Dental Radiology Handout PDF

DENTAL RADIOLOGY—Laura Jansen Howerton, RDH, MS I. RADIATION HISTORY A. Wilhelm Roentgen discovered the x-ray in 1895 B. He discovered x-rays while experimenting with a cathode ray tube II. RADIATION PHYSICS A. Ionization: the pro...

DENTAL RADIOLOGY—Laura Jansen Howerton, RDH, MS I. RADIATION HISTORY A. Wilhelm Roentgen discovered the x-ray in 1895 B. He discovered x-rays while experimenting with a cathode ray tube II. RADIATION PHYSICS A. Ionization: the production of ions (an atom that gains or loses an electron and becomes electrically unbalanced) B. When an electron is removed from an atom in the ionization process, an ion pair results 1. the atom becomes the positive ion 2. the ejected electron becomes the negative ion C. Ionizing Radiation – radiation that is capable of producing ions by removing or adding an electron to an atom; x-rays produce ionization 1. Particulate radiation – tiny particles of matter that possess mass and travel in straight lines at high speeds electrons protons beta particles alpha particles cathode rays neutrons 2. Electromagnetic radiation – the propagation of wave-like energy (without mass) through space or matter cosmic rays gamma rays x-rays* ultraviolet rays microwaves, radio waves visible light Velocity the speed of a wave Wavelength the distance between the crest of one wave to the crest of the next wave Frequency the number of wavelengths that pass a point in a certain amount of time *X-RAY – electromagnetic ionizing radiation of VERY SHORT WAVELENGTH resulting from the bombardment of tungsten by highly accelerated electrons in a vacuum *PROPERTIES OF X-RADIATION 1. X-rays have a wave form; they travel in waves with short wavelengths and high frequency. 2. X-rays travel at the speed of light (186,000 miles/second). 3. X-rays have the power to penetrate substances. 4. X-rays are invisible. 5. X-rays have no mass, no weight and no charge. 6. X-rays are absorbed by matter. 7. X-rays exert an effect on living tissue; x-rays are able to stimulate or destroy living cells. 8. X-rays lose intensity with distance; x-rays travel in straight lines and cannot be focused to a point. 1  D. The X-ray Tube 1. Protective leaded glass housing a. tube enclosure with all the air removed; shielding prevents radiation leakage b. high vacuum glass tube surrounded by refined oil with high insulating powers; the oil helps to absorb excess heat 2. Cathode – made of a tungsten filament and molybdenum cup; NEGATIVE charge a. filament: heated to give off a cloud of electrons; thermionic emission b. cup: focuses electrons toward the anode c. *supplies the electrons necessary to generate x-rays 3. Anode – made of a copper arm and focal spot; POSITIVE charge a. focal spot is made of tungsten b. *converts bombarding electrons into x-ray photons III. RADIATION CHARACTERISTICS A. Kilovoltage Peak (kVp) Voltage is the electrical pressure or potential difference between two electrical charges. In dental radiography, this difference in potential determines the speed of electrons when traveling from cathode to anode. kVp determines the quality of the x-ray beam (quality refers to the penetrating power of the beam). kVp regulates the speed of electrons traveling from cathode to anode (the higher the kVp, the faster the electrons). Higher kVp = harder x-rays = short wavelengths 1. Density and kVp – the overall darkness or blackness of a film a. if the kVp is increased, the film exhibits an increased density and appears darker b. if the kVp is decreased, the film exhibits a decreased density and appears lighter 2. Contrast and kVp – how sharply dark and light areas are separated on a film a. with a low kVp (65 to 70), a high contrast film results demonstrating many black and white areas and a few shades of gray; short-scale of contrast b. with a high kVp (> 90), a low contrast film results demonstrating many shades of gray instead of black and white; long-scale of contrast Adjustment Density Contrast Scale of Contrast Resultant Film Low kVp Low (lighter) High Short-scale Black and white High kVp High (darker) Low Long-scale Many grays **Only kVp and filtration affect contrast! 2  B. Milliamperage (mA) The ampere is the unit of quantity of electric current. An increase in amperage results in an increase in the number of electrons that are available to travel from the cathode to the anode when the exposure switch is depressed. This results in a production of more x-rays. mA also controls the temperature of the tungsten filament (the hotter the filament, the greater number of x-rays produced). 