[The influence of heat treatment on retention force of magnetic attachments].

PURPOSE: To study the influence of heat treatment on retention force of magnetic attachments. METHODS: Three groups of magnetic attachments (including 10 Magfit EX 400W, 10 Magfit EX 600W, 10 Magfit EX 800W) were fixed on universal test machine respectively. The retention force of each attachment was measured. After heat treatment, their retention force was measured again. The difference of retention force before and after heat treatment was compared using SPSS11.0 software package. RESULTS: The average retention force of magnetic attachments (Magfit EX 400W) was (1.58±0.12)N before heat treatment and (1.64±0.11)N after heat treatment. The average retention force of magnetic attachments (Magfit EX 600W) was (2.67±0.19)N before heat treatment and (2.65±0.14)N after heat treatment.The average retention force of magnetic attachments (Magfit EX 800W) was (3.02±0.25)N before heat treatment and (3.02±0.24)N after heat treatment. The retention force of magnetic attachments had no significant change after heat treatment (P>0.05). CONCLUSION: The magnetic attachments can be treated by waterbath heart treatment in the clinic without significant change of their retention force.

[Efficacy of a dentifrice containing 5% potassium nitrate on dental hypersensitivity].

PURPOSE: To evaluate the efficacy of a dentifrice containing 5% potassium nitrate (test) on dental hypersensitivity compared with the fluoride dentifrice (control) over a 4-week period. METHODS: The study design was a randomized ,double-blinded ,controlled clinical trial. 63 subjects were randomly divided into 2 groups, with 31 were given a 5% potassium nitrate dentifrice (experimental group) and the other 32 given a fluoride dentifrice (control group). Both groups were instructed to brush their teeth twice a day. An air blast stimulus was used to measure the degree of pain using a VAS scale. The data were analysed by the nonparametric Mann-Whitney U test and Wilcoxon-test with SPSS13.0 software package. RESULTS: The VAS (baseline=68.29±8.263, 4-week=31.71±6.378) was significantly reduced over the 4 weeks period in the experimental group (P<0.05). After 4 weeks, VAS in the experimental group was significantly lower than that in the control group(P<0.05). CONCLUSION: The study demonstrates that the dentifrice containing 5% potassium nitrate effectively reduces dental hypersensitivity.