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X-Ray Film: Types and Components

As per White and Pharoah's Oral Radiology: Principles and Interpretation

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INTRODUCTION

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TYPES OF X-RAY FILM

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Type 1: Direct Exposure Film (Non-Screen Film)

• This film is sensitive primarily to X-ray photons themselves.
• It is exposed directly by the X-ray beam without the use of intensifying screens.
• All intraoral dental films are direct exposure films.
• Provides higher resolution images compared to screen-film combinations.
• Used when fine detail is required - e.g., detection of incipient (early) caries or early periapical disease.
• The trade-off is that it requires more radiation to produce an adequate image compared to screen film.

Viva key point: "Direct exposure film is used for intraoral examinations because it provides higher resolution, which is needed for detecting subtle changes like incipient caries."

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Type 2: Indirect Exposure Film (Screen Film)

• This film is sensitive primarily to visible light photons, not to X-rays directly.
• It is used in combination with intensifying screens housed inside a cassette.
• The intensifying screens absorb X-ray photons and re-emit them as visible light, which then exposes the film - hence "indirect."
• Used for extraoral projections such as:
  • Panoramic radiographs (OPG)
  • Cephalometric radiographs
  • Skull films
  • TMJ views
• The advantage is that intensifying screens greatly amplify the effect of X-rays, requiring much less radiation dose for the patient.
• The disadvantage is lower resolution compared to direct exposure intraoral film.

Viva key point: "Screen film is sensitive to light, not x-rays. The intensifying screens convert X-ray energy to light, which exposes the film. This reduces patient dose but decreases image resolution."

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COMPONENTS OF X-RAY FILM

1. Emulsion
2. Base

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Layer 1: Base

• The foundation/support of the film.
• Made of polyester (polyethylene terephthalate - PET) - a plastic material.
• Functions:
  • Provides mechanical support for the emulsion.
  • Must be flexible enough for easy handling (especially intraoral film).
  • Must withstand processing solutions (developer, fixer) without distortion.
  • Is uniformly translucent and casts no pattern on the radiograph.
• Thickness: approximately 0.2 mm.
• Modern bases replaced the older cellulose acetate/cellulose nitrate bases (which were flammable - "safety film" emerged as a result).

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Layer 2: Substratum (Adhesive Layer / Subcoat)

• A thin adhesive layer between the base and the emulsion.
• Also called the "tie coat" or subcoating.
• Its sole function is to bond the emulsion firmly to the base so it does not peel off during processing.

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Layer 3: Emulsion (THE MOST IMPORTANT LAYER)

A. Silver Halide Grains (the sensitive component)

• Composed primarily of silver bromide (AgBr) crystals - with small amounts of silver iodide.
• The grains are flat, tabular crystals with a mean diameter of approximately 1.8 µm (in modern films like INSIGHT and Ultra-speed by Carestream Dental).
• Tabular grains are oriented parallel to the film surface - this maximizes their surface area for X-ray/light interaction and increases sensitivity (speed).
• These grains are sensitive to both X-radiation and visible light.
• When struck by X-ray photons or light, silver bromide undergoes photochemical change to form a latent image (invisible image).
• During processing, the latent image is converted to a visible image (metallic silver deposits).

B. Gelatin Matrix (the vehicle/suspending medium)

• A gelatinous matrix (derived mostly from cattle bone collagen) in which the silver halide crystals are suspended.
• Why gelatin?
  • Keeps silver halide grains well dispersed and prevents clumping.
  • Processing solutions (developer and fixer) can penetrate it rapidly without destroying its strength.
  • Remains stable and does not degrade the emulsion.
  • Maintains permanence of the processed film.

Emulsion Facts:

• Emulsion thickness: usually no more than 0.0005 inches (~12.7 µm) - a thicker emulsion would block light from reaching deeper layers.
• Intraoral film is double-emulsion: emulsion is coated on both sides of the base (see Layer 4 below).
• Double emulsion means less radiation is required because two layers of silver halide crystals are available to capture X-ray energy.

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Layer 4: Supercoat (Overcoat / Protective Layer)

• A thin, transparent gelatin coating applied over the emulsion on the outermost surface.
• Functions:
  • Protects the emulsion from scratches, pressure marks, and physical damage.
  • Protects against fingerprints and chemical contamination during handling.
  • Does NOT affect image formation.

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COMPLETE FILM CROSS-SECTION (from outside to center)

Supercoat (protective overcoat)
    ↓
Emulsion (silver halide + gelatin)  [Side 1]
    ↓
Substratum (adhesive layer)
    ↓
BASE (polyester)  ← center
    ↓
Substratum (adhesive layer)
    ↓
Emulsion (silver halide + gelatin)  [Side 2]
    ↓
Supercoat (protective overcoat)

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INTRAORAL FILM - ADDITIONAL DETAILS

1. The film itself
2. A black paper wrapper (light-proof)
3. A lead foil (to absorb back-scatter radiation and protect the film from secondary radiation from behind)
4. An outer plastic or paper cover (waterproof, light-proof)

Film Speeds (ISO/ADA classification):

• D-speed (Ultra-speed) - older standard
• E-speed - faster, less dose
• F-speed (INSIGHT) - fastest currently available intraoral film; tabular grain technology; requires the least radiation dose

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FILM SENSITIVITY - LATENT IMAGE FORMATION

1. Photons ionize the bromide ions (Br⁻ → Br + e⁻)
2. Free electrons migrate to sensitivity specks (crystal imperfections/impurities) on the crystal surface.
3. Silver ions (Ag⁺) migrate to sensitivity specks and are reduced to metallic silver (Ag⁰) by the trapped electrons.
4. This cluster of metallic silver atoms forms the latent image at the sensitivity speck.
5. Development amplifies this latent image to a visible black silver deposit.

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SUMMARY TABLE FOR VIVA

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HIGH-YIELD VIVA QUESTIONS & ANSWERS

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Latent Image Formation and Darkroom Processing

As per White and Pharoah's Oral Radiology: Principles and Interpretation

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PART 1: LATENT IMAGE FORMATION

Definition

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The Grotthuss-Draper Law (Photochemical Basis)

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Mechanism of Latent Image Formation (Step-by-Step)

Step 1: X-ray photon strikes the silver halide crystal

• X-ray photons from the remnant beam (that passed through the patient) strike silver bromide (AgBr) crystals in the emulsion.
• The energy of the photon is transferred to the crystal.

Step 2: Ionization of bromide ions

• The energy ejects electrons from bromide ions (Br⁻):

  Br⁻ → Br⁰ + e⁻

• Free electrons are liberated within the crystal lattice.

Step 3: Electrons migrate to sensitivity specks

• The freed electrons migrate through the crystal lattice toward sensitivity specks - these are crystal imperfections/impurities (commonly silver sulfide, Ag₂S) located on the surface of the silver halide crystal.
• Sensitivity specks act as electron traps.

