Effect of an In-Office Bleaching Agent with Surface Pre-Reacted Glass-Ionomer Filler on the Enamel Surface: A In-Vitro Study.

In-office bleaching with high concentrations of hydrogen peroxide (H2O2) agents causes undesirable alterations in the enamel. Surface pre-reacted glass-ionomer (S-PRG) filler is a functional material known for its acid-neutralizing and demineralization-inhibition properties. This study evaluates the effect of S-PRG filler incorporation in H2O2-based bleaching on the enamel surface. Bovine enamel surfaces were bleached using a bleaching paste formulated with a liquid (35% H2O2) and a powder containing 5% or 10% S-PRG filler. The surface roughness and the Vickers microhardness of the treated enamel surfaces were evaluated. The enamel surfaces were observed under a scanning electron microscope (SEM) and analyzed using energy dispersive X-ray (EDX) technology. The surfaces were challenged by citric acid and observed by SEM. The specimens bleached with the paste containing the S-PRG filler showed lower enamel surface roughness and higher microhardness values than did those bleached with the plain paste (0% S-PRG filler); meanwhile, there were no significant differences between the 5% or 10% S-PRG filler groups. The S-PRG filler groups showed enamel surface morphologies similar to those of the non-bleached enamel, according to SEM observation, and EDX analysis detected the presence of fluoride and strontium ions. The S-PRG filler groups showed a higher resistance to erosion. The S-PRG filler mitigated the detrimental effects of bleaching agents on the enamel surface and provided resistance to erosion.

The bleaching effect of office bleaching agents containing S-PRG filler evaluated by pH value and electron spin resonance.

OBJECTIVES: Surface reaction-type pre-reacted glass-ionomer (S-PRG) filler releases six types of ions with a neutralizing ability. This study evaluated the effect of S-PRG filler incorporation in an H2O2-based bleaching material on the bleaching efficacy, pH, and reaction state. MATERIALS AND METHODS: The experimental bleaching material was formulated by the addition of 5% or 10% S-PRG fillers to the powder part. The stained bovine teeth were treated with the prepared bleaching paste. Commission internationale de l'éclairage (CIE) L*a*b* color space values were recorded before and after bleaching, and the color difference (ΔE) and whiteness index (WID) were calculated. Moreover, the used bleaching formulations were assessed for their pH values and reaction state by evaluating the oxidation state of manganese (Mn+2) using electron spin resonance (ESR). RESULTS: The results of ΔE and WID showed that the addition of S-PRG filler increased the bleaching effect, but there was no significant difference between the groups with 5% and 10% S-PRG filler. A significant increase in pH in S-PRG filler groups (5% pH 6.7, 10% pH 6.8) was found compared to the 0% group (pH 4.8). ESR measurements showed that the signal emitted from Mn+2 decreased over time. The S-PRG filler groups showed a significantly higher reduction in Mn+2 compared to the 0% group, with no significant difference between the 5% and 10% S-PRG groups. CONCLUSIONS: S-PRG filler addition resulted in improved bleaching efficacy, higher reaction rate, and pH values that are close to neutral. CLINICAL RELEVANCE: S-PRG filler addition may be effective on the bleaching outcome of H2O2-based materials.

Effect of Er: YAG laser irradiation with additional low energy on resin-dentin bonding and morphology of bonded interface.

