2 extra-oral radiography

05/01/2305/01/23 Ossama El-ShallOssama El-Shall

Extra-oral Radiography

Dr. Ossama EL-ShallDr. Ossama EL-ShallProfessor and Chairman, Oral Professor and Chairman, Oral

Medicine, Periodontology, Diagnosis Medicine, Periodontology, Diagnosis and Radiology Dept., Faculty of and Radiology Dept., Faculty of

Dental Medicine Al-Azhar University , Dental Medicine Al-Azhar University , Cairo Egypt.Cairo Egypt.

E.mail address: [email protected] address: [email protected]


Extra oral filmsExtra-oral films are the films placed extra-orally during exposure in order to exam the mandible, the maxilla, the TMJ and all the facial bones.

Extra-oral films usually supplied in special light tight boxes in quantities of 50 or 100 films and loaded in a special light protected holder (cassette) inside the dark room.


General indications of use of extra-oral films

1- Patients who cannot open their mouths sufficiently for insertion of intra-oral films due to any causes such as trauma of truisms.

2- Unco-operative patient such as mentally retarded and children.3- Examination of large pathologic involvement, such as large

cyst.4- Obtaining a large generalized view of jaws, sinuses and bones.5- Examination of fracture lines and extension of fracture in skull

bone.6- Localization of foreign bodies.7- Examination and diagnosis of TMJ disorder.8- Obtaining of generalized view of unerupted, impacted or

supernumerary teeth.


Types of extra-oral films.Types of extra-oral films.

Screen filmsScreen films

Non screen filmsNon screen films


Screen filmScreen filmIs used in combination with intensifying Is used in combination with intensifying screens. screens. These films are different from other dental These films are different from other dental films in that they are designed to be films in that they are designed to be particularly sensitive to particularly sensitive to visible lightvisible light rather rather than to X-radiation. than to X-radiation. This is because they are used by being placed This is because they are used by being placed between two intensifying screens. between two intensifying screens. The intensifying screens absorb X rays and The intensifying screens absorb X rays and emit visible light that exposes the screen film. emit visible light that exposes the screen film.


Non screen filmsNon screen films

Or direct exposure films; Or direct exposure films; they are more sensitive to x rays than to light.they are more sensitive to x rays than to light. It requires a longer exposure time as it It requires a longer exposure time as it depends on the depends on the x rays onlyx rays only to affect the film to affect the film not on any emitted light. not on any emitted light. It may be used for thin bones only such as It may be used for thin bones only such as long bone and mandible. long bone and mandible. However its use in dental radiography is not However its use in dental radiography is not recommended.recommended.


Extra-oral film Extra-oral film equipmentsequipments

Intensifying screenIntensifying screen

Cassette Cassette


Intensifying screenIntensifying screen

It is a device used to intensifies the It is a device used to intensifies the photographic effect of X-rays and thus photographic effect of X-rays and thus shortens the exposure time that otherwise shortens the exposure time that otherwise would be long to suit the thickness and would be long to suit the thickness and density of tissues in case of extra-oral density of tissues in case of extra-oral radiography. radiography.


The use of intensifying screen is based on three main principles:

X radiation have a biological damaging effect that should be protected through decrease the exposure time.Certain substances can cause fluorescence if it absorb X radiation.Photographic film is sensitive to both X radiation and visible light.


When x-rays strike intensifying screen, they immediately activate it so it emits light which is going together with the x-rays to expose the film.Thus the light produced by the screen intensifies the effect of the x-rays on the film and helps reduction of exposure time.The intensity of this fluorescence is directly proportional to the intensity of the exiting x-ray.


