Effect of silica coating and laser treatment on the flexural strength, surface characteristics, and bond strength of a dental zirconia.

This study investigated the effect of irradiation with an erbium-doped yttrium aluminium garnet (Er:YAG) laser and coating with silica on the surface characteristics, bond strength, and flexural strength of dental zirconia. Three hundred and forty-three standard zirconia specimens were created, and 49 were assigned to each of seven surface treatment groups: (i) no treatment; Er:YAG laser (80 mJ/2 Hz) with pulse widths of 50 µs (ii), 100 µs (iii), 300 µs (iv), or 600 µs (v); or tribochemical silica coating at the partially sintered stage (vi) or after sintering was complete (vii). All specimens were sintered after the surface treatments, except for the group in which specimens were sintered before treatment. The study outcomes were roughness, surface loss, microshear bond strength (µSBS), and biaxial flexural strength (BFS). Mean roughness and surface loss values were significantly higher in specimens from irradiated groups than in those from silica-coated groups. Regarding µSBS, after aging, specimens from all experimental groups presented very low and similar µSBS values, irrespective of the surface treatment. Silica coating after sintering yielded the highest BFS (1149.5 ± 167.6 MPa), while coating partially sintered specimens with silica resulted a BFS (826.9 ± 60.9 MPa) similar to that of the untreated control group (794.9 ± 101.7 MPa). Laser treatments, irrespective of pulse width used, significantly decreased the BFS. In the group treated with laser at 300 µs pulse width, specimens exhibited the lowest BFS value (514.1 ± 71.5 MPa). Adhesion to zirconia was not stable after aging, regardless of the surface treatment implemented.

Effect of erosive and abrasive challenges on the glaze layer applied to ceramic materials.

PURPOSE: This study aims to evaluate the effect of erosive, abrasive, and erosive/abrasive challenges on the glaze layer of ceramic materials. METHODS: Ninety-five samples of monolithic zirconia (MZ) (LuxaCam Zircon HT-Plus) and lithium disilicate (LD) (IPS e.max CAD) were divided according to the response variables: Surface roughness and surface loss (n = 10), evaluated with optical profilometry; surface topography, with scanning electron microscopy SEM (n = 3); and biofilm deposition, with microbiological assay (n = 5). The evaluations were performed in three different time evaluations: (a) Sintered, (b) Glaze, and (c) Challenge (Erosion, Abrasion, and Erosion/Abrasion). Erosion consisted in immersing specimens in HCl solution, abrasion was performed with brushing machine, and erosion/abrasion consisted of a combination of the two previous protocols. Data were analyzed with parametric tests (P < 0.05). RESULTS: MZ glaze layer presented significantly higher surface roughness (P = 0.00), surface loss (P = 0.03), and biofilm deposition (P = 0.00) than LD. Abrasion and erosion/abrasion showed similar outcomes, generating significantly higher surface roughness (P = 0.00), surface loss (P = 0.00), and biofilm deposition (P = 0.01) than erosion. CONCLUSIONS: Glaze layer properties were altered by the challenges, with abrasion and erosion/abrasion generating higher surface roughness, surface loss, and biofilm deposition than erosion. A significant correlation was found between the surface roughness and biofilm deposition. CLINICAL SIGNIFICANCE: The glaze layer is susceptible to challenges, especially to abrasion and erosion/abrasion, which generated greater surface roughness and surface loss than erosion. The greater surface roughness lead to a greater biofilm deposition on the glaze layer.

Influence of Er:YAG laser pulse duration on the long-term stability of organic matrix and resin-dentin interface.

