the concentration of bleaching agents increased the surface roughness of all the tested alloys. There was a statistical difference between the Ni‐Cr alloy and the other two alloys in all tested subgroups except the in‐office bleached subgroup, for which no difference between the surface roughness of the Ni‐Cr alloy and the Co‐Cr‐Ti alloy was found. Scanning electron microscopic examination revealed surface deteriorations in the two bleached subgroups for all tested ceramometallic alloys. Conclusion: Surface topographic alterations occurred as a result of the application of bleaching agents. These alterations increased with the increase of the carbamide peroxide concentration.     

An evaluation of the effects of handpiece speed, abrasive characteristics, and polishing load on the flexural strength of polished ceramics

STATEMENT OF PROBLEM: Many studies on the strengthening effects of grinding and polishing, as well as heat treatment on ceramics, are not well standardized or use commercially available industrial polishing systems. The reported effectiveness of these strengthening mechanisms on ceramics may not be applicable to clinical dentistry. PURPOSE: The purpose of this study was to evaluate the effects of controlled polishing on the flexural strength of dental ceramics by using a custom-made machine that applied standardized loads and speeds that coincided with the mean loads and speeds used by experienced prosthodontists. MATERIAL AND METHODS: A total of 140 aluminous dental ceramic bar-shaped specimens (Vitadur Alpha Enamel) measuring 1.5 x 2.0 x 25 mm were fabricated and divided into 12 groups (for most groups, n=10). Specimens were untreated, polished with different polishing systems, polished at different speeds, ground and autoglazed, polished and autoglazed, autoglazed and polished, polished with loose (paste) and bonded abrasives, or overglazed. Simulated clinical polishing was performed on the ceramic specimens by using a customized polishing apparatus that allowed independent control over the relevant polishing parameters (abrasive hardness, applied load, linear speed, rotational velocity, and wheel stiffness). Flexural strength (MPa) was measured with a 4-point bending test, and subjective surface roughness was assessed with scanning electron microscopy. Autoglazing was performed at various stages of the polishing sequence to determine the effects of polishing on surface stresses. Mean values, standard deviations, independent-sample t tests, 1-way and 2-way analyses of variance, Dunnett t tests and Kruskal-Wallis tests were applied to the data (alpha=.05). RESULTS: Under a clinical load of 0.6 N for a coarse polishing wheel, 1.0 N for a medium polishing wheel, and 1.3 N for a fine polishing wheel, a linear speed of 499 mm/min, and a rotational velocity of 10,000 rpm, the use of clinical polishing instruments did not affect the flexural strength of the aluminous ceramics studied (P=.274). At higher rotational velocity (20,000 rpm), specimens polished with the diamond polishing system produced statistically weaker specimens compared with those that had been polished at 10,000 rpm (P=.019). Autoglazing treatment of the diamond-polished specimens did not reverse the strength degradation (P=.125). Conversely, diamond polishing of the autoglazed specimens resulted in significant flexural strength reduction (P=.029). Fine-diamond-bonded abrasive significantly reduced flexural strength (P=.025). CONCLUSIONS: Simulated clinical polishing at 10,000 rpm did not appear to substantially strengthen or weaken the ceramic specimens. Polishing at 20,000 rpm reduced flexural strength of the ceramic bars.     

Effect of pre- and postoperative bleaching on marginal leakage of amalgam and composite restorations.

OBJECTIVES: The aim of this study was to investigate the effect of pre- and postoperative bleaching with 10% carbamide peroxide on marginal leakage of amalgam and resin composite restorations. METHOD AND MATERIALS: Three groups were made using 30 extracted, caries-free third molars (n = 10). In the preoperative group, bleaching was performed with 10% carbamide peroxide, followed by the placement of resin composite and amalgam restorations on Class V cavity preparations. In the postoperative group, bleaching was performed after the resin composite and amalgam restorations were fabricated. The third group served as a control in which no bleaching was performed. Dye penetration was used for evaluation of marginal leakage. RESULTS: Chi-square test showed that marginal leakage of resin composite restorations increased in both pre- and postoperatively bleached groups, but marginal leakage of amalgam restorations showed no alterations. CONCLUSION: Bleaching with carbamide peroxide may alter the marginal leakage of resin composite restorations, but amalgam restorations are not affected adversely in vitro.     

