今日は千秋楽でしたね。
横綱2人を破った稀勢の里の
綱取りへの可能性にわくわくしておりましたが
立ち合いで失敗し無念でした。
にわか相撲ファンですが
来場所こそ日本人横綱が誕生することを
願っています。
さて、今回は根管内ポスト除去の際
非注水下で超音波器具を用いた時の歯根外部の温度上昇と
5つの冷却材（3ウェイシリンジからの気銃、3ウェイシリンジからの水
Endoiceを2秒間噴射した直径4mmの小面球をポストに塗布
Endoiceを2秒間噴射した直径9mmの大面球をポストに塗布
大気による冷却）の効果についての文献です。
This study was designed to calculate probabilities for tissue injury and to measure effectiveness of various coolant strategies in countering heat buildup produced by dry ultrasonic vibration during post removal.
A simulated biological model was used to evaluate the cooling efficacy of a common refrigerant spray, water spray, and air spray in the recovery of post temperatures deep within the root canal space. The data set consisted of cervical and apical measures of temperature increase at 1-second intervals from baseline during continuous ultrasonic instrumentation until a 10_C increase in temperature at the cervical site was registered, wherein instrumentation ceased,and the teeth were allowed to cool under ambient conditions or with the assistance of 4 coolant methods.
Data were analyzed with analysis of variance by using the independent variables of time of ultrasonic application (10, 15, 20 seconds) and cooling method. In addition to the customary means, standard deviations,and analysis of variance tests, analyses were conducted to determine probabilities that procedures would reach or exceed the 10_C threshold. Both instrumentation time and cooling agent effects were significant at P <.0001.
Under the conditions of this study, it was shown that injurious heat transfer occurs in less than 1 minute during dry ultrasonic instrumentation of metallic posts. Cycles of short instrumentation times with active coolants were effective in reducing the probability of tissue damage when teeth were instrumented dry. With as little as 20 seconds of continuous dry ultrasonic instrumentation, the consequences of thermal buildup to an individual tooth might contribute to an injurious clinical outcome.
図1
「各冷却法における温度変化の結果」
外気と比較し他の4つの冷却法は
冷却速度が速い事が分かります。
図2
「温度上昇が10度に達する確率」
連続で超音波を使用しても約20秒間は、温度上昇が危険閾値に達する可能性はほとんどない事が分かります。
つまり
20秒未満であれば温度上昇が10度（歯周組織の壊死や歯根吸収が生じるとされる温度）
に達する可能性は低いですが
非注水下で行う場合は大気以外の4つの冷却法で代替えしながら
慎重に使用しなければいけないことが分かりました。
引用文献
Davis S, Gluskin AH, Livingood PM, Chambers DW.
Analysis of temperature rise and the use of coolants in the dissipation of ultrasonic heat buildup during post removal.
J Endod. 2010 Nov;36(11):1892-6.