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Azerbaycan Saytlari

 »  Home  »  Endodontic Articles 2  »  A new technique for the study of periapical bone lesions: ultrasound real time imaging
A new technique for the study of periapical bone lesions: ultrasound real time imaging
Introduction - Materials and methods.



Introduction.
Radiographs are an important part of root canal treatment, especially for the detection, treatment and follow up of periapical bone lesions. However, routine radiographic procedures do not demonstrate reliably the presence of every lesion (Bender & Seltzer 1961, van der Stelt 1985), and they do not show the real size of a lesion and its spatial relationship with anatomical structures. Furthermore, interrater and intrarater variability can influence diagnosis (Goldman et al . 1972, Saunders et al . 2000).
In histopathological terms, apical periodontitis can be divided into periapical granulomas and periapical cysts; however, clinical examination and radiographs alone cannot differentiate between cystic and non-cystic lesions (Nair 1998). Being able to distinguish between the two may be of importance in predicting treatment failure (Nair 1998).
In order to overcome some of these existing shortcomings, it is important that new imaging techniques are evaluated for their ability to diagnose periapical lesions.
Recent findings have shown that direct digital radiography, even when used with imaging processing and colour coding, is no better than conventional radiography in the detection and measurement of periapical lesions (Scarfe et al . 1999).
The use of computerized tomography (CT) has been shown to be of help in the management of extensive periapical lesions (Cotti et al . 1999) and it has been suggested that CT is a non-invasive method that could be used to make a differential diagnosis between a cyst and a granuloma (Trope et al . 1989). Unfortunately, routine use of CT is associated with high dosage of radiation, even though dose reduction methods have been established (Dula et al . 1996).
Echography is a real time ultrasound imaging technique that is of great use in numerous diagnostic fields of medicine (Auer & Van Velthoven 1990). The echographic method, or ‘real time echotomography’, is based on the reflection of ultrasound (US) waves (echos). US waves are generated by a quartz or synthetic ceramic crystal when it is exposed to an alternating current of 3–10 Mhz. As a result of the piezoelectric effect, the crystal distributes US waves oscillating at the same frequency. The US waves arriving in biological tissues encounter areas of different density and different mechanical and acoustic properties. At the interface between two tissues with different acoustic impedance the US waves undergo refraction and reflection. The echo is the part of the US wave reflected back toward the crystal. The echo is transformed by the crystal into electrical energy, which in turn is transformed into a light spot using a grey scale into a TV monitor. The point of origin of the echo along the line of the US wave is calculated by the computer built into the US apparatus from the time delay between the initiation of the wave signal and its return.
The US image seen on the monitor is produced by automatic movement of the crystal over the tissue of interest. As each movement gives one image of this tissue (depending on its plane) and there is a frequency of 30–50 images per s, they appear in a screen as moving images. Moving the US probe by hand over the area of interest changes the sector plane and thus a real time three-dimensional impression of the space is obtained.
The interpretation of grey values on an image is based on a qualitative comparison of the echo intensity with that of normal tissue. ‘Hypoechoic’ or ‘transonic’ is an area with low echo intensity; ‘anechoic’ is an area where no reflection occurs (i.e. any area filled with fluids), and ‘hyperechoic’ is an area which has high echo intensity. Bone exhibits a phenomenon of total reflection (hyperechoic/ totally echogenic), therefore US imaging can only be performed through windows in bone or where the bony architecture has been altered (Auer & Van Velthoven 1990). Areas which have different types of tissues show what is termed a ‘dishomogeneous echo’.
Using ‘Colour Power Doppler Ultrasound’ it may be possible to evaluate and determine the presence and direction of blood flow within the ecographic image of the tissue, together with information concerning flow velocity and perfusion of the area. Power Doppler will give a colour coded representation of the intensity of Doppler signal and its modification with time (Fleischer & Emerson 1993).
The echographic examination of bone lesions of endodontic origin has not been reported to date. The purpose of this study was to use ultrasonic imaging as a diagnostic aid for the management of extensive periapical lesions.

Materials and methods.

Echographic examination.
An Elegra Siemens Apparatus with a regular-size, linear, high definition, multi frequency ultrasound probe (Siemens, Erlangen, Germany) was used at a frequency of 7–9 Mhz. Twelve white patients, aged between 25 and 50 years, were selected for the study. The patients had been diagnosed with periradicular lesions of endodontic origin based on clinical signs and symptoms (Trope & Sigurdsson 1998) and intraoral and panoramic radiographic findings. The patients were scheduled to be treated in the Department of Conservative Dentistry and Endodontics at the University Clinic, Cagliari. Patients who agreed to take part in the study were asked to sign an informed consent form before undergoing the echographic examination.
The area of interest within the mouth was selected for the echography. The ultrasonic probe was covered with an insulating latex finger from a glove. The probe was then positioned on the buccal sulcus corresponding to the apical area of the tooth. Subsequently, it was placed outside the mouth against the skin at the external area in order to assess which technique gave the best results. Once the probe was in contact with the tissue, it was then moved in order to obtain an adequate number of transversal scans to define the bony defect.
The saved echographic images (magneto-optical disk, Eastman Kodak, Rochester, NY, USA) were analysed and discussed by an expert echographist, together with an endodontist and an oral surgeon. The lesions were first identified in the echotomograms, based on semeiotic echographic principles of bone pathosis; then a comparison was made with the radiographic images of the same lesions. A descriptive chart was subsequently made for every case. In the chart there was

  1. one section dedicated to general information on the patient;
  2. a second section describing the lesion of interest as it appeared in the radiograph/s
  3. a third section which described the lesion as seen in the echography.