| Objective:The aim of this study was to observe and evaluate the biomineralization and dentinal tubules occlusion abilities of the generation 3.5 carboxyl-terminated polyamidoamine dendrimer (G3.5 PAMAM-COOH) on the demineralized dentinal tubules, and to provide experimental basis for the treatment of dentin hypersensitivity.Methods:The first experiment (in vitro):forty sensitive dentin models from extracted sound human third molars were divided into four groups (Group A, B, C and D) randomly. Group A to D were treated with G3.5 PAMAM-COOH for a period of time (0min,lmin,30min and 60 min) respectively and subsequently immersed into the artificial saliva for 2 weeks. Finally, the binding capability between G3.5 PAMAM-COOH formulation and dentine surface were characterized by Fourier Transform Infrared Spectroscopy (FT-IR). The morphology of dentin surface were observed by Scanning Electron Microscope (SEM). Energy Dispersive Spectrometer (EDS) and X-Ray Diffraction (XRD) were performed on dentine samples to confirm the chemical composition of the newly generated crystals.The second experiment (in vivo):1 mm-thick dentin slices were obtained from 50 third molar teeth. Those dentin slices were established demineralization dentin models with 37% phosphoric acid gel. The experimental slices were treated with G3.5 PAMAM-COOH for 60min, while the control groups were treated with the deionized water for 60min. Then the dentine models were sutured to the interior side of the rat’s cheeks, that was immersed in the rats’ saliva for 2,4,6 weeks respectively. Then some parts of specimens were treated with 37% phosphoric acid gel for 30s, and the other specimens were treated with ultrasonic oscillation for 5 min. Finally, the morphology of the dentin surface were observed by Scanning Electron Microscope (SEM). In addition, the differences in the samples of dental slices between the 2 groups were also detected by the microhardness test.Results:The first experiment (in vitro):FT-IR results showed that the binding capability between G3.5 PAMAM-COOH formulation and dentine surface was so strongly to resist the water scour. SEM results showed that the minerals on the dentine treated with G3.5 PAMAM-COOH were formed increasingly as time went on, and that the dentinal tubules were occluded partially at last. EDS showed that the Ca/P ratio of group B (1.68±0.039), group C (1.67±0.034) and group D (1.69±0.024) was significantly higher than those in the group A (1.62±0.039) respectively (P<0.05). However, there was no significant difference among the groups of B, C and D (P>0.05). The XRD spectrum exhibited hydroxyapatite (HA) analogue formated on the surface of demineralization dentin after 2 weeks biomineralization treatment.The second experiment (in vivo):SEM results showed that a deposition of some irregular crystalline attached on dentine surface of both two groups. However, the dentinal tubules were occluded by flake-like crystalline in the B group compared to the A group after treating with 37% phosphoric acid gel. After ultrasonic cleaning for 5min, the SEM showed that the minerals on the dentine treated with G3.5 PAMAM-COOH were formed gradually as time went on, and that the dentinal tubules were occluded effectively at last. The microhardness test suggested that the microhardness of the experimental group [69.95±6.53 HV] was significantly higher than the control group [49.75±5.44 HV] (P<0.05).Conclusions:1. G3.5 PAMAM-COOH had an excellent binding capacity with demineralized dentine.2. G3.5 PAMAM-COOH possessed high biomineralization ability and displayed favourable effects on blocking the open dentinal tubules.3. The hydroxyapatite-like layer on the demineralized dentine surface induced by G3.5 PAMAM-COOH had an excellent resistance to 37% phosphoric acid and mechanical challenge procedures.4. G3.5 PAMAM-COOH may be used for the future treatments of dentin hypersensitivity under certain condition. |
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