October 13, 2025 • 19 mins
A comprehensive overview of dental radiography principles and practices. The text explains fundamental concepts related to X-rays, including atomic structure, radiation physics, and the operation of X-ray equipment. It heavily focuses on the biological effects and potential hazards of radiation exposure, detailing the mechanisms of injury and methods for dose measurement and radiation protection for both patients and operators. Furthermore, the material covers practical applications in dentistry, such as the construction and handling of intra-oral dental X-ray films, different radiographic examinations (periapical, bitewing, and occlusal), and various localization techniques.
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Speaker 1 (00:00):
Welcome back to the deep dive. Today, we're really getting
into the nitty gritty of oral radiology, you know, the
foundational science you absolutely need for practice.
Speaker 2 (00:08):
Exactly, we're talking about how X rays are made, how
they affect tissues, and crucially, how we use them safely
and effectively. It's often called the third way of diagnosis,
right after the clinical history and exam.
Speaker 1 (00:20):
So this isn't just theory. We're connecting the dots from
like basic physics all the way to reading that final
image correctly.
Speaker 2 (00:27):
That's the goal, understanding the why behind the what. We're
covering the first eight chapters of the core material here.
Speaker 1 (00:34):
Okay, let's start small atoms, but really the key concept
driving all this is ionization.
Speaker 2 (00:40):
Ionization precisely, it's simply knocking an electron off an atom
that creates an ion pair basically charged particles, and that
simple event is well the basis for how X rays
interact and potentially cause biological effects.
Speaker 1 (00:53):
And these X rays there are specific type of radiation,
not like particles, right, we have.
Speaker 2 (00:58):
Particular radiation like electrons, but in DENTALEX rays we're dealing
almost exclusively with electromagnetic radiation. Think of them as packets
of energy photons moving at the speed of light, no mass.
Speaker 1 (01:09):
And they have super short wavelengths.
Speaker 2 (01:11):
Extremely short, about one ten thousandth the wavelength of visible light.
That's what gives them the power to penetrate tissues. If
they were longer, they just bounce off or get absorbed
too easily.
Speaker 1 (01:22):
Makes sense. So how does the machine, specifically the tube head,
generate these high energy photons?
Speaker 2 (01:28):
Okay, the tube head, it's essentially a high tech energy converter.
Inside this vacuum tube, you've got two main players, the
cathode and the eNode.
Speaker 1 (01:36):
Catode is negative, anode positive.
Speaker 2 (01:38):
You got it. The cathode holds a tiny tungsten filament.
When you apply a small current, just three to five
volts that film, it gets hot, really hot, and that
heat causes thermionic emission. Electrons literally boil off the filament,
creating this electron cloud just sitting there run the cathode
waiting for the signal to go exactly and that signal
(01:58):
is the high voltage circuit. We're talking sixty five thousand
to maybe one hundred thousand volts kicking in. Whoa, yeah.
It creates this massive potential difference pulling those electrons across
the vacuum tube at incredible speed towards.
Speaker 1 (02:11):
The anode which has the target, the.
Speaker 2 (02:13):
Tungsten target embedded in the anode. When those high speed
electrons slam into the target, their kinetic energy is converted
into X rays, well some of it, And this is
a key point. It's incredibly inefficient, right.
Speaker 1 (02:26):
I remember reading this that something like less than one percent, less.
Speaker 2 (02:29):
Than one percent, the other ninety nine percent plus is
just wasted as heat. That's why the anode has that
big copper stem to draw the heat away. Otherwise the
target would melt almost.
Speaker 1 (02:38):
Instantly, so that tiny one percent. Are all those X
rays the same.
Speaker 2 (02:42):
Good question. No, they're produced in two main ways, leading
to two types of radiation in the beam. Okay, the
main one, maybe seventy percent of the energy, is called
general radiation or German term is bremstrulon, which means breaking radiation. Yeah.
It happens when a high speed electron flies close to
the nucleus of a tungsten atom in the target. The
(03:03):
positive charge of the nucleus pulls on the electron, slowing
it down or breaking it. That loss of kinetic energy
is given off as an X ray.
Speaker 1 (03:12):
Photon, and the energy level of that photon can vary.
Speaker 2 (03:15):
Exactly depending on how close it passed to the nucleus
and how much it slowed down. So Brimstrollen gives you
a whole spectrum of X ray energies.
Speaker 1 (03:22):
Okay, what's the other type.
Speaker 2 (03:23):
Then that's characteristic radiation. This only happens if the incoming
electron hits with enough force, needs at least seventy kilovp
to knock out an electron from an inner shell of
the tungsten atom, like the K shell precisely. So, now
there's a hole in that inner shell, an electron from
an outer shell immediately drops down to fill the hole.
(03:44):
When it drops, it releases.
Speaker 1 (03:45):
Energy as an X ray photon.
Speaker 2 (03:47):
Correct And because the energy difference between those shells is
fixed for tungsten, these characteristic photons have very specific energy
levels unique to the target material.
Speaker 1 (03:57):
So we've got this beam made of general and carreteristic
X rays heading towards the patient. What happens when it
hits a.
Speaker 2 (04:04):
The jaw right the moment of truth for image creation.
