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Introduction

Radiography involves the use of x-radiation and thus is potentially dangerous if mishandled. For your own sake, and that of the staff, patient, and public, it is essential that you gain adequate knowledge of radiographic techniques and radiation health and safety, prior to performing clinical procedures.

This course is intended to provide current, vital information on film and tube head placement, to serve as a guide to acquire new skills or refine current skills, and allow you to test yourself as you progress through the pages.

When you complete a continuing education course on the Dental ResourceNet, a form will come up that requests your name, address, etc.  If you are a member of the AGD, make sure to fill out the field that asks for your AGD membership number (if you are not an AGD member, leave blank).  When you hit submit, a copy of the 'proof of completion' is e-mailed directly to the AGD and P&G. For your records, make sure to print a copy of the 'proof of completion' certificate.

Overview

Radiography involves the use of x-radiation and thus is potentially dangerous if mishandled. For your own sake, and that of the staff, patient, and public, it is essential that you gain adequate knowledge of radiographic techniques and radiation health and safety, prior to performing clinical procedures.

This course is intended to provide current, vital information on film and tube head placement, to serve as a guide to acquire new skills or refine current skills, and allow you to test yourself as you progress through the pages

Learning Objectives

Upon the completion of this course, the dental professional will be able to:

  • Understand the basic principles and concepts of intraoral procedures.
  • Demonstrate the paralleling technique of intraoral radiology.
  • Explain the bisecting angle technique of intraoral radiology.
  • Identify proper techniques for bitewing radiography.
  • Describe intraoral occlusal techniques.

Course Contents

  • Introduction
  • Intraoral Procedures
  • Paralleling Technique
  • Paralleling Technique Methodology
  • The Bisecting Angle Technique
  • Bisecting Angle Methodology
  • Bitewing Radiography
  • Intraoral Occlusal Radiography
  • Digital Radiology
  • Summary
  • Glossary
  • Course Test
  • About the Authors

Introduction

Radiography involves the use of x-radiation and thus is potentially dangerous if mishandled.  For your own sake, and that of the staff, patient, and public, it is essential that you gain adequate knowledge of radiographic techniques and radiation health and safety, prior to performing clinical procedures. 

This course is intended to provide current, vital information on film and tube head placement, to serve as a guide to acquire new skills or refine current skills, and allow you to test yourself as you progress through the pages.

Intraoral Procedures

Introduction
The intraoral radiograph, when correlated with the case history and clinical examination, is one of the most important diagnostic aids available to the dental practitioner.  When examined under proper conditions, diagnostic-quality intraoral radiographs reveal evidence of disease that cannot otherwise be found. They also play a major role in forensic identification.

Two of the fundamental rules of radiography are that 1) the central beam should pass through the area to be examined, and 2) the x-ray film should be placed in position so as to record the image with the least amount of image distortion. Each of three types of intraoral radiologic examinations commonly used in dental practice—periapical, bitewing (interproximal), and occlusal examinations—depend on the operator’s adherence to these two rules even though specific techniques, processes, and indications differ widely among them.

Another aspect that these three examinations have in common pertains to the film packet.  The film packet has two sides, a tube side and a tongue side.  The tube side may be plain or textured.  When placed intraorally, the tube side always faces the radiation source, the tube head.  The tongue side may be colored and has a flange to open the packet and remove the film.  When placed intraorally, the tongue side always faces the patient’s tongue, except in the case of the mandibular occlusal examination.

Because of patient anatomic variations such as narrow arches, missing teeth, or the presence of tori, and limitations of the patient’s ability to open sufficiently (caused by age or other factors), or maintain the film placement, a clinical examination must precede the taking of films.  After the clinical examination, the operator can determine the number and size of films to expose, the technique modifications necessary, and the type of film retention devices to be employed.

Advancements are continually being made in the development and manufacturing of the actual film packet.  These advancements have helped to decrease radiation exposure.  Whenever possible the 'fastest' film speed should be used.

Periapical Radiographs
The purpose of the intraoral periapical examination is to obtain a view of the entire tooth and its surrounding structures, as in Figure 1.  Two exposure techniques may be employed for periapical radiography: the paralleling technique and the bisecting angle technique.  The paralleling technique is the preferred method.  This technique provides less image distortion and reduces excess radiation to the patient.  The paralleling technique should always be attempted before other techniques.  The bisecting technique can be employed for patients unable to accommodate the positioning of the paralleling technique.  Candidates may include those with low palatal vaults and children.  Disadvantages to the bisecting technique include image distortion and excess radiation due to increased angulations involving the eye and thyroid glands.  Regardless of the technique, however, the rules of radiography referred to earlier must be followed.


Figure 1


Intraoral Procedures

Bitewing Radiographs
Bitewing examinations were introduced by Raper in 1925.  The greatest value of bitewing radiographs is the detection of interproximal caries in the early stages of development, before it is clinically apparent.  The arrows in Figure 2 indicate areas of interproximal caries.  Bitewing projections also reveal the size of the pulp chamber and the relative extent to which proximal caries have penetrated.

Bitewings also provide a useful adjunct to evaluating periodontal conditions, offer a good view of the septal alveolar crest, and, in addition, permit changes in bone height to be accurately assessed by comparison with adjacent teeth.  Bitewings do not show the apices of the teeth and cannot be used to diagnose in this area.


Figure 2

Occlusal Radiographs
Occlusal radiography is a supplementary radiographic examination designed to provide a more extensive view of the maxilla and mandible (Figure 3).


Figure 3

The occlusal radiograph is very useful in determining the buccolingual extension of pathologic conditions, and provides additional information as to the extent and displacement of fractures of the mandible and maxilla.  Occlusals also aid in localizing unerupted teeth, retained roots, foreign bodies, and calculi in the submandibular and sublingual salivary glands and ducts.  It should be noted that when imaging soft tissues exposure time needs to be appropriately reduced.

Dentulous Adult Survey
The number of films needed for a full mouth series varies greatly.  Some practitioners may prefer 10 films, while others may prefer 18, 20 or more exposures.

The selection of film sizes used in a full mouth series also varies.  A full survey can consist of narrow anterior film (size #1); standard adult film (size #2); #2 bitewing film or long bitewing film (size #3), (Figure 4) and may include anterior bitewings.  It is generally recommended to use 20 films --- four bitewings and 16 periapicals.  Eight anterior #1 films will allow for ease of film placement on patients with narrow palates.  However, in some cases six anterior periapicals will cover the area needed. 

By using #3 film only one film is used on both the right and left sides and opening both the premolar and molar contacts on one film is very difficult. (Figure 5)  With the use of #2 films for bitewings, the operator uses a total of four films.  Each film is assigned either premolars or molars. (Figure 6)  Use of the #2 films instead of #3 films for bitewings is not only more comfortable for the patient but is easier for the operator to open the contacts.


Figure 5


Figure 6

Intraoral Procedures

Edentulous Adult Survey
By definition, an edentulous patient is one without the natural dentition, and a partially edentulous patient is one who retains some, but not all of the natural dentition.  Merely because a patient’s clinical exam reveals an edentulous state does not disqualify him or her from diagnostic radiographic examination.  In fact, it is commonly accepted that certain areas of the patient’s jaws may contain tooth roots or impacted teeth.  Residual infection, tumors, cysts, or related pathology may also be found, which, while not visible to the clinician, would hinder the effectiveness and comfort of an appliance such as a denture and could potentially cause life threatening conditions to the patient.  In addition to the hidden pathology mentioned above, edentulous surveys reveal the position of the foramina and the type of bone present.