OBJECTIVES: To examine the micro tensile bond strength (µTBS) and the resin-dentin interface on a laser-irradiated dentin surface using two different irradiation methods, with or without additional low-energy irradiation. METHODS: The flat bovine dentin surface was divided into three groups: i). control group (C group, no irradiation), ii) 80 mJ/pulse Er: YAG laser group (80 group), iii) 80 + 30 mJ/pulse Er: YAG laser group (80 + 30 group, with an additional 30 mJ/pulse). After the roughness of the dentin surface was recorded, Clearfil SE Bond 2 or Clearfil Universal Bond Quick (Kuraray Noritake Dental Inc., Tokyo, Japan) was applied. After the µTBS testing, the failure mode was observed. The bonded interface was assessed using Rhodamine-dye incorporated adhesives and observed by optical coherence tomography. RESULTS: The dentin surface showed opened dentinal tubules without a smear layer after irradiation. For both adhesives, the µTBS was significantly higher in 80 + 30 group than in the 80 group (p < 0.05). In the 80 group, the thickness of the adhesive layer was not uniform, and the dentin surface was occasionally in direct contact with the composite resin. The failure mode images showed that most of the fractures in the 80 group were at the sub-surface of irradiated dentin. The adhesive layers of the 80 + 30 groups were homogeneous. CONCLUSIONS: The dentin surface was rough and irregular by 80 mJ irradiation, which might result in an inadequate resin-dentin interface and the weak µTBS. The bonded integrity was mitigated by additional irradiation.

A Japanese concept of considerations for evaluation of dental materials for tooth bleaching.

Recent advances in bleaching technology, such as bleaching ingredients, have accelerated the development of tooth whitening materials to change the color of natural teeth toward a lighter or whiter shade. Some bleaching materials are used for patients in combination with auxiliary medical devices to activate the bleaching materials by a light or heat source. Bleaching ingredients can be a poisonous and deleterious substance. Some bleaching materials are used in dental offices and the others at home. In clinical development of bleaching materials, appropriate evaluation of safety and efficacy is required according to the intended use. For appropriate and swift approval of the emerging bleaching materials, guideline on evaluation of dental whitening materials was discussed in a commissioned project by the Ministry of Health, Labour and Welfare of Japan for FY2021. Here, we summarize the current principles of the premarketing evaluation of the safety and efficacy.

Application of Sulfinate Agent in Conjunction with HOCl Smear-Layer Deproteinization Improves Dentin Bonding Durability of One-step Self-etch Adhesives.

PURPOSE: To evaluate the effect of a sulfinate agent on the bonding durability of one-step self-etch adhesives (1-SEAs) to smear-layer-covered dentin deproteinized with hypochlorous acid (HOCl). MATERIALS AND METHODS: Human coronal dentin disks with a standardized smear layer were deproteinized with 100 ppm HOCl solution for 0 s (control), 15 s or 30 s. After rinsing with water for 30 s and air drying, half of the specimens were treated with a sulfinate agent (Scotchbond Universal Dual Cure Activator; SDA) prior to the application of a 1-SEA (Bond Force II [Tokuyama Dental] or Clearfil Universal Bond Quick [Kuraray Noritake]). Microtensile bond strength (µTBS) was measured after 24 h or 10,000 thermal cycles (TC). The data were analyzed by three-way ANOVA with Tukey's post-hoc tests and t-tests at the 0.05 significance level. RESULTS: The 24-h µTBS of both adhesives increased statistically significantly with the HOCl pretreatment for 15 s or 30 s (p < 0.05), but it was not statistically significantly affected by the application of SDA (p > 0.05). However, after TC, the groups treated with the combination of HOCl and SDA maintained their µTBS (p > 0.05), as opposed to untreated dentin and dentin treated with either HOCl or SDA, whose µTBS decreased significantly (p < 0.05). CONCLUSION: The application of the sulfinate agent did not statistically significantly affect the immediate bond strength of 1-SEAs, and it could not prevent a significant decrease in the bond strength to untreated dentin after thermocycling. However, the sulfinate agent significantly improved the bonding durability of 1-SEAs to HOCl smear-layer deproteinized dentin.

Effect of Water Storage and Bleaching on Light Transmission Properties and Translucency of Nanofilled Flowable Composite.

