Evaluation of experimental resin infiltrant containing nanohydroxyapatite on color stability and microhardness in demineralized enamel.

OBJECTIVE: The aim of the study was to evaluate the effect of the addition of 10% nanohydroxyapatite in an experimental resin infiltrant on color stability and mineral loss. MATERIAL AND METHODS: Bovine enamel blocks were randomized into five groups (n = 27/group): SE (sound enamel); ICL (initial caries lesion); I (Icon®); E (experimental infiltrant); EH (experimental infiltrant containing 10% nanohydroxyapatite). Color evaluation (n = 15) was performed and CIEL*a*b* values were obtained at points T0 (baseline), T1 (14 days immersed on coffee solution), and T2 (28 days immersed) and data were calculated ∆E00, ∆WID, ∆L*, ∆a*, and ∆b*. Cross-sectional microhardness (n = 12) was performed and lesion area (∆S) was calculated. Images were obtained with polarized light optical microscopy at 40 × magnification (n = 5). RESULTS: In color stability results, there was significant difference between time (14 and 28 days); ICL demonstrated significant difference among treated groups in all measures (∆L*, ∆a*, ∆b*, ∆E00, ∆WID) regardless of time; I and E demonstrated similar behavior on those measures and EH differed from I in ∆L*. For ∆S, ICL group showed a significant difference compared to I and EH groups, but did not differ from E. CONCLUSION: The nanohydroxyapatite incorporation suggested an effective mineral recovery on initial caries lesion in depth; however, it showed high color variation, such as Icon. In terms of ∆S, I and EH had lower mineral loss, suggesting a reinforcement on initial caries lesion. CLINICAL RELEVANCE: Commercial and experimental infiltrants containing nanohydroxyapatite present low color stability and might reinforce mineral in initial caries lesion.

PEEK and fiberglass intra-radicular posts: influence of resin cement and mechanical cycling on push-out bond strength.

OBJECTIVES: To evaluate the bond strength of four types of posts (pre-fabricated fiberglass post, fiberglass post anatomized with composite resin, milled fiberglass post, and milled polyetheretherketone (PEEK) post), and two types of resin cements (conventional and self-adhesive) by assessing immediate bond strength and post-mechanical aging at each root third. MATERIALS AND METHODS: Bovine endodontically treated roots (16 groups, n = 8) were prepared and the posts were produced and luted; the specimens of aging groups were cycled (300,000 cycles under 50 N load at 1.2 Hz frequency); six slices of each root were obtained; push-out test was performed by using a universal testing machine (500 N load at 1 mm/min cross speed); fracture pattern was classified into five levels. The statistical analyses used were three-way ANOVA, Tukey's test (for bond strength), and Fisher's test (for fracture pattern) (α < 0.05). RESULTS: Differences were found between the cements for posts (conventional: p < 0.001; self-adhesive: p = 0.002), whereas no difference was found for root region (p = 0.941; p = 0.056, respectively); analysis of each root showed significant differences for cements (p < 0.001), posts (p < 0.001), and mechanical cycling (p = 0.001); in terms of double interaction, differences were found for posts and mechanical cycling (p = 0.005); no other interactions were observed (double or triple); the fracture pattern showed difference between the groups for both cements. CONCLUSIONS: Milled PEEK posts seem to be a good clinical option, but they require improvement of CAD-CAM technology and advances towards their adhesion. CLINICAL RELEVANCE: Milled posts are promising and can reduce clinical time for rehabilitation of extensively destroyed teeth.

Effect of diphenyliodonium hexafluorophosphate salt on experimental infiltrants containing different diluents.

