Optimizing drill geometry to limit peri-implant thermal necrosis

Bone drilling is an essential but critical step in implant surgery and oral surgery. High axial forces, torque, and local thermal elevation generated during osteotomy directly impact surgical success and postoperative recovery. For the practitioner, these poorly controlled mechanical and thermal stresses result in concrete risks of cortical micro-cracks, thermal necrosis, and delayed healing, which can lead to primary instability or early implant loss.

The objective of this study was to optimize the geometry of cutting tools to reduce these clinical risks. The authors investigated the performance of split point drills with different geometric parameters compared to standard drills. The scientific approach was based on a finite element method (FEM) simulation of cortical bone drilling processes, coupled with artificial neural network (ANN) modeling to process force, torque, and temperature data.

The study tests the hypothesis that a specific tip configuration — combining the splitting angle, web thickness, and gashing rake angle — significantly reduces mechanical resistance and the extent of the thermal necrosis zone compared to conventional instruments.

Methodology: Finite element simulation and neural modeling

This study is based on an advanced numerical simulation approach using the finite element method (FEM) to analyze cortical bone drilling. Researchers compared the performance of split point drills with different geometric parameters to that of standard drills.

The digital experimental protocol evaluated the impact of three key geometric variables on split-point drills:

• Splitting angle: optimized at 115 degrees.
• Web thickness at the point (split point web thickness): fixed at 0.25 mm.
• Gashing rake angle: optimized at 7 degrees.

The data generated by the FEM simulation, including drilling force, torque, and thermal necrosis formation, were modeled via artificial neural networks (ANN). The robustness of the model was validated by correlation coefficients of 0.99998 for training and 0.99502 for testing, with an average error rate of only 1.84%. This methodology allowed for the isolation of the ideal geometric combination to minimize mechanical and thermal trauma during osteotomy.

Biomechanical and thermal performance: predictive model results

The study validated the accuracy of artificial neural network (ANN) modeling for predicting the effects of cortical drilling. The correlation between the finite element method (FEM) results and the ANN model is nearly perfect, ensuring the reliability of the reported data.

• Correlation coefficient (training): 0.99998
• Correlation coefficient (test): 0.99502
• Average error rate: 1.84 %

Comparison of geometries: Split Point vs Standard

Simulations demonstrate that the "split point" geometry consistently outperforms the standard drill, primarily by reducing mechanical resistance during initial penetration. The optimization of geometric parameters allows for significant reductions in physical and thermal stresses.

The following table compares the performance of an optimized split point drill (115° split angle, 0.25 mm web thickness and 7° cutting angle) compared to a standard drill:

Impact of design parameters

Analysis shows that the specific combination of three parameters is critical for minimizing tissue damage:

• Split angle (115°): Determining factor for the reduction of axial force.
• Core thickness (0.25 mm): Contributes to stability and cutting efficiency.
• Gashing rake angle (7°): Optimizes debris evacuation and reduces local thermal elevation.

In the clinic, these results suggest that the use of drills with an optimized split point tip reduces the required pressure force by nearly half, while limiting cortical heating, a key factor in osseointegration and primary implant stability.

Optimization of geometry: a lever for bone viability

The results of this study, based on finite element modeling (FEM) and artificial neural networks (ANN), demonstrate that drill geometry is not an incidental detail, but a critical parameter for surgical success. The massive 46.8% reduction in axial force achieved with the optimized "split point" drill (115° angle, 0.25 mm web thickness) suggests better stability during cortical penetration and a drastic decrease in the risk of peri-implant micro-cracks.

From a thermal perspective, although the reduction in necrosis is more modest (5.2%), it remains clinically relevant. In a dense cortical environment where heat dissipation is limited, saving a few degrees allows for staying below the critical threshold of 47°C, beyond which osteogenesis is compromised. The coupling of the 7° gashing rake angle with the "split point" design promotes a smoother evacuation of bone debris, thus limiting unnecessary friction and torque (-4.6%).

However, a major limitation of this work lies in its digital nature. While the ANN model displays remarkable accuracy (0.99 correlation), it does not simulate the biological variability of the bone (irrigation, heterogeneous density) nor the actual wear of tools after several sterilization cycles. For the practitioner, these data nevertheless validate the benefit of prioritizing self-centering tip drills with complex geometry to secure the osteotomy and optimize the healing phase.

In concrete terms, for the practitioner:

• Prefer split-point drills: Their use allows the necessary axial force to be halved during cortical penetration, which significantly improves tactile control and limits the risk of drill slippage.
• Reduce mechanical trauma: The drastic reduction in drilling force (-46.8%) minimizes the formation of peri-implant micro-cracks, thereby promoting optimal primary stability and faster post-operative recovery.
• Maintain rigorous irrigation: Although the split point geometry reduces heating by 5.2%, this gain remains modest; tool optimization therefore does not replace a strict cooling protocol to prevent bone necrosis.

Technical lexicon of the study

Split point drills: Cross-point drills featuring a specific tip geometry designed to reduce the non-cutting contact area (chisel edge), thereby significantly decreasing axial forces compared to standard drills.

Finite Element Method (FEM): Numerical simulation technique used in this study to model and predict the complex mechanical and thermal interactions between the cutting tool and the cortical bone.

Artificial Neural Networks (ANN): Computational models used to process data from FEM simulations, allowing the correlation of drill geometric parameters with force and temperature results with 99% accuracy.

Thermal necrosis: Irreversible alteration of bone tissue caused by local temperature elevation during drilling, identified as a major risk factor for implant loss and delayed healing.

Splitting angle: Thinning angle of the drill tip. The study demonstrates that a value of 115° constitutes an optimal parameter to minimize mechanical resistance during bone penetration.

Gashing rake angle: Cutting angle of the notch made on the drill tip. A 7° angle is identified here as ideal for optimizing torque and reducing thermal heating.

Split point web thickness: Web thickness at the center of the point. This parameter (fixed at 0.25 mm in the study optimum) directly influences the axial force required to initiate cortical drilling.

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