In order to evaluate the accuracy of RayPex5 apex locator in measuring root canal working length in clinical practice and to analyze the possible factor resulting in deviation, the working length of total 211 root canals were measured by handing method and electronic method respectively. The exact working length of those root canals were determined by X-ray method. The accuracy rate of electronic method and handing method was 96.21% and 78.2% respectively, with significant difference(P<0.001). The accuracy rate of front teeth group and molar group measured by electronic method was 100% and 92.5% respectively, with significant difference(P<0.05), while the apical paradentitis group and the apical non-paradentitis group, the front teeth group and the premolar group, and the premolar group and the molar group didn' t differ from each other, respectively. The study showed that the accuracy rate of electronic method was high for determining root canal working length, and Raypex 5 apex locator could define apical seat to measure root canal working length accurately.

Objective　The age-related changes of calcitonin gene-related peptide （CGRP）immunoreactive nerve fibers in dental pulp-dentine complex were studied to explore the clinical signs of dental disease and their mechanism of aging.　Methods　Human premolars were collected and divided into 4 groups according to age. All samples were embedded in paraffin and cut into slices. These slices were treated by immunohistochemical reaction of CGRP. The image analysis was used for quantitative analysis and SAS software was used for statistics. 　Results　By aging, the bundle of CGRP-immunoreactive nerve became thin gradually, the numbers of CGRP-immunoreactive nerve branch decreased, the staining density of CGRP-immunoreactive nerve also descended and the distribution of CGRP-immunoreactive nerve fibers into predine was shorter. Image analysis showed that the intergral optical density, volume density, length density and line length of CGRP-immunoreactive nerve were all decreased by aging. The differences in volume density, length density and line length of CGRP-immunoreactive nerve were significant among different groups, but this significance was not found in parameter of integral optical density of CGRP-immunoreactive nerve.　Conclusions　The numbers, branches and extent of distribution of CGRP-immunoreactive nerve fibers decreased by age. The sensitivity of CGRP-immunoreactive nerve may also be lower by age.