Introduction
Periodontal diseases represent one of the most prevalent chronic inflammatory conditions affecting human populations worldwide, characterized by progressive destruction of the tooth-supporting apparatus including gingiva, periodontal ligament, cementum, and alveolar bone. The accurate diagnosis and effective management of these conditions have traditionally relied upon a combination of clinical examination using periodontal probes and radiographic imaging using two-dimensional periapical or panoramic radiographs. While these conventional methods have served the dental profession for decades, they carry inherent limitations that compromise diagnostic precision and patient comfort. Periodontal probing, the current gold standard for assessing pocket depths and attachment levels, is an invasive procedure that causes patient discomfort, produces measurements subject to significant operator variability, and provides no information about subgingival morphology or the condition of underlying bone. Radiographic imaging, while valuable for visualizing interproximal bone loss, exposes patients to ionizing radiation, cannot visualize soft tissues, and provides only a static two-dimensional representation of complex three-dimensional anatomy.
These limitations have driven researchers and clinicians to explore alternative imaging modalities that can overcome these shortcomings. Ultrasonography, a well-established medical imaging technology that uses high-frequency sound waves to produce real-time images of internal body structures, has emerged as a promising solution for periodontal assessment. Unlike conventional methods, ultrasound offers non-invasive, radiation-free, real-time imaging capable of visualizing both hard and soft periodontal tissues simultaneously .
Physics of Ultrasonography
The physical principles governing ultrasonography are fundamental to understanding both its capabilities and limitations in periodontal applications. Ultrasound refers to sound waves with frequencies exceeding the upper limit of human hearing, typically above 20,000 hertz (20 kHz). Medical diagnostic ultrasound operates at significantly higher frequencies, typically between 2 and 20 MHz, with periodontal applications often utilizing frequencies in the 15-55 MHz range to achieve the high resolution necessary for visualizing fine anatomical details . The generation of ultrasound waves relies upon the piezoelectric effect, a phenomenon discovered by Pierre and Jacques Curie in 1880, whereby certain crystalline materials undergo mechanical deformation when subjected to an electrical field and conversely generate electrical charges when mechanically stressed.
In an ultrasound transducer, an alternating electrical current applied to a piezoelectric crystal, typically composed of lead zirconate titanate (PZT), causes the crystal to expand and contract rapidly at the frequency of the applied current, generating sound waves that propagate into adjacent tissues . When these sound waves encounter interfaces between tissues with different acoustic impedances (a property determined by tissue density and the speed of sound through that tissue) a portion of the wave energy is reflected back toward the transducer. The transducer then acts as a receiver, converting the returning echoes back into electrical signals that are processed by a computer to construct a real-time image. The resolution of an ultrasound system is determined by several factors, including the frequency of the sound waves and the characteristics of the transducer. Higher frequencies produce shorter wavelengths and thus better spatial resolution, enabling the discrimination of smaller anatomical details. However, this improved resolution comes at the cost of reduced tissue penetration, as higher frequency waves are more rapidly attenuated as they travel through tissue. This trade-off is particularly relevant in periodontal imaging, where the superficial location of periodontal tissues (typically within 3-10 mm of the tissue surface) allows the use of very high-frequency transducers that can achieve resolutions below 100 micrometers.
The speed of sound through soft tissue is relatively constant at approximately 1540 meters per second, allowing the system to calculate the distance to reflecting structures based on the time delay between pulse emission and echo reception . Additional physical phenomena relevant to periodontal ultrasound include acoustic microstreaming and cavitation. Acoustic microstreaming refers to the formation of steady-state fluid flow patterns around oscillating structures such as gas bubbles or vibrating instrument tips, generating shear stresses that can disrupt bacterial biofilms. Cavitation involves the formation and collapse of gas bubbles within a liquid medium under the influence of an ultrasonic field, producing shock waves and high-velocity liquid jets that contribute to the mechanical disruption of calculus and plaque during ultrasonic scaling procedures .
