Objectives: to evaluate and compare the stress distribution to the abutment teeth roots in a mandible between O-ring coping attachmet overdentures and telescopic overdentures by using the 3-D finite element model method. Methods: After a 3-D finite element model of a mandible with two canine roots remained is made by CT scanning, two kinds of overdentures of the telescopic overdenture and O-ring coping attachmet overdenture are simulated over the 3-D model in the computer by the CAD software. The two kinds of overdentures are loaded on the 3-D model vertically and obliquely. Results: 1.Under the vertical load, the tooth root stress peak of the O-ring coping attachment overdenture is decreased 66.7% compared to the telescopic overdenture, and the tooth root stress distribution in O-ring coping attachment overdenture is more uniform. 2.Under the oblique load, the tooth root stress peaks of the two kinds of overdentures are both higher than those under the vertical load, but the tooth root distribution is mostly the same as that under the vertical load. 3.Under the vertical load, the stress in mucous membrane of O-ring coping attachment overdenture is distributed uniformly. However the stress in mucous membrane of the telescopic overdenture is more focused on the both molar areas of the mandible alveolar ridges. Conclusions: in clinic, the O-ring coping attachment overdenture is better to the health of teeth roots than the telescopic overdenture under the same condition and it is absolutely imperative to avoid the happening of oblique force. Because the stress focuses on different areas by using the two different kinds of overdentures, the O-ring coping attachments should be selected to avoid the pain in mucous membrane when the alveolar ridges of molars cannot endure hard stress in clinic.

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