阅读说明：本技术 配置为检测松质-皮质骨和骨-软组织边界的电阻抗感测牙钻系统 (Electrical impedance sensing dental drill system configured to detect cancellous-cortical and bone-soft tissue boundaries ) 是由 瑞安·哈尔特 丽贝卡·巴特勒 迈克尔·萨林 于 2018-03-08 设计创作，主要内容包括：一种具有电阻抗感测的牙钻系统指示牙钻系统的钻头接近皮质-松质骨或骨-软组织界面。该牙钻系统具有牙钻手持件,所述牙钻手持件具有与钻头电耦接的套管轴承,钻头具有电绝缘部分和暴露部分。套管轴承被耦接到电阻抗谱感测设备,该电阻抗谱感测设备被配置为测量牙钻手持件的套管轴承与接地板之间的阻抗,并且处理系统使用EIS测量结果区分牙钻系统的钻头接近松质-或皮质骨或者骨-软组织界面。(A dental drill system with electrical impedance sensing indicates that a drill bit of the dental drill system is proximate a cortical-cancellous bone or bone-soft tissue interface. The dental drill system has a dental drill handpiece having a sleeve bearing electrically coupled to a drill bit having an electrically insulated portion and an exposed portion. The sleeve bearing is coupled to an electrical impedance spectroscopy sensing apparatus configured to measure an impedance between the sleeve bearing and the ground plate of the dental drill handpiece, and the processing system uses the EIS measurements to distinguish whether the drill bit of the dental drill system is proximate to a cancellous-or cortical bone or a bone-soft tissue interface.)

1. A dental drill system with Electrical Impedance Sensing (EIS) configured to indicate whether a drill bit of the dental drill system is proximate a cancellous-cortical bone interface or a bone-soft tissue interface, the dental drill system comprising:

a dental drill having a casing bit in a handpiece of the dental drill, the casing bit having an insulating coating extending from adjacent a cutting end of the drill bit to a handpiece end of the drill bit,

a casing bearing electrically coupled to a non-insulated interior of a casing of the casing bit,

an EIS measurement and calculation unit configured to measure the impedance between the sleeve bearing and the ground plate, an

A processing system configured to differentiate the drill bit of the dental drill system from approaching a cancellous-cortical bone or bone-soft tissue interface.

2. The dental drill system of claim 1, wherein the electrically insulated portion of the drill bit is insulated using a diamond-like carbon (DLC) coating.

3. The dental drill system of claim 1, wherein the EIS measurement and calculation unit provides a voltage limited current at each of a plurality of frequencies, and measures a resulting voltage and phase.

4. The dental drill system of claim 1, wherein the EIS measurement and calculation unit is configured to provide a visual and/or audible alert when the drill bit is proximate to cortical bone.

5. The dental drill system of claim 1, 2, 3 or 4, wherein the EIS measurement and calculation unit is configured to measure impedance at least two frequencies in the range of 100 to 100000 Hertz.

6. A method of detecting the proximity of a drill bit to cortical bone or to a bone-soft tissue interface while drilling bone using a drill bit, the method comprising:

providing an insulating coating extending from near a cutting end of the drill bit to a handpiece end of the drill bit;

contacting the drill bit with a sleeve bearing;

driving a voltage limited current between the drill bit and a ground plate at least one alternating current frequency;

measuring the voltage and phase between the bit and the ground plate;

determining an impedance from the measured voltage and phase; and

an alarm is generated when the impedance changes, indicating that a cancellous-cortical bone interface or a bone-soft tissue interface is approached.

7. The method of claim 6, wherein the voltage limited current is driven at a plurality of frequencies between 100 and 1,000,000 hertz.

Background

Bone generally has two distinct forms, cortical and cancellous bone. Cortical bone is typically present on the surface of bone included in joints, as well as major portions of the long bone shaft, and other areas that may be subject to high stresses. Cortical or compact bone lines the outer surface of all bone and is more dense and less compact in structure than cancellous bone in nature. It is organized into closely packed bone units, each consisting of a centrally located haversian (diameter about 50 microns) surrounded by concentric rings of matrix. Cancellous bone has a spongy structure, forms a mesh network, and supports and transfers loads to and from cortical bone. Cancellous bone, also known as trabecular bone or spongy bone, exists on the inside of long bones and jawbone (maxilla and mandible). Cancellous bone primarily provides a lighter weight, more flexible structural support than cortical bone. It consists of trabeculae arranged in a cellular structure, and the pores within the cancellous bone are typically filled with bone marrow and blood vessels.

