1 dental radiology

04/11/23 20:21 Ossama El-Shall

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immediate study needs of students enrolled at the University of Al-Azhar, Cairo, A.R.E. for the course directed by

Dr. Ossama El-Shall.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, printed, photocopying, recording or otherwise without the written permission of the author.

Dental Radiology Dental Radiology

Dr. Ossama EL-Shall Professor and Chairman of Oral

Medicine, Periodontology, Diagnosis and Radiology

Department. Faculty of Dental Medicine for

Girls Al-Azhar University , Cairo Egypt.

E-mail address: oelshall@hotmail.com

Dental Radiology course for post graduate students.

Physics of Ionizing Radiation. Physics of Ionizing Radiation. X-ray Machine. X-ray Machine. Biological effects of Radiation. Biological effects of Radiation. Safety &Protection in dentistry. Safety &Protection in dentistry. Dental X ray Film composition, (intra & extra-oral), Types & uses of intra-oral Dental X ray Film composition, (intra & extra-oral), Types & uses of intra-oral

films.films. X-Ray film processing. X-Ray film processing. Intra-oral radiographic techniques .Intra-oral radiographic techniques . Plain Extra-oral film projections .Plain Extra-oral film projections . Panoramic Imaging.Panoramic Imaging. Faults affecting dental radiographs.Faults affecting dental radiographs. Normal Anatomical Landmarks. Normal Anatomical Landmarks. Dental radiographic Dental radiographic interpretation.interpretation. Specialized techniques for imaging (Conventional tomography, CT, MRI, Nuclear Specialized techniques for imaging (Conventional tomography, CT, MRI, Nuclear

medicine, Ultrasonography, Sialography)medicine, Ultrasonography, Sialography) Cone-Beam Computed TomographyCone-Beam Computed Tomography

Contents of part I1- Terminology.2- Radiation Physics.3- Properties of X-ray 4- Dental X-ray apparatus.5- Production of X-rays.6- Types of radiation.7- Dental X-ray films, both intra-oral and

extra-oral.8- X-ray film processing.9- Intra-oral radiographic techniques.

Terminology

1- Radiology2- Roentgenology3- Dental radiology4- Dental radiography5- Radiograph 6- Radiation 7- Radiolucent 8- Radiopaque

Science that deals with diagnosis, therapeutic and researches application of high-energy radiation.

Radiology

Roentgenology

Science that deals with application of X-ray on any field.

Dental radiology

It is the branch of science that deals with the use of radiation in diagnosis of dental diseases.

Dental radiography

It is the art of producing an image or picture for intra- or extra-oral structures on a dental film using X-ray.

Radiograph

It is the shadow features (image) received on a radiation-sensitive film emulsion by exposure to ionizing radiation directed through an area or region or substance of interest, followed by chemical processing of the film.

It is basically dependent on the differential absorption of radiation directed through heterogeneous media.

Radiation

It is the process of emission, propagation and transmission of energy by atoms in the form of waves.

Radiolucent

Objects that permitting the passage of radiant energy with relatively little attenuation by absorption and appear black on the film, such as silicate restoration, pulp tissues, gingiva, and carious lesion.

Another definition; Objects partly or wholly penetrable by roentgen rays; the image of such a material on the film ranges from dark gray to black.

Radiopaque

Objects that absorb X-rays and appear white on radiograph, such as amalgam restoration, enamel, and bone.

Another def.:Objects that not freely penetrable by radiation.

OR Objects highly resistant to penetration by roentgen rays; the image of such a material appears on the film within range of gray to white.

Clinical Exam + Radiographs

Diagnosis

Treatment

Radiation physics

Radiation physics Atomic structure:

1- Atom is the fundamental unit of any particular element, i.e. the basic unit of an element.

2- It is composed of a central nucleus and outer orbits which spaced at a definite distance from the nucleus and are identified by letters, K, L, M, N, O, P, Q.

3-Electrons are negatively charged particles that orbiting shells.

4-The central nucleus is composed of two kinds of particles, proton, +ve charged and neutrons with no charge.

5-Since neutrons have no charge; the magnitude of the charge of the nucleus will depend on the number of protons (Atomic number), which are equal to the number of electrons.

Atom statesGround state (stable): It is the normal or ground

state of atom on which the atom is electrically neutral with equal numbers of protons and electrons.

Excitation state: It occurs when sufficient energy applied to the atom, results in removing of electron from its normal shell to a higher energy shell.

Ionization state: It is the process by which an atom loses its electrical neutrality and become ions by either addition or removing of electrons. If electron is added or removed from the atom, the atom will termed as ion. If the electron is removed, the atom becomes a +ve ion while the removed electron is called –ve ion.

Atom (electrically stable)

Atomic Number (Z) = # of protons

K-shell

L-shellprotons

neutrons

electronsM-shell

Attraction between protons and

electrons

ELECTROSTATIC FORCE

CENTRIFUGAL FORCE

Pulls electrons away from nucleus

Balance between electrostatic force and centrifugal force

keeps electrons in orbit around nucleus

Nature of radiation

Radiation may be either

Corpuscular radiation

Electromagnetic radiation

A- Corpuscular or particulate radiation

1- It is that type of radiation given off from radium, radioisotopes, and during splitting of the atom.

2- It is composed of solid subatomic particles

having mass and charge.

3- It travels in straight lines and is not used in dental diagnostic filed but in therapeutic means.

4- Examples for corpuscular radiation:Alpha (α) rays.Beta (β) rays.

B- Electromagnetic radiation

1-It is that type of radiation formed of units of pure energy, which are propagated in the form of waves as a combination of electric and magnetic fields.

2-It is made of pure energy propagate in a form of waves with no mass or charge.

3-It is generated when the velocity of an electrically charged particle is altered.

4-They travel in straight lines with the same speed of light (3x108 meter/sec.)

5-As they propagate in a form of waves, they have a wavelength (λ) and frequency (ν(

Wavelength (λ) is the distance between 2 crests or bottoms of 2 successive waves.

Frequency (ν) is the number of cycles or waves emitted/sec.

Wavelength x Frequency = Speed of wave

According to the wavelengths, radiations can differ in their properties.

Radiation may be of

Short wavelength Or Long wave

length

The short wavelength increased frequency increase the energy accompanied with it increase the power of penetration the rays will termed Hard radiation which characterized with low power of absorption into matter and low ionization.

