To examine the cytotoxicity of calcium hydroxide on human umbilical cord mesenchymal stem cells (HUCMSC) to understand the characteristics for use in regenerative dentistry procedures especially regenerative endodontics. Material and Methods: HUCMSC was isolated, cultured, and confirmed by flow cytometry. The biological characteristics, such as cell morphology, proliferation, and protein expression, were screened. To check the cytotoxicity, HUCMSC was cultured and divided into two groups, the control group (cultured in minimum essential medium (MEM) alpha) and calcium hydroxide group (cultured in MEM alpha and calcium hydroxide). Methyl-thiazole-tetrazolium (MTT) assay was done on different concentrations of calcium hydroxide (0.39 to 25 µg/mL) and the cells were observed and counted. One-way ANOVA test was used with a significance level set at 5%. Results: Flow cytometric analysis confirmed positive of CD73, CD90, CD105, negative of CD45 and CD34. A significant difference was found between the concentration of 6.25 and 3.125 µg/mL (p=0.004). There was no significant difference among 6.25, 12.5 and 25 µg/mL concentrations. There was also no significant difference among 0.39, 0.78, 1.56, and 3.125 µg/mL concentrations. Conclusion: Even though calcium hydroxide is a medicament of choice in clinical endodontics, it decreases the viability of HUCMSC. The lower the concentration of calcium hydroxide, the higher the viability of HUCMSC.

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Background: There are two kinds of retainers: removable retainer and fixed retainer. Removable retainer is an orthodontic retainer which can be inserted and removed by the patient, whereas fixed retainer is bonded permanently on teeth, it cannot be removed by the patient. It is important to know which retainer that most effective based on the existing case. Purpose: To identify the comparison between removable and fixed retainers in orthodontic treatment. Review: Hawley retainer, Beggs retainer, clip on retainer, Kesling’stooth positioners and invisible retainer  are removable retainers whereas fixed retainers include banded retainer, bonded retainer and band & spur type retainer. Comparison between removable and fix retainer can be evaluated from several aspects such as: cost, aesthetics, fabrication process, durability, occlusion, hygiene and convenience of use. Conclusion: Whether removable or fixed retainers can be effectively used to prevent relapse post orthodontic treatment depending onthe existing case.

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