Higher-concentration carbamide peroxide effects on surface roughness of composites

Background: Ten percent carbamide peroxide has been used extensively within the dental profession for the purpose of bleaching teeth. Although this method has been successful, the use of higher-concentration carbamide peroxides (20–35%) for home bleaching has increased substantially in the past few years. The purpose of this study was to evaluate changes in surface roughness of a hybrid and a microfilled composite after exposure to bleaching agents containing higher concentrations of carbamide peroxide.
Materials and Methods: Sixty-eight circular, resin-based composite specimens (8 mm ± 2 mm) were prepared against a Mylar surface. Half of the specimens were fabricated from a hybrid composite material and the other half with a microfilled composite. Specimens were polished with aluminum oxide finishing disks, divided into four groups, and then exposed either to 20% carbamide peroxide for 3 hours per day for 14 days or to 35% carbamide peroxide for 1 hour per day for 14 days. The mean surface roughness (Ra) was determined for each specimen before and after exposure to bleaching agents, using mechanical profilometry. Data were analyzed by two-way analysis of variance (ANOVA) for differences between composite type, carbamide peroxide concentrations, and interaction of the two factors with respect to average surface roughness. All data analysis was performed at α= 0.05.
Results: Mean change from baseline of surface roughness (R_a) of microfilled composite and 20% carbamide peroxide was −0.03 μm ± 0.10 um; microfilled composite and 35% carbamide peroxide: 0.01 pm ± 0.02 um; hybrid composite and 20% carbamide peroxide: −0.43 um ± 0.91 um; hybrid composite and 35% carbamide peroxide: −0.19 pm ± 0.43 pm. Surface roughness of hybrid or microfilled composite did not change significantly from baseline with either concentration of carbamide peroxide ( p = .300).     

3种浓度过氧化脲漂白剂对牙科陶瓷表面粗糙度的影响

目的评估3种浓度过氧化脲漂白剂对牙科陶瓷表面粗糙度的影响。方法 80个瓷块按随机数字表法分成4组。A、B、C组所有瓷块进行为期3周,每天8 h的漂白,A组漂白剂为质量分数10%的过氧化脲,B组为质量分数15%的过氧化脲,C组为质量分数20%的过氧化脲;D组为空白对照组,浸泡于人工唾液里。表面粗糙度仪测量所有样本初始时和漂白1 d、2 d、3 d、1周、2周、3周后的瓷块表面粗糙度,并进行统计学分析。结果 A、B、C、D 4组瓷块的初始表面粗糙度分别为（0.073±0.003）μm、（0.073±0.002）μm、（0.072±0.003）μm、（0.074±0.003）μm,3周后的粗糙度分别为（0.073±0.004）μm、（0.073±0.005）μm、（0.074±0.006）μm、（0.074±0.005）μm。7个时间点,4组组间和组内表面粗糙度差异均无统计学意义（P＆gt;0.05）。结论 3种浓度过氧化脲漂白剂对牙科陶瓷表面无明显不良影响。     

自身上釉和抛光对瓷表面结构的影响

目的：通过扫描电镜观察和临床菌斑指数的检查,评价磨具打磨后版面知上釉和抛光对金瓷修复体瓷表面光洁度及其上菌斑聚集程度的影响,方法：实验分四组,每组按帝验条件用磨具将瓷表面处理,然后三组自身上釉,一组抛光,结果：扫描电镜观察见身上釉的三组样本瓷表面光洁度主瓷表面抛光组,瓷表面菌斑较少,结论：全身上釉可获得高 滑的瓷表面光洁度、菌斑附着少,而抛光使瓷表面较粗糙,菌斑聚集较多,可能会对牙龈组织有损害。     

The effect of home bleaching agents on the surface roughness of tooth-colored restoratives with time

