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Cephalogram is a standardised radiograph of the head and face. The basic technique was introduced to the orthodontic speciality by Holly Broadbent in 1931 Cephalogram - An 8” x 10” radiographic (xray) image of the human head, taken from the side, front, back, or from an oblique angle. It shows in detail the angular relationships of facial components and their relationship to the cranial base. www.indiandentalacademy.com


Types of Cephalograms  Lateral  Postero anterior  Oblique

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Cephalometry Procedure

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The standardisation comes from patient position and orientation of the x-ray beam established by mechanical devices The mid sagittal plane of the subject's head is placed 5 feet (152 centimetres) from the x-ray target, with the left side of the subject towards the film. The central beam of the x-rays coincides with the trans meatal axes - ear rods of the cephalostat. The distance from the midsagittal plane to the film is held constant, usually at 18 centimetres. The head is usually placed so that Frankfort plane (porion-orbitale) is parallel to the floor. teeth in their normal occlusal position. www.indiandentalacademy.com


Holly Broadbent 1931

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Cephalostat De Nevrez 1936

Hofrath (Germany)

Korkhaus 1937

Waldo 1938

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Cephalostats Broadbent

Marcolis 1940

Thurow 1951 Weingart 1948

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Cephalostats Bjork, 1951

Rebaul 1954

Freeman Rasmussen 1952 www.indiandentalacademy.com


Cephalometric Equipment Nasion Pointer Lead Scale

Soft Tissue Filter

Orbitale Assembly www.indiandentalacademy.com


Technical data      

Focal spot size 0.5 x 0.5mm Total filtration 2.5 mm Al Line voltage 100 - 240 V, 50/60 Hz Line current 8 - 16 A Exposure time Cephalometric 0.2 - 5 s Cephalometric film size 8" x 10"

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Cephalometers

Siora Orthopos

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Cephalometers

Gendex Orthoralix

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Cephalometers

Planmeca ProMax Ceph Digital (Dimax2) www.indiandentalacademy.com


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Digital Cephalometry

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Image is constructed using pixels or small light sensitive elements. These pixels can be a range of shades of grey depending on the exposure, and are arranged in grids and rows on the sensor, The signal that is produced by the sensor is an analogue signal, i.e. a voltage that varies as a function of time.The sensor is connected to the computer and the signal is sampled at regular intervals. The output of each pixel is quantified and converted to numbers by a frame grabber within the computer. The range of numbers is normally from 0 to 256 with 0 representing black, 256 representing white others are shades of grey. www.indiandentalacademy.com


The number of grey levels relates to contrast resolution Size of the pixels is related to spatial resolution. Together these determine the overall resolution Resolution can also be expressed in line pairs per millimetre. Current systems have a spatial resolution of 6–8 LP/mm.

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Image acquisition Indirect acquisition  scanning conventional radiographs using a flatbed scanner and a transparency adaptor,  charged coupled device camera Direct digital imaging  Image immediately on the monitor post-exposure and is therefore called Direct Imaging. The greatest advantage of the direct sensor system is the gain in time  Image is produced on the monitor following scanning by laser www.indiandentalacademy.com - semi-direct imaging.


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Digital radiography has been used widely in medicine, but it was only in the 1980s that the first intra-oral sensors were developed for use in dentistry. Unfortunately, the early systems could not capture panoramic and cephalometric images The first systems - charge coupled device technology (CCD), found in camera systems. Radiation is detected by the sensor and converted into digital data, which are sent immediately to a computer. direct digital radiography’ Static extraoral radiography, anteroposterior and cephalometric projections - a linear scanning procedure is usually applied to cover the whole area. This lengthens the exposure time considerably. www.indiandentalacademy.com


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In the early 1990s, digital storage phosphor systems took over from medical radiology. Storage phosphor plates (SPP) capture radiation energy for a certain period and can be read out by a laser scanner, which converts radiation energy into light energy that is measured and translated into digital data. The scanner stimulates the phosphor plate and stores a record of the number of light photons detected. The lasers used are 600-nm band and are usually of the helium-neon variety Because of the delay caused by the scanning procedure, the digital storage phosphor technique is also called ‘indirect digital radiography’. A technical limitation of extra-oral direct digital radiography is the very small active area of the CCD sensor. For www.indiandentalacademy.com