The physical and biological properties of cortical and cancellous bone differ due to differences in bone structure. In particular, because the porosity of these bone types varies widely, the penetration and adhesion of adhesives, the degree of fixation of screws or nails in bone, and the rate of bone growth into porous implants vary between cortical and cancellous bone.

Remodeling of bone occurs throughout life. When the cortical bone is spread over the cancellous bone, the thickness of the cortical bone varies with the patient's genetics, childhood nutritional and exercise history, age and health status, as well as past medical history (including fracture, periodontal disease, tooth extractions, muscle use and weight carried on the bone), and other factors. The surgeon must anticipate changes in bone structure between patients. In the mandible and maxilla, in particular, clinicians characterize the bone in the dental implant site according to the Lekholm and Zarb classification to determine the likelihood of implant success. There are four types, from homogeneous cortical bone, to a combination of cortical and cancellous bone, to almost completely low-density cancellous bone. The classification depends on the location of the implant site (i.e., in the anterior zone relative to the premolars relative to the molars) and patient characteristics.

Bones, particularly bones of the head including the mandible and maxilla, can be penetrated by nerves and arteries, usually via holes or openings through the bone. These nerves and arteries are key structures because damage to them is likely to cause sensory loss in portions of the mouth or face, or partial necrotic degeneration of bone. For example, the lower alveolar nerve (IAN) penetrates the lower jaw.

When performing surgery, including oral surgery, a surgeon wishes to know the type and size of the bone and surrounding structures (including critical structures) that he is working on. The surgeon may need to modify the surgical technique, such as the depth and trajectory of the drill holes, to remain in the bone to avoid penetrating adjacent structures, such as sinuses such as the maxillary sinus and nerves such as the IAN, depending on the size, type and thickness of the bone layer in which the surgeon is working.

One common dental procedure is the placement of anchor implants for the attachment of abutments or dental prostheses. This procedure requires drilling the bone to form an initial osteotomy or intraosseous cavity for placement of the implant.

When making an initial osteotomy, the surgeon may drill through the first layer of cortical bone before reaching the cancellous bone, he must drill deep enough into the bone to provide a good engagement surface for the implant, but ensure that the drill does not penetrate the thin distal layer of cortical bone to prevent surgical complications such as infection or neurosensory disturbances due to drilling through the maxilla into the maxillary sinus cavity or into nerves or blood vessels.

Disclosure of Invention

A dental drill system with electrical impedance spectroscopy sensing configured to indicate whether a drill bit of the dental drill system is adjacent to cortical or cancellous bone, proximate to a cancellous/cortical bone interface, or proximate to a bone/soft tissue interface, the dental drill system comprising: a dental drill having a casing bit in a handpiece thereof, the casing bit having an insulating coating covering the entire surface except for a portion of a distal surface of a cutting edge; a casing bearing electrically coupled to a non-insulated interior of a casing bit; an electrical impedance spectroscopy sensing (EIS) measurement and calculation unit configured to measure the impedance between the sleeve bearing and the ground plate or return electrode, and a processing system configured to distinguish between changes in electrical properties indicative of an approaching cancellous/cortical bone interface, or changes when a drill bit of the dental drill system approaches an interface between cancellous and cortical bone or a bone-soft tissue interface.

A method of detecting the proximity of a drill bit to cortical or soft tissue while drilling bone using the drill bit, comprising: providing an insulating coating extending from near the cutting end of the drill bit to the handpiece end of the drill bit, the drill bit being in contact with the sleeve bearing; driving a voltage limited current between the drill bit and the ground plate at least one ac frequency; measuring the voltage and phase between the bit and the ground plate; determining an impedance from the measured voltage and phase; and generating an alert when the impedance changes indicating an interface between the bone and soft tissue or between the cancellous bone and the cortical bone.

Drawings

FIG. 1 is a block diagram of a drilling system with electrical impedance spectroscopy sensing.

Fig. 2 is a schematic view of a drill bit of a prior art drilling system.

FIG. 3 is a photograph showing an embodiment of a drill having a bit with a sleeve bearing attached.

Fig. 4 is a graphical representation of the resistance and reactance of cancellous and cortical bone samples measured using prototypes integrated on a norbourine (Nobel Biocare) drill with a 2mm twist drill.

Fig. 5 is a photograph of a DLC coated drill bit with bare cutting ends.