This study evaluated the effects of home bleaching agents on the surface roughness of composite restoratives. Two home bleaching gels (10% and 15% carbamide peroxide, Opalescence) and five different tooth-colored restorative materials from the same manufacturer (3M-ESPE) were selected. They included microfill (Filtek A110 [FO]), flowable (Filtek Flow [FF]), polyacid-acid modified (F2000 [FT]) and minifill (Z100 [ZO]; Filtek Z250 [ZT]) composites. Thirty-six specimens of each material were fabricated, randomly divided into three groups (n=12) and treated as follows: Group 1-Stored in distilled water, Group 2-Bleached with 10% carbamide peroxide (CP) eight hours/day; Group 3-Bleached with 15% CP eight hours/day. All treatment was conducted at 37 degrees C and fresh gel applied and rinsed off daily for eight weeks. For the bleached groups, the specimens were stored in distilled water at 37 degrees C during the hiatus periods. All the specimens were subjected to roughness testing (Ra) at weeks 0, 1, 2, 4, 6 and 8 using a profilometer. The results were analyzed using general linear model with Scheffe's post-hoc tests at significance level 0.05. The results showed that the effect of bleaching on surface roughness was material and time dependent. ZT was not affected by bleaching treatment, while FT was significantly roughened after one week of bleaching with 15% CP compared to the control group. FO, FF and ZO were not significantly roughened until eight weeks of bleaching. Repolishing or replacement of tooth-colored restorations may be required after bleaching procedures.     

Effect of in-office tooth bleaching on the microhardness of six dental esthetic restorative materials.

OBJECTIVES: The aim of this in vitro study was to evaluate the effect of the in-office bleaching technique on the microhardness of six dental esthetic restorative materials. METHODS: Four composite resins (a hybrid, a flowable, a micro-hybrid and a nano-hybrid), an ormocer and a ceramic were tested, after the use of an in-office bleaching product. Fourteen specimens of each composite and the ormocer were fabricated and randomly divided into two groups of seven samples each. One group was polished and the other group remained unpolished. For the ceramic, seven polished samples were fabricated. Two samples of each group were used as negative controls. The specimens were bleached for 15, 30 and 45min. Five Knoop microhardness measurements were made on each sample, for each of the following periods tested: before bleaching, after 15, 30 and 45min of bleaching, 24h and 1 month after the bleaching procedure. Data were analyzed by the repeated measures analysis of variance with three between factors and one within. RESULTS: The differences in the microhardness values between the bleached and the control samples for the composites and the ceramic, were not statistically significant (hybrid: p=0.264; flow: p=0.584; micro-hybrid: p=0.278; nano-hybrid: p=0.405; ceramic: p=0.819). For the ormocer, although bleaching did not have any significant effect on the unpolished samples (p=0.115), it caused an increase on microhardness of the polished samples. SIGNIFICANCE: Bleaching with 38% hydrogen peroxide does not reduce the microhardness of the restorative materials tested. Therefore, no replacement of restorations is required after bleaching.     

Assessment of an Indirect Metal Ceramic Repair System

Purpose: This study was designed to compare an alternative indirect treatment to repair fractured or chipped veneering metal ceramic using recently developed ultra‐low‐fusing ceramics. Materials and Methods: One conventional feldspathic ceramic, Vita Omega, and three ultra‐low‐fusing ceramics (ULFC), Finesse, Duceram LFC, and Vision‐low, were used. Forty ceramic specimens were prepared and divided into two groups. Group I (n = 20) was designed for bond strength testing. It comprised four subgroups (A, B, C, D): one Ceramic‐resin (A) and three Ceramic‐ULFC disc specimens of different diameters (B, C, D). Group II was composed of repaired ceramic discs using direct and indirect repair methods for biaxial testing. It was comprised of five subgroups: the fractured discs from subgroup A; Omega discs (n = 20) formed the repaired specimens of the four remaining subgroups: B, C, D, E. Data were presented as means and standard deviation (SD) values. One‐way analysis of variance (ANOVA) was used for comparison between means. Tukey's post hoc test was used for pairwise comparison between the means when ANOVA test was significant. The significance level was set at p≤ 0.05. Results: Within group I, Omega‐Ducera LFC showed the statistically highest mean bond strength (25.8 MPa) values, followed by Omega‐Finesse (15.8 MPa). No statistically significant difference was apparent between Omega‐Vision (9.3 MPa) and the control Omega‐Composite group (7.5 MPa). Regarding group II, the Control Omega subgroup showed statistically the highest mean biaxial strength values (168.8 MPa). No statistically significant difference was evident between the values of Omega‐Finesse (78.7 MPa), Omega‐Vision (78.4 MPa), and Omega‐Composite (82.5 MPa). Omega‐Ducera LFC subgroup, showed statistically the lowest mean values (53 MPa). Conclusions: Omega‐Ducera LFC yielded the statistically highest mean bond strength values, and the lowest biaxial strength values. All values were within the reported bond strength values for resin repair. All the tested groups showed significantly lower values compared to the initial biaxial strength mean values of the Omega ceramic; however, two of the tested ULFC (Vision, Finesse), recorded means that were statistically equal to the resin‐ceramic direct subgroup. Duceram LFC showed the lowest values, probably due to its totally glass composition, which showed low strength values of the repaired specimens. The recorded bond and biaxial values suggest that indirect repair of fractured LFC using some ULFC ceramics may offer an alternative solution to the traditional direct resin repair method; however, the choice of the used ceramic should be one containing some leucite crystals. Further studies are needed to investigate the long‐term performance of the proposed repair treatment.     

