|Year : 2014 | Volume
| Issue : 4 | Page : 414-418
Therapeutic applications of ultrasonography in dentistry
Jyoti Mago1, Soheyl Sheikh2, Shambulingappa Pallagatti2, Amit Aggarwal2
1 Department of Oral Medicine and Radiology, Shaheed Kartar Singh Sarabha Dental College and Hospital, Ludhiana, Punjab, India
2 Department of Oral Medicine and Radiology, Maharishi Markandeshwar College of Dental Sciences and Research, Mullana, Haryana, India
|Date of Submission||22-Jul-2014|
|Date of Acceptance||28-Feb-2015|
|Date of Web Publication||22-Apr-2015|
Amar Medicos, Ghumar Mandi Chowk, Ludhiana - 141 001, Punjab
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Ultrasonography is one of the most common imaging modality used in dental as well as medical sciences. The use of ultrasonography when discovered was as a therapeutic aid, but in recent times, it has become one of the most common imaging modality next to conventional radiology. Currently, its use as a therapeutic aid has been rediscovered along with its association with other specialized imaging. The aim of this paper is to highlight such advancements in the field of ultrasonography.
Keywords: Specialized, therapeutics, ultrasonography
|How to cite this article:|
Mago J, Sheikh S, Pallagatti S, Aggarwal A. Therapeutic applications of ultrasonography in dentistry. J Indian Acad Oral Med Radiol 2014;26:414-8
|How to cite this URL:|
Mago J, Sheikh S, Pallagatti S, Aggarwal A. Therapeutic applications of ultrasonography in dentistry. J Indian Acad Oral Med Radiol [serial online] 2014 [cited 2019 Jan 24];26:414-8. Available from: http://www.jiaomr.in/text.asp?2014/26/4/414/155689
| Introduction|| |
Ultrasound (US) is one of the advanced imaging techniques which uses sound waves for viewing the normal and pathological conditions of bone and soft tissue of the oral and maxillofacial region.  The role of ultrasonography (USG) is well established in the diagnosis of various soft tissue lesions. But it is worthy to mention that the advancement of its use in therapeutic applications alone or in combination with other imaging modalities have made it a valuable tool in both the arena of medical as well as dental sciences.
Ultrasonics was introduced in the field of medicine by its application in therapeutics by utilizing its effect of heat and acoustic cavitation. This destructive ability of high intensity US was first recognized by Langevin in the 1920s. In 1940s, Gohr and Wedekind presented their paper at the Medical University of Kolhn in Germany entitled "Der Ultraschall in der Medizin" and raised the possibility of using USG as a diagnostic tool on the basis of echo-reflection. Later, in the 1950s US was used experimentally as a diagnostic tool.
Since then, USG has been used more for diagnostic aspects and today, US is the second most utilized diagnostic imaging modality in medicine, next only to conventional radiography and is a critically important diagnostic tool of any medical and dental facility. Nowadays, it is one of the very important tools used for therapeutic purposes as well. It can be used as a therapeutic aid in many ways, which are as follows:
- High-intensity focused ultrasonography.
- Magnetic resonance imaging-guided focused ultrasound surgery.
- Ultrasound-guided ablation.
- Low intensity pulsed ultrasonography.
- Ultrasound-guided drainage of deep neck spaces.
- Extracorporeal lithotripsy.
- Ultrasound therapy in temporomandibular joint disorders.
| High Intensity Focused Ultrasonography|| |
High intensity focused ultrasonography (HIFU) is a non-invasive technique where high power transducers emit a high intensity US beam which are focused. They target a tissue volume inside the body which increases the focal temperature causing coagulative tissue necrosis without affecting the interceding and surrounding tissue. 
Mechanism of action
There are two principles which are responsible for the destruction of the tissue:
As human tissues have viscoelastic characteristics, the acoustic energy which is lost is converted into heat. Therefore, tissue temperature increases rapidly in a focal region. When the temperature rises above 43 ° C, it leads to protein denaturation and the formation of a necrotic lesion with sharp demarcation. It has various advantages over other techniques such as cryotherapy, laser ablation, microwave coagulation and radiofrequency ablation. They are as follows:
- It is non-invasive and non-ionizing. Therefore, it can be used repeatedly for as number of times as desired because it has no long-term cumulative effect.
