Table of Contents
- 1 Intraoral Film or Sensor Placement Techniques
- 2 Radiographic Surveys
Intraoral Film or Sensor Placement Techniques
Intraoral x-rays are those taken with the film or sensor inside the mouth. They include periapical, bitewing, and occlusal x-rays. Periapical radiographs are for diagnosis of the teeth, bone, lamina dura, and periodontal ligament. The radiograph must include at least 3 to 4 millimeters beyond the apex of the tooth being x-rayed. Bitewing radiographs are used to diagnose problems of the crowns and interproximal areas. Decay, calculus, overhanging margins, and interproximal bone loss are best detected in bitewing x-rays because the teeth are not overlapped as in some periapical images. Occlusal x-rays are used to diagnose disorders of the jaw or palate.
Panoramic x-rays, particularly when combined with intraoral bitewing films are an excellent screening device. A panoramic radiograph can serve as a primary film in situations in which resolution is not an overriding factor, or if intraoral x-rays are not possible.
The three most common series of radiographs taken in the dental office are Bitewing Surveys, Full Mouth Surveys and panoramic film. The bite wings consist of a premolar view and a molar view for each side of the mouth taken in occlusion (2 or 4 films). The Full Mouth Survey consists of a series of x-rays that properly represent every tooth in the patient’s mouth (with 3 to 4 millimeters of surrounding bone) and all other tooth bearing areas of the mouth even if edentulous (no teeth are present). Usually, bitewing x-rays are taken to examine the contact areas of the premolar and molar regions, and periapicals for the other teeth and edentulous areas.
The bitewing series
A bitewing series consists of either 2 or 4 x-rays taken of the back teeth (although some offices take them on front teeth as well), with the patient biting down so the films or sensor 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. On children under the age of 12, two x-rays, one on either side are sufficient. On any person over age 12 it is advisable to take two on either side in order to account for the increased distal dimension added by second and developing third molars and to adjust for the difference in the mesial/distal angulation between the molars and the premolars. On patients over the age of 25, it is generally a good idea to take a full series of x rays.
This example of a full mouth series consists of 4 bite wing x-rays which are taken at an angle specifically to look for decay, and 14 periapical x-rays 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. It is generally a good idea to have a full series on every patient over the age of 25 who comes to your office for comprehensive treatment. New full series are taken at intervals determined by the need to assess new or ongoing conditions.
Notice that each tooth is seen in multiple x-rays. This redundancy is important because it gives the dentist a lot of information that cannot be learned from clinical examination alone. 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. 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. Different angulations may cause some structures to overlap others in some views causing obscuration of important information while an adjacent view shot from a slightly different angle may convey all the important information.
Start the Full Mouth Series with anterior views because beginning with easy placement will help establish your credibility with the patient. Then he or she is more relaxed as the molar films are placed. The recommended order for taking a Full Mouth Series is:
- Central and lateral Incisors
- Right Cuspid
- Right Bicuspid
- Right Molars
- Left Cuspid
- Left Bicuspid
- Left Molars
- Central and lateral incisors
- Right Cuspid
- Right Bicuspid
- Right Molars
- Left Cuspid
- Left Bicuspid
- Left Molars
- Bite wings
Maxillary Central and Lateral Incisors
Begin the full mouth series with the maxillary central incisor region. Patients usually tolerate this x-ray easily. The film or sensor is inserted into the holder in a vertical orientation. The beam should pass perpendicular to the film plane and the film should be at a 90º angle to the interproximal area of the maxillary central incisors. The film or sensor is placed well into the palatal region, in the area of the second bicuspid. If it is too close to the teeth, the curve of the palate may prevent the most parallel placement of the apparatus.
For the maxillary cuspids, the film or sensor is placed into the holder in a vertical orientation. The cuspid is centered on the film and it is placed well into the palate. The central x-ray beam is perpendicular to the film or sensor and at a right angle to the long axis of the tooth. The mesial contact should be open, but often the distal contact is unavoidably overlapped. The next film will display the distal contact area.
For the maxillary bicuspids, the film or sensor is placed in the holder in a horizontal orientation. The contact between the first and second premolar is centered on the film with the central x-ray beam perpendicular to the film or sensor. The contacts for the distal of the canine through the distal of the second premolar should be open. Sometimes, a cotton roll will need to be placed between the bite block and the mandibular teeth opposing in occlusion. This will stabilize the bite and keep the block from rotating because of the occlusion of the canine.
For the maxillary molars, the film or sensor is placed in the holder in a horizontal orientation. The second molar is centered on the film with the central x-ray beam perpendicular to the film. The contacts of the first, second, and third molars should be open. The third molar region should be included in this x-ray even if the tooth is not present. In practice, it may not always be possible to place the film or sensor parallel to the teeth. It the event that a non parallel technique is necessary, refer to the shadow casting page to learn how to bisect the angle between the tooth and the film.
For the mandibular anteriors, the film or sensor is placed in the holder in a vertical orientation. The mandibular central incisors are centered on the film or sensor with the central x-ray beam perpendicular to it. The contact between the two central incisors should be open. The film or sensor should be placed as far into the patient’s mouth as possible without causing discomfort, usually as far back as the second premolar. The tongue is moved back and must not be between the film or sensor and the teeth or it will show on the radiograph. The lateral incisors should be visible in this x-ray as well. Two smaller films or a smaller sensor may be used if the patient’s mandible is unusually narrow.
