如上圖,在拔牙的案例當中,牙列因為擁擠的關係,必須設計口腔中,把可能的牙齒請出去,讓其它牙齒重新取得排列,這個过程當中就好比停車場的情形是一樣的,例如停車位有10個,現在有12部車,因此會產生2部車沒有位置停,所以只好把這2部車請出車場外,,,
牙列的擁擠或是暴牙的案例,要做牙列的重排或是內收前牙,必須採取拔牙的手段,也因此會產生洞洞,很多病友會覺得不好看,甚至怕這個洞不會閉起來,甚或有要做假牙的幻想,其實只要時間,慢慢的這些洞洞終將關閉起來,所以是不必要擔心的,這也就是矯正奧妙之處,,,
First), and most important, the biology of tooth movement is more important in determining the rate of space closure than the particular technique used. Osteoclasts and osteoblasts must do their job; human premolar and molar roots can move bodily through bone at the rate of about 1mm per month. In most cases, movement faster than this amount means teeth are tipping into the extraction site. This type of movement is usually counter-productive(無效果的).
Second), the arch must be completely leveled before space closure can occur(牙弓需先整平才可以關縫). That means the practitioner must leave the working wires (usually .019x.025 st.steel in a .022 slot) in the arch passively for at least a month. Once the arch is leveled, space closure can commence(開始).
Third, many practitioners inform me they prefer to close space on a round working wire (most commonly .020 st. steel in a .022 slot). They claim that friction due to the rectangular wire filling the slot inhibits space closure. I believe this is false. Closing space on round wire is usually not indicated for the following reasons:
1) Loss of torque control. Torque is the weak link of the pre-adjusted appliance. Closing space without torque control uprights anterior teeth. This gives the completed extraction case a “rabbitted” (混雜的)appearance- the teeth end up too upright.
This is especially problematic in upper bicuspid extraction cases, as the uprighted maxillary anteriors can occlusally interfere with the lower anteriors.
2) Speed of space closure. The rate of ostoblastic and osteoclastic activity, not the amount of friction, determines the speed of space closure.
(1) Controlled force levels on a rigid wire eliminate nearly all of the potentially deleterious side-effects associated with space closure mechanics. Remember, if the rate of space closure exceeds 1mm per month, the teeth are probably tipping into the extraction site. This is detrimental(不利於) to the orthodontic result.(關縫速度過快,不利於矯正的結果)
Fourth, many practitioners ask what is the best force system to use. Many systems work well, as the big issue is to provide adequate amounts of force after the arch has been leveled. I prefer en-masse space closure (moving the 6 anterior teeth as 1 unit) to canine retraction.
En-masse closure takes full advantage of the principle of sliding mechanics, which is one of the big advantages of the pre-adjusted appliance. As for force application, many effective methods exist.
Nitinol coil springs or active tie-backs are very effective. However, I like to use elastics. The proper force is usually provided by ¼" medium Class I elastics when the exraction site is larger than 4mm.
When the site is 2-4 mm wide, switch to 3/16" medium. For the last mm or 2 of space closure, use chain elastic. My patients wear the elastics full time and change them every 12 hours.
They attach the elastic from the hook on the canine bracket to the hook on the last bracketed molar. The anterior 6 teeth are held together (as 1 unit) by chain elastic or a figure-8 steel ligature tie.
Delays in space closure(關縫發生延遲的因素):
A couple of reasons exist which can cause delays. Often, upper premolar brackets are placed too gingivally. This results in over eruption of the premolars, resulting in occlusal interferences.(咬合干擾)
Also, gingival tissue can build up in the extraction site, causing delays.
In addition, dented (凹陷)or bent tubes or bracket slots can inhibit sliding. So if the space is not closing appropriately, check these three items. Chances are, you will discover the problem.
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