Applications in the Medical Field
Ultrasonography has become an indispensable diagnostic tool across virtually all medical specialties since its introduction into clinical practice in the mid-20th century, valued for its safety, versatility, and real-time imaging capabilities. Unlike imaging modalities that rely on ionizing radiation such as X-ray, computed tomography (CT), and nuclear medicine, ultrasound produces no cumulative radiation exposure, making it particularly valuable for imaging pregnant women, children, and patients requiring serial examinations. In obstetrics and gynecology, ultrasound has revolutionized prenatal care by enabling clinicians to confirm pregnancy, estimate fetal age, monitor fetal growth and development, detect congenital abnormalities, evaluate placental position, and guide procedures such as amniocentesis . The real-time nature of ultrasound imaging allows visualization of fetal cardiac activity and body movements, providing reassurance to expectant parents and critical clinical information to healthcare providers. In cardiology, echocardiography provides detailed assessment of cardiac structure and function, including valve performance, chamber dimensions, wall motion, and blood flow patterns through the heart and great vessels. This information is essential for diagnosing and managing conditions such as valvular heart disease, cardiomyopathies, congenital heart defects, and pericardial effusions.
Abdominal ultrasound is routinely employed to evaluate the liver, gallbladder, pancreas, kidneys, spleen, and abdominal vasculature, enabling detection of conditions including cholelithiasis, nephrolithiasis, hepatic steatosis, cirrhosis, and abdominal aortic aneurysms. The portability of modern ultrasound systems has expanded its utility to emergency and critical care settings, where focused assessment with sonography in trauma (FAST) protocols enable rapid detection of intra-abdominal and pericardial fluid following traumatic injury . Vascular ultrasound, incorporating Doppler capabilities to assess blood flow velocity and direction, is the first-line imaging modality for evaluating carotid artery disease, deep vein thrombosis, peripheral arterial disease, and chronic venous insufficiency. Musculoskeletal ultrasound provides detailed visualization of tendons, ligaments, muscles, and joints, making it invaluable in sports medicine and orthopedics for diagnosing tendon tears, ligament sprains, muscle injuries, and joint effusions. The technology also plays an increasingly important role in interventional procedures, where real-time ultrasound guidance improves the accuracy and safety of biopsies, fluid aspirations, central line placements, and peripheral nerve blocks . The safety profile of ultrasound, combined with its relatively low cost compared to CT and magnetic resonance imaging (MRI), has driven the development of point-of-care ultrasound (POCUS) devices, including handheld systems that can be used at the patient’s bedside .
Ultrasonography in Dentistry
The introduction of ultrasound technology into dentistry represents a fascinating example of technology transfer from industrial and medical applications to the unique requirements of oral healthcare. The first documented use of ultrasound in dentistry was reported by Matthew C. Catuna in 1953, who employed an ultrasonic cutting device for cavity preparation in teeth . This early application utilized the mechanical vibrations of an ultrasonic instrument to remove dental hard tissues, often in combination with an abrasive slurry to enhance cutting efficiency. However, the introduction of high-speed air turbine handpieces in the early 1960s, which offered superior cutting efficiency and convenience, temporarily eclipsed interest in ultrasonic technology for restorative procedures.
The enduring entry of ultrasound into dentistry came through periodontics, when Zinner introduced ultrasonic scalers for periodontal debridement in 1955 . These early devices were large, heavy units with bulky universal tips, but they demonstrated the potential of ultrasonic energy for the efficient removal of calculus and plaque from tooth surfaces. Over subsequent decades, ultrasonic scaling devices underwent progressive refinement, including miniaturization of components, development of site-specific slim tips (some termed “microultrasonic”), and improved power delivery systems incorporating computer chips for consistent tip vibration.
The therapeutic success of ultrasonic scalers established ultrasound as a valuable treatment modality in periodontics, but it was not until decades later that researchers began exploring ultrasound as a diagnostic imaging tool for periodontal tissues. The roots of diagnostic periodontal ultrasonography can be traced to NASA Langley Research Center, where scientists in the Non-Destructive Evaluation Sciences Laboratory had developed ultrasound-based time-of-flight techniques for measuring material thickness in aircraft components and bolt tension in structural assemblies . Recognizing that the same principle could be applied to measure periodontal attachment levels, researchers adapted this industrial technology for dental use, developing miniaturized intraoral probes capable of directing ultrasound beams into the periodontal sulcus.
The first efforts to apply diagnostic ultrasound to periodontology were reported by Spranger, who attempted to measure alveolar crest height, and subsequent studies by Palou and colleagues who imaged alveolar bone by directing ultrasound beams perpendicular to the long axis of teeth. These pioneering studies demonstrated the feasibility of periodontal ultrasonography but also revealed significant technical challenges, including the need for very small transducers that could access the narrow confines of the periodontal sulcus and interdental spaces, the requirement for a coupling medium (typically water) to transmit sound waves from the probe to the tissues, and the complexity of interpreting echoes from the multiple tissue interfaces present in the periodontium . Despite these challenges, the potential benefits of non-invasive, radiation-free, real-time periodontal imaging drove continued technological development, culminating in commercially available systems such as the ULTRADERM® ultrasonic scanner and the periodontal ultrasonography probe developed by Companion and Heyman at NASA .