In the case of the partially edentulous patient, placement of the film holding device may be complicated by its tendency to tip or slip into the voids which would normally be occupied by the crowns of the missing teeth.  This can usually be overcome by placing cotton rolls between the patient’s alveolar ridge and the film holder, thereby supporting the film holding device in position.

A 14 or 16 film intraoral periapical survey will usually examine the tooth bearing region in most edentulous patients (Figure 7).  Bitewings are not needed because there are no interproximal areas to be examined.


Figure 7

The use of film holders allow the paralleling technique to be used with edentulous patients.  The operator may be able to reduce radiation exposure in the edentulous patient by 25% by using the paralleling technique.  The film can be held in biteblocks to which cotton rolls have been taped.  To prevent patient discomfort on biting due to missing teeth and resultant over-closing of the arches, the cotton rolls can be attached to the upper and lower surfaces of the biteblocks.  Opposing arch denture or partial denture appliances can be left in place to make contact with the biteblock.

The radiographic film should be positioned with approximately one-third of the film’s vertical dimension protruding beyond the alveolar ridge; that is, the radiographic image should occupy two-thirds of the film. The horizontal angulation of the central beam is perpendicular to the film in the horizontal plane.  If bisecting, the vertical angulation of the central beam is much increased for an edentulous patient with minimal ridges.  The film placement may be similar to that of an occlusal film, and this flat film placement is the principal cause of dimensional distortion.  To determine vertical angulation it is necessary to estimate the long axis of the ridge instead of the tooth.

Intraoral Procedures

Mixed Dentition Survey
The full mouth survey for pediatric patients may vary, depending on the patient’s age, eruption pattern, behavior, and the size of the child’s mouth. In the six to nine-year-old group, a 12 film survey, using #1 narrow film is recommended, and would include:

  • Maxillary:
    • Central incisors
    • Right and left lateral incisors and canines
    • Right and left primary/permanent molars
  • Mandibular:
    • Central incisors
    • Right and left lateral incisors and canines
    • Right and left primary/permanent molars
  • Bitewings:
    • Right and left primary/permanent molars

An adult-sized periapical film is used in the posterior region if the child’s first permanent molar is fully developed.  The size of the tooth requires the use of a large periapical film to capture the complete image.

Pre-School Child Survey
Since pre-school children have smaller mouths, reduced size pediatric films (film size #0) are used to examine the posterior teeth, and adult films are used for anterior examinations in children who have only primary (deciduous or 'baby') teeth.  For this group, an eight film survey is recommended.

  • Maxillary:
    • Central incisors
    • Right and left primary molars
  • Mandibular:
    • Central incisors
    • Right and left primary molars
  • Bitewings:
    • Right and left primary molars

The paralleling technique should be used whenever possible.  This technique delivers the lowest dose of radiation possible.  The bisecting angle technique is a viable alternative for pediatric radiography because the apices of the permanent molar teeth tend to lie above the palate and below the floor of the mouth in the undeveloped mandible.  These positions prevent the image of the apices of the teeth from being projected into the oral cavity when the x-ray beam is perpendicular to the long axis of the teeth as it is when using the paralleling technique.

Quiz

  1. What should be done before any radiographic examination?
  2. What are the fundamental rules of radiography?
  3. What is the purpose of the intraoral periapical examination?
  4. What are the two primary techniques used in periapical radiography?
  5. What is the primary purpose of bitewing radiographs?
  6. What else can be accurately assessed with bitewings?
  7. List five indications for taking occlusal radiographs.
  8. What sizes of periapical films are commonly used in a dentulous adult survey?
  9. Why should a radiographic examination be performed for a clinically edentulous patient?
  10. How should film be positioned relative to the alveolar ridge?

Answers

  1. A good clinical examination should be carried out before every radiographic examination.
  2. The central beam should pass through the area to be examined and the x-ray film should be placed in position to record the image with the least amount of distortion.
  3. To obtain a view of the entire tooth and surrounding structures.
  4. Paralleling and bisecting angle technique.
  5. The detection of caries in the early stages of development.
  6. The detection of periodontal disease in the early stages.
  7. Detection of pathological lesions; fractures of the mandible and maxilla; foreign bodies; salivary calculi; localizing unerupted teeth.
  8. Number 1, 2 and 3 film.
  9. It is commonly accepted that certain areas in the jaws may contain roots, impacted teeth, residual infections, tumors, cysts, etc.
  10. The film should be placed with approximately one-third of the vertical dimension protruding beyond the alveolar ridge.

Paralleling Technique

Basic Principles
The paralleling technique of intraoral radiography was developed by Gordon M. Fitzgerald, and is so named because the object (tooth), receptor (film packet), and end of the position indicating device (PID) are all kept on parallel planes.  Its basis lies in the principle that image sharpness is primarily affected by focal-film distance (distance from the focal spot within the tube head and the film), object-film distance, motion, and the effective size of the focal spot of the x-ray tube.

Successfully using the paralleling technique depends largely on maintaining certain essential conditions as illustrated in Figure 8.  These are: 1) the film packet should be flat; 2) the film packet must be positioned parallel to the long axis of the teeth; and 3) the central ray of the x-ray beam must be kept perpendicular to the teeth and film.


Figure 8

To achieve parallelism between the film and tooth (i.e., to avoid bending or angling the film) there must be space between the object and film.  However, remember that as the object-to-film distance increases, the image magnification or distortion also increases.  To compensate, manufacturers are recessing the target (focal spot) into the back of the tube head.  Depending on the machine's age, and placement of the focal spot within the tube head, you may encounter long, medium, or short cones/PIDs.  The goal is to have the focal spot at least 12' or 30 cm from the film to reduce image distortion.

The anatomic configuration of the oral cavity determines the distance needed between film and object and varies among individuals.  However, even under difficult conditions, a diagnostic quality radiograph can be obtained provided that the film packet is not more than 20 degrees out of parallel with the tooth, and that the face of the PID/cone is exactly parallel to the film packet to produce a central beam which is perpendicular to the long axis of the tooth and the film packet.

The major advantage of the paralleling technique, when done correctly, is that the image formed on the film will have both linear and dimensional accuracy.  The major disadvantages are the difficulty in placing the film packet and the relative discomfort the patient must endure as a result of the film holding devices used to maintain parallelism.  The latter is particularly acute in patients with small mouths and in children.  In certain circumstances the film and holder may be slightly tipped toward the palate to accommodate oral space and patient comfort.  Too much palatal tipping will throw off all parallel planes.

Paralleling Technique

Beam Angulation
The position of the x-ray tube head is usually adjusted in two directions: vertically and horizontally.  The vertical plane is adjusted by moving the tube head up and down.  The horizontal plane is adjusted by moving the tube head from side to side.  By convention, deflecting the head so that it points downward is described as positive vertical angulation or + vertical.  Correspondingly, an upward deflection is referred to as negative vertical angulation or - vertical (Figure 9).  The degree of vertical angulation is usually described in terms of plus or minus degrees as measured by a dial on the side of the tube head.


