Effect of Drilling Speed on Dental Implant Insertion Torque
The specific aim of this study was to examine whether slow drilling speeds (15 rpm) produce pilot holes that result in different implant insertion torques than pilot holes made with higher speed drilling (1500 rpm). To accomplish this, a new method is presented for transferring samples from a drilling machine onto an implant insertion torque measuring apparatus while maintaining the same center of rotation. Simulated bone blocks of polyurethane were used with 2 densities of foam to mimic trabecular and cortical bone. Pilot holes drilled using both drilling methods were morphologically characterized at macro and micro scales. Nobel Biocare Nobel Active implants were then placed. Profilometer and optical imaging were used to determine changes in the pilot hole morphology. Recorded insertion torque measurements were used to quantitatively contrast implants inserted into holes drilled using the 2 speeds. Although there were slight qualitative and quantitative differences between the low- and high-speed drilled pilot holes, the differences were insufficient to cause a statistically significant change in insertion torque.
Setup used to measure torque vs. displacement curves when drilling and placing implants into simulated bone blocks. (a) custom made platform that rotates the sample (b) at a preset rate. The implant driver (c) is attached to the lower chuck. A modified compact disc (d) is used as a reflecting surface that moves in lockstep with the implant driver. The axial compensator (e) allows the implant driver to move freely up and down while the sample is rotating. The lower bar of the compensator moves while the upper bar remains stationary and transmits the torque felt by the implant to the torque sensor (g) via the upper chuck located between the sensor and the compensator. Displacements are measured using a laser sensor (f), which is fixed in the lab frame by a ring stand and probes the position of the reflecting surface. The implant is initially brought into contact with the sample and the lower bar of the compensator raised to nearly touch the upper bar using the axial actuator handle (h).
Images of the 2 implant types used in this study: Nobel Biocare regular platform (RP) and narrow platform (NP). The RP implant has a retrograde slope near the top of the implant while the NP implant does not. In addition, the thread patterns are clearly complex, which adds structure to the torque vs displacement data not typical of a more simply threaded screw.
Boat for mounting samples. (a) Rigid polyurethane bone substitute (left) and an aluminum boat containing green wax used to fix the bone substitute inside the boat. (b) Rigid polyurethane bone substitute embedded in the aluminum boat using green wax, which hardens when cooled. Letter “a” marks the evenly spaced indents used to adjust the aluminum boat about the machine platform.
Figure 4. Binary thresholded optical images of cross-sections of pilot holes drilled for regular platform implant. Holes were drilled using a 3.6-mm drill bit. (a) Hole drilled using a low-speed drilling protocol. The hole contains a major axis of 3.79 mm and a minor axis of 3.43 mm. (b) Hole drilled using a high-speed drilling protocol. The hole contains a major axis of 3.77 mm and a minor axis of 3.59 mm. Figure 5. Binary thresholded optical images of pilot hole drilled for narrow platform implant. Holes were drilled using a 2.8-mm diameter drill bit. (a) Hole drilled with low-speed protocol. The hole contains a major axis of 2.95 mm and a minor axis of 2.77 mm. (b) Hole drilled using high speed drilling protocol. The hole contains a major axis of 2.97 mm and a minor axis of 2.83 mm.
Figure 6. Profilometer data collected running a stylus profilometer along inner surface of a pilot hole. (a) Hole made using a 3.6-mm drill at a low speed. (b) Hole made using a 3.6-mm drill at a high speed. Figure 7. Plots of insertion torque required to insert an RP implant into the sawbones block, as a function of axial displacement of the implant. Each line (N = 4) represents a single trial of torque measurement. All of the iterations follow a similar pattern. Each trial has a total displacement of about 13 mm. (a) Pilot holes drilled with a low-speed drill. As displacement of the implant increases, the torque values increase toward a max torque value of 92.6 ± 3.2 Ncm and then experience 16% dropoff. (b) Pilot holes drilled with a high-speed drill. As displacement of the implant increases, the torque values increase to a max torque value of 92.6 ± 1.6 Ncm, and then experience an 11% dropoff. Each iteration has a total displacement of about 13 mm. Figure 8. Plots of insertion torque required to insert an NP implant into the sawbones block, as a function of axial displacement of the implant. Each line (N = 6) represents a single trial of torque measurement. All of the iterations follow a similar pattern. The torque values increase towards a max torque while the displacement increases to 13 mm. Torque values increase in a smooth manner with some variability in values between the iterations. (a) Pilot holes drilled using a low-speed drill. (b) Pilot holes drilled using a high-speed drill. Figure 9. Plots of average insertion torque required to insert implants into the sawbones block as a function of axial displacement of the implant. Solid lines are for pilot holes drilled using a low-speed drill. Dashed lines are for pilot holes drilled using a high-speed drill. Error bars are the standard deviations among the curves at particular axial displacements. (a) NP implants. (b) RP implants.
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