Wilcox L R, Roskelley C, Sutton T
Department of Endodontics, University of Iowa, Iowa City 52242, USA.
J Endod. 1997 Aug;23(8):533-4. doi: 10.1016/S0099-2399(97)80316-0.
The purpose of this study was to assess the effect of lateral condensation forces on the development of vertical root fracture (VRF) in teeth that have undergone controlled, measured internal root reduction (i.e. canal preparation). Thirty-four straight-rooted maxillary anterior teeth were used. For each tooth a simulated PDL was fabricated from a uniform 0.15 mm layer of silicone impression material. The teeth were mounted in resin to facilitate removal for observation. They were radiographed and measured at 2, 4, 6, and 8 mm from the apex. They were prepared with the step-back method so that the canal width was 20% of the total root width at 2, 4, 6, and 8 mm from the apex. They were obturated using a fine finger spreader attached to a jig that produced a static force of 3.3 kg for 15 s after placement of each gp point. Obturation was complete when the spreader did not penetrate apical to 8 mm from the apex. Twenty-four h after obturation the teeth were examined by transillumination for VRF. Teeth not exhibiting VRF were tested further after gp removal and canal enlargement of 30%, 40%, and 50% The teeth were sectioned at 2-mm increments with a diamond wafering saw and examined under stereomicroscope. No VRF occurred at 20% or 30%; 5 teeth fractured at 40% and 7 at 50%. These teeth had root surface craze lines that developed during testing. Craze lines had also developed in all 17 of the remaining unfractured samples. No VRF occurred after testing unless craze lines were previously present.
本研究的目的是评估侧向加压力量对已进行可控、测量性根管内牙根减径（即根管预备）的牙齿垂直根折（VRF）发生情况的影响。使用了34颗直根上颌前牙。对于每颗牙齿，用均匀的0.15毫米厚的硅橡胶印模材料制作模拟牙周膜。将牙齿固定在树脂中以便于取出观察。在距根尖2、4、6和8毫米处进行X线片拍摄和测量。采用逐步后退法进行预备，使在距根尖2、4、6和8毫米处根管宽度为牙根总宽度的20%。使用附着在夹具上的细手指式充填器进行充填，在放置每个牙胶尖后产生3.3千克的静力，持续15秒。当充填器不能穿透距根尖8毫米以上时，充填完成。充填24小时后，通过透照检查牙齿有无垂直根折。未出现垂直根折的牙齿在去除牙胶并进行30%、40%和50%的根管扩大后进一步测试。用金刚石薄片锯以2毫米的增量对牙齿进行切片，并在立体显微镜下检查。在根管扩大20%或30%时未发生垂直根折；40%时5颗牙齿折断，50%时7颗牙齿折断。这些牙齿在测试过程中出现了牙根表面裂纹线。在其余所有未折断的17个样本中也出现了裂纹线。除非之前存在裂纹线，否则测试后未发生垂直根折。