This study investigated the effect of water sorption and bleaching on light transmission properties (Straight-light transmission (G0), Light diffusion (DF) and Amount of transmitted light (AV)) and translucency parameters (TP) of nano-filled flowable composites. A total of 35 composite disks (0.5 mm thickness) were prepared using A2 shade of 5 nanofiller composites (n = 7/each); Beautifil Flow Plus X F03 (SHOFU INC), Clearfil Majesty ES Flow (Kuraray Noritake Dental), Estelite Universal Flow (EUF, Tokuyama Dental), Estelite Flow Quick (Tokuyama Dental) and Filtek Supreme Ultra Flowable Restorative (FSU, 3M ESPE). Then, they were cured by LEDs (VALO, Ultradent) on standard mood (1000 mW/cm2) for 20 s. Samples were tested for straight-line transmission (G0), diffusion (DF), the amount of transmitted light (AV) and (TP) immediately after 24 h (dry storage), after 1-week water storage and after each of the three cycles of in-office bleaching (HiLite, SHOFU INC). Result: G0, DF, AV and TP were significantly affected by different materials (p < 0.001). The AV of FSU increased significantly after the 1-week water storage, then after the second bleaching cycle (p < 0.001). The TP for EUF slightly decreased (p = 0.019) after 1-week water storage, then increased throughout bleaching. Conclusion: Ageing/bleaching conditions do not affect G0, DF, AV and TP. The compositional variation between nano-filler composites resulted in a significant difference between materials.

Bonding performance of self-etch adhesives to enamel bleached with different peroxide concentrations.

The aim of this study was to evaluate the micro-shear bond strength (µSBS) of one and two steps self-etch adhesive systems after enamel bleaching with photo-activated bleaching systems of different hydrogen peroxide (HP) concentration. Occlusal enamel of forty intact human molars were flattened and assigned into four groups. GI Unbleached, GII, GIII, and GIV were bleached with Pyrenees (3.5% HP), GC TiON (20% HP), and Hi-Lite (35% HP) respectively. Enamel treatment with one and two steps self-etch adhesives (Clearfil S3 Bond- S3, and Clearfil SE Bond-SE) then micro-tubes were fixed on enamel and filled with AP-X composite (n=5). Bond was tested with the universal testing machine. Data were analyzed using two-way ANOVA and Tukey's tests at 5 % level of significance. The µSBS was significantly different between adhesives (F=154.46; p<0.05) and bleaching systems (F=77.33; p<0.05) with significant interaction. Specimens bonded with S3 shows a significantly lower µSBS than those bonded with SE (p<0.05) in all groups. For both adhesives the bleached groups demonstrate lower µSBS than unbleached except specimens bleached with Pyrenees and bonded with SE (p>0.05). A significant difference was observed between groups of the bleaching systems (p<0.05). Different peroxide concentrations photo-activated bleaching systems adversely affect µSBS of one and two steps self-etch adhesives. Low concentration system (Pyrenees) does not influence the bond strength of two steps adhesive.

Bonding performance of self-etch adhesives to enamel bleached with different peroxide concentrations

Abstract The aim of this study was to evaluate the micro-shear bond strength (µSBS) of one and two steps self-etch adhesive systems after enamel bleaching with photo-activated bleaching systems of different hydrogen peroxide (HP) concentration. Occlusal enamel of forty intact human molars were flattened and assigned into four groups. GI Unbleached, GII, GIII, and GIV were bleached with Pyrenees (3.5% HP), GC TiON (20% HP), and Hi-Lite (35% HP) respectively. Enamel treatment with one and two steps self-etch adhesives (Clearfil S3 Bond- S3, and Clearfil SE Bond-SE) then micro-tubes were fixed on enamel and filled with AP-X composite (n=5). Bond was tested with the universal testing machine. Data were analyzed using two-way ANOVA and Tukey's tests at 5 % level of significance. The µSBS was significantly different between adhesives (F=154.46; p<0.05) and bleaching systems (F=77.33; p<0.05) with significant interaction. Specimens bonded with S3 shows a significantly lower μSBS than those bonded with SE (p<0.05) in all groups. For both adhesives the bleached groups demonstrate lower µSBS than unbleached except specimens bleached with Pyrenees and bonded with SE (p>0.05). A significant difference was observed between groups of the bleaching systems (p<0.05). Different peroxide concentrations photo-activated bleaching systems adversely affect μSBS of one and two steps self-etch adhesives. Low concentration system (Pyrenees) does not influence the bond strength of two steps adhesive.

