[Histomorphological effects of Nd:YAG laser for debonding ceramic brackets on rabbit pulp].

OBJECTIVE: Ceramic brackets debonding by Nd:YAG laser is based on the thermal effect of laser, which may cause injury of the pulp tissue. In this study, the histological changes of pulp tissue that subjected to Nd: YAG laser irradiation with different power and time were observed. METHODS: 20 New Zealand rabbits were included in this study. Ceramic brackets were bonded to the 4 incisors as routine. The ceramic brackets of left upper teeth that debonded mechanically were used as control group, while the brackets of right upper, left lower and right lower incisors were debonded by laser with 3 W 3 s (group A), 2 W 5 s (group B) and 5 W 2 s (group C) energies, respectively. The teeth were pulled out at 5 minutes, 1 day, 3 days, 1 week and 1 month after the debonding operations. Slides prepared from the pulp tissues of the debonded teeth were used to evaluate the injury of laser. RESULTS: In comparison with the control group, pulp tissue of teeth that exposed to laser with different energy for 5 minutes showed mild capillary dilation. One day later, group A, B and C showed moderate capillary dilation, and group C also showed moderate infiltration. At 3 days, inflammation was disappeared in group B, whereas capillary dilation was found in group A. Hemorrhage and inflammation cells infiltration were found in group C. At 1 week, alleviation of capillary dilation was found in group A but not in group C. One month later, inflammation disappeared in group A, while pulp tissue in group C showed mild edema and capillary dilation. CONCLUSION: Nd:YAG laser of high energy may cause injury of the pulp tissue during debonding. Laser energy of 3 W 3 s could effectively debond ceramic brackets without irreversible pulp injury.

Development of a new sampling medium for bioaerosols.

OBJECTIVE: To develop a new sampling medium for detecting of bioaerosols. METHODS: The sampling media were tested by using Escherichia coli, Staphylococcus aureus and Serratia marcescens under static and active conditions, preliminary applications were performed using AGI-10 and high volume sampler. RESULTS: The average recovery rates were raised to 24.7%, 58.2%, 40.5%, 44.1%, 20.5%, and 15.4%, respectively in six consecutive experiments under static condition for 60 min at room temperature. Four kinds of sampling media were singled out after static experiments, which were referred to as "samplutions" PD1, PX2, TD1, and TX2, respectively. Under the active condition, the protective efficacy of PD1, PX2, TD1, and TX2 was 226% (153/47), 553% (111/17), 150% (120/48), and 268% (419/114), respectively. CONCLUSION: The samplutions have some effects on the subsequent nucleic acid detection, which could be avoided by employing standard nucleic acid extraction procedure. The newly developed samplution can be applied to the detection of bioaerosols.

Genetic variations in the pgm locus among natural isolates of Yersinia pestis.

A PCR-based screening method was used to study the genetic variations of the pgm locus among natural isolates of Yersinia pestis from China. Our results indicate that genetic variations in the pgm locus are well correlated with biovars of Y. pestis and plague foci, suggesting that the pgm locus plays a role in Y. pestis adaptation to its environment. The gene encoding two-component regulatory system sensor kinase became a pseudogene in all strains of biovar Orientalis due to a thymidine deletion, while it is intact in all the strains of the other biovars. Only strains from Foci H and L are the same as Yersinia pseudotuberculosis in that they have an intact transmembrane helix in the sensor kinase protein, which is lost in all the other strains because of the 18 bp in-frame deletion. The IS100 element that flanks the 39 terminus of the pgm locus was inserted into the chromosome during the within-species microevolution of Y. pestis, which is absent in strains from Foci G, H and L and also in Y. pseudotuberculosis. This fact indicates that the strains from these three foci are of an older lineage of Chinese Y. pestis. It is this IS100 element's absence that maintained high stability of the pgm locus in the Y. pestis strains from these three foci. The IS285 element insertion in the pigmentation segment and the IS100 element insertion in the downstream flanking region of the pgm locus are only present in strains from Foci H and L. The flanking region outside the 59 terminus of the upstream IS100 element is identical in the strains from these two foci, which is different in the other strains. All of these unique characteristics suggest that they are of a special lineage of Chinese Y. pestis.

[Comparison on shear bond strength of Edgewise brackets bonding with three orthodontic adhesives against salivary contamination].

OBJECTIVE: To compare the shear bond strength and ARI score of Edgewise brackets bonding with three adhesives under moist and dry conditions after salivary contamination. METHODS: Sixty extracted human premolars were randomly and equally divided into 3 groups. Edgewise brackets were bonded directly with composite resin, super bond C&B and single component adhesive under moist and dry conditions after salivary contamination. The shear bond strength and ARI score were measured and recorded. RESULTS: The shear bond strength of Edgewise brackets bonding with composite resin and single component adhesive under moist condition after salivary contamination decreased significantly and it can't meet the requirement of orthodontic therapy (6-8 MPa) while that under dry condition can. Super bond C&B can meet the requirement of orthodontic therapy on both conditions. CONCLUSION: Super bond C&B can be used under both moist and dry conditions after salivary contamination. Composite resin and single component adhesive can only be used under dry condition after salivary contamination.