The purpose of this study was to explore the influence of Er:YAG laser irradiation with different pulse durations on the organic matrix, micromorphology of the hybrid layer (HL), and bond strength over time. Sixty caries-free human molars were cut to obtain flat dentin surfaces which were randomly divided into 4 groups: control (not irradiated-G1) and laser groups (80 mJ/2 Hz) with pulse duration ranging between 50 (G2), 300 (G3), and 600 µs (G4). A self-etch adhesive system (Universal 3M ESPE) was applied on pre-treated dentin surfaces and cylinders of resin composite were built up and stressed in a universal testing machine (µSBS) at 24 h and after12 months (n = 12). In addition, 3 other dentin-bonded specimens were prepared as previously described for each group with the adhesive doped with 0.1 wt% Rhodamine B to analyze hybrid layer morphology under Confocal Laser Microscope Scanning (CLMS). Organic matrix and collagen fibrils were analyzed by second harmonic generation (SGH). Two-way ANOVA and Tukey's test detected significantly higher µSBS values for the control group, whereas the lower values were observed in all laser groups at 24 h (p < 0.05). Storage in artificial saliva did not reduce µSBS in all groups. The low signal emitted by SHG images below the irradiated area demonstrated thermal damage of the collagen matrix. CLMS images of laser groups exhibited thicker and irregular resin-dentin interfaces than the control group. Regardless of the pulse duration, Er:YAG laser pre-treatment altered the organic matrix and HL formation which resulted in low µSBS values at 24 h. The alterations on dentin's organic structure did not jeopardize the µSBS after 1 year of saliva storage.

Effect of thermal and acid challenges on the surface properties of pink restorative materials.

PURPOSE: To compare the effect of thermal cycling and erosive challenge on color change, surface roughness, surface loss and biofilm deposition of three resin-based composites. METHODS: Three resin-based composites that reproduce the color of gingival tissues [two nanohybrid composites (A and B) and a giomer (C) ] were tested before and after distinct challenges [ thermal cycling (TC) and erosive challenge (EC) ] in regard to its color stability, surface roughness, surface loss and biofilm deposition. Surface roughness and surface loss specimens (n=10) were measured with an optical profilometer and, color stability (n=10) was measured with a spectrophotometer. Biofilm deposition (n=5) was measured after 3 and 24 hours by safranin staining. RESULTS: Two-way ANOVA test was performed to analyze color change, roughness and surface loss. A significant color change was detected for resin-based composites (P< 0.05) and its interaction with tested challenges (P< 0.05). The highest color variation was observed on the giomer after erosive challenge. Surface loss was not different between tested groups (P= 0.708). The roughness was significantly higher in specimens submitted to thermal cycling (P> 0.05). For biofilm quantification, after 3 and 24 hours, ANOVA (3-way) detected significance for the interaction of challenges and resin-based composites (P< 0.05 and P< 0.05, respectively). All resin-based composites presented color changes after challenges; higher roughness was observed after thermal cycling for all resin-based composites tested, without significant surface loss; and higher biofilm deposition was observed on the giomer samples when submitted to erosive challenge after 3 and 24 hours. CLINICAL SIGNIFICANCE: Pink esthetic is as important as dental esthetics and some restorative materials can mimic gingival tissue. However, the tested giomer must be indicated with caution, since it presented significant changes after thermal and acid challenges.

Optical coherence tomography and polarized light microscopy for the evaluation of artificial caries: a preliminary study.

This study was designed to investigate whether there is a correlation between the findings of optical coherence tomography (OCT) and polarized light microscopy (PLM) when these techniques are used to evaluate standard enamel white-spot lesions developed by distinct cariogenic challenges. Bovine enamel fragments (N = 168) were randomly allocated into 6 experimental groups according to the microbiologic model (Streptococcus mutans UA159, Streptococcus sobrinus ATCC 33478, or mixed S mutans and S sobrinus) and carbohydrate sources (1% sucrose or combined 1% sucrose and 1% starch). Specimens were examined by OCT and PLM every day within a period of 7 days. Five measurements of demineralization depth were recorded for each specimen, and means were calculated. Data were analyzed with analysis of variance and Tukey tests (α = 0.05), and a correlation test was performed. All cariogenic challenges created sub-superficial lesions. In both the OCT and PLM analyses, the demineralization depth reached its peak between days 6 and 7 of the cariogenic challenge, except for the group challenged with S sobrinus supplemented with combined sucrose and starch; for that group, demineralization peaked on day 5 in the OCT analysis. There was a significant correlation between OCT and PLM (P = 0.00; r = 0.842). This preliminary study suggests that OCT is a reliable, nondestructive method to measure the demineralization depth of enamel white-spot lesions, which can be useful for the laboratory and has potential for clinical studies. Using the 1% sucrose and S mutans model for 6 days is a simple and effective method to induce enamel caries-like lesions without compromising the depth and morphologic features of the obtained lesions.

Effects of different treatments on chemical and morphological features of eroded dentin.

