Device and Method for Detecting Tooth Cracks Based on Rayleigh Wave Transmission Attenuation and Nonlinear Response

Abstract

This invention relates to a device and method for detecting dental microcracks based on Rayleigh wave transmission attenuation and nonlinear response, belonging to the fields of biomedical engineering and nondestructive testing technology. The device includes a flexible dental crown detection device composed of two sets of flexible semi-circular probe assemblies. An ultrasonic transceiver array is embedded in the inner wall of each set of flexible semi-circular probe assemblies. The ultrasonic transceiver array is composed of several micro piezoelectric transducer elements arranged circumferentially. The front end face of the micro piezoelectric transducer elements faces the enamel surface, and the opposite end face is provided with an air backing layer, which can adaptively conform to the complex curved surface of the tooth and realize early qualitative identification and quantitative assessment of the depth of microcracks.

Description

Technical Field

[0001] This invention belongs to the fields of biomedical engineering and nondestructive testing technology, and in particular to a device and method for detecting tooth microcracks based on Rayleigh wave transmission attenuation and nonlinear response. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Early diagnosis of dental microcracks is a clinical challenge. Microcracks are often closed in their early stages, making them difficult to detect with the naked eye. Without timely intervention, they can lead to serious consequences such as tooth fracture or even pulpitis. Currently, clinical methods mainly include X-rays, staining, fiber optic transillumination, and conventional linear ultrasound. However, these techniques have a high rate of missed detection for early closed cracks, cannot quantitatively assess crack depth, and ionizing radiation is not suitable for frequent screening. Accurate determination of the depth of a dental microcrack directly determines the treatment plan—whether to continue conservative observation or perform timely fillings or root canal treatment. Therefore, achieving quantitative depth assessment is a core prerequisite for ensuring the long-term integrity of the tooth.

[0004] Rayleigh waves possess advantages such as concentrated surface energy, low attenuation, and sensitivity to minute near-surface defects, making them promising for detecting dental cracks. However, current technologies present challenges: conventional piezoelectric ultrasonic probes struggle to conform to the complex curvature of teeth, leading to unstable coupling; while laser ultrasound, though non-contact, suffers from excessively wide signal bandwidths, making it easy for weak nonlinear damage signals to be drowned out by the fundamental wave; furthermore, the devices are bulky and have complex optical paths, unsuitable for intraoral operation. Therefore, a portable detection device is needed that can adaptively conform to the curved surface of teeth, effectively amplify nonlinear signals, and quantitatively assess the depth of dental cracks. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention provides a device and method for detecting tooth microcracks based on Rayleigh wave transmission attenuation and nonlinear response.

[0006] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions: In a first aspect, a tooth microcrack detection device based on Rayleigh wave transmission attenuation and nonlinear response is disclosed, comprising: a flexible brace detection device, wherein the flexible brace detection device consists of two sets of flexible semi-circular probe assemblies, and an ultrasonic transceiver array is embedded in the inner wall of each set of flexible semi-circular probe assemblies. The ultrasonic transceiver array is composed of several micro piezoelectric transducer elements arranged circumferentially, wherein the front end face of the micro piezoelectric transducer elements faces the enamel surface, and an air backing layer is provided on the opposite end face.

[0007] Furthermore, the front end face of the micro piezoelectric transducer array element is provided with a micro wedge, and the incident angle of the micro wedge is configured to be greater than the first critical angle of enamel and less than the second critical angle.

[0008] Furthermore, the flexible semi-circular probe assembly also includes an acoustic impedance matching layer, which is disposed between the front end face of the micro piezoelectric transducer array element and the enamel surface.

[0009] Furthermore, the flexible semi-circular probe assembly also includes a flexible cable layer with parallel lines.

[0010] Furthermore, the acoustic impedance matching layer, micro wedge, micro piezoelectric transducer array, air back layer, and flexible cable layer in the flexible semi-circular probe assembly are embedded as a whole in a medical-grade flexible covering and integrally formed.

[0011] Furthermore, the flexible braces testing device also includes a signal excitation and acquisition unit connected to the ultrasonic transceiver array via a flexible cable.

[0012] Furthermore, the ultrasound transceiver array includes a tongue-side transducer excitation array and a buccal-side transducer receiving array.

[0013] Secondly, a method for detecting tooth microcracks based on Rayleigh wave transmission attenuation and nonlinear response is disclosed, including: The flexible dental prosthesis is worn on the patient's teeth, and it is manually pressed to make it adapt to the tooth surface. The signal excitation and acquisition unit drives the lingual transducer excitation array to emit high-frequency Rayleigh waves, and the sound waves propagate along the enamel surface to the buccal transducer receiving array. The signal collected by the cheek transducer receiving array is received by an oscilloscope, and the time domain amplitude and frequency domain harmonic characteristics of the signal are analyzed. Opening cracks are determined based on the attenuation of the fundamental amplitude, and closed microcracks are determined based on the second harmonic component.