Figure 9

When applying the paralleling technique, the vertical angulation is ALWAYS dictated to maintaining the parallel plane. There is no set degree number to follow.  As stated earlier under basic principles, the object (tooth), receptor (film packet), and end of the position indicating device (PID) are all kept on parallel planes.  If the vertical angulation is excessive the image will appear foreshortened.  Insufficient vertical angulation procedures an elongated image.

The beam’s horizontal direction determines the degree of overlap among the tooth images at the interproximal spaces.  If the beam is not perpendicular to the specific interproximal space(s) as it approaches several relatively aligned objects, the objects overlap and the space(s) between them close.  Imagine a flashlight beam approaching a picket fence perpendicularly at a 90-degree angle.  The spaces between the pickets will remain open in the shadow image unless the beam angle varies from perpendicular or 90 degrees.  The degree of overlapping of the image will increase or decrease as the beam angle increases or decreases from the perpendicular.

Film Holding Devices
The paralleling technique requires the use of film holding devices to maintain the relatively precise positioning needed.  A great variety of film holders are commercially available—simple, complex, light, heavy, reusable, disposable, autoclavable, and non-autoclavable.  A few of the more common include XCP (extension cone paralleling) with localizing rings, Snap-a-ray, Precision rectangular paralleling device, Uni-Bite, and Stabe biteblock (Figure 10 and 11).  Having several options available will provide the operator different opportunities for enhanced patient comfort.  It is not uncommon to employ more than one option during the same radiographic survey.


Figure 10


Figure 11

The dental radiographer should be able to assess which holder best conforms to the technical and diagnostic requirements of the job, the needs of the patient, and infection control protocols within the office.

(Table 1: Paralleling - Exposure Guide and Film Placement - Helpful hints when utilizing Stabe or Snap-a-ray film holders)

Paralleling - Exposure Guide and Film Placement
Helpful hints when utilizing Stabe or Snap-a-ray film holders

BITEWINGS

Teeth to include

C.R. Entry Point

Vertical. Angulation

R Molar BWX

#1, 2, 3, 30, 31, 32 & D. of 4 & 29

contact of #2 & #3

+ 10 (down angle of PID)

R Premolar BWX

#4, 5, 28, 29 & D. of 6 and 27

contact of #4 & #5

+ 10 (down)

L Premolar BWX

D. of #11 and 22, and #12, 13, 20, 21

contact of #12 & #13

+ 10 (down)

L Molar BWX

D. of #13 and 20, 14, 15, 16, 17, 18, 19

contact of #14 & 15

+ 10 (down)

*     *     *     *     *

An imaginary plane can be visualized on the face to offer approximate C.R. placement. For Maxillary exposures, imagine the plane to extend between the ala of the nose and the tragus of the ear (a.k.a. the ala-tragus line.) For Mandibular exposures, imagine this plane to extend between the commissure of the mouth and the tragus of the ear (a.k.a. the commissure-tragus line.) Once this plane is established, the following entry points will be a guide for C.R. placement. Approximate vertical angulations are only guides and must be checked for paralleling before exposure as each person’s anatomy is different.

PERIAPICALS

Teeth to include

Approx. C.R. Entry Point

Approx. Vert. Ang.

UR Molars

#1, 2, half of #3

outer canthus of the eye

+20 - +30 (down)

UR Premolars

M. of #3, 4, 5, and half of #6

pupil of the eye

+30 - + 40 (down)

UR Canine

center #6 – c.r. at D. of 6

ala of the nose

+45 - + 55 (down)

Max. Incisors

center #7, 8, 9, 10 (I.U. method)

tip of the nose

+40 - +50 (down)

UL Canine

center #11 – c.r. at D. of 11

ala of the nose

+45 - + 55 (down)

UL Premolars

half of #11, and 12, 13, M. of 14

pupil of the eye

+30 - + 40 (down)

UL Molars

half of #14, and 15, 16

outer canthus of the eye

+20 - +30 (down)

LL Molars

#17, 18, and half of 19

outer canthus of the eye

- 5 – 0 (up angle of PID)

LL Premolars

M. of #19, and 20, 21, and half of 22

pupil of the eye

-10 - -15 (up)

LL Canine

center #22 – c.r. at D. of 22

ala of the nose

-20 - -30 (up)

Mand. Incisors

center #23, 24, 25, 26 (I.U. method)

cup the chin

-15 - -25 (up)

LR Canine

center #27 – c.r. at D. 27

ala of the nose

-20 - -30 (up)

LR Premolars

half of #27, and 28, 29 and M. of #30

pupil of the eye

-10 - -15 (up)

LR Molars

half of #30, and 31, 32

outer canthus of the eye

- 5 – 0 (up)

Care of: Willie Leeuw, CDA, BS - Indiana University Purdue University Fort Wayne , Department of Dental Assisting

Quiz

  1. What is the basic principle of the paralleling technique?
  2. What is the major advantage of the paralleling technique?
  3. What are the major disadvantages?
  4. What must be done to achieve parallelism between the tooth and film?
  5. List several devices available to position the film properly when using the paralleling technique.

Answers

  1. The film packet must be positioned parallel to the long axis of the teeth and the x-ray beam must be kept perpendicular to the teeth and film.
  2. Linear and dimensional accuracy.
  3. Difficulty in placement of the film packet, relative discomfort to the patient caused by film holding devices.
  4. The film must be placed away from the tooth.
  5. XCP with localizing rings, Snap-a-ray, Precision rectangular devices, Uni-Bite, and Stabe biteblock.

Paralleling Technique Methodology

When taking a full mouth survey, a definite order of exposure should be preplanned and then followed.  Since patients tolerate anterior films better, they should be done first.  Starting with the maxillary central incisors and proceeding distally, first along one side, then the other, is recommended.  The radiographic parameters or exposure factors should also be determined prior to placing films in the patient’s mouth. 

Patient Positioning
When positioning a patient, there are two imaginary planes that must be considered.  The occlusal plane runs horizontally, dividing the patient’s head into upper and lower portions.  It can be visualized by imagining the patient holding a ruler between his or her teeth.  A midsagittal plane divides a mass (the patient’s head or body) on a vertical dimension into equal right and left portions.

When using the paralleling technique to examine the maxillary region, the patient is positioned so that the occlusal plane of the maxilla is parallel to the floor and the sagittal plane of the patient’s head is perpendicular to the floor.

When paralleling the mandibular region, the patient’s position must be modified slightly so that when the mouth is open, the mandible is parallel to the floor and the sagittal plane is perpendicular.  This could mean that the patient must be tilted back in the chair.

Before any radiographs are exposed, the patient must be protected with a lead apron and thyroid collar. The apron must be properly placed to avoid interference with the radiographic exposure.  (Figure 12)

Figure 12

Paralleling Technique Methodology

Full Mouth Exposure with the Use of XCP Device

Procedure for the Maxillary Central/Lateral Incisors

  1. Assemble the anterior film holder and insert the film packet vertically on the anterior biteblock. Use a #1 film.
  2. Center the film on the central/lateral incisors (Figure 13).  Position the film in the palate as posteriorly as possible so that the entire tooth length will appear on the film, with approximately a one-eighth inch border of the film extending below the incisal edge of the centrals.  Position the biteblock on the incisal edges of the teeth to be radiographed (Figure 14).  Proper positioning in this step will place the central ray of the x-ray beam at the interproximal contact desired.