Step 4: Silver ions are reduced at sensitivity specks

• Positively charged silver ions (Ag⁺) within the crystal are attracted to the negatively charged sensitivity speck.
• At the sensitivity speck, Ag⁺ combines with the trapped electron:

  Ag⁺ + e⁻ → Ag⁰ (metallic silver)

• A cluster of neutral metallic silver atoms (Ag⁰) accumulates at the sensitivity speck.

Step 5: Latent image center formed

• This growing cluster of metallic silver atoms at the sensitivity speck constitutes the latent image center (also called a developable silver speck).
• Crystals that have received sufficient exposure have latent image centers; unexposed crystals do not.
• At this stage, the image is completely invisible - hence the term "latent" (hidden).

Viva key point: "The latent image is an invisible collection of metallic silver atoms at sensitivity specks on exposed silver halide crystals. It requires development to become visible."

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Summary Equation:

X-ray/light photon + AgBr → Ag⁰ (at sensitivity speck) + Br⁻ released
(latent image center formed on exposed crystals)
Unexposed crystals = no latent image centers = remain as AgBr

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Why is the Latent Image Invisible?

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PART 2: DARKROOM AND FILM PROCESSING

Purpose of Processing

1. Immerse exposed film in developer
2. Rinse in water bath
3. Immerse film in fixer
4. Wash film in water bath to remove fixer
5. Dry film and mount for viewing

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THE DARKROOM

• A light-tight room where film is unwrapped and processed safely.
• Illuminated only by a safelight - a light source filtered to wavelengths that do NOT expose film.
  • Standard intraoral film (blue-sensitive): use a red/orange safelight (Kodak GBX-2 or Wratten 6B filter)
  • Rare-earth screen film (green-sensitive): use a dark red safelight
• The safelight must be at least 4 feet (1.2 m) from the work surface.
• Room must be checked for light leaks (penny test / coin test).

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MANUAL PROCESSING - 9 STEPS (White & Pharoah)

Step 1: Replenish Solutions

• Check and replenish developer and fixer levels.
• Ensure solutions cover films on the top clips of film hangers.
• Regular replenishment maintains chemical activity.

Step 2: Stir Solutions

• Stir both developer and fixer with separate paddles to:
  • Mix the chemicals
  • Equalize temperature throughout the tanks
• Use a separate paddle for each solution to prevent cross-contamination.
• Label paddles clearly (one for developer, one for fixer).

Step 3: Check Temperature

• The developer temperature is critical - it determines development time.
• Standard manual processing: 68°F (20°C)
• Use time-temperature chart:
  • At 68°F: 4.5-5 minutes development
  • Higher temperature = shorter development time (and vice versa)

Step 4: Set Timer

• Set an accurate darkroom timer according to the time-temperature chart.
• Do NOT use guesswork - under- or over-development ruins the film.

Step 5: Unwrap Films and Load onto Hangers

• Turn off white lights; use only safelight.
• Unwrap films and attach to film hangers (stainless steel clips).
• Handle films only by their edges to prevent fingerprint artifacts.

Step 6: DEVELOP (MOST IMPORTANT STEP)

• Immerse film hangers into the developer solution.
• Gently agitate (lift and lower hangers) at the beginning and every 30 seconds to eliminate air bubbles and ensure fresh developer reaches all film surfaces.
• Developer converts silver bromide crystals with latent image centers into black, metallic silver grains (visible image).
• Crystals without latent image centers are unaffected at this stage.
• Development time: typically 4.5-5 minutes at 68°F (20°C).

• Developer is an alkaline reducing agent (pH ~10-11).
• The developing agents (reducers) donate electrons to silver ions:

  Ag⁺ + e⁻ → Ag⁰ (black metallic silver deposit)

• The neutral silver atoms at the latent image center act as a catalyst - they initiate the conversion of ALL silver ions in the entire crystal into one large grain of metallic silver.
• The bromine dissolves into the developer solution.
• Result: areas of greater X-ray exposure → more developed crystals → darker (more black) areas on the film.

Hydroquinone - produces the blacks and contrast (slow-acting); sensitive to temperature. Elon/Metol/Phenidone - produces the grays and detail (fast-acting); active at lower temperatures. Together they show superadditivity (synergism) - they work better together than the sum of their individual effects.

Step 7: RINSE

• After development, remove films and rinse in a water bath for 30 seconds with continuous gentle agitation.
• At this point, the emulsion has swollen and is saturated with developer.
• Rinsing:
  • Dilutes and removes developer from the film surface.
  • Slows the development process (stops development).
  • Removes the alkali activator, preventing it from neutralizing the acid fixer.
• Note: Rinsing is used in manual processing but is NOT typically used in most automatic processors (which use a squeeze roller system instead).

Step 8: FIX

• Immerse films into the fixer solution.
• Fixing time: at least twice the clearing time (typically 10 minutes in manual processing, or until film appears clear + same amount of time more).
• Fixer removes all unexposed, undeveloped silver bromide crystals from the emulsion - crystals that did NOT have latent image centers.
• This leaves the film clear (transparent) in areas that received more X-rays (less dense tissues) and black (opaque) in areas that received fewer X-rays (dense tissues like bone/enamel blocked X-rays).
• After fixing, the film can be briefly viewed under white light during the process (after minimum fixing time) and then returned to complete fixation.

Viva key point: "The fixer clears away all unexposed silver halide crystals, making those areas transparent. The black silver deposits from development remain, giving the final radiographic image."

Step 9: FINAL WASH

• After fixing is complete, wash films in running water for at least 20 minutes (some sources say 20-30 minutes).
• Removes residual fixer chemicals (especially thiosulfates) from the emulsion.
• If fixer is not completely removed:
  • Thiosulfate reacts with residual silver to form silver sulfide - a brownish-yellow stain that appears over time (archival failure).
  • Radiograph discolors and becomes diagnostically useless.

Step 10: DRY

• Remove films from water and allow to dry completely before mounting.
• Can be done by:
  • Air drying at room temperature (hang on rack or in drying cabinet).
  • Warm air drying cabinet (faster).
• Do NOT wipe films with cloth - scratches the emulsion.
• Once dry, films are mounted on a film mount for viewing on the viewbox.

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WHAT HAPPENS IN EACH STEP - VISUAL SUMMARY

EXPOSED FILM
   Exposed crystals → have latent image (Ag⁰ specks)
   Unexposed crystals → no latent image (pure AgBr)
        ↓
   DEVELOPER
   Exposed crystals → Ag⁰ specks catalyze full reduction → BLACK metallic silver
   Unexposed crystals → no change (protected by restrainer)
        ↓
   RINSE
   Removes developer chemicals from emulsion
        ↓
   FIXER
   Black Ag⁰ deposits → REMAIN (the image)
   Unexposed AgBr → DISSOLVED and removed → area becomes CLEAR
        ↓
   WASH
   Removes all residual fixer from emulsion
        ↓
   DRY → PERMANENT VISIBLE RADIOGRAPH

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AUTOMATIC PROCESSING

• Use higher temperature (~82°F/28°C) and stronger chemicals for rapid development.
• Process is completed in 4-6 minutes total.
• Film is transported through developer, fixer, wash, and dryer compartments by roller systems.
• The top rollers at the crossover point between developer and fixer tanks squeeze out developing solution, minimizing carryover of developer into the fixer tank and maintaining chemical uniformity.
• No rinse step is needed - squeegee rollers remove excess developer.
• The fixer contains an additional hardener to help the emulsion withstand transport rollers.