[0014] Furthermore, when no significant signal is detected in static testing, the patient is guided to perform periodic biting movements, and Rayleigh waves are emitted continuously and the periodic fluctuations of the received signal amplitude are monitored to determine microcracks.

[0015] Furthermore, by controlling the excitation frequency to scan from low to high frequencies, the peak frequency of the normalized nonlinear coefficient β is extracted and combined with the deep inversion model. Calculate the crack depth, where Rayleigh wave velocity in tooth enamel This is the calibration coefficient.

[0016] The above one or more technical solutions have the following beneficial effects: This invention adopts a universal flexible dental crown structure, which utilizes the natural elasticity and plasticity of flexible materials to achieve adaptive full fit to the complex curved surfaces of teeth of different patients. It eliminates the need for complex mechanical scanning mechanisms and solves the problems of difficult coupling, inconvenient operation, and unstable positioning of traditional rigid probes on curved surfaces of teeth, making it suitable for rapid chairside screening in clinical settings.

[0017] This invention combines Rayleigh wave transmission attenuation and nonlinear response characteristics for dual discrimination and innovatively introduces a master dynamic modulation mechanism based on physiological alternating occlusion. This mechanism utilizes the alternating load generated by the patient's occlusion to drive the periodic opening and closing of closed microcracks, explicitly amplifying weak nonlinear damage signals without the need for external hardware, thus completely overcoming the shortcomings of traditional ultrasound, such as low signal-to-noise ratio and easy failure to detect early closed cracks.

[0018] This invention overcomes the limitations of existing technologies that can only perform qualitative screening, providing a non-destructive quantitative assessment method for the depth of microcracks. Utilizing the characteristic that Rayleigh wave penetration depth varies with frequency, nonlinear characteristic peaks are extracted through frequency conversion scanning, allowing for precise inversion of crack depth and dimensions. This not only provides crucial objective data support for clinical determination of whether root canal treatment is necessary, but also avoids complex imaging algorithms, enabling diagnosis through intuitive waveform feature interpretation, significantly reducing equipment costs and operational barriers.

[0019] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0020] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0021] Figure 1 This is a schematic diagram of the overall appearance of the flexible braces testing device according to Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the circumferential arrangement of the probe assembly in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the detection principle of the probe assembly in Embodiment 1 of the present invention; Figure 4 This is a partially enlarged cross-sectional schematic diagram of the flexible detection probe assembly according to Embodiment 1 of the present invention; Figure 5 This is a rear view schematic diagram of the transducer array portion according to Embodiment 1 of the present invention; Figure 6 This is a schematic diagram of the circuit interface and circumferential probe assembly instantiation in Embodiment 1 of the present invention; Figure 7This is a schematic diagram of the adaptive force application of the flexible dental brace in Embodiment 2 of the present invention; Figure 8 This is a comparison diagram of the time-domain waveforms in Embodiment 3 of the present invention; Figure 9 For example, in embodiment 3 of the present invention, corresponding to Figure 8 Comparison of signal spectrum under two conditions; Figure 10 This is a schematic diagram of frequency scanning characteristic curves corresponding to different crack depths in Embodiment 4 of the present invention; In the diagram, 1. Flexible braces testing device; 2. Flexible semi-circular probe assembly; 100. Main cable; 3. Lingual transducer excitation array; 4. Buccal transducer receiving array; 5. Miniature piezoelectric transducer element; 6. Rayleigh wave; 7. Flexible covering; 8. Miniature wedge; 9. Enamel; 10. Piezoelectric plate; 11. Acoustic impedance matching layer; 12. Air backing layer; 13. Ultrasonic gel; 14. Flexible cable layer; 15. Wire; 101. Front electrical connection; 102. Back electrical connection; 201. Front electrode; 202. Back electrode; 16. Tooth invisible crack detection system; 17. Multi-channel signal generator; 18. Multi-channel high-voltage amplifier; 19. Oscilloscope; 20. Pressing pressure. Detailed Implementation

[0022] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0023] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0024] It should be noted that the directional terms used in the following embodiments are described based on the accompanying drawings and actual usage habits.

[0025] Example 1 In dental clinical practice, the accurate determination of the depth of a tooth crack directly determines the choice of treatment plan: for superficial cracks that are limited to the enamel layer, conservative observation is usually adopted; while for deep cracks that have penetrated into the dentin layer or even involved the pulp, timely filling and restoration or root canal treatment is required.