The long wavelength decreases frequency decrease the energy accompanied with it decrease the power of penetration the rays are termed Soft radiation which characterized with high power of absorption into matter and high ionization effects.

CHighest energy?

Highest energyShortest wavelengthHighest frequency

Examples of electromagnetic radiation

arranged in an ascending order according to their wavelength:1-Cosmic rays.2-Gamma Ray3-X.Ray. wavelength = 0.1-1Ao, Ao = 10-10 m4-Ultraviolet rays.5-Visible light.6-Infra-red.7-Microwaves.8-Radio, radar, T.V waves.

Electromagnetic Spectrum

radio tv visible light

x-rays gamma rays

cosmic rays

X-rays were first discovered in 1895 by Wilhelm Conrad Roentgen, the professor of physics and director of the physics institute at the University of Wurzburg in Bavaria.

Hence the term ROENTGEN

RAYS, often applied to mechanically generated x-rays. He won a Noble prize for his discovery of X-ray.

Roentgen called them X-rays after the mathematical symbol X for unknown.

HistoryHistoryHistory

History HistoryHistory

Roentgen soon found that photographic plates were sensitive to the newly discovered rays.

He convinced his wife to participate in an experiment.

Roentgen placed her hand on a cassette loaded with a photographic plate. He then aimed the activated cathode ray tube at her hand for fifteen minutes.

When the image was developed, the bones of her hand and the two rings she wore were clearly visible.

X-ray of Bertha Roentgen's Hand

History HistoryHistory

Within 2 weeks after Roentgen was made his discovery public, the first dental radiograph was made by German dentist Otto Walkoff, who placed in his own mouth small glass photographic plates wrapped in rubber dam and exposed them for 25 minutes.

Early x-ray machine. Arrow points to “live” electrical wire.

HistoryHistoryHistory

Definition of X-ray

- It is a type of electromagnetic radiation characterized by wavelengths between approximately 1 A and 10-4 A.

- They are invisible, penetrative

especially at higher photon energies, and travel with the same speed as visible light.

- They are usually produced by bombarding a target of high atomic number with fast electrons in a high vacuum

In brief: X rays are a form of pure energy units belonging to electromagnetic spectrum characterized by having a very short wave length and have the ability of producing shadiness’ or images of the body tissues.

Properties of X-ray

1- They have a very short wave length: As the wavelength decrease, the power of penetration of the x-ray increased. The power of penetration depends on several factors in addition to the wavelength such as: Atomic number of the object, thickness of the object, and the density of the object.

Properties of X-ray

2- They have a selective penetration, absorption power: When the x-ray hit an object, certain interactions occur, these interactions may occur in either of 3 forms or possibilities: a) Penetrate the object, b) Absorbed by the object, c) Deflected from certain objects e.g. heavy metals

3- It affects photographic film’s emulsion: X-rays upon falling on the emulsion of a photographic film they cause physical changes producing what is termed Latent Image formation, which cannot be seen except after chemical application.

4- It causes certain substances to fluoresce: X-ray can cause certain fluorescing substances to fluoresce or emit “violet blue visible light” which is of a longer wave length than the x-rays so this was used in dentistry in the formation of intensifying screen.

5- They cause ionization of atoms: X-rays have the power of converting atoms into ions with the formation of ion pairs which are electrically charged, unbalanced, non-functioning cells thus will have a harmful effect later on the body cells and fluids.

6-They have biological damaging effects: May be of somatic effects such as skin burns, erythema or cancer or genetic effects

7. Travel in straight lines in wave motion with the same speed of light.3x108 meter/sec.

8. Short waves about 1/10000 of that of light. (0.1-0.001nm)

9. Invisible, can’t be felt, smelled or heard.

10. Weightless, mass less, and changeless.

11. They cannot be focused or collected by a lens.

12. They cannot be reflected by a mirror or by fluids.

13. They cannot be deviated by a magnet.

14. They can deflect on heavy metals by deviated into a new linear trajectory.

X-Ray Machine

Dental X-ray apparatus

How are X-rays created?

When fast-moving electrons (minute particles each consisting of a negative electrical charge) collide with matter, X-radiation is produced.

The most efficient means of generating X-rays is an X-ray tube.

In it, X-rays are produced by directing a high-speed stream of electrons against a metal target.

As they strike the atoms of the target, the electrons are stopped.

Most of their energy is transformed into heat, but a small proportion is transformed into X-rays.

X-ray machine consists of

Tube: Cathode + Anode

Accessories: Filters + collimators + cones

Automatic

Manual

X-ray Tubehead

Tubehead

support arms

Automatic timers

1- Direct or immediate timers: It attached to a long cord to enable the operator to go away from the field of radiation. Operator press on a button just to activate the exposure while the time is pre adjusted and the exposure will stop automatically even if the operator continuous to press the button.

2- Delayed timers: This type provide about 9 second before the start of exposure, so it provides the operator a period to get away from the field of radiation.

exposure time adjustment

Manual timers

- Direct type in old x-ray machines

-The exposure is controlled manually (like the clock alarm) and exposure will stop only if the operator stop pressing on the button.

- The main disadvantage of this type that it adjusted only for 1 second not in fraction of seconds.

Manual Timer

Head of X-ray machine.

It consists of two main parts Tube

Accessories.

The Tube The Tube is an Evacuated glass tube

with two arms or electrodes extending in two opposite directions, which are the cathode and anode.

The tube is evacuated for two reasons 1) This will prevent collision of the moving

electrons with the molecules of the air. 2) This evacuation will prevent oxidation

and burn out of the filaments.

Tube head of X-ray machine

Cathode

It is the negative electrode of the tube, which serves as the source of electrons. It consists of two parts

a) Filament. b) Focusing cup.

(molybdenum)

(tungsten)

Cathode

Focusing cup

Filament

It made of tungsten coil, which is 0.2cm in diameter and 1 cm or less in length.

Tungsten is used because; 1) It has a very high melting point so it can

withstand the high temperature accompanied with the process of X-ray production.

2) It has a high atomic number, which denoting a high number of protons resulting in high number of electrons.

Focusing cup

It is a negatively charged concave reflector cup made of molybdenum, act as focusing to the electrons to a narrow beam to fall on the target.

The high negative charge of the

cathode repels the negatively charged electrons, thus this cup collects the electrons and repels them till the anode attracts them.

filament hotfilament

The hotter the filament gets, the greater the number of electrons that are released.

electrons

Electrons Emission

Release of electrons from hot filament when current flows after depressing exposure switch

It consisting of two main parts

a) Target.

b) Copper head.

