Effects of three at-home bleaching agents on enamel structure and structure-related mechanical properties / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the effects of three differently concentrated at-home bleaching agents on the structure and the structure-related mechanical properties of human enamel.</p><p><b>METHODS</b>Sixty enamel specimens were randomly divided into four groups and treated with 10% carbamide peroxide (CP), 15% CP, 20% CP and distilled water, respectively. The bleaching process was 8 h/day for 14 consecutive days. Baseline and final atomic force microscopy (AFM) surface detection, Raman spectroscopy, attenuated total reflectance-infrared spectroscopy (ATR-IR), microhardness and fracture toughness (FT) measurements were carried out before and after bleaching experiments.</p><p><b>RESULTS</b>CP didn't change the morphology of enamel. Meanwhile, the three bleached groups and the control group had no significant difference in root mean square detection (P = 0.774), ν(2)CO(3)(2-) : ν(1)ν(3)PO(4)(3-) (P = 0.263) and microhardness (P = 0.829). The percentage of relative Raman intensity in the three bleached groups and the control group were (105.74 ± 11.34)%, (104.46 ± 8.83)%, (99.52 ± 9.32)% and (97.62 ± 7.46)%, respectively. There was no significant difference among them (P = 0.062). However, the percentage of laser-induced fluorescence in the three bleached groups and the control group were (20.86 ± 7.23)%, (22.14 ± 7.34)%, (21.10 ± 7.59)% and (100.78 ± 3.70)%, respectively. There was significant difference between either of the bleached groups and the control group (P < 0.001). Moreover, FT declined significantly in the three groups (P = 0.024, P = 0.005, P = 0.013) when compared with the control group.</p><p><b>CONCLUSIONS</b>Under in vitro condition, three differently concentrated at-home bleaching agents wouldn't induce the demineralization and the decline of microhardness on enamel. However, the decrease of FT on enamel seemed to be inevitable after bleaching.</p>

The preparation of nano-hydroxyapatite and preliminary observation on its effects on the occlusion of dentinal tubule / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To synthesize nano-hydroxyapatite (nano-HA) and evaluate its effect on the occlusion of dentinal tubules in vitro, and therefore provide evidence for the clinical application.</p><p><b>METHODS</b>(NH(4))(2)HPO(4) and Ca(NO3)2 were used to form nano-HA, which was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectrometer (FTIR) and X-ray diffractometer (XRD) respectively. Twenty-four dentin slabs were obtained from 8 healthy third molars and randomly divided into 3 groups, which were control group, casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) group, and nano-HA group. After the CPP-ACP and nano-HA were topically applied to the slabs of two study groups twice a day for 7 days, the surface of slab dentin was observed using SEM.</p><p><b>RESULTS</b>SEM, TEM, FTIR, and XRD tests showed that nano-HA was synthesized successfully. SEM observations revealed that the sealing of dentinal tubules of nano-HA group was extremely high when compared with those of control and CPP-ACP group.</p><p><b>CONCLUSIONS</b>In comparison with CPP-ACP, nano-HA could occlude dentinal tubules more effectively in vitro.</p>