A review on recent advances in numerical modelling of bone cutting

Research on ultrasonic bone cutting mechanism based on extended finite element method

The research on the crack propagation mechanism of bone has important research significance and clinical medical value for the selection of cutting parameters and the development of new surgical tools. In this paper, an extended finite element method (X-FEM) model of ultrasonic bone cutting considering microstructure was developed to further study the ultrasonic bone cutting mechanism and to quantitatively analyze the effects of cutting direction, ultrasonic parameters, and cutting parameters on the mechanism of ultrasonic bone cutting crack propagation. The results show that ultrasonic bone cutting is essentially a controlled crack propagation process, in which brittle crack and fatigue crack are the main crack propagation mechanisms. In order to improve the efficiency of ultrasonic bone cutting, large amplitude and high-frequency ultrasonic vibration are preferred. Compared with the other two cutting directions, the crack propagation deflection angle in the transverse cutting direction is the largest, resulting in the worst cutting surface. Therefore, in the path planning of orthopedic surgical robots, the transverse cutting direction should be avoided as much as possible. Frequency only has a significant effect on the crack propagation rate and has a positive correlation. There is a positive correlation between the deflection angle, propagation length, propagation rate, and amplitude, which provides the possibility to control the direction and length of crack propagation by controlling the amplitude of ultrasonic. The feed speed is much lower than the ultrasonic vibration speed, which makes the influence of ultrasonic vibration speed on the crack propagation characteristics dominant. The X-FEM model of ultrasonic bone cutting provides an effective method for selecting reasonable machining parameters of orthopedic robot and optimize the design of ultrasonic osteotome.

Fast and precise collision detection for detailed and complex physiological structures

BACKGROUND AND OBJECTIVES

Virtual reality has been proved indispensable in computer-assisted surgery, especially for surgical planning, and simulation systems. Collision detection is an essential part of surgery simulators and its accuracy and computational efficiency play a decisive role in the fidelity of simulations. Nevertheless, current collision detection methods in surgical simulation and planning struggle to meet precise requirements, especially for detailed and complex physiological structures. To address this, the primary objective of this study was to develop a new algorithm that enables fast and precise collision detection to facilitate the improvement of the realism of virtual reality surgical procedures.

METHODS

The method consists of two main parts, bounding spheres formation and two-level collision detection. A specified surface subdivision method is devised to reduce the radius of basic bounding spheres formed by circumcenters of underlying triangles. The spheres are then clustered and adjusted to obtain a compact personalized hierarchy whose position is updated in real time during surgical simulation, followed by two-level collision detection. Triangular facets with collision potential through interaction between hierarchies and then accurate results are obtained by means of precise detection phase. The effectiveness of the algorithm was evaluated in various models and surgical scenarios and was compared with prior relevant implementations.

RESULTS

Results on multiple models demonstrated that the method can generate a personalized hierarchy with fewer and smaller bounding spheres for tight wrapping. Simulation experiments proved that the proposed approach is significantly superior to comparable methods under the premise of error-free detection, even for severe model-model collision.

CONCLUSIONS

The algorithm proposed through this study enables higher numerical efficiency and detection accuracy, which is capable of significantly enlarging the fidelity/realism of haptic simulators and surgical planning methods.

Effect of drill quality on biological damage in bone drilling

Bone drilling is a universal procedure in orthopaedics for fracture fixation, installing implants, or reconstructive surgery. Surgical drills are subjected to wear caused by their repeated use, thermal fatigue, irrigation with saline solution, and sterilization process. Wear of the cutting edges of a drill bit (worn drill) is detrimental for bone tissues and can seriously affect its performance. The aim of this study is to move closer to minimally invasive surgical procedures in bones by investigating the effect of wear of surgical drill bits on their performance. The surface quality of the drill was found to influence the bone temperature, the axial force, the torque and the extent of biological damage around the drilling region. Worn drill produced heat above the threshold level related to thermal necrosis at a depth equal to the wall thickness of an adult human bone. Statistical analysis showed that a sharp drill bit, in combination with a medium drilling speed and drilling at shallow depth, was favourable for safe drilling in bone. This study also suggests the further research on establishing a relationship between surface integrity of a surgical drill bit and irreversible damage that it can induce in delicate tissues of bone using different drill sizes as well as drilling parameters and conditions.