Copper head Target

side view front view

Target

It made up of tungsten due to

1) It has a very high atomic number (i.e. large number of protons and electrons).

2) It has a high melting point.

3) It has a very poor thermal conductivity.

Copper head

Due to the poor thermal conductivity of the tungsten target, it is embedded in a large block of copper, which is a good thermal conductor so it allows proper dissipation of heat which accompanies the process of X-ray production.

X-ray Production

A simplified diagram of x-ray tube

Focusing cup

Filament

Metal housing

Copper head

Target

Evacuated Glass tube

Insulating oil

Step-down transformer

Step-up transformer

8-12 v60-90 kvpE

Useful beam

1ry Ray

AnodeCathode

Production of X-raysTerminology:

Voltage

Ampere

Transformer

Volt: It is the unit of electrical pressure or electromotive force necessary to produce a current of 1 ampere through a resistance of 1 ohm.

It is the unit of measuring the potential difference of a charge to move from one electrode to the other

Voltage: It is the potential or electromotive force of an electric charge, expressed in volts.

The potential difference between 2 electrical charges, e.g. between cathode and anode.

Ampere: It is the practical unit of quantity of electronic current, equal to a flow of 1 coulomb per second or the flow of 6.25 x 1018 electrons per second.

Transformer: It is an electrical device, which increases or reduces the voltage of an alternating current by mutual induction between primary and secondary coils.

Step-down transformer: A transformer in which the secondary voltage is less than primary voltage.

Step-up transformer: A transformer in which the secondary voltage is greater than the primary voltage.

When an electric current, -which composed of a steam of negatively charged electrons having kinetic energy- passes through a filament or wire, it will be heated so the orbiting electrons within its atoms will acquire sufficient energy to escape from their shells. Finally this electron cloud will be given from the heated wire of filament.

If these electrons sudden stopped, they will loose the accompanying kinetic energy and converted into heat and X radiation.

The principles of X-ray production

Application of this principle on dental X-ray machine

The step-down transformer will decrease the electric current into 8-12 volts.

This current is sufficient enough to heat

the tungsten filament of the cathode and produce electrons according to the degree of heating by thermo ionic emission.

These electrons will form a cloud around

the cathode, which will be collected by the concave focusing cup but they have no velocity to move.

The step-up transformer will raise the potential difference between the cathode and the anode by raising the voltage into 60-70 KV.

This increase in potential difference will accelerate the electron cloud to move towards the anode, as there is a force of attraction between the positive anode and the negative cathode.

By the action of the focusing cup, the electrons will hit only the tungsten target of the anode, loosing their kinetic energy in a form of 99.8% heat and only 0.2% X-rays.

The produced X-rays (primary beam) are conducted to get out from the tube housing through the filters and collimators to be used as a useful beam.

Tube of x-ray machine

exposure button

filterfilament

X-ray Machine Components

Accessories

Filters

Collimators

Filters A thin sheet of pure aluminum placed in the way

of the X-ray beam at the end of the X-ray tube in order to improve the quality of the beam.

The X-ray beam is heterogeneous in characteristics i.e. containing a ray of different energies and wavelength. Because of this, the filter is used in order to absorb unnecessary x-rays of the longer wavelengths being both useless in radiography and dangerous to the patient and the dentist.

The thickness of the filters varies according to the Kvp of the machine being used, 2mm.Al thickness with up to 70Kvp and 2.5mm over 70Kvp.

filter

The filter is usually located in the end of the PID which attaches to the tubehead.

Types of filters

Added filters: They are external filters that can be removed or added by the clinician.

Inherent filters: These include the glass wall of the X-ray tube, The insulating oil, and the metal housing

Total filters = Inherent filters + added filters.

04/11/23 20:21

Inherent

Glass window of x-ray tube

Aluminum filter (s)

Total 70 kVp

1.5 mm

2.5 mm

Total Filtration

Oil/Metal barrier

Collimator

It is a device used to limit or restrict the size of an X-ray beam just to cover the film to produce the desire image.

Types of collimators

Diaphragm collimator: A thin sheet of lead with an opening in the center.

Tubular collimator: A tube of lead with one of its ends connected or in conjunction to the diaphragm collimator. This tube will help in decrease diverging rays and almost increase more parallel rays, which in turn helps in increase quality of image and more safe to the patient.

Rectangular collimators: It provides a beam of a rectangular shape that larger than the size of Periapical films.

collimated beamcollimator

target(x-ray source)

front views side view

Collimation

2.75 inches (7 cm) = maximum diameter of circular beam or maximum length of long side of rectangular beam at end of PID.

Collimator

You are looking up through the PID at the collimator, which is a circular lead washer with a circular cutout in the middle. This will produce a round x-ray beam. The light gray area in the center is an aluminum filter, which is placed on the tubehead side of the PID.

6 cm round

film(4.5 cm long)

entrance

7 cm If you switch from a 7 cm round PID to a 6 cm round PID, the patient receives 25% less radiation.

Rectangular collimation results in 55 % less radiation when compared to 7 cm round PID.

Cones, Position indicating device (PID)

It is a device used to 1-Fix the target film distance

2-Indicate the point of the entry

3-Determine the direction and distribution of the X-ray tube.

It may make of plastic, glass or metal. The majority of cones are made of plastic because it is light. In case of metal one (lead) it may act as collimator and cone in the same time, but it is not practical as it very heavy on the tube itself and will cause decrease beam intensity as some of it will be absorbed by the lead.

It may be of opened end or pointed end shape. The pointed end shape has harmful effects that it acts as a source of scattered radiation as the rays will hit its walls.

It may be short one 8” or long one 16”.

Increasing the distance from the target of the x-ray tube (focal spot, focus) to the object (teeth/film) (FFD = focus-film distance) will result in an increase in sharpness and a decrease in magnification. This results when a longer PID (cone) is used.

Target16” from film

Target8” from film 8” FFD image

16” FFD image

Moving the film closer to the teeth will also increase sharpness and decrease magnification.

Types of X-ray

Types of X-Radiation

1- Primary radiation.2- Useful beam 3- Central ray 4- Secondary radiation 5- Scattered radiation 6- Stray radiation 7- Remnant radiation 8- Leakage radiation 9- Soft radiation 10-Hard radiation

Primary radiation: It is the radiation coming directly out of the target, most of it is absorbed by the tube housing except for the useful beam.