For the mandibular cuspids, the film or sensor is placed in the holder in a vertical orientation. The mandibular canine is centered on the film or sensor with the central x-ray beam perpendicular to the film. The mesial contact of the lateral and the distal of the first premolar should be present in this film, with the mesial and distal contact of the canine open. The tongue should be mildly displaced so the film or sensor can be inserted into the floor of the mouth and far enough away from the teeth so that the film doesn’t bend. The canine shot is very rarely accomplished keeping the film or sensor parallel to the tooth because of the shape of the space available. For this reason, it is generally more practical to place the film or sensor at a steep incisal/apical angle and use the angle splitting technique to aim the beam.
Mandibular Premolars and Molars
For mandibular premolars, the film or sensor is placed in the holder in a horizontal orientation. The contact between the second premolar and the first molar is centered on the x-ray. The central beam should be perpendicular with the long axis of the tooth. The x-ray should contain the distal of the canine through the mesial of the second molar, with the contacts of the premolars open. The film or sensor should be placed as far into the patient’s mouth as his or her anatomy will allow. The mandibular premolar x-ray generally includes a complete view of the mandibular first molar as well. The trick to taking the premolar shot is to position the film or sensor as far anterior as the curvature of the mandible will allow.
For the mandibular molars, the film or sensor is placed in the holder with a horizontal orientation. The second molar is centered on the film or sensor with the central beam perpendicular to it. The contacts between the molars should be open and the distal of the third molar region should be visible even if there is no tooth present. Be careful about the placement of film or sensor because the edge can be uncomfortable in the sensitive floor of the mouth. If the patient is instructed to gently close rather than “bite” the film holder will be more secure and more comfortable.
Dealing with the tongue
There are two keys to placing the film or sensor painlessly in mandibular molar and premolar area. The first is to explain to the patient that there really is enough room provided he/she relaxes the tongue. Nervous patients frequently raise the tongue which causes the mylohyoid muscle to contract. The floor of the mouth rises along with the mylohyoid muscle causing pain as the film or sensor is placed. Once the patient relaxes the tongue, the amount of room increases dramatically. The second key to placing the film or sensor painlessly is to angle it to the lingual, medially toward the tongue itself. This places the edge of the apparatus well away from the area where the mylohyoid muscle attaches to the lingual aspect of the mandible. Once the film or sensor is placed to its most inferior position using this technique, it is an easy matter to push the dorsum of the tongue out of the way to bring the film or sensor approximately parallel to the tooth. The mylohyoid muscle slopes inferiorly as it approaches the mid line, and when the inferior border of the film is placed in this position, it is less likely to encounter strong resistance.
Of course, not every patient can be persuaded to relax the tongue, and it is not always possible to extend the inferior border of the film so that it falls below the apices of the teeth. In cases like this, it becomes necessary to place the film or sensor at a steep angle leaving the inferior border of the film angled far lingually to the top of the film or sensor. In these cases, aiming the beam from a low angle will shift the shadow up so that the apex will appear on the x-ray. This is done at the expense of foreshortening the tooth. (See shadow casting tricks.)
Bitewings are designed to visualize interproximal decay and the overall shape of the coronal portions of the teeth with the least possible distortion. Placement of the sensor is more easily accomplished than with periapical films because the sensor rarely impinges on either the palate, or the floor of the mouth, and because the sensor is almost always perfectly parallel with the mesial-distal alignment of the teeth. Tube alignment is fairly easy since it can be aligned with the bitewing tab as it projects between the teeth as shown in the diagram above. This is most easily facilitated by asking the patient to”smile wide”, allowing the operator to see down the buccal corridor, which is defined as the space between the buccal aspects of the teeth and the buccal mucosa. The objective of the alignment is to aim the x-rays parallel with the mesial and distal coronal aspects of the teeth. This eliminates overlap of these surfaces, which would otherwise obscure the interproximal decay.
The Panoramic Film (Panorex)
The panoramic radiograph is a large, single x-ray image that shows the entire bony structure of the teeth and face. It takes in 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 radiographs. In addition to medical and dental uses, panoramic x-rays are especially good for forensic (legal) purposes in the identification of otherwise unrecognizable bodies after plane crashes or other mishaps.
The main disadvantage to the routine use of panoramic oral surveys is the lower resolution of the shadowed structures. Properly exposed intraoral films are always crisp and sharp while panoramic films show slightly fuzzy outlines. They are, therefore, not especially good at diagnosing caries, and for this reason, most first visits that include a panoramic radiograph also include a set of bitewing x-rays as well. In the event of a severe gagger, however, a panoramic film may prove adequate by itself.
Panoramic x-rays differ from the others in that they are entirely extra oral, which means that the film or sensor 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 radiograph as if there were no other structures outside of that slice. It has a number of real advantages over the intraoral variety of x-ray. Since it is entirely extra oral, 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 above), and the x-ray tube swivels around behind his head. Another advantage of the panoramic film is that it takes very little radiation to expose it. The amount of radiation needed to expose a panoramic x-ray film is about the same as the radiation needed to expose two intraoral films (periapical or bitewing). The reason for this is that the film cassette contains an intensifying screen which fluoresces upon exposure to x-rays and exposes the film with visible light as well as x-rays.