Figure 13

Figure 14

 

 

  1. A cotton roll may be inserted between the mandibular teeth and the biteblock for patient comfort.  Ask the patient to slowly, but firmly, bite onto the block to maintain film position.
  2. Slide the aiming ring down the indicator rod to the skin surface, align the x-ray tube close to the aiming ring, and center (Figure 15).  
  3. Follow the film and equipment manufacturer’s recommendation concerning exposure factors.  Make the exposure.

 

Figure 15

Paralleling Technique Methodology

Full Mouth Exposure with the Use of XCP Device

Procedure for the Maxillary Canines

  1. Assemble the anterior film holder and insert the film packet vertically on the anterior biteblock.  Use a #1 film.
  2. Center the film on the canine and first premolar (Figure 16).  Position the film in the palate as posteriorly as possible so that the entire tooth length will appear on the film with approximately a one-eighth inch border below the incisal edge of the canine.  Position the biteblock on the incisal edges of the teeth to be radiographed (Figure 17).  Proper positioning in this step will place the central ray of the x-ray beam at the interproximal contact desired.

Figure 16

Figure 17

  1. A cotton roll may be inserted between the mandibular teeth and the biteblock for patient comfort. Ask the patient to slowly, but firmly, bite onto the block to maintain film position.
  2. Slide the aiming ring down the indicator rod to the skin surface, align the x-ray tube close to the aiming ring, and center (Figure 18).
  3. Follow the film and equipment manufacturer’s recommendation concerning exposure factors. Make the exposure.


Figure 18

Procedure for the Maxillary Premolars

  1. Assemble the posterior film holder and insert the film packet horizontally in the posterior biteblock.  Use a #2 film.
  2. Center the film on the premolars so that it is parallel to the long axis of the teeth (Figure 19).  Position the film in the palate so that the entire tooth length will appear on the film with approximately a one-eighth inch border below the cuspal ridge.  Align the anterior edge of the film packet with the canine so that the image captured on the anterior border of the film will include the distal third of the canine.  Position the biteblock on the occlusal surfaces of the teeth to be radiographed (Figure 20).  Proper positioning in this step will place the central ray of the x-ray beam at the interproximal contact desired.

Figure 19

Figure 20

  1. A cotton roll may be inserted between the mandibular teeth and the biteblock for patient comfort.  Ask the patient to slowly, but firmly, bite onto the block to maintain film position.  (The occlusal border of the film tends to slip lingually.)
  2. Slide the aiming ring down the indicator rod to the skin surface, align the x-ray tube close to the aiming ring, and center (Figure 21).
  3. Follow the film and equipment manufacturer’s recommendation concerning exposure factors.  Make the exposure.


Figure 21


Paralleling Technique Methodology

Full Mouth Exposure with the Use of XCP Device

Procedure for the Maxillary Molar Region

  1. Assemble the posterior film holder and insert the film packet horizontally in the posterior biteblock.  Use a #2 film.
  2. Center the film on the molars so that it is parallel to the long axis of the teeth (Figure 22).  Position the film in the palate so that the entire tooth length will appear on the film with approximately a one-eighth inch border below the cuspal ridge.  Align the anterior border of the film packet with the second premolar so that the image captured on the anterior edge of the film will be the distal third of the second premolar.  Position the biteblock on the occlusal surfaces of the teeth to be radiographed (Figure 23).  Proper positioning in this step will place the central ray of the x-ray beam at the interproximal contact desired.

Figure 22

Figure 23

  1. A cotton roll may be inserted between the mandibular teeth and the biteblock for patient comfort. Ask the patient to slowly, but firmly, bite onto the block to maintain film position.
  2. Slide the aiming ring down the indicator rod to the skin surface, align the x-ray tube close to the aiming ring, and center (Figure 24).
  3. Follow the film and equipment manufacturer’s recommendation concerning exposure factors.  Make the exposure.


Figure 24

Procedure for the Mandibular Central/Lateral Incisors

  1. Assemble the anterior film holder and insert the film packet vertically on the anterior biteblock.  Use a #1 film.
  2. Center the film on the mandibular central and lateral incisors (Figure 25).  It may be necessary to displace the tongue distally and depress the film onto the floor of the mouth so that the entire tooth length will show with approximately a one-eighth inch border above the incisal edges.  The film must be as posterior as the anatomy allows and the biteblock should be positioned on the edges of the incisors to be radiographed (Figure 26).  Proper positioning in this step will place the central ray of the x-ray beam at the interproximal contact desired.

 

 

Figure 25

Figure 26

  1. A cotton roll may be inserted between the maxillary teeth and the biteblock for patient comfort.  Ask the patient to slowly, but firmly, bite onto the block to maintain film position.  The film should be straightened as the patient closes and the floor of the mouth relaxes.
  2. Slide the aiming ring down the indicator rod to the skin surface, align the x-ray tube close to the aiming ring, and center (Figure 27).
  3. Follow the film and equipment manufacturer’s recommendation concerning exposure factors.  Make the exposure.


Figure 27

Paralleling Technique Methodology

Full Mouth Exposure with the Use of XCP Device

Procedure for the Mandibular Canines

  1. Assemble the anterior film holder and insert the film packet vertically on the anterior biteblock.  Use a #1 film.
  2. Center the film on the mandibular canine (Figure 28).  It may be necessary to displace the tongue distally and depress the film onto the floor of the mouth so that the entire tooth length will show with approximately a one-eighth inch border above the cuspal edge.  The film must be as posterior as the anatomy allows and the biteblock should be positioned on the edges of the teeth to be radiographed (Figure 29).  Proper positioning in this step will place the central ray of the x-ray beam at the interproximal contact desired.

Figure 28

Figure 29

  1. A cotton roll may be inserted between the maxillary teeth and the biteblock for patient comfort.  Ask the patient to slowly, but firmly, bite onto the block to maintain film position.  The film should be straightened as the patient closes and the floor of the mouth relaxes.
  2. Slide the aiming ring down the indicator rod to the skin surface, align the x-ray tube close to the aiming ring, and center (Figure 30).
  3. Follow the film and equipment manufacturer’s recommendation concerning exposure factors.  Make the exposure.


Figure 30

Procedure for the Mandibular Premolars

  1. Assemble the posterior film holder and insert the film packet horizontally on the posterior biteblock.  Use a #2 film.
  2. Center the film on the premolars so that it is parallel to the long axis of the teeth (Figure 31).  The object-to-film distance in both the mandibular premolar and molar regions is minimal since the oral anatomy only allows the film to be positioned very close to the teeth and still remain parallel.  Align the anterior border of the film packet with the canine so that the image captured on the anterior edge of the film will be the distal third of the canine.  Position the biteblock on the occlusal surfaces of the teeth to be radiographed (Figure 32).  Proper positioning in this step will place the central ray of the x-ray beam at the interproximal contact desired.