Useful beam: It is that part of the

primary radiation, which is not absorbed by the housing but passes through the apparatus and affects the film.

Central ray: It is that part occupying

the central portion of the useful beam on which the rays are relatively parallel to each other.

Secondary radiation: It is that radiation

generated from the patient’s surrounding objects due to passage, interaction of the primary beam with these objects. They are of a long wavelength and so increased absorption and are more dangerous to the patient.

Scattered radiation: It is a form of secondary radiation which has been deviated in direction during passage of the X- rays through objects.

Stray radiation: This radiation occurs when the primary beam hits a metal heavier than AL, e.g. metallic eyeglasses.

Remnant radiation: It is that portion of radiation remaining or emerging from the object after the passage of the primary beam through it, to expose the film and produce the image.

Leakage radiation: The radiation that escapes through the protective housing of the X-ray tube.

Soft radiation: Radiation produced by

decreased kilo-voltage, are of longer wavelength, decreased penetration, increased absorption so have a more damaging effect.

Hard radiation: Radiation produced by increased kilo-voltage, are of shorter wavelength, increased energy, increased penetration, decreased absorption and are the ones used to produce the image, i.e. of diagnostic value.

Factors affecting the quality of an image

Terminology Image Contrast Density Exposure Roentgen Rad Rem

Image: The representation or semblance of a

structure or structures produced by passage of X-radiation,

visible only when transmitted onto a fluorescent screen or an x-ray film (in

the latter case, visible only after processing the film).

Contrast:

It is the difference in density appearing on a radiograph.

OR Is the differentiation between black,

white and gray shades on the radiograph.

Density: It is the degree of darkening of exposed

and processed photographic or x-ray film, expressed as the logarithm of the opacity of a given area of the film.

Exposure: A measure of the x radiation to

which a person or object, or a part of either, is exposed at a certain place, this measure being based on its ability to produce ionization.

Roentgen; R: X-radiation has a property of causing

ionization of the matter that passes through it.

So, the unit of x-rays is Roentgen, which is the measurement of ionization.

It is defined as the amount of radiation

that passes in one c.c. air producing two billion ion pairs (–ve and +ve) under standard conditions of temperature and atmospheric pressure

Rad: It is unit of absorbed dose; it is amount

of ionizing Radiation absorbed dose by one gram of the tissues.

Rem: It is the unit of biological damaging

effect of radiation (B.D.E), it is the amount of ionizing radiation

produces biologic damage effects (B.D.E) in one gram of tissue.

It is Roentgen equivalent mass, i.e. measurement unit denoting amount of a radiation dose that produced biological damaging effects equal that in a person with one Roentgen of X-ray.

The factors affecting the quality of an image

1- Kilo-voltage 2- Milliamp rage 3- Collimation4- Filtration 5- Distance 6- Atomic number and thickness (density)

of the object

Kilo-voltage

Kilo voltage power of conventional dental X-ray machine ranges from 65-90 kvp.

X-ray penetration power is controlled with kvp, i.e. the higher the kvp is, the shorter wavelength x-ray with high penetration power.

So kvp is the factors, which determine the

quality of the x-ray beam, and when the thickness of the structure increased we need a higher kvp.

Kilo-voltage

If the kvp is increased above the normal range it will affect the contrast of the image.

In this case of very high kvp, the

penetration power of the x-ray will increase resulting in nearly complete penetration of the objects and finally blacking the film and the areas which should have been white (as metal) will appear gray.

The end result of such image will be image with black and gray shades with low contrast image (long gray scale).

Kilo-voltage

If the kvp will decrease than the normal, the penetration power of the beam will decreased resulting in image with white color representing hard objects and few blacking or gray represent soft tissue objects, which is called high contrast image or (low gray scale).

Thus an optimum contrast is required which is achieved by range of kvp between 65-90, any alterations in this range either increase or decrease will affect the quality of the image contrast.

Milliamp rage

The normal range of mA is about 5-15, it is affecting the quantity of the x-ray.

By controlling mA and time we can

control the quantity of the beam, and thus control the density of the image.

Milliamp rage

The higher mA (within normal range) will result in increase the quantity of the current, increase heating of the coil, increase the amount of electrons emitted, increase the number of x-ray photons, increase the amount of x-ray reaching the film, with final resultant of increasing the amount of blacking of the image resulting in an image with good density.

While if the mA is increased above the normal range this will result in increasing the darkness of the image (high density), which may controlled or avoided by decreasing the time of exposure.

If the mA is low than the normal range it will result in a very light image with low density, which is may control by increasing the exposure time.

Collimation Collimators exerts three main functions, the first increase the safety to the

patient, the second, increase the quality of the image the third is increase the sharpness of the image.

It helps on reduction the amount of x-ray reached to the patient and in the same time increase the image quality by decreasing the amount of scattered radiation. The image sharpness will also increased by reduction of the beam size, leads to reduction the more diverging rays and increase the more parallel rays.

Filtration

Proper filtration will provide x-rays with short wavelength, results in a good quality image.

Over-filtration will result in decrease the amount of x- ray photons and in decreased density image, while under-filtration will give a long wavelength x-rays with low penetration power and low contrast image..

Distance The distance between the source and the

object may affect the image quality as follow; if the distance is increased, the intensity of

the beam will decreased leading to decrease of the quality of the rays and affection to the density, but in the same time if the distance is increased it help on production of less diverging rays leading to increase the quality of the beam and increase the sharpness.

If the distance is decrease, this will help on increase the intensity of the beam and increase the density; while in the same time will increase the divergent rays leading to decrease the sharpness.

Atomic number and thickness (density) of the object

As the atomic number, density and thickness of the object increase, the need for more powerful x-radiation will increase to produce a good image. So the kvp should increased but within limits in order not to alter the contrast. So this may compensate with increase the exposure time, but also within limits in order not to affect the density.

Dental X-ray film

It is a thin, transparent sheet of plastic material coated on both sides with an emulsion sensitive to radiation and light.

Radiographic films closely resemble the

films used by photographers to produce black and white negatives.

There are differences in that photographic films only carry an emulsion on one side of the film base, whereas both sides of radiographic films are coated, to double the response to an X-ray exposure.

