Effect of Grinding and Polishing Protocols on Surface Roughness, Flexural Strength, and Phase Transformation of High-Translucent 5 mol% Yttria-Partially Stabilized Zirconia.

OBJECTIVES: This study evaluated surface roughness, biaxial flexural strength, and phase transformation of 5Y-PSZ after grinding and polishing with different protocols. MATERIAL AND METHODS: Two commercial 5Y-PSZ, Lava Esthetic (L) and Cercon xt (C), were used and divided into 3 groups: LC and CC represented unpolished control groups; LE and CE were polished with protocol I (EVE DIASYNT® PLUS HP following with EVE DIACERA RA); and LJ and CJ were polished with protocol II (Superfine diamond bur following with Jota ZIR Gloss polishing kit). Surface roughness was evaluated after polishing step-by-step with a contact-type profilometer. After high-gross polishing, the specimens were subjected to biaxial flexural strength test, crystallographic microstructure analysis using an X-ray diffractometer (XRD), and surface micro-topography using scanning electron microscopy (SEM). STATISTICAL ANALYSIS: Surface roughness differences after each step and biaxial flexural strength between groups were evaluated with one-way ANOVA, followed by Bonferroni post-hoc analysis. Changes in surface roughness across four different time points within groups were assessed using one-way repeated measures ANOVA, followed by Bonferroni post-hoc analysis. RESULTS: After high-gross polishing, both polishing protocols showed significantly lower surface roughness than the grinding group (p < 0.05). The LE and CE groups exhibited the highest surface roughness values, which were significant differences from the LJ and CJ groups (p < 0.05). The LE group showed significantly lower biaxial flexural strength compared to the LC group (p < 0.05). However, there was no statistically significant difference in the CE and CJ groups compared to the control group (p > 0.05). Furthermore, all polishing protocols did not change the phase transformation of zirconia. CONCLUSION: Polishing protocol II provided a smoother surface than the protocol I after high-gross polishing, while the biaxial flexural strength of materials remained unaffected.

Effect of ionizing radiation on the mechanical properties of current fluoride-releasing materials.

OBJECTIVES: This study aimed to evaluate the effect of fractional radiation on the mechanical properties of fluoride-releasing materials. MATERIALS AND METHODS: High-viscosity glass ionomer cement (F9), resin-modified glass ionomer cement (F2), glass hybrid restoration (EQ), and bioactive composite (AC) were divided into 3 subgroups: 0, 35, and 70 Gy fractional radiation doses. The specimens were subjected to surface roughness, Vickers microhardness, and compressive strength tests. The chemical components and morphology of the tested specimens were observed via energy dispersive spectroscopy and scanning electron microscopy. The data were analyzed using two-way ANOVA with Bonferroni post hoc analysis. RESULTS: After exposure to fractional radiation, the surface roughness increased in all the groups. F9 had the highest surface roughness, while AC had the lowest surface roughness within the same radiation dose. The Vickers microhardness decreased in F9 and EQ. The AC had the highest compressive strength among all the groups, followed by F2. More cracks and voids were inspected, and no substantial differences in the chemical components were observed. CONCLUSIONS: After fractional radiation, the surface roughness of all fluoride-releasing materials increased, while the Vickers microhardness of F9 and EQ decreased. However, the compressive strength increased only in F2 and AC.

Calcium phosphate ceramic as a model for enamel substitute material in dental applications.

OBJECTIVE: This study aimed to develop enamel substitute material using a mechanochemical technique. MATERIALS AND METHODS: Hydroxyapatite was synthesized with and without tricalcium phosphate under uniaxial pressing of 10 and 17 MPa (HA10, HA17, BCP10, and BCP17), followed by sintering at 1250 °C for 2 h. Human enamel and dentin blocks were used as control groups. The mechanical properties were determined by compressive strength test and Vickers microhardness. The data were analyzed with one-way ANOVA and LSD post-hoc test (α = 0.05). The phase formation and morphology of the specimens were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). RESULTS: HA17 and HA10 had compressive strength values comparable to enamel and dentin, respectively (p > 0.05). The microhardness of all synthesized groups was significantly higher than that of tooth structures (p < 0.05). From the XRD graphs, only the hydroxyapatite peak was observed in the control and HA groups. SEM images showed homogeneous hydroxyapatite grains in all groups, while the BCP groups contained higher porosities. CONCLUSIONS: Both HA10 and HA17 are suitable for use as the inorganic part of dentin and enamel substitutes.

The Effects of Radiotherapy on Microhardness and Mineral Composition of Tooth Structures.