Four things can happen to any individual photon.
Speaker 1 (04:09):
Four possible fates.
Speaker 2 (04:10):
Yeah, one, no interaction at all, the photon zip straight
through the patient, hits the film or.
Speaker 1 (04:15):
Sensor, and that makes the dark areas on the image
the radiolucent part exactly like.
Speaker 2 (04:19):
Soft tissues or pulp chambers. Two absorption, also called the
photoelectric effect. This is vital for the image, accounts for
about thirty percent of interactions.
Speaker 1 (04:29):
So what happens here.
Speaker 2 (04:30):
The incoming photon hits an inner shell electron in the
patient's tissue uses all its energy to eject that electron,
and the photon itself just disappears. It's absorbed completely, and.
Speaker 1 (04:40):
Because it's absorbed, no radiation reaches the film there.
Speaker 2 (04:44):
Correct, which is why those areas appear white or light
gray radiopaqu That's how we see bone enamel fillings. Okay,
Number three, Compton scatter. This is the most common one, unfortunately,
about sixty two percent of interactions.
Speaker 1 (04:56):
Most common.
Speaker 2 (04:57):
Why unfortunately because it degrades the image. Here, the photon
hits an outer shehell electron ejects it, but the photon
itself isn't absorbed. It loses some energy and then scatters
off in a random new direction.
Speaker 1 (05:09):
Ah. So it still reaches the film, but from an angle.
Speaker 2 (05:12):
Right it hits the film in a place it shouldn't,
causing this overall grayness or fog. It reduces the contrast,
making it harder to see subtle details like early cavities.
It's the biggest headache in terms of image quality, and it.
Speaker 1 (05:25):
Also contributes to patient dose unnecessarily.
Speaker 2 (05:28):
Absolutely and operator dose too if scatter bounces back towards it.
Speaker 1 (05:31):
Okay. In the last one, number four.
Speaker 2 (05:33):
Coherent scatter sometimes called unmodified scatter, it's only about eight percent.
The photon interacts with an outer electron changes direction, but
crucially without losing energy and without causing ionization. Its impact
on the image is pretty minor compared to compton.
Speaker 1 (05:50):
So photoelectric effect gives us the image contrast Compton scatter
degrades it.
Speaker 2 (05:54):
Got it.
Speaker 1 (05:55):
Now, let's link this ionization business to the biology. How
does it actually harm living tissue?
Speaker 2 (06:00):
Well, there are two main mechanisms. The direct theory is
like it sounds the X ray photon directly hitting a
critical molecule like DNA and damaging it. But that's rare,
very rare statistically speaking, because critical targets are small and
cells are mostly water. So the indirect theory is much more.
Speaker 1 (06:16):
Common, and that involves the water exactly.
Speaker 2 (06:18):
The body is what seventy eighty percent water. When an
X ray photon ionizes a water molecule H two oh,
it can create these highly unstable molecules called free radicals.
Speaker 1 (06:29):
Like hydrogen peroxide.
Speaker 2 (06:30):
Hydrogen peroxide is a common example. Yes, these free radicals
are incredibly reactive because they have an unpaired electron. They
float around and can damage other molecules nearby, like DNA
or cell membranes. So the damage is indirects. The X
ray hits water, water creates toxins. Toxins damage to cell.
Speaker 1 (06:49):
That makes sense why it's more frequent, and these effects
they build up over time.
Speaker 2 (06:54):
They absolutely do. That's the concept of cumulative effects. Each
exposure adds a little bit of potential damage. There's also
a latent period, the time delay between the radiation exposure
and when you might see any clinical signs or effects.
It could be hours, days, or.
Speaker 1 (07:06):
Even years, which leads us to the dose response curve.
Speaker 2 (07:09):
I know this is important, crucial for the low doses
used in diagnostic radiology. We assume a linear non threshold relationship.
Speaker 1 (07:17):
Linear non threshold break that down.
Speaker 2 (07:19):
Linear means the response or the risk is directly proportional
to the doose. Double the dose double the risk. Non
threshold means there is no dose below which the risk
is zero.
Speaker 1 (07:31):
So technically any amount of radiation carries some level of risk.
There's no safe dose.
Speaker 2 (07:37):
That's the current scientific consensus and the basis for all
our safety protocols. Even the smallest exposure contributes to that
cumulative permanent residual injury.
Speaker 1 (07:46):
Okay, So which tissues in the head and neck area
are we most concerned about? The critical organs a good term.
Speaker 2 (07:53):
The most radiosensitive ones we irradiate in dental settings are
the skin, the thyroid gland, the lens of the eye,
and the active bone marrow, particularly in the mandible.
Speaker 1 (08:02):
And potential effects. We mentioned skin damage.
Speaker 2 (08:04):
Right, you could see dermatitis with high doses, alokesia or
temporary hair loss, changes in blood counts. Maybe leukemia risk
is associated with bone marrow exposure, though the risk from
dental X rays is extremely low.
Speaker 1 (08:14):
What about inside the mouth?
Speaker 2 (08:16):
Oral effects are significant, especially with therapeutic radiation doses, but
can occur with high diagnostic doses too, things like mucositis,
inflammation of the lining, degeneration of taste buds, zero stomia,
or dry mouth because the salidary glands are quite sensitive
and can atrophy.
