Abstract
Purpose: This study investigated the effects of the removal direction of the impression on the accuracy of working casts for implants with the transfer system.
Methods: A master model was fabricated from a single standing ITI implant with a solid abutment. Working casts were fabricated using two methods, the conventional method and the transfer system with an impression cap and a shoulder analog. The impression was removed at 0°, 10° and 15° toward the long axis of a master model. An improved dental stone was poured into the impression. The master model and the working casts were measured with a profile projector and distortions were analyzed with 2-way ANOVA.
Results: Removal direction of the impression significantly influenced the height of the implant die and the upper position of the abutment, but did not influence other characteristics. The height of the implant die and the upper distortion of the upper position of the abutment decreased with an increase of the removal angle. The method of fabricating the model significantly affected the widths of the head and shoulder, the height of the implant die and the shoulder position. The widths of the head and shoulder, and the height of the implant die with the transfer method were significantly narrower and greater than those with the conventional method, respectively. The shoulder position with the conventional method distorted upwards; however, that with the transfer method distorted downwards. The interactions between the removal angle and the fabrication method were not significant.
Conclusions: When the removal angle of the impression was less than 15°, the accuracy of the working cast with the transfer system was acceptable for clinical use.
