Intra 103

The Posterior Exposure Sequence 

• After completing the anterior teeth, begin the posterior teeth.
• Always expose the premolar film before the molar film because: 
  • Premolar film placement is easier for the patient to tolerate than molar film placement. 
  • Premolar exposure is less likely to evoke the gag reflex. 

The Maxillary Premolar Region 

• Insert the film packet horizontally into the posterior bite-block, pushing the film packet all the way into the slot.
• Center the film packet on the second premolar. Position the film in the midpalate area. 
• With the instrument and film in place, instruct the patient to close his or her mouth slowly but firmly. 
• Position the localizing ring and PID, then expose the film.

The Maxillary Premolar Region

The Maxillary Molar Region 

• Insert the film packet horizontally into the posterior bite-block. 
• Center the film packet on the second molar. Position the film in the midpalate area. 
• With the instrument and film in place, instruct the patient to close his or her mouth slowly but firmly. 
• Position the localizing ring and PID, then expose the radiograph. 

The Maxillary Molar Region 

The Mandibular Premolar Region 

• Insert the number 2 film horizontally into the posterior bite-block. 
• Center the film on the contact point between the second premolar and first molar. Position the film as far in the lingual direction as the patient’s anatomy will allow. 
• With the instrument and film in place, instruct the patient to close his or her mouth slowly but firmly. 
• Slide the localizing ring down the indicator rod to the patient’s skin. 
• Position the localizing ring and PID, then expose the film. 

The Mandibular Premolar Region 

The Mandibular Molar Region 

• Insert the number 2 film horizontally into the posterior bite-block. 
• Center the film on the second molar. Position the film as far in the lingual direction as the tongue will allow. This position will be closer to the teeth than that for the premolar and anterior views. 
• With the instrument and film in place, instruct the patient to close his or her mouth slowly but firmly. 
• Position the localizing ring and PID, then expose the film. 

The Mandibular Molar Region 

The Bisecting Tissue

• The bisection of the angle technique is based on a geometric principle of bisecting a triangle (bisecting means dividing into two equal parts).
• The angle formed by the long axis of the teeth and the film is bisected, and the x-ray beam is directed perpendicular to the bisecting line.
• “Perpendicular” means at a right angle to the film.

Left, A diagram of an anterior tooth with the central ray perpendicular to the “imaginary” bisector of the angle between the long axis of the tooth and the film plane. Right, A posterior tooth using the bisecting-angle concept. (From Miles D, et al: Radiographic imaging for dental auxiliaries, ed 3, Philadelphia, 1999, Saunders.)

Things to remember:

Remind the patient not to open his or her mouth during the exposure.

As you move more posterior in the oral cavity, remind the patient to breathe through his or her nose (to avoid gagging).

Mandibular premolar filming – Remind the patient to not open his or her mouth during the exposure and to breathe through the nose.

The Bisecting Technique – Also known as the BAI (bisecting-angle instrument) or short-cone technique. Used as an alternative to the paralleling technique.

Unlike paralleling, in which the film is placed away from the teeth, the bisecting angle places the film directly against the teeth. One disadvantage of this approach is that the images may be distorted.