Advantages Image manipulation  Contrast enhancement. This can effectively compensate for over or under exposure of the digital image.  Measurements. application in cephalometric analysis.  3-D reconstruction  Filtration. clarify the soft tissue profile Time - Much time is gained especially with the CCD system where the image is displayed at the chairside immediately post exposure. Storage - CD ROM can hold over 30,000 images. This means that images can be stored cheaply and indefinitely. Teleradiology Environmentally friendly - No processing chemicals are used or disposed www.indiandentalacademy.com


Disadvantages  

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Cost Sensor dimensions quite bulky for the CCD system and awkward to position due to trailing fibre optic wires. Cross-infection control Medicolegal manipulate the images for fraudulent purposes. Manufacturers of software programmes have installed ‘audit trails’, which can track down and recover the original image.

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Image quality 

Intensifying Screens convert the invisible energy of the x-ray beam to the visible light required to expose the photographic film.by producing fluorescent light via radiation-sensitive phosphorescing minerals imbedded in the plastic sheets. Film \ Screen Compatibility The phosphorescing minerals in your intensifying screens glow a specific color - either blue or green. Films are manufactured in various color sensitivities to correspond with the light produced by your intensifying screens. Low Power X-ray Machines - Properly exposed cephalometric films require an x-ray machine of at least 85 kVp and 10 mA. Use of a hang-on soft tissue shield can improve soft tissue definition by absorbing the excess radiation in the anterior areas of the anatomy. www.indiandentalacademy.com


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Exposure Parameters When using a 90 kV x-ray source at 10mA with Kodak LANEX screens and TMAT type films, a good starting point is 12 impulses (or 1/5 second) for an adult patient. When using a 70 kV x-ray source, start at 40 impulses (2/3 second) for determining proper exposure. Grids Processing Over 85% of the image problems our technicians trouble shoot can be traced to lack of control over the development process. poor control over temperature Lack of sufficient replenishment of chemicals. www.indiandentalacademy.com


Magnification ď Ž

Magnification Cephalometric 1.08 - 1.13

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In two-dimensional radiographs, there are two axes (the vertical and the horizontal axes), while the Cartesian coordinates system in 3D images consists of the x-axis (or the transverse dimension), y-axis (or the vertical dimension), and the z-axis (the anteroposterior dimension ‘depth axis’). www.indiandentalacademy.com


3D Cephalometry ď Ž

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Broadbent stressed the importance of coordinating the lateral and postero anterior cephalometric films to arrive at a distortion-free definition of skeletal craniofacial form. Computer programs have since been developed to collect three-dimensional coordinates directly from digital cephalogram images, eliminating the need for hand tracing and mouse-based X–Y digitizing tablets.

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CT Cephalometry

The spatial visualization of the patient’s CT data delivers the required information for a 3D cephalometry. After the interactive definition of a lateral reference plane in CT, the user sets the exact position of cephalometrical marks pre-defined by the system. The best viewing direction and the best data visualization method skin surface images or in the original data slices, Functions evaluate the angles and distances between the given profile marks. In combination, all these marks serve as a complete 3D profile analysis and can be used for an accurate diagnosis www.indiandentalacademy.com


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Disadvantages :  patient exposure to a high dose of ionizing radiation  limited resolution of facial soft tissues due to slice spacing  the possibility of having artifacts created by metal objects inside the mouth

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Radiation Doses

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higher organ doses are found for direct digital cephalometric radiography compared to indirect digital effective doses for direct digital cephalometric imaging are 9% 1.7 µSv 56% - 3.4 µSv compared to indirect digital cephalometric exposures. 1.6 µSv 2.2 µSv

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Cephalometry/ dental implant courses by Indian dental academy  

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