Over the last three decades, dentistry has experienced significant progress across all its branches. These developments have highlighted the necessity for highly accurate diagnostic tools, particularly advanced imaging techniques [1]. Alongside clinical examinations, two-dimensional (2D) imaging techniques such as periapical radiography (PR) and panoramic radiography (PANO), as well as three-dimensional (3D) cone beam computed tomography (CBCT), are imaging exams commonly employed. CBCT provides enhanced information compared to standard 2D dental radiographs, particularly concerning the bucco-lingual dimension [2]. The diagnostic process also relies on spiral CT, magnetic resonance imaging (MRI), and ultrasound (US) [1]. Due to the exposure of ionizing radiation, both for patients and healthcare providers, and the consequent potential biological damage, in recent years, awareness regarding the frequency of radiographs has increased [3, 4]. Advancements in technology have recently enabled significant reductions in radiation doses from the latest-generation devices while providing increasingly high-resolution diagnostic imaging and broadening applications across all areas of dentistry [5, 6]. Furthermore, the development of ionizing-radiation-free diagnostic exams in dentistry, aimed at overcoming the limitations of traditional methods, has driven scientific research to achieve promising results for the future. MRI and ultrasound imaging (UI) represent significant advancements in this field, as highlighted by extensive evidence supporting their applications across various branches of dentistry [7].

UI is commonly used in medical practice primarily because of its low cost, low risk for the patient, and capability to deliver real-time images. Frequencies ranging from 2 to 20 MHz are typically operated [8]. Ultrasonography operates by exploiting the acoustic properties of biological tissues to generate cross-sectional images. A transducer emits high-frequency sound waves that are reflected at the interfaces between structures of differing densities, producing echoes [9, 10]. The magnitude of these echoes is directly proportional to the difference in acoustic impedance between adjacent tissues [11]. High-intensity echoes (hyperechoic, appearing white) are typically associated with structures such as bone or gas, whereas low-intensity echoes (hypoechoic, appearing black) are characteristic of fluids. Intermediate intensities are displayed as various shades of gray [11]. Because materials like bone and air impede sound wave transmission, they generate acoustic shadows, preventing the visualization of tissues located beyond these interfaces [12]. This phenomenon represents a key limitation of ultrasonography, particularly when examining tissues with low water content. However, advancements in image-processing software have significantly mitigated these challenges, resulting in markedly improved diagnostic imaging capabilities [13].

The implementation of the Doppler effect has led to the development of techniques for analysing blood flow, starting with continuous and pulsed Doppler methods. This was later followed by Color Doppler, which incorporates directional data and blood velocity into ultrasound images [14]. Furthermore, ultrasound technology has advanced to include 3D and four-dimensional (4D) imaging, delivering real-time volumetric representations of tissues [15]. With the recent technological advancements, ultrasound has become portable. More recently, the introduction of pocket-sized ultrasound devices has facilitated the use of handheld ultrasounds, significantly enhancing the ease of transport to perform examinations [16]. The primary benefit is their portability due to their smaller and lighter design, which facilitates transport to remote or hard-to-reach places [17]. High-intensity focused ultrasound (HIFU) has gained popularity among aesthetic medicine practitioners in recent years. It was initially utilized in oncology for treating cancers of many organs, including the liver (such as hepatocellular carcinoma), prostate, pancreas, kidneys, breasts, thyroid, and bones [18]. Currently, it is also employed in procedures focused on facial and neck rejuvenation as well as the reduction of subcutaneous fat [18]. Moreover, current research is focusing on AI-empowered ultrasonography, although the implementation of AI in medical ultrasonography encounters various challenges [19].