Figure 31

Figure 32

  1. A cotton roll may be inserted between the maxillary teeth and the biteblock for patient comfort. Ask the patient to slowly, but firmly, bite onto the block to maintain film position. The film should be straightened as the patient closes and the floor of the mouth relaxes.
  2. Slide the aiming ring down the indicator rod to the skin surface, align the x-ray tube close to the aiming ring, and center (Figure 33).
  3. Follow the film and equipment manufacturer’s recommendation concerning exposure factors.  Make the exposure.


Figure 33


Paralleling Technique Methodology

Full Mouth Exposure with the Use of XCP Device

Procedure for the Mandibular Molars

  1. Assemble the posterior film holder and insert the film packet horizontally on the posterior biteblock.  Use a #2 film.
  2. Center the film on the molars so that it is parallel to the long axis of the teeth (Figure 34).  Depress the film onto the floor of the mouth so the entire length of the teeth will appear with approximately a one-eighth inch border above the occlusal surface.  Place the film horizontally and position it lingually to the molars so that the long axis of the film is parallel to the long axis of the tooth.  Align the anterior border of the film packet with the second premolar so that the image captured on the anterior edge of the film will be the distal third of the second premolar.  Position the biteblock on the occlusal surfaces of the mandibular teeth (Figure 35).  Proper positioning in this step will place the central ray of the x-ray beam at the interproximal contact desired.

Figure 34

Figure 35

  1. A cotton roll may be inserted between the maxillary teeth and the biteblock for patient comfort.  Ask the patient to slowly, but firmly, bite onto the block to maintain film position.  The film should be straightened as the patient closes and the floor of the mouth relaxes.
  2. Slide the aiming ring down the indicator rod to the skin surface, align the x-ray tube close to the aiming ring, and center (Figure 36).
  3. Follow the film and equipment manufacturer’s recommendation concerning exposure factors. Make the exposure.


Figure 36

Quiz

  1. What is the recommended patient positioning for examining the maxillary region using the paralleling technique?
  2. What is the recommended patient positioning for examining the mandibular region using the paralleling technique?

Answers

  1. The occlusal plane of the maxilla is parallel to the floor and the sagittal plane of the patient’s head is perpendicular to the floor.
  2. When the mouth is open, the mandibular occlusal plane is parallel to the floor and the sagittal plane of the patient’s head is perpendicular to the floor.

The Bisecting Angle Technique

Basic Principles
The bisecting-the-angle or bisecting angle technique is based on the principle of aiming the central ray of the x-ray beam at right angles to an imaginary line which bisects the angle formed by the longitudinal axis of the tooth and the plane of the film packet.  While it is not necessary to go into a long dissertation on plane geometry to understand this concept, a quick review will help make the technique more clear.  To bisect is to divide a line or angle into two equal portions.  A bisector is a plane or line that divides a line or angle into two equal portions.  Figure 37 shows an equilateral triangle, with legs AB=BC=CA, and the angles ABC=60 degrees, CAB=60 degrees and BCA=60 degrees.


Figure 37

We see in Figure 37 the following:

  1. The dotted line BD bisects the triangle, dividing it exactly in half.  Thus, two equal triangles are formed from the original. Legs AB and BC were unchanged and thus are still equal.
  2. The original line CA was divided in half by D, and thus the lines AD and CD are equal.
  3. We know that the angle at point B was 60 degrees, and since it was bisected (divided equally), it now is 30 degrees at the intersections of AD and BD.
  4. We also know that bisecting the angle did not affect the angle at the old point A which was 60 degrees, and still is.
  5. The angle at the bisecting point DC must be 90 degrees because the sum of all the angles in any triangle is 180 degrees, and thus 180-(60+30)=90.
  6. Cyzynski’s Rule of Isometry states that two triangles are equal when they share one complete side, and have two equal angles.  We can see that triangles ADB and BDC share the common side BD.
  7. We know further that the angles ADB and BDC are equal because D was defined as a bisector of the old angle ABC.
  8. Lastly, we know that the angles CAB and BCA were unchanged by bisecting and are still equal.  Therefore, under Cyzynski’s Theorem, we can prove the triangles ABD and CBD are equal.

In dental radiography, the theorem is applied in the following manner.  The film is positioned resting on the palate or on the floor of the mouth as close to the lingual tooth surfaces as possible.  The plane of the film and the long (vertical) axis of the teeth to be radiographed form an angle with the apex at the point where the film packet contacts the teeth.  The apex in Figure 38 is located at the point labeled B.

In Figure 38, the long axis through the tooth forms one leg of a triangle (AB), the plane of the film packet another leg, (BC), both of which intersect at the apex, point B.  A line representing the central x-ray beam will form the third leg of the triangle, AC.  If an imaginary line bisected this axis-packet-ray triangle, the bisector, DB, would form the common side of two equal triangles as defined by Cyzynski’s Theorem.


Figure 38

Since the sides formed by the tooth’s long axis and the film packet are equal, the image cast onto the radiographic film would be the same length as the tooth or teeth casting that image.  This linear equality is the basis for diagnostic quality bisecting angle radiographs.


The Bisecting Angle Technique

Anatomical Considerations
The bisecting angle technique is of value when the paralleling technique cannot be utilized.  This may include patients with small mouths and those with low palatal vaults.  Because of the increased exposure to radiation in this technique, it should only be employed as necessary.

Beam Angulation
The bisecting technique calls for varying beam angulations, depending on the region to be examined.

Horizontal angulation:  The horizontal angulation of the tube head should be adjusted for each projection to position the central ray through the contacts in the region to be examined.  This angulation will usually be at right angles to the buccal surfaces of the teeth to be radiographed.

Vertical angulation:  In practice, the operator should position the central ray of the x-ray beam so that it is perpendicular to the imaginary line bisecting the angle formed between the tooth long axis and the film.  This principle works well with flat, two-dimensional structures, but teeth that have depth or are multirooted will produce distorted images.  If the vertical angulation is excessive the image will appear foreshortened.  Insufficient vertical angulation produces an elongated image.

The optimum angle will vary from patient to patient, but the chart below serves as a general guideline for beam angulation.

Projection

Maxilla

Mandible

Incisors

+40 degrees

-15 degrees

Canine

+45 degrees

-20 degrees

Premolar

+30 degrees

-10 degrees

Molar

+20 degrees

2-5 degrees

Film Holding Devices
Supporting the film pack with the patient’s forefinger is not recommended.  This method has several drawbacks.  In addition to exposing the patient’s digit to additional radiation, the patient may exert excessive force, thus bending the film and distorting the radiograph.  The film may slip without the operator’s knowledge, and produce a radiograph outside the proper image field.  Therefore, intraoral support is best accomplished using instruments that restrain the film and help align the beam properly.

Quiz

  1. On what principle is the bisecting angle technique based?
  2. How did this principle originate?

Answers

  1. The bisecting angle technique is based on the principle of aiming the central ray of the x-ray beam at right angles to an imaginary plane bisecting the angle formed by the longitudinal axis of the tooth and the plane of the film packet.
  2. The principle originated from Cyzynski’s Rule of Isometry (Cyzynski’s Theorem) which states that two triangles are equal when they share one complete side and have two equal angles.

Bisecting Angle Methodology

Patient Positioning
Maxillary region:  For bisecting angle radiographs of the maxilla, the patient should be positioned so that the maxillary occlusal plane is parallel to the floor and the sagittal plane of the patient’s head is perpendicular to the floor.