The X-ray film basically consists of four components:

Film base

Adhesive layer

Film emulsion

Protective layer

Film base

Is a flexible piece of plastic, about 0.008 inches thick to provide the desired degree of stiffness and flatness for handling.

It is transparent and has a slight blue

tint to make it easier to visualize the image.

Film base serve as a stable support for the emulsion.

Adhesive layer

It is a thin layer of adhesive material to act as attachment between the base and emulsion from both sides.

Film emulsion

1. This is the most important constituent of the film.

2. It is a homogeneous mixture of gelatin and silver halide crystals coated on both sides of the film base to provide maximum speed to the film (sensitivity).

3. Gelatin is used to suspend and evenly disperse the silver halide crystals.

4. Halide crystal is a chemical compound that is sensitive to radiation or light.

5. The halides used in a dental X-ray film are silver bromide and to a lesser extent silver iodide.

6. On exposure to the X-ray this silver

bromide absorb the rays and physical changes take place in the emulsion. This change called the latent image.

Protective layer

It is a thin, transparent, clear layer of gelatin covers the emulsion to protect it from mechanical damage.

What is the latent image and how it formed?

Silver bromide crystals absorb X-radiation, and store the energy of the radiation as a certain pattern to an extent depending on the density of objects.

This pattern of energy on the exposed film

cannot be seen and is referred to as latent image.

The latent image remains invisible within the emulsion until the film undergoes chemical processing, then it become visible.

When the X-ray hit the surface of emulsion, the silver bromide crystals that exposed to the rays ionized and separated to silver and bromide atoms.

However, when the exposed film is treated with a solution called a developer, a chemical reaction takes place, and the exposed grains of silver compound are transformed to tiny masses of black metallic silver.

The unexposed grains are essentially unaffected. It is this silver suspended in the gelatin that constitutes the visible image on the radiograph.

Latent Image

Many x-rays penetrate and ionize many silver halide crystals

Fewer x-rays penetrate and not as many silver halide crystals are exposed

Few, if any, x-rays penetrate; silver halide crystals not exposed

Air/soft tissue Bone Amalgam/Metal

Types of Dental X-ray films

Intra-oral films

Extra-oral films

Films used in dental radiography come in a variety of sizes and packaging.

Those of the smaller sizes suitable for Intra-oral use, ranging from 22 to 31 mm across and from 35 to 54 mm in length, come individually enclosed in light-tight envelopes of thin plastic or paper.

Other films of large size are used for extra-oral exposure in dental radiography. They positioned outside the oral cavity in a special light protected holder (cassette) that is loaded within the selected film inside the dark room.

I- Intra-oral films

Intra-oral films usually supplied inside special film packets. The film packet consists of:

1-Outer packet wrapping or envelope

2-Black paper film wrapping

3-The film

4-Lead foil sheet

black paper surrounds film;protects emulsion

lead foil

single or double;raised dot in one corner

protects film from backscatter; reduces patient exposure; strengthens packet; pattern identifies when film is placed backwards (reversed)

Outer packet wrapping or envelope:

It is a soft plastic wrapper to protect the film completely from the light and saliva.

It has two sides; white smooth side (tube

side), which has a raised bump on one corner, corresponds to the identification dot on the film.

The other side (the label side) has a flap used

to open the film packet during processing. It contains data about the number of films

per packet, and the film speed. It also contains a circle of concave dot that

represent the identification dot of the film.

dotplastic paper

Outer film coverKeeps out light and moisture; protects emulsion

# of filmsin packet

Tab #2 #1

Black paper film wrapping: Are two black papers enclose the

film between them and further protect it from light.

The film: It is a double emulsion film; the

packet may contain one or two films.

At one of the film corners there is

a small raised dot (identification dot). It used after film processing to distinguish between the left and right side of the patient mouth during reading of radiograph (interpretation).

This identification dot or bump has a convex and concave surfaces the convex surface should face the rays while the concave side being back to the film during exposure.

Also it should be always away from any anatomical landmarks to avoid misdiagnosed as any pathologic lesion, so it should be occlusally or incisally during exposure.

Lead foil sheet: Placed back to the film away

from the smooth side of the film packet (back side).

Its function is to absorb the back scattered radiation and thus protects the film from fogging.

It also adds to the rigidity of the film packets.

It has a special pattern (herring

bone) stamped on the exposed finished radiograph if the film is exposed from the wrong side.(back side film)

black paper surrounds film;protects emulsion

lead foil

single or double;raised dot in one corner

protects film from backscatter; reduces patient exposure; strengthens packet; pattern identifies when film is placed backwards (reversed)

Backscatter(scattered x-rays that go “back” toward the film)

Primary x-rays

Scatter (secondary) x-rays

Reversed Films (back side film)

Types of intra-oral films

Intra-oral films

Intra-oral films can be classified mainly according to their usage into

Periapical films

Bite-wing films

Occlusal films.

Also intra-oral films can classified according their

* Speed * Size

* Number of films per packet * Whether the film packet is lead

backed or not.

Classification of intra-oral films according to use

Periapical films Occlusal films

Bite wing films

Periapical Film

Apical pathology

Periodontal evaluation

Caries detection

Endodontic treatment

Periapical pathology

internalresorption

caries

Periapical films

It is the most frequently used intra-oral view, which shows the entire tooth and surrounding structure on the film.

There are three basic sizes for Periapical films,

No. 0 or child film 22x35mm. No. 1 or narrow adult 27x54mm. No. 2, or standard adult film 31x41mm.

Periapical films used to exam the following:

I-Enamel:

1-Normally appears as a Radiopaque structure.

2-Caries of the enamel: which appears as a radiolucent area.

3-Enamel hypoplasia: appears as a radiolucent area surrounded with radio-opaque margin.

4-Amilogenesis imperfecta: all the enamel appears as radiolucent area.

5-Congenital syphilis: Hutchinson’s incisors; appears as v-shaped radiolucent area surrounded by radio-opacity.

II-Dentin:

1-Normally appears as a Radiopaque structure

-2Caries of the dentin; appears as a v-shaped radiolucent area.

3-Dentinogenesis imperfecta: dentin appears as a radiolucent area surrounded by faint radio-opaque margin

4-Dense in dente: appears as a radio-

opaque structure within the tooth surrounded by radiolucent margin.

5- Internal resorption: radiolucent lines on the apex or lateral side of the root dentin.

III-Pulp:

1-Normally appears as a radiolucent area within the tooth.

