Effectiveness and cytotoxicity of two desensitizing agents: a dentin permeability measurement and dentin barrier testing in vitro study.

BACKGROUND: When evaluating the efficacy and safety of various desensitizing products in vitro, their mechanism of action and clinical utility should be considered during test model selection. This study aimed to evaluate the effects of two desensitizers, an in-office use material and an at-home use material, on dentin specimen permeability, and their dentin barrier cytotoxicity with appropriate test models. METHODS: Two materials, GLUMA desensitizer (GLU) containing glutaraldehyde and remineralizing and desensitizing gel (RD) containing sodium fluoride and fumed silica, were selected. Human dentin specimens were divided into three groups (n = 6): in groups 1 and 2, GLU was applied, and in group 3, RD was applied and immersed in artificial saliva (AS) for 24 h. Dentin specimen permeability before and after each treatment/post-treatment was measured using a hydraulic device under a pressure of 20 cm H2O. The perfusion fluid was deionized water, except in group 2 where 2% bovine serum albumin (BSA) was used. The representative specimens before and after treatment from each group were investigated using scanning electron microscopy. To measure cytotoxicity, test materials were applied to the occlusal surfaces of human dentin disks under which three-dimensional cell scaffolds were placed. After 24-h contact within the test device, cell viability was measured via 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. RESULTS: GLU significantly reduced the dentin permeability and occluded the dentinal tubules when 2% BSA was used as perfusion fluid. RD significantly reduced dentin permeability and occluded the tubules, but permeability rebounded after AS immersion. GLU significantly decreased cell viability, but RD was non-cytotoxic. CONCLUSIONS: In vitro GLU application induced effective dentinal tubule occlusion only following the introduction of simulated dentinal fluid. RD provided effective tubule occlusion, but its full remineralization potential was not realized after a short period of immersion in AS. GLU may harm the pulp, whereas RD is sufficiently biocompatible.

Oriented face-centered cubic to hexagonal close-packed martensitic transition, grain morphology, and mechanical properties of Co-Cr alloy fabricated by selective laser melting.

STATEMENT OF PROBLEM: Removable partial dentures (RPDs) can be fabricated by selective laser melting (SLM) with different build orientations. How microstructures and mechanical properties of SLM Co-Cr alloy are affected by different build orientations is unclear. PURPOSE: The purpose of this in vitro study was to investigate the phase structures, grain morphology, and mechanical properties of SLM Co-Cr alloy with different build orientations. MATERIAL AND METHODS: SLM Co-Cr tensile specimens were fabricated at orientation angles of 0, 45, and 90 degrees between the building and longitudinal direction named the T0, T45, and T90 design groups (n=14). Mechanical properties were obtained by tensile testing conducted by using a universal testing machine according to the International Organization for Standardization (ISO) 22674. The grains along the longitudinal direction of the specimens and phase structures were observed before and after tensile testing by electron backscatter diffraction. One-way analysis of variance followed by the Bonferroni post hoc test and Kruskal-Wallis test were used for statistical analysis (α=.05). RESULTS: The 0.2% yield strengths in descending order were T90 (870 MPa)>T45 (840 MPa)>T0 (786 MPa) (P<.05); the elongations were T0 (21.8%)>T45 (15.6%)>T90 (8.7%) (P<.05); the ultimate tensile strengths were T45 (1226 MPa)>T90 (1200 MPa)>T0 (1149 MPa) (P<.05). The average grain sizes in the T0, T45, and T90 groups were 22 µm, 18 µm, and 14 µm, respectively. After the tensile test, a face-centered cubic (FCC) to hexagonal close-packed (HCP) martensitic transition was found in each group, and the phase transition area fractions were T0 (38.3%)>T45 (11.4%)>T90 (0.7%). CONCLUSIONS: The FCC to HCP martensitic transition, grain morphology, and mechanical properties of SLM Co-Cr alloy depended on the build orientations. The oriented phase transition and grains affected the anisotropic mechanical properties of SLM Co-Cr alloy.

The evaluation of the desensitization effect of a desensitizing agent and desensitizing toothpastes in vitro.

