Objective: To measure the position of the mandibular nerve canal at the mandibular second molar by CBCT image data, analyze the theoretical implantation range of trans-alveolar implantation, and provide a theoretical solution to insufficiency of posterior mandibular bone volume in clinical practice. Methods: Eighty patients with missing mandibular second molars whose vertical bone height of the edentulous area was less than 9 mm were selected for CBCT image measurement, and the distances from the mandibular nerve canal to the buccal cortex, lingual cortex, and alveolar crest were measured to simulate trans-inferior alveolar nerve implantation. The angular range of the buccolingual inclination of the implant was also measured. Results: The distances from the mandibular nerve canal to the buccal cortex, lingual cortex and alveolar crest at the mandibular second molar were(6.913±1.222)mm, (2.859±0.891)mm and (7.991±0.783)mm, respectively. The distance from the mandibular nerve canal to the buccal cortex was significantly greater than that to the lingual cortex. And, 75% of the patients could be implanted by the inferior alveolar nerve. The minimum angle of buccolingual inclination of the simulated implant was 19.360°±7.086°, and the maximum angle was 39.462°±6.924°. Conclusion The mandibular nerve canal at the mandibular second molar is inclined toward the lingual side, which ensures sufficient buccal bone volume. Most patients with severe mandibular atrophy can still adopt implants of conventional length by trans-inferior alveolar nerve implantation to keep a safe distance from the nerve canal.

ObjectiveTo assess the level of internal exposure to PCP in a community population in Shanghai， to investigate the factors affecting the level of PCP， and to analyze the correlation between the exposure and thyroid hormone levels. MethodsA total of 464 residents of a community in Shanghai were selected as the study subjects. A questionnaire survey was conducted to obtain the demographic information， dietary situation， lifestyle and behavioral habits， and disease history of the individuals， and blood samples were collected. Gas chromatography-electron trap was applied to determine the PCP levels in serum. Multicategorical logistic regression analysis was used to analyze the possible influencing factors of PCP exposure in humans. Thyroid hormone levels were used as the dependent variable and serum PCP as the independent variable. Multiple linear regression analysis was used to assess the association between PCP and thyroid hormones in the community population after controlling the confounding factors such as age， gender， literacy， annual personal income， and chronic diseases. ResultsThe detection rate of serum PCP in 464 subjects was 90.3%， and the median serum PCP level was 0.43 μg·L^-1. The differences in PCP levels among different age groups were statistically significant. There were no significant differences in PCP levels among different gender and BMI groups. The study of PCP exposure factors showed that age， frequency of using plastic products， consumption of freshwater fish， type of occupation， annual income， and consumption of tea or coffee were the potential influencing factors for PCP exposure. Among them， age， frequency of using plastic products， consumption of tea or coffee， and consumption of freshwater fish were positively associated with PCP levels， and annual personal income was negatively associated with it. The results of multiple linear regression analysis showed that among men， PCP levels were positively correlated with TSH （b=0.105， 95%CI：0.017‒0.313） and negatively correlated with FT4 （b=-0.026， 95%CI：-0.057‒0.004）， and among women， PCP levels were positively correlated with TSH （b=0.092， 95%CI：-0.211‒0.904） and FT3 （b=0.017， 95%CI：-0.058‒0.230） and negatively correlated with FT4 （b=-0.013， 95%CI：-0.011‒0.037）. ConclusionSerum PCP detection is common among community residents in Shanghai. Different demographic characteristics or behavioral habits may increase or decrease PCP exposure. PCP exposure then affects human thyroid hormone levels.