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|
 X-rays
|
Computer
Digital Radiography (CDR)
What
are Dental X-rays? |
 |
No Cavity on X-ray |
Months later, cavities that start between the teeth
can't be seen by a visual examination, but they can be detected on an
X-ray. |
This cavity was detected and filled before the patient felt any discomfort, and before the nerve became infected or the tooth became abscessed.
There is another cavity shown in the X-ray on the left. Can you find it? It's difficult for the untrained eye to spot. If you think you know where it is, send an e-mail to webmaster@doctorhuff.net and we will tell you if you're right! (Hint: It's not the left edge of the top left tooth. That's just the edge of the frame around the X-ray).
How Often Do I Need Dental X-rays?
The number and type of X-rays you will need depends on several factors such as age, current dental health, and external signs that may trigger a cause for concern. We are sensitive, however, to your concerns about exposure to radiation, and we only perform those X-ray procedures that are necessary for your continued dental health.
The Full Mouth Series (FMX)
This is an example of the full mouth series we take in our office. It consists of 4 bite wing films which are taken at an angle specifically to look for decay, and 14 periapical films which are taken from other angles to show the tips of the roots and the supporting bone. Not all full series look exactly like this one, but they all use some combination of bite wing and periapical x-rays to show a complete survey of the teeth and bones. We take a full mouth series on everyone over the age of 25 at the initial oral examination, and retake it again every 3 to 5 years.
Notice that each tooth is seen in multiple films. This redundancy is important because it gives us lots of information we would not otherwise have. Each x-ray is shot from at least a slightly different angle and the difference in angulation can reveal many different aspects of the tooth in question. X-rays are not ordinary 2 dimensional pictures. They are actually 3 dimensional shadows. As you know, shadows may be longer or shorter than the object which casts them depending on the angle of the light source and the screen upon which they are projected. They may also be distorted in other ways as well. The shadow of your hand may show all 5 fingers spread out if you hold it palm forward facing the light source with the screen directly behind the back of the hand. On the other hand, the fingers will not be visible at all if the hand is turned so that the thumb is facing the light source and the little finger is facing the screen. This happens with x-rays also, except that the objects which cast the shadow appear translucent on the film, and it is actually possible to see several objects superimposed over each other. This is what gives x-rays their 3 dimensional quality, and this is why it is very helpful to have several views, taken from different angles, of any given tooth.
The bitewing series
A bitewing series consists of either 2 or 4 films taken of the back teeth (although some offices take them on front teeth as well), with the patient biting down so the films contain images of both the top and bottom teeth. A bitewing series is the minimum set of x-rays that most offices take to document the internal structure of the teeth and gums. In our office, we take 2 on children under the age of 12, and 4 on everyone older, supplemented by the other periapical films associated with a full series of x rays if the patient is over the age of 25.
The difference between bitewing and periapical films
| In a bitewing film, all three elements, the teeth,
the film, and the x-ray beam are optimized to give the most
undistorted shadows possible. (The film and teeth are parallel,
and the beam is aimed directly at both; at a 90 degree angle.)
Thus bitewing films afford the most accurate representation
of the true shape of the teeth and associated structures such
as decay, fillings, shape of nerves and bone levels. (To see
how the big cavity in the lower tooth was filled, click
here.) |
 |
| A periapical film like the one on the right is shot from an angle in which the three elements are not necessarily aligned parallel. Some distortion is introduced on purpose to be sure that the shadow of the entire tooth or teeth in question falls on the film. This is done because in many instances, the space available in the mouth, or the curvature of the roof of the mouth will not permit parallel placement of the film. This patient had an abscess and was in pain when the film was shot. (To see how this situation is treated, click here.) |  |
The Panoramic Film (Panorex)
As you can see from the image above, the Panorex is a large, single x-ray film that shows the entire bony structure of the teeth and face. It takes a much wider area than any intra oral film showing structures outside of their range including the sinuses, and the Temperomandibular Joints. It shows many pathological structures such as bony tumors and cysts, as well as the position of the wisdom teeth. They are quick and easy to take, and cost a little more than a full series of intraoral films. In addition to medical and dental uses, panoramic films are especially good for forensic (legal) purposes in the identification of otherwise unrecognizable bodies after plane crashes or other mishaps.
| Panoramic films differ from the others in that they are entirely extraoral, which means that the film remains outside of the mouth while the machine shoots the beam through other structures from the outside. It fits into a broad category of medical x-rays called tomographs. A tomograph is a computer assisted method of focusing x-rays on a particular slice of tissue and showing that slice on the film as if there were no other structures outside of that slice. It has a number of real advantages over the intraoral variety of film discussed above. Since it is entirely extraoral, it works quite well for gaggers who could not otherwise tolerate the placement of films inside their mouths. The patient stands in front of the machine (pictured on the right), and the x-ray tube swivels around behind his head. |  |
The
film on the right is a panoramic view of a child under the age of
12. You can see the adult teeth that are forming underneath the
baby teeth. You can also see the adult second molars which are the
4 half formed teeth toward the outside of the film. The fact that
the second molars are not yet erupted is the reason a dentist or
anthropologist can tell that this child is under the age of 12.
These films have one major disadvantage. The panoramic film is a lower resolution picture than the intraoral films. This means that the individual structures which appear on them (such as the teeth and bone) are somewhat fuzzy, and structures like caries (tooth decay) and bony trabeculation (the spongelike bone inside the marrow spaces) are imaged without the fine detail seen on intraoral films. They are not considered sufficient for the diagnosis of decay, and must be accompanied by a set of bitewing x-rays if they are to be used as an aid for full diagnostic purposes. The combination of a set of bitewings and a panoramic film is particularly useful for those patients who are to be referred for orthodontic consult, and for extraction of wisdom teeth. We use the bitewing/panorex combination frequently instead of a full series of intraoral films on patients between the ages of 13 and 30.
Some material on this page reprinted by permission from Martin S. Spiller, DMD