Non-invasive treatments for caries lesions are increasingly required for oral health; resin infiltration is one possible conservative option. In this study, we evaluated the effects of diphenyliodonium hexafluorophosphate salt (DPI) on experimental resin infiltrants with either (hydroxyethyl)methacrylate (HEMA) or ethanol as the diluent. A monomeric base with diglycidyl methacrylate ethoxylated (BisEMA, 25 wt%) and triethylene glycol dimethacrylate (TEGDMA, 75 wt%), 0.5 mol% of camphorquinone, and 1 mol% of ethyl-4-(dimethylamino)benzoate (EDAB) was prepared. The mixtures were divided into 12 groups according to DPI concentration (0; 0.25; 0.5; 1 mol%) and diluents (10 wt% HEMA, 10 wt% ethanol, or none). Degree of conversion (DC), water sorption (Ws), solubility (Sol), contact angle (CA), and cohesive strength (CS) tests were performed and compared to a commercial infiltrant control group (Icon). Only ethanol negatively affected DC and Sol, but both diluents negatively affected Ws and CS. Nevertheless, the presence of DPI, mainly at the 0.5 mol% concentration, compensated for the negative effects of the diluents. The commercial control group was less effective only for CS. In conclusion, 0.5% DPI seems to be the most suitable concentration to compensate for the negative effects of diluents.

Effect of Heavy Metals Contamination from Cigarette Smoke on Sound and Caries-Like Enamel.

In this study, we sought to evaluate the influence of cigarette smoke and pH cycling on the chemical composition and surface/cross-sectional enamel microhardness. A total of 40 dental blocks obtained from bovine incisors were divided into four groups (n=10): no treatment (control); exposure to cigarette smoke (CS); exposure to pH cycling (PC); and exposure to cigarette smoke and pH cycling (CS-PC). The samples were analyzed by synchrotron radiation micro X-ray fluorescence, bench mode X-ray fluorescence, as well as surface microhardness (SMH) and cross-sectional microhardness (CSMH) testing. The SMH results were submitted to analysis of variance (ANOVA) and Tukey's test. The CSMH results were evaluated using split-plot ANOVA and Tukey's test. A high amount of Cd and Pb and traces of Ni and As were observed in enamel and dentin after exposure to cigarette smoke (CS and CS-PC). The SMH and CSMH of CS were statistically higher when compared with the control. The PC and CS-PC showed lower SMH and CSMH. We conclude that exposure to cigarette smoke promoted heavy metal deposition in enamel/dentin. In addition, it increased the enamel microhardness but did not promote a protective effect on the in vitro development of caries. The clinical significance of this work is that there is significant bioaccumulation of heavy metals from cigarette smoke on the surface and in the enamel and dentin.

Influence of successive light-activation on degree of conversion and Knoop hardness of the first layered composite increment.

PURPOSE: To evaluate the influence of light-activation of second, third and fourth increments on degree of conversion (DC) and microhardness (KHN) of the top (T) and bottom (B) surface of the first increment. MATERIALS AND METHODS: Forty samples (n = 5) were prepared. In groups 1-4, after each increment light-activation (multiple irradiation), T and B of the first increment were measured in DC and KHN. In groups 5-8, only the first increment was made (single irradiation) and measurements of DC and KHN were taken at 15 min intervals. The light-activation modes were (XL) 500 mW/cm(2) × 38 s (G1/G5); (S) 1000 mW/cm(2) × 19 s (G2/G6), (HP) 1400 mW/cm(2) × 14 s (G3/G7); (PE) 3200 mW/cm(2) × 6 s (G4/G8). Data for DC and KHN were analyzed separately by using PROC MIXED for repeated measures and Tukey-Kramer test (α = 0.05). RESULTS: For KHN, B showed lower values than T. PE resulted in lower values of KHN in B surface. For single and multiple irradiations, T and B of first measurement showed the lowest KHN and the fourth measurement showed the highest, with significant difference between them. For single irradiation, first and second increments presented similar KHN, different from the third and fourth increment, which did not differ between them. For multiple irradiations, the second light-activation resulted in KHN similar to first, third and fourth increments. For DC, except QTH, T presented higher DC than B. CONCLUSION: The light-activation of successive increments was not able to influence the KHN and DC of the first increment.

Impact of the distance of light curing on the degree of conversion and microhardness of a composite resin.

OBJECTIVE: This study evaluated the impact of the distance between the light guide tip of the curing unit and material surface on the degree of conversion and Knoop microhardness of a composite resin. MATERIALS AND METHODS: Circular samples were carried out of a methacrylate micro-hybrid resin-based composite and light cured at 0, 2 and 4 mm distance. Monomer conversion rate was measured using a Fourier-transform Raman spectrometer and Knoop hardness number was obtained using a microhardness tester on the top and bottom surfaces. Data were statistically analyzed by analysis of variance and Tukey's test (α=0.05). RESULTS: Overall, the increase of curing distance reduced the microhardness (p≤0.05), but did not influence the carbon double bond conversion rate (p>0.05) of the composite resin tested; and the top surface showed better properties compared to the bottom (p≤0.05). CONCLUSIONS: The light curing at distance can reduce mechanical properties and could affect long-term durability of the composite restorations. Thus, the use of a curing device with high irradiance is recommended.