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PROCESSING ERRORS AND THEIR CAUSES

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TIME-TEMPERATURE CHART FOR MANUAL DEVELOPMENT (Kodak Standard)

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HIGH-YIELD VIVA Q&A

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Types of Radiation Produced in the X-Ray Tube

As per White and Pharoah's Oral Radiology: Principles and Interpretation

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INTRODUCTION

1. Bremsstrahlung Radiation (General/Braking Radiation) - the primary source
2. Characteristic Radiation - a minor contribution

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TYPE 1: BREMSSTRAHLUNG RADIATION

Name & Meaning

• "Bremsstrahlung" is a German word meaning "braking radiation" or "slowing-down radiation".
• Also called general radiation or white radiation.

How it is Produced

Mechanism A - Near Miss (Most Common)

• Most high-speed electrons pass near (but do not hit) tungsten nuclei (Fig. 1.12A in White & Pharoah).
• The electron is attracted toward the positively charged nucleus.
• Its path is deflected/bent toward the nucleus and it loses velocity (decelerates).
• This deceleration causes the electron to lose kinetic energy.
• This lost kinetic energy is emitted as an X-ray photon.
• The closer the electron passes to the nucleus, the greater the electrostatic attraction, the greater the deceleration, and the higher the energy of the photon emitted.
• Since electrons pass at varying distances from nuclei, photons of many different energies are produced.

Mechanism B - Direct Hit (Less Common)

• Occasionally, an electron directly hits the nucleus of a tungsten atom (Fig. 1.12B).
• All of the kinetic energy of that electron is transformed into a single X-ray photon in one interaction.
• The energy of this photon (in keV) equals the voltage applied across the X-ray tube at that instant.
• This produces the highest-energy photon possible at that kVp setting.

Key Characteristics of Bremsstrahlung

Why a Continuous Spectrum?

Viva key point: "A dental X-ray machine operating at 70 kVp produces a continuous spectrum of Bremsstrahlung photons ranging from near-zero up to a maximum of 70 keV. The vast preponderance of radiation from an X-ray tube is Bremsstrahlung."

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TYPE 2: CHARACTERISTIC RADIATION

Name & Meaning

• Called "characteristic" because the photon energies produced are specific (characteristic) to the target material (tungsten in this case).
• Also called characteristic X-rays or fluorescence radiation.

How it is Produced

1. A high-speed electron from the filament strikes a tungsten atom with enough energy to eject an inner-shell electron (from the K or L shell) out of the atom entirely.
2. This creates a vacancy (void) in the inner orbital.
3. An electron from an outer orbital is quickly attracted inward to fill the vacancy.
4. As it drops to the lower energy level, it releases the difference in binding energy between the two orbitals as a photon of X-radiation.
5. The photon energy = difference in binding energies of the two electron shells involved.

Key Characteristics of Characteristic Radiation

Viva key point: "Characteristic radiation is produced when an incident electron ejects an inner-shell electron from tungsten. An outer orbital electron fills the void, releasing a photon equal to the energy difference between the two orbitals. The energies are discrete (not continuous) because they represent fixed differences between specific electron orbital energy levels."

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COMPARISON TABLE

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THE X-RAY SPECTRUM (Fig. 1.13, White & Pharoah)

• A large continuous Bremsstrahlung curve (blue in the figure) - ranging from near-zero up to 70 keV maximum
• Small sharp peaks superimposed on the curve = Characteristic radiation peaks at discrete energy values

Intensity
    |         Bremsstrahlung
    |        /‾‾‾‾‾‾\
    |       /   char. \  (small peaks)
    |      / ↑↑       \
    |     /            \
    |____/_______________\_______
    0    20   40   60   70     keV (Photon Energy)
                         ↑
                    Max = kVp value

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HIGH-YIELD VIVA QUESTIONS & ANSWERS

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Voltage (kVp) and Other Exposure Controls at the X-Ray Machine Control Panel

As per White and Pharoah's Oral Radiology: Principles and Interpretation

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THE THREE EXPOSURE CONTROLS AT THE CONTROL PANEL

1. kVp - Kilovoltage Peak (tube voltage)
2. mA - Milliamperage (tube current)
3. Exposure Time (in seconds or pulses)

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1. kVp - KILOVOLTAGE PEAK (TUBE VOLTAGE)

Definition

• kVp is the peak voltage applied across the X-ray tube between the cathode (filament) and the anode (target).
• It is measured in kilovolts peak (kVp).

What it Controls

• kVp determines the quality (penetrating power / energy) of the X-ray beam.
• Higher kVp = more energetic photons = beam penetrates tissue more easily.
• Higher kVp also increases the quantity (number) of X-ray photons produced.
• kVp is the factor that sets the maximum energy of Bremsstrahlung photons:
  • At 70 kVp → max photon energy = 70 keV

Standard Settings (White & Pharoah)

• In most intraoral dental X-ray units, the kVp is fixed by the manufacturer - the operator cannot change it.
• The standard/typical fixed kVp for dental intraoral radiography = 70 kVp
• Acceptable range for dental radiography: 60 - 90 kVp

Effect of Changing kVp on the Radiograph

Viva key point (White & Pharoah): "The kVp is fixed, usually at 70 kVp, and the exposure time is varied to account for patient size and location of the area of interest in the mouth."

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2. mA - MILLIAMPERAGE (TUBE CURRENT)

Definition

• mA is the current flowing through the X-ray tube - i.e., the number of electrons flowing from cathode to anode per second.
• Measured in milliamperes (mA).

What it Controls

• mA controls the quantity (number) of X-ray photons produced per unit time.
• Higher mA = more electrons from the filament = more X-ray photons = greater beam intensity.
• mA does NOT affect photon energy or beam quality - only quantity.

Standard Dental Settings

• Dental intraoral units typically operate at 7-15 mA.
• In most units, the mA setting is fixed (not adjustable by the operator).
• White & Pharoah: "If the mA setting is variable, the operator should select the highest mA value available and operate at this setting" - because a higher mA allows the shortest possible exposure time, reducing patient movement blur and improving image sharpness.

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3. EXPOSURE TIME

Definition

• The duration for which X-rays are produced and the film is exposed.
• Measured in seconds or pulses (impulses).

What it Controls

• Exposure time determines the total quantity of radiation reaching the film.
• It is the most variable and most important factor the operator adjusts in dental radiography.

Time - Pulse Conversion

• Some dental X-ray units display time as number of pulses instead of seconds.
• Conversion: Number of pulses ÷ 60 = time in seconds
  • Example: 30 pulses ÷ 60 = 0.5 seconds
• Other units have preset times for different anatomic regions (anterior, posterior, upper, lower jaw).

