EA037773B1 - Electrical impedance sensing dental drill system configured to detect cancellous-cortical bone and bone-soft tissue boundaries - Google Patents

Abstract

A dental drill system with electrical-impedance sensing indicates when a bit of the drill system approaches cortical-cancellous bone, or bone-soft tissue interfaces. The drill system has a dental drill handset having a cannula bearing electrically coupled to a drilling bit, the drilling bit having an electrically insulated portion and an exposed portion. The cannula bearing is coupled to an electrical impedance spectroscopy sensing device configured to measure impedance between the cannula bearing of the dental drill handset and a ground plate, and a processing system uses EIS measurements to distinguish when the bit of the drill system approaches cortical- or cancellous bone, or bone-soft tissue interfaces.

Description

Priority claims

This application claims priority under US Provisional Application No. 62/475724, filed March 23, 2017. This application also claims priority under US Provisional Patent Application No. 62/468490, filed March 8, 2017. Full Contents of Both Provisional Applications referred to in this paragraph is incorporated herein by reference.

State interest

The present invention was created with state support under the grant no. 1 R41 DE 024938-01 supplied by the National Institutes of Health. The state has certain rights to this invention.

Prior art

Bone tissue usually exists in two significantly different forms: as compact bone tissue and cancellous bone tissue. Compact bone tissue is usually found on the surfaces of the bone entering the joints, as well as large areas of the shaft of the tubular bones, and other areas that can be under heavy stress. Compact, or cortical, bone tissue covers the outer surfaces of the entire bone and is denser and more structured in nature than cancellous bone. It consists of densely spaced osteons, each of which consists of a Haversian canal (approximately 50 µm in diameter) in the center, surrounded by concentric circles of the matrix. Spongy bone tissue has a spongy structure, forming a cellular mesh that supports and transfers loads to the compact bone tissue and from the compact bone tissue. Spongy bone, also called trabecular or cancellous bone, is found on the inner side of tubular bones and jaw (upper and lower) bones and primarily provides lightweight, more flexible structural support than compact bone. It is formed by trabeculae arranged in a honeycomb-like structure, and the pores within the cancellous bone are often filled with bone marrow and blood vessels.

The physical and biological properties of compact and cancellous bone tissue differ due to differences in structure. In particular, due to the significantly different porosity of these types of bone tissue, penetration and adhesion of adhesives, the degree to which a screw or rod will be retained in the bone, the rate of bone invasion into the pores of implanted objects differs between compact and cancellous bone tissue.

Bone tissue is rebuilt throughout life. Where compact bone tissue covers cancellous bone tissue, the thickness of compact bone tissue varies depending on genetic factors, nutrition and physical activity during childhood, the patient's age and health status, and medical events that have occurred, including fractures, periodontal disease, extraction of teeth, the load on the bone tissue from muscle and weight, and other factors. Surgeons should expect differences in bone structure in different patients. In the lower and upper jaws, in particular, clinicians characterize the bone tissue at the sites of the dental implant according to the classification of Legholm and Zarb to determine the chances of successful implantation. There are four types, ranging from homogeneous compact bone to a combination of compact and cancellous bone to almost completely cancellous bone with low density. This classification depends on the location of the implant (i.e. anterior region, premolar and molar region) and patient characteristics.

Bone, and in particular the bones of the head, including the lower jaw and the upper jaw, can be penetrated by nerves and arteries, usually through an opening, or opening, through the entire bone. These nerves and arteries are very important structures, because if they are damaged, there is the possibility of loss of sensitivity in parts of the mouth or face, or this can lead to necrotic changes in parts of the bone. For example, the lower alveolar nerve (IAN) passes through the lower jaw.

In a surgical procedure involving oral surgery, it is desirable for the surgeon to be aware of the type and size of the bone and the surrounding structures, including the very important structures in which he works. The surgeon may need to modify surgical techniques, such as drilling depth and path, according to the size, type and thickness of the layers of bone with which he is working, to prevent penetration of adjacent structures, such as sinuses, such as the maxillary sinus, and nerves, such as the IAN.

One common dental surgical procedure is the placement of an anchor implant to which abutments or dentures can be attached. This procedure requires drilling into the bone to form an initial osteotomy, or cavity in the bone, into which the implant is placed.

In the initial osteotomy, the surgeon can drill through the first layer of compact bone to cancellous bone, must drill deep enough into the bone to obtain good implant connection surfaces, but ensure that the drill does not penetrate the thin distal layer of compact bone to prevent such surgical complications,

- 1 037773 as infections or neurosensory disorders that occur when entering the maxillary sinus cavity through the upper jaw, or into a nerve or blood vessel.