Mandibular region:  For bisecting angle radiographs of the mandible, the patient should be positioned so that the mandibular occlusal plane is parallel to the floor and the sagittal plane of the patient’s head is perpendicular to the floor.

Before any radiographs are exposed, the patient must be protected with a lead apron and thyroid collar.  The apron must be properly placed to avoid interference with the radiographic exposure.

Full Mouth Exposure

Procedure for the Maxillary Central/Lateral Incisors

  1. Assemble the anterior film holder and insert the film packet vertically on the biteblock.  Use a #1 film.
  2. Center the film on the central/lateral incisors as close as possible to the lingual surfaces of the teeth with approximately a one-eighth inch border of the film extending below the incisal edge of the centrals (Figure 39).  Position the biteblock on the incisal edges of the teeth to be radiographed (Figure 40).

Figure 39

Figure 40

  1. A cotton roll may be inserted between the mandibular teeth and the biteblock for patient comfort.  Ask the patient to slowly, but firmly, bite onto the block to maintain film position.
  2. Align the central ray perpendicular to the bisector vertically and at the desired interproximal contact to be viewed.  Horizontally, the central ray should bisect the central/lateral (Figure 41).  For maxillary exposures the tube head will be pointed down for positive (+) angulation.
  3. Follow the film and equipment manufacturer’s recommendation concerning exposure factors.  Make the exposure.


Figure 41

Bisecting Angle Methodology

Full Mouth Exposure

Procedure for the Maxillary Canines

  1. Assemble the anterior film holder and insert the film packet vertically on the biteblock.  Use a #1 film.
  2. Center the film on the canine as close as possible to the lingual surfaces of the teeth with approximately a one-eighth inch border of the film extending below the incisal edge of the centrals (Figure 42).  Position the biteblock on the incisal edges of the teeth to be radiographed (Figure 43).

Figure 42

Figure 43

  1. A cotton roll may be inserted between the mandibular teeth and the biteblock for patient comfort.  Ask the patient to slowly, but firmly, bite onto the block to maintain film position.
  2. Align the central ray perpendicular to the bisector vertically and at the desired interproximal contact to be viewed.  Horizontally, the central ray should bisect the canine (Figure 44).  For maxillary exposures the tube head will be pointed down for positive (+) angulation.
  3. Follow the film and equipment manufacturer’s recommendation concerning exposure factors.  Make the exposure.


Figure 44

Procedure for the Maxillary Premolars

  1. Assemble the posterior film holder and insert the film packet horizontally on the biteblock.  Use a #2 film.
  2. Center the film on the premolars as close as possible to the lingual surfaces of the teeth (Figure 45).  Position the film in the palate so that the entire tooth length will appear on the film with approximately a one-eighth inch border below the cuspal ridge.  Align the anterior border of the film packet with the canine so that the image captured on the anterior edge of the film will be the distal third of the canine.  Position the biteblock on the occlusal surface of the teeth being radiographed (Figure 46).

Figure 45

Figure 46

  1. A cotton roll may be inserted between the mandibular teeth and the biteblock for patient comfort. Ask the patient to slowly, but firmly, bite onto the block to maintain film position.  (Watch the occlusal border of the film packet; it tends to slip down anteriorly.)
  2. Align the central ray perpendicular to the bisector vertically and at the desired interproximal contact to be viewed. Horizontally, the central ray should pass between the contact of the first and second premolar (Figure 47).  For maxillary exposures the tube head will be pointed down for positive (+) angulation.
  3. Follow the film and equipment manufacturer’s recommendation concerning exposure factors.  Make the exposure.


Figure 47


Bisecting Angle Methodology

Full Mouth Exposure

Procedure for the Maxillary Molars

  1. Assemble the posterior film holder and insert the film packet horizontally on the biteblock.  Use a #2 film.
  2. Center the film on the molars as close as possible to the lingual surfaces of the teeth (Figure 48).  Position the film in the palate so that the entire tooth length will appear on the film with approximately a one-eighth inch border below the cuspal ridge.  Align the anterior border of the film packet with the second premolar so that the image captured on the anterior edge of the film is the distal third of the second premolar.  Position the biteblock on the occlusal surface of the teeth being radiographed (Figure 49).

Figure 48

Figure 49

  1. A cotton roll may be inserted between the mandibular teeth and the biteblock for patient comfort. Ask the patient to slowly, but firmly, bite onto the block to maintain film position.
  2. Align the central ray perpendicular to the bisector vertically and at the desired interproximal contact to be viewed. Horizontally, the central ray should pass between the contact of the first and second molar (Figure 50).  For maxillary exposures the tube head will be pointed down for positive (+) angulation.
  3. Follow the film and equipment manufacturer’s recommendation concerning exposure factors.  Make the exposure.


Figure 50

Procedure for the Mandibular Central/Lateral Incisors

  1. Assemble the anterior film holder and insert the film packet vertically on the biteblock.  Use a #1 film.
  2. Center the film on the central/lateral incisors as close as possible to the lingual surfaces of the teeth with approximately a one-eighth inch border of the film extending above the incisal edge of the centrals.  Position the biteblock on the incisal edges of the teeth to be radiographed (Figure 51).


Figure 51

  1. A cotton roll may be inserted between the maxillary incisors and the biteblock for patient comfort.  Ask the patient to slowly, but firmly, bite onto the block to maintain film position.  The film should be straightened as the patient closes and the floor of the mouth relaxes.
  2. Align the central ray perpendicular to the bisector vertically and at the desired interproximal contact to be viewed.  Horizontally, the central ray should pass between the central/lateral incisors (Figure 52).  For mandibular exposures the tube head will be pointed up for negative (-) angulation.
  3. Follow the film and equipment manufacturer’s recommendation concerning exposure factors.  Make the exposure.


Figure 52

Bisecting Angle Methodology

Full Mouth Exposure

Procedure for the Mandibular Canines

  1. Assemble the anterior film holder and insert the film packet vertically on the biteblock. Use a #1 film.
  2. Center the film on the canine as close as possible to the lingual surfaces of the teeth with approximately a one-eighth inch border of the film extending above the incisal edge of the canine. Position the biteblock on the incisal edges of the teeth to be radiographed (Figure 53).


Figure 53

  1. A cotton roll may be inserted between the maxillary teeth and the biteblock for patient comfort. Ask the patient to slowly, but firmly, bite onto the block to maintain film position. The film should be straightened as the patient closes and the floor of the mouth relaxes.
  2. Align the central ray perpendicular to the bisector vertically and at the desired interproximal contact to be viewed. Horizontally, the central ray should bisect the canine (Figure 54). For mandibular exposures the tube head will be pointed up for negative (-) angulation.
  3. Follow the film and equipment manufacturer’s recommendation concerning exposure factors. Make the exposure.


Figure 54

Procedure for the Mandibular Premolars

  1. Assemble the posterior film holder and insert the film packet horizontally on the biteblock. Use a #2 film.
  2. Center the film on the premolars as close as possible to the lingual surfaces of the teeth. Align the anterior border of the film packet with the canine so that the image captured on the anterior edge of the film will be the distal third of the canine. Position the biteblock on the occlusal surface of the teeth to be radiographed (Figure 55).


