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FAQs – Dentistry

In our travels visiting dental practices and surveying x-ray machines, we’re often asked questions about handling x-ray machines and how dental radiation workers can best protect themselves against harmful exposure. Following are some of the most common questions we field:

How to I prepare for an X-ray inspection of my facility?

The inspection covers a number of steps dealing with the actual performance of the x-ray machines, processing of images, radiation safety and Quality Assurance Programs. The best way to prepare for the inspection is to ensure that technique charts are posted for each machine, lead aprons are in good repair and a Quality Assurance Program is in place. The rest of the inspection is technical and there is little that can be done ahead of the inspection.

When should mirrors be used to view patients during an X-ray?

You must be able to see your patient when you are taking an X-ray and be adequately protected. The rule is that without a suitable barrier, you must be 3 meters from the patient when taking an X-ray. If you cannot see your patient when behind the barrier, place a mirror positioned in such a way that you can view the patient and not positioned in the direction of the primary beam as you take the X-ray.

What is a Quality Assurance (QA) program in dental imaging?

It is a way to independently determine the quality of your dental stepwedge or approved phantom images. It consists of monitoring and recording developer temperature, chemical changes, retakes and processing system maintenance. It also involves taking, cataloguing and examining stepwedge images on a regular basis. An important part of the QA program is having regular, independent inspections of the X-ray machines.

Why should I measure the temperature in processors?

Developer temperature is a major determinant of X-ray image quality. It must be kept at the manufacturer’s recommended level. This is best accomplished with the use of a thermometer. Film is designed to be processed in a time and temperature fashion. Often the label on the film box will state that the optimum developing times occur within a specific temperature range. Automatic film processors are designed to treat film for fixed periods of time that frequently do not change. Hence, the temperature must be controlled to accommodate the fixed times that the film is in the processor. The problem is that the temperature controlling device in the processor does not always work properly. Some processors display the developer temperature. Others use lights or some other indicator to show that the temperature is in the correct range and still others have no indicators at all. One of the most common failures associated with automatic film processors is incorrect developer temperature. In the case of wet line development (also known as tank development) the temperature of the water bath around the developer and fixer tanks is often controlled by a thermostatic valve. This valve can malfunction over time and change the water temperature of the bath. Therefore it is necessary to track the temperature of the developer with a suitable thermometer.

Do I have to monitor the developer temperature if I have an automatic processor?

Yes, unless you have a fully automatic processor with a digital temperature display. In this instance, you need only log the temperature on your log sheet. If your processor has a “ready” light, you still have to monitor the temperature with a thermometer and record it on the log sheet.

Do I have to monitor the developer temperature with a digital system?

No.

What should I look for when monitoring developer temperature?

The key is consistency. Every processing system has its optimum developing temperature.

What is a suitable thermometer and where can I purchase one?

Any good quality digital or analog thermometer can be used to measure developer temp. Do not use a mercury in glass thermometer. Pet shops sell simple thermometers which can display either colors or numbers that indicate the temperature. These can be immersed in the developer solution or attached to the walls of the tank. Electronic shops sell simple indoor/outdoor thermometers that have a remote probe for measuring outdoor temperature. The probe is often very small and is covered with PVC, Teflon or some other material that is immune to developer chemicals. This probe can be immersed in the developer tank and the temperature display attached to a wall near the processor for easy reading. Use your imagination. Just monitor and record the developer temperature in a way that is simple, easy to record and reliable. Optimum image quality depends a great deal on the correct developer temperature.

What are test X-rays?

Test X-rays are X-ray images that should be taken on a regular basis using an aluminum stepwedge or approved phantom and bitewing exposure factors.

What should my stepwedge X-ray look like?

A full range of grey should be visible – one end of the X-ray should be light grey and the opposite end should be almost black. 8 to 10 lines of grey should be clearly visible.

Why do I have to use a stepwedge?

A manufactured aluminum stepwedge tends to produce images of consistent quality. This allows you to evaluate the performance of the X-ray machine and the processing system.

Who must use a stepwedge?

All general dentistry offices.

Where do I buy a stepwedge?

From any major dental supply company.

What are exposure factors?

These are the dial settings on your X-ray machine that determine the quality of the X-ray image. Often denoted as kV, mA and time. kV (the penetrating energy of the X-ray beam), mA (also known as tube current and which determines the quantity of X-rays in the beam) and Exposure Time (which determines the amount of time that the beam is exposing the patient). Older X-ray machines frequently allow all three to be selected over a wide range of values. Newer machines tend to be more restrictive and may allow only one or two kV or mA settings but almost all allow for a full range of exposure time settings. Today, many machines allow the operator to only select exposure time values. kV and mA are fixed and cannot be adjusted. There are some X-ray machines that do not even display exposure time values. Instead, they allow the operator the option of selecting a picture of a desired tooth or range of teeth to be radiographed. In this case, the optimum exposure factors are presumably selected by the machine when the appropriate button is pushed by the operator. In other cases, these pre-select buttons will also allow the operator to see the important exposure factors just for reference purposes. It is not uncommon to have a variety of X-ray machines of all types in a dental office.

What are Technique Charts?

Technique charts are printed charts attached to the wall or printed on the X-ray machine showing what the exposure factors should be for each particular exam. It is essential to have technique charts posted. All X-ray units perform differently, so a chart showing what one particular machine requires to make a good exposure needs to be in plain view at each machine. Not all staff use the same machine all the time and frequently, part time staff will be called in to perform work. Cleaning staff can sometimes bump the settings. All these factors can and do lead to a confusing array of potentially inappropriate selection of exposure factors. The inspection program tests the accuracy of these charts.

How much radiation is emitted from dental X-ray machines?

A typical bite-wing exposure results in an effective radiation of between 0.01 to 0.03 milli Sieverts. Normal background radiation from the earth will yield an effective dose of between 2 to 4 milli Sieverts per year in most of Canada. A bite-wing, therefore, represents about 1 day of normal radiation exposure at the Earth’s surface.

Are lead aprons required in a dental facility?

Yes. In B.C., a minimum of one approved lead apron is required for each dental practice. The patient must be provided with a shielded apron, for gonad protection, and a thyroid shield, especially during occlusal radiographic examinations of the maxilla. The use of a thyroid shield is especially important in children. The shielded apron and thyroid shield should have a lead equivalence of at least 0.25 mm of lead. In panoramic and cone beam radiography, since the radiation is also coming from the back of the patient, a conventional lead apron is not adequate and dual (front and back) lead aprons should be worn.

How should I store lead aprons?

Hang it up on hooks or drape it over a towel bar – do not fold as this will damage the inner lead lining.

How do I get dosimeter badges?

Access BC Center for Disease Control website for a list of suppliers, call 1-800-261-6689 or download a current version (May 2012) of the .pdf here RIN07.

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