Heat generation during implant site preparation: an in vitro study

Thermal changes elicited during drilling and tapping procedures used in site preparation for screw-shaped and cylindrical implants were measured in vitro in blocks of bovine cortical femur bone. Heat-sensitive thermocouples were placed in the bone specimens at 4- and 8-mm depths and at a constant distance from the periphery of the drilling site; this distance was preset for each type of bur used. Rotary cutting was performed with 10-mm-long twist drills (2- and 3-mm diameter) and triflute drills (3.3- and 4-mm diameter) running at 1,500 rpm with external irrigation. A special guide drill was used to ensure unidirectional continuous drilling with a load of 2,000 g. In addition, the effect of irrigation was evaluated during tapping procedures with 10-mm-long taps used at 20 rpm. The greatest temperature increase was observed with the 2-mm twist drill at both 4- and 8-mm depths. Significantly greater temperature increase was noted at the 8-mm depth versus the 4-mm depth with the twist drills. Such significant difference between temperature rise at the two different drilling depths was not observed with the triflute burs. The time interval required for the maximum temperature reached during rotary cutting to return to baseline values was two times longer for the 2-mm twist drill than for the 3.3-mm triflute bur at both drilling depths. No statistically significant differences could be found between the maximum temperatures generated when tapping was performed with and without irrigation at both 4- and 8-mm depths. It can be suggested that the geometry of triflute burs combines cutting efficacy with greater heat dissipation capabilities than twist drills at the drilling depths of 4 and 8 mm used in this study.