[0026] Therefore, achieving quantitative assessment of the depth of microcracks is a core prerequisite for avoiding overtreatment or undertreatment and ensuring the long-term integrity of tooth structure.

[0027] Rayleigh waves, as elastic waves whose energy is mainly concentrated within a depth range of about one wavelength on the surface of a medium, have advantages such as high surface energy density, small propagation attenuation, and extremely high sensitivity to near-surface micro-defects. They have broad application prospects in the non-destructive detection and monitoring of early microcracks on and near the enamel surface.

[0028] The inventors discovered that conventional piezoelectric ultrasonic testing technology utilizes a coupling agent to transmit acoustic energy, offering advantages such as high signal-to-noise ratio and large detection depth. However, unlike the regular planar or pipe structures used in industrial testing, the tooth surface exhibits an extremely irregular and complex curved shape. Traditional rigid planar probes struggle to achieve a good fit with the tooth surface, leading to unstable coupling and severely impacting the repeatability and accuracy of the test results.

[0029] In addition, although laser ultrasound technology can achieve non-contact detection and avoid coupling problems, the ultrasonic signal it generates has an excessively wide bandwidth. Weak nonlinear damage signals are easily drowned out by the broadband fundamental wave. Furthermore, the equipment is bulky and the optical path adjustment is complex, making it difficult to adapt to the narrow operating space inside the oral cavity.

[0030] More importantly, existing linear ultrasonic testing methods mainly rely on changes in the energy of sound waves reflected or transmitted at the defect interface. However, early tooth cracks are often in a tightly closed state, and sound waves can easily pass through the closed interface without significant reflection, resulting in a very high rate of missed detection of early micro-lesions, which is difficult to meet the clinical need for accurate early diagnosis of tooth cracks.

[0031] To address the aforementioned issues, this embodiment provides a tooth invisible crack detection device based on Rayleigh wave transmission attenuation and nonlinear response characteristics.

[0032] refer to Figures 1 to 6 The detection device includes a flexible braces detection device 1, a flexible semi-circular probe assembly 2, a lingual transducer excitation array 3, and a buccal transducer receiving array 4; wherein, two sets of flexible semi-circular probe assemblies 2 constitute the flexible braces detection device 1, and each set consists of a lingual transducer excitation array 3 and a buccal transducer receiving array 4.

[0033] like Figure 1 As shown, the flexible braces testing device 1 consists of two sets of flexible semi-circular probe assemblies 2. The biting part of the flexible braces testing device 1 can be provided with an opening to allow the patient to breathe. The entire testing device is connected to external components via a main cable 100.

[0034] The flexible semi-circular probe assembly 2 is made of medical-grade polydimethylsiloxane (PDMS) or transparent silicone rubber with high transparency and low Shore A hardness (e.g., Shore A hardness below 40). This material has excellent optical transmittance, allowing operators to visually identify the position of the internal teeth through the carrier during wear for assisted alignment.

[0035] Meanwhile, the edge area of ​​the flexible semi-circular probe assembly 2, that is, the extension without circuitry and array, is configured as a trimmable area. The operator can use scissors to trim and adjust this edge area according to the actual depth of the patient's oral vestibule to avoid compressing the gums and ensure the comfort and stability of the device.

[0036] like Figure 2 As shown, to achieve acoustic coverage of the internal structure of the tooth, each flexible semi-circular probe assembly 2 contains two flexible ultrasonic transducer arrays in the inner wall of the crown corresponding to the flexible semi-circular probe: a lingual transducer excitation array 3 for lingual excitation and a buccal transducer receiving array 4 for buccal reception. With this distribution, corresponding transducers are installed in four locations of the oral cavity—maxillary buccal, maxillary lingual, mandibular buccal, and mandibular lingual—for excitation and reception of ultrasonic waves, respectively.

[0037] Specifically, the tongue-side transducer excitation array 3 and the buccal-side transducer receiving array 4 are respectively embedded in the flexible semi-circular probe assembly 2. The tongue-side transducer excitation array 3 and the buccal-side transducer receiving array 4 are each composed of 16 miniature piezoelectric transducer elements 5 arranged in a circumferential linear pattern.

[0038] like Figure 3 As shown, Rayleigh wave 6 is excited from the lingual transducer excitation array 3, passes through the flexible cover 7, and undergoes modal adjustment via a micro-wedge 8. The incident angle of the micro-wedge is configured to be greater than the first critical angle of the enamel and less than the second critical angle to ensure that the excited ultrasound waves propagate primarily in the Rayleigh wave mode along the enamel surface. Rayleigh wave 6 propagates along the enamel surface 9 until it is received at the buccal transducer receiving array 4.