Applications in Periodontics
The applications of ultrasonography in periodontics can be broadly categorized into diagnostic imaging applications and therapeutic applications, each with distinct technological requirements and clinical objectives. In diagnostic imaging, ultrasound offers the potential to non-invasively visualize both hard and soft periodontal tissues in real-time, providing information that complements or potentially surpasses that available from conventional clinical and radiographic examination. Clinical studies have demonstrated that ultrasound can accurately measure gingival thickness, a critical parameter for mucogingival surgery and implant site assessment. The thickness and quality of gingival tissue influences surgical outcomes for root coverage procedures, the selection of appropriate flap designs, and the predictability of restorative and implant treatments.
Ultrasound has also been successfully employed to measure the height of the alveolar crest and to classify furcation involvement in multi-rooted teeth . The ability to image furcation areas, which are notoriously difficult to assess with conventional radiography due to superimposition of anatomical structures, represents a significant potential advantage of ultrasound imaging. A recent systematic review by Figueredo and colleagues, encompassing 25 human studies, concluded that ultrasound appears to be a feasible and valuable diagnostic tool for the periodontium, with the potential to complement the shortfalls of current radiographic technologies. The review identified studies using ultrasound to assess natural teeth, dental implants, edentulous ridges, and to quantify blood flow using color Doppler and power Doppler techniques. The ability to assess blood flow is particularly intriguing, as changes in tissue perfusion may indicate the presence and severity of inflammation before irreversible tissue destruction occurs.
In therapeutic applications, ultrasound has been used for several decades in the form of ultrasonic scalers for subgingival debridement. The mechanism of calculus removal involves both the mechanical chipping action of the vibrating tip upon direct contact with calculus deposits and the cavitational activity generated in the surrounding fluid medium, which contributes to the disruption of bacterial biofilms. Acoustic microstreaming, the formation of shear stresses around oscillating bubbles and the vibrating tip itself, also contributes to biofilm disruption and may enhance the removal of endotoxins from contaminated root surfaces . Studies have demonstrated that ultrasonic scaling can achieve calculus removal comparable to hand instrumentation while requiring less operator time and causing less patient discomfort, particularly in cases of moderate to deep pocketing.
More recently, piezoelectric bone surgery (piezosurgery) has emerged as an application of ultrasound in periodontal and implant surgery, offering precise cutting of mineralized tissues with minimal damage to adjacent soft tissues . The selective cutting action of piezoelectric instruments, which are highly effective on mineralized tissues but cause minimal injury to soft tissues, has proven valuable for procedures such as sinus lift surgery, ridge augmentation, and crown lengthening. Beyond the mechanical effects of ultrasonic energy for tissue disruption, there is evidence that low-intensity pulsed ultrasound may stimulate bone healing following osteotomy or osteodistraction procedures, suggesting potential applications in periodontal regeneration and implant site development.
The periodontal ultrasonography probe, a specialized device developed specifically for periodontal assessment, consists of a transducer housed within a contra-angled handpiece with a hollow conical tip that focuses the acoustic beam into the periodontal tissues. The probe tip incorporates a slight flow of water, which serves as the coupling medium to ensure efficient transmission of ultrasound energy from the probe to the tissues. When the tip is placed gently on the gingival margin until slight blanching is visible, the probe is activated, and a narrow frequency (1-20 MHz) ultrasonic pulse is projected into the sulcus or pocket. As the examiner passes the probe tip across the gingival margin, the computer records incoming echo data and employs artificial intelligence algorithms to translate these data into estimates of probing depth in millimeters. Unlike manual probing, which obtains discrete measurements at six specific sites per tooth, the ultrasonic probe can be swept along the entire gingival margin, capturing a continuous series of depth measurements and producing a contour map of the subgingival area that provides more comprehensive information than conventional probing .
