Objective: to observe the effects of different root canal file and the restoration of occlusal surface on the fracture resistance of premolars.

目的：观察不同根管锉预备根管及不同面充填物对前磨牙牙体抗折强度的影响。

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Objective: To compare the clinical effects after root canal preparation with hand use stainless steel file, nickel titanium alloy engine file and root canal ultrasonic file.

目的：比较手用不锈钢锉，镍钛合金机用锉和超声根管锉在根管预备后的临床效果。

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Root canal preparation with hand use stainless steel file.

手用不锈钢锉根管预备。

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