The Effect of Resterilization and Storage Time on Microbial Contamination of Paper/Plastic Pouches
Pachimsawat P, Puangsa-ard Y, Thaweboon S Faculty of Dentistry, Mahidol University, Bangkok, Thailand.
Paper-plastic pouches have become popular packaging materials in dentistry because of their convenience, visible content, and long-term sterility maintenance. While these pouches are recommended for single use, they have been generally reused in Thailand.
Objective: This study aimed to compare the effects of different frequencies (1, 3, and 5 times) of resterilization and storage time on microbial contamination of paper/plastic pouches.
Method: A sample size of 6,720 paper/plastic pouches were used and divided into 4 groups: 1) new pouches, 2) 1 time resterilization, 3) 3 times resterilization, and 4) 5 times resterilization. A filter paper was inserted in each pouch and was used for microbial cultivation to indicate the microbial contamination after sterilization. Three groups of resterilized pouches were measured for microbial contamination and results were compared with new pouches. The experiment procedures were done 7 times and measurement of microbial contamination was done on day 1 and new sets of pouches were measured at different storage periods of 30, 60, 90, 120, 150, 180 days.
Results: The results showed that all filter papers in the new and resterilized pouch groups had no microbial contamination in all study groups with different storage time.
Conclusion: Resterilization, whether 1, 3 or 5 times, had no effect on microbial contamination of paper-plastic pouches. Similarly, the length of storage time from 1 to 180 days had no effect on microbial contamination of paper-plastic pouches. However, this study only focused on the resterilization factor as an efficiency barrier of paper-plastic pouches. Future studies on the reuse of plastic-paper pouches in actual dental practice should look at deterioration factors like handling, storage environment as well as the combination of various factors. At present, the single use of paper/plastic pouches is still recommended.
Key Words: paper/plastic pouches, microbial contamination, resterilization, storage time
Cytotoxicity Evaluation of Thai Herbs between MTT and NRR Assays
Korsuwannawong S, Srichan R, Vajarbhaya L
Research Office, Faculty of Dentistry, Mahidol University, Bangkok, Thailand.
Faculty of Dental Medicine, Rangsit University, Bangkok, Thailand.
Objective: The aim of this study was to compare the cytotoxicity screening assays of Thai herbs between MTT (The dimethylthiazoldiphenyl-tetrazoliumbromide) and NRR (The neutral red release) assays.
Method: Mouse fibroblast (L929) cells were exposed to the concentration of Thai herbs of 0.01%, 0.1%, 0.25% and 0.5% (w/v) in the 96-wells tissue culture plate for 24 h. Cell viability after exposed to Thai herbs was determined by MTT and NRR assays.
Results: The result revealed no significant difference between two assays of cytotoxicity evaluation at the high concentration of Thai herbs (p>0.05). However, more viable cells were found in the minimal concentration of 0.01% evaluated by NRR.
Conclusion: Various assay methods are used for evaluating the cytotoxic effects of chemicals on cultured cells. In general, both the MTT and NRR assays could be performed very effectively. They are equally effective for cytotoxicity screening of Thai herbs at high concentration. However, the MTT solution is hazardous, toxic and may cause heritable genetic defects. Therefore, data from this study shows that NRR assay is recommended for the cytotoxicity evaluation at the minimal concentration of 0.01% (p<0.05).