1. Density and mA – an increase in mA results in increased density and a darker image 2. both mA and exposure time have a direct influence on the number of electrons produced; when combined, they form a factor termed milliampere-seconds (mAs) 3. mA change problems Bitewings are exposed with good density and contrast at 15 mA, 90 kVp and 8 impulses. What exposure time would be appropriate if the machine were set at 10 mA and 90 kVp? mAs (old) = mAs (new) 15 mA x 8 sec. = 10 mA x sec?? 120 mAs = 10 x sec?? 12 sec = new time (note: x-ray units produce 60 bursts or impulses of radiation per second; therefore, ½ second would equal 30 impulses) Milliamperage Number of photons INCREASE increased Exposure time Number of photons INCREASE increased Kilovoltage peak Number of photons INCREASE Penetration INCREASE increased Aluminum filtration Number of photons DECREASE Penetration INCREASE increased Distance increased Number of photons DECREASE INVERSE SQUARE LAW - the intensity of radiation is inversely proportional to the square of the distance from the source of radiation; intensity is the product of the quality and the quantity. If the cone length is changed from 8 to 16 inches, how does this affect the intensity of the beam? If the cone length is changed from 16 to 8 inches, how does this affect the intensity of the beam? If a person standing three feet from an x-ray source receives 4 Rads of exposure, how much would they receive at six feet? 3 IV. RADIATION BIOLOGY – not all x-rays pass through the patient and reach the dental film; some x- rays are absorbed by patient tissues A. Ionization – results in the formation of a positive atom and a dislodged negative electron 1. may have little effect on cells if the chemical changes do not alter sensitive molecules 2. may have profound effect on structures of great importance to cell function (ie: DNA, nucleus) B. Free Radical Formation – an uncharged (neutral) atom or molecule that exists with a single, unpaired electron in its outermost shell 1. free radicals are unstable and highly reactive 2. water is broken into free radicals by x-ray energy 3. the ionization of water is the most common mechanism of damage in humans free radicals --- > combine to form --- > toxins such as H2 O2 (hydrogen peroxide) C. Radiation Injury Sequence 1. Latent period is the time that elapses between exposure to radiation and the appearance of observable clinical signs 2. A period of injury follows; many cellular injuries may result including cell death, changes in cell function, abnormal mitotic activity, etc. 3. Not all cellular radiation injuries are permanent; with each radiation exposure, cells can repair the damage in the recovery period 4. Radiation effects are additive and damage that remains unrepaired accumulates in the tissues; cumulative effects of repeated radiation exposure can lead to health problems (ie: cancer, cataract formation, birth defects) a. Adverse reactions of the body to radiation never return exactly to the original state b. Additive effects accumulate to some degree over time Gonadal exposure for the average full mouth series = 3-7 days of background radiation Panoramic dose is equivalent to the dose received from four bitewing radiographs D. Somatic vs. Genetic Effects 1. Somatic effects are seen in the person irradiated; these changes are not transmitted to future generations 2. Genetic effects are not seen in the person irradiated but are passed on to future generations E. Radiation Effects on Cells – the response of a cell to radiation exposure is determined by the following: Mitotic activity Cells that divide frequently or undergo many divisions over time are more sensitive to radiation Cell Cells that are immature or are not highly specialized are more sensitive to differentiation radiation Cell metabolism Cells that have a higher metabolism are more sensitive to radiation 4 Cell Sensitivity to Radiation High Medium Low reproductive tissue fine vasculature nerve tissue lymphoid system growing cartilage, bone skeletal muscle bone marrow salivary glands heart intestines lungs optic lens mucous membranes kidneys, liver mature bone F. Radiation Measurements – used to define three quantities of radiation Measurement Traditional Unit SI Unit Exposure in air Roentgen Coulomb/kg (C/kg) Dose Rad Gray (Gy) Dose equivalent Rem Sievert (Sv) V. RADIATION PROTECTION A. Before Exposure 1. Filtration - produces an x-ray beam with a greater percentage of short wavelength x- rays by filtering out the weaker x-rays; allows the more penetrating x-rays pass through by absorbing long wave radiation a. dental x-ray machines operating at or below 70 kVp require a minimum of 1.5 mm aluminum filtration b. machines operating above 70 kVp require a minimum of 2.5 mm aluminum filtration 2. Collimation – reduces the surface area exposed by the use of a lead washer; shapes the x-ray beam into a more restricted area and reduces scatter a. beam size at the patient’s face can be no larger than 2.75 inches b. rectangular collimation reduces the skin’s surface area by 