Susceptibility of bleached enamel and root dentin to artificially formed caries-like lesions

PURPOSE: To evaluate in vitro the susceptibility of caries-like lesion formation on enamel and root dentin that had been bleached with carbamide peroxide agents. METHODS: 150 slabs of bovine enamel and root dentin were ground flat and polished. According to a randomized complete block design, the specimens were then allocated to be bleached with agents (Rembrandt) containing 12% [CP12], 16% [CP16], 22% [CP22] or 30% [CP30] of carbamide peroxide over 21 days. The control group remained unbleached. Afterwards, all specimens were randomly distributed between two subgroups (n= 15): one was subjected to alternating demineralizing and remineralizing solutions to induce caries-like lesions and the other was not. Enamel specimens were cycled four times in demineralizing (pH 5.0) and remineralizing solutions (pH 7.0), while root dentin specimens were cycled twice. Microhardness measurements were carried out at the post-bleaching and at the post-caries lesion formation phases. RESULTS: In the post-bleaching condition, microhardness values for both enamel and root dentin were dependent on the bleaching agent used. At the post-caries formation stage, there was a significant interaction between the bleaching treatment and substrate condition (carious or noncarious) for enamel and root dentin. Regardless of the bleaching agent, carious enamel and root dentin presented significantly lower microhardness values as compared to the noncarious counterparts. For carious enamel, those specimens exposed to CP16 exhibited higher microhardness values than the subset group formed by CP22, CP30 and unbleached samples. Both subsets did not differ from CP12. For carious root dentin, no difference was observed among the microhardness values attained as a result of the different bleaching treatments.     

The effect of different bleaching agents on the surface texture of restorative materials

This blind in vitro study evaluated the effect of a home and an in-office bleaching agent on the surface texture of different tooth-colored restorative materials. Four composites (a hybrid, a flowable, a microhybrid and a nano-hybrid), an ormocer and a ceramic were used, and 2 bleaching agents were tested: 38% hydrogen peroxide and 15% carbamide peroxide. For 38% hydrogen peroxide, the surface morphology of the restorative materials was evaluated after the following time periods: before bleaching, after 15, 30 and 45 minutes of bleaching, 24 hours and 1 month after bleaching. For 15% carbamide peroxide, the time periods were: before bleaching, after 8 and 56 hours of bleaching and 24 hours and 1 month after bleaching. For the 4 composite materials and the ormocer, 2 samples groups were prepared; in 1 group, the specimens were polished and in the other, they stayed unpolished. For the ceramic group, polished samples were prepared. For every material, 3 samples per category and time period were prepared, respectively. Subsequently, the appropriate bleaching procedure was performed on samples of every group. Scanning electron micrographs were produced at 60x, 200x and 2000x magnifications of respective areas of the samples. The results showed that the effect of bleaching on the surface texture was material- and time-dependent. Within the limitations of this study, it was concluded that bleaching with 38% hydrogen peroxide and 15% carbamide peroxide did not cause major surface texture changes on the polished surfaces of the restorative materials.     