Typical Exposure Times for Intraoral Radiography (at 70 kVp, 7-10 mA)

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MILLIAMPERE-SECONDS (mAs) - COMBINED FACTOR

• mAs = mA × Time (seconds)
• mAs represents the total quantity of X-radiation produced.
• Doubling the mA and halving the time gives the same mAs and same film density - this is the reciprocity law.
• White & Pharoah: "Exposure time is the most crucial factor in influencing diagnostic quality."

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THE RADIOGRAPHIC EXPOSURE CHART

• All operators use appropriate exposure factors consistently.
• Patient doses are optimized (ALARA principle).
• Radiographs are neither overexposed (too dark) nor underexposed (too light).

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SUMMARY - PRACTICAL SETUP AT THE CONTROL PANEL

The operator typically adjusts ONLY the exposure time. kVp and mA are fixed in most intraoral units.

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EFFECT OF EACH FACTOR ON THE RADIOGRAPH

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HIGH-YIELD VIVA QUESTIONS & ANSWERS

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Tube Head Angulation for Periapical Radiographs

As per White and Pharoah's Oral Radiology: Principles and Interpretation

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INTRODUCTION

1. Vertical Angulation - up-and-down tilt of the tube head
2. Horizontal Angulation - side-to-side angulation of the tube head

• The technique used (Paralleling vs. Bisecting angle)
• The region being radiographed (incisors, canines, premolars, molars)
• Whether the tooth is in the maxilla or mandible

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PART A: TYPES OF ANGULATION

1. Vertical Angulation

• Refers to the up-and-down tilt of the PID/tube head in the vertical plane.
• Measured in degrees, registered on the outside of the tube head.
• Expressed as:
  • Positive (+) vertical angulation = tube head tilted downward toward the floor (beam directed downward) - used for maxillary teeth
  • Negative (−) vertical angulation = tube head tilted upward toward the ceiling (beam directed upward) - used for mandibular teeth
• Zero (0°) = tube head perfectly horizontal (beam parallel to the floor)

Effect of incorrect vertical angulation:

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2. Horizontal Angulation

• Refers to the side-to-side angulation of the tube head in the horizontal plane.
• The central ray must be directed through the contact points between adjacent teeth.
• If not aligned correctly: overlapping of proximal surfaces occurs (contacts are not open/separated on the image).

Rules for horizontal angulation:

• The edge of the beam collimator (cone) should be parallel to the buccal surfaces of the teeth being examined.
• The central ray passes perpendicular to the receptor in the horizontal plane (paralleling technique).
• For the bisecting technique without a beam-aiming device: angle horizontally to direct the beam through interproximal contacts of the region.

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PART B: ANGULATION BY TECHNIQUE

TECHNIQUE 1: PARALLELING TECHNIQUE (Long-Cone Technique)

• The film/receptor is placed parallel to the long axis of the tooth.
• The central ray is directed perpendicular to BOTH the receptor AND the long axis of the tooth.
• A receptor-holding device with an external aiming ring (e.g., Rinn XCP, DENTSPLY) is used to align the tube head.
• Vertical angulation: determined by the aiming ring - tube is positioned so the beam is at right angles (90°) to the receptor.
• Because the tooth-film distance is greater (film away from the tooth), a long cone (open-ended, 16 inches / 40 cm) is used to reduce beam divergence and minimize geometric distortion.
• White & Pharoah: "The aiming cylinder of the X-ray machine is aligned with the aiming ring in both vertical and horizontal planes."

Advantages of paralleling technique:

• More accurate image (no elongation or foreshortening)
• Better reproducibility
• Less geometric distortion
• Preferred technique in clinical practice

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TECHNIQUE 2: BISECTING ANGLE TECHNIQUE (Short-Cone Technique)

Principle:

1. An imaginary line is drawn that bisects the angle formed between the long axis of the tooth and the plane of the receptor/film.
2. The central ray is directed perpendicular to this imaginary bisector.
3. This theoretically produces an image the same length as the actual tooth.

How to find the bisector:

• The receptor is placed as close to the tooth as possible (often touching the palate/floor of mouth).
• The angle between tooth long axis and receptor is bisected.
• The tube is then angled perpendicular to that bisector.

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PART C: ANGULATION TABLE FOR BISECTING ANGLE TECHNIQUE

(TABLE 7.1 - White and Pharoah, Chapter 7)

Standard North American Settings (most commonly tested):

(+) = tube tilted downward (maxilla); (−) = tube tilted upward (mandible)

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Indian Settings (as per Dr. Freny Karjodkar - cited in White & Pharoah):

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Why do the angles differ by region?

• Maxillary anterior teeth (incisors/canines) are more vertically inclined and the palatal vault is deep → needs steeper positive angulation (+40 to +45°).
• Maxillary posterior teeth (molars) are more horizontally inclined and lie lower → needs less angulation (+20°).
• Mandibular teeth are radiographed with negative (upward) angulation because the beam must come from below to be perpendicular to the bisector; mandibular teeth are angled slightly lingually.
• Molars (both jaws) need the least angulation because their roots are more horizontally positioned.

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PART D: REGION-BY-REGION GUIDE (PARALLELING TECHNIQUE)

Maxillary Periapical Projections:

Mandibular Periapical Projections:

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PART E: SPECIAL ANGULATION SITUATIONS

Multi-rooted Teeth - Separating Roots

Endodontic Periapical

• Normal vertical and horizontal angulation is used.
• Special file-holding devices (endodontic film holders) allow files to remain in canals during exposure.
• Sometimes a second horizontal shift is done to separate canals (SLOB/Clark's rule).

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PART F: ERRORS DUE TO WRONG ANGULATION

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SUMMARY TABLE (Most Important for Viva)

Memory trick: Maxilla - "40-45-30-20" (I, C, PM, M) | Mandible - "15-20-10-5" all negative

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HIGH-YIELD VIVA Q&A

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X-Ray Film Faults (Radiographic Errors)

As per White and Pharoah's Oral Radiology: Principles and Interpretation

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INTRODUCTION

• Loss of diagnostic information
• Loss of professional and patient time
• Need for retake - which means additional radiation dose to the patient

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CLASSIFICATION OF RADIOGRAPHIC FAULTS

RADIOGRAPHIC FAULTS
├── 1. Density Errors (Too Light / Too Dark / Fog)
├── 2. Contrast Errors
├── 3. Geometric / Positioning Errors (Distortion)
└── 4. Handling & Artifact Errors (Film damage, spots, stains)

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CATEGORY 1: DENSITY ERRORS

A. LIGHT RADIOGRAPH (Fig. 5.31)

• Insufficient mA
• Insufficient kVp
• Insufficient exposure time
• Film-source (focal spot-film) distance too long
• Film packet reversed in mouth (lead foil faces tube - herringbone/tire track pattern)

• Underdevelopment - temperature too low; time too short; thermometer inaccurate
• Depleted (exhausted) developer solution
• Diluted or contaminated developer
• Excessive fixation (film left in fixer for hours - fixer bleaches the image)