= phosphor crystal

film

Mechanism of action of the screen


Composition of intensifying screen:

Plastic or cardboard base.Reflecting layer: It is a layer of titanium oxide that covers the base of the screen and lies beneath the phosphor layer. Its function is to reflect any light emitted from the phosphor layer back to the film and thus increase the effect of the screen.The phosphor layer: It is the light sensitive crystals layer, it formed from Calcium tungestate or Barium lead sulphate (conventional type that emit a blue light) or formed from a rare earth phosphors as Gadolinium or Lanthanium (rare earth type that emit green light).Protective layer: made up of a plastic layer with smooth surface.


Intensifying Screen Composition

-Base (thick white line) = plastic for support

-Reflecting layer (red line) = reflects

light back

toward film-Phosphor layer (green line) = rare earth -Protecting coat (thin white line) = plastic

(10)

(this side toward film)


Types of intensifying screens:I- According to the phosphor layers:

Conventional screens: the phosphor layer made of Calcium tungestate or Barium lead sulphate and it emit a blue light. For example: Kodak X-Omatic screens.Rare earth screens: the phosphor layer made of rare earth phosphors, Gadolinium or Lanthanium and it emit a green light. For example: Kodak Lanex screens.


II- According to speed: (phosphor crystal size)

Slow: has the smallest crystals and give the best image details.Intermediate: Have larger crystals and less detail.Fast: The largest crystals and least details.


= phosphor crystal

film

Light Emission from the screen


Loaded Screen film

film


Cassettes

Cassette holder is another equipment necessary for the extra-oral films.

The extra-oral film is sandwiched between 2 intensifying screens of matching size and type and secured in a cassette holder.


Cassette and its contents

1. Cassette front: made of plastic, aluminum or carbon fibers to allows more rays to pass and thus reducing patient exposure.

2. Two intensifying screens.3. The screen film4. Felt padding: to assure intimate and even

contact between film & screens5. Cassette back: made of lead


Cross section of loaded cassette

Cassette front

Screen

Film

Screen

Felt padding

Cassette back


Cassette/Film


Cassettes

Hold intensifying screens (2) in tight contact with film

Rigid (metal) or soft (vinyl)

Rigid metal cassette

Flexible vinyl cassette


Extra-Oral radiographic projections.Extra-Oral radiographic projections.

(Plain radiographs).(Plain radiographs).

Lateral skull projectionLateral skull projectionPosteroanterior projection: (PA). Posteroanterior projection: (PA). Mandibular Lateral oblique projections.Mandibular Lateral oblique projections.Water’s view: (occiptomental projection).Water’s view: (occiptomental projection).Reverse-Towne projection.Reverse-Towne projection.Submentovertx projection: (base view).Submentovertx projection: (base view).


Plain radiographs.Plain radiographs.Frankfort plane:Frankfort plane: It extended from the It extended from the anterior border of the external auditory anterior border of the external auditory meatus to the infra-orbital rim.meatus to the infra-orbital rim.

The canthomeatal line:The canthomeatal line: It is the line between It is the line between the central points of the external auditory the central points of the external auditory meatus to the outer canthus of the eye. It meatus to the outer canthus of the eye. It makes 10 degree with the frankfort plane. makes 10 degree with the frankfort plane. (radiographic base line)(radiographic base line)


Frankfort planeFrankfort planeCanthomeatal lineCanthomeatal line


Concerning the nomenclature of the Concerning the nomenclature of the film projection, the film projection, the firstfirst word of the word of the description is description is where the tube is;where the tube is; the the secondsecond word is word is where the film iswhere the film is i.e. PA i.e. PA film has the tube at the back of the film has the tube at the back of the head (P) and the film is placed by the head (P) and the film is placed by the face (anterior).face (anterior).


Lateral skull projectionLateral skull projection Lateral cephalometric, True lateral, Dead lateralLateral cephalometric, True lateral, Dead lateral

It used to survey the skull and facial bones for evidence of trauma, disease, or developmental abnormality.

This view reveals the nasopharyngeal soft tissues, paranasal sinuses, and hard palate.

Orthodontists use it to assess facial growth, and in oral surgery and prosthetics it establishes pretreatment and post-treatment records.