The effect of 2 different bleaching regimens on the surface roughness and hardness of tooth-colored restorative materials.

OBJECTIVE: The purpose of this in vitro study was to evaluate the effects of 10% carbamide peroxide (Vivastyle/Vivadent) and 6.5% hydrogen peroxide strip bands (Crest Professional Whitestrips) on the surface roughness and hardness of the 3 different tooth-colored restoratives: an ormocer (Definite), a packable composite (Filtek P60), and a flowable composite (Filtek Flow). METHOD AND MATERIALS: A total of 48 specimens (10 mm in diameter and 2 mm thick) of each material were fabricated against a mylar surface. After being polished with Sof-Lex discs, they were randomly divided into 3 groups of 16 and treated as follows: group I was stored in distilled water at 37 degrees C for 2 weeks (control), group II was treated with Vivastyle for 2 hours per day for 2 weeks, and group III was treated with Whitestrips for 30 minutes twice a day for 2 weeks. For groups II and III, the specimens were stored in distilled water at 37 degrees C during the hiatus period. At the end of the test period, the specimens were first subjected to surface roughness and then to microhardness tests. The data were analyzed by Kruskal-Wallis and Mann-Whitney U tests. RESULTS: Both bleaching regimens increased the surface roughness of the materials (P <.05), but Whitestrips significantly increased the roughness of materials more than did Vivastyle (P <.05). Both bleaching regimens decreased significantly the hardness of tested materials except Filtek P60 (P <.05). CONCLUSION: Bleaching agents may affect the surface of existing restorations; therefore, they should not be used indiscriminately when tooth-colored restorations are present.     

Protective effect of resin coating on the microleakage of Class V restorations following treatment with carbamide peroxide in vitro

This in vitro study evaluated the effects of a resin coating on the microleakage of Class V restorations due to bleaching. One-hundred and sixty Class V cavities were randomly restored with one of four different restorative materials (n = 40): a compomer (Dyract AP), a conventional glass-ionomer cement (Ketac Molar Easymix), a resin modified glass-ionomer cement (Fuji II LC) and a resin composite (Filtek Z350). For each kind of material, 40 restorations were divided into four subgroups: bleached with resin coating (group BC), bleached without resin coating (group B), immersed in artificial saliva with resin coating (group SC), immersed in artificial saliva without resin coating (group S). In groups B and BC, the specimens were bleached with 10% carbamide peroxide gel for eight hours daily, while groups SC and S were stored in artificial saliva instead. After 28-day treatment, all the samples were subjected to a dye penetration test using the multiple-sectioning technique. In addition, one more test was performed to investigate the color difference between the coated and uncoated tooth surface after bleaching. There was a statistically significant increase in cervical microleakage in the group B specimens of Fuji II LC and Ketac Molar Easymix compared to their respective control specimen (group S). These effects on microleakage were not found in the bleached specimens with resin coating (group BC). There was also no visually-detectable color difference between the coated and uncoated tooth surface. In conclusion, resin coating is an effective method for avoiding the bleaching-induced microleakage of glass-ionomer cement.     

Effects of different concentrations of carbamide peroxide and bleaching periods on the roughness of dental ceramics

The wide use of dental bleaching treatment has brought concern about the possible effects of hydrogen peroxide on dental tissue and restorative materials. The objective of this study was to evaluate in vitro the effect of nightguard bleaching on the surface roughness of dental ceramics after different periods of bleaching treatment. Fifteen specimens of 5 × 3 × 1 mm were created with three dental ceramics following the manufacturers' instructions: IPS Classic (Ivoclar-Vivadent); IPS d.Sign (Ivoclar-Vivadent); and VMK-95 (Vita). A profilometer was used to evaluate baseline surface roughness (Ra values) of all ceramics by five parallel measurements with five 0.25 mm cut off (Λc) at 0.1 mm/s. Afterwards, all specimens were submitted to 6-h daily bleaching treatments with 10% or 16% carbamide peroxide (Whiteness- FGM) for 21 days, while control groups from each ceramic system were stored in artificial saliva. The surface roughness of all groups was evaluated after 18 h, 42 h, 84 h, and 126 h of bleaching treatment. The surface roughness of each specimen (n = 5) was based on the mean value of five parallel measurements in each time and all data were submitted to two-way repeated measures ANOVA and Tukey's post-hoc test (α = 0.05). No significant differences in ceramic surface roughness were observed between untreated and bleached ceramic surfaces, regardless of bleaching intervals or bleaching treatments. This study provided evidence that at-home bleaching systems do not cause detrimental effects on surface roughness of dental ceramics.     

