| Summary: | 碩士 === 中國醫藥大學 === 醫學研究所碩士班 === 95 === More and more people are showing great concerns about the functions and aesthetics of their teeth and therefore asking for orthodontic treatment. Regular orthodontic treatment ideally takes about one or two years to finish. During the treatment we have to utilize many orthodontic appliances in order to realign the teeth. It’s quite difficult for patients to maintain good oral hygiene during the procedure. If we can find a way to decrease total orthodontic treatment time, it would help patients not only decrease the incidence of dental diseases like caries or periodontitis but also reduce discomfort during the treatment. In our clinical practice of orthodontic treatment, closing space performed by elastic chains is the most time-consuming procedure because elastic chains always degrade with time and we only replace them on a regular one-month recall. If we learn more about the force decay pattern of the elastic chains and replace them before they completely lose their elasticity, the total treatment time can be shortened.
One hundred and twenty (120) pieces of Tomy super chains (heavy force, short span) containing 8 rings on each piece were extended on 24 customized acrylic plates. All the samples were divided into four groups and each group had 30 pieces of elastic chains. Group 1 (group M) was immerged into 37℃ water bath. Group 2 (group T) was immerged into the same water bath but suffered from thermocyling (15-45℃) three times a day. Group 3 (group P) was also immerged into the same water bath but suffered from pH variations (pH 4.9-7.3) three times a day. The last group was placed in dry air under room temperature (group A, control). The force was examined by force gauge (Algol HF-10, Japan) at six intervals (4d, 7d, 11d, 14d, 18d, 21d). Statistic analysis (one-way ANOVA) was performed to compare the differences among these groups.
The results revealed A group always preserved more force level than the other three groups during 21days, while there was no obvious difference among the other three groups (M, T, and P groups). Elastic chains lost their force rapidly at the first time point when they were stretched, no matter under what kind of environment they were in. T group showed a consistent force decay pattern. This may represent that thermocycling has greater influence upon force decay than the other factors. P group had very rapid force decay in the first week (the first two time points) than the others. This means pH variations may influence the force level mainly in the initial stage. All the groups preserved a force level of more than 228.4 gm (the lowest one was T group), which is enough to realign a tooth. So it is not necessary to change the elastic chains within 3 weeks according to our research results.
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