Lateral skull projectionLateral skull projection


Film placement: the film is positioned vertically in a cassette-holding device.

Head position: the head should be positioned with the side of the face near the cassette, the interpupillary line perpendicular to the film, and the midsagittal plane parallel to the plane of the film.

Projection of the central ray: It directed toward the external auditory meatus and perpendicular to the plane of the film and midsagittal plane. Therefore, superimposition of both sides of the skull, facial bones and mandible.

Lateral Cephalometric Identify trauma, abnormalitiesAssess facial growth; treatment record

film at set distance from MSPfilm horizontal

extraoral x-ray unit

MSP

floor

MSP


Patient and film position during lateral projection


Cephalometric MachineCephalometric Machine


Position of the patient in the cephalometric machine for lateral cephalometric film


Posteroanterior projection: (PA)Posteroanterior projection: (PA)It is so named because the X-ray beam passes in a posterior-to-anterior direction through the skull.

It used to examine the skull for disease, trauma or developmental abnormalities.

It provides a good record to detect progressive changes in the mediolateral dimensions of the skull.

It also offers a good visualization of facial structures, including the frontal and ethmoid sinuses, nasal fossae, and orbits.


PAPA


Film placement: the cassette is positioned vertically in a hold in device in front to patient.

Head position: the head is centered in the front of the cassette with the canthomeatal line parallel to the floor and the tip of the nose and forehad are in contact with the cassette.

Projection of the central ray: the central ray is directed perpendicular to the plane of the film and coincident with the midsagittal plane of the head at the level of the bridge of the nose.


Patient head position in relation to the cassette during P.A projection

Posteroanterior (PA) SkullIdentify trauma, pathology, ordevelopmental abnormalities

FP

floor

MSP



Position of the patient for posteroanterior projection produced by cepalometric machine


It is a variant of the postero-anterior view.

It particularly used for evaluation of maxillary sinuses, in addition to frontal and ethmoid sinuses, the orbit, nasal cavity and the coronoid process of the mandible.

Water’s view Water’s view (Occiptomental projection)(Occiptomental projection)


Film placement: the cassette is positioned vertically.

Head position: the sagittal plane of the head is perpendicular to the plane of the film. The chin is raised to elevate the canthomeatal line 37 degrees above horizontal plane. A bite block is used to secure max. jaw opening.

Projection of the central ray: the central ray

should be perpendicular to the film, through the midsagittal plane, at the level of the maxillary sinus.


Water’s view (Occiptomental projection)

Waters

Evaluate the maxillary sinus

MSP

floor


(Sinus view)

tip of nose 1” from cassette

CR

FP


Position of the patient for Water’s view using cephalometric machine


Mandibular posterio-anterior viewMandibular posterio-anterior view(Reverse-Towne projection)(Reverse-Towne projection)

It used to examine a patient with a It used to examine a patient with a suspected fracture of the condylar suspected fracture of the condylar neck,neck, especially in cases of medially especially in cases of medially displaced condyle.displaced condyle.


Film placement: the cassette is positioned in a holding device in front to the patient.

Head position: the head is centered in front of the cassette with the canthomeatal line oriented downward 25 degree. The patient instructed to open his mouth as wide as possible to help visualize the condyles.

Projection of the central ray: the central ray is directed to the film in the sagittal plane through the occipital bone.


CM lineCM line RaysRays


Mandibular posterioanterior view(Reverse-Towne projection)


Position of the patient for Reverse-Towne Reverse-Towne projectionprojection using cephalometric machine


Submentovertx projectionSubmentovertx projection (base view) (base view)

This view used to exam the base of the skull, condyles, sphenoid sinus, curvature of the mandible, fractured zygomatic arch, and foramina of the base of the skull.


Film placement: the cassette is placed vertically in a holding device.

