1. Radiology
Dental Assistant Registration Course

2. Discovery of the X-Ray
William Conrad Roentgen discovered x-rays in 1895 by using a glass vacuum tube with an electrical circuit connected to each end.
The stream of electrons traveled from the cathode end to the anode end.
Also in 1895, Dr. Otto Walkoff was the first to use the x-ray to take the first dental radiograph.

3. Discovery of the X-Ray
In 1896, Dr. C. Edmund Kells took the first intraoral radiograph and Dr. William Rollins, the inventor of the first dental x-ray unit, reported effects of radiation exposure.
In 1913, Dr. William Coolidge invented the hot cathode x-ray tube.
Victor X-Ray Corporation, later known as General Electric Corporation, developed a dental x-ray machine known as the Coolidge tube.

4. X-Ray Techniques
A variety of techniques were discovered in an effort to capture dental x-rays.
In 1905, Dr. Howard Robert and A. Cieszykski developed the bisecting technique, in which isometry is employed.
The parallel technique, developed by Frank McCormack in 1920, used the right angle technique to expose dental x- rays.
The panoramic technique was discovered in 1959 by a team of doctors and Dr. Paatero was credited with developing the first unit to capture an x-ray of the entire dental arch on one film.
Currently, mouth structures can be visualized using tomography in which certain planes are selected for view.

5. Dental X-Ray Film
Halide crystals suspended in gelatin store energy when exposed to x-rays, thus forming a black mark on the film.
There are several speeds used by dentists; D-speed (Ultraspeed), E-speed, (Ektaspeed), and F-speed (InSight).
Five basic sizes are used in intraoral x-rays, depending on the size of the patient’s oral cavity and the area to be radiographed.
Film is placed in the intraoral film packet, which is sealed in plastic wrap and backed with lead foil.
Dental film should be stored carefully to prevent exposure to stray radiation.

6. Safety Precautions
Precautions to ensure safety for staff and patients are necessary to ensure safety.
The federal government has mandated that all manufacturers ensure that their x-ray units have separate control switch to cut power and also have an electric timer to stop electricity automatically.
The PID must be lead lined and the x-ray tube sealed according to guidelines.
Indicators displaying mA, kV, and impulses [per exposure time are to be set in the control panel and the collimator is to be fitted directly over the tubehead where the x-ray beam exits.
Additionally, film head of 2.5 mm of aluminum must be built into the head of all x-ray machines operating at kV higher than 70.
It is the responsibility of the dentist to have all x-ray equipment installed and maintained properly.
He or she must prescribe x-rays responsibly and train staff accordingly.
The dental assistant must be trained to understand safety as well.
Finally, it is the patient’s responsibility to notify staff of physical conditions, such as pregnancy, that may affect the prescription of x-rays.

7. Radiation Physics and Biology
Energy travels in waves that move in straight lines at the speed of light (186,000 miles per second).
There is no mass involved and it travels through space in the form of transverse waves

8. Wavelengths
Wavelength is measured in cycles: the measurement between two peaks of adjacent waves.
Longer wavelengths include visible light, television, and radio waves.
Shorter wavelengths are x-rays and gamma rays.
The more cycles that pass a given point in a specified time frame, the higher the frequency.
More energy is given by shorter wavelengths with higher frequency and less energy is emitted when the wavelength is long and has lower frequency.

9. Radiation Types
Dental radiographs employ hard radiation, which is in the form of short wavelengths that have high frequency and high energy, and therefore a higher penetrating power.
Soft radiation, called Grenz rays, is a longer wavelength with low energy due to lower frequency.
There are four types of radiation; primary, secondary, scatter, and leakage.
Primary radiation is a high energy, short wavelength that is the central beam originating from the x-ray tube head.
Secondary radiation waves are often transformed into longer wavelengths that lose their energy as they form when primary x-rays contact matter.
Radiation deflected from its path as it strikes matter is called scatter radiation and is dangerous to anyone in its path.
It is recommended that operators stand at least six feet from the patient while conducting radiographs.
Leakage radiation is the radiation that escapes from the tube or tube head.

