Ultrasonography - it's revival in dentistry

Ultrasonography has been a useful diagnostic tool in dentistry since its inception in 1960s. It is a process that uses the reflection of high-frequency (3 to 10MHz) sound waves to make an image of structures deep within the body. Ultrasound is produced by the vibration of a synthetic crystal that possesses piezoelectric properties. Ultrasound is generated when a rapidly alternating electrical potential causes the crystal to vibrate. When the burst meets an acoustic boundary part of the energy is reflected, this echo is detected by the transducer. By means of the reversed piezoelectric effect the reflected sound waves are transformed by the crystals in the transducer into an electrical signal. The amplitude of the electrical signal is proportional to the acoustic properties of the tissue interface. In the scan converter the amplified signal is converted into a digital signal enabling it to be easily processed and stored.The types of ultrasonography include A-mode ultrasonography, B-mode ultrasonography, Gray-scale ultrasonography, M-mode ultrasonography, Doppler ultrasonography, real time and endoscopic ultrasonography. Technological progress in sonography has made this noninvasive procedure with multiple operating modes the initial imaging technique of choice for the salivary glands and head & neck cancer. Owing to the superficial location of these glands, high-frequency ultrasound transducers provide markedly better spatial resolution than other imaging modalities. Ultrasound can also effectively guide and improve the safety of aspiration biopsy of inflammatory and tumoral lesions. Color doppler allows assessment of salivary gland function and accurate analysis of tumor vascularity. The vascular pattern and displacement of vascularity of the lymph nodes are also assessed using ultrasonography.Metastatic and lymphomatous nodes tend to have sharp borders, whereas reactive and normal nodes usually show unsharp borders. Also, serial change in size of malignant nodes is useful in monitoring patient's response to treatment. Normal, reactive, lymphomatous and tuberculous nodes are predominantly hypoechoic when compared with the adjacent muscles. In cellulitis, well defined hypoechoic septa between fat and connective tissue is seen[characteristic cobblestone appearance] In abscess, anechoic to hyperechoic areas due to sediment, septa or gas may be seen. Ultrasonography is used in the assessment of Temporomandibular joint. Head of the condyle and the articular eminence, is generally hypoechoic ,the margin of the bone is hyperechoic. The joint capsule, retrodiscal tissue,lateral pterygoid and masseter muscles,are isoechoic and appear grey.More recently it has been useful in the diagnosis of fracture of teeth, measurement of enamel thickness and periodontal pocket depth and distraction osteogenesis. Thus ultrasonography is a non-ionizing, non-invasive and relatively inexpensive imaging modality which can be used effectively in maxillofacial imaging. Keywords: ultrasonography