Speaker 1 (08:32):
And that dry mouth leads to radiation carries.
Speaker 2 (08:35):
It's a rampant form of decay that happens because there's
not enough saliva to protect the teeth. And of course
we have to mention the embryo.
Speaker 1 (08:42):
Or fetus extremely sensitive right, especially early on.
Speaker 2 (08:45):
Incredibly so the first trimester, particularly the first forty five
days during organogenesis is the most critical period. That's why
strict precautions like lead apron use are mandatory for pregnant patients,
even though dental doses are low.
Speaker 1 (08:59):
Okay, we need to quantify this risk. Let's talk units
rote grin for red rum cranch and the SI units.
Speaker 2 (09:05):
Right, it can be confusing. Let's clarify. First, exposure This
measures the amount of ionization the radiation produces in air.
The traditional unit is the ronkin R. The SI unit
is Coulum's per kilogram c kg. Think of it as
BM intensity.
Speaker 1 (09:18):
Okay, ionization in air. What's next?
Speaker 2 (09:21):
Absorbed dose? This is the amount of energy actually deposited
in the absorbing material like patient tissue. Traditional unit rad
radiation absorbed dose SI unit gray gray gray, and the
conversion is important. One gray equals one hundred.
Speaker 1 (09:36):
Rads energy absorbed by the tissue, got it, and the
third one dose equivalent.
Speaker 2 (09:41):
This tries to account for the sact that different types
of radiation cause different amounts of biological damage even at
the same absorbed dose. It relates dose to potential harm.
Traditional unit rem runken equivalent man si unit severt sev. Again,
one severt equals one hundred.
Speaker 1 (09:58):
Rems, so for X rays, re and are pretty much
equivalent for X rays.
Speaker 2 (10:02):
Yes, the quality factor is one, so the absorbed dose
in rad is numerically equal to the dose equivalent in REM.
Same for gray and severt, but it's good.
Speaker 1 (10:09):
To know the distinction, and these units feed into safety limits.
Speaker 2 (10:11):
The MPD exactly. The maximum permissible dose or MPD is
the maximum dose that a person can receive in a
given period with negligible risk of significant bodily injury.
Speaker 1 (10:21):
And what are those limits currently?
Speaker 2 (10:22):
For occupational workers like dentists or assistance it's five rem
per year or fifty milliseiverts, okay, But for the general
public or a pregnant worker specifically concerning the fetus, the
limit is much lower zero point five rem per year
or five milliseiverts ten times stricter.
Speaker 1 (10:39):
How do we track that? How does someone know their
cumulative dose?
Speaker 2 (10:42):
Through docimetr using personal monitoring devices called docimeters common types
of the film badge, which is like a little piece
of dental film in a holder. I've seen those, yeah,
or thermoaluminescent docimeters TLDs, which often use lithium fluoride crystals.
They absorb energy and when heated, release light proportional to
the dose. They're also ionizing chambers and newer glass dose
(11:03):
simmeters you wear for a month or a quarter, send
it in.
Speaker 1 (11:06):
And get a report, essential for tracking occupational exposure. Okay,
let's shift to protection. We know the risks, the units.
How do we minimize dose? The guiding principle is alara.
Speaker 2 (11:17):
Alara as low as reasonably achievable. That's the mantra. It
applies to protecting the patient, the operator, and anyone else nearby.
Speaker 1 (11:25):
Let's start with the patient. What's the first step?
Speaker 2 (11:27):
Justification? Only take radiographs when there's a specific clinical need
indicated by the patient's history or exam findings. No routine screening,
especially on kids just because they hit a certain age.
Professional judgment is key.
Speaker 1 (11:42):
Makes sense. What's next Probably the biggest single.
Speaker 2 (11:45):
Factor, fast film or now digital sensors. Using faster image
receptors is the single most effective way to reduce patient dose.
E speed film was a big jump, and F speed
is even faster, about twice as fast as D speed,
cutting exposure time in half. Digital sensors can reduce dose
even further.
Speaker 1 (12:03):
Okay, justification fast receptors. What about the machine itself?
Speaker 2 (12:06):
Proper equipment is crucial. Two main things here, filtration and colimation.
Speaker 1 (12:11):
Filtration first, that's about removing weak X rays.
Speaker 2 (12:14):
Exactly, removing the low energy long wavelength X rays. They
don't have enough energy to penetrate and reach the film
to contribute to the image, but they do have enough
energy to be absorbed by the patient's skin, increasing their
dose unnecessarily.
Speaker 1 (12:25):
So we filter them out.
Speaker 2 (12:27):
Right, there's inherent filtration the glass tube, the oil, the seal.
Then we add aluminum discs. The total filtration required depends
on the machine's peak VOLTAGEKVP. Below seventy kvvp, you need
at least one point five millimeters of aluminum equivalent. At
seventy KVP and above it's two point five millimeters.
Speaker 1 (12:45):
Got it now. Colimation that's about shaping the.