Figure 55

  1. A cotton roll may be inserted between the maxillary premolars and the biteblock for patient comfort. Ask the patient to slowly, but firmly, bite onto the block to maintain film position. The film should be straightened as the patient closes and the floor of the mouth relaxes.
  2. Align the central ray perpendicular to the bisector vertically and at the desired interproximal contact to be viewed. Horizontally, the central ray should pass between the first and second premolars (Figure 56). For mandibular exposures the tube head will be pointed up for negative (-) angulation.
  3. Follow the film and equipment manufacturer’s recommendation concerning exposure factors. Make the exposure.


Figure 56

Bisecting Angle Methodology

Full Mouth Exposure

Procedure for the Mandibular Molars

  1. Assemble the posterior film holder and insert the film packet horizontally on the biteblock.  Use a #2 film.
  2. Center the film on the molars as close as possible to the lingual surfaces of the teeth.  Align the anterior border of the film packet with the second premolar so that the image captured on the anterior edge of the film will be the distal third of the second premolar.  Position the biteblock on the occlusal surface of the teeth to be radiographed (Figure 57).


Figure 57

  1. A cotton roll may be inserted between the maxillary molars and the biteblock for patient comfort.  Ask the patient to slowly, but firmly, bite onto the block to maintain film position.  The film should be straightened as the patient closes and the floor of the mouth relaxes.
  2. Align the central ray perpendicular to the bisector vertically and at the desired interproximal contact to be viewed.  Horizontally, the central ray should pass between the contact of the first and second molar (Figure 58). For mandibular exposures the tube head will be pointed up for negative (-) angulation. 
  3. Follow the film and equipment manufacturer’s recommendation concerning exposure factors.  Make the exposure.


Figure 58


Bitewing Radiography

Bitewing radiographs are of particular value in detecting interproximal caries in the early stages of development, before it is clinically apparent.  For this reason it is critical that horizontal angulation be accurately projected following the direction of the interproximal contacts and no overlapping contacts be present on the film.  Bitewing films are also useful in evaluation of the alveolar crests for detection of early periodontal disease.

Basic Principles
Bitewing radiographs are parallel films because the film is positioned parallel to the long axis of the teeth and the beam is perpendicular to the film as in Figure 59.  A bitewing tab is utilized to stabilize the film as the patient bites together (Figure 60).

Figure 59

Figure 60

Beam Angulation and Film Holding Devices
Bitewing radiographs are usually exposed with an indicated vertical angulation of +10 degrees (tube head points down for positive (+) angulation). This, angulation provides an acceptable compromise for the differences between the long axis inclinations of the maxillary and mandibular teeth.  Horizontal angulation is aligned with the direction of the contact, and the central ray is directed between the contact of the teeth to be radiographed.  Horizontal angulation is achieved when the central ray of the x-ray beam is directed specifically between the contacts of the teeth to be radiographed.

The interproximal examination may be done using special #3 bitewing film but is preferably achieved by using #2 films fitted with a tab.  There are also film holding devices available that support the film as well as provide an external reference for positioning the tube head.  The patient stabilizes the film by gently biting together on the manufactured tab or on the instrument.

Tube head position is illustrated in Figure 61, and a sample set of bitewing radiographs is illustrated in Figure 62.

Before any radiographs are exposed, the patient must be protected with a lead apron and thyroid collar. The apron must be properly placed to avoid interference with the radiographic exposure.

Figure 61


 

Figure 62


Quiz

  1. What is the main purpose for taking bitewing radiographs?
  2. Why are bitewings exposed with a vertical angulation of +10 degrees?

Answers

  1. To detect interproximal caries.
  2. To compromise for the differences in the long axis angulations of the maxillary and mandibular teeth.

Intraoral Occlusal Radiography

Maxillary Topographical Occlusal
This projection (Figure 63) shows the palate (roof of the mouth), zygomatic process of the maxilla (a projection from the maxilla), antero-inferior aspects of each antrum (in this case, the maxillary sinuses), nasolacrimal canals (tear ducts), teeth from the left second molars to the central incisors, and the nasal septum (cartilage dividing the nose).


Figure 63

Uses:  To view the maxilla for anterior alveolar fractures, cysts, supernumerary teeth and impacted canines, and to view pathology at the apices of the incisors.  It is not used to diagnose peridontal conditions.

Patient positioning:  The patient is seated with the sagittal plane perpendicular to the floor and the occlusal plane parallel to the floor.  Before any radiographs are exposed, the patient must be protected with a lead apron and thyroid collar.  The apron must be properly placed to avoid interference with the radiographic exposure.

Film placement:  With the tube side of the film (size #4) toward the maxilla, the film is placed crosswise in the mouth, like a sandwich.  It is gently pushed backwards until it contacts the anterior border of the mandibular ramus.  The patient bites down gently to maintain position.

Exposure factors:  Follow the recommendations of the film and equipment manufacturer. 

Direction of the central ray:  The central ray is directed at the center of the film with a vertical angulation of +65 degrees and a horizontal angulation of 0 degrees.  In this case, the central ray will pass through the bridge of the nose, as in Figure 64.


Figure 64

Mandibular Topographical Occlusal
Uses:  To view the anterior portion of the mandible for fractures, cysts, root tip and periapical pathology.  It provides a very good view of the symphysis region of the mandible. (Figure 65)


Figure 65

Patient positioning:  The patient is seated with the head tilting slightly backward, so that the occlusal plane (ala-tragus line) is 45 degrees above the horizontal plane.  Before any radiographs are exposed, the patient must be protected with a lead apron and thyroid collar.  The apron must be properly placed to avoid interference with the radiographic exposure.

Film placement:  With the tube side of the film (size #4) toward the mandible, the film is placed crosswise in the mouth, like a sandwich.  It is gently pushed backwards until it contacts the anterior border of the mandibular ramus.  The patient bites down gently to maintain position.

Exposure factors:  Follow the recommendations of the film and equipment manufacturer.

Direction of the central ray:  The central ray is directed between the apices of the mandibular central incisors and the tube is angled at -55 degrees relative to the film plane, as in Figure 66.


Figure 66

 

Intraoral Occlusal Radiography

Maxillary Vertex Occlusal
Uses:  To view the buccopalatal relationships of unerupted teeth in the dental arch. (Figure 67)


Figure 67

Patient positioning:  The patient is seated with the sagittal plane perpendicular to the floor and the occlusal plane parallel to the floor.  Before any radiographs are exposed, the patient must be protected with a lead apron and thyroid collar.  The apron must be properly placed to avoid interference with the radiographic exposure.

Film placement:  The film (size #4) is placed in the same manner as the Maxillary Topographical Occlusal.

Exposure factors:  Follow the recommendations of the film and equipment manufacturer.

Direction of the central ray:  The central ray is directed through the top of the skull (hence the name vertex occlusal). Since the beam must penetrate a considerable amount of bone and soft tissue, the exposure time must be increased.  The central ray is perpendicular to the film plane and is directed to the center of the film as in Figure 68.


Figure 68

Mandibular Cross-Sectional Occlusal
Uses:  To view the entire mandible for fractures, foreign bodies, root tips, salivary calculi, tori, etc. (Figure 69)


Figure 69

Patient positioning:  The patient’s head may be in any comfortable position that allows the central ray to be directed perpendicular to the plane of the film packet.  Before any radiographs are exposed, the patient must be protected with a lead apron and thyroid collar.  The apron must be properly placed to avoid interference with the radiographic exposure.