The essence of the invention

Dental system for drilling with determination of electrical impedance spectroscopy, configured to indicate the location of the nozzle of the system for drilling in adjacent compact or cancellous bone tissue, approaching the border of cancellous / compact bone tissue or approaching the border of bone / soft tissue, includes a drill having in its hand unit, a tubular nozzle, wherein the tubular nozzle has an insulating coating covering the entire surface except for a portion of the distal surface of the incisal edge; a tubular liner electrically connected to the non-insulated inner surface of the tubular nozzle tube, an electrical impedance spectroscopy (EIS) measuring and calculating unit configured to measure the impedance between the tubular liner and a ground plate or return electrode, and a data processing system adapted to discriminate between changes in electrical properties indicating that the cancellous / compact bone boundary is approaching, or changes when the drilling attachment approaches the cancellous / compact bone boundary or the bone and soft tissue boundary.

The method for detecting the proximity of the nozzle to compact bone tissue or soft tissue when drilling the bone with the nozzle includes the steps of providing an insulating coating extending from a place near the cutting end of the nozzle to the end of the nozzle facing the hand unit, providing contact of the nozzle with the tubular insert, feeding a voltage limited current between the nozzle and the ground plate at at least one AC frequency; measure the voltage and phase between the nozzle and the grounding plate; determine the impedance from the measured voltage and phase and generate a signal when the impedance changes, indicating the boundary between bone and soft tissue or between cancellous and compact bone tissue.

Brief Description of Drawings

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

FIG. 2 is a schematic drawing of a drill bit of the present drilling system.

FIG. 3 is a photograph showing an embodiment of a drill having a nozzle with an attached tubular liner.

FIG. 4 is an illustration of the electrical resistance and reactance of cancellous and compact bone samples measured on a prototype integrated into a Nobel Biocare Drill with a 2mm twist drill.

FIG. 5 is a photograph of a DLC coated drill bit having an uncoated cutting end.

FIG. 6 illustrates the difference between the normalized mean resistance and reactance of cancellous and compact bone, measured on a prototype integrated into a standard Nobel Biocare Drill with an ex vivo drill bit.

FIG. 7 illustrates the difference between the normalized mean resistance and reactance of cancellous and compact bone, measured on a prototype integrated into a standard Nobel Biocare Drill with a drill bit in fresh in situ bone.

FIG. 8 is a flowchart of a method for determining the approach of a drill bit to compact bone tissue during surgery.

Detailed Description of Embodiments

Significantly different cellular elements of compact and cancellous bone tissue provide different capacities for transfer and storage of electric charge, which is characterized, respectively, by electrical conductivity (σ) and electrical permeability (ε) (σ and ε are inversely proportional to resistance and reactivity). When registering such electrical properties in a wide frequency range (from hundreds of Hz to tens of MHz) when performing electrical impedance spectroscopy (EIS), significant differences were recorded between compact and cancellous bone tissue. Measurements of electrical impedance in a pedicle screw insert in the spine were studied, and it was found that the difference in electrical characteristics of cancellous and compact bone tissue could be used to guide surgeons through the vertebral bone.

In this document, we describe an EIS device combined with a drill for drilling holes in bone, which may be required, for example, for a variety of dental surgeries and some non-dental surgeries. The drill is particularly configured to measure in vivo bioimpedance spectra during an initial osteotomy in dental implantation procedures. The drill, in particular, is configured to measure the electrical impedance spectra of bone structures in vivo while advancing the drill into the structure. This EIS drill provides the clinician with real-time feedback, such as an audible or visual signal, to allow the clinician to stop drilling before the perforation of the bed occurs (if immediate intervention is required). In a particular embodiment, the drill is a dental drill.