10. Radiation Measurements
The amount of radiation that ionizes one cubic centimeter of air is called a roentgen (R).
The radiation absorbed dose (rad) or Gray (GY) refers to the amount if ionizing radiation absorbed into a substance.
The dose to which body tissues are exposed is called the roentgen equivalent man (rem) or sievert (Sv), and is measured in terms of its estimated biological effects in relation to an exposure dose of one R or x or gamma radiation.

11. Radiation Measurements
A milliroentgen (mR) is one one thousandth (1/1,1000) of an R. The measurement unit used to compare the biological effects of different tissues compares effects of different forms of energy on different tissues is called relative biological effectiveness (rbe).

12. Structure of Atom
Ionization is the process in which atoms change into negatively or positively charged ions during radiation.
All matter is composed of atoms, which are composed of electrons, protons, and neutrons.
The protons are positively charged particles inside the nucleus.
Negatively charged particles orbiting the nucleus are called electrons and are comprised of tinier particles called hadrons, leptons, and quarks. The neutrons have no charge.

13. Radiation Production Thermionic Emission
Thermionic emission occurs as the filament is heated by electricity, sending electrons through the tube. Electrons travel from cathode to anode
The X-ray is produced at the exact moment the electrons collide.

14. Radiation Exposure
The maximum permissible exposure (MPD) is the maximum dose of radiation that is an allowable exposure not expected to harm an individual.
Most individuals are exposed to natural and artificial radiation.
Natural radiation, such as the radiation produced by the sun and atmosphere, comprises about 55 percent of the daily radiation exposure.
Artificial radiation contributes almost 41 percent of the daily radiation exposure and comes from x-rays and consumer products.
Because the effects of radiation are cumulative, long-term effects of exposure can result.

15. Components of the Dental X-Ray Unit
The dental assistant should understand the components that make up the dental x-ray unit.
Settings, adjustments, and selections of milliamperage, kilovoltage, and the electric timer are made on the control panel.
The amount or quantity of electrons is determined by the milliamperage.
The quality or penetrating power of the central beam is determined by kilovoltage (KV).
The higher the KV, the greater the penetrating power of the x-rays, and therefore, less exposure time is necessary.

16. Components of the Dental X-Ray Unit
The electronic timer controls the total time rays flow from the x-ray tube.
It is located in a safe area outside the room or behind a lead barrier to keep the operator safe.
The amount of radiation exposure a patient receives is determined by milliamperage seconds (mAs).
Contrast is indicated on an x-ray by differing shades of gray.
The degree of darkness on an x-ray is referred to as density, and is affected by distance to the x-ray tube, patient tissue thickness, and amount of radiation reaching the film.

17. Components of the Dental X-Ray Unit
The arm assembly is a flexible extension attached to the x-ray room wall that enables the operator to position the unit as needed. The x-ray vacuum and the step-up (high voltage) and step-down (low voltage) transformers are located in the tubehead.
X-rays travel through the x-ray tube to a metal filter, known as an inherent filter, which separates hard and soft x-rays.
Hard x-rays, called the central beam, pass through the collimator, a lead disc used to filter out weaker x- rays.

18. Safety Precautions
Precautions to ensure safety for staff and patients are necessary to ensure safety.
The federal government has mandated that all manufacturers ensure that their x-ray units have separate control switch to cut power and also have an electric timer to stop electricity automatically.
The PID must be lead lined and the x-ray tube sealed according to guidelines.
Indicators displaying mA, kV, and impulses [per exposure time are to be set in the control panel and the collimator is to be fitted directly over the tubehead where the x-ray beam exits.

19. Safety Precautions
Additionally, film head of 2.5 mm of aluminum must be built into the head of all x-ray machines operating at kV higher than 70.
It is the responsibility of the dentist to have all x-ray equipment installed and maintained properly.
He or she must prescribe x-rays responsibly and train staff accordingly.
The dental assistant must be trained to understand safety as well.
Finally, it is the patient’s responsibility to notify staff of physical conditions, such as pregnancy, that may affect the prescription of x-rays.

20. Film Exposures
The periapical radiograph shows the entire tooth and surrounding structures.
The bite-wing radiograph shows the crowns, interproximal spaces, and the crest of the alveolar bone.
Occlusal radiographs picture large areas of the mandible and maxilla.

