IAEAInternational Atomic Energy Agency

Dental Radiology

Radiation Sources in medicine diagnostic Radiology

Day 7 – Lecture 2(2)

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Objective

• To become familiar with dental x-ray systems.

• To become familiar with specific radiation risks associated with this equipment.

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Contents

• Description and characteristics of equipment for intra-oral radiography.

• Description and characteristics of equipment for panoramic radiography.

• Description and characteristics of equipment for cephalometric radiography.

• Equipment malfunction affecting radiation protection.

• Minimum requirements for routine maintenance.

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Dental X-ray Equipment

• Dental radiography is one of the most common x-ray examinations in the industrialized world.

• Although individual radiation doses and risks are low, many extensive examinations are performed in younger age groups.

• As for other radiological procedures, patient doses can be significantly influenced by the equipment and techniques used and the quality assurance measures in place.

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• x-ray equipment for intra-oral radiography uses small intra-oral non-screen x-ray films for bitewing or periapical radiography;

Different types of equipment are used depending on the type of image required. e.g.

• equipment for panoramic tomographic radiography uses a narrow fan shaped x-ray beam (~5-10 mm wide and 150 mm high) which rotates around different axes within the patient’s head to provide a defined image of the plane of the dental arch. Other unwanted structures are deliberately blurred during this process.

Dental X-ray Equipment (cont)

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Intraoral x-ray examination

FILM HOLDER AND POSITIONING DEVICE

Dental X-ray Equipment (cont)

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• The filtration in the useful beam should be equivalent to at least 1.5 mm Al at x-ray tube voltages up to 70 kV peak and 2.5 mm if greater than 70 kV peak.

• X-ray tube focus to skin distances of 200 mm or greater are recommended.

• The diameter of the x-ray beam should not be greater than 60 mm at the outer end of the beam applicator.

• Rectangular collimation is recommended.

• The operating tube voltage should be at least 60 kV peak.

Specific Requirements for Intraoral Equipment

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• The fastest films consistent with the required clinical results should be used.

• Whenever practicable, film holders incorporating beam aiming devices should be used.

• On new equipment, manufacturers should provide a range of x-ray outputs and exposure times so that different speed image receptors (faster film and digital image receptors) can be correctly exposed.

Specific Requirements for Intraoral Equipment (cont)

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Dental X-ray Equipment (cont)

Older “pointer cone” equipment. Open ended collimation (right) should be used

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• Patient positioning devices should be simple, reliable and accurate.

• A fast intensifying screen / film combination (or comparable speed image receptors) should be used.

• All new equipment should incorporate a range of radiographic exposures consistent with clinical requirements, the patient’s build (i.e. adults, children) and the speed of the image receptor.

• The rotation of the x-ray tube around the head that provides the tomographic image of the entire dental arch must be precise and reproducible.

Specific Requirements for Panoramic Equipment

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Panoramic tomographic x-ray equipment

Dental X-ray Equipment (cont)

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Panoramic tomographic x-ray equipment - patient positioning

devices

Dental X-ray Equipment (cont)

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For orthodontic analysis (the diagnosis and treatment of dental disorders), two techniques are routinely employed:

• cephalometry, which provides reproducible images of the skull, dentition and facial profile including the soft tissue;

Dental X-ray Equipment (cont)

• CT examinations (dedicated dental Cone Beam CT (CBCT) scanner).

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Image development

Improper x-ray film development is a significant cause of unnecessary patient exposure and reduced film quality.

0

20

40

60

80

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0 1 2 3 4 5 6 7 8 9 10

mGy (air kerma at skin entrance surface)

Num

ber

Bitewing exposuresSample size651Mean dose (mGy)3.14

Radiological Council, Western Australia 2000 Annual Report

This survey of bitewing doses indicates problems with film development.

Doses should range from 2.5 to 3.0 mGy (without back scatter).

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Malfunctions affecting radiation protection

• inaccuracy and inconsistency of the x-ray tube voltage and radiation output;

Basically the same as for general x-ray system (see modules 2.1, 2.2 and 2.3) but the tests performed and the measuring instruments used shall be adapted to the particular characteristics of the dental system under investigation: e.g.

• inaccurate or defective timer;• misalignment between the x-ray beam and the image receptor;• unsatisfactory film storage conditions, image development and

viewing conditions.