[0039] It should be understood that in ultrasonic testing, when sound waves are incident from a micro-wedge onto the enamel surface, as the incident angle increases, the first critical angle is reached. At this point, the refracted longitudinal wave propagates along the surface, and then the longitudinal wave no longer enters the enamel interior, leaving only the refracted transverse wave and surface wave. As the incident angle continues to increase to the second critical angle, the refracted transverse wave also begins to propagate along the surface, after which only Rayleigh waves crawl along the enamel surface. It should be noted that the definitions of the first and second critical angles and their physical significance in surface wave excitation are mature theories in the field of ultrasonic nondestructive testing, and are content that can be understood by those skilled in the art based on basic acoustic principles.

[0040] In this embodiment, the incident angle of the micro-wedge is configured to be greater than the first critical angle and less than the second critical angle. The purpose is to make the excited ultrasonic waves mainly propagate in Rayleigh wave mode, confining the energy to the superficial layer of enamel, thereby effectively enhancing the detection sensitivity of early microcracks.

[0041] The energy of high-frequency Rayleigh waves is highly concentrated within approximately one wavelength of the medium surface and preferentially propagates along high-velocity, high-stiffness media. Since the acoustic impedance and elastic modulus of tooth enamel are significantly higher than those of flexible covering materials, sound waves excited from the lingual side will follow the external contour of the enamel, continuously traversing the lingual, occlusal, and buccal surfaces of the tooth. The energy is effectively confined within the superficial layer of the enamel and strictly conforms to its external contour, being directionally transmitted to the buccal side via the occlusal region. Therefore, any hidden cracks on the occlusal surface located along the inevitable path of this rigid sound wave will inevitably block the Rayleigh wave or generate nonlinear harmonics, thus being effectively captured by the system.

[0042] like Figure 4 As shown, the tongue-side transducer excitation array 3 also includes a piezoelectric plate 10, which can be made of a piezoelectric material, such as PZT (lead zirconate titanate), BaTiO3 (barium titanate), or PbNb2O6 (lead mastanionate).

[0043] Furthermore, the flexible semi-circular probe assembly 2 also includes an acoustic impedance matching layer 11 and an air backing layer 12. The acoustic impedance matching layer 11, as part of the overall flexible enclosure 7, is disposed between the front end face of the micro piezoelectric transducer array 5 and the tooth surface.

[0044] The miniature piezoelectric transducer element 5 is tightly connected to the acoustic impedance matching layer 11 by glue or other means, ensuring that there is no air gap in the middle, thereby effectively reducing the reflection loss of sound waves at the interface between the transducer and the enamel, and improving the excitation and transmission efficiency of Rayleigh waves.

[0045] The thickness of the acoustic impedance matching layer 11 is configured to be an odd multiple of the ultrasonic wavelength at the operating frequency, preferably a quarter wavelength, to minimize the absorption of Rayleigh waves during penetration. For example, when the acoustic impedance matching layer 11 is made of materials such as polypropylene, copolyester, or ethyl vinyl acetate (EVA), its thickness is approximately between 0.3 and 0.5 mm, and the specific value can be adjusted according to the material used and its acoustic parameters.

[0046] An air back layer 12 is located on the back of the miniature piezoelectric transducer element 5. It suppresses rearward-radiated acoustic energy, reflecting it forward to enhance the amplitude of the forward-propagating Rayleigh wave. The air back layer 12 can be implemented using a foam layer, such as foam tape, sputtered or deposited foam, or directly using an air layer. The foam material can be a flexible material such as polyurethane, containing a high proportion of air or neutral gas, with a thickness of approximately 1 mm or less, contributing to a compact transducer structure.

[0047] In addition, the air back layer 12 can also be formed by applying a substance to the back of the micro piezoelectric transducer element 5 to prevent the adhesion of the flexible coating 7 material. Due to the elasticity of the flexible coating 7 material itself, when the back of the micro piezoelectric transducer element 5 is not coated with adhesive, an extremely fine gap will be formed between the two. The air layer in this gap can also serve as the air back layer of the micro piezoelectric transducer element 5, playing a role in reflecting sound waves.

[0048] To achieve good acoustic coupling between the flexible covering 7 and the crown, allowing Rayleigh waves 6 to efficiently penetrate from the flexible covering 7 into the crown, an ultrasonic gel 13 is placed between them. The acoustic impedance of the ultrasonic gel 13 is between that of the flexible covering 7 and the enamel 9, which can significantly reduce interface reflection loss. At the same time, it has appropriate viscosity and biocompatibility, which can maintain stable adhesion during use and will not irritate oral tissues.

[0049] It should be understood that in the local area where the micro piezoelectric transducer element 5 is located, from the tooth surface to the back of the tooth surface, the layers are, in sequence, the crown, ultrasonic gel 13, acoustic impedance matching layer 11, micro piezoelectric transducer element 5, air backing layer 12, and flexible covering 7.