Influence of irrigation protocols on the bond strength of fiber posts cemented with a self-adhesive luting agent 24 hours after endodontic treatment.

The aim of this in vitro study was to evaluate the influence of different irrigation protocols on the bond strength, at different root depths, of fiber posts cemented with a self-adhesive cement 24 hours after endodontic treatment. Fifty-six bovine incisor roots were endodontically prepared and separated into 7 groups (n = 8) according to irrigation protocols: group 1, sterile saline (control); group 2, chlorhexidine (CHX) gel 2% and saline; group 3, sodium hypochlorite (NaOCl) 5.25% and saline; group 4, CHX and saline (final irrigation with ethylenediaminetetraacetic acid [EDTA] 17%); group 5, NaOCl and saline (final irrigation with EDTA); group 6, CHX and saline (final irrigation with NaOCl and EDTA); and group 7, NaOCl (final irrigation with CHX and EDTA). No statistically significant difference was found among the groups. Within the limitations of this study, it can be concluded that the different irrigation protocols did not influence the bond strength of self-adhesive resin cement, which presented similar behaviors at the 3 root depths studied.

Effect of light polymerization time, mode, and thermal and mechanical load cycling on microleakage in resin composite restorations.

This study evaluated the effect of polymerization mode and time and thermal and mechanical loading cycling (TMC) on microleakage in composite resin restorations. One hundred and eighty cavities were prepared and randomly divided according to the light curing time (20, 40, or 60 s), modes (quartz-tungsten-halogen (QTH)-420 mW/cm(2), LED 2 (2nd degree generation)-1,100 mW/cm(2), or LED 3 (3rd degree generation)-700 mW/cm(2)), and TMC. Following standard restorative procedures, the samples were prepared for analysis in an absorbance spectrophotometer. All results were statistically analyzed using the three-way ANOVA and Tukey test (p ≤ 0.05). The results revealed that the groups QTH and LED 3 submitted to TMC showed higher microleakage than those that were not submitted to TMC. Only for LED 3, 60 s showed higher microleakage than 20 s. For LED 2 and QTH, there were no differences between the times. QTH showed lower microleakage means than LED 2, when photoactivated for 20 s, without TMC. When photoactivated for 60 s, QTH showed lower microleakage means than LED 3, for the groups with or without TMC. It was concluded that TMC, the increase in polymerization time, and the irradiance were factors that may increase the marginal microleakage of class II cavities.

Effect of low-level laser therapy on odontoblast-like cells exposed to bleaching agent.

The aim of the present study was to evaluate the effect of low-level laser therapy (LLLT) on odontoblast-like MDPC-23 cells exposed to carbamide peroxide (CP 0.01%-2.21 µg/mL of H2O2). The cells were seeded in sterile 24-well plates for 72 h. Eight groups were established according to the exposure or not to the bleaching agents and the laser energy doses tested (0, 4, 10, and 15 J/cm(2)). After exposing the cells to 0.01% CP for 1 h, this bleaching solution was replaced by fresh culture medium. The cells were then irradiated (three sections) with a near-infrared diode laser (InGaAsP-780 ± 3 nm, 40 mW), with intervals of 24 h. The 0.01% CP solution caused statistically significant reductions in cell metabolism and alkaline phosphate (ALP) activity when compared with those of the groups not exposed to the bleaching agent. The LLLT did not modulate cell metabolism; however, the dose of 4 J/cm(2) increased the ALP activity. It was concluded that 0.01% CP reduces the MDPC-23 cell metabolism and ALP activity. The LLLT in the parameters tested did not influence the cell metabolism of the cultured cells; nevertheless, the laser dose of 4 J/cm(2) increases the ALP activity in groups both with and without exposure to the bleaching agent.

