Methods: Maxillary first and second molars on both sides were extracted of sixteen 4-weeks old male Wistar rats. After 4 weeks, 2-mm implants were inserted with slight perforation of nasal floor in the left alveolar bone. 4 weeks later, 8 rats (Control group) were sacrificed. In the other 8 rats, distally extended cantilever type superstructures were set. Hard diet was given and after 5 days, they were sacrificed and divided into Mesial group (occluded right on the implant) and Distal group (occluded on the cantilever arm), according to the shining spot locations on the superstructures. After taking μ-CT images of all samples, bone volume around implant was measured by a bone structure analysis program (TRI/3D-Bon, RATOC). This program and FEM software (TRI/3D-FEM) were used to create 3D-FEM models of the samples and to calculate von Mises stresses under 20N-vertical load applied to the shining spot locations. The relationship between bone volume and stress distributions was investigated.
Results: The average bone volume around implant decreased in the order of: Control, Mesial, and Distal groups. In the Distal rather than Mesial group, higher stresses tended to concentrate over larger areas distally from implant, as predicted by Control-group FEM. Under cantilever-arm occlusion, predicted high-stress concentrations corresponded with areas of bone resorption in vivo, which probably resulted in bone volume decrease and stress increase in the Distal group.
Conclusions: These findings suggest that bone volume change tendencies around loaded implants may be predicted by 3D-FEM.