Resumo O objetivo deste estudo foi avaliar a resistência ao cisalhamento (µSBS) de sistemas auto-adesivos de um e dois passos após clareamento do esmalte com sistemas de clareamento foto-ativados de diferentes concentrações de peróxido de hidrogênio (HP). O esmalte oclusal de quarenta molares humanos intactos foi aplainado e atribuído em quatro grupos. GI Unbleached, GII, GIII, e GIV foram branqueados com Pyrenees (3,5% HP), GC TiON (20% HP), e Hi-Lite (35% HP) respectivamente. Tratamento de esmalte com adesivos de um e dois passos auto-adesivos (Clearfil S3 Bond- S3, e Clearfil SE Bond-SE), depois os microtubos foram fixados no esmalte e preenchidos com composto AP-X (n=5). A resistência ao cisalhamento foi testada com a máquina universal de testes. Os dados foram analisados usando os testes de ANOVA e Tukey de duas vias a um nível de 5% de significância. O µSBS foi significativamente diferente entre adesivos (F=154,46; p<0,05) e sistemas de clareadores (F=77,33; p<0,05) com interação significativa. Os espécimes colados com S3 mostram um μSBS significativamente inferior aos colados com SE (p<0,05) em todos os grupos. Para ambos os adesivos, os grupos clareados demonstram µSBS inferiores aos não clareados exceto os espécimes clareados com Pyrenees e colados com SE (p>0,05). Foi observada uma diferença significativa entre os grupos dos sistemas de clareamento (p<0,05). Diferentes concentrações de peróxidos foto-ativados nos sistemas de clareamento afetam negativamente μSBS dos adesivos de uma e duas etapas de auto-colagem. O sistema de baixa concentração (Pyrenees) não influenciou a resistência ao cisalhamento do adesivo de duas etapas.

Regional ultimate tensile strength and water sorption/solubility of bulk-fill and conventional resin composites: The effect of long-term water storage.

The effect of long-term water storage on the regional ultimate tensile strength (UTS), water sorption (Wsp) and water solubility (Wsl) of conventional and bulk-fill resin composites at various depths was investigated. Composite specimens light-cured from one side were sectioned into beams corresponding to different depths (1-5 mm) and stored in water for 24 h, 1 week, 1 month, 6 months or 1 year. UTS increased during the first week and then gradually decreased over time, especially in deeper regions. Bulk-fill composites initially exhibited similar UTS at all depths, whereas the UTS of conventional composites at 1 mm and 5 mm differed significantly at all time points. Wsp and Wsl increased with depth and storage time, markedly at 3-5 mm after 1 month for conventional composites and after 6 months for bulk-fill composites. The signs of degradation at depths beyond 3 mm suggested that even bulk-fill composites have suboptimal properties in layers more than 3 mm in thickness.

The effect of in-office bleaching materials with different pH on the surface topography of bovine enamel.

This study evaluated the alterations of surface topography of the bovine enamel caused by different pH of in-office bleaching agents. 23% H2O2 with pH 5.5, 7.0 and 8.5 were applied on the bovine tooth specimens (n=10) and photo-irradiated for 10 min. The bleaching procedure was repeated three times and specimens were subjected to linear surface roughness (Ra) and Vickers microhardness test (VHN) at baseline and after three consecutive applications. The morphological alterations were observed before and after third bleaching application. Data were analyzed by two-way ANOVA followed by Tukey's HSD. The pH of the bleaching agent significantly affects the Ra and VHN (p<0.05). Low pH yielded a significant increase in Ra and decrease in VHN. All the groups showed morphological alterations and profound effect was found in pH 5.5 group. It was concluded that the pH of the bleaching agent can affect Ra, VHN and surface morphology.