Effect of different monomer-based composites and acid etching pre-treatment of enamel on the microleakage using self-etch adhesives systems.

OBJECTIVE: To evaluate quantitatively the marginal microleakage of restorations carried out with self-etching adhesives with or without prior phosphoric enamel acid etching of silorane or methacrylate resin-based composite restorations subjected to thermal cycling. MATERIALS AND METHODS: Forty cavities were prepared at the proximal surface of bovine incisors and randomly divided according to the etching of the enamel and restorative system used. The groups were restored with methacrylate [Adper SE Plus adhesive (3M ESPE) + Filtek Z250 (3M ESPE)] or silorane [Filtek LS adhesive (3M ESPE) + Filtek LS composite (3M ESPE)] restorative systems, light-cured using a LED unit (Bluephase 16i, Vivadent). After restorative procedure and thermocycling (1000 cycles), the specimens were immersed in methylene blue for 2 h. The specimens were triturated and the powder was used for analysis in an absorbance spectrophotometer. Data were statistically analyzed by 2-way ANOVA (alpha = 0.05). RESULTS: No statistical difference between the restorative materials tested with or without previous acid etching of enamel in Class II marginal microleakage was observed (p > 0.05). CONCLUSIONS: The use of acid etching prior to self-etching adhesives did not interfere on the microleakage of methacrylate- or silorane-based restorations.

The effect of surface treatment and bonding procedures on the bond strength of silorane composite repairs.

OBJECTIVE: The aim of this study was to evaluate the effect of surface treatments and adhesive protocols on the microtensile bond strength of a low-shrinkage composite repair. MATERIALS AND METHODS: Ninety-six blocks of composite resin Filtek LS were prepared using a half-hourglass-shaped silicone matrix. The specimens were storage for 24 h in distilled water and were randomly divided into the experimental (6) and negative control (2) groups (n = 12) according to the surface treatment (diamond bur and aluminum oxide sandblasting) and adhesive protocol (none; Filtek LS adhesive; phosphoric acid + Filtek LS adhesive; and phosphoric acid + silane + Filtek LS adhesive). After the adhesive procedure, the specimens were fixed in an hourglass-shaped silicone matrix and the other half of the specimen was restored. Hourglass shaped specimens (n = 12) were used as positive control (cohesive strength of the resin). The microtensile bonding test was performed at a crosshead speed of 0.5 mm/min. The data were analyzed using ANOVA, Tukey's and Dunnett's tests (α = 0.05). RESULTS: The bond strength values were similar for all experimental groups, except the groups without adhesive application. None of the experimental groups presented results similar to the positive control group. CONCLUSIONS: The repair of silorane restorations is viable; nevertheless, the different bonding procedures tested were incapable to produce bond strengths similar to the cohesive strength of the material.

Effect of light curing protocol on degree of conversion of composites.

OBJECTIVE: To evaluate the degree of conversion (DC) of two light-cured composites with different protocols of light curing. MATERIALS AND METHODS: One hundred and ninety two specimens (n = 8) were prepared (5 mm × 2 mm) according to experimental groups: two composite resins (Filtek Supreme and four seasons); three light curing protocols [20 s with the tip of the light curing unit (LCU) device touching composite surface (C); 20 s with the tip of the LCU at 8 mm distant from composite surface (D); and tip of the LCU at 8 mm distant from composite surface and polymerization time required to obtain a radiant exposure of 16 J/cm(2) (DS)]. Four LCUs (Bluephase 16i, Ultralume LED 5, XL 3000 and Optilux 501C) were used. DC of the bottom and top surface of specimens were measured using a FTIR spectrometer. Data were statistically analyzed by 3-way split splot ANOVA and Tukey's test (alpha = 0.05). RESULTS: The results showed that DC of the top surface was higher than the bottom at all experimental conditions (p < 0.0001). Overall, the curing at 8 mm of distance did not affect conversion rate on the top surface (p > 0.05), but bottom surfaces showed DC reduction (p < 0.05). The highest monomer conversion values were observed for C and DS situations. CONCLUSION: The distance between the LCU and material surface and radiant exposure can affect the DC. Polymerization at distance should be performed with curing units with higher light power and/or extended exposure time.

Effect of Phytic Acid Etching and Airborne-Particle Abrasion Treatment on the Resin Bond Strength.