Review of Literature
The scientific literature on ultrasound applications in periodontics has grown substantially over the past two decades, encompassing diagnostic accuracy studies, clinical trials of therapeutic applications, and systematic reviews synthesizing available evidence. A comprehensive systematic review published in 2024 by Figueredo and colleagues evaluated the diagnostic applications of ultrasound imaging for periodontal assessment in human subjects, searching major databases including Medline, EMBASE, Web of Science, Scopus, and Cochrane up to April 2023. The review identified 25 eligible studies, of which 15 used ultrasound on natural teeth, 4 used ultrasound on dental implants, 2 used ultrasound on edentulous ridges, and 4 used color flow or power Doppler techniques to evaluate blood flow. The authors concluded that ultrasound appears to be a feasible and valuable diagnostic tool for the periodontium with the potential to complement the shortfalls of current radiographic technologies, including the inability to visualize soft tissues and the requirement for ionizing radiation exposure .
A review by Yeung and colleagues, published in Periodontology 2000, examined non-ionizing diagnostic imaging modalities for visualizing periodontal and peri-implant tissues, comparing ultrasound with MRI and optical coherence tomography. The authors reported that clinical studies have shown ultrasound can accurately measure gingival height and crestal bone level and classify furcation involvement. However, they noted that due to physical constraints, ultrasound may be more applicable to buccal surfaces of the dentition, even with intraoral probes, and that technological breakthroughs will be needed before ultrasound can replace conventional radiography for routine diagnostics.
The therapeutic applications of ultrasound have been extensively reviewed by Saluja and colleagues, who traced the evolution of ultrasonic scalers from their introduction in 1955 to modern computer-controlled devices. Their review detailed the mechanisms of action including cavitation and acoustic microstreaming, the differences between magnetostrictive and piezoelectric ultrasonic systems, and the clinical evidence supporting ultrasonic debridement. Magnetostrictive devices, which operate by applying an alternating current to a wire coil surrounding a ferromagnetic stack or metal rod, produce tip vibrations typically between 18,000 and 45,000 cycles per second and can achieve linear, elliptical, or circular tip movement patterns. Piezoelectric devices, which rely on the dimensional changes of crystalline structures when subjected to an electrical field, operate at frequencies between 25,000 and 50,000 cycles per second and produce primarily linear tip movement. The review also examined evidence for the use of piezosurgery in bone procedures, noting that piezoelectric instruments produce more favorable osseous repair and remodeling compared to conventional carbide and diamond burs. Research on the diagnostic accuracy of periodontal ultrasonography has yielded promising but variable results.
Early studies by Eger and colleagues demonstrated that an ultrasonic device with a 5 MHz transducer could accurately measure gingival thickness, with results showing good correlation with direct clinical measurements . Subsequent studies using higher frequency transducers (20 MHz) in animal models demonstrated that periodontal ultrasonography could produce images suitable for assessing the dimensional relationships between hard and soft periodontal structures . In human subjects, ultrasound has been successfully employed to evaluate gingival thickness before and after mucogingival therapy for root coverage, to assess the dynamics of mucosal dimensions after root coverage with connective tissue grafts and bioresorbable barrier membranes, and to measure the thickness of masticatory mucosa . A study by Meissner and colleagues developed an ultrasound-based device with computerized calculus detection capabilities, demonstrating that dental surfaces could be discriminated by analysis of tip oscillations of an ultrasonic instrument, potentially enabling automated detection of subgingival calculus. Regarding infection control considerations during ultrasonic scaling, research has shown that use of a high-volume evacuator attachment to an ultrasonic handpiece can reduce detectable aerosols by 93%, and that a 30-second rinse with an essential oil mouthrinse before instrumentation reduces bacterial counts in aerosols by 92.1% . These findings have important implications for clinical practice, particularly in the context of airborne infection control.
Future Aspects
The future of ultrasonography in periodontics appears exceptionally promising, driven by ongoing technological advances in transducer design, signal processing, artificial intelligence, and device miniaturization. One of the most significant trends is the continued miniaturization of ultrasound devices, with device volumes having shrunk from approximately 4 cubic meters in the 1950s to less than 0.001 cubic meters in 2023, representing an annual size reduction of approximately 9.8% . This dramatic reduction in size has enabled the development of handheld and even smartphone-attachable ultrasound systems that could be deployed in general dental practices, community health centers, and potentially even for patient self-monitoring.