Effect of photo-thermal acceleration on in-office bleaching.

The purpose is to evaluate the effect of photo-thermal acceleration on in-office bleaching efficiency using a bleaching agent without photocatalysts in vitro. Artificially discolored bovine lower incisors were prepared, and the mixed in-office bleaching material contained hydrogen peroxide 23% was applied by following treatment for 10 min: high-(HI group) and low-intensity LED lights (LI group), oven at 38 °C (OV group), and room temperature at 23 °C (RT group). Color was measured before and after bleaching and color difference (∆E*) was calculated. The data were statistically analyzed using a two-way ANOVA and Tukey's post hoc test. The temperature change (∆T) of applied bleaching agent in HI and LI groups was measured using a thermography and was analyzed using a T test. The bleaching procedures were repeated 6 times. Irradiation in the HI group resulted in the highest ΔE, followed by the LI group whose ΔE was significantly lower. Both irradiated modes exhibited higher ΔE compared to non-irradiated OV and RT groups which were not significantly different from each other. The average temperature rise of bleaching agents in HI and LI groups after 10 min irradiation was 15.00 °C and 11.80 °C, respectively. The effect of photo-thermal acceleration was proved for an in-office bleaching agent without photocatalysts in vitro.

Effect of pH of bleaching agent on tooth bleaching action in vitro.

This study investigated the effect of pH of bleaching agent, photo-irradiation time or application times on bleaching action using hematoporphyrin-stained papers (HSPs) and artificially stained bovine-teeth (BT). 23% H2O2 with pH 5.5, 6.0, 7.0, 8.0 and 9.0 were applied on the specimens. HSP was photo-irradiated for 1, 3 and 5 min. BT were photo-irradiated for 10 min and the bleaching was repeated ten times (n=10). CIE L*a*b* of the specimens were measured before and after the procedure. Data were analyzed by repeated-measures ANOVA followed by multiple comparisons with Bonferroni correction. For the HSP, longer irradiation time and higher pH yielded significantly higher color difference (ΔE). As for BT, increasing application times and higher pH resulted in higher ΔE. It was concluded that the pH of the bleaching agent significantly improved the bleaching effect with increased photo-irradiation time for HSP and with an increase of repeated application times for BT.

Effect of phytic acid as an endodontic chelator on resin adhesion to sodium hypochlorite-treated dentin.

OBJECTIVES: Phytic acid (IP6), a naturally occurring agent, has been previously reported as a potential alternative to ethylenediaminetetraacetic acid (EDTA). However, its effect on adhesion to sodium hypochlorite (NaOCl)-treated dentin and its interactions with NaOCl have not been previously reported. Thus, in this study, the effects of IP6 on resin adhesion to NaOCl-treated dentin and the failure mode were investigated and the interactions between the used agents were analyzed. MATERIALS AND METHODS: Micro-tensile bond strength (µTBS) testing was performed until failure on dentin treated with either distilled water (control), 5% NaOCl, or 5% NaOCl followed with chelators: 17% EDTA for 1 minute or 1% IP6 for 30 seconds or 1 minute. The failed specimens were assessed under a scanning electron microscope. The reaction of NaOCl with EDTA or IP6 was analyzed in terms of temperature, pH, effervescence, and chlorine odor, and the effects of the resulting mixtures on the color of a stained paper were recorded. RESULTS: The µTBS values of the control and NaOCl with chelator groups were not significantly different, but were all significantly higher than that of the group treated with NaOCl only. In the failure analysis, a distinctive feature was the presence of resin tags in samples conditioned with IP6 after treatment with NaOCl. The reaction of 1% IP6 with 5% NaOCl was less aggressive than the reaction of the latter with 17% EDTA. CONCLUSIONS: IP6 reversed the adverse effects of NaOCl on resin-dentin adhesion without the chlorine-depleting effect of EDTA.