- It increases tissue temperature in a localized area.
- It minimizes blood perfusion effects.
- It does not damage the intervening and surrounding tissue.
High-intensity focused USG has been promoted as a non-invasive method of treating benign and malignant tumors in human tissues. It generates tumor tissue necrosis. This was supported by Clement in 2004 who verified this concept by conducting a study on cultured cell lines and animals.  He concluded that HIFU also appeared to be a valuable technique facilitating drug delivery to tumor tissue by helping cell uptake of cytotoxic drugs and overcoming multidrug resistance (MDR) of tumor cells.  Further, the use of HIFU is also approved by the Food and Drug Administration (FDA) in the United States of America (USA) for bone fracture healing and eye disorders such as refractory glaucoma, ocular tumors, incipient cataracts, retinal detachment or reattachment and to reshape the cornea.  Dogra et al. in 2009  reported that HIFU can be used for the modification of cardiac tissue structure and function, pain relief, and cosmetic surgery.
| Magnetic Resonance Imaging-Guided Focused Ultrasound Surgery|| |
Magnetic resonance imaging-guided focused ultrasound surgery (MRIgFUS) is combination of two technologies i.e., magnetic resonance imaging (MRI) and ultrasonography. Ultrasonography through precise focused, high-power acoustic beam helps in focused tissue necrosis by protein denaturation and capillary bed destruction. On the contrary, MRI serves as an excellent imaging modality which provides the image in three-dimensions. Magnetic resonance imaging has various advantages:
- It is non-ionizing.
- It has high sensitivity to measure the temperature changes.
- It has high sensitivity for locating tumor margins or any soft tissue pathology.
The capability of MRI to measure temperature changes in the body is with an accuracy of -3 ° C at 1.5T. A greater accuracy can be achieved at higher field strengths. Because of its excellent temperature sensitivity, the focal point can be visualized and localized well before any irreversible tissue damage is induced at about 20 ° C above normal body temperature. Moreover, the ability of MRI to capture the temperature change enables the physician to delineate temperature maps and tumor volume and apply this quantitative information in real time to allow for "closed loop therapy."  There are many parameters that can provide temperature sensitive contrast. The temperature dependence and sensitivity of these several parameters that have been proven useful for monitoring temperature changes in soft tissue during delivery of hyperthermia or thermal therapies are:
- The apparent diffusion constant of water.
- The spin-lattice relaxation time.
- The water proton resonance frequency.
These parameters allow observing temperature-dependent changes quantitatively over a range of temperatures for thermal therapy using MRI. The combination of these technologies has led to a breakthrough in image guided therapy delivery system. It also fulfills requirement of an "ideal surgery." It has various advantages over the other surgical treatments, which are as follows:
- It requires no incision.
- It does not have any bio-effect.
- It can be repeated multiple times, whenever necessary.
- Thermal ablations can be monitored due to the temperature sensitivity of MRI.
- It provides a precise definition of the targeted tumor volume when compared to actual visual inspection after surgery.
- It is a better imaging modality for tumor localization or any soft tissue pathology as compared to US or computed tomography (CT).
- It does not require an aggressive approach.
- It can be used for debulking cancerous tissue.