50-60% 3. Position indicating device (PID, cone) – less volume of tissue is irraditated if a long cone is used B. During Exposure 1. Thyroid collar protects the radiosensitive tissues of the thyroid gland 2. The lead apron protects the reproductive and blood-forming tissues a. the lead apron absorbs 90% of the scatter radiation that would have reached the reproductive tissues b. the lead equivalent is usually.25 mm 3. *Fast film is the most effective method of radiation protection; each alphabetical film group is twice as fast as the previous group and needs half the radiation exposure (ex: E-speed film is twice as fast as D-speed and needs half the exposure time) 5  4. Intensifying screens (used in extraoral radiography) reduce the amount of radiation needed to properly expose a film, therefore reducing the amount of radiation the patient receives C. Operator Protection – the dental radiographer must avoid the primary beam 1. Distance a. stand at least 6 feet away from the x-ray tubehead b. if this distance is not possible, stand behind a barrier or wall c. remember, x-rays lose intensity with distance 2. Positioning – be positioned at a 90-135 angle to the beam D. Maximum Permissible Dose (MPD): the maximum dose that a body is permitted to receive in a specific period of time with little or no injury Traditional unit SI Unit MPD: Occupational 5 rem/year (5000 mrem) 0.05 Sv/year (50 mSv) MPD: Non-occupational (1/10) 0.5 rem/year (500 mrem) 0.005 Sv/year (5 mSv) E. ALARA Principle: radiation must be kept “As Low As Reasonably Achievable” VI. DENTAL X-RAY IMAGE CHARACTERISTICS A. Sharpness – the capability of the x-ray film to reproduce the distinct outlines of an object, or how well the smallest details of an object are reproduced on a dental radiograph 1. the smaller the focal spot size, the sharper the image appears 2. the composition of the film emulsion influences sharpness; the larger the crystal, the less image sharpness is produced 3. a loss of image sharpness occurs if the film or patient moves during exposure B. Magnification – refers to an image that appears larger than the actual size of the object it represents 1. a longer PID (cone) and target-to-film distance results in less image magnification 2. a decrease in object-to-film distance results in a decrease in magnification C. Distortion – a variation in the true size and shape of the object being radiographed 1. to minimize distortion, the object and film must be parallel to each other 2. to minimize distortion, the x-ray beam must be directed perpendicular to the tooth and film 6  Geometric Influencing Factors Effect of Influencing Result Characteristics Factors Sharpness Focal spot size Decrease focal spot size Increase sharpness Film composition Decrease crystal size Increase sharpness Movement Decrease movement Increase sharpness Magnification Target-film distance Increase target-film Decrease magnification distance Object-film distance Decrease object-film Decrease magnification distance Distortion Object-film alignment Object and film parallel Decrease distortion X-ray beam alignment Beam perpendicular to Decrease distortion object and film VII. DENTAL X-RAY FILM PROCESSING A. Manual Film Processing Basics 1. the developer solution reduces the exposed, energized silver halide crystals into black metallic silver a. hydroquinone and elon soften the film emulsion b. changes exposed silver halide crystals to black c. 5 minutes at 68 degrees 2. a rinsing step removes the developer from the film and stops the development process; usually 30 seconds 3. the fixer solution removes the unexposed, unenergized silver halide crystals from the film emulsion a. sodium thiosulfate and ammonium thiosulfate harden the film emulsion b. removes all unexposed crystals; clears the film c. 10 minutes (twice the development time) 4. a water bath thoroughly removes all excess chemicals from the emulsion; 20 minutes 5. the films are completely dried B. Automatic Film Processing Basics 1. the chemicals are more concentrated a. the films are developed at 80 degrees for 1.5 minutes b. the films are fixed for 1.5 minutes c. the films are washed for 30 seconds d. the films are dried for 30 seconds 2. automatic processors are designed to work at higher temperatures 3. no rinse step exists between developer and fixer C. Safelighting – provides sufficient illumination in the darkroom to carry out processing activities without exposing or damaging the film 1. low wattage bulb (7 ½ or 15 watts) placed a minimum of 4 feet away from the film and working area 2. GBX-2 filter can be used for extraoral and intraoral films 3. extraoral films have an increased sensitivity to light 7 VIII. PROCESSING AND TECHNIQUE ERRORS EXAMPLE APPEARANCE ERROR Film exposed to light Completely black Film was exposed to light before processing