Fig. 6 shows a comparison of normalized average resistance and reactance of cancellous and cortical bone measured using prototypes integrated on a standard Nobel Biocare drill, with the drill bit located in the excised bone.

Fig. 7 shows a comparison of normalized average resistance and reactance of cancellous and cortical bone measured using prototypes integrated on a standard Nobel Biocare drill, with the drill bit located in fresh in situ bone.

Fig. 8 is a flow chart of a method of detecting the approach of a drill bit to cortical bone during a surgical procedure.

Detailed Description

The large difference in cellular composition of cortical and cancellous bone provides a spectrum of charge carrying and charge storing capabilities, represented by conductivity (σ) and permittivity (ε), respectively (σ and ε are inversely proportional to resistance and reactance). When these electrical properties are recorded over a wide frequency range (100Hz to 10MHz), as is done in Electrical Impedance Spectroscopy (EIS), it has been reported that cortical and cancellous bone differ significantly. Studies have investigated electrical impedance measurements when inserting pedicle screws into vertebrae, and indicate that differences in electrical properties between cancellous and cortical bone can be used to guide a surgeon through vertebrae.

Herein we describe an EIS device integrated with a drill configured for drilling a hole in a bone, such as may be required during various surgical procedures in dental and some non-dental procedures. The bur is particularly configured for measuring bioimpedance spectra in vivo during an initial osteotomy of a dental implant procedure. The drill is particularly adapted to measure the electrical impedance spectrum of a bone structure as the drill enters the bone structure in the body. Such EIS drills provide real-time feedback to the clinician in the form of an audible or visual signal to allow the clinician to stop drilling before cortical perforation occurs (if desired, to allow immediate clinical intervention). In a particular embodiment, the drill bit is a dental drill.

An EIS sensing dental drill system 100 is shown in fig. 1. The dental drill handpiece 102 contains a high speed motor and drive shaft 104 leading to a right angle bevel gear unit 106, which bevel gear unit and housing 110 of the drive shaft 104 are insulated by an insulating coating 108. The drill bit 112 is coupled to a bevel gear unit, the drill bit 112 having an insulated portion 114 and an exposed cutting portion 116. The exposed cutting portion 116 is a portion of a spherical burr in some embodiments, and the tip of a twist drill in other embodiments; the insulating portion extends from the cutting portion to a hand-held end of the drill bit that is mechanically coupled to the dental drill handpiece. A sleeve bearing 118 is provided in the bevel gear unit 106 to be electrically connected to the bit 112. The handpiece 102 has an umbilical-type tubular housing 120, the tubular housing 120 holding a tube 122 for irrigation fluid, electrical drive leads for the motor of the handpiece 102, and electrical leads adapted to couple the sleeve bearing 118 to an Electrical Impedance Spectroscopy (EIS) measurement and calculation unit 130, the EIS measurement and calculation unit 130 also being coupled to a second electrode plate 134 by another lead 132. Within the EIS measurement and calculation unit 130, an EIS excitation unit 136 and an EIS impedance measurement unit 140 are provided, the EIS excitation unit 136 being capable of operating at 100, 1000, 10000 and 100000Hz under the direction of the processor 138. In alternative embodiments, the EIS impedance measurement and calculation unit 130 is capable of operating at two or more frequencies in the range of 100Hz to 1 MHz. The processor 138 has a memory 142, the memory 142 having EIS measurement firmware and classifier firmware 144 adapted to use the EIS measurements to determine whether the drill bit 112 is drilling in cancellous or cortical bone, and to use an indicator 146 to inform which bone type the drill bit 112 is in.

A threaded drill embodiment is shown in more detail in fig. 2. The thread drill 160 has an exposed or uninsulated end 162, the end 162 having a cutting edge that may contact and drill a hole in bone. The drill bit 160 also has an electrically insulating portion 164, the electrically insulating portion 164 carrying a diamond-like carbon (DLC) coating, a coating that is both very hard so as to wear very little when drilling into bone, and has a high electrical resistivity. The DLC coating extends over the remainder of the exterior of the drill bit 160 up to the bit end of the drill bit 160, including the portion 170 that engages the bevel gear of the bit head, and including the portion 171 above the flutes (flutes). The drill bit 160 also has an uninsulated axial bore 172 extending from the bit end of the drill bit into the drill bit, but not all the way through.

