Methods: 156 premolars were collected and divided into two groups.The experimental group was prepared with ultrasonic instrument;the control group was prepared with manual instrument.

• 方法：收集临床初诊病例156个，按随机化原则分成两组，分别用超声波根管器械和手用器械预备根管并对其预备时间及疼痛发生率进行对比分析。