Ultrasonography has been less commonly used in dentistry due to the absence of suitable transducers capable of navigating the confined oral space and the challenges associated with achieving effective coupling between the transducer and target tissues [20]. The intraoral transducer is designed explicitly for intraoral use, featuring an 18-MHz center frequency and a spatial resolution of up to 64 µm [21]. Ultrasound has traditionally been used in dentistry to diagnose major salivary gland conditions, particularly sialolithiasis [22]. In recent years, increasing scientific evidence has highlighted the role of ultrasound in the study of periapical lesions, monitoring their healing, and differentiating between various diagnoses [23]. Additionally, ultrasound examinations have proven valuable for assessing the temporomandibular joint (TMJ), including evaluating the health of the articular disc and detecting possible displacements [24]. Beyond joint evaluation, the ultrasound allows for a detailed examination of soft tissues, including the oral mucosa. Tzoumpas et al. [25] emphasized the importance of measuring the thickness of the maxillary attached gingiva, particularly when planning connective tissue grafts (CTGs) from the palate, making this application highly useful in periodontal surgery planning. Similar evaluations can be applied to implant surgery and peri-implant health, with the benefit of avoiding ionizing radiation and its associated biological risks [26]. Bohner et al. [27] demonstrated no statistical difference in the measurements of buccal bone thickness around dental implants when comparing ultrasound and optical microscopy. Although this study had ex vivo limitations, it provided a strong starting point for studying peri-implant hard tissues. To validate these findings, the same research group simulated peri-implant bone defects in porcine bone and compared measurements from CBCT and ultrasound. The results showed no statistically significant differences in defect width and height, highlighting the potential of ultrasound for diagnosing and monitoring peri-implant bone defects [27]. This technology has also been found useful for evaluating intraosseous lesions, supporting their diagnosis, differential diagnosis, and follow-up after treatment, all without the risks associated with ionizing radiation [28].

Another important application of the ultrasound is in the study of blood vessels. In dentistry, it is particularly valuable for planning oral surgeries near large blood vessels or assessing vascular lesions to determine their nature and blood flow [29].

The aim of this scoping review is to map and synthesize the clinical applications of ultrasonography in periodontology, focusing on evidence derived from human clinical studies evaluating its diagnostic and research use in periodontal and peri-implant contexts. The following research questions were developed to meet the aims of this scoping review:

1.

“What are the main clinical fields of application of ultrasonography in periodontology based on available human studies?” This question aims to explore the various clinical and diagnostic areas within dentistry where ultrasonography has been utilized, identifying its primary indications.

The proposed scoping review will follow the JBI methodology for scoping reviews [30]. This project is registered as DOI: https://doi.org/10.17605/OSF.IO/7MJWA on OSF.

The first PRISMA diagram schematically shows the selection process for the application of ultrasonography in periodontology (Figure 1). Through digital research, carried out on three different databases (PubMed, Scopus, and Web of Science), 51,747 studies were identified, and 3 records were selected through other sources. 51,401 records were screened after duplicates removal and underwent preliminary analysis based on the evaluation of title and abstract. Inclusion and exclusion criteria were applied, and a total of 51,391 studies were excluded from this first screening survey, reducing the total of studies subjected to the final screening to 10. Finally, 10 studies were included, as no records were excluded based on the full-text evaluation. Inter-rater reliability was assessed using Cohen’s Kappa coefficient, which demonstrated an almost perfect level of agreement between the reviewers, both during the initial screening phase (κ = 0.93) and in the full-text eligibility evaluation (κ = 0.87).

This review investigated the current applications of ultrasonography in dentistry to evaluate its true diagnostic and operational potential. Ultrasonography has proven useful in other dental fields, such as periodontology, where research often focuses on assessing the quality of regenerated soft and hard tissues [42].

Accurate diagnosis of periodontal and peri-implant diseases begins with the evaluation of soft tissues through clinical inspection and periodontal probing, and radiographic imaging techniques such as full-mouth intraoral radiographs, which are useful for assessing the presence of periodontal lesions around natural teeth and the misfit between implant and abutment or abutment and prosthesis [43], and finally CBCT.

Studies by Galarraga-Vinueza et al. [32], Majzoub et al. [33], and Barootchi et al. [34] have highlighted the potential role of ultrasonography in diagnosing periodontal and peri-implant diseases. Indeed, ultrasonographic imaging provides a detailed interpretation of tissue characteristics through ultrasonographic imaging, distinguishing healthy sites from those affected by periodontal disease and enabling precise measurements.

