Isidor published a series of experimental studies using four monkeys to compare the loss of the bone around dental implants following an excessive load or plaque accumulation. He used both machined and titanium dioxide-surfaced implants. After 18 months of loading, the histological result showed that 6 out of 8 loaded implants lost osseointegration. It was concluded that occlusal overload can be the main factor for bone loss for an implant already osseointegrated. In agreement, Miyata et al. experimented with different heights of the superstructure (100, 180, 250 μm) using the same breed of monkeys and found increased bone resorption occurred with an excess of 180 μm or higher after 4 weeks of loading.

However, Heitz-Mayfield et al. using Labrador dogs found no marginal bone loss due to excessive occlusal forces. This study included six dogs and each dog’s bilateral mandibular premolar and molar was removed. After 3 months of healing, two titanium plasma sprayed and two sandblast, large grit acid-etched implants were placed in each side of the mandible in all dogs. A split-mouth design was conducted with supra-occluding crowns on the one side and on the other side unloaded. Plaque control was performed on all implants throughout the experimental time. After 8 months of loading, histology revealed that mineralized bone in contact with the control and test surfaces was not statistically disparate, 72.6% and 73.9%, respectively.