[Occupational protection effect of two protective devices for manual cleaning and oiling of dental handpieces on operators].

Objective: To explore the occupational protective effect of different protective devices on the operators during manual cleaning and oiling of dental handpieces, and to provide a basis for the selection of appropriate protective methods. Methods: From November 2020 to December 2021, 20 high-speed dental handpieces of the same brand were selected and randomly divided into disposable protective bag group and small aerosol safety cabinet group by drawing lots, with 10 in each group. After recording the model, they were distributed to the clinical fixed consulting room for use, and were collected by specially-assigned personnel every day for manual cleaning under the protection of the two devices. By measuring the number of airborne colonies, the concentrations of particulate matter and the satisfaction of operators, the occupational protection effect of the two protective devices on operators was evaluated. Results: Under the protection of the two devices, the average number of airborne colonies after operation was less than 1 CFU/ml. When no protective device was used, the number concentration of particulate matter produced during operation was (21595.70±8164.26) pieces/cm(3). The number concentrations of particles produced by disposable protective bag group [ (6800.24±515.05) pieces/cm(3)] and small aerosol safety cabinet group [ (5797.15±790.50) pieces/cm(3)] were significantly lower than those without any protective device (P<0.001). The number concentration of particle matter of small aerosol safety cabinet group was significantly lower than that of disposable protective bag group (P<0.001). In the satisfaction evaluation of operators, small aerosol safety cabinet group [ (3.53±0.82) points] was significantly better than disposable protective bag group [ (2.23±1.10) points] (P<0.001) . Conclusion: The use of small aerosol safety cabinet during manual cleaning and oiling of dental handpieces has good protective effect, superior safety performance and strong clinical applicability, and has advantages in occupational protection of clinical operators.

[Effect of three types of rapid maxillary expansion: a three-dimensional finite element study].

Objective: To evaluate the transverse displacement, stress distribution and tendency of change in tooth, alveolar bone and mid-palatal suture using three kinds of rapid maxillary expansion methods. Methods: Cone-beam CT image data was obtained by scanning skulls of a volunteer. Three-dimensional models of maxillary complex were re-established using Mimics and Geomagic Studio and models of Hyrax expander, Haas expander and miniscrew-assisted rapid palatal expander (MARPE) were established using ANSYS Workbench. Stress distribution, displacement and tendency of change in tooth, alveolar bone and mid-palatal suture were evaluated. Results: Hyrax expander brought 0.105 mm lateral displacement of crown, 0.022 mm mid-palatal suture width increase, wedge opening and clockwise rotation tendency of maxilla. Haas expander created uniform stress distribution, 0.216 mm lateral displacement of crown, and 0.031 mm mid-palatal suture width increase. In MARPE model, the lateral displacement of crown was 0.267 mm, and mid-palatal suture width increased 0.315 mm. The maximum of mid-palatal suture expansion and stress distribution appeared in the middle region, and maxilla had tendency of counterclockwise rotation. Conclusions: The lateral changes of teeth and bones brought by MARPE were the most significant. Haas expander had some advantages in comparison with Hyrax.