This study was evaluating how three desensitizing toothpastes used at home influence the effect associated with desensitizing agents after application in the clinic. Fifty dentine disks measure it permeability and 32 dentine disks with similar permeability levels were selected. Following Dental desensitizer treatment, dentine disks were randomly divided into three subgroups (n=10) that received applications of three toothpastes, respectively. The permeability (Lp) of each specimen was measured after each treatment. One specimen was selected from each group for scanning electron microscopy (SEM) observation. After each treatment, the Lp values decreased significantly for each group (p<0.05) and either completely or partially blocked the dentine tubules upon SEM observation. However, no significant differences in Lp values were observed amongst subgroups (p>0.05). After using the Dental desensitizer, Sensodyne, Crest and Colgate desensitizing toothpastes both can continued to reduce the permeability of the dentine disk, and no significant differences were found amongst them.

Effects of two disinfection/sterilization methods for dentin specimens on dentin permeability.

OBJECTIVES: To investigate the effects of two disinfection/sterilization methods on the permeability of dentin specimens. MATERIALS AND METHODS: Forty intact human third molars were freshly extracted and cut, close to the pulp chamber, into dentin disks with a 500-µm thickness. The disks were randomized (n = 20 each) into a 70% ethanol group (acid-etched dentin disks soaked in 70% ethanol for 15 min) and a steam autoclaving group (acid-etched dentin disks autoclaved for 25 min). The permeability (Lp) of each dentin disk was measured before and after either treatment using a hydraulic device, and intra- and inter-group differences in values before and after treatment were analyzed using t tests. Field emission scanning electron microscopy (FE-SEM) micrographs of the dentin surface were acquired and examined. FE-SEM samples were prepared using the critical point drying (CPD) method. RESULTS: Immersion in 70% ethanol increased the Lp values of dentin specimens by 17%, which was not statistically significant. Steam autoclaving significantly reduced dentin permeability by 66% because the dentin collagen mesh became compact and collapsed, as detected by FE-SEM. CONCLUSIONS: The disinfection of acid-etched dentin disks using 70% ethanol for 15 min does not significantly affect dentin permeability, whereas sterilization of acid-etched dentin disks via autoclaving significantly reduces dentin permeability. CLINICAL RELEVANCE: Considering the influences of dentin permeability by disinfection/sterilization methods, the disinfection of the acid-etched dentin disks using 70% ethanol for 15 min could be used for the study related to dentin permeability, while the sterilization of autoclaving could not.

Porous zirconia ceramic as an alternative to dentin for in vitro dentin barriers cytotoxicity test.

OBJECTIVES: This study assessed the potential of porous zirconia ceramic as an alternative to dentin via an in vitro dentin barrier cytotoxicity test. METHODS: The permeability of dentin and porous zirconia ceramic was measured using a hydraulic-conductance system, and their permeability was divided into two groups: high and low. Using an in vitro dentin barrier test, the cytotoxicity of dental materials by dentin and porous zirconia ceramic was compared within the same permeability group. The L-929 cell viability was assessed by MTT assay. RESULTS: The mean (SD) permeability of the high and low group for dentin was 0.334 (0.0873) and 0.147 (0.0377) µl min-1 cm-2 cm H2O-1 and for zirconia porous ceramic was 0.336 (0.0609) and 0.146 (0.0340) µl min-1 cm-2 cm H2O-1. The cell viability of experimental groups which are the low permeability group was higher than that of the high permeability group for both dentin and porous zirconia ceramic as a barrier except for Maxcem Elite™ by porous zirconia ceramic. There was no significant difference between dentin and porous zirconia ceramic in cell viability, within either the high or low permeability group for all materials. The SD for cell viability of the porous zirconia ceramic was less than that of the dentin, across all materials within each permeability group, except for Maxcem Elite™ in the high permeability group. CONCLUSIONS: Porous zirconia ceramic, having similar permeability to dentin at the same thickness, can be used as an alternative to dentin for in vitro dentin barrier cytotoxicity tests. CLINICAL RELEVANCE: In vitro dentin barrier cytotoxicity tests when a standardized porous zirconia ceramic was used as a barrier could be useful for assessing the potential toxicity of new dental materials applied to dentin before applying in clinical and may resolve the issue of procuring human teeth when testing proceeds.