Investigation of transient machining in the cortical bone drilling process by conventional and axial vibration-assisted drilling methods

A temperature exceeding the safety threshold and excessive drilling force occurring during bone drilling may lead to irreversible damage to bone tissue and postoperative complications. Previous studies have shown that vibration-assisted drilling methods could have lower temperatures and drilling forces than those of the conventional drilling method; we hypothesized that the main reason for these reductions stems from the differences in the transient machining processes between conventional and vibration-assisted drilling methods. To investigate these differences, comparative experiments and two-dimensional finite element models were performed and developed. The differences in the transient machining processes were verified by experimentation and clearly exhibited by the finite element models. Compared with the steady cutting process that produced continuous-spiral chips in the conventional drilling method, transient machining in the low-frequency vibration-assisted drilling method was a periodically dynamic cutting-separation process that produced uniform petal chips with specific settings of drilling and vibration parameters. Moreover, the transient machining process in the ultrasonic vibration-assisted drilling method was transformed into a combined action with high-speed impact and negative rake angle cutting processes; this action produced a large proportion of powdery chips. Therefore, it could be concluded that the superposed axial vibration significantly changed the transient machining process and radically changed the mechanical state and thermal environment; these changes were the main reason for the apparent differences in the drilling performance levels.

Intelligent temperature modeling in robotic cortical bone milling process based on teaching-learning-based optimization algorithm

Bone milling is one of the most important and sensitive biomechanical processes in the field of medical engineering. This process is used in orthopedic surgery, dentistry, treatment of fractures, and bone biopsy. The use of automatic numerical control surgical milling machines has revolutionized this procedure. The most important possible complication in bone surgery is the rise of temperature above permissible range and the formation of thermal necrosis or cell death in bone tissue. In the present article, a study on the design of experiment is first conducted by considering the rotational speed of the utilized tool, feed rate, depth of cut and tool diameter as the most important input factors of this process. Then, an adaptive neuro-fuzzy inference system (ANFIS) is developed to model and estimate the temperature behavior in the process of robotic bone milling. The optimal parameters of the ANFIS system are obtained using teaching-learning-based optimization (TLBO) algorithm. In order to model the process behavior, the results of experiments are used for the training (75% of the data) and testing (25% of the data) of the adaptive inference system. The accuracy of the obtained model is investigated via different plots, and statistical criteria, including root mean square error, correlation coefficient, and mean absolute percentage error. The findings show that the ANFIS network successfully predicts the temperature in the automatic bone milling process. In addition, the network error in estimating the temperature of the automatic bone milling process in the training and test section is equal to 1.74% and 3.17%, respectively.

Custom Massive Allograft in a Case of Pelvic Bone Tumour: Simulation of Processing with Computerised Numerical Control vs. Robotic Machining

The use of massive bone allografts after the resection of bone tumours is still a challenging process. However, to overcome some issues related to the processing procedures and guarantee the best three-dimensional matching between donor and recipient, some tissue banks have developed a virtual tissue database based on the scanning of the available allografts for using their 3D shape during virtual surgical planning (VSP) procedures. To promote the use of future VSP bone-shaping protocols useful for machining applications within a cleanroom environment, in our work, we simulate a massive bone allograft machining with two different machines: a four-axes (computer numerical control, CNC) vs. a five-axes (robot) milling machine. The allograft design was based on a real case of allograft reconstruction after pelvic tumour resection and obtained with 3D Slicer and Rhinoceros software. Machining simulations were performed with RhinoCAM and graphically and mathematically analysed with CloudCompare and R, respectively. In this case, the geometrical differences of the allograft design are not clinically relevant; however, the mathematical analysis showed that the robot performed better than the four-axes machine. The proof-of-concept presented here paves the way towards massive bone allograft cleanroom machining. Nevertheless, further studies, such as the simulation of different types of allografts and real machining on massive bone allografts, are needed.

Piezoelectric Bone Surgery. Overview in Applications and Proof of Feasibility in Hand and Plastic Surgery

PURPOSE

Piezoelectric bone surgery was already extensively used in a number of surgical procedures ranging from dental to maxillofacial surgery. The authors aimed to determine whether piezosurgery was suitable and advantageous for performing osteotomies in Hand and Plastic reconstructive surgery.

METHODS

The authors overviewed a variety of applications for Piezosurgery^® Device, from Mectron, in bone reconstructive surgery with over the last 8 years. An overall number of 156 bone cutting procedures in adults and children was described at the phalanges, metacarpal bones and distal radius level, as well as in bone graft harvesting and bone remodeling following carpal scaphoid nonunion, scapho-lunate bone-ligament-bone reconstruction and fibula free flap in maxillofacial defects.