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FIG. 1 illustrates a drilling system 100 with an EIS definition. The hand unit 102 of the drill includes a high-speed motor and a drive shaft 104 leading to a rectangular bevel gear unit 106, the bevel gear unit and the drive shaft casing 110 being insulated by an insulating cover 108. The bevel gear unit is connected to a drill bit 112 having an insulated portion 114 and an open cutting portion 116. In some embodiments, the open cutting portion 116 is a ball burr portion, and in other embodiments, the tip of a twist drill; the insulated portion extends from the cutting portion to the end of the nozzle facing the handpiece, the nozzle being mechanically inserted into the dental drilling handpiece. Inside the bevel gear assembly 106 is a tubular liner 118 electrically connected to the attachment 112. The handpiece 102 has a tubular connecting casing 120 housing the irrigation fluid tube 122, an electrical drive wire for the handpiece motor 102, and an electrical wire for connecting said tubular liner 118 to the unit 130 for measuring and calculating impedance spectroscopy (EIS), while the unit 130 for measuring and calculating the EIS is also connected via another wire 132 to the second electrode plate 134. The unit 130 for measuring and calculating the EIS contains an EIS excitation unit 136, capable of operating at 100, 1000, 10000 and 100000 Hz under the control of processor 138, and an EIS impedance measurement unit 140. In alternative embodiments, the EIS impedance measurement and computation unit 130 is configured to operate at two or more frequencies in the 100 Hz to 1 MHz range. The processor 138 has a memory 142 with EIS measurement software and classifier software 144, the classifier software is configured to use the EIS measurements to determine whether the tip 112 is drilling cancellous bone or compact bone and to notify , the tip 112 for which type of bone is inserted using the indicator 146.

The twist drill embodiment is illustrated in more detail in FIG. 2. Twist drill bit 160 has an open, or non-insulated, end 162 having cutting edges that can contact and drill holes in bone. The bit 160 also has an electrically insulated portion 164 bearing a diamond-like carbon (DLC) coating, a coating that is both very hard so that it has little wear when drilling holes in bone and has an electrically high resistivity, with a DLC coating extends along the remainder of the outside of the bit 160 to the boring end of the bit 160, which includes portions engaging the bevel gear of the boring head 170 and includes portions along the grooves 171. The bit 160 also has an uninsulated axial hole 172 extending from the boring end of the bit inward nozzles, but not through.

Within the axial bore 172, an uninsulated end portion 174 of the tubular liner 166 is disposed in electrical contact with the uninsulated surface of the nozzle 160 in the bore. A tubular liner 166 extends from the end of the nozzle 160 through the insulation 176 to the electronic unit 130 for measuring and calculating the EIS (FIG. 1). The drive shaft 178 and the bevel gear 180 rotate to drive the bevel gear 168 of the drill head 170 to rotate the drill bit 160 for drilling holes in the bone.

FIG. 1 and 2 are diagrams and FIG. 3 is a photograph showing an embodiment of an experimental tip 202 having a nozzle 204 provided with a tubular liner 206 and an attached insulated wire 208, and FIG. 4 is a photograph showing a pair of uninsulated tubular bushings 210. In an embodiment, tubular bushings 210, 206 are made of stainless steel.

In various embodiments, the uninsulated end portion 174 of the nozzle 160 or the uninsulated ball portion of the nozzle 116 has a length of one to three millimeters.

EIS drilling system operation.

The EIS system for drilling consists of an EIS measurement and calculation unit, a drill and a nozzle with a tubular insert. The location of the liner 206 within the drill bit tube does not reduce the working surgical space and still allows irrigation through the tube or around the outer surface of the drill bit. The tubular liner connects to a wire that mates with the impedance analyzer. Similarly, return electrode 134 (FIG. 1) is connected to another wire that mates with the impedance analyzer. A voltage limited alternating current (AC) is applied between the two electrode elements at multiple frequencies and the voltage and phase induced between them are recorded. From these measurements, impedance is calculated as the ratio of voltage to current.

Impedance (Z) is calculated as the ratio of the measured voltage to the applied current; we consider impedance to be a complex quantity consisting of a real resistive component (R) and an imaginary reactive component (X), according to the equation Z = R + jX. The electronics unit calculates R and X from the measurements at each test frequency. From this we calculate impedance, conductivity, resistivity, and the like.

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We have shown in previous ex vivo and in situ experiments on pig femurs that compact bone has higher resistivity and impedance than cancellous bone. The resistivity ratio of compact bone to cancellous bone is in the range of 1.28-1.48 in ex vivo bone and 2.82-2.94 in fresh bone in situ. As a result, we would expect that as the drill bit moves through the cancellous bone towards the compact bone interface, we will see an increase in impedance / resistivity as we approach this border.

In an embodiment, the EIS measurement and calculation unit is configured to provide visual and / or audible signals when the drill bit approaches the compact bone.

The clinical use of this device includes the use of a drill to create an initial osteotomy (hole in the bone) for implant insertion. Electrical characteristics such as bone resistivity and reactance are recorded at one or multiple frequencies as the drill moves into the bone. These measurements are entered into a real-time grading unit used to determine the approximation of the tissue boundary (i.e. the cancellous-compact bone boundary). As clinical feedback, a visual or audible signal is used, which increases in pulse repetition rate depending on the change in impedance.