21. Bisecting Technique
The bisecting technique is used to expose periapical, bite-wing or occlusal radiographs.
To expose a quality film using this technique the patient’s hard must be correctly positioned, the film must be placed as close as possible to the lingual surface, and the vertical angulation must be appropriately set.
This is generally not the technique of choice as it may cause distortion and guesswork.

22. Full Mouth Survey
This consists of a number of periapical and bite-wing radiographs to collectively display all teeth and surrounding structures.
The dental assistant should form a consistent sequence or routine for exposing these films to avoid double exposure of the patient.

23. Bite-wing series
These are typically used for caries detection and are taken at six to twelve month intervals.
The film is usually placed in the horizontal position, but may also be placed vertically if the dentist wants to see more of the root of the tooth.

24. Special Radiographs
Occlusal radiographs are used in children and patients who have difficulty opening the mouth or controlling muscular movement.
The two techniques used for obtaining occlusal radiographs are the topographic technique and the cross- section technique.
Pediatric radiographs are an important part of maintaining oral health in children and are used to detect caries and various other anomalies.
Care must be taken not to overexpose children to radiation.

25. Special Radiographs
Radiographs are taken of edentulous patients to show cysts, impacted teeth, retained root tips, or other pathological conditions.
Radiographs may be taken during endodontic procedures to assess the progress of the procedure and to take necessary measurements.
The dental assistant must be able to adapt radiographic techniques for patients who have special needs, such as those in wheelchairs, those who may be deaf, or those with physical impairments.

26. Processing Quality Radiographs
The darkroom where processing of the radiographs takes place, must be well ventilated and must omit all white light.
Manual processing tanks are made of stainless steel. There is one large tank for a water bath and two large insert tanks.
The tank cover must be kept on at all times.
The developer is normally on the left and the fixer is normally on the right.
A thermometer, timer, racks, stirring rods, dryer, brushes, and sponges are all necessary equipment to have on hand.

27. Processing Quality Radiographs
The solutions must be prepared in the proper concentrations and placed in the proper tanks. The solutions are stirred and the temperature is checked.
The x-rays are carefully unwrapped and placed on the racks then placed in the developer solution.
After enough time has passed the x-rays are removed from the developer, rinsed, and then placed in the fixer tank.
After enough time has passed the x-rays are removed from the fixer and bathed in water and hung to dry.

28. Automatic Processors
Automatic processors are used in most dental offices. They reduce processing time. The film undergoes the same basic steps as the manual processing but moves from one area to the next automatically.
Care must be taken to maintain the equipment.

29. Common Errors- Distortion
Caused by the bending or curving of film along the palate or mandible.

30. Common Errors- Elongation
Caused by a vertical angulation error. Occurs most commonly with the bisecting technique

31. Common Errors- Overlapping
Caused by incorrect horizontal angulation

32. Common Errors- Cone Cutting
The x-ray beam missed part of the film.

33. Common Errors- Double Exposure
A film that is exposed twice.

34. Common Errors Overexposed Film
Film has a dark image.

35. Common Errors Backward Film
Images will appear light and a Herringbone pattern will appear on the film.

36. Processing Errors
Light film – underprocessed; developing time too short or developer temperature too low.
Dark film – overprocessed; developing time too long or developer temperature too high or too strong.
Fogged film – detail is lost, contrast is lessened. Caused by improper storage, outdated film, or light leaks.
Partial image – solution levels in processing tank too low causing film to only be partially immerged.
Film artifacts – spots or marks on the film from improper handling of the film and uncleanliness of the work area.

37. Processing Errors Torn or scratched film – rough handling of film.
Air bubbles – due to failure to agitate the film when placed in the developed and fixer solutions.
Reticulation – exposure of film to high temperatures and then low temperatures; causes film to have tiny cracks.
Streaks – unclean rollers.

38. Quality Assurance
A quality assurance program refers to routine procedures that have been developed to ensure the highest quality and minimal risk to the patients in radiation exposure.
Keep a log of daily, monthly, and yearly procedures used to maintain quality radiographs.
If the faster films are used, then the red filter is correct
Coin test – place a coin on unwrapped, unexposed x-ray film under the safelight for 2-3 minutes; then process the film.
If the outline of the coin is evident on the film, then the safelight illumination is inadequate or a white light leak is possible.
The x-ray machine will have manufacturer’s suggested tests and equipment.

