Analysis of thermal changes in bone by various insertion torques with different implant designs / 대한치과보철학회지

ABSTRACT

PURPOSE: This study aims at investigating the influence of various insertion torques on thermal changes of bone. A proper insertion torque is derived based on the thermal analysis with two different implant designs. MATERIALS AND METHODS: For implant materials, bovine scapula bone of 15 - 20 mm thickness was cut into 35 mm by 40 - 50 mm pieces. Of these, the pieces having 2 - 3 mm thickness cortical bone were used as samples. Then, the half of the sample was immersed in a bath of 36.5degrees C and the other half was exposed to ambient temperature of 25degrees C, so that the inner and surface temperatures reached 36.5degrees C and 28degrees C, respectively. Two types of implants (4.5 x 10 mm Branemark type, 4.8 x 10 mm Microthread type) were inserted into bovine scapula bone and the temperature was measured by a thermocouple at 0.2 mm from the measuring point. Finite element method (FEM) was used to analyze the thermal changes at contacting surface assuming that the sample is a cube of 4 cm x 4 cm x 2 cm and a layer up to 2 mm from the top is cortical bone and below is a cancellous bone. Boundary conditions were set on the basis of the shape of cavity after implants. SolidWorks was used as a CAD program with the help of Abaqus 6.9-1. RESULTS: In the in-vitro experiment, the Microhead type implant gives a higher maximum temperature than that of the Branemark type, which is attributed to high frictional heat that is associated with the implant shape. In both types, an Eriksson threshold was observed at torques of 50 Ncm (Branemark type) and 35 Ncm (Microthread type), respectively. Based on these findings, the Microthread type implant is more affected by insertion torques. CONCLUSION: This study demonstrate that a proper choice of insertion torque is important when using a specific type of implant. In particular, for the Microthread type implant, possible bone damage may be expected as a result of frictional heat, which compensates for initial high success rate of fixation. Therefore, the insertion torque should be adjusted for each implant design. Furthermore, the operation skills should be carefully chosen for each implant type and insertion torque.