Swept-source optical coherence tomographic observation on prevalence and variations of cemento-enamel junction morphology.

To investigate the prevalence of different patterns of cemento-enamel junction (CEJ) morphology under swept-source optical coherence tomography (SS-OCT). One hundred extracted human teeth were used consisting of incisors, premolars, and molars. Each sample was observed for every 500 µm circumferentially along CEJ and OCT images of the pattern were noted. Microscopic observations were done for the representative sample using confocal laser scanning microscope (CLSM) and transmission electron microscope (TEM). The OCT images exhibited four CEJ patterns: edge-to-edge (type I), exposed dentin (type II), cementum overlapping enamel (type III), and enamel overlapping cementum (type IV). The prevalence of CEJ patterns was further statistically considered for mesial, distal, buccal, and lingual surfaces. The real-time imaging by SS-OCT instantly determined CEJ morphology. CLSM and TEM observation revealed morphological features along CEJ, which corresponded to OCT images of CEJ anatomy. OCT results showed 56.8% of type I pattern predominantly found on proximal surfaces, followed by 36.5% of type II pattern on buccal and lingual surface, 6.4% of type III pattern, and 0.3% of type IV pattern. There was a significant difference in prevalence of CEJ patterns among different types of teeth, but there was no statistically significant difference among the four surfaces in each type of teeth. OCT is a non-invasive diagnostic tool to examine the CEJ patterns along the entire circumference. OCT observation revealed even minor dentin exposure that would need clinical and home procedures to prevent any symptoms.

Effect of application of desensitizers before bleaching on change of tooth shade.

The aim of this in vitro study was to evaluate the effects of desensitizer pre-treatment on in-office bleaching using an artificial discoloration tooth model. The stained specimens were divided into four groups (n=10); without application (Control group), Shield Force plus (SF group), UltraEz (UE group) and Teeth Mate AP paste (TM group) applied before bleaching. Each group was bleached by an in-office bleaching agent. The CIE L*a*b* values were measured by a colorimeter before and after ten consecutive bleaching treatments and the color difference (∆E) was calculated. There was no statistical difference among ∆E values of Control, UE, and TM groups (p>0.05). There was a significant difference between SF and Control groups (p<0.001). It was concluded that application of TM and UE did not affect the change of tooth shade while SF application impeded the bleaching effect.

Effect of pH conditioners on tooth bleaching.

The purpose of this study was to evaluate the effect of pH conditioners on tooth bleaching using hematoporphirin-stained paper and artificially discolored bovine tooth model. Experimental bleaching gels containing 23% hydrogen peroxide, adjusting pH 7.0 by different pH conditioners (NaOH, NaHCO3, Na2CO3, KOH, KHCO3, and K2CO3), were prepared. Each bleaching gel was applied on a hematoporphirin-stained paper, and the light was exposed for 5 min. Before and after bleaching, color was measured and color difference was calculated. Artificially discolored bovine tooth samples were prepared and bleached by four experimental bleaching gels containing NaOH, NaHCO3, Na2CO3, or KHCO3. The bleaching time was 10 min with light exposure, and bleaching was repeated 10 times. The color of bleached surface was measured at each bleaching period, and color difference was calculated. In the experiment using hematoporphirin-stained paper, degrees of color difference were KHCO3 > NaHCO3 > KOH > NaOH > Na2CO3 ≥ K2CO3. In the experiment using bovine teeth, degrees of color difference were KHCO3 > NaHCO3 > NaOH > Na2CO3. It was concluded that the bleaching materials with same pH and different pH conditioners showed different bleaching effects and that both cation and anion in the pH conditioners affected bleaching effect.

