Dental X-Rays, 3D CT, orthopantomogram – what’s the difference?

Maksym Makarenko

Максим Макаренко Oral surgeon, prosthodontist, PhD in Medical Science

X-ray → radiation → exposure to diseases - approximately the same sequence builds the imagination of many patients of dental clinics, who are assigned X-ray diagnostics.

In this article we will talk about what types of X-ray diagnostics exist in dentistry, is it worth to be afraid of dental X-rays, is it possible to do tooth X-rays for pregnant women and why you need an X-ray of the jaw of a child with milk teeth.

What does a X-ray show?

Implantation, prosthetics, sinus lifting, treatment root canals of the tooth - all these operations are impossible without X-ray. It is necessary to take a picture of the teeth to assess the condition of the bone tissue, check the filling of the root canals, reveal a caries, which may appear under the filling, crowns or in the interdental spaces.

Also, an X-ray examination shows the condition of the periodontium (tissue around the root of the tooth) and parodontium (tissue around the tooth), cracks or inflammation of the root canals.

With the help of X-rays, the dentist can make a more accurate diagnosis, especially if the patient's complaints and symptoms suggest several diseases.

What are the types of X-ray examinations?

The dentist can prescribe one of three existing types of radiography: intraoral Х-ray, panoramic Х-ray, computed tomography of a segment or the both jaws.

  1. Intraoral (so-called dental) X-ray is used when we need image of a specific tooth or several teeth (from one to four).
  2. If you need to assess the condition of the maxillary sinus, temporomandibular joint, prepare for the tooth removal, prosthetics, a panoramic image of the teeth is prescribed (the so-called orthopantomography).
  3. Computed tomography (3D CT) is indispensable for planning bone grafting, sinus lifting or dental implantation.

So, I propose to talk about each type of X-ray examination in more detail.

Dental intraoral X-ray

Quite a few patients are concerned about the question of whether it is harmful to do an x-ray of the tooth. The dose of X-ray radiation that a person receives during a targeted X-ray of a tooth is 2 microSievert (Sievert is a unit used to indicate the amount of radiation).

Digital technologies have replaced the traditional X-ray with a sensor that converts X-rays into a digital signal. In this case the radio device remains the same, only the receiving device changes. But for a digital sensor a shutter speed is five times shorter than for a film, which means that the radiation dose is reduced proportionally.


You should know that some common foods are naturally radioactive. For example, bananas contain naturally occurring radioactive isotopes, particularly potassium-40, one of several naturally occurring isotopes of potassium.


When we eat one banana we get about 0.1 microSievert (0,1 μSv) radiation. Accordingly, one targeted X-ray image is equal to the radiation dose from 20 bananas eaten. And you can easily find information about the Banana equivalent dose (BED) on Wikipedia.

Оrthopantomography X-ray (OPG)

It is very important to take a panoramic X-ray to determine the position and condition of the lag-tooth. Orthopantomography can give a correct idea of ​​the "eights", a periapical X-ray will not help much here. Therefore, competent dentists decide whether to treat or remove wisdom teeth, only after an X-ray.

Also, it is necessary to make an orthopantomography when planning orthodontic treatment with braces or aligners.

How to do a panoramic dental X-ray?

No preparation is required to take a panoramic dental scan. It is only necessary to remove jewelry: earrings, piercings - so that there are no distortions in the picture and important details are not hidden by so-called "artifacts". You will be placed at the machine, put on a special protective collar and asked to bite the plastic holder, and the X-ray emitter together with the film or digital sensor will rotate around your head for no more than 15 seconds.

An orthopantomography of the jaws made on a digital device is immediately transferred to the doctor's computer. It is much easier to store such a picture: it simply remains in the patient's electronic card and can be viewed at any time.

Is it harmful to do an orthopantomography?

Electronic devices have almost drive out film devices. Their cost is higher but at the same time they do not require a large amount of consumables as for film orthopantomographs. Unlike a panoramic image on film a digital orthopantomography will not be lost, which means that the patient will not have to undergo the radiation that is present during dental x-rays again, albeit in very small doses: only 7 microSievert. By the way the irradiation effect of film devices is several times higher than that of electronic ones.

3D Computed Tomography (3D CT Scan)

If you come to an orthodontist, maxillofacial surgeon or implantologist for a consultation, most likely one of his first appointments will be a computed tomography (CT) scan of the jaws. This is a very accurate diagnostic technique that allows the doctor to view the image of the patient's jaw from any angle and in any projection.

CT in contrast to a panoramic image gives a three-dimensional image of the jaw without distortion and allows you to look into any layer of tissue, making a kind of virtual cut, without the need to carry out unnecessary traumatic procedures to the patient.