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B. DARK RADIOGRAPH (Fig. 5.32)

• Excessive mA
• Excessive kVp
• Excessive exposure time
• Film-source distance too short

• Overdevelopment - temperature too high; development time too long
• Developer concentration too high
• Accidental exposure to light (white light leak)
• Improper safelighting (safelight too bright, too close, or wrong filter)

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C. FILM FOG (Fig. 5.34)

• Improper safelighting - wrong filter, too bright, or placed too close to work area
• Light leaks in the darkroom
• Accidental exposure to light during unwrapping or processing
• Storage problems: films stored at too high a temperature, without radiation shielding, or past their expiration date
• Scatter/secondary radiation fogging the film
• Developer contamination (fixer in developer)
• Excessive kVp (can contribute to fog appearance)

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CATEGORY 2: CONTRAST ERRORS

INSUFFICIENT CONTRAST (Fig. 5.33)

• Underdevelopment
• Underexposure
• Excessive kVp - high kVp reduces contrast (produces long-scale, low-contrast image)
• Excessive film fog
• Developer exhausted or diluted

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CATEGORY 3: GEOMETRIC / POSITIONING ERRORS (Distortion)

A. FORESHORTENING

• In the bisecting angle technique: too much positive vertical angulation (over-angulation)
• The beam "compresses" the image of the tooth

White & Pharoah (Fig. 6.5): "Foreshortening results when the central ray is perpendicular to the image receptor but the object is not parallel with the image receptor."

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B. ELONGATION

• In the bisecting angle technique: insufficient vertical angulation (under-angulation)
• The beam "stretches" the image

White & Pharoah (Fig. 6.6): "Elongation results when the central ray is perpendicular to the object but not to the image receptor."

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C. OVERLAPPING (Horizontal Angulation Error)

• Beam is not perpendicular to the receptor in the horizontal plane
• Contacts cannot be assessed for interproximal caries

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D. CONE CUT (Partial Image / Clear Unexposed Area)

• Part of the film was outside the beam field entirely
• That portion receives no radiation → appears clear (white) on the developed film

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E. BLURRED / UNSHARP IMAGE

• Patient movement during exposure
• Film/receptor movement during exposure
• Long exposure time (increases chance of movement)
• Excessive object-film distance without corresponding long cone (geometric unsharpness)
• Movement of the tube head during exposure

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F. MAGNIFICATION (Size Distortion)

• Increased object-to-film distance (without increasing focus-film distance)
• Short focus-film distance (short cone)
• All radiographic images are slightly magnified; the goal is to minimize this

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G. DOUBLE EXPOSURE

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CATEGORY 4: FILM HANDLING AND ARTIFACT ERRORS

A. FILM REVERSED IN MOUTH (Herringbone / Tire Track Pattern)

• Lead foil partially absorbs the beam (hence light image)
• The embossed diamond/herringbone pattern of the lead foil is imprinted on the image

This is one of the most recognizable film faults - easily identified in a viva by the characteristic pattern.

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B. FINGERPRINT MARKS

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C. DEVELOPER SPLASH MARKS (Dark Spots/Streaks)

• Pre-exposed emulsion develops faster at those spots → dark marks

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D. FIXER SPLASH MARKS (Clear/White Spots)

• Fixer removes emulsion at those spots before it can develop → clear (white) areas

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E. RETICULATION (Cracked Emulsion)

• Sudden temperature change causes the gelatin to contract/expand rapidly → cracking

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F. PRESSURE MARKS / CRIMP MARKS

• Bending the film sharply during placement in the mouth (crescent-shaped black marks)
• Pressing too hard on the film packet

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G. STATIC ELECTRICITY MARKS

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H. SCRATCHES

• Rough handling of wet emulsion during processing
• Dirty or damaged rollers in automatic processor
• Nails/instruments touching the film surface

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I. YELLOW/BROWN STAINS

• Inadequate final washing - residual thiosulfate (fixer) remains in emulsion
• Exhausted fixer used for processing
• Over time, thiosulfate reacts with silver deposits → silver sulfide (brown-yellow stain)
• Renders the radiograph diagnostically useless eventually

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J. RADIOGRAPHIC NOISE

1. Radiographic mottle - uneven density from the physical structure of the film or intensifying screens (structural granularity)
2. Radiographic artifacts - defects from film handling errors (fingerprints, bends) or processing errors (splashes, scratches)

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SUMMARY TABLE - ALL FAULTS AT A GLANCE

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QUALITY ASSURANCE TO PREVENT FAULTS (White & Pharoah)

• Maintain a retake log - record all errors that require re-exposure; review weekly to identify recurring problems.
• Post a radiographic exposure chart at the control panel with correct kVp, mA, and time for each region.
• Check solution levels and temperature daily before processing.
• Stir developer and fixer with separate paddles before use.
• Check darkroom for light leaks regularly (coin/penny test).
• Replace processing solutions on schedule to prevent depletion.

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HIGH-YIELD VIVA Q&A

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Dosimetry

As per White and Pharoah's Oral Radiology: Principles and Interpretation

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DEFINITION

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RADIATION QUANTITIES AND UNITS

(TABLE 1.4 - White and Pharoah)

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1. EXPOSURE

• Exposure applies only to X-rays and gamma rays (not other radiation types).
• It applies only to air as the medium (not tissue).
• It tells us how much ionization the beam can produce, but does NOT directly measure energy absorbed by the patient.

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2. AIR KERMA (Kinetic Energy Released in Matter)

• KERMA = Kinetic Energy Released per unit MAss
• More precise than "Exposure" for characterizing the X-ray beam in air.
• Used in modern radiation measurements instead of the Roentgen.

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3. ABSORBED DOSE

• Absorbed dose varies with:
  • Type and energy of radiation
  • Type of matter absorbing the energy
• It is a physical quantity - it does not account for the biological harm of different radiation types.

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4. EQUIVALENT DOSE (Radiation-Weighted Dose)

Why is it needed?

• Different types of radiation cause different amounts of biological damage for the same absorbed dose.
• Alpha particles (high LET) are far more damaging than X-rays (low LET) for the same amount of energy deposited.
• Equivalent dose corrects for this using a Radiation Weighting Factor (W_R).

Formula:

H_T = W_R × Absorbed Dose (Gy)

Radiation Weighting Factors (W_R) per White & Pharoah:

• For dental X-rays (photons): W_R = 1, so 1 Gy of X-rays = 1 Sv
• For alpha particles: 1 Gy = 20 Sv (20× more biologically damaging)

White & Pharoah: "Deposition of 1 Gy of alpha particles causes much more biologic damage than 1 Gy of X-ray photons."

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5. EFFECTIVE DOSE

Why is it needed?

• Different tissues have different radiosensitivities - the gonads and bone marrow are much more sensitive than muscle or skin.
• When only some tissues are exposed (as in dental radiography), effective dose allows fair comparison of risk with other exposures (e.g., chest X-ray) where different tissues are irradiated.

