To study the blocking effect and abrasion resistance of hydroxyapatite (HA) with differentparticle sizes and morphologyies on dentinal tubules from the qualitative and quantitative aspects.

Dentindiscs were etched and divided into 4 groups randomly: 20 nm HA group; 30 nm HA group; 12 μm HA group; controlgroup (without any experimental treatment). Each group was brushed with correspondent materials for 7 days. Then, thedentin disk was divided into two parts, the one was detected by the scanning electron microscopy (SEM); the other wasobserved by SEM after toothbrush abrasion test. The Image-Pro Plus 6.0 image analysis software was used to calculatethe plugging rate of dentinal tubules.

SEM showed that the blockage is granular, the plugging rate of the den-tinal tubules were about 82% to 96%. 30 nm HA group (short rod) range the first in the average plugging rate, followedby the 20 nm HA group (needles) and 12 μm HA group (spherical). After mechanical brushing for 7 days, SEM imagesshowed that deposited layer in each group was smooth and compact, and more than 63% of the tubules still had beenblocked.

HA with different particle sizes and morphologies had good plugging effect and abrasion resis-tance on dentine tubules. The blocking effect of HA was affected not only by particle size but also by the morphology.

To establish an animal model that clinically conforms to the characteristics of severe alveolar ridge atrophy.

Beagle dogs were used as experimental subjects. Bilateral fourth premolars and first molars in mandible were extracted. A horizontal groove was made on alveolar ridge which was 8 mm from the cemento-enamal junction of mandible third premolar and second molar. Rongeur was used to remove the alveolar bone above this groove and bone chisel was used to level the bone-free area. A box-shaped defect cavity of the size 25 mm × 8 mm was formed with sterile silicone prosthesis implanted. After careful suture we waited for the subjects to heal naturally. Eight weeks after operation, CBCT examination was performed.

Eight weeks after bone remodeling the top of alveolar ridge of operation area appeared to be a circular arc. The average distance from the bottom of the ridge to inferior alveolar nerve canal was 2.5 mm.

This study successfully established the Beagle dog animal model for severe alveolar ridge atrophy and laid the foundation for experiments on vertical bone augmentation.

To investigate the effects of X-ray irradiation on the proliferation and protein secretion in vitro in a cultured mouse osteoblast precursor cell line (MC3T3-E1) and to provide a basis for the prevention and treatment of radiation-induced bone injury.

Mouse osteoblast precursor cells (MC3T3-E1) in the logarithmic growth phase were divided into a 0 Gy control group, 2 Gy group, 4 Gy group and 8 Gy group according to the irradia-tion dose. The corresponding dose of X-rays was applied, and the changes in cell morphology after irradiation were observed. Cell proliferation was detected by the CCK-8 method, and alkaline phosphorus was detected at 7 days after irradiation. The alkaline phosphatase (ALP) activity and expression of secreted proteins were detected by high-throughput protein chip technology. The differential expression of proteins due to radiation damage was screened and verified by an ELISA.

After irradiation, the soma and nucleus of MC3T3-E1 cells were enlarged. Compared to the control group, the cell proliferation rates of the 4 Gy and 8 Gy groups were significantly decreased starting at 3 days in culture (P < 0.05), and the cell proliferation decreased in a dose-dependent manner. After 7 days of culture, the ALP activity in the cells of each irradiated group was lower than that of the control group, and the difference was statistically significant (P < 0.05). Compared to the control group, 36 differentially expressed proteins were found in the supernatant after irradiation. Among them, the content of regulated upon activation, normal T cell expression and secreted factor (RANTES) was significantly increased in a dose-dependent manner.

A certain dose of irradiation can inhibit the proliferation of mouse osteoblast precursor cells (MC3T3-E1), and RANTES may be an important signaling factor induced by radiation damage.

To observe the effect of different etching time of citric acid on enamel blocks to acquire a reliable in vitro model for early enamel caries, and explore more effective experiment method for enamel demineralization.

Human premolars were selected and made into enamel blocks. The morphologies of enamel blocks surfaces etched by 10% citric acid for different time periods (90 s, 120 s, 150 s) and partially saturated acid buffer demineralization system for a week were observed by scanning electron microscope. And the surface micro hardness of these specimen before and after demineralization were tested by the micro hardness tester.

After demineralization, enamel surface had an obvious acid etching appearance. In the 90 s etching time group, only a small part of enamel prism lattice was demineralized and dissolved, and the ability of demineralization was limited. In 120 s etching time group, the morphology of enamel blocks surface was similar to natural early enamel lesions, like the honeycomb. In the 150 s etching time group, the enamel surface had an acid corrosion damage morphology, and it was excessive etched. However, the demineralization effect of partially saturated acid buffer demineralization system was relatively low.

Citric acid has a strong etching effect, and its ability of demineralization is enhanced with the extension of time. The model of early enamel lesions can be obtained by 10% citric acid for 120 s.