2-Calcification of the pulp: appears as a localized area of radiopacity = pulp stone. If it generalized it appears as a generalized radioopacity of the pulp chamber.

3-Shell tooth : appears as a wide pulp chamber.

IV-Cementum:

1-Normally it cannot be differentiated from the dentin.

2-Hypercementosis: appears as Radiopaque areas cover the cementum line.

3-Cementoma: appears at the apex of the tooth as a radiolucent area in its early stages and converted into a Radiopaque area at its terminal stages.

V-Periodontal ligament space:

1-Normally appears as a radiolucent line surround the root surface

2-Narrowing of it as a result

of an oeteoblastic process e.g. scleroderma

3-Widening of the space as results of osteolytic process e.g. osteolytic osteoma, .

VI-Lamina dura:

-Appears as Radiopaque clear continues band covers the alveolar bone ie. lining the socket and cover the crest of the crest of alveolar bone (crestal lamina dura).

-Discontinuities of lamina dura indicate pathological changes.

VII-Alveolar bone:

Bone resorption either horizontal or vertical.

Bite wing films

These films often have a paper tab projecting from the middle of the film, on which the patient bites to support the film. This tab is not visualized and does not interfere with the diagnostic quality of the image.

It used to record the coronal portions of

maxillary and mandibular teeth in one image. The apices of the teeth are not shown.

It used for the following:

Interproximal Caries

Alveolar Bone Involvement

Bitewing Film

Overhanging amalgam filling

1. Detection of initial proximal caries.2. Detection proximal overhanging

margins of fillings and crowns.3. Approximate estimation of the size of

the pulp chamber and pulp horns.4. Detection of initial interproximal

crestal alveolar bone resorption indicating periodontal disease.

5. Determination of the position of permanent forming teeth in relation to deciduous ones.

6. Determination of any proximal calculus formation.

Detection of proximal caries by bite wing radiographs compare to Periapical

radiograph

Occlusal films

Occlusal films are use to radiographically clarify the anatomical structures and the pathological conditions of the maxilla or mandible in the bucco-lingual dimension.

Occlusal films may use for the following purposes:

Occlusal FilmIdentify large lesions

Locate bucco-lingually

Developing anterior teeth

Imaging trismus patients

1. Obtaining gross views for the jaws in the bucco-lingual dimension.

2. Detection location and extent of fractures.

3. Detection of the bucco-lingual direction of impactions and supernumerary teeth.

4. Detection of bucco-lingual direction of displaced fracture.

5. Detection of salivary gland or duct stone especially in the mandible.

6. Localization of foreign bodies such as broken needle.

7. Determination of the shape of dental arches.

Classification of intra-oral films according to the speed

Film speed (sensitivity) can be defined as the efficiency by which a film can respond to an X-ray exposure,

i.e; a fast film requires low exposure time to produce a standard density image, while a slow film requires longer time of exposure to produce the same standard quality.

or it refers to the amount of radiation required to produce a radiograph of standard density.

Intra-oral films vary in speed, fast films need less X-radiation and using such films routinely plays a major role in the field of radiation protection.

Factors affecting film speed

1-Whether the film is coated only on one side with the silver halide grains (slow films) or on both sides (medium and fast films)

2-The size of the silver halide grains, the larger the size, the more sensitive the film.

The speed of dental X-ray films is expressed in a letter form.

Speed groups are A, B, C, D, E and F

A being the slowest film and each subsequent group being approximately twice as fast as the preceding group to give a final image of the same object with the same density.

This mean that; for example: E-speed film requires one half the exposure time of D-speed film.

Groups A & B are called slow films (regular).

Group C is called medium speed (radiatized).

Groups D & E are called high speed films (ultra-speed and ecta-speed respectively).

Groups D-speed films and E-speed films are the most common intra-oral film in every day’s use.

Kodak introduced E-speed plus film, this film provides the superior image quality of D-speed film at a reduced radiation exposure.

Classification of intra-oral films according to size:

Periapical and bitewing film comes in three sizes:

0 For small children (about 22 X 35mm)

1 Which is relatively narrow and used for anterior projections (about 24 X 40mm)

2 The standard film used for adults (about 32 X 41mm(

Classification of intra-oral films according to number of films per

packets.

Usually intra-oral films supply in packets containing one film. Some film packets include 2 films instead of 1.

This may be helpful for record keeping, research purposes, teaching purposes, medico-legal aspects or if it is meant to control the density of each of the 2 films in a different way during processing.

Film Processing

Processing

It is a chemical treatment, which is applied to the Exposed film to convert the invisible latent image to visible image from which useful diagnostic data can be obtained

Latent image formation

1. After film exposure, the silver halide molecules in the emulsion that become exposed will absorb the X-ray and undergo ionized.

2. As a result of this ionization; minute amounts of metallic silver are formed on crystal surface & bromide is liberated.

3. The degree of ionization within the crystals depends upon the amount of exposure received (latent image).

4. The image remains within the emulsion till changed into silver image by chemical processing.

5. In definition, the processing of the film is the process of changing of the latent image into a visible image from which useful diagnosis can be obtained.

Latent Image

Chemistry of processing

There are five major steps of chemical processing:

1- Developing, 2- Rinsing. 3- Fixation. 4- washing. 5- drying.

1-Developing Developer solution treats the exposed grains (ionized). Developer

solution has affinity to react with bromide part of the crystal leaving the black reduced silver grains. It consists of five elements:

1-Reducing agent: It converts the exposed silver crystals into black metallic silver. It consists of Metol and Hydroquinone.

2-Activator: Sodium Carbonate; it swells and softens the emulsion gelatin and provide alkalinity for the reducing agent.

3-Restrainer: K. Bromide; it slow down rate of development of unexposed crystals, so it restrain the reducing agent from making the film fogged appears .

4-Preservative agent: Sodium sulphate; it prevent oxidization.5-Water as dissolving agents.

Air/soft tissue Bone Amalgam/metal

Developing

Crystal centers converted to black metallic silver

Air/soft tissue Bone Amalgam/gold

Developing (continued)

Entire crystal converted to black metallic silver

2-Rinsing

With fresh water in order to

1- Neutralize the alkalinity of the developer solution

2- To stop the developer action

3- Remove the remnants of developer solution from the film

3-FixationIt removes the unexposed undeveloped silver bromide

granules and hardens the gelatin. It consists of:Clearing agent: Aluminum thiosulfate, it clear the

unexposed silver bromides.Acidifier: Acetic acid, to provide required acidity to

neutralize the developer alkalinity.Hardener: Aluminum chloride, to shrinks and

hardens the gelatin.Preservative: Sodium sulphate: it maintains the

chemical balance of fixer chemicals.Water as a solvent.