Formula:

E = Σ (W_T × H_T)

• W_T = Tissue weighting factor (radiosensitivity of that tissue)
• H_T = Equivalent dose to that tissue

Tissue Weighting Factors (W_T) - selected examples:

Salivary glands, bone surface, and skin are the most relevant tissues in dental radiography and have low W_T values (0.01) - meaning dental X-rays carry relatively low risk.

• Effective dose is used to:
  • Compare risk across different radiographic procedures
  • Set radiation dose limits
  • Make decisions about radiation protection

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6. RADIOACTIVITY

• Not directly relevant to diagnostic dental radiography but included in dosimetry tables.

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COMPLETE SUMMARY TABLE (Table 1.4 - White & Pharoah)

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RADIATION DOSE LIMITS (TABLE 3.4 - White & Pharoah)

Occupational Exposure (Dental Professionals/Radiographers):

Public Exposure (Patients):

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BIOLOGIC EFFECTS OF RADIATION (Related to Dosimetry)

A. STOCHASTIC EFFECTS

White & Pharoah: "Diagnostic radiation doses place the patient at risk for stochastic effects but not deterministic effects."

B. DETERMINISTIC EFFECTS

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COMPARISON OF DENTAL RADIOGRAPH DOSES

Dental radiographic doses are very small - a full mouth series equals roughly 4 days of natural background radiation.

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ALARA PRINCIPLE

"As Low As Reasonably Achievable"

• Every exposure should be justified - benefit must outweigh risk.
• Dose should be kept as low as possible without sacrificing diagnostic quality.
• Achieved through: fast films (F-speed), rectangular collimation, lead aprons, correct technique, and selecting radiographs based on clinical need.

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HIGH-YIELD VIVA Q&A

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Clinical Indications of Intraoral Dental Radiographs

As per White and Pharoah's Oral Radiology: Principles and Interpretation

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INTRODUCTION

1. Periapical (PA) radiographs - show the entire length of the tooth and surrounding bone
2. Bitewing (BW) radiographs - show only the crowns of teeth and adjacent alveolar crests
3. Occlusal radiographs - show a larger area of teeth and bone than periapical images

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PART 1: PERIAPICAL RADIOGRAPHS

What They Show

• The entire length of the tooth - from crown tip to root apex
• The surrounding alveolar bone and periodontal ligament space
• The periapical region (tissue around the root apex)

Clinical Indications (Box 7.2 - White & Pharoah)

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1. Assess Extent of Dental Caries

• Detect caries that cannot be seen clinically - especially proximal (interproximal) caries that are hidden between teeth.
• Evaluate the depth of caries relative to the pulp - important for treatment planning (restoration vs. pulp therapy).
• Detect recurrent (secondary) caries under existing restorations.
• Identify cervical caries at the gingival margin.

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2. Detect Presence and Assess Extent of Periapical Inflammation

• Diagnose periapical abscesses, periapical granulomas, and radicular cysts - all appear as radiolucencies at the root apex.
• Monitor healing of periapical lesions after root canal treatment.
• Differentiate between vital and non-vital teeth when periapical changes are present.

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3. Evaluate Consequences of Traumatic Injuries

• Assess tooth fractures (crown, root, or alveolar bone fractures).
• Detect tooth displacement - intrusion, extrusion, lateral luxation, avulsion.
• Evaluate alveolar bone fractures following trauma.
• Monitor root resorption that may develop after traumatic injury.
• Assess pulp canal obliteration following trauma.

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4. Assess Periodontal Bone Loss

• Evaluate the level and pattern of alveolar bone loss - horizontal vs. vertical/angular bone loss.
• Identify furcation involvement in multi-rooted teeth.
• Detect calculus (supragingival and subgingival deposits) as calcified deposits on roots.
• Monitor bone levels over time to assess progression or response to periodontal treatment.

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5. Evaluate Root Morphology

• Assess number, length, curvature, and form of roots - critical before extractions, endodontic treatment, and implant placement.
• Detect dilaceration (abnormal bend in root), taurodontism, dens invaginatus, etc.
• Evaluate root proximity to adjacent structures (inferior alveolar canal, maxillary sinus).

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6. Assess Implant Osseointegration and Peri-implant Bone Loss

• Evaluate bone levels around implants after placement.
• Detect peri-implant bone loss in peri-implantitis.
• Assess osseointegration during healing phase.
• Pre-operative assessment of bone height and density at proposed implant sites (in conjunction with CBCT).

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7. Evaluate Unerupted and Impacted Teeth

• Determine position, orientation, and depth of impacted teeth (especially third molars and maxillary canines).
• Assess relationship of impacted teeth to adjacent roots and structures.
• Detect associated pathology (dentigerous cyst, resorption of adjacent roots).
• Monitor eruption path of developing permanent teeth.

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8. Evaluate External and Internal Root Resorption

• External root resorption - loss of root substance from the outside (appears as irregular shortening or notching of root outline).
• Internal root resorption - loss of dentine from within the pulp canal (appears as a round/oval radiolucency within the root canal, "pink spot" clinically).
• Monitor progression and guide treatment decisions.

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9. Assess Pulp Morphology

• Evaluate pulp chamber size and shape.
• Detect pulp stones (pulp calcifications/denticles) - appear as radiopaque bodies within the pulp chamber.
• Assess pulp canal obliteration (calcific metamorphosis) following trauma or ageing.
• Evaluate pulp size before pulp therapy or restorations involving the pulp.

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10. Determine Length of Endodontic Instrumentation During Treatment

• Working length radiographs during root canal treatment - with files in place to determine the distance from the reference point to the root apex.
• Master cone radiographs - assess fit of gutta percha cone before obturation.
• Post-obturation radiographs - verify quality of root canal filling (length, density, lateral canals).
• Monitor healing after endodontic treatment.

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PART 2: BITEWING RADIOGRAPHS

What They Show

• Crowns of both upper and lower teeth on the same film simultaneously
• Alveolar crest bone levels interproximally
• Interproximal surfaces of posterior teeth (and anterior in some cases)

Clinical Indications

1. Detection of Interproximal (Proximal) Caries

• The PRIMARY and most important indication for bitewing radiographs.
• Detects caries on the mesial and distal surfaces of posterior teeth that cannot be seen clinically.
• Detects early (incipient) enamel caries before cavitation occurs.
• White & Pharoah: "If disease is limited, only bitewing images may be made to investigate the patient for interproximal caries."

2. Detect Recurrent (Secondary) Caries Under Restorations

• Identifies caries that has developed at the margins of existing restorations.
• Evaluates adequacy of restoration margins (overhangs, open margins).

3. Assess Alveolar Bone Crest Levels

• Evaluate early-to-moderate periodontal bone loss at the crestal bone level.
• The normal bone crest is approximately 1.5-2 mm below the cemento-enamel junction (CEJ).
• Detect horizontal bone loss in periodontal disease.
• Identify interproximal calculus (subgingival).

4. Evaluate Height of Pulp Horns and Pulp Chamber

• Helps plan restorations - ensures adequate tooth structure remains to avoid pulp exposure.
• Detect pulp stones.