We collected a significant amount of data on the electrical characteristics of compact and cancellous bone ex vivo and in situ, and showed a significant difference in impedance between the two types of bone.

In an ex vivo experiment, we placed standard tubular drill bits at a depth of 3 mm in 10 samples of each - compact and cancellous - bone tissue freshly obtained from a pig, and recorded the impedance in the range of 100 Hz - 1 MHz at 41 frequencies. We have shown that there are significant differences in R and X (p <0.05) between these two types of bone, with a difference in resistivity of 41, 37, 29 and 32%, respectively, at 0.1, 1, 10 and 100 kHz. ... These trends recorded in our prototype are similar to those described earlier for cancellous and compact bone tissue.

In an in situ experiment, we used a specially made DLC coated drill bit to record the impedance from 40 samples of each compact and cancellous bone tissue in the femur of pigs 30 min after sacrifice. We have demonstrated that there are significant differences in R and X (p <0.001) between these tissue types, with the maximum difference in resistance being ~ 300% at 100 kHz, and the maximum difference in reactance being ~ 250% at 1 kHz.

The electrical impedance varies not only with the type of tissue in which the tip is located, but also with the types of tissue near the tip. The system can therefore monitor changes in impedance as the tip pierces bone and generates a signal when changes in impedance indicate that the tip is approaching the cancellous-compact bone boundary, or when the tip is approaching the bone-soft tissue boundary; the boundaries of bone tissue and soft tissue include the boundaries between bone tissue and blood vessels, nerves, sinus lining, muscles, and other non-ossified tissues.

Distinctive features.

Features of this Dental Impedance Spectroscopy Drilling System include:

1) a coated dental drill bit as a sensing or triggering electrode,

2) a diamond-like carbon (DLC) coating to isolate the entire drill bit, with the exception of a few millimeters located in the distal region,

3) an intratubular insert for interaction of the drilling nozzle with the impedance determination module,

4) collecting impedance measurements at multiple frequencies for that particular surgical drilling application,

5) extension of the function of determining the boundary beyond the purely threshold definition.

In addition, due to the interaction of our system with the dental handpiece for implantology through the tubular space, we do not need in any way to modify the drill, nor to reduce the working volume available to the surgeon. Irrigation is still possible despite a liner that allows surgeons to continue to use tubular drill bits for their intended purpose.

DLC coatings have extremely high hardness (4000-9000 HV), high resistivity (up to 106 ohm-cm) and are biocompatible. By applying this insulating coating to most of the drill bit and leaving only 1-3 mm distal open for detection, we provide more reliable and reproducible impedance measurements that are independent of the depth of the drill bit immersed in the material. While some prior art solutions provide an insulating material to be applied to the boring device, they do not define the type of insulating material, nor do they leave an uncovered area at the distal end to define.

Collecting impedance measurements at multiple frequencies instead of a single frequency allows better discrimination between cancellous and compact bone. The increased number of measurements will allow us to explore additional characteristics that can be used to distinguish between these two types of bone. Much of the prior art relies on single frequency threshold detection to alert clinicians when tissue boundaries are approaching. We use a variety of features and algorithms to find the optimal combination to use in boundary detection.

In an embodiment, a method for detecting the approach of a tip to a compact bone tissue when drilling a bone with a tip includes the steps of: providing 302 (FIG. 8) an insulating cover extending from a location near the cutting end of the tip to the tip of the tip facing the handpiece , provide contact of the nozzle with the tubular liner; supplying a voltage limited current between the nozzle and the ground plate at at least one AC frequency; measure the voltage and phase between the nozzle and the grounding plate; and determining the impedance from the measured voltage and phase and generating a signal when changes in impedance indicate an approach to the cancellous-compact bone boundary or the bone-soft tissue boundary.

In an alternative embodiment, the contact portion of the handpiece end of the handpiece is not covered with a DLC insulating coating and the handpiece is modified to provide electrical contact of the EIS measurement and computation device with this uncoated handpiece end of the handpiece while isolating the rest of the parts of the drilling hand unit from the EIS measurement and calculation device.

Combination of distinctive characteristics.