How is a 3D scan of teeth taken?
  • A dental CT scanner is a bit like an orthopantomograph. During the procedure the patient stands or in special cases sits.
  • A protective apron with a lead layer is put on the neck.
  • The patient squeezes a special bite block with his teeth, rests his forehead against the fixing support and holds the handles with his hands. This allows him to take the correct position and not move of 14-24 seconds depending on the selected mode and shooting frequency. This is exactly how long it takes for the sensor of the tomograph to make one revolution around the patient's head. During this time the sensor manages to take about 600 images in different projection slices.

 

Processing the data and building a 3D model takes a few minutes plus writing the data to disk. In 10-15 minutes you will have accurate information about the state of your dentition.

Computer scan of teeth: indications

The indications for CT of the jaw are: anomalies in the structure of the jaw, of the temporomandibular joint, the presence of unerupted or not fully erupted teeth, complicated fracture of the jaws, damage to the dentition, preparation for maxillofacial operations.

Also CT is significantly superior to orthopantomography in planning dental implantation, in diagnosing inflammation of ​​the roots of teeth, determining the number of roots and root canals of a tooth, diagnosing cracks of the roots and detecting tumors at an early stage.

When planning a sinus lift or bone grafting you will also need to take a 3D scan of your teeth. If the bone tissue is visible on a panoramic image, CT allows you to make out soft tissues, blood vessels, canals and changes in the mucous membrane. It is believed that a 3D image of teeth is more informative than one panoramic image and a set of periapical X-rays of all teeth together.

Is it harmful to do CT scan of teeth

The radiation exposure of CT fluctuates of 13 - 166 microSievert. The amount of radiation exposure from CT depends on the type of image. It can be a CT scan of a segment of three teeth, a CT scan of one jaw, or two. Less exposure means less radiation.

13 - 166 microSievert is relatively small when you consider that the upper threshold for radiation exposure for research purposes is 2,4 milliSievert per year. But if we compare CT with X-ray of a tooth where the irradiation occurs in the range of 2 microSieverts a 3D image of teeth no longer seems so harmless.

It is acknowledged that the conventionally normal dose of radiation from a flight by plane is 20 microSievert per hour, then we can say that the CT scan of one jaw is equal to a four-hour flight by plane.

Can i take x-rays of a tooth during pregnancy?

You should prepare for pregnancy in advance and a visit to the dentist should be included in the plan of such preparation. However, if it so happened that it is necessary to take an X-ray of the tooth during pregnancy you should be guided by specific indications and listen to the doctor's instructions.

It is not recommended to do a CT scan in the first trimester of pregnancy, but rather abstain from it until the fifth month. A good doctor will always consider the need for radiation exposure of a pregnant patient, based on the ratio of benefits to the mother and risks to the fetus.

Also, you need to ensure that the total radiation dose during pregnancy does not exceed 1 milliSievert. You should to remember that stress from visiting of the doctor and anxiety about the safety of a particular procedure can bring much more harm to pregnant women than the X-ray itself.

Is a tooth X-ray dangerous when breast-feeding?

X-ray radiation does not accumulate in the environment but like light waves, penetrate  objects. It lingering a little longer in a solid medium and a little less in a rare medium. So everyone who is concerned about the question of whether it is possible for a nursing mother to do an X-ray of a tooth "Yes, you can!". Irradiation will not “spoil” the milk. It can only linger in the mammary glands.

In dentistry micro doses of radiation are use tens and hundreds of times less than those recognized as dangerous and causing negative consequences. So, an X-ray of a tooth during breast-feeding if indicated and high-quality devices are available is quite safe.

For your own comfort after the procedure you can skip one feeding - this will be enough.

Why x-ray a child's teeth?

For an correct diagnosis of diseases of the oral cavity in children and adolescents, it is necessary to have as much information as possible. Such information can be provided by an X-ray of the baby's milk teeth. A picture of milk teeth will show whether there is caries between the teeth, perhaps the roots of the teeth, like the located immature of permanent teeth.

The dentist can predict the timing of the loss of milk teeth and identify the presence of impacted, or curved immature teeth.

This early diagnosis helps to recognize the likely curvature of the bite and prevent it. At this stage it is much easier to correct the bite. There is a possibility get out of wearing braces in the future.

Сonclusion

Modern dentistry is impossible without radiography. This diagnostic method allows you to look into those areas in the patient's mouth that were previously inaccessible to the eye.

Well, as far as radiation is concerned modern X-ray procedures are not dangerous. If we consider the admissible doses of radiation, then without much harm to the body approximately 300 periapical X-ray or 100 OPG or 20 CT of the jaws can be taken per year. But this does not mean that you need to do so many of them. And who needs so many pictures? The benefits of X-rays will be greater than harm.

An X-ray of the jaws can and should be done if there are questions about the health of the invisible part of the teeth. It will be able to show inflammation at the roots or the position of the wisdom tooth. But remember that X-rays must be done only according to indications, not in any way for prophylactic purposes. There are no compelling evidence that annual or prophylactic X-rays are needed for everyone.

I hope this information was helpful to you!

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