Abstract: A normal mandibular molar and its post-core prosthesis were embedded in periodontal support simulated by composite resin and formed a embedded block with size 18 mm×16 mm×22 mm.By digital optical test, their displacement and strain were obtained under a vertical applied force.Meanwhile, mechanical characteristic were analyzed.Based on the study, the following results are obtained. (1) With loads at the same level, the strain of postcore prosthesis is higher than the strain of original molar;therefore, high occlusion loads should be avoided. (2) By postcore prosthesis, advantage of inherent geometry features of left root can be taken, which is a gradual process of dispersing occlusion loads. (3) It is proved that the digital optical method is an alternative means in stomatology.

Key words: engineering mechanics, strain, mandibular molar, post-core prosthesis, digital image analysis