Head position: patient’s head is fully extended backward as far as possible with the vertex of the skull touches the center of the cassette.

Projection of central ray: the central ray is directed from below the mandible upward toward the vertex of the skull.


Submentovertx projection Submentovertx projection (base view)(base view)

(Reverse-Towne projection)Occiptomental projectionPA

Water’s view Mandibular Posterioanterior view


Specialized radiography


Specialized radiography.Specialized radiography.Panoramic radiography.Computed Tomography.Sialography.Magnetic resonance image.Digital imaging.


Panoramic radiography rotational radiography, or curved surface

tomography

It is a radiographic technique for producing a single image of the facial structures that includes both maxillary and mandibular arches and their supporting structures.

PanoramaPanorama Panoramic radiography is an extraoral Panoramic radiography is an extraoral radiographic technique that is used to radiographic technique that is used to examine the upper and lower jaws on a examine the upper and lower jaws on a single filmsingle film . .

The film and the tubehead rotate The film and the tubehead rotate around the patient, producing a series around the patient, producing a series of individual imagesof individual images . .


As Tomographic principles, the x-ray tube and film cassette rotate in opposite directions around the patient’s head to produce a specific curved image of the maxilla and mandible on the film.


Panoramic principles are combination of Scanography and Tomography principles.

In order to understand the principle of panoramic radiography, we have to explain the meaning and principles of both Tomography and Scanography


Tomography

Conventional film-based tomography is a special radiographic technique designed to image more clearly objects lying in a plane of interest.

This is accomplished by focusing on the plane of interest and blurring the image of structures lying superficial and deep to this plane.

Word Tome in Greek = Section


Conventional tomography is applied primarily to high contrast anatomy, such as encountered in dental implant diagnostics.

In the other word, we can define the tomography as a radiographic presentation of a layer within the body while body structures above and below that layer are blurred out of focus.


Tomographic methods are divided into 2 major categories:

I- Conventional tomography.

II- Computerized tomography (C.T).


Scanography

Scanography is a process by which an x-ray tube and a dental film are linked together through a mechanical linkage and rotate around a fixed object (patient’s head).


In panoramic technique, during exposure, the x-ray source moves in one direction while the film moves in the opposite direction

The area of the object in the center of this movement will appears in focus and very sharp on the resultant radiograph as its shadow.

All other structures will appears blurred or out of focus


Advantage of panoramic radiography

1. Give a complete image for both jaws as well as cervicofacial bones to exam any abnormality such as, fractures, tumors, cysts, impaction anomalous of teeth , etc……..

2. Simple technique, as it requires less co-operation of the patient especially handicapped, children, and jaw-fractured patients.

3. Low patient radiation dose; it is about 3 times less than the amount received via full mouth Periapical survey (14 films).


4. Quick procedure, the time required to complete a panoramic radiographic examination is quite short, usually in the range of 3-4 minutes; this includes the time necessary for positioning and the actual exposure cycle (about22 sec.)

5. Panoramic films are readily accepted by patients as a visual aid in case presentation and for patient education.


Disadvantages:

The resultant Image does not resolve the fine anatomical details that may be seen on intra-oral Periapical radiographs.

Interproximal caries and changes of lamina dura can not be diagnosed in most cases due to lack of fine details and sharpness.

Magnification, geometric distortion and overlapped images of teeth, especially in the premolar region.


4. Due to superimposition of the spine, specially in short-necked patients, there is always lack of clarity in the central portion of the film (Ghost shadow appearance of the spine)

5. Soft tissues and air shadows can overlie the required hard tissue

6. High coast, 2-4 times that of an intra-oral X-ray machine.


Indications:

1. Overall view of the teeth and facial bones.2. Evaluations of trauma, extensive disease, tumor

extension, fracture, and gross swelling.3. It reveals fractures of the mandible from the

midline to the neck of the condyle.4. Cases of truisms, to locate or exam impaction,

pathology or fracture.5. It reveals the maxillary sinuses floor of the orbits

and nasal bone.