Objective: This study aimed to evaluate the bond strength of a universal adhesive to dentin (µTBS) using different time periods of airborne particle abrasion (APA) and two types of acid etching. Methods: Seventy-two human third molars were divided into 9 groups (n=8) according to dentin pretreatment: APA duration (0, 5, or 10s) and acid etching (no acid - NA, 37% phosphoric acid - PhoA, or 1% phytic acid - PhyA). APA was performed at a 0.5 cm distance and air pressure of 60 psi using 50 µm aluminum oxide particles. Afterwards, two coats of Single Bond Universal adhesive (3M) were applied to the dentin surface. Composite blocks were built using the incremental technique, sectioned into 1×1 mm slices and subjected to microtensile bond strength (µTBS) testing. Fracture patterns and surface topography of each dentinal pretreatment were evaluated using a Scanning electron microscope (SEM). Bond strength data were analyzed using two-way ANOVA and Bonferroni post-hoc tests. Results: The group that received pretreatment with 5s APA and PhoA presented higher µTBS values among all groups, which was statistically different when compared with the PhoA, 10APA+PhoA, and 5APA+PhyA groups. PhyA did not significantly influence the bond strength of the air-abraded groups. Finally, adhesive failure was considered the predominant failure in all groups. Conclusion: Dentin pretreated by airborne particle abrasion using aluminum oxide demonstrated an increase in bond strength when abraded for 5 seconds and conditioned with phosphoric acid in a universal adhesive system.

Achieving property enhancements in dental resin composites via reduced concentrations of camphorquinone within a ternary initiator system.

OBJECTIVES: The study aimed to assess the impact of diphenyliodonium hexafluorophosphate (DPI) on the physicochemical properties of experimental resin composites (ECRs) featuring reduced concentrations of camphorquinone (CQ)/amine. METHODS: Five concentrations of CQ (0.125, 0.25, 0.5, 0.75, and 1 mol%) with dimethylaminoethyl amine benzoate (EDAB) in a 1:2 mol% ratio (CQ:EDAB) were incorporated into a 50:50 mass% monomer blend of bisphenol glycidyl methacrylate (BisGMA) and triethyleneglycol dimethacrylate (TEGDMA). An additional 5 groups with the same CQ:EDAB concentrations had 0.5 mol% DPI added. Each resin group contained 60 wt% of 0.7 µm barium-alumino-silicate glass. Light transmission (n = 3), real-time degree of polymerization (n = 3), temperature change during polymerization (n = 5), polymerization shrinkage strain (n = 3), flexural strength, and modulus (n = 12), as well as water sorption and solubility (n = 5), were evaluated. Data were analyzed using two-way ANOVA and Tukey's post-hoc test (α = 0.05). RESULTS: Light transmission was reduced in groups containing 0.125 and 0.25 mol% of CQ without DPI. DPI increased temperature, degree and rate of polymerization, despite the reduction in CQ/amine concentration. Additionally, there was an increase in polymerization shrinkage strain, flexural strength and modulus, and a reduction in water sorption and solubility in ECRs with DPI, even with lower concentrations of CQ/EDAB. SIGNIFICANCE: DPI improved the assessed properties of composites across various concentrations of CQ/EDAB, showing the benefit of reducing the quantity of CQ used without compromising the properties and curing of the resin composites.

Effects of the Incorporation of Bioactive Particles on Physical Properties, Bioactivity and Penetration of Resin Enamel Infiltrant.