To evaluate the treatment of eroded dentin (Sensodyne Repair & Protect™, Er:YAG laser and combinations). The occlusal surfaces of 25 third molars were sectioned 1.5 mm in thickness. After an erosion cycle (5 min in demineralizing solution + 3 h in remineralizing solution; six cycles a day for 8 days), the samples were divided into five groups (n = 5): (E) erosion - control; (ES) erosion + Sensodyne Repair & Protect (NovaMin); (EL) erosion + Er:YAG laser (40 mJ, 10 Hz, 0.4 W, 50 µs, 3.1 J/cm2, 63 W/cm2); (ELS) erosion + Er:YAG laser + Sensodyne; and (ESL) erosion + Sensodyne + Er:YAG laser. Following storage in ultrapure water (37 °C/14 days), the Ca/P ratio was evaluated by EDXRF and the morphology surfaces examined in SEM. The percentage of exposed dentin tubules was calculated. One-way analysis of variance and Tukey's test at 5% were used to treat the data. The Ca/P ratio was higher in E and ES groups. More exposed dentin tubules were found in E group and less exposed tubules were found in the ES group (p < 0.0001). When the toothpaste and laser were combined, the number of occluded dentin tubules was higher when laser was performed first (ELS). A positive effect was found when the laser and toothpaste were combined.

Laser phototherapy enhances mesenchymal stem cells survival in response to the dental adhesives.

BACKGROUND: We investigated the influence of laser phototherapy (LPT) on the survival of human mesenchymal stem cells (MSCs) submitted to substances leached from dental adhesives. METHOD: MSCs were isolated and characterized. Oral mucosa fibroblasts and osteoblast-like cells were used as comparative controls. Cultured medium conditioned with two adhesive systems was applied to the cultures. Cell monolayers were exposed or not to LPT. Laser irradiations were performed using a red laser (GaAlAs, 780 nm, 0.04 cm(2), 40 mW, 1 W/cm(2), 0.4 J, 10 seconds, 1 point, 10 J/cm(2)). After 24 h, cell viability was assessed by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide reduction assay. Data were statistically compared by ANOVA followed by Tukey's test (P < 0.05). RESULTS: Different cell types showed different viabilities in response to the same materials. Substances leached from adhesives were less cytotoxic to MSCs than to other cell types. Substances leached from Clearfil SE Bond were highly cytotoxic to all cell types tested, except to the MSCs when applied polymerized and in association with LPT. LPT was unable to significantly increase the cell viability of fibroblasts and osteoblast-like cells submitted to the dental adhesives. CONCLUSION: LPT enhances mesenchymal stem cells survival in response to substances leached from dental adhesives.

Influence of gender, anxiety and depression symptoms, and use of oral contraceptive in color perception.

OBJECTIVE: The color is a psychophysical phenomenon, and much has been studied about its physical components. However, the psychological part is poorly investigated, except for the difference between genders in the literature shows that more men are color deficient than women. Dental students are trained to better understand the differences in color, so we became interested in studying whether psychological variables such as anxiety and depression and use of hormonal contraceptives may interfere with this ability. The aim of this in vitro study was to investigate if factors, such as, hormonal contraceptive use, depressive symptoms, anxiety and quality of life, influence on the ability of color discrimination of dental school students. MATERIALS AND METHODS: Sixty-one subjects participated and the following instruments apply: (1) test that consists in the observation of a set of 25 labels (Pantones) with values of known colors, (2) scales of depression, anxiety, and quality of life assessments, and (3) Ishihara test. RESULTS: No difference was observed between genders as color perception (p = 0.868). Symptoms of anxiety and depression were significantly more frequent in the female population that showed worse quality of life (p < 0.000) but did not interfere with color perception. Women using hormonal contraceptives had lower color perception than men (p = 0.04). CONCLUSION: No difference between the genders in the perception of colors was observed, contrary to common sense that women discriminate more colors than men, but women using hormonal contraceptives showed more difficulty in color perception. CLINICAL SIGNIFICANCE: The ability to understand and distinguish color differences is extremely important in clinical dentistry. There could be differences in color perception between men and women that would influence clinical performance.

Obtaining artificially caries-affected dentin for in vitro studies.