OBJECTIVE: The purpose of this study was to evaluate the microhardness and mineral composition alterations in enamel and dentine after radiotherapy. MATERIALS AND METHODS: Forty human maxillary premolar teeth (20 pairs) were assigned to nonirradiated and irradiated groups, the latter irradiated by fractional radiation to achieve a total dose of 70 Gy. Microhardness measurement was performed on a Knoop microhardness tester. Chemical components were analyzed using energy dispersive spectroscopy and Fourier transform Raman spectroscopy. The morphology was observed using a scanning electron microscope. The microhardness data were analyzed using a paired t-tested and one-way repeated analysis of variance (ANOVA), and the mineral composition data using related-samples Wilcoxon signed rank test and related-samples Friedman's two-way ANOVA by ranks. RESULTS: The irradiated teeth had a significantly lower microhardness in both enamel and dentine compared with the nonirradiated teeth. The irradiated dentine at 50 µm from the external tooth surface at the cemento-enamel junction showed the lowest microhardness compared with other locations. There was no statistically significant difference in calcium:phosphate ratio and chemical components. There was a reduction in protein:mineral ratio in dentine and at the cemento-enamel junction after irradiation. The irradiated teeth exhibited crack lines at the dentine-enamel junction and in dentine. CONCLUSION: Fractional radiation reduced microhardness in both enamel and dentine. The cervical dentine exhibited the highest microhardness reduction compared with other enamel and dentine locations.

Betaine promotes osteogenic differentiation in immortalized human dental pulp-derived cells.

OBJECTIVES: This study aimed to evaluate the effect of betaine (BET) on immortalized human dental pulp stem cell (ihDP) osteogenic differentiation. MATERIALS AND METHODS: hDPs were immortalized using SV40 T-antigen transfection. Characterization, multilineage differentiation, proliferation, cell cycle, colony-forming unit, and cellular senescence were evaluated (n = 4). The effect of BET on ihDP response was assessed (n = 4). Osteogenic differentiation was detected using ALP, ARS staining, and RT-qPCR (n = 4). To investigate the involvement of calcium signaling, the cells were pretreated with either 8-(NN-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) or thapsigargin before BET treatment (n = 6). RESULTS: ihDPs retained similar phenotypic characteristics presented in hDPs but exhibited an increase in cell proliferation and extended culture to passage 25. An increased proportion of cells in S and G2/M phases without senescence was observed in ihDPs. BET (50 mM) treatment significantly increased mineral deposition at 14 days and upregulated ALP, MSX2, BMP2, and RUNX2 expression. TMB-8 pretreatment reduced the effect of BET-induced ihDP osteogenic differentiation, whereas thapsigargin promoted osteogenic differentiation in ihDPs synergistically with BET. CONCLUSION: ihDPs showed superior proliferation ability and a longer life span, which could serve as a promising cell for regenerative dentistry. BET promoted odonto/osteogenic differentiation via intracellular calcium regulation.

Effect of Whitening Toothpaste on Surface Roughness and Colour Alteration of Artificially Extrinsic Stained Human Enamel: In Vitro Study.

Objective: The aim of this study was to compare five toothpastes in terms of alteration of surface roughness and colour of red-wine-stained human enamel over time after brushing simulation. Methods: Stained specimens were randomly divided into five groups (n = 8): Oral-B Gum and Enamel (C), ZACT Stain Fighter (ZW), Colgate Optic White Volcanic Mineral (CW), Oral-B 3D White Luxe Fresh Breath (3DW), and Thepthai (TW). The colour and surface roughness of the specimens were measured after brushing simulation for four durations; two weeks, one month, six months, and twelve months. Abrasive particles in toothpaste were inspected under a scanning electron microscope. Results: Surface roughness was increased in the specimens that underwent brushing simulation in all groups (p < 0.05). ZW (6.33 ± 0.98 µm) exerted the most changes in surface roughness for all durations. Other groups showed similar surface roughness at each time point. ΔE00 and ΔL were increased in all groups until twelve months; however, there were no significant differences between C (ΔE00 = 30.17 ± 4.16, ΔL = 38.19 ± 4.34), CW (ΔE00 = 24.25 ± 10.52, ΔL = 31.12 ± 11.00), and TW (ΔE00 = 29.00 ± 3.96, ΔL = 36.68 ± 4.53) at any time period. Moreover, ZW (ΔE00 = 45.6 ± 8.01, ΔL = 53.03 ± 6.71) and 3DW (ΔE00 = 43.6 ± 7.33, ΔL = 51.03 ± 6.47) exhibited a substantial change and were statistically differed from the other groups after four-weeks. Various characteristics of abrasive particles were inspected under SEM. Conclusion: All five toothpastes increased the surface roughness altered the colour of red wine-stained human enamel over time.