Fixing

Unexposed crystals removed from film

4-Washing: with water to remove all the residual processing chemicals.

5-Drying: with air or dryer to makes the film finally ready for interpretation and mounting, and facilitates film handling with lesser mechanical damage.

Latent Image

Developing

Crystal centers converted to black metallic silver

Air/soft tissue Bone Amalgam/gold

Developing (continued)

Entire crystal converted to black metallic silver

Fixing

Unexposed crystals removed from film

Methods of processing.

1. Fixed time and temperature. (Manual)

2. Visual method. (Manual)

3. Automatic processing:

4. Polaroid land radiography.

5. Inject able intra-oral films.

6. Self-processing solutions contained intra-oral films.

7. Film less dental radiographic tech.

1-Fixed time and temperature.

1- It is a reliable and standardized method2- The optimal temp. is 203- The higher temp. the less time required and vice

4- the fixed times for each step are: a- 5min developing b-15-20 sec. for rinsing c-10min. Fixation d-20 sec. washing

2-Visual method.

1. Films are immersed in developer and removed every now and then to be checked on safe light till image is visible

2. Then rinsed and fixed

3. It is not standardized method as it depends mainly on human factors

3-Automatic processing

Automatic processor is a special machine, which can perform all the steps of processing of both extra-oral and intra-oral films until the dry radiograph is obtained in about 5 minutes.

The film is opened manually in a light tight compartment of the machine and then placed in its place to be automatically carried by the rollers of the machine from one step to the other.

Advantages of automatic processor:1-Rapid and easy method 2-Standardization of processing.3-No need for dark room and its equipments.

Disadvantages of automatic processor:1-Highly expensive.2-Need for regular maintenance3-Need minimum amounts of films per day4-High temperature of machine tends to produce

chemical fog in the radiograph and rapid deteriorates the strength of the solutions.

Automatic Processor

Developing Water Fixing Solution Rinse Solution

Film Exit

DryingElements

FilmEntry

insert

developer

water rinse

Daylight Loader

4-Polaroid land radiography.

Extra-oral films could be made using an emulsion on a paper backing instead of the usual film base.

A special cassette and screen are used during film exposure by conventional dental x-ray machine.

It required more exposure time but processing is a one step dry method, only 10 sec. carried out in a special electric small table top unit.

5-Injectable intra-oral films.

In these types of processing, the processing solutions are respectively injected into the closed film packed which is supplied with an inject able sits. As processing takes place inside the packet, such film packets must have no lead foil or black paper folds.

Advantage of inject able intra-oral films: 1-Easy and rapid method. 2-No need for the dark room. Disadvantage of this method: 1-Fogged image. 2-Need further fixation to avoid loosing details.

6-Self-processing solutions contained intra-oral films.

These films contain 2 small packets attached to the film packet. After exposure, they are pulled one after one to pour first the developer and then the fixer into the film packet. This method has the same advantage and disadvantage of the injection method.

The Dark Room Light tight (against light leakage). Both white light and safe light illumination: The white light is

used for cleaning the tanks and preparation of the solutions. The safe light is used during opining film packets and processing.

Safe light specifications. Coin on film test. Processing tanks. Running water source. Timer. Either stop watch or florescent. Thermometer. Dryer. Storage space.

Processing tanks

Films holder

D-speed Intraoral, Extraoral(all films)

Safelight Filters

Morlite GBX-2

Twice as much light

Safe lighting

Problem

Everything OK

Safelight Test (Coin on film test)

Intra-Oral Radiographic Techniques.

1. Techniques for Periapical radiographs.

2. Techniques for Bite-wing radiographs.

3. Techniques for Occlusal radiographs.

Periapical radiographic techniques.

Typical 14 Periapical film survey for adults

Typical 14 film survey for adults The central rays is targeted onto the apex; depiction of the

alveolar crest is of only secondary importance.

Periodontal 14-film survey for adults The central rays is targeted onto the alveolar crest; depiction

of the root apices is only of secondary importance.

Techniques for Periapical radiography

Paralleling technique

Bisecting angel technique.

Paralleling techniqueRight angle technique Long cone technique

Paralleling technique

Head Position

Head position for the paralleling technique is not critical, since you will be aligning the PID with the ring.

In the paralleling technique, the film is positioned in the mouth so that the long axis of the film and the long axis of the tooth are parallel. We can not see the long axes of the teeth but, in general, all the teeth incline toward the middle of the head. Thus the film/instrument will almost always be tipped slightly (up or down, depending on the arch). In the illustration above right, the film is placed straight up and down and is not parallel; the patient is unable to close completely on the biteblock and the apices of the teeth would not appear on the film.

correct incorrect

ANTERIOR POSTERIOR

Rinn XCP Paralleling Instruments

Why long coneWhy long cone??

To prevent the magnification of the image and the un-sharpness of the film due to increasing the film object distance

A parallel non-diverging x-ray beam is required, this is achieved by increase target film distance by using a long cone (16inches)

Measures how well the details (boundaries) of an object are reproduced on a radiograph

Increased by: Source-object distance Object-film distance Film crystal size

Motion will decrease sharpness

Sharpness

Decreased by: Source-object distance Object-film distance

Magnification

Increasing the distance from the target of the x-ray tube (focal spot, focus) to the object (teeth/film) (FFD = focus-film distance) will result in an increase in sharpness and a decrease in magnification. This results when a longer PID (cone) is used.

Target16” from film

Target8” from film 8” FFD image

16” FFD image

Moving the film closer to the teeth will also increase sharpness and decrease magnification.

Target-object-film relation.

FilmObjecttarget

Most newer x-ray machines have a recessed target (away from the PID). This helps to increase the focus-film distance (FFD), resulting in a sharper image and less magnification without an increase in the length of the PID (position indicating device). A longer PID is effective, but it makes positioning the tubehead more difficult.