Effect of bleaching agents on the hardness and morphology of enamel

Purpose: The goal of the present laboratory study was to analyze the effect of two home bleaching agents (Opalescence 10%, Ultradent, and Hi‐Lite II, Shofu) as well as the separate solutions of 10% carbamide peroxide primary components (3% hydrogen peroxide and 7% urea) on enamel microhardness and surface morphology. Materials and Methods: Thirty human molars stored in water for no longer than 3 months were selected. Their facial and lingual surfaces were embedded in acrylic resin, and the specimens were polished with up to 600‐grit sandpaper. The 30 molar sections were divided into five groups as per treatment modality (n = 6); group 1, 10% carbamide peroxide bleach with carbopol (Opalescence, Ultradent); group 2, oxygen‐free gel bleach (Hydroxylite, Hi‐Lite II, Shofu); group 3, 3% hydrogen peroxide with carbopol (Dermus Pharmacy, Florianopolis, SC, Brazil); group 4, 7% urea treatment (Dermus Pharmacy); and control, group 5, artificial saliva (Dermus Pharmacy). Prior to treatment, six indentations (Vickers) were made on each of the six surfaces in each group under a load of 100 g for 30 seconds. Bleaching procedure was conducted for 3 hours per day for 2 weeks, the control group excepted. Following each bleaching session, the specimens were washed with deionized water and kept in artificial saliva at 37°C, this solution being changed daily. Pre‐ and post‐treatment microhardness data were analyzed using a two‐way analysis of variance. In a similar way, 30 other specimens underwent the same procedures. After the bleaching period, the samples were observed under the scanning electron microscope. Results: Specimens submitted to bleaching treatment with 3% hydrogen peroxide gel as described in this study showed a significant reduction of surface microhardness (p < .0001). The other treatment modalities had no effect on surface microhardness. No morphologic alterations were observed on enamel submitted to bleaching gel of 10% carbamide peroxide (Opalescence), oxygen‐free gel (Hi‐Lite II, Shofu), or 7% urea solution compared with the control (artificial saliva). However, the specimens bleached for 3 hours per day for 2 weeks with 3% hydrogen peroxide gel presented areas of mild erosion. The effect, nevertheless, was not uniform, occurring with varying intensity on all samples of enamel bleached with 3% hydrogen peroxide. CLINICAL SIGNIFICANCE Bleaching treatment conducted with two home bleaching agents (Opalescence 10%, Ultradent, and Hi‐Lite 11, Shofu) had no adverse effects on enamel microhardness or on surface morphology. Bleaching with 3% hydrogen peroxide can have a negative effect on enamel hardness and surface morphology when performed as described in this study     

The effect of current bleaching agents on the color of light-polymerized composites in vitro