AIM: This study evaluated and improved a protocol for obtaining standard caries-affected dentin (CAD) by Streptococcus mutans biofilm demineralization process. MATERIALS AND METHODS: Forty-eight human molars were divided in six experimental groups, according to: period of cariogenic challenge (7, 14 or 21 days) and type of dentin (erupted or unerupted teeth). After complete cariogenic challenge sound and CAD dentin were evaluated by: visual inspection (VI), digital radiography (DR), optical coherence tomography (OCT) and laser fluorescence (LF). RESULTS: Visual inspection confirmed the formation of CAD based on tissue yellowing and loss of surface gloss. Digital radiography detected the presence of radiolucent images, suggesting caries. Three calibrated examiners viewed all images obtained by VI and DR and were able to distinguish healthy from CAD. Fisher's exact statistical test (p < 0.05) confirmed no difference between groups by VI (G1/G4: p = 0.6; G2/G5: p = 1; G3/G6: p = 1) or DR (G1/G4: p = 1; G2/G5: p = 1; G3/G6: p = 1). Both LF values and demineralization depth, as determined by OCT, were subjected to ANOVA (p < 0.05). For LF, a statistically significant difference was observed for the type of substrate (p = 0.001). For OCT, no statistically significant differences in the type of substrate (p = 0.163), length of cariogenic challenge (p = 0.512) or interaction between factors (p = 0.148) were observed. Scanning electron micrographs confirmed the presence of CAD; a more uniform demineralization surface was observed in the dentin of unerupted teeth. CONCLUSION: This protocol suggests that standard CAD can be obtained in 7 days of cariogenic challenge using unerupted teeth. Clinical significance: With the new perspective on the clinical treatment of caries lesions, bonding is increasingly performed to demineralize CAD, which is susceptible to remineralization. A useful protocol to standardize the production of CAD, by microbiological cariogenic challenge, would be an important contribution to laboratorial test in the field of operative dentistry.

Comparison of biofilm models for producing artificial active white spot lesions.

OBJECTIVE: This study compared three protocols for developing artificial white spot lesions (WSL) using biofilm models. METHODOLOGY: In total, 45 human enamel specimens were sterilized and allocated into three groups based on the biofilm model: Streptococcus sobrinus and Lactobacillus casei (Ss+Lc), Streptococcus sobrinus (Ss), or Streptococcus mutans (Sm). Specimens were incubated in filter-sterilized human saliva to form the acquired pellicle and then subjected to the biofilm challenge consisting of three days of incubation with bacteria (for demineralization) and one day of remineralization, which was performed once for Ss+Lc (four days total), four times for Ss (16 days total), and three times for Sm (12 days total). After WSL creation, the lesion fluorescence, depth, and chemical composition were assessed using Quantitative Light-induced Fluorescence (QLF), Polarized Light Microscopy (PLM), and Raman Spectroscopy, respectively. Statistical analysis consisted of two-way ANOVA followed by Tukey's post hoc test (α=0.05). WSL created using the Ss+Lc protocol presented statistically significant higher fluorescence loss (ΔF) and integrated fluorescence (ΔQ) in comparison to the other two protocols (p<0.001). RESULTS: In addition, Ss+Lc resulted in significantly deeper WSL (137.5 µm), followed by Ss (84.1 µm) and Sm (54.9 µm) (p<0.001). While high mineral content was observed in sound enamel surrounding the WSL, lesions created with the Ss+Lc protocol showed the highest demineralization level and changes in the mineral content among the three protocols. CONCLUSION: The biofilm model using S. sobrinus and L. casei for four days was the most appropriate and simplified protocol for developing artificial active WSL with lower fluorescence, higher demineralization, and greater depth.

Comparison between a bulk-fill resin-based composite and three luting materials on the cementation of fiberglass-reinforced posts.

Objectives: This study verified the possibility of cementing fiberglass-reinforced posts using a flowable bulk-fill composite (BF), comparing its push-out bond strength and microhardness with these properties of 3 luting materials. Materials and Methods: Sixty endodontically treated bovine roots were used. Posts were cemented using conventional dual-cured cement (CC); self-adhesive cement (SA); dual-cured composite (RC); and BF. Push-out bond strength (n = 10) and microhardness (n = 5) tests were performed after 1 week and 4 months of storage. Two-way repeated measures analysis of variance (ANOVA), 1-way ANOVA, t-test, and Tukey post-hoc tests were applied for the push-out bond strength and microhardness results; and Pearson correlation test was applied to verify the correlation between push-out bond strength and microhardness results (α = 0.05). Results: BF presented higher push-out bond strength than CC and SA in the cervical third before aging (p < 0.01). No differences were found between push-out bond strength before and after aging for all the luting materials (p = 0.84). Regarding hardness, only SA presented higher values measured before than after aging (p < 0.01). RC and BF did not present 80% of the maximum hardness at the apical regions. A strong positive correlation was found between the luting materials' push-out bond strength and microhardness (p < 0.01, R2 = 0.7912). Conclusions: The BF presented comparable or higher push-out bond strength and microhardness than the luting materials, which indicates that it could be used for cementing resin posts in situations where adequate light curing is possible.