The non-insulated end 174 of the sleeve bearing 166 is within the axial bore 172 and is in electrical contact with the non-insulated surface of the drill bit 160 in the bore. The sleeve bearing 166 extends from the end of the drill bit 160 through the insulator 176 to the electronic EIS measurement and calculation unit 130 (fig. 1). The drive shaft 178 and bevel gear 180 rotate to drive bevel gear 168 of drill bit 170 to rotate drill bit 160 to drill a hole in bone.

Fig. 1 and 2 are schematic diagrams, fig. 3 is a photograph showing an embodiment of a trial drill 202 having a drill bit 204, the drill bit 204 having a sleeve bearing 206 and an attached insulated wire 208, and fig. 4 is a photograph showing a pair of uninstalled sleeve bearings 210. In an embodiment, the sleeve bearings 210, 206 are formed from stainless steel.

In various embodiments, the length of the non-insulated end 174 of the bur 160 or the non-insulated ball section of the bur 116 is 1 to 3 millimeters.

Operation of the EIS drill system:

the EIS measurement and calculation unit, the drill and the drill bit with the sleeve bearing together form an EIS drilling system. Positioning the bearing 206 within the cannula of the drill bit does not reduce the surgical working space and still allows irrigation through the passage in the cannula or around the outer surface of the drill bit. The sleeve bearing is connected to a lead that interfaces with the impedance analyzer. Similarly, return electrode 134 (fig. 1) is connected to another lead that interfaces with an impedance analyzer. A voltage-limited Alternating Current (AC) current is applied between two electrode elements at several frequencies, and the voltage and phase induced between them is recorded. From these measurements, the impedance is calculated as the ratio of voltage to current.

Calculating an impedance (Z) as a ratio of the measured voltage to the injected current; we treat the impedance as a complex quantity, which consists of a real resistive component (R) and an imaginary reactive component (X), according to the equation Z-R + jX. The electronics box calculates the R and X measurements at each frequency tested. From these, we calculate impedance, conductivity, resistivity, etc.

We have shown in previous ex vivo and in situ porcine femoral experiments that cortical bone has a higher resistivity and impedance than cancellous bone. The ratio of cortical to cancellous resistivity is 1.28-1.48 in ex vivo bone and 2.82-2.94 in fresh in situ bone. As a result, we expect that as the drill bit moves through cancellous bone toward the cortical interface, we will see the impedance/resistivity increase as the interface is approached.

In an embodiment, the EIS measurement and calculation unit is configured to provide a visual and/or audible alert when the drill bit is proximate to cortical bone.

Clinical use of the device involves the use of a drill to create an initial osteotomy (hole in bone) which is marked for implant insertion. As the drill bit enters the bone, electrical properties, particularly the resistance and reactance of the bone, are recorded at a single or multiple frequencies. These measurements will be input into a real-time classification unit for sensing the proximate tissue transition zone (i.e., the cancellous-cortical interface). Based on the varying impedance, a visual or auditory signal with an increased repetition rate will be used as clinician feedback.

We have collected important data sets of ex vivo and in situ electrical properties of cortical and cancellous bone, and have shown a significant impedance contrast between the two bone types.

In ex vivo experiments, we placed a standard casing bit 3mm deep into 10 samples, each of cortical and cancellous bone freshly harvested from pigs, and recorded the impedance of 100Hz-1MHz at 41 frequencies. The results show that there are significant R and X differences (p < 0.05) between the two bone types, with resistance contrasts at 0.1kHz, 1kHz, 10kHz and 100kHz of 41%, 37%, 29% and 32%, respectively. These trends recorded with our prototype are similar to those previously reported for cancellous and cortical bone.

In the in situ experiment, we used a custom-made DLC coated drill bit and recorded the impedance of 40 samples each of cortical and cancellous bone in a pig femur 30 minutes after euthanasia. The results show that there is a significant difference in R and X between tissue types (p < 0.001), with a maximum resistive contrast of-300% at 100kHz and a maximum reactive contrast of-250% at 1 kHz.

Electrical impedance sensing is responsive not only to the type of tissue in which the tip is located, but also to the type of tissue in the vicinity of the tip. Thus, the system can observe changes in impedance as drilling through the bone and generate an alert when the impedance changes indicate that the tip is proximate to a cancellous-cortical bone interface, or when the tip is proximate to a bone-soft tissue interface; bone-soft tissue interfaces include interfaces between bone and blood vessels, nerves, sinus walls, muscles, and other non-ossified tissue.

