Quantitative assessment of the enamel machinability in tooth preparation with dental diamond burs.

Enamel cutting using dental handpieces is a critical process in tooth preparation for dental restorations and treatment but the machinability of enamel is poorly understood. This paper reports on the first quantitative assessment of the enamel machinability using computer-assisted numerical control, high-speed data acquisition, and force sensing systems. The enamel machinability in terms of cutting forces, force ratio, cutting torque, cutting speed and specific cutting energy were characterized in relation to enamel surface orientation, specific material removal rate and diamond bur grit size. The results show that enamel surface orientation, specific material removal rate and diamond bur grit size critically affected the enamel cutting capability. Cutting buccal/lingual surfaces resulted in significantly higher tangential and normal forces, torques and specific energy (p<0.05) but lower cutting speeds than occlusal surfaces (p<0.05). Increasing material removal rate for high cutting efficiencies using coarse burs yielded remarkable rises in cutting forces and torque (p<0.05) but significant reductions in cutting speed and specific cutting energy (p<0.05). In particular, great variations in cutting forces, torques and specific energy were observed at the specific material removal rate of 3mm(3)/min/mm using coarse burs, indicating the cutting limit. This work provides fundamental data and the scientific understanding of the enamel machinability for clinical dental practice.

[Human ß-defensin-3 regulates the proliferation and the secretion of prostaglandin E2 and matrix metalloproteinase-1 in human gingival fibroblasts].

OBJECTIVE: To observe the effect of human ß-defensin-3 (HBD-3) on proliferation and the secretion of prostaglandin E2 (PGE2) and matrix metalloproteinase-1(MMP-1) in human gingival fibroblasts(HGF). METHODS: The HGF were cultured with tissue-explant method and the fourth-generation HGF were plated in 96-well plate. All groups except the control group were treated with different concentrations of HBD-3 for 7 days. Then the HGF proliferation was evaluated with methyl thiazolyl tetrazolium(MTT) colorimetry and the secretions of PGE2 and MMP-1 at the 12th hours of each group were detected by enzyme-linked immunosorbent assay (ELISA). RESULTS: The result of MTT dynamic monitoring showed that the amount of HGF increased with time in all groups in concentration dependent manner.ELISA showed that the secretions of PGE2 and MMP-1 in 1.0 mg/L HBD-3 group were (350.56 ± 63.96) ng/L and (13.22 ± 0.59) µg/L, significantly higher than those in the control group and 10.0 mg/L HBD-3 group (P < 0.05). CONCLUSIONS: HBD-3 promoted the proliferation of HGF. The low concentration of HBD-3 may play a role in immunoregulation through increasing the secretions of PGE2 and MMP-1.

[Effect of estrogen-deficiency on expression of osteoprotegerin in alveolar bone: experiment with rats with periodontitis].

OBJECTIVE: To investigate the effects of estrogen-deficiency upon the expression of osteoprotegerin (OPG) in alveolar bone so as to clarify the role of estrogen in alveolar bone metabolism. METHODS: Fifty-three SD rats were randomly divided into 3 groups: OVX group (n=18) undergoing bilateral ovariectomy, OVX + E2 group (n=18), undergoing bilateral ovariectomy and subcutaneous injection of estradiol once 3 days since day 2 after the operation, and sham operation group (n=17) undergoing sham operation. Four weeks after the operation periodontal ligature was conducted and high-sugar diet was fed to establish periodontitis models. Four weeks later the rats were killed. The morphological changes and expression of OPG in alveolar bone were observed by light microscopy and immunohistochemistry. RESULTS: All the rats showed sparseness of bone trabeculae in alveolar bone and osteoclasts and lacuna at the surface of alveolar bone, especially the rate of the group OVX. The A values (absorption of the OPG expression) in the alveolar bone of the OVX groups was 27 854 +/- 5246, significantly lower than those of the sham operation group and OVX + E2 group (38 799 +/- 6228 and 37 146 +/- 6394 respectively, both P < 0.05) without significant difference between the sham operation group and OVX + E2 group (P > 0.05). CONCLUSION: Estrogen deficiency decreases the expression of OPG in alveolar bone, and enhances the absorption of alveolar bone.