Comparison of chemical aging and water immersion time on durability of resin-dentin interface produced by an etch-and-rinse adhesive.

AIM: The aim of this study was to analyze and compare the influence of short-term NaOCl-storage and long-term water storage on the microtensile bond strength (µTBS) of etch-and-rinse adhesive system to human dentin. MATERIALS AND METHODS: Thirty-six third human molars were randomly divided into 6 groups (n = 6) according to the aging protocol: G1 (water, 24 hours); G2 (water, 6 months); G3 (water, 12 months); G4 (10% sodium hypochlorite--NaOCl, 1 hour); G5 (10% NaOCl, 3 hours) and G6 (10% NaOCl, 5 hours). A two-step etch-and-rinse adhesive (Adper Single Bond 2) was applied according to the manufacturers' instructions. A composite (Filtek Z250) was applied in four horizontal increments and was individually cured. Specimens were cut following the microtensile test technique, submitted to the different aging protocols, and tested in tension. The fracture pattern was observed in a stereomicroscope (40* magnification) and in a scanning electron microscope. The µTBS data were analyzed by ANOVA and Tukey's test (α = 0.05). RESULTS: The effect of storage in 10% NaOCl for 1 or 3 hours was not significantly different from that of aging in distilled water (DW) for 6 or 12 months (p > 0.05). Beams immersed in DW for 24 hours and in 10% NaOCl for 5 hours showed the highest and lowest µTBS values respectively. CONCLUSION: The aging protocols negatively influenced dentin bond strength. Aging specimens in 10% NaOCl for 1 or 3 hours can be an alternative method for long-term water storage (6 or 12 months) bond strength studies. CLINICAL SIGNIFICANCE: This aging protocol allows a quick achievement of longitudinal bond strength data, so that results are available to the professionals in this area while the materials are yet present at the dental market.

The interference of the cleaning procedure of root walls with two different solvents on the adhesion of fiberglass intraradicular posts.

AIM: This study was undertaken to examine the effect of root canal (RT) sealers content and the cleaning procedure of RT walls on bond strength (BS) of a fiber reinforced composite (FRC) post cemented with resin-based or zinc phosphate cement. MATERIALS AND METHODS: Forty bovine roots were divided into 2 groups (n = 20) and obturated with gutta-percha points plus Sealer 26 sealer or gutta-percha points plus N-Rickert sealer. In each group, half (n = 10) of intracanal walls was cleaned with ethanol and the other half with sulfuric ether. In each of these subgroups, half of intracanal posts (n = 5) were cemented with Bistite resin-based cement and half with zinc phosphate cement. Specimens were submitted to pull-out test and tensile force until post dislodgement. The maximum forces required for post removal was expressed in MPa, means were submitted to statistical analysis (Analysis of Variance Test, a = 0.05). RESULTS: Fiber reinforced composite cemented with zinc phosphate were significantly more retentive than those cemented with Bistite (p < 0.05). Regarding the influence of eugenol-based sealer on post retention, there was a statistically significant difference (p < 0.05) only between groups cemented with Bistite, in which canals filled with N-Rickert + gutta-percha showed lower BS than canals filled with Sealer 26 + gutta-percha. CONCLUSION: Despite endodontic cement used, higher pull-out bond strength were obtained when posts were cemented with zinc phosphate. CLINICAL SIGNIFICANCE: The importance of ethanol or sulphuric ether application to properly replace water from intraradicular dentine still requires further investigations, especially to clarify if this technique may reduce the effect of aging and improve the stability of the bond, when used to cement fiber posts into the root canal.

Comparison of collagen features of distinct types of caries-affected dentin.

