Heat transfer in a bone-implant system: an advanced FEM Model

Aims: Implant removal, required in case of malpositions or failures, can result in significant bone defects. Few case reports describe implant removal after heating of the fixture: however, a standardization is necessary to obtain predictable results. Aim of this study is to create a high-fidelity FEM model of a bone-implant system, validated by in vitro tests, to set the most appropriate parameters for a minimally invasive implant removal using heating. Materials and methods: An advanced 3-D FEM model was cre- ated to simulate the behavior of a bone-implant system under thermal variations. Its validation was performed by in vitro tests using implants inserted in bovine bone and heated with a 100 ° C source. Temperatures were recorded using thermocou- ples at different depths and distances from the implant. Results: The threshold temperature of 47 ° C was reached after 65.2 s at 0.5 mm from the implant, after 89.3 s at 1 mm, after 110.9 s at 1.5 mm. The temperature of 47 ° C was never reached within 140 s at 2 mm distance. Differences between temperatures resulted statistically significant. Implant length and distance from heat source are factors influencing thermal variations. Conclusions: It seems possible to produce a controlled ther- mally-induced injury to the bone-implant interface, allowing for a minimally invasive implant removal. In vivo histologic studies are necessary to analyze quality and quantity of bone- implant interface modifications after heat-induced injury.