RESULTS

The consolidation rate was 87.5% in scaphoid nonunion grafting and fixation. Bone healing was achieved in all other cases. No intra-operative complications were recorded.

CONCLUSION

Piezosurgery^® allowed high precision in bone cutting as well as custom-made graft and surface roughness were obtained, while preserving nerves, vessels and tendons integrity. The instrument may be handling moved into the surgical space in absence of vibrations, with a clear view onto the bone. The mechanical and biological characteristics of the piezoelectrical effect perfected this technique as an effective and useful instrument in Hand and Plastic surgery. The selective bone cutting properties avoided injuries to the surrounding soft tissues and thermal damage of the bony cells. Best advantages were described in feasibility and flexibility for intra-articular osteotomies, custom-made grafts and reconstructive microsurgical techniques.

Advances in tissue state recognition in spinal surgery: a review

Spinal disease is an important cause of cervical discomfort, low back pain, radiating pain in the limbs, and neurogenic intermittent claudication, and its incidence is increasing annually. From the etiological viewpoint, these symptoms are directly caused by the compression of the spinal cord, nerve roots, and blood vessels and are most effectively treated with surgery. Spinal surgeries are primarily performed using two different techniques: spinal canal decompression and internal fixation. In the past, tactile sensation was the primary method used by surgeons to understand the state of the tissue within the operating area. However, this method has several disadvantages because of its subjectivity. Therefore, it has become the focus of spinal surgery research so as to strengthen the objectivity of tissue state recognition, improve the accuracy of safe area location, and avoid surgical injury to tissues. Aside from traditional imaging methods, surgical sensing techniques based on force, bioelectrical impedance, and other methods have been gradually developed and tested in the clinical setting. This article reviews the progress of different tissue state recognition methods in spinal surgery and summarizes their advantages and disadvantages.

Human-Inspired Haptic Perception and Control in Robot-Assisted Milling Surgery

Bone milling is one of the most widely used and high-risk procedures in various types of surgeries, and it is important to be noted that the experienced surgeon can perform such an operation safely. The objective of this article is to enhance the safety of the robot-assisted milling operation with the inspiration of human haptic perception. The emergence, coding and perception of the human haptic are introduced. Following this, a single axis accelerometer that measures the vibration of the surgical power tool is mounted in the robot arm, and the recorded acceleration signal is encoded as parallel stream of binary data. The data are subsequently inputted to the Hopfield network so as to identify the milling state. Inspired by human inference procedure, the fuzzy logic controller is introduced to control the robot to track the desired state when performing bone milling operations. A real-time implementation of the proposed method on a digital signal processing is also described. The experimental results in milling porcine spines prove that the robot accurately discriminates different milling states even when the additive noise is serious, and the safe motion control of the robot is also realized.

Finite element simulation and integration of CEM43 °C and Arrhenius Models for ultrasonic-assisted skull bone grinding: A thermal dose model

The aim of the study was to develop a novel automated setup for bone grinding to limit the temperature to below 43 °C. The feasibility of using ultrasonic actuation during bone osteotomy was explored with different machining variables, such as rotational speed, feed rate and ultrasonic frequency, in terms of the criterion variable (i.e., temperature). A thermal dose model based on the CEM43 °C and the Arrhenius model was developed for the prediction of tissue damage during bone grinding. CEM43 °C is a normalizing method to convert the time-temperature relationship into an equivalent number of minutes at 43 °C. For every degree rise in temperature above 43 °C, the cell viability significantly increased. The temperature generated during bone grinding was measured with an infrared thermography technique. The increase in temperature above threshold levels of 43 °C and 47 °C may harm the bone tissues and cause thermogenesis and osteonecrosis, respectively. A finite-element simulation was conducted to visualise the spatial and temporal distribution of temperature on the bone surface after bone grinding. Furthermore, simulation results were used to measure the depth of thermogenesis and osteonecrosis at the grinding site. Evaluation of the optimised set of bone grinding process parameters was supported with analysis of variance at the 95% confidence level.