Speaker 2 (12:48):
Beam precisely, restricting the size and shape of the X
ray beam so it's only slightly larger than the film
or sensor. Round colimation is common, but rectangular colimation is
much better. Why better Because it shapes the beam to
match the rectangular film much more closely. This can reduce
the total tissue volume exposed by up to fifty five
percent compared to a round beam. Less tissue exposed means
(13:09):
less scatter generated.
Speaker 1 (13:10):
Ah so, less scatter means less fog and better contrast too.
Speaker 2 (13:13):
Exactly, so a win win, better safety and a better image.
It's amazing how often those go hand in hand.
Speaker 1 (13:18):
What about the cone or PID? Does a length matter?
Speaker 2 (13:21):
Yes, the position indicating device or PID. Longer PIDs, typically
sixteen inches are preferred over shorter eight inch ones.
Speaker 1 (13:28):
Why is that?
Speaker 2 (13:28):
A longer PID results in less divergence of the X
ray beam as it travels it's more parallel. This reduces
exposure to tissues outside the intended area and also slightly
improves image sharpness by reducing magnification and distortion. And definitely
use open ended lead line PIDs. Those old closed pointed
plastic cones produced a ton of scatter and are totally obsolete.
Speaker 1 (13:52):
Okay. One more patient protection item, the classic barrier, the.
Speaker 2 (13:56):
Lead apron, and thyroid collar, especially a thyroid collar since
the thyroid gland is so sensitive. These should be used
on all patients really, but especially children and pregnant women.
Speaker 1 (14:04):
Right now, protecting ourselves, the operator, what are the key rules?
Speaker 2 (14:09):
Rule Number one, Never ever hold the film or sensor
in the patient's mouth during exposure. Never hold the tube
head either, get away from the beam distance is your friend.
Stand at least six feet or two meters way from
the X ray tube head during exposure, and position yourself
carefully ideally between ninety and one hundred and thirty five
degrees to the primary beam path because the least amount
(14:29):
of scatter radiates in that direction.
Speaker 1 (14:31):
Behind a barrier impossible.
Speaker 2 (14:33):
If the room layout allows. Absolutely stand behind a protective
barrier like a lead lined wall or window, and always
aim the primary beam towards an appropriately shielded wall, never
towards a doorway or an occupied area.
Speaker 1 (14:47):
Makes perfect sense. Okay, let's switch gears slightly. We've taken
the X ray safely. Now the image itself, the film,
what's it.
Speaker 2 (14:54):
Made of the heart of traditional X ray film is
the emulsion that's a layer of mond microscopic silver halide
crystals suspended in gelatine. These crystals are what are sensitive
to X radiation.
Speaker 1 (15:07):
Silver halide in photography.
Speaker 2 (15:10):
Exactly the same principle. This emulsion is coded onto a
flexible polyester film base, which just provides support and has
a slight blue tint to help with viewing, and.
Speaker 1 (15:19):
The whole thing is wrapped up in a packet. What's
in there?
Speaker 2 (15:21):
Okay, the packet, You've got the outer wrapper, usually vinyl
or paper that protects it from saliva. Inside that, there's
often a black paper wrapping to protect it from light leaks.
Then the film itself often double emulsion, meaning coated on
both sides, which makes it faster.
Speaker 1 (15:34):
And behind the film something important back there.
Speaker 2 (15:36):
Yes, the lead foil backing a thin sheet of lead foil.
Its job is to absorb any X rays that pass
completely through the film.
Speaker 1 (15:45):
Why absorb them.
Speaker 2 (15:46):
To prevent them from scattering back from the tissues behind
the film and hitting the film again from the backside.
That backscatter would cause fog and reduce the image clarity.
It also reduces some dose to the tissues behind the film.
Speaker 3 (15:59):
Clever and there's that little bump on the film packet,
the identification dot, a small raised bump usually found near
one corner of the film, crucial for orienting the film
correctly later when you mount it.
Speaker 1 (16:09):
Okay. Types of intral films, we use three main ones.
Speaker 2 (16:12):
Routinely correct First, the periapical or PA shows the entire
tooth from the crown down to the root tip and
the surrounding bone, used for diagnosing abscesses, cysts, bone loss
around the root trauma. Comes in different sizes zero for
small kids, one for narrow interior areas, and two is
the standard adult size.
Speaker 1 (16:31):
Then the bite wing bw.
Speaker 2 (16:33):
By wings are essential. They show the crowns of both
the upper and lower teeth together when the patient bites
down on a tab, perfect for detecting interproximal carries, cavities
between the teeth and assessing the height of the alveolar
bone crest for pyidontal disease. And the big one, the
occlusal film. It's much larger, about four times the size
of a standard PA. The patient bites directly on it.
(16:55):
Used to show a large area of the maxilla or
mandible looking for impacted teeth For objects, fractures, salivary stones
or large lesions.
Speaker 1 (17:03):
Okay, so we have our processed pas and bite wings.
Now comes Mounting seems simple but critical for interpretation.
Speaker 2 (17:10):
Absolutely critical. Mounting means arranging the radiographs in a holder
and their correct anatomical position. It prevents confusion and allows
for systematic viewing. You usually use cardboard or plastic mounts,
and opaque ones are better because they block out extraneous light,
improving contrast.
