Methods first, the pulp cavity walls of 25 maxillary premolars were systematically observed and photographed by scanning electron microscopy, then, these photographs were analysed by morphometry.

• 方法：首先采用扫描电镜对25颗4的髓腔壁进行系统观测，并分区定点摄影，然后对扫描电镜照片进行形态测量。