OBJECTIVES: To compare the biodegradability, mechanical behavior, and physicochemical features of the collagen-rich extracellular matrix (ECM) of artificial caries-affected dentin (ACAD), natural caries-affected dentin (NCAD) and sound dentin (SD). METHODS: Dentin specimens from human molars were prepared and assigned into groups according to the type of dentin: ACAD, NCAD, or SD. ACAD was produced by incubation of demineralized SD with Streptococcus mutans in a chemically defined medium (CDM) with 1% sucrose for 7 days at 37 °C under anaerobic conditions. Specimens were assessed to determine collagen birefringence, biodegradability, mechanical behavior, and chemical composition. Data were individually processed and analyzed by ANOVA and post-hoc tests (α = 0.05). RESULTS: CDM-based biofilm challenge reduced loss, storage, and complex moduli in ACAD (p < 0.001), while the damping capacity remained unaffected (p = 0.066). Higher red and lower green birefringence were found in ACAD and NCAD when compared with SD (p < 0.001). Differently to ACAD, SD and NCAD presented higher biodegradability to exogenous proteases (p = 0.02). Chemical analysis of the integrated areas of characteristic bands that assess mineral quality (carbonate/phosphate and crystallinity index), mineral to matrix (phosphate/amide I) and post-translational modifications (amide III/CH2, pentosidine/CH2, and pentosidine/amide III) (p<0.05) showed that NCAD was significantly different from SD while ACAD exhibited intermediate values. CONCLUSIONS: CDM-based biofilm challenge produced a dentin ECM with decreased mechanical properties and increased collagen maturity. The compositional and structural conformation of the ACAD suggested that CDM-based biofilm challenge showed potential to produce artificial lesions by revealing a transitional condition towards mimicking critical features of NCAD. CLINICAL SIGNIFICANCE: This study highlights the importance of developing a tissue that mimics the features of natural caries-affected dentin ECM for in vitro studies. Our findings suggested the potential of a modified biofilm challenge protocol to produce and simulate a relevant substrate, such as caries-affected dentin.

Influence of blood contamination on bond strength of a self-etching adhesive to dental tissues.

PURPOSE: The aim of this study was to detect the influence of (1) storage period of heparinized blood, (2) type of blood and presence of contaminant, (3) application mode of cleansing agents, and (4) efficacy of cleansing agents on contaminated enamel and dentin during the adhesion process of a one-step adhesive system. MATERIALS AND METHODS: One hundred four human molars were sectioned into halves along the long axis for enamel and dentin tests. Heparinized and fresh blood were obtained from the same donor, applied and dried to maintain a layer of dry blood on the top of samples. The cleansing agents used were hydrogen peroxide, anionic detergent, and antiseptic solution. A one-step adhesive system (Clearfil S3 Bond) was applied on the dental surface, and composite resin cylinders were built up using Tygon tubing molds. After 24 h, the µSBS test (1 mm/min) and fracture analysis were performed. RESULTS: There was no statistically significant difference in bond strength values regarding the storage period of heparinized blood and the types of blood. Groups without contamination presented higher bond strengths than contaminated groups. The application mode of the cleansing agents had no influence on bond strength results. There was no statistically significant difference among cleansing agents and they were as effective as a water stream in counteracting the effect of blood contamination. CONCLUSION: Heparinized blood can be used as a contaminant for up to one week, and it is a reliable procedure to standardize the contaminant. The cleansing agents can be used without friction. A water stream is sufficient to remove blood contamination from dental tissues, before the application of a one-step adhesive system.

Gelatinolytic Activity and Adhesion Studies of Artificial Caries-affected Dentin do not Simulate Natural Caries.