Feature(s)

Features of such a dental drill system with electrical impedance spectroscopy sensing include:

1) a coated dental drill as a sensing or driving electrode,

2) a diamond-like carbon (DLC) coating for insulating all but a few millimeters of the distal end of the drill bit,

3) an in-casing bearing for interfacing the drill bit with the impedance sensing module,

4) collecting impedance measurements at a plurality of frequencies for the particular surgical drill application, an

5) The interface detection feature is extended beyond pure threshold detection.

In addition, by interfacing the present system to a dental implant bur via the cannula space, we do not need to augment the bur in any way, nor do we reduce the working volume available to the surgeon. Despite the presence of the bearing, irrigation is still possible, allowing the surgeon to continue using the casing bit as desired.

DLC coatings are designed to have very high hardness (4000-. By applying this insulating coating to a large portion of the drill bit and leaving only 1-3mm of the distal end exposed for sensing, we provide a more reliable and repeatable impedance measurement independent of the depth of the drill bit into the material. While some prior art techniques include providing an insulating material for application to the drilling apparatus, they do not specify the type of insulating material, and they also do not leave an area exposed at the distal end for sensing.

Collecting impedance measurements at multiple frequencies rather than a single frequency has the potential for better classification between cancellous and cortical bone. The increased number of measurements will allow us to explore additional features that can be used to compare two bone types. Most prior art techniques are based on threshold detection at a single frequency to alert the clinician of the proximity to the tissue interface. We use a number of features and algorithms to find the best combination for interface detection.

In an embodiment, a method of detecting access of a drill bit to cortical bone while drilling bone using the drill bit includes providing 302 (fig. 8) an insulating coating extending from near a cutting end of the drill bit to a handpiece end of the drill bit and contacting 304 the drill bit with a sleeve bearing. The EIS measurement and calculation unit then drives 306 a voltage limiting current between the bit and the ground plate at least one AC frequency and measures voltage and phase, then determines 308 an impedance from the measurement of the voltage and phase between the bit and the ground plate; and an alarm is generated 310 when the impedance changes, indicating an approaching cancellous-cortical bone or bone-soft tissue interface.

In an alternative embodiment, the contact portion of the handpiece end of the drill bit is exposed outside of the DLC insulating coating, and the handpiece is modified to provide electrical contact from the EIS measurement and computing equipment to this exposed portion of the handpiece end of the drill bit while insulating the remainder of the drill handpiece from the EIS measurement and computing equipment.

Combinations of features

A dental drill system having Electrical Impedance Sensing (EIS), designated as a, configured to indicate whether a drill bit of the dental drill system is proximate a cancellous-cortical bone interface or a bone-soft tissue interface, the dental drill system comprising: a dental drill having a casing bit in a handpiece of the dental drill, the casing bit having an insulating coating extending from adjacent a cutting end of the drill bit to a handpiece end of the drill bit; a casing bearing electrically coupled to a non-insulated interior of a casing bit; an EIS measurement and calculation unit configured to measure an impedance between the sleeve bearing and the ground plate; and a processing system configured to distinguish whether a drill bit of the dental drill system is proximate to a cancellous-cortical bone or a bone-soft tissue interface.

A dental drill system designated AA, comprising a dental drill system designated a wherein an electrically insulated portion of the drill bit is insulated using a diamond-like carbon (DLC) coating.

A dental drill system designated AB, comprising a dental drill system designated a or AA, wherein the EIS measurement and calculation unit provides a voltage limited current at each of a plurality of frequencies, and measures the resulting voltage and phase.

A dental drill system designated AC, comprising a dental drill system designated A, AA or AB, wherein the EIS measurement and calculation unit is configured to provide a visual and/or audible alert when the drill bit is proximate to cortical bone.

A dental drill system designated AD, comprising a dental drill system designated a, AA, AB or AC, wherein the EIS measurement and calculation unit is configured to measure impedance at least two frequencies in the range of 100 to 100000 hertz.

A method, designated B, of detecting the proximity of a drill bit to cortical bone or to a bone-soft tissue interface while drilling bone using the drill bit, the method comprising: providing an insulating coating extending from near the cutting end of the drill bit to the handpiece end of the drill bit, the drill bit being in contact with the sleeve bearing; driving a voltage limited current between the drill bit and the ground plate at least one alternating current frequency; measuring the voltage and phase between the bit and the ground plate; and determining an impedance from the measured voltage and phase; and generating an alert when the impedance changes indicating proximity to a cancellous-cortical bone interface or a bone-soft tissue interface.

A method designated BA, comprising the method designated B, wherein the voltage limited current is driven at a plurality of frequencies between 100 and 100000 hertz.