Unexposed film Completely clear Film was not exposed to x-radiation Underdeveloped film Light Inadequate or depleted developer, developer too cool Overdeveloped film Dark Excessive developing time, developer too hot, concentrated developer Developer spots Dark spots Developer splashed on film before processing Fixer spots Light spots Fixer splashed on film before processing Yellow-brown stains Yellow, brown color Exhausted chemicals, insufficient rinsing, incomplete fixation Air bubbles White spots Air is trapped on the film surface after being placed into processing solutions Static electricity Thin, black lines Occurs when a packet is opened quickly Backwards film Herringbone or tire- Film placed backwards in the mouth track pattern Scratched film White lines Soft emulsion removed from the film by a sharp object Slightly bent film Elongated roots Film may be bent to accommodate the patient’s anatomy, such as in the area of the anterior maxilla Severely bent film Black line Film bent too severely to accommodate patient Light leak Exposed area is black Accidental exposure of film to white light Fogged film Gray; lack of contrast Improper safelight, outdated films, improper film storage, contaminated solutions Overlapped images Overlapping of teeth Incorrect horizontal angulation contacts Foreshortened images Short teeth with blunted Too much vertical angulation roots Elongated images Long, distorted teeth Too little vertical angulation Cone-cut Unexposed area on film Central ray not in center of film Cervical burnout May appear as dental Radiolucent artifact seen in areas of different caries; radiolucent densities 8 IX. LOCALIZATION TECHNIQUES A. Buccal Object Rule 1. one film is exposed using proper technique and angulation 2. a second film is exposed after changing the direction of the x-ray beam a. when the structure seen in the second film appears to have moved in the same direction as the shift of the PID, the structure is positioned to the lingual b. when the structure seen in the second radiograph appears to have moved in the direction opposite the shift of the PID, the structure is positioned to the buccal “SLOB” RULE SAME LINGUAL; OPPOSITE BUCCAL B. Right Angle Technique 1. one film is exposed using proper technique and angulation 2. an occlusal film is exposed directing the central ray at a right angle (perpendicular) to the film 3. the occlusal film shows the object in the buccal-lingual and anterior-posterior relationships 4. this technique is primarily used for locating objects in the mandible 9 X. NORMAL ANATOMY BASICS – INTRAORAL FILMS MAXILLARY DESCRIPTION RADIOGRAPHIC LANDMARKS APPEARANCE Incisive foramen A hole in bone located at the midline Small ovoid radiolucency of the anterior portion of the hard between the roots of the palate maxillary central incisors Median palatal suture An immovable joint between the two Thin, radiolucent line between palatine processes of the maxilla the maxillary central incisors Nasal cavity Pear-shaped compartment of bone Large, radiolucent area above located superior to the maxilla the maxillary incisors Nasal septum Vertical bony wall or partition that Vertical, radiopaque partition divides the nasal cavity into the right that divides the nasal cavity and left nasal fossae Anterior nasal spine A sharp projection of the maxilla V-shaped radiopaque area located at the anterior and inferior located at the intersection of portion of the nasal cavity the floor of the nasal cavity and the nasal septum Maxillary sinus Paired compartments of bone located Radiolucent area above the within the maxilla located above the apices of the maxillary maxillary premolar and molar teeth posterior teeth Inverted “Y” The intersection of the maxillary sinus Radiopaque upside-down “Y” and the nasal cavity located above the maxillary canine Maxillary tuberosity A rounded prominence of bone that Radiopaque bulge distal to the extend posterior to the third molar third molar region region Hamulus A small, hook-like projection of bone Radiopaque hook-like located posterior to the maxillary projection posterior to the tuberosity region tuberosity Zygomatic process of A bony projection of the maxilla that J- or U-shaped radiopacity the maxilla articulates with the zygoma located superior to the maxillary first molar region Zygoma Cheek bone; composed of dense Diffuse, radiopaque band cortical bone extending posterior from the zygomatic process of the maxilla **may also see the outline of the nose on the radiographs in the maxillary anterior region 10 MANDIBULAR DESCRIPTION RADIOGRAPHIC LANDMARKS APPEARANCE Genial tubercles Tiny bumps of bone that serve as Ring-shaped radiopacity muscle attachment sites below the apices of the mandibular incisors Lingual foramen A hole in the bone located on the Small, radiolucent dot internal surface