Ultrasound has been employed not only for the assessment of soft tissues but also for hard tissues, including teeth. Kim et al. [44] explored HFUS for measuring caries sizes, comparing the results with those obtained from CT. The promising findings suggest that, with the development of suitable probes, HFUS could become a reliable tool for assessing caries dimensions.

The predictability of a surgical procedure involving soft or hard tissue grafting depends on factors such as graft stability, biocompatibility, and the ability of the graft to revascularize [45]. In the study of Sameera et al. [35], ultrasonography was used to evaluate blood flow in regenerated tissues, comparing different techniques. Blood flow analysis is necessary to investigate the change of the grade of soft tissue, such as muscle, so using ultrasound is helpful, as the study of Yalcin et al. [46] showed, conducting an ultrasonographic analysis to assess the blood flow parameters of the external carotid artery, maxillary, facial, and mental artery before and after splint application on the masseter muscle.

Furthermore, recent studies by Tavelli et al. [36] have evaluated the morphological characteristics of soft tissues, particularly mucogingival grafts, by assessing keratinized mucosa thickness. Similarly, the strain and elasticity of soft tissue could be evaluated through ultrasound strain elastography, comparing these parameters concerning the soft tissue around natural tooth crowns and implant-supported crowns [47].

Since the autologous keratinized mucosa graft requires donor site evaluation and wound management after soft tissue harvesting, some authors, such as Torumtay Cin et al. [38] and Koca-Ünsal et al. [39], have used ultrasonographic imaging to assess tissue vascularization in the palate and the efficacy of platelet concentrates like PRF and T-PRF in improving donor site healing. Meschi et al. [40] also evaluated bone tissue healing following regenerative procedures incorporating L-PRF.

The recent literature demonstrated that ultrasonography could have a potential in other clinical fields involving the maxillofacial district, thanks to its effectiveness in assessing the morphological characteristics of other types of soft tissues, such as glandular and muscular tissue, about different pathological conditions or clinical treatments such as esthetic medicine injection procedures. de Souza Nobre et al. [48] used ultrasonography to assess the reduction of muscle thickness after botulinum toxin injection. Ultrasound probes are commonly used to analyze the clinical anatomy of the target areas in many surgical disciplines, allowing for the identification of soft tissues, particularly during procedures involving injecting drugs such as local anesthetics [49]. As regards the guided anesthesia technique in esthetic medicine, ultrasonography showed promising results, as Hernández et al. [50] used the ultrasound to guide anesthesia of the infraorbital nerve.

Moreover, drug injection procedures are frequently employed in the treatment of gnathological disorders such as myofascial pain, as the study of Saglam et al. [51] aimed to investigate the effects of occlusal splint (OS) and masticatory muscle trigger point (TP) local lidocaine injections of masseter muscle on patients diagnosed with myofascial pain, performing shear wave elastography. Kheder et al. [52] compared ultrasound-guided versus non-guided Dextrose 10% injections in patients affected by internal derangement in the TMJ. In another study conducted by De la Torre Canales et al. [53] on 60 patients affected by myofascial temporomandibular-disorder pain (MFP-TMD) who were treated with BoNT-A, the thickness of both masseters and anterior temporalis muscles during maximum voluntary contraction (MVC) was measured using ultrasonography. Similarly, Alkaya et al. [54] compared the changes in the thickness of the masseter and anterior temporalis muscle of 30 edentulous patients following the reconstruction of implant-supported fixed prostheses with 30 dentate individuals using ultrasonographic probes, revealing an increase in the thickness of the masseter and anterior temporalis muscle, as well as a decrease in asymmetry between left and right muscle.

Besides, Park et al. [55] investigated the effects of synchronized neuromuscular electrical stimulation (NMES) and chewing exercises on bite force and masseter muscle thickness using a portable ultrasound, while Lione et al. [56] evaluated the effects of posterior bite blocks on masseter muscles and facial growth in prepubertal dolichofacial patients through ultrasonographic scans.