Further, MRIgFUS has been approved by the FDA in USA for the treatment of uterine fibroids. Currently, its use is being further investigated for several other clinical applications.  Mariam in 2010  reported that MRIgFUS can ablate soft-tissue tumors in the bone. It also has the potential to provide very effective pain palliation in a single treatment that can be repeated in the case of pain recurrence. This form of therapy has a great potential and can be combined with radiation. This provides improved pain relief, particularly for very painful metastases, which are refractory to other therapies. 
| Ultrasound Guided Ablation|| |
Surgery is expensive. It may be more than usually aggressive in some patients and is more difficult in the neck that has undergone previous surgery or surgeries. There is also a practical limit to how many surgical explorations can be performed. Due to advances in US imaging and imaging-guided ablation, they can be used in diseases of the cervical lymph nodes. These are also cost effective. These techniques show a promising role of USG in maxillofacial radiology as well as in other arena of radiology. Lewis et al. in 2002 reported that there has been little research published on the value of ablation of metastatic cervical lymph nodes. 
| Sonoporation|| |
Sonoporation is defined as the interaction of US with ultrasonic contrast agents to temporarily permeabilize the cell membrane allowing the uptake of various substances such as DNA, drugs, and other therapeutic compounds, from the extracellular environment.  After exposure to US, the compound remains trapped inside the cell following a transient alteration in the cell membrane.  With the help of sonoporation, gene and drug transfer can be enhanced restricting the effect to the desired area and the desired time.  Thus, after exploring in vitro and in vivo studies on this technique, the therapeutic potential of sonoporation as a drug delivery and gene therapy technique seems promising in the future.
Currently, sonoporation devices are commercially available which are manufactured by various companies. The normal US device can be used with certain kinds of probes. The probes are based on the type of functions like nuclear transfer, cell fusion, tooth germ, tissues, etc. The sound waves can give its effect on the formation of pores in the following four ways:
- Cavitation effects.
- Thermal effects.
- Induction of convective transport.
- Mechanical effects.
Sonoporation can be used for gene delivery, osteoinduction, induction of dental pulp stem cell differentiation into odontoblasts, site-specific gene delivery, DNA transfer, local drug delivery, targeted drug delivery, tumor cell killing, induction of apoptosis, and gene transduction. 
| Low-Intensity Pulsed Ultrasonography|| |
Low-intensity pulsed ultrasonography (LIPU) was approved by the FDA to conservatively manage fresh fracture healing in 1994. This was reported by Rubin et al. in 2001. He further reported the approval of its use by the FDA for the treatment of established non-unions in the year 2000.  Basic science research has also emphasized the beneficial effects of LIPU. Low-intensity pulsed ultrasonography accelerates bone healing. It has a positive impact on signal transduction, gene expression, blood flow, and tissue modeling and remodeling. This was reported by Khan et al. in 2008.  Recent Canadian surveys reported the use of LIPU by 40% of senior residents in orthopaedic surgery. It also revealed its use by 21% of trauma surgeons in the management of tibial fractures. This was reported by Busse et al. in 2008 in his study conducted in Canada. 
| Ultrasound-Guided Drainage of Deep Neck Space|| |
One of most important emergencies that a dentist encounters is infection. Osborn et al. in 2008,  emphasized that infections are the most common presentation to the oral and maxillofacial surgeons which can result in significant morbidity with potential mortality. Infections spread through fascial planes and can compromise vital structures in the head and neck region. Vieria et al.  reported that traditionally, surgical incision and drainage accompanied with antibiotics has been the mainstay of treatment in such cases. Recently, drainage with the help of images produced by USG has become a promising therapeutic aid. With USG, the vital structures are preserved which could otherwise be damaged during blind exploration of an abscess. Thus, there is an advantage of minimal or no scar formation. Further, Biron et al. reported that this procedure can be performed under local anesthesia or conscious sedation. 
Gudi et al. in 2013, in India,  conducted a study to evaluate the usefulness of US-guided surgical drainage in submasseteric space abscess of odontogenic origin without incision. They supported USG as an intraoperative aid in the assessment of the abscess cavity. They concluded that its real-time imaging function would help in the location and drainage of the abscess cavity effectively. A study was undertaken by Biron et al. in 2013 in Germany  in a randomized controlled clinical trial to compare incision and drainage vs US-guided drainage in cases of well-defined deep neck spaces. The primary outcome was decreased length of hospital stay and increased safety. The secondary outcome was decreased overall cost. They identified 41% cost reduction with US-guided drainage of deep neck spaces when compared with incision and drainage. Pandey et al. in 2011,  conducted a study in India to establish the role of USG in determining the involvement of specific fascial spaces in the maxillofacial region and the stage of infection, to help in indicating the appropriate time for surgical intervention and then to compare clinical and ultrasonographic findings. They concluded that USG is a quick and painless procedure which can be repeated as often as necessary without any complications to the patient.
