ultrasound in dentistry

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JOURNAL CLUB ONULTRASOUND IN DENTISTRY – A REVIEW

Dr Sourav Malhotra2nd year P.G

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Sonography was introduced in the Medical field in early 1950's with steady development and requirement of Ultrasound equipment for diagnosis has improved the Medical field & now in dentistry.

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Anything below this is called infrasonic and above this Ultrasound.

The transducers are designed to produce longitudinal waves hence only those waves can pass through tissues get reflected, Audiofrequency of a sound wave is 20 KHz.

In diagnostic Ultrasound high frequency sound waves are transmitted in to the body by a transducer and echoes from tissue interface are detected and displayed on a screen.

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The following Modes are in use :

• A Mode Amplitute mode – not in use

• B Mode Brightness Mode – Producing different echogenicity

• TM Mode Motion mode – used in foetal

• Time Motion ECG and Doppler study.

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The technique is similar to the method of location used by bats, whales and dolphins, as well as SONAR used by submarines. (Sound navigation and ranging).

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The phenomenon perceived as sound is the result of periodic changes in the pressure of air against the eardrum.

The periodicity of these changes lies anywhere between 1500 and 20,000 cycles per second ([Hz]).

By definition, ultrasound has a periodicity greater than 20 kHz.

Diagnostic ultrasonography (sonography), the clinical application of ultrasound, uses vibratory frequencies in the range of 1 to 20 MHz.

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Currently, the most widely used piezoelectric material is lead zirconate titanate (PZT).

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PRINCIPLE Scanners used for sonography generate electrical impulses that are converted into ultra-high-frequency sound waves by a transducer, a device that can convert one form of energy into another.

The most important component of the transducer is a thin piezoelectric crystal or material made up of a great number of dipoles arranged in a geometric pattern.

A dipole may be thought of as a distorted molecule that appears to have a positive charge on one end and a negative charge on the other.

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The shapes of scans from different transducers are – 1. Linear Arrays –. Used for small parts, vascular and obstetric applications. 2. Curved Arrays – linear arrays that have been shaped into convex curves. 3. Phased Arrays 4. Two-Dimensional Arrays –

Sharma, et al. : Ultrasound in Dentistry; International Journal of Scientific Study | May 2014 | Vol 2 | Issue 2

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The transducers are designed to produce longitudinal waves hence only those waves can pass through tissues get reflected, Audiofrequency of a sound wave is 20 KHz.

Anything below this is called infrasonic and above this Ultrasound. Medical Ultrasound uses the frequency of 1-15 MHz (2.5, 3.5, 7.5 and 10 MHz). The transducer has a special property called piezoelectric effect i.e. they can convert sound waves in to electrical waves

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As the ultrasonic beam passes through or interacts with tissues of different acoustic impedance, it is attenuated by a combination of absorption, reflection, refraction, and diffusion.

Sonic waves that are reflected back (echoed) toward the transducer cause a change in the thickness of the piezoelectric crystal, which in turn produces an electrical signal that is amplified, processed, and ultimately displayed as an image on, a monitor.

JIADS VOL -1 Issue 4 October -December,2010 |44|

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In this system the transducer serves as both a transmitter and a receiver.

Current techniques permit echoes to be processed at a sufficiently rapid rate to allow perception of motion; this is referred to as real time imaging.

The higher the frequency of the sound waves, the higher the image resolution but less the penetration of the sound through soft tissues.

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Tissue that do not produce signals, such as fluid filled cyst, are said to be anechoic and appear black.

Tissues that produces weak signal are hypoechoic appear fairly dark. Eg muscles

Tissues that produce intense signals such as catilages or needles or bone are hyperechoic and appear white.