5. Assess Existing Restorations

• Evaluate overhanging restorations (appear as radiopaque excess extending below contact).
• Assess open contacts and marginal fit of restorations.
• Detect fractures within or adjacent to restorations.

6. Recall/Monitoring Radiographs

• Most commonly used recall radiograph for detecting new interproximal caries between dental visits.
• White & Pharoah: Frequency based on caries risk:
  • High risk (poor diet, poor hygiene, active caries): every 6-12 months (children) or 6-18 months (adults)
  • Low risk: every 24-36 months

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PART 3: OCCLUSAL RADIOGRAPHS

What They Show

• A relatively large segment of a dental arch at one time
• May include the palate or floor of the mouth and adjacent lateral structures
• Show larger areas than periapical images - useful for survey of an entire arch

Clinical Indications

1. When Patients Cannot Accept Periapical Receptors

• Patients with a strong gag reflex
• Patients who cannot open wide enough for periapical film placement
• Children with small or shallow mouths - occlusal film placed on the occlusal surfaces is more tolerable
• Patients with trismus or limited mouth opening

2. Survey of Large Pathological Lesions

• Evaluate extent of large cysts, tumours, or other jaw lesions that exceed the field of a periapical film.
• Assess large unerupted or supernumerary teeth.
• Detect odontomes, osteomas, or fibro-osseous lesions.

3. Localization of Objects in Three Dimensions

• Used in combination with periapical radiographs (right-angle technique or Clark's SLOB rule) to determine the bucco-lingual position of unerupted teeth, roots, foreign bodies, salivary stones, etc.
• Because occlusal radiographs are taken at a steep angulation, combining them with standard periapical views gives a 3D perspective.

4. Detection of Salivary Calculi (Sialoliths)

• Mandibular occlusal radiograph is used to detect submandibular duct (Wharton's duct) calculi.
• Very effective as the calculus lies directly under the film.

5. Assess Fractures of the Jaw

• Detect fractures of the anterior maxilla or mandible.
• Assess palatal fractures and symphyseal fractures.

6. Assess Midpalatal Suture

• Evaluate palatal expansion during orthodontic treatment.
• Monitor mid-palatal suture opening during rapid maxillary expansion (RME).

7. Assess Development and Eruption of Teeth

• Particularly useful in children to assess developing teeth in mixed dentition.
• Detect supernumerary teeth (mesiodens), odontomas, or other developmental abnormalities.

8. Cleft Palate Assessment

• Evaluate bone availability for bone grafting in cleft alveolus cases.

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RADIOGRAPHIC SELECTION CRITERIA (White & Pharoah)

• Patient's medical and dental history
• Clinical examination findings
• Age and dentition stage (primary, mixed, permanent)
• Caries risk status
• Evidence of past or current disease

Guidelines by Patient Category:

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FULL-MOUTH SERIES (FMX) - INDICATIONS

• New patients with evidence of widespread disease
• Generalized caries or periodontal disease
• Pre-treatment assessment for comprehensive dental treatment
• Baseline records when significant disease is present

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SUMMARY TABLE

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HIGH-YIELD VIVA Q&A

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The ALARA Principle

As per White and Pharoah's Oral Radiology: Principles and Interpretation - Chapter 3 "Radiation Protection"

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DEFINITION

ALARA = "As Low As Reasonably Achievable"

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BASIS OF ALARA

1. Justification

• Every exposure must be justified - the benefit to the patient must outweigh the risk.
• Radiographs should be made only when they are likely to contribute to diagnosis and treatment planning.
• No radiograph should be taken as a routine without a clinical reason.

2. Optimization (= ALARA itself)

• Once an exposure is justified, the dose must be kept as low as reasonably achievable while still producing a diagnostically useful image.
• This is the core of the ALARA principle.

3. Dose Limitation

• Exposure must not exceed established dose limits for occupational workers and the public (NCRP/ICRP limits).

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MEANS OF REDUCING X-RAY EXPOSURE (BOX 3.1 - White & Pharoah)

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STRATEGY A: Use Good Clinical Judgment and Apply Evidence-Based Imaging Guidelines

1. Radiographic Selection Criteria

• Take radiographs only when they are likely to contribute to diagnosis and treatment planning.
• Use ADA/FDA selection criteria to determine the type and frequency of radiographic examinations.
• Base decisions on:
  • Patient's medical and dental history
  • Clinical examination findings
  • Caries risk assessment
  • Age and dentition stage
• Do NOT take routine radiographs for every patient at every visit without clinical indication.
• White & Pharoah: "The principal tenet of ALARA must be applied: There should be justification of the exposure so that the total potential diagnostic benefits are greater than the detriment radiation exposure might cause."

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STRATEGY B: Use Best Practices in Radiographic Imaging

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1. USE FAST RECEPTORS (Film Speed / Digital Sensors)

• Use E-speed or F-speed film (fastest available film = least radiation required).
  • F-speed (INSIGHT) requires approximately 60% less dose than D-speed (Ultra-speed).
• Use digital sensors - these require even less dose than F-speed film (up to 80% less than D-speed).
• White & Pharoah: "Use E/F-speed film or digital sensors" for intraoral radiography.

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2. USE RECTANGULAR COLLIMATION

• A collimator restricts the size of the X-ray beam to only what is needed to expose the film.
• Round collimation (standard): produces a circular beam ~7 cm diameter.
• Rectangular collimation: restricts beam to just the size of the film/sensor.
  • Rectangular collimated area is approximately 66% smaller than round collimation (Fig. 3.6 - White & Pharoah).
  • This means 66% less tissue is irradiated with rectangular vs. round collimation.
• White & Pharoah: "Use rectangular collimation" - it is one of the most effective dose reduction methods.
• Rectangular collimators are attached to the end of the aiming cylinder and must be used with receptor-holding devices for accurate alignment.

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3. USE FILM/SENSOR HOLDING DEVICES

• Use receptor-holding instruments (e.g., Rinn XCP, DENTSPLY Rinn) to:
  • Ensure correct film placement first time - reduces retakes.
  • Facilitate rectangular collimation alignment.
  • Prevent the patient or operator from holding the film (which would expose their hands).
• White & Pharoah: "Use holders to support film or digital sensors."
• Under no circumstances should office staff hold the film during exposure.

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4. USE OPTIMAL kVp SETTINGS

• White & Pharoah recommend: "Make exposures with 60-70 kVp" for intraoral radiography.
• Higher kVp (within the recommended range) produces a more penetrating beam with fewer low-energy (skin-dose) photons - reducing patient skin dose.
• However, excessively high kVp reduces image contrast, so 60-70 kVp is the optimal balance for intraoral work.

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5. USE THYROID COLLAR

• The thyroid gland is a radiosensitive organ (tissue weighting factor W_T = 0.04) and lies in the primary beam path for many dental projections.
• A lead-lined thyroid collar wrapped around the patient's neck significantly reduces thyroid dose.
• White & Pharoah: "Use thyroid collars" for intraoral radiography.
• Especially important for children (more radiosensitive than adults) and pregnant patients.
• For cephalometric radiography: use a thyroid collar only if it does not obstruct anatomic landmarks needed for the tracing.
• For CBCT: highly recommended to use a lead thyroid collar provided it does not interfere with the scan.