| Extracorporeal Lithotripsy|| |
Sialolithiasis is the formation of salivary stones due to the crystallization of minerals in saliva which causes a blockage of the salivary ducts resulting in painful inflammation, especially during or after meals. It is one of the most common disease of the salivary glands. Salivary stones tend to occur more frequently in the submandibular gland, lesser in the parotid gland and scarcely in the sublingual or minor salivary glands. There are various diagnostic modalities like radiography, USG and MRI for use in such cases. Out of these, USG can be used to diagnose radiolucent stones and is more economical. Smaller stones flush out on their own. The larger stones may require medical or surgical intervention. Surgery, however, carries risks, such as a possible injury to the facial nerve. Hence, minimally invasive and nonsurgical treatment techniques are a better option.
Lithotripsy is non invasive and an alternative to surgery, which has progressively improved over the past 20 years. Extracorporeal lithotripsy avoids any surgical procedure including a minimal incision of papilla or duct during interventional sialendoscopy. Extracorporeal shock wave lithotripsy uses high energy shock waves that are generated outside the body that pulverizes the stones inside the body. There are two energy sources i.e., piezoelectric and electromagnetic extracorporeal lithotripsy which aim to crush these stones. This modality is the treatment of choice for all parotid calculi as well as perihilar or intraparenchymal submandibular calculi (the size of the stone should be less than 7 mm). The drawback of this technique is that it requires multiple sessions as well as the presence of residual stone fragments in the duct after treatment.
| Ultrasound Therapy in Temporomandibular Joint Disorders|| |
The American Academy of Craniomandibular Disorders and Minnesota Dental Association have suggested physical therapy as an important therapeutic aid which relieves musculoskeletal pain, reduces the inflammation and restores oral motor function.  The mechanism of action of US therapy is based on massage and thermal effects. Electrophysical modalities, such as shortwave diathermy, US, laser, and transcutaneous electrical nerve stimulation (TENS), are commonly used for treatment of temporomandubular joint (TMJ) disorders. Electrophysical modalities reduce inflammation, promote muscular relaxation, and increase blood flow by altering capillary permeability. Ultrasound therapy uses high-frequency sound waves directed to the TMJ, to reduce pain and swelling and improve circulation. It has been suggested that therapeutic ultrasound alone is not useful for the treatment of TMJ disorders. The literature suggests that treatments with electrophysical modalities are beneficial in reducing symptoms when performed early in the treatment process.
A weak intensity of 0.1-0.6W/cm 2 is used for therapy and in any case it should not cross 0.6 W/cm 2 [Figure 1]. Absorption is higher in cases with tissues rich in protein for e.g., skeletal muscle and low in tissues with high water content for e.g., fat.  A typical treatment session lasts between 3 and 10 minutes depending on the injury. Low-intensity US is used for a short duration to provide anti-inflammatory effect as it inhibits the release of inflammatory mediators from cells. Further, it increases vascular and fluid circulation, increases pain threshold, cell permeability and break in pain cycle. 
|Figure 1: Application of transducer over the TMJ area for therapeutic effects|
Click here to view
| Conclusion|| |
Ultrasonography has proven to be a useful therapeutic aid especially in cases of US-guided drainage of abscesses and in the treatment of TMJ disorders. The advances of US imaging in imaging-guided ablation in diseases of cervical lymph nodes in past years have been remarkable. Further advancements and enhancement in current ablative techniques can be done. Further, there has been an increased interest in imaging-guided US therapy for hyperthermia and for high-intensity focused tissue ablation. Therefore, USG appears to be one of the promising therapeutic aids in the near future.
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