Senthil Kumar B , Nazargi Mahabob M :Ultrasound in dentistry – a review, JIADS VOL -1 Issue 4 October - December,2010 |44|

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Head of the condyle and the articular eminence, is generally hypoechoic (low reflection of sound waves) and appears black in ultrasonography images

Margin of the bone is hyperechoic (high reflection of sound waves) and appears white

Senthil Kumar B , Nazargi Mahabob M :Ultrasound in dentistry – a review, JIADS VOL -1 Issue 4 October - December,2010 |44|

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Therapeutic ultrasound

Diagnostic ultrasound

DEPENDING ON THE APPLICATION AND ULTRASONIC INTENSITIES IT IS

DIVIDED INTO TWO-

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Diagnostic ultrasound – the ultrasonic intensities used are typically 5 to 500 mW/cm2 and it includes: Swellings in orofacial region Salivary glands disorders Periapical lesions Lymph nodes – benign/malignant Intraosseous lesions Temporomandibular disorders Primary lesions of the tongue

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Salivary gland

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Normal parotid gland Sharply defined, homogenous hypoechoic lesion indicates a benign tumor( pleomorphic adenoma)

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Longitudinal and transverse US sections of a submandibular gland demonstrating a sharply defined, hypoechoic round lesion. This appearance is consistent with an abscess formation in the gland, supported a diagnosis of acute sialadenitis.

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Submental region which shows a small hyperechoic structure, a sialolith.

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Parotid gland showing a small sialolith .

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Normal lymphnode of the neck.Health lymphnodes are generally hypoechoic apart from centre hyperechoic area( hilum of the node)

Metastatic lymphnode of the neck, apart from the large size also seen round shape and necrotic area shows hypoechoic, cystic in appearance lesions.

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Therapeutic ultrasound – use intensities of 1 to 3 W/cm2

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Increased vascular and

fluid circulation

Increase in cell

permeability

Increase in pain

threshold and a break

in pain cycle

THERAPEUTIC RESULTS OBTAINED BY ULTRASONIC ENERGY ARE THOUGHT TO BE

DUE TO:

It is estimated that thermal effects can occur with elevation of tissue temperature to 40-45°C for at least 5 min.Excessive thermal effects, seen in particular with higher ultrasound intensities, may damage the tissue

Atef Abd El Hameed:The Journal of Oral and Maxillofacial Surgery. Photon 117 (2014) 232-237

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Physiological effect of ultrasound may induce thermal and non-thermal physical effects in tissues.

• Increased blood flow• Reduction in muscle

spasm• Increased

extensibility of collagen fibers

• Pro-inflammatory responseThermal effects

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Non Thermal Effects

CAVITATION

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Stable (regular) cavitation is considered to be beneficial to injured tissue, whereas unstable (transient) cavitation is considered to cause tissue damage and can be suppressed by the use of very short pulses

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ACOUSTIC MICROSTREAMING

The unidirectional movement of fluids along cell membranes, within the ultrasound field as a result of mechanical pressure.

It may alter cell membrane structure, function and permeability which have been suggested to stimulate tissue repair.

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• Stimulation of fibroblast activity

• Increased in protein synthesis

• Increased blood flow

• Tissue regeneration• Bone healingCavitation and Microstreaming effect

Shubham Sharma, Deepali Rasila, Mohit Singh, Mansha Mohan. "Ultrasound as a diagnostic boon in Dentistry-A Review". Int J Sci Stud. 2014;2(2):70-76.

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Ultrasound Therapy in TemporomandibularJoint Disorders

Mechanism of action is based on massage and thermal effects.

• Shortwave diathermy, • Us• Laser• Transcutaneous electrical

nerve stimulation (TENS)

Electrophysical modalities

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Electrophysical modalities

Inflammation

Promote muscular relaxation

Increase blood flow by altering capillary permeability.

Mandeep Kaur:Prospective utility of therapeutic ultrasound in dentistry—Review with recent comprehensive update 2012; 1: 47.

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A weak intensity of 0.1-0.6W/cm2 is used for therapy and in any case it should not cross 0.6 W/cm2

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.

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The use of low intensity US with short duration has been shown to have a major anti inflammatory effect and could be related to an inhibition in release of inflammatory mediators from cells.

The objectives of ultrasound treatment are to accelerate healing, increase the extendibility of collagen fibers, decrease joint stiffness, provide pain relief, improve mobility, and reduce muscle spasm. (Esposito et al., 1984).

Baker KG, Robertson VJ, Duck FA. A review of therapeutic ultrasound: Biophysical effects. Phys Ther.2001;81:1351–8.