Speaker 1 (17:26):
And the standard way to orient them. There's a convention, right, yes.
Speaker 2 (17:29):
The universal standard is labial mounting. You mount the films
as if you are outside the patient looking in the key.
Is that identification dot we mentioned the raised bump. With
labial mounting, the convex or raise side of that dot
on each film should be facing you the viewer.
Speaker 1 (17:44):
Okay, dot facing out and that means it means.
Speaker 2 (17:47):
The patient's left side will be on your right side
as you look at the mound, and their right side
will be on your left, just like looking at the
patient face to face.
Speaker 1 (17:56):
Got it. Labial mounting, dot raised towards you, and then
view them systematically.
Speaker 2 (18:00):
Always don't just jump around start say with the maxillary
anterior PAS. Move posteriorly on the maxilla, then view the
bite wings left to right, then move to the mandibular
films anterior to posterior. Look for everything underrupted teeth carries,
pulp chambers, bone levels, root tips, lesions follow a pattern
every time.
Speaker 1 (18:21):
We've definitely covered a lot of ground from electrons boiling
off a filament to exactly how that little dot tells
you left from right on the final image.
Speaker 2 (18:28):
It's quite a journey, isn't it. But what I find
fascinating is how interconnected it all is. Like how using
rectangular collimation isn't just about alori and patient safety.
Speaker 1 (18:37):
Right It directly improves the image quality by cutting down scatter.
Speaker 2 (18:41):
Exactly. Understanding the basic physics, the interactions, the biology, it
all feeds directly into making you a better, safer, and
more diagnostically accurate clinician. It's not just rules to memorize,
it's understanding the system.
Speaker 1 (18:54):
So for everyone listening, mastering these fundamentals, the machine, the science,
the safety really is step one for reliable diagnosis using radiographs.
Speaker 2 (19:03):
Coodn't agree more. And to help make some of this stick,
maybe a quick review scenario, let's do it? Okay, imagine this.
You've just processed a full mouth series of intro oral
films for an adult patient, but uh oh, the assistant
who mounted them used lingual mounting by mistake instead of
the standard labial mounting. What's the immediate critical interpretation error
this creates? And how could you quickly figure out the
(19:26):
correct left right orientation without taking all the films out
and remounting the entire set. Think about that identification dot,
where would it be facing in lingual mounting
Welcome back to the deep dive. Today, we're really getting
into the nitty gritty of oral radiology, you know, the
foundational science you absolutely need for practice.
Speaker 2 (00:08):
Exactly, we're talking about how X rays are made, how
they affect tissues, and crucially, how we use them safely
and effectively. It's often called the third way of diagnosis,
right after the clinical history and exam.
Speaker 1 (00:20):
So this isn't just theory. We're connecting the dots from
like basic physics all the way to reading that final
image correctly.
Speaker 2 (00:27):
That's the goal, understanding the why behind the what. We're
covering the first eight chapters of the core material here.
Speaker 1 (00:34):
Okay, let's start small atoms, but really the key concept
driving all this is ionization.
Speaker 2 (00:40):
Ionization precisely, it's simply knocking an electron off an atom
that creates an ion pair basically charged particles, and that
simple event is well the basis for how X rays
interact and potentially cause biological effects.
Speaker 1 (00:53):
And these X rays there are specific type of radiation,
not like particles, right, we have.
Speaker 2 (00:58):
Particular radiation like electrons, but in DENTALEX rays we're dealing
almost exclusively with electromagnetic radiation. Think of them as packets
of energy photons moving at the speed of light, no mass.
Speaker 1 (01:09):
And they have super short wavelengths.
Speaker 2 (01:11):
Extremely short, about one ten thousandth the wavelength of visible light.
That's what gives them the power to penetrate tissues. If
they were longer, they just bounce off or get absorbed
too easily.
Speaker 1 (01:22):
Makes sense. So how does the machine, specifically the tube head,
generate these high energy photons?
Speaker 2 (01:28):
Okay, the tube head, it's essentially a high tech energy converter.
Inside this vacuum tube, you've got two main players, the
cathode and the eNode.
Speaker 1 (01:36):
Catode is negative, anode positive.
Speaker 2 (01:38):
You got it. The cathode holds a tiny tungsten filament.
When you apply a small current, just three to five
volts that film, it gets hot, really hot, and that
heat causes thermionic emission. Electrons literally boil off the filament,
creating this electron cloud just sitting there run the cathode
waiting for the signal to go exactly and that signal
(01:58):
is the high voltage circuit. We're talking sixty five thousand
to maybe one hundred thousand volts kicking in. Whoa, yeah.
It creates this massive potential difference pulling those electrons across
the vacuum tube at incredible speed towards.
Speaker 1 (02:11):
The anode which has the target, the.
Speaker 2 (02:13):
Tungsten target embedded in the anode. When those high speed
electrons slam into the target, their kinetic energy is converted
into X rays, well some of it, And this is
a key point. It's incredibly inefficient, right.
Speaker 1 (02:26):
I remember reading this that something like less than one percent, less.
Speaker 2 (02:29):
Than one percent, the other ninety nine percent plus is
just wasted as heat. That's why the anode has that
big copper stem to draw the heat away. Otherwise the
target would melt almost.