of the mandible near surrounded by the genial the midline tubercles Mental ridge A linear prominence of bone Thick, radiopaque band that extending from the premolar region to extends from the premolars to the midline the incisor region Mental fossa A scooped out, depressed area of bone A radiolucent area located located above the mental ridge above the mental ridge Mental foramen A hole in bone located on the external Small ovoid or round surface of the mandible in the region radiolucency in the apical of the mandibular premolars region of the mandibular premolars Mandibular canal A tube-like passageway through bone A radiolucent band outlined that travels the length of the mandible by radiopaque lines and appears below the apices of the mandibular molar teeth Internal oblique ridge A linear prominence of bone located A radiopaque band extending on the internal surface of the mandible downward from the ramus; that extends downward and forward may continue on as the from the ramus mylohyoid ridge External oblique ridge A linear prominence of bone located A radiopaque band extending on the external surface of the body of downward from the ramus; the mandible typically ends in the third molar region Submandibular fossa A scooped out, depressed area of bone A radiolucent area in the located on the internal surface of the mandibular molar region mandible below the mylohyoid ridge Coronoid process A marked prominence of bone on the A triangular radiopacity anterior ramus of the mandible superimposed over the maxillary tuberosity region; **only mandibular landmark to appear on maxillary films 11 XI. COMMON RESTORATIVE MATERIALS RESTORATIVE MATERIAL RADIOGRAPHIC APPEARANCE Amalgam Completely radiopaque amalgam overhangs amalgam fragments Gold restorations Completely radiopaque crown, bridges gold foil Stainless steel and chrome crowns Radiopaque, but not as dense as amalgam Do not appear to fit the tooth well; “see-through” areas Composite restorations Radiolucent to radiopaque Post and core restorations Seen in endodontically-treated teeth Core resembles the prepped portion of a tooth Post extends into the pulp canal Porcelain restorations Slightly radiopaque Porcelain-fused-to-metal crown The metal component is completely radiopaque; the porcelain component is slightly radiopaque Endodontic materials Gutta percha is slightly radiopaque to radiolucent Silver points are very radiopaque XII. EXTRAORAL FILMS, PANORAMIC ERRORS Bony Landmarks of the Mastoid process, styloid process, external auditory meatus, Maxilla glenoid fossa, articular eminence, maxillary tuberosity, orbit, And Surrounding Structures incisive canal, anterior nasal spine, nasal cavity, nasal septum, hard palate, maxillary sinus, zygomatic process of the maxilla, zygoma, hamulus Bony Landmarks of the Mandibular condyle, coronoid process, mandibular foramen, Mandible mandibular canal, mental foramen, mental ridge, mental And Surrounding Structures fossa, lingual foramen, genial tubercles, mylohyoid ridge, internal oblique ridge, external oblique ridge, angle of the mandible, hyoid bone Air Space Images seen on Panoramic Radiographs: Palatoglossal Air Space seen between the palate and tongue horizontal radiolucent band Nasopharyngeal Air Space refers to the portion of the pharynx posterior to the nasal cavity diagonal radiolucency Glossopharyngeal Air Space refers to the portion of the pharynx posterior to the tongue vertical radiolucent band 12 Frankfort plane: passes through the floor of the orbit and the external auditory meatus Midsagittal plane: divides the body into right and left sides Focal trough: three-dimensional curved zone in which structures are clearly demonstrated on a panoramic radiograph PANORAMIC ERRORS ERROR APPEARANCE Frankfort plane upwards Maxillary incisors appear blurred and magnified; reverse (chin up) smile line Frankfort plane down Mandibular incisors blurred; exaggerated smile line; (chin down) condyles may not be visible Teeth anterior to focal trough Anterior teeth appear skinny and out of focus Teeth posterior to focal trough Anterior teeth appear fat and out of focus Midsagittal plane not centered Unequal magnification; posterior teeth are larger on one (head turned) side than the other Position of the spine Cervical spine appears as a radiopacity in the center of the (patient slumped or slouched, ex: film scoliosis) Position of the tongue A dark radiolucent shadow obscures the apices of the (tongue not against hard palate) maxillary teeth Lead apron placed too high A radiopaque cone-shaped artifact obscuring the mandible Ghost images (earrings, found on the opposite side of the film eyeglasses, necklaces, partial higher than its actual counterpart dentures, orthodontic retainers, indistinct, distorted than the actual counterpart hearing aids, napkin chains) 13