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Extracorporeal Lithotripsy

Lithotripsy is non invasive and an alternative to surgery..

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

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Drawback of this technique is that it requires multiple sessions as well as the presence of residual stone fragments in the duct after treatment

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Ultrasound therapy in bone healing and osteointegration

Therapeutic low intensity pulsed ultrasound has been shown to accelerate bone fracture healing indicating that ultrasound may be used as a tool to facilitate hard tissue regeneration.

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Certain studies on animals were carried out on bilateral midshaft femur fractures and showed an 16.9% greater bone mineral content, 81.3% greater mechanical strength, 25.8% increase in bone size at active ultrasound-treated fracture site and increased vascularity around the fracture sites.

Ultrasound on the healing of full thickness excised lesions

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Ultrasound is widely used as a therapeutic agent in medicine and dentistry to accelerate repair, modify scar tissue production, and to reduce pain.Young in his study suggested that US therapy can be useful in accelerating the inflammatory and early proliferative stages of repair.

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• 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.

Ultrasound-Guided Drainage of Deep Neck Space

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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.

SONOPORATION

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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

Mago J et al.: Therapeutic applications of ultrasonography: Journal of Indian Academy of Oral Medicine & Radiology | Oct-Dec 2014 | Vol 26 | Issue 4

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The sound waves can give its effect on the formation of pores in the following four ways:

1. Cavitation effects. 2. Thermal effects. 3. Induction of convective transport. 4. Mechanical effects.

Mago J et al.: Therapeutic applications of ultrasonography: Journal of Indian Academy of Oral Medicine & Radiology | Oct-Dec 2014 | Vol 26 | Issue 4

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These are 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.

ULTRASOUND GUIDED ABLATION

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ADVANTAGES OVER CONVENTIONAL X-RAY IMAGING

Sound waves are NOT ionizing radiation.There are no known harmful effects on any tissues at the energies

and doses currently used in diagnostic ultrasound. Images show good differentiation between different soft tissues

and are very sensitive for detecting focal disease in the salivary glands.

Technique is widely available and relatively inexpensive

Eric Whaites; Essentials of Dental Radiography and Radiology:FOURTH EDITION Page 237-240

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DISADVANTAGES

Ultrasound has limited use in the head and neck region because sound waves are absorbed by bone. Its use is therefore restricted to the superficial structures.

Technique is operator dependent. Images can be difficult to interpret for inexperienced operators.Real-time imaging means that the radiologist must be present

during the investigation.

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Conclusion

Ultrasound is an inexpensive, non-invasive and readily available imaging technique, that can be used as an primary investigative Imaging technique So as to avoid radiation hazards caused by X-ray radiation (or) MRI which may be highly economical to the patients. So proper application and Utilization of this technique can be of great use in dentistry.

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References • White SC, Pharoah MJ. Oral radiology: Advanced imaging, (6th

ed); 2004.

• Eric Whaites; Essentials of Dental Radiography and

Radiology:FOURTH EDITION Page 237-240

• Sharma, et al. : Ultrasound in Dentistry; International Journal of

Scientific Study | May 2014 | Vol 2 | Issue 2

• Senthil Kumar B , Nazargi Mahabob M :Ultrasound in

dentistry – a review, JIADS VOL -1 Issue 4 October -

December,2010 |44|

•

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• Mago J et al.: Therapeutic applications of ultrasonography: Journal of

Indian Academy of Oral Medicine & Radiology | Oct-Dec 2014 | Vol 26 |

Issue 4

• Baker KG, Robertson VJ, Duck FA. A review of therapeutic ultrasound:

Biophysical effects. Phys Ther.2001;81:1351–8.

• Atef Abd El Hameed:The Journal of Oral and Maxillofacial Surgery. Photon

117 (2014) 232-237

• Melis et al: Use of ultrasonography for the diagnosis of temporomandibular

joint disorders: A review ,American Journal of Dentistry, Vol. 20, No. 2,

April, 2007

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• Shubham Sharma, Deepali Rasila, Mohit Singh, Mansha

Mohan. "Ultrasound as a diagnostic boon in Dentistry-A

Review". Int J Sci Stud. 2014;2(2):70-76.

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