Speaker 1 (02:38):
Instantly, so that tiny one percent. Are all those X
rays the same.
Speaker 2 (02:42):
Good question. No, they're produced in two main ways, leading
to two types of radiation in the beam. Okay, the
main one, maybe seventy percent of the energy, is called
general radiation or German term is bremstrulon, which means breaking radiation. Yeah.
It happens when a high speed electron flies close to
the nucleus of a tungsten atom in the target. The
(03:03):
positive charge of the nucleus pulls on the electron, slowing
it down or breaking it. That loss of kinetic energy
is given off as an X ray.
Speaker 1 (03:12):
Photon, and the energy level of that photon can vary.
Speaker 2 (03:15):
Exactly depending on how close it passed to the nucleus
and how much it slowed down. So Brimstrollen gives you
a whole spectrum of X ray energies.
Speaker 1 (03:22):
Okay, what's the other type.
Speaker 2 (03:23):
Then that's characteristic radiation. This only happens if the incoming
electron hits with enough force, needs at least seventy kilovp
to knock out an electron from an inner shell of
the tungsten atom, like the K shell precisely. So, now
there's a hole in that inner shell, an electron from
an outer shell immediately drops down to fill the hole.
(03:44):
When it drops, it releases.
Speaker 1 (03:45):
Energy as an X ray photon.
Speaker 2 (03:47):
Correct And because the energy difference between those shells is
fixed for tungsten, these characteristic photons have very specific energy
levels unique to the target material.
Speaker 1 (03:57):
So we've got this beam made of general and carreteristic
X rays heading towards the patient. What happens when it
hits a.
Speaker 2 (04:04):
The jaw right the moment of truth for image creation.
Four things can happen to any individual photon.
Speaker 1 (04:09):
Four possible fates.
Speaker 2 (04:10):
Yeah, one, no interaction at all, the photon zip straight
through the patient, hits the film or.
Speaker 1 (04:15):
Sensor, and that makes the dark areas on the image
the radiolucent part exactly like.
Speaker 2 (04:19):
Soft tissues or pulp chambers. Two absorption, also called the
photoelectric effect. This is vital for the image, accounts for
about thirty percent of interactions.
Speaker 1 (04:29):
So what happens here.
Speaker 2 (04:30):
The incoming photon hits an inner shell electron in the
patient's tissue uses all its energy to eject that electron,
and the photon itself just disappears. It's absorbed completely, and.
Speaker 1 (04:40):
Because it's absorbed, no radiation reaches the film there.
Speaker 2 (04:44):
Correct, which is why those areas appear white or light
gray radiopaqu That's how we see bone enamel fillings. Okay,
Number three, Compton scatter. This is the most common one, unfortunately,
about sixty two percent of interactions.
Speaker 1 (04:56):
Most common.
Speaker 2 (04:57):
Why unfortunately because it degrades the image. Here, the photon
hits an outer shehell electron ejects it, but the photon
itself isn't absorbed. It loses some energy and then scatters
off in a random new direction.
Speaker 1 (05:09):
Ah. So it still reaches the film, but from an angle.
Speaker 2 (05:12):
Right it hits the film in a place it shouldn't,
causing this overall grayness or fog. It reduces the contrast,
making it harder to see subtle details like early cavities.
It's the biggest headache in terms of image quality, and it.
Speaker 1 (05:25):
Also contributes to patient dose unnecessarily.
Speaker 2 (05:28):
Absolutely and operator dose too if scatter bounces back towards it.
Speaker 1 (05:31):
Okay. In the last one, number four.
Speaker 2 (05:33):
Coherent scatter sometimes called unmodified scatter, it's only about eight percent.
The photon interacts with an outer electron changes direction, but
crucially without losing energy and without causing ionization. Its impact
on the image is pretty minor compared to compton.
Speaker 1 (05:50):
So photoelectric effect gives us the image contrast Compton scatter
degrades it.
Speaker 2 (05:54):
Got it.
Speaker 1 (05:55):
Now, let's link this ionization business to the biology. How
does it actually harm living tissue?
Speaker 2 (06:00):
Well, there are two main mechanisms. The direct theory is
like it sounds the X ray photon directly hitting a
critical molecule like DNA and damaging it. But that's rare,
very rare statistically speaking, because critical targets are small and
cells are mostly water. So the indirect theory is much more.
Speaker 1 (06:16):
Common, and that involves the water exactly.
Speaker 2 (06:18):
The body is what seventy eighty percent water. When an
X ray photon ionizes a water molecule H two oh,
it can create these highly unstable molecules called free radicals.
Speaker 1 (06:29):
Like hydrogen peroxide.
Speaker 2 (06:30):
Hydrogen peroxide is a common example. Yes, these free radicals
are incredibly reactive because they have an unpaired electron. They
float around and can damage other molecules nearby, like DNA
or cell membranes. So the damage is indirects. The X
ray hits water, water creates toxins. Toxins damage to cell.
Speaker 1 (06:49):
That makes sense why it's more frequent, and these effects
they build up over time.
