In daily practice, cases of unilateral free-end saddle involving loss of two teeth are apt to cause problems such as a loss of function and injury on the abutment teeth due to instability of the dentures. In attempting to remedy these problems, a variety of prosthesis have been used and their dynamics analyzed. Nevertheless, dynamics during function, one basis for judging the relative worth of prostheses, remain unclear. In this study, modal analysis and linear-value analysis were used to derive values for the dynamics of the denture during function of a cone telescopic denture, an attachment denture and a clasp denture as well as impact on the abutment teeth. The following results were obtained: 1. Characteristic frequency and observation of animation showed that: (a) Mode #1 is the vibration mode for the entire system including the denture. (b) Mode #2 is the vibration mode for the abutment tooth itself. (c) Mode #3 is the mode for the resin or the metal frame of the denture. 2. In the direction of the tooth axis, the tendency for displacement of the abutment tooth decreased in the following order: unilateral clasp denture greater than bilateral clasp denture greater than cone telescopic denture greater than attachment denture. 3. In a bucco-labial direction, the order was as follows: unilateral clasp denture greater than bilateral clasp denture greater than cone telescopic denture greater than attachment denture. 4. In a mesio-distal direction, the order was as follows: unilateral clasp denture greater than attachment denture greater than cone terescpic denture greater than bilateral clasp denture. 5. A comparison with the clasp denture in terms of attenuation hints at the possibility that the design is superior with the cone telescopic denture and the attachment denture in cases of free-end saddle.