Biomechanical behavior analysis of four types of short implants with different placement depths using the finite element method.

STATEMENT OF PROBLEM: The clinical application of short implants has been increasing. However, studies on the marginal bone loss of short implants are sparse, and clinicians often choose short implants based on their own experience rather than on scientific information. PURPOSE: The purpose of this finite element analysis study was to evaluate the microstrain-stress distribution in the peri-implant bone and implant components for 4 types of short implants at different placement depths of platform switching. MATERIAL AND METHODS: By using short implants as prototypes, 4 short implant models were 1:1 modeled. The diameter and length of the implants were 5x5, 5x6, 6x5, and 6x6 mm. The restoration was identical for all implants. Three different depths of implant platform switching were set: equicrestal, 0.5-mm subcrestal, and 1-mm subcrestal. The models were then assembled and assigned an occlusal force of 200 N (vertical or 30-degree oblique). A finite element analysis was carried out to evaluate the maximum equivalent elastic strain and von Mises stress in the bone and the stress distribution in the implant components. RESULTS: The 5x5 implant group showed the largest intraosseous strain (21.921x10(3) muepsilon). A 1-mm increase in implant diameter resulted in a 17.1% to 37.4% reduction in maximum intraosseous strain when loaded with oblique forces. The strain in the bone tended to be much smaller than the placement depth at the equicrestal and 0.5-mm subcrestal positions than that at the 1-mm subcrestal position, especially under oblique force loading, with an increase of approximately 37.4% to 81.8%. In addition, when the cortical bone thickness was less than 4 mm, 5x6 implants caused significantly higher intraosseous stresses than 6x6 implants. CONCLUSIONS: Large implant diameters, rather than long implants, led to reduced intraosseous strain, especially under oblique loading. Regarding the implant platform switching depth, the short implant showed small intraosseous strains when the platform switching depth was equicrestal or 0.5-mm subcrestal.