Film placement:  The film (size #4) is placed in the same manner as the Mandibular Topographical Occlusal.

Exposure factors:  Follow the recommendations of the film and equipment manufacturer.

Direction of the central ray:  The central ray is perpendicular to the film plane and is directed to the center of the film as in Figure 70.


Figure 70


Intraoral Occlusal Radiography

Posterior Oblique Maxillary Occlusal
Uses:  To view the maxillary posterior region and provide a topographical view of the maxillary sinus.  The projection may be used in place of periapical films in patients who have a tendency to gag and for examining periapical pathology and root tips. (Figure 71)


Figure 71

Patient positioning:  The patient is seated with the occlusal plane parallel to the floor and the sagittal plane perpendicular to the floor.  Before any radiographs are exposed, the patient must be protected with a lead apron and thyroid collar.  The apron must be properly placed to avoid interference with the radiographic exposure. 

Film placement:  The film (size #4) plane should be parallel to the floor, and the packet should be pushed posteriorly as far as possible.  The lateral border of the film should be positioned parallel to the buccal surfaces of the posterior teeth and extend laterally approximately one-half inch past the buccal cusps on the side of interest.  The patient should bite down gently to maintain film position.

Exposure factors:  Follow the recommendations of the film and equipment manufacturer.

Direction of the central ray:  The tube is directed at right angles to the curve of the arch, and strikes the center of the film packet as in Figure 72.


Figure 72

Posterior Oblique Mandibular Occlusal
Uses:  The projection is used to view the posterior teeth of the mandible to locate cysts, fractures, supernumerary teeth, and periapical pathology.  It can be used in place of posterior periapical films. (Figure 73)


Figure 73

Patient positioning: The patient is seated with the occlusal plane parallel to the floor and the sagittal plane perpendicular to the floor.  Before any radiographs are exposed, the patient must be protected with a lead apron and thyroid collar.  The apron must be properly placed to avoid interference with the radiographic exposure.

Film placement: The film (size #4) plane should be parallel to the floor, and the packet should be pushed posteriorly as far as possible.  The lateral border of the film should be positioned parallel to the buccal surfaces of the posterior teeth and extend laterally approximately one-half inch past the buccal cusps on the side of interest.  The patient should bite down gently to maintain film position.

Exposure factors:  Follow the recommendations of the film and equipment manufacturer.

Direction of the central ray:  The tube is directed at the apex of the mandibular second premolar, and the central ray should strike the center of the film packet.  The vertical angulation is -50 degrees as in Figure 74.


Figure 74

Intraoral Occlusal Radiography

Modified Oblique Posterior Mandibular Occlusal
Uses:  This projection is especially useful to detect calculi in the submandibular gland.  Calculi are often difficult to detect on conventional radiographs due to superimposition of the mandibular bone. (Figure 75)


Figure 75

Patient positioning and film placement:  With the tube side of the film (size #4) toward the mandible the film is placed in the patient’s mouth crosswise like a sandwich.  The film plane should be parallel to the floor, and the packet should be pushed posteriorly as far as possible.  The lateral border of the film should be positioned parallel to the buccal surfaces of the posterior teeth and extend laterally approximately one-half inch past the buccal cusps on the side of interest.  The patient’s head is then rotated to the side and lifted up.  Before any radiographs are exposed, the patient must be protected with a lead apron and thyroid collar.  The apron must be properly placed to avoid interference with the radiographic exposure.

Exposure factors:  Follow the recommendations of the film and equipment manufacturer.

Direction of the central ray:  The tube is positioned under and behind the mandible and the central ray is directed onto the center of the film so that it passes inside the ascending ramus so that the submandibular gland will be between the tube and the film as in Figure 76.


Figure 76

Digital Radiology

Digital imaging was introduced into dentistry in 1987. Digital sensors are used instead of x-ray film. Sensors can be wired or wireless depending on the system used. (Figures 77 and 78) Sensors and tube head placement are the same for digital imaging as film and tube head placement is for traditional radiology. Most standard radiographic machines can be converted to acquire digital images. Digital imaging still uses ionizing radiation, and therefore, before any radiographs are exposed, the patient must be protected with a lead apron and thyroid collar. The apron must be properly placed to avoid interference with the radiographic exposure.

The sensors are slightly thicker than a regular film. Modified film holders must be utilized in the placement of the sensors. These modified holders can be purchased from any major dental supply company. The sensors can be reused several times. Proper use of intraoral barrier and OSHA techniques must be observed.

The advantages of digital radiology are decreased exposure time to the patient, elimination of darkroom processing time and exposure to processing chemicals, immediate viewing, and ability to easily and cost effectively transmit directly to third party facilities or affiliating dental offices. Additional computerized advantages include the ability to enhance the image for viewing. Once an image is in the computer, brightness and contrast and image reversal can be enhanced for optimal viewing of tissue and bone levels. The radiograph can be rotated and magnified to enhance details. An additional feature shows embossed images creating a stacked effect of the oral tissues.

The main disadvantages are substantial start up costs including machinery and operatory computer technology, and compatibility with other software program and RAM capacity. Considerations must also be noted that although your office may utilize digital radiography, other facilities may not and the transfer of images between them could be more difficult.

Figure 77

Figure 78

Summary

Proper film and tube head placement are a critical component of the total radiographic procedure.

Periapical, bitewing, and occlusal surveys are critical components of diagnosis and treatment of dental patients. Because of the exposure to ionizing radiation, proper techniques must be employed to reduce radiation exposure to the patient through the use of lead aprons, high speed film, and proper technique; thus decreasing additional film retakes. As technology advances in dental radiology operators must maintain current knowledge and adapt their abilities for the best treatment of the patient.

Glossary

Alveolar Crest – highest part of the alveolar bone
Alveolar Ridge – part of the bone that contains the tooth sockets
Anterior – in front
Apices – plural for apex or tip of root
Bisector – a straight line that bisects an angle
Buccal – towards the cheek
Calculi – plural of calculus; a hard rough deposit on the tooth surface
Digit – finger or toe
Distal – tooth surface away from the midline
Edentulous – without teeth
Foramina – plural for foramen; an opening
Horizontal – line extending from side to side
Impacted – trapped below the surface as in an impacted third molar
Incisal Edge – biting surface of front teeth
Interproximal – between the teeth
Intraoral – inside the oral cavity
Lingually – towards the tongue
Mandible – lower jaw
Mandibular Ramus – portion of the mandible that extends back and up
Maxilla – upper jaw
Mesial – tooth surface towards the midline
Occlusal – biting surface of back teeth
Palatal – pertaining to the roof of the mouth
Parallel – extending in the same direction and same distance apart
Periapical – surrounding the apex or tip of the tooth
Periodontal – surrounding the tooth
Periodontal disease – disease of the gums and supporting areas of the teeth
Perpendicular – intersecting at a right angle
Posteriorly – behind
Sagittal Plane – vertical plane dividing the body
Supernumerary teeth – extra teeth
Tori – hard bony projections
Vertical – line extending from top to bottom (up and down)

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