| 摘要: | 牙齒擁擠常常是令人困擾的問題，主要是因為不美觀，而且清潔不易，進而容易併發牙周病或齟齒的問題，也因此成為病人尋求矯正治療的主要訴求。傳統上若要將擁擠的牙齒排列整齊，首先要面臨到的就是空間不足的問題。若是對於不拔牙的病例必須先利用擴張牙弓的方式將空間挪出；而對於拔牙的病例，則會將鄰近牙後移來獲得空間後，進而將擁擠牙齒排列整齊。這兩種方式都強調獲得足夠空間的重要性，且不建議在空間挪出前，即將擁擠牙齒黏上矯正器與綁入超彈性金屬線來獲得牙齒的自然排列整齊。
此外，近年來隨著矯正裝置與材料工程的發展與進步，伴隨著不同矯正線綁法的改變與矯正器和超彈性鎳鈦合金線的改良發展，進而於近幾年來有所謂”自鎖性矯正器”的出現，它除了強調不需像傳統矯正方式必須在每顆牙齒上綁入結紮線”ligature wire”以外，也強調在搭配超彈性矯正線的情況下，能有效降低牙齒移動時產生的磨擦力與提供很輕的矯正力量，來快速而有效的完成初期的牙齒平齊化效用，但對於臨床上各種不同的治療結果，其在骨骼中所造成的應力分佈仍未有深入的探討。
本實驗主要藉由具有光彈性質的環氧樹脂來模擬齒槽骨，並利用樹脂牙齒排列來模擬下顎前牙擁擠的情形，接著使用較細的超彈性矯正線(0.014inch)，並搭配不同的矯正器與不同的綁法來觀察牙齒受力的情形。結果發現，牙根間應力在自鎖性矯正器組中明顯降低許多；再者，若更改不同的矯正綁法，如合併橡皮分離物(separator)的使用，能明顯提供與一般傳統綁法較多的側方應力分佈。
另外，本實驗也試圖了解鄰接牙存在有無、不同型態與材質的矯正線對於牙齒根尖應力分佈的作用上，會有如何的影響。結果發現，矯正線的粗細對於應力的產生遠較矯正線的型態(圓線或方線)、材質來得重要；在分析牙根間的應力分佈上，應了解到過度的應力分佈也意味著更多的牙根吸收的可能。這些都是我們在臨床上面對牙齒不同擁擠程度與搭配何種矯正方式所應注意到的。而本實驗之結果將可提供有用的數據協助臨床醫師解決下顎前牙擁擠之相關問題。
Dental crowding is a perplexing problem, mainly due to its unestheticity. Also its difficulty in maintaining oral hygiene may cause problems like periodontal disease and caries as well. Therefore, it is quite often the chief complaint of patient in daily orthodontic practice.
Traditionally, if we try to align crowded teeth, we will face the problem of space deficiency. We can partially retract the neighboring tooth to create space in extraction cases, or expand dental arch to gain space. And then, we move the desired tooth into desired position.
Recently, with developing of the orthodontic appliance like “self-ligation bracket” and material engineering, and in combination of developing superelastic NiTi, it emphasizes in achieving initial phase of aligning teeth efficiently in light force. However, manufacturers only provide data of clinical result, lacking in discussion of stress distribution.
Besides, photoelasticity has been used in analyzing force distribution for a long time. The main mechanism is that one polarized light will separate into two light beams with different velocity when passing through solid materials with capability of transparence and isotropy. It also produces different colored flanges that can be observed as the guide of stress distribution.
Several models were set with mal-aligned teeth and silicone index in the epoxy resin to simulate situation of lower anterior crowding. Ligaiton methods were altered, including conventional- approaching, conventional-approaching with separator, and lingual-approaching methods, to evaluate whether ligation method with same orthodontic wire will cause different patterns of stress distribution. Also, different bracket system, including conventional bracket and self-ligation bracket, were investigated for the effect acting on stress distribution. Wire materials, whether size or patterns of geometry, were not altered. In result, we found that there is less stress distribution concentrated along the root surface in combination with self-ligation bracket. Meanwhile, in investigation on the effect of different ligation methods, both lingual-approaching and conventional-approaching with separator methods show more lateral stress distribution than conventional approaching method do.
Therefore, we think that it is quite essential to provide available space before using superelastic wire in dealing with crowded teeth, and both lingual-apporaching and conventional- approaching with separator. Using self-ligation bracket also demonstrated result less force concentrated on the apical portion of the root, which may result from less friction was generated. We think this study can provide another method of thinking in dealing with lower anterior crowding. |
