| 摘要: | 矯正用橡皮圈在固定式矯正裝置治療中扮演了非常重要的角色。目前，矯正醫師常利用顎間橡皮圈從上牙弓傳導力量到下牙弓，以達到良好咬合。橡皮圈為橡膠彈性體，它能表現出高彈性，但也會隨時間發生應力鬆弛、蠕變、力學耗損等現象而造成彈力衰減。口腔是一個動態的環境，包括唾液的存在以及各種口腔運動(力量)，這些因素對彈力之影響曾被討論過，但它們的影響機制或是依存關係仍未清楚，因此尚缺乏針對橡皮圈使用之臨床建議的科學根據。因此本研究的目的：第一是檢驗橡皮圈的初始彈力；第二是研究24小時內人工唾液與反覆拉伸這兩個因素，在單獨與合併的作用下對橡皮圈彈力表現的影響。期望由體外的力學模擬研究可以提供矯正醫師更精確選用橡皮圈與教導病人配戴橡皮圈，以產生最佳的矯正力達到高效率的矯正治療。
本研究依照人工唾液與反覆拉伸這兩個變項設計出五個實驗組別：分別是在室溫空氣中作靜態拉伸、在室溫空氣中作反覆拉伸、在37℃人工唾液中作靜態拉伸、在37℃人工唾液中作反覆拉伸，在37℃人工唾液中加快反覆拉伸。採用3M UnitekTM公司生產的3/16英吋、99.2克的天然橡膠橡皮圈作為樣本，而樣本數為每組15個。橡皮圈彈力測試之裝置由力量傳輸金屬桿其上貼有應變計的自製夾具、可進行靜態與反覆拉伸的材料測試機，以及一個匯集應變計訊號的電腦系統所組成。
實驗結果為橡皮圈的初始彈力範圍廣（74.46～131.67克）；以及人工唾液的浸泡時間與反覆拉伸的循環次數會加速橡皮圈彈力的衰減。人工唾液造成橡皮圈的殘留彈力在15分鐘、1小時、4小時、16小時、24小時，分別是90.8% 、85.4%、81.4%、74.2%、73.3%；而反覆拉伸造成橡皮圈的殘留彈力在15分鐘、1小時、4小時、16小時、24小時，分別是73.4%、68.9%、65.7%、55.5%、50.8%。兩者合併作用下會造成橡皮圈發生斷裂，而加快拉伸速度更會讓橡皮圈斷裂的時間提早。
因此我們對橡皮圈使用的建議是一天至少更換兩條橡皮圈: 第一、早餐後更換新的橡皮圈防止白天的口腔活動與環境刺激造成橡皮圈斷裂; 第二、並於晚餐後再更換另一條新的橡皮圈以確保橡皮圈有足夠的彈力讓牙齒移動。
Orthodontic elastics plays a major role in the fixed orthodontic appliance therapy. Currently, orthodontists often use intermaxillary elastics transmitting force from the upper arch to the lower arch to achieve a good
interdigitation of the teeth. Elastics is a kind of elastomers, which possesses high flexibility while also undergoes force relaxation, creep, and mechanical loss leading to a force decay over time. Among contributing factors to the force decay of elastics, the dynamic environment of the oral cavity, which includes the presence of saliva as well as multiple oral activities (forces) has often been discussed. However the mechanism and dependences of these factors are not clear. No scientific-based force levels could be recommended for the changes of elastics in clinical orthodontics. Therefore, the objectives of this study are: (1) to test the initial forces generated by elastics (2) to study the independent / combining effects of artificial saliva and cyclic stretching during a 24-hour period on the force decay of elastics. With a view to offering optimal orthodontic forces to facilitate an efficient orthodontic treatment, we adopted a mechanical in vitro simulation to offer chances for both orthodontists accurately choosing intermaxillary elastics and patients properly using elastics.
This study includes five experimental groups that are designed based on two variables (artificial saliva, cyclic stretching): static stretching at room temperature, cyclic stretching at room temperature, static stretching in 37℃artificial saliva, cyclic stretching in 37℃artificial saliva, rapid cyclic stretching in 37℃artificial saliva. Samples of 3M UnitekTM elastics 3/16 inch, 99.2g latex elastics were used and a sample size of 15 elastics per group was tested. The force testing apparatus was composed of a custom-built jig with strain gauges on force transmission beams, a material testing machine used to stretch the elastics statically and cyclically, and a computer system to accumulate the signals from the strain gauges.
The results of this study showed that the initial force of the elastics was in a wide range (74.46～131.67g), and both artificial saliva and cyclic stretching led to a significant forces decay over the immersion time and cyclic number. For artificial saliva, the percentages of residual force are 90.8% at 15 mins, 85.4% at 1hr, 81.4% at 4hr, 74.2% at 16hr, 73.3% at 24hr. For cyclic stretching, the percentages of residual force are 73.4% at 15 mins, 68.9% at 1hr, 65.7% at 4hr, 55.5% at 16hr, 50.8% at 24hr. Combination of these two factors will result in an increasing rate of breakage of the elastics. A more rapid cyclic rate was found to also shorten the timing of breakage.
Based on this study, we recommend that orthodontic patients should change the elastics twice a day: (1) new one after the breakfast to prevent elastics from breakage under multiple oral acitivites and envioronmetal stimuli during the day, (2) replacing another one after dinner so as to ensure that elastics has sufficient tooth moving forces at night. |