PURPOSE: To investigate whether interfacial enzymatic activity and adhesion receptiveness of artificial caries-affected dentin (ACAD) simulate those of natural caries-affected dentin (NCAD). MATERIALS AND METHODS: Thirty dentin specimens were prepared from human molars to determine interfacial gelatinolytic activity using in situ zymography and adhesion experiments (micropermeability and bond strength [µTBS]). Groups were formed according to the type of dentin: artificial caries-affected dentin (ACAD), natural caries-affected dentin (NCAD), or sound dentin. ACAD was produced by incubating dentin with Streptococcus mutans in a chemically defined medium (CDM) with 1% sucrose for 7 days at 37°C under anaerobic conditions. CDM was replaced daily, and the sterility as well as the pH of the culture was monitored. Adhesion experiments employed Single Bond Universal (3M Oral Care) in self-etch mode. Data were individually processed and analyzed using ANOVA and post-hoc tests (α = 0.05). RESULTS: The enzymatic activity of ACAD was similar to that of sound dentin, but was lower than that of NCAD, which elicited the highest activity (p < 0.05). Interfacial micropermeability intensity at the hybrid layer or in underlying dentin (5 µm below the interface) was similar in all types of dentin (p > 0.05). On the other hand, substrate permeability was higher for NCAD than for ACAD. The highest sealing ability was detected in sound dentin. Bond strengths to ACAD were higher than to NCAD. However, the highest µTBS was observed in sound dentin (p < 0.05). CONCLUSION: Artificial caries-affected dentin simulated neither the gelatinolytic activity nor bonding receptiveness of natural caries-affected dentin.

In vitro microleakage of composite restorations prepared by Er:YAG/Er,Cr:YSGG lasers and conventional drills associated with two adhesive systems.

PURPOSE: The objective of this in vitro study was to compare the degree of microleakage of composite restorations performed by lasers and conventional drills associated with two adhesive systems. MATERIALS AND METHODS: Sixty bovine teeth were divided into 6 groups (n = 10). The preparations were performed in groups 1 and 2 with a high-speed drill (HD), in groups 3 and 5 with Er:YAG laser, and in groups 4 and 6 with Er,Cr:YSGG laser. The specimens were restored with resin composite associated with an etch-and-rinse two-step adhesive system (Single Bond 2 [SB]) (groups 1, 3, 4) and a self-etching adhesive (One-Up Bond F [OB]) (groups 2, 5, 6). After storage, the specimens were polished, thermocycled, immersed in 50% silver nitrate tracer solution, and then sectioned longitudinally. The specimens were placed under a stereomicroscope (25X) and digital images were obtained. These were evaluated by three blinded evaluators who assigned a microleakage score (0 to 3). The original data were submitted to Kruskal-Wallis and Mann-Whitney statistical tests. RESULTS: The occlusal/enamel margins demonstrated no differences in microleakage for all treatments (p > 0.05). The gingival/dentin margins presented similar microleakage in cavities prepared with Er:YAG, Er,Cr:YSGG, and HD using the etch-and-rinse two-step adhesive system (SB) (p > 0.05); otherwise, both Er:YAG and Er,Cr:YSGG lasers demonstrated lower microleakage scores with OB than SB adhesive (p < 0.05). CONCLUSION: The microleakage score at gingival margins is dependent on the interaction of the hard tissue removal tool and the adhesive system used. The self-etching adhesive system had a lower microleakage score at dentin margins for cavities prepared with Er:YAG and Er,Cr:YSGG than the etch-and-rinse two-step adhesive system.

Investigation of five α-hydroxy acids for enamel and dentin etching: Demineralization depth, resin adhesion and dentin enzymatic activity.

OBJECTIVES: Surface conditioning of enamel and dentin is a key step during adhesive restorative procedures and strategies. The aim of this study was to investigate the effectiveness of five α-hydroxy-acids (AHAs) as enamel and dentin surface etchants. METHODS: Enamel and dentin specimens were prepared from human molars to determine the depth of demineralization by optical profilometry (Δz), the resin bond strength to enamel and dentin (µTBS), the micro-permeability of dentin-resin interfaces, and the gelatinolytic activity of dentin matrix induced by AHAs [glycolic (GA), lactic (LA), citric (CA), malic (MI) and tartaric (TA)] and controls [phosphoric (PA) and maleic (MA)]. All acids were prepared at 35% concentration. Adhesion studies employed Adper Single Bond Plus bonding system. Data were individually processed and analyzed by ANOVA, post-hoc tests and Pearson correlations (α = 0.05). RESULTS: AHA exhibited statistically lower depth of demineralization of enamel and dentin (average 4 fold) than controls (p < 0.001). In enamel, MA and PA etching resulted in higher µTBS than AHA groups (p < 0.001). In dentin, GA, TA, CI and LA etching resulted in statistically similar µTBS than PA (p < 0.05). The hybrid-layer (HL) thickness and interfacial micro-permeability intensity were statistically lower for AHA groups (p < 0.05). A significant positive correlation was observed between the intensity of micro-permeability and the thickness of HL (p < 0.05). AHA etchants elicited lower dentin enzymatic activity than controls (p < 0.05). SIGNIFICANCE: AHAs effectively etched enamel and dentin surfaces. In particular, GA and TA resulted in suitable µTBS and sealing ability as well as induced less gelatinolytic activity in dentin than PA and MA.

