OBJECTIVETo establish more rational three dimensional finite element model (FEM) of the first permanent mandibular molar and to study the internal stress distribution.

METHODSThe FEM was applied to analyze the stress distribution of the first permanent mandibular molar under various loading conditions.

RESULTSUnder all five loading conditions, the maximum von-Mises stress and compressive stress in enamel were larger than that in dentin, and the tensile stress in enamel was smaller than that in dentin. When vertical force and buccal-lingual oblique force were loaded, the stresses in the enamel and dentin were minimum; when lingual-buccal oblique force was loaded, the stresses were maximum; the stresses were mainly distributed at cervical region, furcation and apical area of the mesial-lingual root canal wall.

CONCLUSIONSThe stress value changes and stress distribution in the enamel and dentin were closely related with the direction of the occlusion force.