[0050] like Figure 4 As shown, the flexible semi-circular probe assembly 2 also includes a flexible cable layer 14 with parallel lines. The flexible cable layer 14 can be a flat flexible cable (FFC) or a flexible printed circuit (FPC), and it includes independent conductors 15 stacked between two dielectric films for connecting a single micro piezoelectric transducer element to an external dental controller. Multiple conductors 15 in the flexible cable layer 14 are electrically connected to corresponding electrical connection terminals and electrodes, wherein the first conductor is electrically connected to the front electrode 201 via a front electrical connection 101; and the second conductor is electrically connected to the back electrode 202 via a back electrical connection 102.

[0051] Each miniature piezoelectric transducer element 5 is electrically connected to its corresponding electrical connection terminal and electrode via wires in the flexible cable layer 14. In the array arrangement, some elements can also be connected to their corresponding electrical connection terminals via common wires to achieve unified lead-out of the corresponding electrodes. The above connection method constitutes an array arrangement, and the cheek-side receiving array adopts the same arrangement structure.

[0052] To achieve mechanical protection and spatial positioning constraint for the micro piezoelectric transducer array elements, the acoustic impedance matching layer 11, micro wedge 8, micro piezoelectric transducer array element 5, air back layer 12, and flexible cable layer 14 in each flexible semi-circular probe assembly 2 are embedded as a whole in the medical-grade flexible covering 7 and integrally formed to form the corresponding flexible semi-circular probe assembly 2.

[0053] The acoustic impedance matching layer 11 is disposed on the side of the micro piezoelectric transducer element 5 facing the tooth surface, forming a local functional layer of the flexible encapsulation 7 on that side. The air back layer 12 is disposed on the side of the micro piezoelectric transducer element 5 away from the tooth surface, and can be formed by a local cavity, a foam layer, or an air gap. When the air back layer is formed by an air gap, it is not part of the solidified material. This flexible encapsulation structure not only provides excellent mechanical buffer protection for the fragile piezoelectric chip, preventing structural damage caused by external pressure 20 or accidental impact, but also forms a reliable waterproof barrier to prevent oral saliva from entering and causing short circuits.

[0054] In addition, each miniature piezoelectric transducer element 5 is fixed on the flexible cable layer 14 and then encapsulated as a whole. Through the internal constraint of the flexible substrate, even if the flexible braces detection device 1 undergoes macroscopic bending deformation under external force, the relative microscopic spacing and topological order between each element remain constant, thereby ensuring the precise correspondence between the lingual excitation element and the buccal receiving element in terms of physical structure.

[0055] The flexible semi-circular probe assembly 2 is electrically connected to external components via the main cable 100, together forming the tooth invisible crack detection system 16. For example... Figure 6 As shown, the system includes a signal excitation and acquisition unit and an optional external computer.

[0056] The signal excitation and acquisition unit consists of a multi-channel signal generator 17, a multi-channel high-voltage amplifier 18, and an oscilloscope 19. The multi-channel signal generator 17 and the multi-channel high-voltage amplifier 18 are used to generate and amplify the excitation signal, and the oscilloscope 19 is used to receive and display the signal. The external computer is used to perform frequency domain analysis, normalized nonlinear coefficient calculation, and crack depth inversion on the acquired signal in frequency scanning mode.

[0057] The multi-channel signal generator 17 outputs a sinusoidal pulse signal modulated by a Hanning window. This modulation method can effectively reduce the spectral sidelobes of the excitation signal, making the guided wave energy of the excitation more concentrated. After being amplified by the multi-channel high-voltage amplifier 18, the signal drives the tongue-side transducer excitation array 3 to emit ultrasonic Rayleigh waves.

[0058] During the testing phase, the system is configured to execute a sequential excitation control strategy: under the static pressure-holding state of the flexible brace, the multi-channel signal generator 17, through its internal relay array, sequentially and independently drives the individual micro piezoelectric transducer elements in the lingual transducer excitation array 3 to emit ultrasonic pulses. Based on the physical characteristic that the buccal transducer receiving array 4 only passively responds to the actual arriving sound wave signal, under the state of independent emission from a single sound source, the receiving elements distributed opposite to the excitation element can sequentially receive the transmitted signals arriving along the corresponding transmission paths and transmit them to the oscilloscope 19 for real-time display and recording.

[0059] Through the above-mentioned sequential excitation control mechanism, and in conjunction with the fixed physical topology of the array, this device eliminates the acoustic crosstalk caused by the simultaneous emission of multiple array elements from the physical source. Without the need to add a complex synchronous switching circuit at the receiving end, it can ensure a high-precision one-to-one correspondence between the exciter and the receiver on the spatial acoustic transmission path.