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6. USE OF LEAD APRON

• A lead apron covers the patient's torso (chest, abdomen, gonads) during exposure.
• White & Pharoah note the NCRP and ADA position:
  • Lead aprons to cover gonads are technically unnecessary because gonadal exposure from dental X-rays is already negligible.
  • Far more important to emphasize reduction of primary beam exposure to facial structures through selection criteria, fast receptors, and rectangular collimation.
  • However: "Use of a leaded apron is particularly advisable for pregnant patients and for children."
• Despite the NCRP/ADA statement, most dental offices still use lead aprons as a reassurance measure and for patient confidence.

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7. EXTRAORAL RADIOGRAPHY (Panoramic, Cephalometric)

• Panoramic: Use rare-earth intensifying screens (for film imaging) or digital systems - these require significantly less radiation than calcium tungstate screens.
• Cephalometric: Use rare-earth screens or digital systems; use thyroid collar if landmarks not obscured.

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8. CBCT-SPECIFIC ALARA MEASURES

• Restrict the field of view (FOV) to only the area of clinical interest - smaller FOV = less dose.
• Adjust tube current (mA) and tube voltage (kVp) based on:
  • Patient size
  • Specific diagnostic task
• Use pulsed X-ray beam (built into most CBCT units) rather than continuous beam.
• White & Pharoah: "CBCT exposure factors should be adjusted on the basis of patient size and specific diagnostic task."
• CBCT delivers higher dose than conventional dental radiography - strict ALARA application is essential.

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9. OPERATOR PROTECTION (Protecting Dental Staff)

• Stand at least 6 feet (1.8 m) from the X-ray tube head during exposure, behind a protective barrier if available.
• If no barrier exists, the operator must stand outside the primary beam and at an angle of 90-135° to the primary beam direction (where scatter is minimal).
• Never hold the tube head during exposure (except for specifically designed handheld units).
• Never hold the film/sensor in the patient's mouth - always use a holder.
• For handheld radiographic devices: hold the device horizontally, perpendicular to the operator, with the backscatter shield close to the patient; do NOT angle the device (changes the protective zone).

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10. EQUIPMENT MAINTENANCE AND QUALITY ASSURANCE

• Regularly inspect and maintain X-ray equipment.
• Check for filtration adequacy - aluminum filtration removes low-energy photons that add to patient skin dose without contributing to the image.
  • Minimum total filtration: 1.5 mm aluminum for units up to 70 kVp; 2.5 mm aluminum for units above 70 kVp.
• Maintain a retake log - minimize diagnostic retakes as each retake doubles dose for that patient.
• Review retake log weekly to identify and correct recurring errors.

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ALARA AND THE THREE PRINCIPLES - INTEGRATED VIEW

┌─────────────────────────────────────────────────────┐
│                  RADIATION PROTECTION                │
├─────────────┬──────────────────┬────────────────────┤
│ JUSTIFICATION│  OPTIMIZATION   │  DOSE LIMITATION   │
│             │    (= ALARA)     │                    │
│ Is this     │ Minimize dose    │ Stay within NCRP/  │
│ X-ray       │ while keeping    │ ICRP dose limits   │
│ necessary?  │ diagnostic       │ for workers and    │
│             │ quality          │ public             │
└─────────────┴──────────────────┴────────────────────┘

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ALARA SUMMARY - ALL METHODS AT A GLANCE

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HIGH-YIELD VIVA Q&A

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Cone Cut - Definition, Causes, Types, and Correction

As per White and Pharoah's Oral Radiology: Principles and Interpretation

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DEFINITION

White & Pharoah: "The x-ray beam may miss part of the receptor, resulting in a partial image (cone cut)."

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APPEARANCE ON THE RADIOGRAPH

• A sharply defined, clear (radiolucent/white) area on one edge or corner of the film.
• The clear area has a curved or straight border (corresponding to the edge of the circular or rectangular beam).
• The rest of the image is normally exposed and developed.
• The unexposed area may cut off root apices, alveolar crest, crowns, or interproximal contacts - depending on which direction the beam missed.

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WHY DOES IT OCCUR? - CAUSES

PRIMARY CAUSE

Specific Reasons (White & Pharoah):

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1. Not Using a Receptor-Holding Device with a Beam-Localizing Ring

• This is the most common and most important cause per White & Pharoah.
• When the patient holds the film with their finger (finger-holding technique), there is no external guide to show where the receptor is positioned inside the mouth.
• The operator has no reference to align the tube head over the film accurately.
• White & Pharoah: "Without an external guide to the position of the receptor, the x-ray beam may miss part of the receptor, resulting in a partial image (cone cut)."
• A receptor-holding device with an external aiming ring (e.g., Rinn XCP) provides a visible ring outside the mouth that the operator aligns the cone with - preventing cone cuts.

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2. Poor Alignment of the Tube Head with the Film

• Even when a holder is used, if the operator does not align the aiming cylinder precisely with the external ring, part of the beam misses the film.
• Tube head was not centered over the film - shifted too far mesially, distally, superiorly, or inferiorly.

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3. Film/Sensor Displacement or Slipping

• The receptor may slip out of proper position inside the mouth (especially when the patient holds it without a holder).
• The patient may use excessive force, bending or displacing the film from its intended location.
• The film moves but the tube head stays in its set position - they no longer align.
• White & Pharoah: "The receptor might slip, resulting in an improper image field."

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4. Use of Rectangular Collimation Without Precise Alignment

• Rectangular collimation produces a smaller beam field that must be precisely aligned with the receptor.
• The smaller the beam, the more critical accurate alignment becomes.
• If the rectangular collimator is even slightly off-center, a cone cut results.
• This is why rectangular collimation must be used with receptor-holding devices - never freehand.

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5. Incorrect Horizontal or Vertical Angulation

• Extreme misdirection of the tube head in either horizontal or vertical plane can shift the beam away from the film entirely.
• For example, excessive mesial or distal horizontal angulation with a standard round cone can shift the beam edge off the film margin.

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TYPES OF CONE CUT (by Location of Unexposed Area)

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CLINICAL SIGNIFICANCE

• Root apices - cannot diagnose periapical pathology
• Alveolar crest - cannot assess bone levels
• Proximal contacts - cannot diagnose interproximal caries
• Crown - cannot assess coronal caries or restorations

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CORRECTION / PREVENTION

White & Pharoah: The use of receptor-holding instruments "facilitates alignment with the x-ray beam, so that the central ray is directed through the contacts in the region being examined" - and prevents cone cuts.

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DISTINCTION FROM SIMILAR FAULTS

Key distinguishing feature of cone cut: The clear area has a sharp, well-defined curved/straight border (the beam edge), and the rest of the film is normally exposed. Underexposure affects the whole film uniformly.

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HIGH-YIELD VIVA Q&A

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