Speaker 2 (06:54):
They absolutely do. That's the concept of cumulative effects. Each
exposure adds a little bit of potential damage. There's also
a latent period, the time delay between the radiation exposure
and when you might see any clinical signs or effects.
It could be hours, days, or.
Speaker 1 (07:06):
Even years, which leads us to the dose response curve.
Speaker 2 (07:09):
I know this is important, crucial for the low doses
used in diagnostic radiology. We assume a linear non threshold relationship.
Speaker 1 (07:17):
Linear non threshold break that down.
Speaker 2 (07:19):
Linear means the response or the risk is directly proportional
to the doose. Double the dose double the risk. Non
threshold means there is no dose below which the risk
is zero.
Speaker 1 (07:31):
So technically any amount of radiation carries some level of risk.
There's no safe dose.
Speaker 2 (07:37):
That's the current scientific consensus and the basis for all
our safety protocols. Even the smallest exposure contributes to that
cumulative permanent residual injury.
Speaker 1 (07:46):
Okay, So which tissues in the head and neck area
are we most concerned about? The critical organs a good term.
Speaker 2 (07:53):
The most radiosensitive ones we irradiate in dental settings are
the skin, the thyroid gland, the lens of the eye,
and the active bone marrow, particularly in the mandible.
Speaker 1 (08:02):
And potential effects. We mentioned skin damage.
Speaker 2 (08:04):
Right, you could see dermatitis with high doses, alokesia or
temporary hair loss, changes in blood counts. Maybe leukemia risk
is associated with bone marrow exposure, though the risk from
dental X rays is extremely low.
Speaker 1 (08:14):
What about inside the mouth?
Speaker 2 (08:16):
Oral effects are significant, especially with therapeutic radiation doses, but
can occur with high diagnostic doses too, things like mucositis,
inflammation of the lining, degeneration of taste buds, zero stomia,
or dry mouth because the salidary glands are quite sensitive
and can atrophy.
Speaker 1 (08:32):
And that dry mouth leads to radiation carries.
Speaker 2 (08:35):
It's a rampant form of decay that happens because there's
not enough saliva to protect the teeth. And of course
we have to mention the embryo.
Speaker 1 (08:42):
Or fetus extremely sensitive right, especially early on.
Speaker 2 (08:45):
Incredibly so the first trimester, particularly the first forty five
days during organogenesis is the most critical period. That's why
strict precautions like lead apron use are mandatory for pregnant patients,
even though dental doses are low.
Speaker 1 (08:59):
Okay, we need to quantify this risk. Let's talk units
rote grin for red rum cranch and the SI units.
Speaker 2 (09:05):
Right, it can be confusing. Let's clarify. First, exposure This
measures the amount of ionization the radiation produces in air.
The traditional unit is the ronkin R. The SI unit
is Coulum's per kilogram c kg. Think of it as
BM intensity.
Speaker 1 (09:18):
Okay, ionization in air. What's next?
Speaker 2 (09:21):
Absorbed dose? This is the amount of energy actually deposited
in the absorbing material like patient tissue. Traditional unit rad
radiation absorbed dose SI unit gray gray gray, and the
conversion is important. One gray equals one hundred.
Speaker 1 (09:36):
Rads energy absorbed by the tissue, got it, and the
third one dose equivalent.
Speaker 2 (09:41):
This tries to account for the sact that different types
of radiation cause different amounts of biological damage even at
the same absorbed dose. It relates dose to potential harm.
Traditional unit rem runken equivalent man si unit severt sev. Again,
one severt equals one hundred.
Speaker 1 (09:58):
Rems, so for X rays, re and are pretty much
equivalent for X rays.
Speaker 2 (10:02):
Yes, the quality factor is one, so the absorbed dose
in rad is numerically equal to the dose equivalent in REM.
Same for gray and severt, but it's good.
Speaker 1 (10:09):
To know the distinction, and these units feed into safety limits.
Speaker 2 (10:11):
The MPD exactly. The maximum permissible dose or MPD is
the maximum dose that a person can receive in a
given period with negligible risk of significant bodily injury.
Speaker 1 (10:21):
And what are those limits currently?
Speaker 2 (10:22):
For occupational workers like dentists or assistance it's five rem
per year or fifty milliseiverts, okay, But for the general
public or a pregnant worker specifically concerning the fetus, the
limit is much lower zero point five rem per year
or five milliseiverts ten times stricter.
Speaker 1 (10:39):
How do we track that? How does someone know their
cumulative dose?
Speaker 2 (10:42):
Through docimetr using personal monitoring devices called docimeters common types
of the film badge, which is like a little piece
of dental film in a holder. I've seen those, yeah,
or thermoaluminescent docimeters TLDs, which often use lithium fluoride crystals.
They absorb energy and when heated, release light proportional to
the dose. They're also ionizing chambers and newer glass dose
(11:03):
simmeters you wear for a month or a quarter, send
it in.
Speaker 1 (11:06):
And get a report, essential for tracking occupational exposure. Okay,
let's shift to protection. We know the risks, the units.
How do we minimize dose? The guiding principle is alara.
Speaker 2 (11:17):
Alara as low as reasonably achievable. That's the mantra. It
applies to protecting the patient, the operator, and anyone else nearby.