Influence of oil contamination on in vitro bond strength of bonding agents to dental substrates.

PURPOSE: To evaluate the influence of cleaning procedures (pumice, anionic detergent and both procedures together) on the tensile bond strength of etch-and-rinse and self-etch adhesive systems to bovine enamel and dentin in vitro. METHODS: Eighty non-carious, bovine incisors were extracted, embedded in acrylic resin to obtain enamel/dentin specimens. Flat bonding surfaces were obtained by grinding. Groups were divided according to substrate (enamel or dentin), adhesive system [etch-and-rinse, Adper Single Bond 2 (SB) or self-etch, Clearfil Protect Bond (PB)]; and cleaning substances (pumice, anionic detergent and their combination). The teeth were randomly divided into 20 groups (n=8): G1--Enamel (E) + SB; G2--E + oil (O) + SB; G3--E + O + Pumice (P) + SB; G4--E + O + Tergentol (T) + SB; G5--E + O + P + T + SB; G6--E + PB; G7--E + O + PB; G8--E + O + P + PB; G9--E + O + T + PB; G10--E + O + P + T + PB; G11--Dentin (D) + SB; G12 D + SB + O; G13--D + SB + O + P; G14--D + SB + O + T;G15--D + SB + O + P + T; G16--D + PB; G17--D + O + PB +; G18--D + O + P + PB; G19--D + O + T + PB; G20--D + O + P + T + PB. Specimens were contaminated with handpiece oil for 5 seconds before bonding. Adhesive systems and resin composite were applied according to manufacturers' instructions. Specimens were tested in tension after 24 hours of immersion using a universal testing machine at a crosshead speed of 0.5 mm/minute. Bond strengths were analyzed with ANOVA. Failure sites were observed and recorded. RESULTS: Tensile bond strength in MPa were: G1 (23.6 +/- 0.9); G2 (17.3 +/- 2.2); G3 (20.9 +/- 0.9); G4 (20.6 +/- 0.5); G5 (18.7 +/- 2.3); G6 (23.0 +/- 1.0); G7 (21.5 +/- 2.4); G8 (19.9 +/- 1.3); G9 (22.1 +/- 1.2); G10 (19.1 +/- 1.2); G11 (18.8 +/- 1.3); G12 (15.7 +/- 2.1); G13 (17.8 +/- 3.3); G14 (15.3 +/- 2.9); G15 (15.6 +/- 1.9); G16 (14.7 +/- 2.3); G17 (5.5 +/- 0.9); G18 (19.3 +/- 1.8); G19 (15.6 +/- 1.6); G20 (20.3 +/- 3.9). Statistical analysis showed that the main factors substrate and cleaning were statistically significant, as well as the triple interaction between factors of variance. However, the factor adhesive system did not show statistical difference. Oil contamination reduced bond strengths, being less detrimental to enamel than to dentin. Etch-and-rinse (SB) and two-step self-etch (PB) systems had similar bond strengths in the presence of oil contamination. For etch-and-rinse (SB), the cleaning procedures were able to clean enamel, but dentin was better cleaned by pumice. When self-etch (PB) system was used on enamel, anionic detergent was the best cleaning substance, while on dentin the tested procedures were similarly efficient.

Bonding efficiency and durability: current possibilities.

Bonding plays a major role in dentistry nowadays. Dental adhesives are used in association with composites to solve many restorative issues. However, the wide variety of bonding agents currently available makes it difficult for clinicians to choose the best alternative in terms of material and technique, especially when different clinical situations are considered. Moreover, although bonding agents allow for a more conservative restorative approach, achieving a durable adhesive interface remains a matter of concern, and this mainly due to degradation of the bonding complex in the challenging oral environment. This review aims to present strategies that are being used or those still in development which may help to prevent degradation. It is fundamental that professionals are aware of these strategies to counteract degradation as much as possible. None of them are efficient to completely solve this problem, but they certainly represent reasonable alternatives to increase the lifetime of adhesive restorations.