JOHNSON–COOK MODEL COMBINED WITH COWPER–SYMONDS MODEL FOR BONE CUTTING SIMULATION WITH EXPERIMENTAL VALIDATION

Constitutive models are widely used to predict the mechanical behavior of different kinds of materials. Although the Johnson–Cook model for bovine bone and Cowper–Symonds model for human thoracic rib and tibia was developed, the predictability of these models was found good only at particular strain rates. This study addresses this lack of information by investigating the Cowper–Symonds model, Johnson–Cook model, and Johnson–Cook model combined with Cowper–Symonds model at different strain rates to utilize in the bone cutting simulation. Specimens prepared using two rear femurs harvested from a 3.50-year-old bovine were investigated at different strain rates (0.00001–1/s). A comparative study made among the stresses predicted from these models showed 29.41%, 10.91%, and 11.11% mean absolute percentage errors using Cowper–Symonds model, and 2.03%, 7.19%, and 3.62% mean absolute percentage errors using Johnson–Cook model, respectively, at 0.0001, 0.001 and 1/s strain rates. However, the Johnson–Cook model combined with the Cowper–Symonds model predicted the stress with a maximum of only 2.03% mean absolute percentage error. The potential of each model to utilize in the orthogonal bone cutting was also evaluated using Ansys® and found that the combined model predicted the cutting force close to experimental cutting force with minimal error (5.20%). The outcomes of this study can be used in the surgical practice and osteotomy procedure before commencing actual surgery.

EXPERIMENTAL ANALYSIS, STATISTICAL MODELING AND OPTIMIZATION OF EFFECTIVE PARAMETERS ON SURFACE QUALITY IN CORTICAL BONE MILLING PROCESS

Knee joint surgery for artificial joint replacement is common in orthopedic surgeries. In this operation, there is a need to prepare the surface of the cortical bone for mounting the artificial joint. Therefore, milling process is frequently performed. Since the surgeon should be careful not to hurt bone tissue and neurons and also minimize waste of blood, the operation should be performed in the shortest possible time. This study, for the first time, focuses on modeling and optimization of effective parameters of bone milling including cutting speed, feed rate and tool diameter on surface roughness and material removal rate using response surface method. Results showed that in order to achieve maximum surface quality, minimum feed rate, maximum tool diameter and down milling procedure should be selected. On the other hand, the maximum material removal rate coincides with maximum feed rate and tool diameter. Therefore, cutting speed of 3000[Formula: see text]rpm, feed rate of 50[Formula: see text]mm/min, tool diameter of 5[Formula: see text]mm and down milling procedure can satisfy both high surface quality and high material removal rate.

Parallelized collision detection with applications in virtual bone machining

BACKGROUND AND OBJECTIVES

Virtual reality surgery simulators have been proved effective for training in several surgical disciplines. Nevertheless, this technology is presently underutilized in orthopaedics, especially for bone machining procedures, due to the limited realism in haptic simulation of bone interactions. Collision detection is an integral part of surgery simulators and its accuracy and computational efficiency play a determinant role on the fidelity of simulations. To address this, the primary objective of this study was to develop a new algorithm that enables faster and more accurate collision detection within 1 ms (required for stable haptic rendering) in order to facilitate the improvement of the realism of virtual bone machining procedures.

METHODS

The core of the developed algorithm is constituted by voxmap point shell method according to which tool and osseous tissue geometries were sampled by points and voxels, respectively. The algorithm projects tool sampling points into the voxmap coordinates and compute an intersection condition for each point-voxel pair. This step is massively parallelized using Graphical Processing Units and it is further accelerated by an early culling of the unnecessary threads as instructed by the rapid estimation of the possible intersection volume. A contiguous array was used for implicit definition of voxmap in order to guarantee a fast access to voxels and thereby enable efficient material removal. A sparse representation of tool points was employed for efficient memory reductions. The effectiveness of the algorithm was evaluated at various bone sampling resolutions and was compared with prior relevant implementations.

RESULTS

The results obtained with an average hardware configuration have indicated that the developed algorithm is capable to reliably maintain < 1 ms running time in severe tool-bone collisions, both sampled at 1024³ resolutions. The results also showed the algorithm running time has a low sensitivity to bone sampling resolution. The comparisons performed suggested that the proposed approach is significantly faster than comparable methods while relying on lower or similar memory requirements.

CONCLUSIONS

The algorithm proposed through this study enables a higher numerical efficiency and is capable to significantly enlarge the maximum resolution that can be used by high fidelity/high realism haptic simulators targeting surgical orthopaedic procedures.