6. Uncooperative patient, such as children, or handicapped.

7. Full mouth survey instead of full mouth X-ray, 14 film.

8. Bilateral comparison of any pathology.

9. Orthodontic treatment

10. Evaluation of tooth development (especially in the mixed dentition), retained teeth or root tips (in edentulous patients), and developmental anomalies.


Contra-indications:

Panoramic films are not suitable for diagnostic examinations requiring high image resolution, such as detection of early bone loss, dental caries, periodontal diseases, or analysis of trabecular bone changes associated with early Periapical lesions.


Computerized TomographyC.T.


C.T.1. Simply the computed tomographic scanner consists of a

multiple radiographic tubes with narrow beams that are mounted in a circular gantry opposite an array of scintillation receptors designed to accept these beams.

2. The patient is placed in the center of the gantry and the gantry rotates, allowing the x-ray beams to irradiate patient from various angles.

3. The receptors record the radiation passing through each small section of the patient and convert it into electric impulses, which are sent to a computer for storage and manipulation.


4. It provides excellent imaging of TMJ, salivary gland, facial fractures and lesions, and tumor extension and assists in the positioning of implants.

5. It completely eliminates the superimposition of images of structures superficial or deep to the area of interest within the patient.

6. It give a good differentiation between tissues due to its high contrast resolution

7. The main disadvantages of it that, anything denser than enamel produces serious artifacts. This causes some problems when examining the jaws of patients with metal restorations or implants.


Magnetic Resonance Imaging.(MRI)

Magnetic resonance imaging is a technique, which uses a combination of magnetic fields and radio-frequency waves to generate images of the body.


Able to image soft tissue without contrast agents

Magnetic Resonance

1. Magnetic field aligns atoms (Hydrogen)2. Radiowaves alter alignment3. Atoms realign, releasing energy4. Computer produces image

NO IONIZING RADIATION


Instead of detecting tissues by the x-ray, magnetic resonance detects the presence of hydrogen nuclei through their resonance in a magnetic filed.

Human tissues consist of molecules containing hydrogen nuclei (protons). Each proton has an axial spin and, because of its charge, behaves as a small magnet, have both north and south poles.

Normally the protons are randomly arranged; however, when the patient is placed in a strong magnetic field, the direction of the spine of the protons aligns with that of the filed.


The application of a pulsed resonant radio-frequency waves, causes the protons to tilt away from the magnetic filed. Once radio-frequency waves are turned off, the protons return to their preferred alignment with the magnetic filed, and gives off the acquired radio wave signals.

Magnetic Resonance Imaging is the process of locating these individual protons radio-signals in a three dimensional visual image.


To produce a MR image. The patient is placed inside a large magnet, which induce a relatively strong static magnetic field. This cause the nuclei of many atoms in the body, including hydrogen to align them with the magnetic filed.

Magnetic resonance imaging specifically image the presence of H2 nuclei, water, lipids and the degree of H2 are bound with molecules. So the tightly bound hydrogen atoms as in bone appears black as that of cortical plate, and loosely bound or mobile H2 atoms such that of salivary glands and liquids appears gray.


Magnetic Resonance

radiofrequency coils

Magnet(0.5 – 2.0 tesla = 5,000 – 20,000 gauss)

sliding table


Advantages: Excellent soft tissues imaging especially T.M.J and

salivary glands without radiation exposure or contrast media injection.

Disadvantages: 1. Long scan time.2. Some patients can not stay motionless for long

times.3. Noisy MR scanner4. Any vascular clips can move due to magnetic filed.5. High coast.


Thank you all for listening

Dr. Ossama El-Shall

Professor of Oral Medicine & Periodontology, Faculty of Dental

Medicine, Al-Azhar University, Cairo, Egypt.

E-mail address: [email protected]

2 extra-oral radiography

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