8" FFD

12" FFD

Object-film distance small

parallelingbisecting

Maxillary anterior region

Photograph and radiograph of the region

Film holder and positioning for maxillary anterior area

Maxillary anterior region

Maxillary Incisor

centered on contact between central and

lateral incisors

film placed far back in patient’s mouth

Maxillary canine region

Film holder and positioning for maxillary canine area

Maxillary canine region

Maxillary Canine

film centered on canine

film placed against the opposite side of the arch, far away from the canine

Maxillary premolar region

Maxillary Premolar

front edge of film anterior to middle of canine; approximately centered on 2nd premolar

film equidistant from lingual surfaces of teeth (red arrows); this opens contacts between the

teeth.

film in center of palate

Maxillary molar region

Maxillary Molar

film centered on second molar

film in center of palate

film equidistant from lingual surfaces of teeth (red arrows); this opens contacts between the

teeth.

Mandibular anterior region

Film holder and positioning for mandibular anterior area

Mandibular Incisor

film centered on midlinefilm positioned away from teeth, pushing tongue back slightly

Mandibular canine region

Film holder and positioning for mandibular canine area

Mandibular Canine

film centered on caninefilm positioned away from

teeth, pushing tongue back slightly

Mandibular premolar region

Mandibular Premolar

film equidistant from lingual surface of teeth

(red arrows); film placed toward center of mouth,

displacing tongue

front edge of film anterior to middle of canine; approximately

centered on 2nd premolar

Mandibular molar region

centered on second molar

Mandibular Molar

film equidistant from lingual surface of teeth; in this case the film will usually contact

lingual of molars

Bisecting angel technique

X-ray beam perpendicular to bisecting line

X-ray beam

The film is positioned with the long axis vertical and the dot-end of film extending ¼” beyond the incisal edge. With the all-white side of film facing the teeth, the finger pressure is applied at the cervical portion of the crown to avoid film bending.

The film is positioned with the long axis horizontal and the dot-end of film extending ¼” beyond the occlusal surface. With the all-white side of film facing the teeth, the finger pressure is applied at the cervical portion of the crown to avoid film bending.

Film placement, as indicated above, is the same for maxilla or mandible. The film is placed vertically for anterior teeth (canine to canine) and horizontal for posterior teeth.

The film is held in the proper position using the thumb (maxillary anterior,

above left), Index finger of opposite hand (all other

areas, above right).

Maxilla (+ve) Mandible(-ve)

Incisors: 45-55 25-15

Canines: 45-50 15-20

Premolars: 35-40 5-15

Molars: 25-30 0-5

Vertical angulations during bisecting angle

technique

Horizontal angulations during bisecting angle

technique

Central rays should be parallel to interproximal surface of the teeth

Central rays should pass through the contact area of the teeth.

Advantages of Bisecting Angle Technique

•More comfortable: because the film is placed in the mouth at an angle to the long axis of the teeth, the film doesn’t impinge on the tissues as much.

•A film holder, although available, is not needed. Patients can hold the film in position using a finger.

•No anatomical restrictions: the film can be angled to accommodate different anatomical situations using this technique

Anatomical Variations:

Anatomical situations which might require using the bisecting angle technique are:

a shallow palate

a large palatal tours

a shallow or tender floor of the mouth

a short lingual frenum (tongue-tie)

Disadvantages of Bisecting Angle Technique

•More distortion: because the film and teeth are at an angle to each other (not parallel) the images will be distorted.

•Difficult to position x-ray beam: because a film holder is often not used it is difficult to visualize where the x-ray beam should be directed.

•Film less stable: using finger retention, the film has more chance of moving during placement

Distortion

In the bisecting technique, the long axis of the tooth is not parallel with the long axis of the film. This results in a distortion of the image produced using this technique. In the left radiograph below, the buccal roots appear much shorter than the palatal root, even though in the actual tooth the lengths are not that much different. In the other radiograph taken with the paralleling technique, the lengths are projected in their proper relationship (minimal distortion).

Techniques for Bite-wing radiography

Diagram of correct film position and central rays targeting in bite-wing film

The paper extension from the film packet must not be pulled too much. The central ray is targeted through either the maxillary second premolar or the first permanent molar.

Bitewing Head Position

The head should be positioned so that the maxillary arch is parallel to the floor, both side-to-side and front-to-back, when using bitewing tabs.

Bitewing Film Placement

Front edge anterior to middle of

mandibular canine (approximately centered on 2nd

premolar)

Film centered on second molar (if 3rd molars are

erupted; otherwise center on contact between 1st and

2nd molar).

The stick-on bitewing tab is always centered top-to-bottom with the film oriented horizontally (see picture above). The tab is placed on the Clinasept cover on the all-white side of the film. When some teeth are missing, the tab may be placed more anteriorly or posteriorly to allow maximum contact with the teeth that are present.

The film is placed in the mouth between the teeth and the tongue. Hold on to the tab and instruct the patient to close slowly and completely.

The vertical angulation is always set at +10 degrees (the tubehead is pointing downward).

positioning guide

The horizontal angulation is adjusted so that a line connecting the front and back edge of the PID (yellow line above) is parallel with a line connecting the buccal surfaces of the premolars and molars (green line above). Instruct the patient to open their lips so that you can see the buccal surface (see next slide). The front edge of the PID should be ¼” anterior to the front edge of the film.

correct incorrect

Patient opening lips (“smiling with teeth together”) to allow

visualization of buccal surface of posterior teeth.

Techniques for Occlusal radiography

Maxillary Topographical Occlusal

Mandibular Topographical Occlusal

Maxillary Vertex Occlusal

Mandibular Cross-Sectional Occlusal

Posterior Oblique Maxillary Occlusal

Posterior Oblique Mandibular Occlusal

Modified Oblique Posterior Mandibular Occlusal

Occlusal Film

-Identify large lesions

-Determine bucco-lingual

location

-View developing anterior

dentition

-Image patients with trismus (if

panorama not available)

Head PositionMaxillary occlusal: Maxilla parallel to floorMandibular occlusal: Mandible perpendicular to floor

Film PositionCentered on area of interestAll-white side facing x-ray tubePatient bites gently on film

Exposure Settings

Normal Maxillary = PA/ BWMandibular = PA/BWTrue Maxillary = 4X PA/BW

X-ray Beam Position Centered on area of interest

Vertical angulations (see below)

Thank you all for listening

Dr. Ossama El-Shall

E-mail address: oelshall@hotmail.com

Believe in yourself, for if you don’t believe

in yourself, it will be hard for others to

believe in you

1 dental radiology

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