stepwise chain-end degradation是什么意思

用法例句

Methods Forty-five mesiobuccal root canals in fleshly extracted n u a a n molar teeth were instrumented by the step-back technique , the step-down technique or the passive step-back technique.

目的 对逐步后退法、逐步深入法、被动逐步后退法(超声波与手用器械联合应用)三种不同方法预备后牙细弯根管的根管清理能力及操作时间进行比较研究。