Objective To determine the jaw bone stress variation affected by cylinder implant diameter and length simultaneously in Ansys DesignXplorer module. Methods Finite element model of segment mandible with a cylinder implant was created. The range of the implant diameter（D） and length（L） were set from 2.5 mm to 5.0 mm and from 6.0 mm to 16.0 mm respectively. The maximum Von Mises stresses in jaw bone and sensitivity to D and L were evaluated. Results Under axial（buccolingual） load, when one variable equaled to median, the amplification of maximum Von Mises stresses in cortical bone and cancellous bone were 44.66%（71.32%） and 51.45%（58.50%） respectively with the D increasing. The amplification of maximum Von Mises stresses in cortical bone and cancellous bone were 45.97%（21.66%） and 52.15%（37.75%） espectively with the L increasing. When D exceeded 3.7 mm and L exceeded 10.0 mm, the response curve curvatures of maximum Von Mises stresses to L and D in jaw bone ranged from - 1 to 0. And the variation of the maximum Von Mises stresses in jaw bone was more sensitive to D than to L. Conclusion Stresses in jaw bone under buccolingual and axial load are apt to be affected by implant diameter and length respectively. And to a cylinder implant, the diameter exceeds 3.7 mm and length exceeds 10.0 mm are optimal selections. Diameter should pay more attention to than to length for cylinder implant. Expanding the width of the jaw bone is more important than expanding the height of the jaw bone in clinical experience.