STATEMENT OF PROBLEM: Bleaching agents may affect the color of existing composite restorations. PURPOSE: The purpose of this study was to compare the effect of 10% carbamide peroxide and 10% hydrogen peroxide on the color of light-polymerized hybrid, macrofilled, and polyacid-modified composites. MATERIAL AND METHODS: Two light-polymerized hybrid composites (3M Valux and Spectrum TPH), 1 macrofilled condensable composite (Solitaire), and 2 polyacid-modified composites (Dyract AP and Compoglass) were used. The hybrid composites served as controls. The color of 8 specimens of each material was analyzed by use of a spectrophotometer before bleaching. The specimens were then divided randomly into 2 subgroups (n=4). One group was immersed in 10% carbamide peroxide solution and the other in 10% hydrogen peroxide, for 8 hours each for 14 consecutive days. After bleaching, color changes (Delta E) were determined for each material and compared by use of the Kruskal-Wallis test, followed by the Mann-Whitney U test (P<.05). RESULTS: After bleaching with carbamide peroxide, the color changes (Delta E) for Dyract AP (2.18; SD = 1.41), Compoglass (1.14; SD = 0.26) and Solitaire (1.56; SD = 0.89) were higher than the color changes recorded for 3M Valux (0.63; SD = 3.60), and Spectrum TPH (0.66; SD = 1.24). The differences between materials bleached with carbamide peroxide were not statistically significant. After bleaching with hydrogen peroxide, the color changes for Dyract AP (9.39; SD = 0.53) and Compoglass (5.15; SD = 0.52) were higher than the changes recorded for Spectrum TPH (4.53; SD = 1.53) and 3M Valux (3.41; SD = 4.40), whereas the color change of Solitaire (3.69; SD = 0.57) was significantly higher than that of 3M Valux (P=.01). The color changes for all restorative materials tested were clinically detectable after the application of 10% hydrogen peroxide. However, clinically noticeable discoloration was observed only for Dyract AP treated with 10% carbamide peroxide. CONCLUSION: In comparison to 10% carbamide peroxide, 10% hydrogen peroxide caused more color changes in the composites tested.     

In situ and in vitro effects of bleaching with carbamide peroxide on human enamel

This study evaluated in vitro and in situ the potential adverse effects of 10% carbamide peroxide on human enamel using microhardness, calcium loss and surface morphology analysis. Twenty-four enamel slices (4 mm2) were obtained from recently extracted premolars. The specimens were polished under water-cooling down to 1,200-grade sandpaper. After initial microhardness readings (100 g), the specimens were randomly divided into two groups for in situ and in vitro conditions. The specimens were covered with 10% carbamide peroxide for eight hours. After removing the bleaching gel, the in vitro specimens were stored in deionized water and the in situ specimens, included in an intra-oral appliance, were placed in the oral cavity of four volunteers. These cycling sequences took place for 14 days. Upon conclusion of the bleaching treatment, new microhardness readings were performed on all specimens. Calcium dosage was assessed from the bleaching gel collected after initial exposure on day one, then from gel collected between days two and seven and gel collected between day eight and 14 using an atomic absorption spectrophotometer. Surface morphology was observed from two non-treated control specimens and two specimens of each experimental bleached group under SEM evaluation. Statistical analysis (ANOVA and Tukey tests) disclosed that specimens bleached in situ showed similar microhardness to unbleached specimens and had statistically higher (p < 0.01) hardness than in vitro bleached specimens. The loss of calcium in the in vitro situation at 14 days was 2.5 times higher than the in situ condition. SEM micrographs demonstrated that surface alterations were more pronounced in the in vitro condition. The adverse effects of carbamide peroxide on enamel were evident in specimens bleached in vitro but were not seen in situ. The presence of saliva could prevent the demineralizing effect of bleaching gel in situ.     

Effect of bleaching versus repolishing on colour and surface topography of stained resin composite

Background: The aim of this study was to examine the effect of ozonated gel, carbamide peroxide bleaching agent and polishing paste on the colour and surface topography of stained resin composite. Methods: Ninety disc‐shaped resin composite specimens were used in this study. They were randomly divided into three groups of 30 specimens each according to the immersion solutions used, i.e., tea, cola or artificial saliva. Each group was further subdivided into three equal subgroups (n = 10) according to the type of whitening treatment applied; 30% carbamide peroxide, ozonated KY gel or polishing paste. Colour and surface roughness was measured at baseline, after immersion, also following whitening procedures by using a stereomicroscope. The results were recorded, tabulated and statistically analysed. Results: The colour values of artificial saliva displayed the highest statistically significant mean colour difference compared to cola and tea. However, there was no statistically significant difference in surface roughness. Also, a superior whitening effect was demonstrated with ozonated gel. Ozonated gel showed statistically significant lowest roughness compared to both carbamide peroxide and polishing paste. Conclusions: Immersion solutions have a positive influence on the colour of resin composite. Also, ozonated gel is an efficient bleaching agent with the least adverse effect on surface roughness.