[0060] In practical applications, to address the problem that traditional probes are difficult to fit the complex curved surfaces of teeth and to ensure the effective propagation of Rayleigh waves along the enamel surface, this embodiment adopts a manual pressing-adaptive fitting mechanism.

[0061] like Figure 7 As shown, in the initial unworn state, the flexible cover 7 maintains a universal U-shaped contour, providing ample space. During the test preparation stage, the flexible dental appliance is placed on the tooth being tested; at this time, there may be gaps between the transducer array and the tooth surface.

[0062] Subsequently, the operator applies pressure 20 to the flexible cover 7 with their fingers. Thanks to the high elasticity and rheological properties of the matrix material, the dental cover deforms and fills the irregular grooves on the tooth surface, effectively eliminating air from the contact surface. This allows for conformal acoustic coupling between the probe and the enamel 9 without the need for a large amount of liquid coupling agent, ensuring high-precision static detection during the signal acquisition stage.

[0063] To verify the actual detection effect of the high-frequency Rayleigh wave on the early microcracks of teeth by transmission attenuation and nonlinear ultrasonic effect described in this invention, this embodiment built the tooth invisible crack detection system 16 and designed a comparative experiment.

[0064] The test subjects were two extracted human teeth: one was a healthy, undamaged tooth, and the other had a naturally closed microcrack on its surface. During the experiment, a 5-cycle Hanning window modulated sinusoidal pulse train with a center frequency of fc=1MHz was transmitted through a multi-channel signal generator, and the received waveform was displayed on an oscilloscope.

[0065] The experiment was divided into two groups: the first group tested healthy, undamaged extracted human tooth samples; the second group tested human tooth samples containing naturally closed microcracks.

[0066] The comparison diagram of the received time-domain echo signals is as follows: Figure 8 As shown in the figure, the solid line represents the signal without cracks, and the dashed line represents the signal with microcracks. It can be seen from the figure that the waveforms of the dashed line and the solid line are generally similar, but there is a certain deviation between the two wave packets, indicating that the signal may contain multiple frequency components; at the same time, this deviation also reflects the transmission attenuation characteristics of Rayleigh waves when they encounter cracks.

[0067] The corresponding signal spectrum comparison diagram is as follows Figure 9 As shown, the solid-line spectrum contains only a 1MHz fundamental frequency signal, indicating that Rayleigh waves do not generate second harmonics when passing through a crack-free linear elastic structure. The dashed-line spectrum, however, contains not only the 1MHz fundamental frequency signal but also harmonic components such as the second harmonic and third harmonic, with the second harmonic being the strongest. This proves that the presence of microcracks leads to the generation of second harmonics.

[0068] Example 2 Based on the apparatus of Embodiment 1, the purpose of this embodiment is to provide a method for detecting hidden cracks in teeth based on Rayleigh wave transmission attenuation and nonlinear response characteristics.

[0069] This method utilizes the high elastic deformation capability of flexible dental braces to achieve adaptive acoustic coupling to complex curved surfaces, and through dual analysis of the time-domain amplitude and frequency-domain harmonic characteristics of ultrasonic guided waves, it achieves rapid qualitative identification of the crack state on the tooth surface. The specific workflow is as follows: First, the flexible braces testing device 1 is placed on the patient's dentition. Utilizing the excellent rheological properties of the flexible braces testing device 1 and its integrated flexible semi-circular probe assembly 2, the operator applies normal pressure to the outer wall of the carrier by manually pressing, forcing the flexible substrate to undergo elastic deformation to fill the irregular grooves on the tooth surface and effectively eliminate air from the contact surface. Thus, without the need for a large amount of liquid coupling agent, a tight acoustic coupling between the lingual transducer excitation array 3, the buccal transducer receiving array 4, and the tooth surface is achieved.

[0070] Subsequently, a multi-channel signal generator 17 is activated to generate a narrowband pulse excitation signal with a center frequency of 1MHz. This signal is amplified by a multi-channel high-voltage amplifier 18 and then drives the lingual transducer excitation array 3 to emit high-frequency Rayleigh waves onto the tooth surface. The sound waves propagate along the enamel surface and pass through the area to be tested, where they are received by the buccal transducer receiving array 4. The echo signals are then acquired and displayed in real time by an oscilloscope 19.

[0071] Finally, dual-mode discrimination is performed based on the signal characteristics displayed on oscilloscope 19: On the one hand, time-domain amplitude is monitored for discrimination: the amplitude change of the received signal's time-domain waveform is monitored. If the amplitude of the Rayleigh wave fundamental frequency signal decreases significantly relative to the defect-free reference signal, it indicates the presence of an open-type crack or macroscopic defect on the tooth surface that obstructs the propagation of sound waves.