The development of intraoral ultrasound probes with sufficiently small dimensions to access interdental areas and posterior teeth remains a significant engineering challenge, but advances in transducer fabrication techniques, including the use of capacitive micromachined ultrasonic transducers (CMUTs) and piezoelectric micromachined ultrasonic transducers (PMUTs), may enable the production of ultra-miniaturized probes suitable for comprehensive intraoral scanning. Another important frontier is the improvement of spatial resolution to enable visualization of finer anatomical details. Current dental ultrasound systems can achieve resolutions in the range of 100-200 micrometers, but next-generation systems aim to achieve resolutions below 20 micrometers, which would enable visualization of the periodontal ligament space (normally 0.15-0.38 mm in width) and potentially even individual collagen fiber bundles. Achieving such high resolutions will require the use of very high frequency transducers (50-100 MHz or higher) and advanced signal processing algorithms to overcome the increased signal attenuation associated with higher frequencies. The integration of artificial intelligence and machine learning algorithms into periodontal ultrasound systems represents a transformative opportunity.
These algorithms can be trained to automatically identify anatomical landmarks, measure clinically relevant parameters, and distinguish between health and disease based on subtle features in ultrasound images that may not be apparent to the human eye . Artificial intelligence could also enable the development of “smart” ultrasound probes that automatically adjust their imaging parameters based on the tissues being examined, optimizing image quality while minimizing the need for operator expertise. Three-dimensional and four-dimensional (real-time 3D) ultrasound, already well-established in obstetrics, could be adapted for periodontal imaging, providing volumetric data that would enable comprehensive assessment of periodontal defects and more accurate surgical planning. Photoacoustic ultrasound, an emerging technique that combines the high spatial resolution of ultrasound with the high contrast of optical imaging, has shown promise for enhanced visualization of periodontal tissues and could potentially enable functional imaging of inflammatory processes at the molecular level. From a clinical implementation perspective, the development of standardized imaging protocols, normative databases of healthy periodontal tissue dimensions, and evidence-based guidelines for the interpretation of periodontal ultrasound images will be essential for widespread adoption. Cost-effectiveness analyses comparing ultrasound-based diagnostic pathways to conventional approaches will also be needed to support reimbursement decisions and technology adoption by healthcare systems and insurance providers.
Conclusion
Ultrasonography represents a transformative technology for periodontics, offering the potential to overcome many of the inherent limitations of conventional diagnostic and therapeutic approaches. The physical principles underlying ultrasound imaging—particularly the piezoelectric effect, acoustic impedance, and echo reflection—enable the non-invasive, real-time visualization of both hard and soft periodontal tissues without the risks associated with ionizing radiation exposure. While ultrasound has been used for therapeutic purposes in periodontics since the introduction of ultrasonic scalers in 1955, the application of ultrasound for diagnostic imaging is a more recent development that has gained substantial momentum over the past two decades.
Clinical studies have demonstrated that ultrasound can accurately measure gingival thickness, assess alveolar bone levels, classify furcation involvement, and potentially quantify tissue perfusion using Doppler techniques. The development of miniaturized intraoral probes, higher frequency transducers, and artificial intelligence-powered image analysis algorithms promises to further enhance the capabilities of periodontal ultrasound, potentially enabling resolutions below 20 micrometers and automated detection of pathological changes. However, several challenges remain to be addressed before ultrasound can be integrated into routine periodontal practice. These include the need for improved probe designs to access interdental and posterior sites, standardized imaging protocols, normative databases of healthy tissue dimensions, and robust clinical evidence demonstrating that ultrasound-guided diagnosis and treatment lead to improved patient outcomes compared to conventional approaches. The COVID-19 pandemic has heightened awareness of aerosol generation during ultrasonic scaling procedures, emphasizing the importance of appropriate infection control measures including high-volume evacuation and pre-procedural antimicrobial rinses.
Despite these challenges, the trajectory of technological development is clear: ultrasound devices will continue to become smaller, more affordable, more powerful, and easier to use. For the practicing periodontist, this means that the ability to visualize periodontal tissues non-invasively and in real-time may soon become as routine as taking a radiograph or performing a periodontal probe examination. For patients, it means the prospect of more accurate diagnosis, more precisely targeted treatment, and the elimination of the discomfort associated with invasive probing and the cumulative radiation exposure from serial radiographs. As research continues to validate and refine these applications, ultrasonography is poised to become an indispensable tool in the periodontal armamentarium, advancing the specialty toward the goal of more precise, personalized, and patient-centered care.
References
References available in Periobasics textbook.