39. Extraoral Radiographs
Panoramic
Common in general and specialty offices
Cephalometric
Common with orthodontists
Digital
Becoming standard
Easier for the staff

40. Panoramic Radiography
Tomography shows the imaging of one layer or section of the body while blurring images from other areas.
Rotational centers include a tubehead that rotates around the patient while the cassette that holds the x-ray rotates in the opposite direction. Conforms to the dental arches.
The focal trough is the three dimensional curved zone in which the dental arches are positioned to achieve the sharpest image possible.

41. Panoramic Radiography
Exposure controls
Located outside the x-ray room.
Manufacturers determine the exposure time; see manual.
Head positioner
Lateral head supports or guides, chin rest, notched bite block, and forehead rest.
Some have handles for the patient to hold on to.
X-ray tubehead
Similar to an internal x-ray tubehead, although the collimator is different; narrow verticals slit instead of round/rectangular
Patient receives minimum radiation exposure due to small slit
Cassette holder
Flat, hard containers that open on back Or flexible, thin sleeves that open on one end (to prevent light entering)
Lined with intensifying screens

42. Panoramic Technique
Lead apron without a thyroid collar because the collar interferes with the image and because the x- ray beam is directed upward, the exposure is minimal.
Explaining the procedure to the patient can help with nervousness and not knowing what to expect.
The patients need to have any jewelry, hair clips, or bulky sweaters removed.
Patient must be still for the machine to accurately reflect data.
This procedure is done by the dental assistant at the directions of the dentist.

43. Cephalometric Radiographs Mainly used by orthodontists to plan treatment for their patients, although some oral maxillofacial surgeons and general practitioners include these radiographs for patient assessment

44. Radiographic Interpretation
It is important to be familiar with the terminology used in radiographic interpretation; the dental assistant will be prepared and perform better.
Anatomical landmarks – assist in identifying abnormal areas for mounting x-rays so that good communication can exist.
Radiopaque/Radiolucent – structures that are dense and do not allow x-rays to pass through them (light gray to white shades).
Diagnosis – structures that are not dense (dark gray to black).
Interpretation – explain the meaning of something.
Superimposition – one structure lying over another.

45. Tooth and Surrounding Structures
Parts of the tooth and surrounding structures:
Enamel – radiopaque area on crown.
Dentin – area just inferior to the enamel; less radiopaque than enamel.
Cementum – radiopaque like dentin; thin covering on the roots.
Pulp chamber – radiolucent area surrounded by dentin; pulp horns can be seen.

46. Tooth and Surrounding Structures
Pulp canals or root canals – radiolucent areas in the root; extend from pulp chamber to apex.
Periodontal ligament/space – radiolucent area that surrounds the roots.
Lamina dura – radiopaque line of cortical bone that surrounds the roots.
Cortical plate – dense compact bone that forms the tooth socket.

47. Mandibular Landmarks
Mental foramen – radiolucent area between the roots of the premolar.
Mandibular canal – radiolucent but it is outlined by radiopaque lines that extend between foramens.
External oblique ridge – oblique line found on the external surface of the mandible from the middle of the rami to beyond molars.
Trabucular patterns – spongy/cancellous bone that surrounds the teeth and forms the mandible.
Alveolar crest - compact edge of cortical bone that shows as radiopaque between teeth.
Mandibular retromolar area – behind the last mandibular molar; shows varying tissues in this triangular space.

48. Mandibular Landmarks
Internal oblique ridge – bone on the mylohyoid ridge internal surface of the mandible that runs from the middle of the rami to third molar region; sometimes continues past molars to cuspids and is known as the mylohyoid ridge and show superimposed over the root area.
Mandibular foramen – radiolucent area in the middle of the ramus of the mandible on the interior surface.
Condyle – back projection on top of the ramus; shows radiopaque and is articulated in the glenoid fossa.
Coronoid process – front projection of tip of ramus; shows radiopaque.
Medial sigmoid notch – indented area between condyle and coronoid processes on the ramus; also known as the coronoid notch or the mandibular notch.