Purpose: The resinous infiltrant lacks remineralizing activity. This research aimed to develop and evaluate bioactivity, physico-mechanical properties and penetration of resin infiltrants containing Biosilicate or nanohydroxyapatite. Methods: Experimental resin infiltrant (ERI; 75/25 wt.% TEGDMA/BisEMA) was divided among the groups Pure Experimental (PE); ERI + Biosilicate 5 or 10% (Bio5; Bio10), ERI + 10% nanohydroxyapatite (Hap10), and Icon (DMG, Germany). Bioactivity was analyzed by SEM, EDS and FT-IR/ATR after soaking in SBF. Degree of conversion (DC), sorption and solubility (SO; SOL), flexural strength, modulus of elasticity (FS; E-modulus), contact angle (CA) and penetration were characterized. Extent of penetration was analyzed by treating white spot lesions (WSL) in human dental enamel samples with the infiltrants and subsequently analyzing specimens by confocal laser scanning microscopy. Data from each test were submitted to ANOVA and Tukey's tests (p < 0.01). Results: SEM, EDS and FT-IR showed the formation of precipitates and increase in the rates of Ca and P in the groups with bioactive particles, after storage in SBF. Hap10 showed higher DC and CA values than all the other groups. Groups Bio5 and Bio10 showed CA values similar to those of Icon, higher SO and SOL values, and reduction in other properties. All infiltrants were capable of penetrating into the WSLs. Conclusion: The incorporation of Biosilicate (5 or 10%) or nanohydroxyapatite (10%) into ERI induced mineral deposition on the surface and did not compromise infiltration and penetration into WSLs, however, compromising their physico-mechanical properties.

Radiopacity and physical properties evaluation of infiltrants with Barium and Ytterbium addition.

Radiopaque properties in the infiltrant should be interesting for clinicians to feel more confident to indicate this treatment. Thus, the aim of this study was to evaluate the effect of the incorporation of barium and ytterbium particles on the physical properties of resin infiltrants. Groups were divided according to the addition of ytterbium oxide (Y) alone (30 or 40%) or Y with barium (YB) (15/15% or 20/20% respectively) in the Icon commercial infiltrant and in the experimental infiltrant base. Digital radiography (n=5), Microradiography (n=5), Microtomography (n=3), degree of conversion (n=5), water sorption (n=16), solubility (n=16), contact angle (n=16), flexural strength (n=16), elastic modulus (n=16) and Energy dispersive X-ray Spectroscopy (n=10) were performed. Analyses were performed using the R program, with a significance level of 5%, and microradiography and Microtomography analyses were evaluated qualitatively. In groups with 30 or 40% of ytterbium, radiopacity was higher or equal to enamel. Microradiography and Microtomography appear to have more radiopacity in groups with 40% (Y). Among the groups with no particle addition, those of the experimental infiltrant presented a higher degree of conversion than those of Icon®. In most groups, there was solubility below the ISO-recommended levels. The addition of particles resulted in higher viscosity. Groups with Icon had higher flexural strength and elastic modulus than groups with experimental infiltrant. The addition of 40% (Y) improved polymerization, had low solubility, and had greater radiopacity than enamel, however negatively affected the viscosity increasing then. Experimental groups with the base showed a higher water sorption than Icon groups.

Effect of surface sealants on microleakage of Class II restorations after thermocycling and long-term water storage.

PURPOSE: To evaluate interface degradation leading to marginal microleakeage in Class II restorations that had received an application of surface sealant at the tooth/restoration interface or not. MATERIALS AND METHODS: Eighty bovine incisors were used, and the teeth were split obliquely, 10 mm from the amelodentinal proximal junction, and finished with water abrasive papers to obtain a smooth, flat incisal surface. Cavities were made to simulate Class II preparations (8 mm high, 4 mm wide and 1.5 mm deep), and the restorations were performed with a composite resin. Teeth were then randomly allocated into 8 groups according to the surface sealant (none, Fortify, Single Bond 2, or Scothbond MP Plus) and aging process (none or thermocycling and storage for 6 months). Microleakage was then evaluated using a dye penetration method immediately after the restoration or after aging. The samples were triturated and assessed by spectrophotometer. RESULTS: Microleakage was statistically similar in all groups when assessed immediately after the restorative procedure. After aging, teeth sealed with Fortify presented better results than the other groups. CONCLUSION: Aging causes interface degradation and increased microleakage. Surface sealant can reduce these effects and decrease microleakage in Class II restorations.

Effect of bleaching treatment and reduced application time of an antioxidant on bond strength to bleached enamel and subjacent dentin.