The dental drilling system, designated A, with electrical impedance determination (EIS), configured to indicate whether the drilling attachment approaches the cancellous-compact bone boundary or the bone-soft tissue boundary, includes a drill having in its the hand unit has a tubular nozzle, while the tubular nozzle has an insulating coating extending from a place near the cutting end of the nozzle to the end of the nozzle facing the hand unit, a tubular liner electrically connected to the uninsulated inner surface of the tube of the tubular nozzle, an EIS measurement and calculation unit made with the possibility of measuring the impedance between the tubular liner and the grounding plate, and a data processing system configured to determine the approach of the drilling system nozzle to the cancellous-compact bone tissue boundary or to the bone-soft tissue boundary.

A dental drilling system, designated AA, includes a dental drilling system, designated A, in which an electrically insulated portion of the drill bit is insulated with a diamond-like carbon (DLC) coating.

A dental drilling system, designated AB, includes a dental drilling system, designated A or AA, in which an EIS measuring and calculating unit provides a voltage-limited current at each of a plurality of frequencies and measures the resulting voltage and phase.

The dental drilling system, designated AC, includes a dental drilling system A, AA, or AB, in which the EIS measurement and calculation unit is configured to provide visual and / or audible signals when the drill bit approaches the compact bone.

A dental drilling system, designated AD, includes a dental drilling system, designated A, AA, AB, or AC, in which an EIS measurement and calculation unit is configured to measure impedance at at least two frequencies in the range 100-100,000 Hz.

The method, indicated by B, of determining the approach of the tip to the compact bone tissue or the approach of the tip to the bone-soft tissue boundary, while drilling the bone tissue with the tip includes the steps of providing an insulating coating extending from a location near the cutting end of the tip to the end nozzles facing the hand unit ensure contact of the nozzle with the tubular liner; supplying a voltage limited current between the nozzle and the ground plate at at least one AC frequency; measure the voltage and phase between the nozzle and the ground plate, determine the impedance from the measured voltage and phase, and generate a signal when changes in impedance indicate an approach to the cancellous compact bone or to the bone-soft tissue boundaries.

The method indicated by BA, including the method indicated by B, wherein the voltage limited current is supplied at a frequency of 100-100000 Hz.

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Conclusion.

Changes can be made to the methods and systems described above without going beyond their scope. Thus, it should be noted that the subject matter contained in the above description or represented in the accompanying drawings is to be construed in an illustrative and not a limiting sense. The formula below is intended to cover all the general and particular features described in it, as well as all the statements of the formula of the presented method and system, which, from the point of view of the language, can be considered to be within their framework.

Claims (7)

CLAIM 1. Dental system for drilling with determination of electrical impedance (EIS), made with the possibility of indicating the approach of the nozzle of the system for drilling to the border of spongy and compact bone tissue or to the border of bone and soft tissue, containing a drill having a tubular nozzle in its hand unit, when this, the tubular nozzle has an insulating coating extending from a location near the cutting end of the nozzle to the end of the nozzle facing the hand unit, a tubular liner electrically connected to the uninsulated inner side of the tube of the tubular nozzle, an EIS measuring and calculating unit adapted to measure the impedance between the tubular liner and a grounding plate, and a data processing system configured to determine the approach of the drilling system nozzle to the cancellous-compact bone tissue boundary or to the bone and soft tissue boundary. 2. The dental drilling system of claim 1, wherein the electrically insulated portion of the drill bit is insulated with a diamond-like carbon (DLC) coating. 3. The dental drilling system of claim 1, wherein the EIS measuring and calculating unit provides a voltage limited current at each of the plurality of frequencies and measures the resulting voltage and phase. 4. A dental drilling system according to claim 1, wherein the EIS measuring and calculating unit is configured to provide visual and / or audible signals when the drilling bit approaches the compact bone tissue. 5. Dental drilling system according to claims 1 to 3 or 4, wherein the EIS measurement and calculation unit is configured to measure impedance at at least two frequencies in the range 100-100000 Hz. 6. A method for determining the approach of the nozzle to a compact bone tissue or the approach of the nozzle to the boundary of bone and soft tissues when drilling a bone with a nozzle using the system according to claim 1, the method comprising the steps of forming an insulating coating extending from a location near the cutting end of the nozzle the end of the nozzle facing the hand unit; bring the nozzle into contact with the tubular liner; supplying a voltage limited current between the nozzle and the ground plate at at least one AC frequency; measure the voltage and phase between the nozzle and the grounding plate; determine the impedance of the measured voltage and phase; and generate a signal when changes in impedance indicate an approach of the cancellous-compact bone boundary or the bone-soft tissue boundary. 7. The method of claim 6, wherein the voltage limited current is applied at multiple frequencies between 100 and 1,000,000 Hz.