Effect of nonthermal atmospheric discharge on stain removal of tooth.

The purpose of this study was to evaluate the effect of the repeated nonthermal atmospheric discharge (NADC) exposure without peroxide or water on bleaching effect of cycling stained tooth and to evaluate surface roughness and microhardness of the enamel surface exposed by NADC. Specimens with 5×5mm were prepared from extracted bovine teeth. Staining with tea and exposure by NADC were repeated for five times and color was measured at each step. Other specimens were prepared and surface roughness (Ra) and microhardness (Vickers hardness) were measured after exposure by NADC. The repeated NADC exposure without peroxide or water showed bleaching effect for stained bovine teeth. The surface roughness was not changed by NADC exposure. The less microhadness was shown by NADC exposere.

Effect of lights with various wavelengths on bleaching by 30% hydrogen peroxide.

The objective of this study was to evaluate the bleaching effect of light sources with various wavelengths using 30% hydrogen peroxide (HP) in vitro. The hematoporphyrin-stained paper was bleached with HP and irradiated for 10 min using LED light sources with 265, 310, 365, 405, or 450 nm respectively. In control group, HP was applied for 10 min without light irradiation. The bleaching procedure was repeated two times. The L*a*b* values of the samples before bleaching and after each bleaching step were measured using a colorimeter. Color changes of specimens were then calculated and statistically analyzed. There was an interaction between light sources and time of irradiation in the color change (p < 0.05). Time and light sources significantly affected ΔE and ΔL (p < 0.05). The light source of 256 nm showed the highest bleaching effect over time followed by that of 310 nm, which were statistically different from other groups (p < 0.001). The 365 nm, 450 nm groups, and control group showed low bleaching effect visually with no significant differences in ΔE and ΔL (p > 0.05). It was concluded that the wavelengths of the light sources affected the bleaching by HP. The 310-nm light can be a potential source for bleaching.

Effect of sodium fluoride pretreatment on the efficacy of an in-office bleaching agent: An in vitro study.

This in vitro study evaluated the effect of sodium fluoride (NaF) on the bleaching efficacy using an artificial discolored bovine tooth model. Twenty specimens were prepared from bovine teeth by staining with black tea extract and were divided into two groups (n = 10). In control group, specimens were immersed in distilled water for 30 min. In NaF group, specimens were applied with 0.2% NaF for 30 min. Then, the specimens in each group were bleached by an in-office bleaching material (Shofu Hi-Lite, Shofu, Kyoto, Japan). The CIE L*a*b* values were measured by a dental colorimeter before and after 10 consecutive bleaching treatments, and the color difference (ΔE) was calculated. Brightness and color difference (ΔE) increased in both groups per bleaching cycle. There were no statistical differences in ΔE values between both groups (p > 0.05). It was concluded that the application of NaF before bleaching did not interfere with the bleaching effect.

The strategies used for curing universal adhesives affect the micro-bond strength of resin cement used to lute indirect resin composites to human dentin.

We evaluated the effect of different curing strategies for universal adhesives on micro-tensile bond strength (µTBS) between resin cement and dentin and/or between resin cement and indirect resin composite. Flat coronal dentin surfaces and composite resin disks were pretreated with silane-containing universal adhesives, with or without light-curing on the dentin-side and/or composite resin disk-side. Resin disks were luted onto the pretreated dentin surfaces with the corresponding dual-cure adhesive resin cements and light-cured, and cut into beams after 24-h water storage. After 0 or 10,000 thermocycles (5ºC/55ºC) in a water bath, the µTBS of the composite resin disk-dentin beam was tested. The µTBS was highest when universal adhesives were applied to both the dentin- and the indirect composite resin disk-side, followed by light-curing. Thermocycling decreased µTBS in all but the Scotchbond Universaltreated group, with light-curing on both sides. The effect of curing strategies is dependent upon the materials.