PURPOSE: To evaluate the influence of bleaching on bond strength to enamel and subjacent dentin, and to determine whether a reduced application time (1 min) of the antioxidizing agent can obviate the compromised bond strength after bleaching. MATERIALS AND METHODS: One hundred twelve bovine incisors were obtained, and the enamel and dentin surfaces were standardized to a thickness of 1 mm. The specimens were divided into two control groups (enamel and dentin without treatment) and 12 experimental groups (n = 10), based on the concentration of bleaching agents (carbamide peroxide 16% and hydrogen peroxide 35%), time interval between bleaching and restorative procedures (24 h; 24 h + sodium ascorbate (SA) 10%/1 min; 14 days), and substrate (enamel or dentin). All samples were submitted to the bleaching treatment on enamel. After the stipulated interval, a microshear test was performed. RESULTS: The bleaching treatment compromised the bond strength to the enamel when the restoration was performed 24 h after the end of bleaching. The bond strength to dentin was not affected by bleaching. CONCLUSIONS: The SA 10% application for 1 min obviates the detrimental effect of bleaching on bond strength. The bleaching performed on enamel does not affect the bond strength to the subjacent dentin.

Evaluation of dentin hardness and bond strength at different walls of class II preparations.

PURPOSE: The aim of this study was to evaluate the Knoop hardness number (KHN) of dentin and the microtensile bond strength (microTBS) at different walls of MOD preparations, and the correlation between microTBS and the KHN of dentin. MATERIALS AND METHODS: Human molars with MOD preparations were allocated into 3 groups according to the preparation wall (axial, gingival, pulpal). Each tooth was sectioned into halves, resulting in two similar preparation walls: one was used for measuring the KHN of dentin and the other for microTBS testing. Flat surfaces of the respective walls were obtained by cutting away adjacent walls. For the KHN measurement, twelve indentations were performed along the preparation wall (50 g/15 s). For microTBS testing, specimens were distributed into 3 groups according to the adhesive system (Adper Single Bond Plus/SB, Clearfil SE Bond/SE, Adper Prompt/AP). Composite blocks were built over surfaces; specimens were sectioned (3 slabs/wall) and trimmed to an hourglass shape (1 mm(2)). RESULTS: The KHN of dentin walls was significantly different (ANOVA/Tukey); pulpal wall > axial wall > gingival wall. The effect of preparation walls on microTBS was dependent on the bonding system (2-way ANOVA/Tukey's test). SB had higher bond strength than the other systems at the gingival wall; and higher than SE at the axial wall. At the pulpal wall, SE presented a higher mean compared to AP. A significant negative correlation between microTBS and KHN was observed at the gingival wall. CONCLUSION: It could be concluded that dentin structure can affect bond strengths, but the impact of the substrate varies according to the type of adhesive system.

Effect of the diffusion of bleaching agents through enamel on dentin bonding at different depths.

PURPOSE: To evaluate the influence of two concentrations of bleaching agents applied over enamel surfaces on the dentin bonding at different depths. METHODS: Twenty-four bovine incisors were sectioned, obtaining three fragments per tooth (4x4 mm). Each fragment presented a 0.7 mm enamel thickness; and the dentin thickness varied according to the experimental group: 0.5 mm, 1 mm or 1.5 mm. Fragments from each dentin-thickness were allocated into three groups (n=8): G1: Control (no bleaching); G2: 16% carbamide peroxide (6 hours/14 days); G3: 35% hydrogen peroxide (three 15-minute treatments). 24 hours after enamel bleaching, the adhesive system was applied and dentin surfaces were restored with resin composite cylinders (2 mm diameter and 1 mm height). The micro-shear testing was performed immediately after restorative procedures, at a speed of 0.5 mm/minute until failure. Bond strength values, in MPa, were statistically analyzed (split-plot ANOVA/Tukey alpha=0.05). RESULTS: Means obtained were: G1-0.5 mm: 13.5, G1-1 mm: 9.48, G1-1.5 mm: 9.01; G2-0.5 mm: 9.64, G2-1 mm: 9.44, G2-1.5 mm: 9.27; G3-0.5 mm: 11.68, G3-1 mm: 11.64, G3-1.5 mm: 7.63. Regardless of the dentin thickness, bleached groups presented bond strengths similar to that of control groups. Nevertheless, significant differences among dentin depths were detected (P=0.02); and the lowest bond strength was observed on the deepest dentin (1.5 mm). The diffusion of bleaching agents through enamel surfaces did not affect the bond strength to dentin, which is highly dependent on the morphology/depth of the substrate.