Effects of desensitizing toothpastes on the permeability of dentin after different brushing times: An in vitro study.

PURPOSE: To investigate the effects of three commercially available desensitizing toothpastes on dentin permeability, and compare the efficacy of each product for reducing dentin permeability in the short term according to the frequency and duration of usage. METHODS: 100 dentin discs with no caries were prepared from freshly extracted human third molar teeth. The dentin discs were brushed with three desensitizing toothpastes or with a non-desensitizing toothpaste and distilled water, which served as control. The 100 dentin slices were randomly divided into two groups (n= 50): one group underwent continuous brushing (brushed for 3 minutes continuously), and the other group underwent discontinuous brushing (brushed three times, each time for 1 minute). Then, the two groups were divided into five subgroups (n = 10) for the five brushing applications. Dentin permeability was measured with a hydraulic permeability system before and after brushing. RESULTS: All desensitizing toothpastes reduced dentin permeability significantly after treatment. Sensodyne Repair and Protect (calcium sodium phosphosilicate) and discontinuous brushing reduced dentin permeability significantly compared with continuous brushing. Dentin permeability values showed no significant difference between the three toothpastes after 3 minutes of continuous brushing. When comparing the three toothpastes under discontinuous brushing conditions after 3 minutes, Sensodyne Repair and Protect (calcium sodium phosphosilicate) reduced dentin permeability significantly. CLINICAL SIGNIFICANCE: Sensodyne Repair and Protect (calcium sodium phosphosilicate) and discontinuous brushing reduced dentin permeability significantly compared with continuous brushing. Moreover, brushing with Sensodyne Repair and Protect (calcium sodium phosphosilicate) resulted in the lowest dentin permeability compared with those of the other two toothpastes. These results indicated that Sensodyne Repair and Protect may relieve dentin hypersensitivity.

[Effect of SiO2-ZrO2slurry coating on surface performance of zirconia ceramic].

OBJECTIVE: To evaluate the effect of SiO2-ZrO2slurry coating on surface performance of zirconia ceramic. METHODS: Seventy pre-sintered zirconia discs were randomly divided into seven groups with 10 discs per group. Sample discs in each group received one of the following seven different surface treatments, namely, sintered (group AS), sand blasting after sintered (group SB), coated with slurry of mole ratio of SiO2to ZrO22:1 (group 2SiO2-1ZrO2), coated with slurry of mole ratio of SiO2to ZrO21:1 (group 1SiO2-1ZrO2), coated with slurry of mole ratio of SiO2to ZrO21:2 (group 1SiO2-2ZrO2), coated with slurry of mole ratio of SiO2to ZrO21:3 (group 1SiO2-3ZrO2), coated with slurry of mole ratio of SiO2to ZrO21:4 (group 1SiO2-4ZrO2). Profilometer, X-ray diffractometer (XRD), energy dispersive spectrometer, scanning electron microscopy (SEM) were used to analyze surface performance. RESULTS: The surface roughness of the discs in group AS was lower than those in the other groups [(0.33 ± 0.03) µm] (P < 0.05), there was no statistically significant difference (P > 0.05) among group 2SiO2-1ZrO2[(3.85 ± 0.38) µm], group 1SiO2-1ZrO2[(3.78 ± 0.56) µm] and group 1SiO2-2ZrO2[(4.06 ± 0.48) µm], and no difference (P > 0.05) was observed between group 1SiO2-3ZrO2[(1.02 ± 0.09) µm] and group 1SiO2-4ZrO2[(1.53 ± 0.23) µm] either. However, surface roughness in all coating groups was higher than those in group SB [(0.86 ± 0.05) µm] (P < 0.05). According to the XRD pattern, group AS and all coating groups consisted of 100% tetragonal airconia and monoclinic zirconia was detected at surface of group SB. Contents of surface silicon of coating groups increased significantly, however, no silicon was detected at sample surface of group AS and group SB. SEM showed that zirconia grains of coating exposed since part of silicon was etched by hydrofluoric acid, a three-dimensional network of intergrain nano-spaces was created. CONCLUSIONS: SiO2-ZrO2slurry coating could make surface of zirconia rough and increase Si content without creating monoclinic zirconia.