[Cyclic strain promotes migration of human periodontal ligament cell via extracellular signal-regulated kinase (ERK) signaling pathway].

OBJECTIVE: To study the effect of cyclic strain on migration of human periodontal ligament cell(hPDLC) and underlying mechanism. METHODS: The cultured hPDLC were subjected to 10% or 20%-elongation magnitude cyclic strain at frequency of 0.1 Hz by FX-4000T system for 6 or 24 hours-duration respectively, while the static group serves as control. hPDLC migration was assayed by wound healing method. The expressions of matrix metalloproteinases-9 (MMP-9) and p-ERK1/2 in hPDLC without or with cyclic strain were analyzed by Western blotting. To investigate the effect of ERK signaling pathway and MMP-9 on migration of hPDLC, the cells were incubated with PD98059, a specific extracellular signal-regulated kinase (ERK) kinase inhibitor, or doxycycline, a MMP inhibitor. Then the expressions of p-ERK1/2 and MMP-9 and hPDLC migration were analyzed. RESULTS: In wound healing tests, the migration of hPDLC exposed to 10% or 20%-cyclic strain at 0.1 Hz-frequency for 6 hours was not apparent but became significantly different for 24 hours (P < 0.05) compared to control. Furthermore, the 20%-elongation magnitude of cyclic strain had more remarkable effect on migration of hPDLC than 10%-elongation magnitude at 24 hours-duration (P < 0.05). Cyclic strain obviously increased the expression of MMP-9 in hPDLC (P < 0.05). PD98059 could repress not only the activation of p-ERK1/2 but also the expression of MMP-9 induced by cyclic strain in hPDLC. The migration of hPDLC enhanced by cyclic strain was repressed by DOX or PD98059 in wound healing tests. CONCLUSIONS: Cyclic strain promotes the migration of hPDLC through activating ERK signaling pathway and inducing the expression of MMP-9.

[The crown inclination of the teeth and its clinical value].

The crown inclination, representing an angle formed by the clinical crown axis and a line which bears 90 degrees to the occlusal plane, reflects the labiolingual or buccolingual inclination of the long axis of the crown. The crown inclination is related to the races. And it is compensated by different vertical or sagittal jaw relationships. It plays an important role in fine occlusal relationship and achieving functional, artistic and stable treatment goal. The torque design of the straight wire bracket is based on the normal crown inclination. There is much discrepancy in the torque design of the different straight wire bracket because of the different race and philosophy. This review gave a brief introduction of the influential factors, the clinical meaning of the crown inclination and the torque design of the different bracket system.

[Clinical survey of the association between age and maturation of cervical vertebra in 216 adolescents in Shanghai municipality].

PURPOSE: To investigate the relationship between age and maturation of cervical vertebra in 216 adolescents in Shanghai municipality. METHODS: 216 adolescents from 10 to 20 years old were investigated by lateral cephalometric radiographs. The growth status and the relationship of C2- C5 cervical vertebra were evaluated by SAS 6.12 software package with Fisher's test. RESULTS: The shapes of cervical vertebra bodies varied in regular manner. Although female went into the young quick growing period 2 years earlier than male, the shape changes had no significant difference between gender.The beginning and the peak of the puberty spurt was with great individual diversity. CONCLUSION: The morphological variation of cervical vertebra can be used as an indicator of skeletal age to determine adolescents' growth and development status.

[The application of headgear in treatment of the upper crowding].

PURPOSE: To evaluate the treatment effect of headgear for distal movement of maxillary first molars to correct the crowding caused by molar anterior displacement. METHODS: 12 crowding cases were treated with headgear combining with fixed appliances if necessary. Cephalometric radiographs and casts were taken and analyzed before and after treatment. SPSS13.0 software package was used for paired-samples t test. RESULTS: The crowding of upper arch was significantly decreased (P<0.05), the amount of crowding decrease was from 3.0 mm to 6.0 mm, the average crowding decrease of 12 cases was 4.52 mm. The decrease was mainly due to the distal movement of the first upper molar, the amount of decrease of Ptm-U6 was from 1.2 mm to 3.5 mm, the average was 2.14 mm. CONCLUSION: Distal movement of the first upper molar by headgear is one of the effective way to solve the upper crowding.

[The effect of premolar extractions on Bolton index.].

PURPOSE: The purpose of this study is to investigate the effect of premolar extractions on Bolton index. METHODS: 213 plaster casts were divided into Bolton big, normal and small groups according to Bolton normal value and one standard deviation. Bolton overall ratios and number of patients in each group were measured and compared between parameters before and after hypothetical premolar extractions. RESULTS: The Bolton overall ratios in each group were smaller after premolar extractions than those before extractions. Part of patients in the Bolton normal group and big group were changed into Bolton small group and normal group after premolar extractions, respectively. CONCLUSION: The Bolton overall ratios decreased after premolar extractions.