Mechanism of material removal in orthogonal cutting of cortical bone

ANALYSIS

of a mechanism of bone cutting has an important theoretical and practical significance for orthopaedic surgeries. In this study, the mechanism of material removal in orthogonal cutting of cortical bone is investigated. Chip morphology and crack propagation in cortical bone for various cutting directions and depth-of-cut (DOC) levels are analysed, with consideration of microstructural and sub-microstructural features and material anisotropy. Effects of different material properties of osteons, interstitial matrix and cement lines on chip morphology and crack propagation are elucidated for different cutting directions. This study revealed that differences in chip morphology for various DOCs were due to comparable sizes of the osteons, lamellae and DOC. Acquired force signals and recorded high-speed videos revealed the reasons of fluctuations of dynamic components in tests. Meanwhile, a frequency-domain analysis of force signals showed a frequency difference between formation of a bulk fractured chip and small debris for different cutting directions. In addition, SEM images of the top and side surfaces of the machined bone were obtained. Thus, the analysis of the cutting force and surface damage validated the character of chip formation and explained the material-removal mechanism. This study reveals the mechanism of chip formation in the orthogonal cutting of the cortical bone, demonstrating importance of the correlation between the chip morphologies, the depth of cut and the microstructure and sub-microstructure of the cortical bone. For the first time, it assessed the fluctuations of cutting forces, accompanying chip formation, in time and frequency domains. These findings provide fundamental information important for analysis of cutting-induced damage of the bone tissue, optimization of the cutting process and clinical applications of orthopaedic instruments.

Statistical modeling, Sobol sensitivity analysis and optimization of single-tip tool geometrical parameters in the cortical bone machining process

Machining and cutting of cortical bones are very common and important in the field of orthopedic surgeries. Considerable advances in bone machining are obtained by using computer numerical control machines and automatic surgery robots but still, researches are needed to investigate the effects of machining parameters in bone machining. In this article, for the first time, the effect of geometrical parameters of the single-tip tool on cortical bone machining is studied. The machining parameters included in the investigation are rake angle, back rake angle and side cutting edge angle and the response surface methodology is used to analyze the obtained surface quality according to a second-order regression model. The sensitivity of surface quality to the input parameters was measured by applying Sobol sensitivity analysis and the results are optimized by the Derringer algorithm. Finally, the optimum tool is determined as 15° rake angle, -5° back rake angle and 30° side cutting edge angle. Furthermore, the sensitivity of the surface quality to the input parameters is determined as 52% for rake angle, 31% for side cutting edge angle and 17% for back rake angle.

Numerical modelling of hip fracture patterns in human femur

BACKGROUND AND OBJECTIVE

Hip fracture morphology is an important factor determining the ulterior surgical repair and treatment, because of the dependence of the treatment on fracture morphology. Although numerical modelling can be a valuable tool for fracture prediction, the simulation of femur fracture is not simple due to the complexity of bone architecture and the numerical techniques required for simulation of crack propagation. Numerical models assuming homogeneous fracture mechanical properties commonly fail in the prediction of fracture patterns. This paper focuses on the prediction of femur fracture based on the development of a finite element model able to simulate the generation of long crack paths.

METHODS

The finite element model developed in this work demonstrates the capability of predicting fracture patterns under stance loading configuration, allowing the distinction between the main fracture paths: intracapsular and extracapsular fractures. It is worth noting the prediction of different fracture patterns for the same loading conditions, as observed during experimental tests.

RESULTS AND CONCLUSIONS

The internal distribution of bone mineral density and femur geometry strongly influences the femur fracture morphology and fracture load. Experimental fracture paths have been analysed by means of micro-computed tomography allowing the comparison of predicted and experimental crack surfaces, confirming the good accuracy of the numerical model.

Determination of a tissue-level failure evaluation standard for rat femoral cortical bone utilizing a hybrid computational-experimental method

Macro-level failure in bone structure could be diagnosed by pain or physical examination. However, diagnosing tissue-level failure in a timely manner is challenging due to the difficulty in observing the interior mechanical environment of bone tissue. Because most fractures begin with tissue-level failure in bone tissue caused by continually applied loading, people attempt to monitor the tissue-level failure of bone and provide corresponding measures to prevent fracture. Many tissue-level mechanical parameters of bone could be predicted or measured; however, the value of the parameter may vary among different specimens belonging to a kind of bone structure even at the same age and anatomical site. These variations cause difficulty in representing tissue-level bone failure. Therefore, determining an appropriate tissue-level failure evaluation standard is necessary to represent tissue-level bone failure. In this study, the yield and failure processes of rat femoral cortical bones were primarily simulated through a hybrid computational-experimental method. Subsequently, the tissue-level strains and the ratio between tissue-level failure and yield strains in cortical bones were predicted. The results indicated that certain differences existed in tissue-level strains; however, slight variations in the ratio were observed among different cortical bones. Therefore, the ratio between tissue-level failure and yield strains for a kind of bone structure could be determined. This ratio may then be regarded as an appropriate tissue-level failure evaluation standard to represent the mechanical status of bone tissue.