[0072] On the other hand, frequency domain harmonic discrimination of the monitoring signal: monitor the frequency domain spectrum characteristics of the received signal. If obvious second harmonic or higher harmonic components appear in the spectrum outside the fundamental frequency, it indicates that there are closed microcracks on the tooth surface that cause distortion of the acoustic waveform.

[0073] To address the issue of weak signals from very early-stage microcracks under static detection, this embodiment also provides an optional signal enhancement detection step.

[0074] If no obvious waveform attenuation or nonlinear signal is found in the above static test, the operator can guide the patient to perform a preset number of alternating biting and relaxing movements while keeping the flexible brace testing device 1 in a stable fit.

[0075] In a preferred embodiment, the observation period is set to 10 seconds, and the preset number of bites is set to 5. Simultaneously, the multi-channel signal generator 17 is activated to continuously output a narrowband pulse excitation signal with a center frequency of 1MHz, driving the tongue-side transducer excitation array 3 to emit continuous Rayleigh waves, which are continuously received by the cheek-side transducer receiving array 4. The evolution of the echo signal within the observation period is recorded in real time by the oscilloscope 19.

[0076] During this process, the patient's alternating biting motion exerts dynamic mechanical pressure on the teeth, causing the originally tightly closed microcracks to periodically open and close with each biting motion. This opening and closing of the physical interface directly alters the transmission conditions of sound waves, resulting in the periodic attenuation and transmission of high-frequency Rayleigh wave energy passing through the crack area.

[0077] Therefore, the operator only needs to observe the changes in the signal amplitude: if the received waveform amplitude shows a periodic fluctuation that strictly corresponds to the number of alternating biting movements of the patient, that is, there are 5 obvious attenuation and rebound phenomena with 5 biting movements, it can be determined that there is a microcrack in the area to be tested.

[0078] To further achieve non-destructive quantitative assessment of microcrack depth, this implementation proposes a measurement method for quantitative inversion of microcrack depth using frequency scanning technology. The specific steps include: The multi-channel signal generator 17 drives the tongue-side transducer excitation array 3 to perform a frequency scanning mode. The center frequency of the excitation signal starts from 1MHz and increases to 10MHz in steps of 0.5MHz.

[0079] For each frequency point, the received signal from the cheek-side transducer receiving array 4 is acquired using an oscilloscope 19, and the received signal is then analyzed in the frequency domain by an external computer to extract the second harmonic amplitude. A 2f With fundamental amplitude A f Calculate the normalized nonlinear coefficients β ,Right now β = A 2f / A f 2 And plot the "frequency-nonlinear coefficient" characteristic curve.

[0080] It should be noted that the evolution of the normalized nonlinear coefficient with frequency directly characterizes the depth of the microcrack. When the incident Rayleigh wave wavelength... With crack depth When specific geometric matching conditions are met, the nonlinear interface response of the microcrack is maximized, and the nonlinear coefficient exhibits a significant peak frequency. There is a quantitative relationship between it and the crack depth.

[0081] Since the effective penetration depth of Rayleigh waves is approximately equal to their wavelength, that is... λ = v R / f ,in v R The Rayleigh wave velocity in tooth enamel is approximately 3000 m / s. f To excite the frequency.

[0082] Crack depth With characteristic curve peak frequency Satisfy the following physical model: D ≈ k v R / f peak , Where D is the crack depth. k The calibration coefficient can be obtained through pre-calibration using standard samples.

[0083] Using the above method, this embodiment can achieve non-destructive quantitative measurement of the depth of microcracks without damaging the tooth structure. It only requires controlling the hardware to perform frequency conversion scanning and extracting the peak frequency of the nonlinear coefficient.

[0084] To verify the accuracy of the quantitative inversion of microcrack depth, a comparative experiment was designed in this embodiment.

[0085] The test subjects were two sets of extracted tooth models with different pre-fabricated crack depths, set at 0.2 mm and 1.0 mm, respectively. During the experiment, the multi-channel signal generator 17 was used to drive the lingual transducer excitation array 3 to execute a frequency scanning mode, obtaining the following results: Figure 10 The “frequency-nonlinear coefficient” characteristic curve shown exhibits significant frequency selectivity.

[0086] The method calculates the crack depth value, and the relative error between the value and the actual depth of the sample is within the allowable range.

[0087] Experimental results show that the nonlinear modulation effect of the crack on the sound wave is most severe when the ultrasonic wavelength and crack depth satisfy a specific matching relationship. For a relatively deep crack with a depth of 1.0 mm, the nonlinear coefficient... β The peak frequency is reached at a lower frequency of about 3 MHz, corresponding to a wavelength of about 1 mm; while for shallow cracks with a depth of 0.2 mm, the peak frequency shifts significantly to higher frequencies, reaching about 7 MHz.