49. Mandibular Landmarks
Lingual foramen – radiolucent area on lingual surface of the mandible at midline/symphysis.
Genial tubercle – raised areas of bone that surround lingual foramen
Ramus – section of each side of mandible that runs vertically.
Body of mandible – section that runs horizontally.
Border of the mandible – lower edge of body of the mandible that is made of compact bone.
Symphysis – “chin” area; anterior portion of the mandible.
Hyoid bone – “U” shaped bone suspended by ligaments below the mandible but anterior to the larynx; occasionally seen on dental x- rays.
Nutrient canals – radiolucent paths that extend toward the alveolar crest.

50. Maxillary Landmarks
Hard plate – radiopaque structure that forms roof of mouth.
Incisive foramen – radiolucent area at midline of palate behind central incisors.
Maxillary suture – aka median palatine suture – radiolucent line joining right and left halves of maxillary bone and palatine bones.
Zygomatic process – process on external surface beginning around the first molar region.
Malar – part of zygomatic bone that forms the cheek.
Nasal septum – radiopaque line that divides the nasal fossae.
Nasal cavities – two side by side openings of the nose.
Nasal conchae – bony, scroll-shaped plates in the lateral walls of the nasal cavity.
Maxillary sinuses – left and right cavities above apices of the teeth, can extend from canines to molars.

51. Maxillary Landmarks
Intraorbital foramen – radiolucent area below the inferior border of eye sockets.
Maxillary tuberosity – radiopaque area behind most posterior molar on the maxilla.
Glenoid fossa – depression on the lower border of temporal bone where the condyloid process of the mandible articulates as temporomandibular joint.
Mastoid process – temporal bone that lies in the lower, anterior section just behind the ear canal.

52. Maxillary Landmarks
External auditory meatus – radiolucent area in the temporal bone for auditory canal.
Hamular process – slender projection of the bone that lies behind medial to the maxillary tuberosity.
Styloid process – projection of bone, larger than hamular process, which comes from the temporal bone and lies behind the glenoid fossa.

53. Computed tomography (CT)
Used to plan implant surgery and to locate and define lesions associated with oral cavity.
Patient is placed in unit, where the radiation and image detector rotates around them; then information is sent to a computer and image displayed on screen.
Magnetic resonance imaging (MRI)
Mainly used to diagnose TMJ disease.
Ability to look at soft tissues with very little risk to the patient.
Electromagnetic radiation instead of ionizing.

54. Digital Radiography
Projected to replace conventional film exposure completely.
Allows dentist to take an intraoral or extraoral radiograph and display on computer screen without exposing or processing dental film.
The image can be digitized, enhanced, printed, stored, or sent to another office by fax or modem.
Term “image” is used when speaking of – not “radiograph” or “x- ray”
Pixels are the dots that make up an image; the more pixels, the higher the resolution and sharper the image.
A computer can display over 200 shades of gray, although humans can detect only 32.
The computer software can enhance these shades for better comparison and evaluation from the dentist.

55. Direct Digital Imaging
Sensor is placed in the patient’s mouth and exposed to x-rays.
It is then transmitted to the computer almost immediately.

56. Indirect Digital Imaging
Scanner digitized the image and then sends to the computer. Indirect is not used as much in dentistry because the quality of the image is inferior to a direct digital image; however, this technique does offer a means to digitize existing x-rays for storage.
Storage phosphor:
Second type of indirect digital imaging system.
Wireless that uses coated plates instead of sensors to record the image; which must be cleared between each use and sterilized.
They are placed on a high-speed scanner and sent to the computer

57. Producing Quality Radiographs
All appropriate barriers should be placed on the chair and radiographic equipment prior to seating the patient.
The materials that are going to be needed for the exposure should also be set up.
The DA should be wearing appropriate PPE during exposure.
Seat the patient comfortably and place the lead apron and thyroid collar on the patient.
Position the tubehead. Place the exposed film into a paper cup.
Take the lead apron from the patient and dismiss the patient to the treatment room.
Make necessary notations in the patient’s chart and remove barriers and clean the equipment

58. References
Dental Assisting: A Comprehensive Approach, Phinney, D.J., Halstead, J.H. (3rd. Ed.) Thomson /Delmar Learning,2008
Dental Radiography: Principles & Techniques, 3rd Ed; Iannucci & Howerton, Elsevier, St. Louis, 2006