THERMAL ANALYSIS IN DRILLING OF EX VIVO BOVINE BONES

Bone drilling is a common procedure in Medicine, mainly in traumatology and orthopedic procedure for fractures fixation and in reconstructive surgery. The success of this surgical procedure is dependent on many factors, namely, on heat generation control during the bone drilling. The main concern in bone drilling is the mechanical and thermal damage of the bone induced by inappropriate parameters such as drill speed and feed-rate during the drilling. This study focuses on the temperature generated during drilling of cortical bone tissue (bovine origin) and solid rigid polyurethane foams with similar mechanical properties to the human bone tissue. Different parameters such as drill speed, feed-rate and hole depth were tested. All results showed that improvement of the drilling parameters and the drill temperatures can be estimated. It was concluded that when the drill speed and feed-rate were higher, the bone temperature increase was lower. The obtained results of temperature in the drilling process of polyurethane foam blocks or bovine bone were compared with a good agreement in between both.

Real-Time Prediction of Temperature Elevation During Robotic Bone Drilling Using the Torque Signal

Bone drilling is a surgical procedure commonly required in many surgical fields, particularly orthopedics, dentistry and head and neck surgeries. While the long-term effects of thermal bone necrosis are unknown, the thermal damage to nerves in spinal or otolaryngological surgeries might lead to partial paralysis. Previous models to predict the temperature elevation have been suggested, but were not validated or have the disadvantages of computation time and complexity which does not allow real time predictions. Within this study, an analytical temperature prediction model is proposed which uses the torque signal of the drilling process to model the heat production of the drill bit. A simple Green's disk source function is used to solve the three dimensional heat equation along the drilling axis. Additionally, an extensive experimental study was carried out to validate the model. A custom CNC-setup with a load cell and a thermal camera was used to measure the axial drilling torque and force as well as temperature elevations. Bones with different sets of bone volume fraction were drilled with two drill bits ([Formula: see text]1.8 mm and [Formula: see text]2.5 mm) and repeated eight times. The model was calibrated with 5 of 40 measurements and successfully validated with the rest of the data ([Formula: see text]C). It was also found that the temperature elevation can be predicted using only the torque signal of the drilling process. In the future, the model could be used to monitor and control the drilling process of surgeries close to vulnerable structures.

Reducing temperature elevation of robotic bone drilling

This research work aims at reducing temperature elevation of bone drilling. An extensive experimental study was conducted which focused on the investigation of three main measures to reduce the temperature elevation as used in industry: irrigation, interval drilling and drill bit designs. Different external irrigation rates (0 ml/min, 15 ml/min, 30 ml/min), continuously drilled interval lengths (2 mm, 1 mm, 0.5 mm) as well as two drill bit designs were tested. A custom single flute drill bit was designed with a higher rake angle and smaller chisel edge to generate less heat compared to a standard surgical drill bit. A new experimental setup was developed to measure drilling forces and torques as well as the 2D temperature field at any depth using a high resolution thermal camera. The results show that external irrigation is a main factor to reduce temperature elevation due not primarily to its effect on cooling but rather due to the prevention of drill bit clogging. During drilling, the build up of bone material in the drill bit flutes result in excessive temperatures due to an increase in thrust forces and torques. Drilling in intervals allows the removal of bone chips and cleaning of flutes when the drill bit is extracted as well as cooling of the bone in-between intervals which limits the accumulation of heat. However, reducing the length of the drilled interval was found only to be beneficial for temperature reduction using the newly designed drill bit due to the improved cutting geometry. To evaluate possible tissue damage caused by the generated heat increase, cumulative equivalent minutes (CEM43) were calculated and it was found that the combination of small interval length (0.5 mm), high irrigation rate (30 ml/min) and the newly designed drill bit was the only parameter combination which allowed drilling below the time-thermal threshold for tissue damage. In conclusion, an optimized drilling method has been found which might also enable drilling in more delicate procedures such as that performed during minimally invasive robotic cochlear implantation.