[0088] Based on the peak frequency obtained from the above experiments, and combined with the preset depth inversion physical model, the relative error between the calculated crack depth value and the actual sample depth is within the allowable range. The above experiments confirm the accuracy and reliability of the sweep frequency-peak frequency inversion method proposed in this invention. This demonstrates that this method does not require damaging the tooth structure; it only requires controlling the hardware to perform a frequency conversion scan to achieve a non-destructive quantitative assessment of the depth of minute microcracks.

[0089] Those skilled in the art will understand that the modules or steps of the present invention described above can be implemented using general-purpose computer devices. Optionally, they can be implemented using computer-executable program code, thereby allowing them to be stored in a storage device for execution by a computer device, or they can be fabricated as separate integrated circuit modules, or multiple modules or steps can be fabricated as a single integrated circuit module. The present invention is not limited to any particular combination of hardware and software.

[0090] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A device for detecting tooth crack based on Rayleigh wave transmission attenuation and nonlinear response, characterized in that, include: A flexible braces testing device, comprising two sets of flexible semi-circular probe assemblies, wherein an ultrasonic transceiver array is embedded in the inner wall of each set of flexible semi-circular probe assemblies, the ultrasonic transceiver array being composed of several miniature piezoelectric transducer elements arranged circumferentially, the front end face of the miniature piezoelectric transducer elements facing the enamel surface, and an air backing layer provided on the opposite end face.

2. The Rayleigh wave based transmission attenuation and nonlinear response device for tooth crack detection of claim 1, wherein, The front end face of the micro piezoelectric transducer element is provided with a micro wedge, and the incident angle of the micro wedge is configured to be greater than the first critical angle of enamel and less than the second critical angle.

3. The Rayleigh wave based transmission attenuation and nonlinear response device for tooth crack detection of claim 1, wherein, The flexible semi-circular probe assembly also includes an acoustic impedance matching layer, which is disposed between the front end face of the micro piezoelectric transducer array element and the enamel surface.

4. The tooth microcrack detection device based on Rayleigh wave transmission attenuation and nonlinear response as described in claim 1, characterized in that, The flexible semi-circular probe assembly also includes a flexible cable layer with parallel lines.

5. The tooth microcrack detection device based on Rayleigh wave transmission attenuation and nonlinear response as described in claim 1, characterized in that, The acoustic impedance matching layer, micro wedge, micro piezoelectric transducer array, air back layer, and flexible cable layer in the flexible semi-circular probe assembly are embedded as a whole in a medical-grade flexible covering and integrally formed.

6. The tooth microcrack detection device based on Rayleigh wave transmission attenuation and nonlinear response as described in claim 1, characterized in that, The flexible braces testing device also includes a signal excitation and acquisition unit connected to the ultrasonic transceiver array via a flexible cable.

7. The tooth microcrack detection device based on Rayleigh wave transmission attenuation and nonlinear response as described in claim 1, characterized in that, The ultrasonic transceiver array includes a tongue-side transducer excitation array and a buccal-side transducer receiving array.

8. A method for detecting tooth cracks based on Rayleigh wave transmission attenuation and nonlinear response, based on the tooth crack detection device based on Rayleigh wave transmission attenuation and nonlinear response as described in claims 1-7, characterized in that, include: The flexible dental prosthesis is worn on the patient's teeth, and it is manually pressed to make it adapt to the tooth surface. The signal excitation and acquisition unit drives the lingual transducer excitation array to emit high-frequency Rayleigh waves, and the sound waves propagate along the enamel surface to the buccal transducer receiving array. The signal collected by the cheek transducer receiving array is received by an oscilloscope, and the time domain amplitude and frequency domain harmonic characteristics of the signal are analyzed. Opening cracks are determined based on the attenuation of the fundamental amplitude, and closed microcracks are determined based on the second harmonic component.

9. The method for detecting tooth microcracks based on Rayleigh wave transmission attenuation and nonlinear response as described in claim 8, characterized in that, When no significant signal is detected in static testing, the patient is guided to perform periodic biting movements, and Rayleigh waves are emitted continuously and the periodic fluctuations of the received signal amplitude are monitored to determine microcracks.

10. The method for detecting tooth microcracks based on Rayleigh wave transmission attenuation and nonlinear response as described in claim 8, characterized in that, By controlling the excitation frequency to scan from low to high frequency, the peak frequency of the normalized nonlinear coefficient β is extracted and combined with the deep inversion model. Calculate the crack depth, where Rayleigh wave velocity in tooth enamel This is the calibration coefficient.

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