Speaker 1 (11:25):
Let's start with the patient. What's the first step?
Speaker 2 (11:27):
Justification? Only take radiographs when there's a specific clinical need
indicated by the patient's history or exam findings. No routine screening,
especially on kids just because they hit a certain age.
Professional judgment is key.
Speaker 1 (11:42):
Makes sense. What's next Probably the biggest single.
Speaker 2 (11:45):
Factor, fast film or now digital sensors. Using faster image
receptors is the single most effective way to reduce patient dose.
E speed film was a big jump, and F speed
is even faster, about twice as fast as D speed,
cutting exposure time in half. Digital sensors can reduce dose
even further.
Speaker 1 (12:03):
Okay, justification fast receptors. What about the machine itself?
Speaker 2 (12:06):
Proper equipment is crucial. Two main things here, filtration and colimation.
Speaker 1 (12:11):
Filtration first, that's about removing weak X rays.
Speaker 2 (12:14):
Exactly, removing the low energy long wavelength X rays. They
don't have enough energy to penetrate and reach the film
to contribute to the image, but they do have enough
energy to be absorbed by the patient's skin, increasing their
dose unnecessarily.
Speaker 1 (12:25):
So we filter them out.
Speaker 2 (12:27):
Right, there's inherent filtration the glass tube, the oil, the seal.
Then we add aluminum discs. The total filtration required depends
on the machine's peak VOLTAGEKVP. Below seventy kvvp, you need
at least one point five millimeters of aluminum equivalent. At
seventy KVP and above it's two point five millimeters.
Speaker 1 (12:45):
Got it now. Colimation that's about shaping the.
Speaker 2 (12:48):
Beam precisely, restricting the size and shape of the X
ray beam so it's only slightly larger than the film
or sensor. Round colimation is common, but rectangular colimation is
much better. Why better Because it shapes the beam to
match the rectangular film much more closely. This can reduce
the total tissue volume exposed by up to fifty five
percent compared to a round beam. Less tissue exposed means
(13:09):
less scatter generated.
Speaker 1 (13:10):
Ah so, less scatter means less fog and better contrast too.
Speaker 2 (13:13):
Exactly, so a win win, better safety and a better image.
It's amazing how often those go hand in hand.
Speaker 1 (13:18):
What about the cone or PID? Does a length matter?
Speaker 2 (13:21):
Yes, the position indicating device or PID. Longer PIDs, typically
sixteen inches are preferred over shorter eight inch ones.
Speaker 1 (13:28):
Why is that?
Speaker 2 (13:28):
A longer PID results in less divergence of the X
ray beam as it travels it's more parallel. This reduces
exposure to tissues outside the intended area and also slightly
improves image sharpness by reducing magnification and distortion. And definitely
use open ended lead line PIDs. Those old closed pointed
plastic cones produced a ton of scatter and are totally obsolete.
Speaker 1 (13:52):
Okay. One more patient protection item, the classic barrier, the.
Speaker 2 (13:56):
Lead apron, and thyroid collar, especially a thyroid collar since
the thyroid gland is so sensitive. These should be used
on all patients really, but especially children and pregnant women.
Speaker 1 (14:04):
Right now, protecting ourselves, the operator, what are the key rules?
Speaker 2 (14:09):
Rule Number one, Never ever hold the film or sensor
in the patient's mouth during exposure. Never hold the tube
head either, get away from the beam distance is your friend.
Stand at least six feet or two meters way from
the X ray tube head during exposure, and position yourself
carefully ideally between ninety and one hundred and thirty five
degrees to the primary beam path because the least amount
(14:29):
of scatter radiates in that direction.
Speaker 1 (14:31):
Behind a barrier impossible.
Speaker 2 (14:33):
If the room layout allows. Absolutely stand behind a protective
barrier like a lead lined wall or window, and always
aim the primary beam towards an appropriately shielded wall, never
towards a doorway or an occupied area.
Speaker 1 (14:47):
Makes perfect sense. Okay, let's switch gears slightly. We've taken
the X ray safely. Now the image itself, the film,
what's it.
Speaker 2 (14:54):
Made of the heart of traditional X ray film is
the emulsion that's a layer of mond microscopic silver halide
crystals suspended in gelatine. These crystals are what are sensitive
to X radiation.
Speaker 1 (15:07):
Silver halide in photography.
Speaker 2 (15:10):
Exactly the same principle. This emulsion is coded onto a
flexible polyester film base, which just provides support and has
a slight blue tint to help with viewing, and.
Speaker 1 (15:19):
The whole thing is wrapped up in a packet. What's
in there?
Speaker 2 (15:21):
Okay, the packet, You've got the outer wrapper, usually vinyl
or paper that protects it from saliva. Inside that, there's
often a black paper wrapping to protect it from light leaks.
Then the film itself often double emulsion, meaning coated on
both sides, which makes it faster.
Speaker 1 (15:34):
And behind the film something important back there.
Speaker 2 (15:36):
Yes, the lead foil backing a thin sheet of lead foil.
Its job is to absorb any X rays that pass
completely through the film.
Speaker 1 (15:45):
Why absorb them.
Speaker 2 (15:46):
To prevent them from scattering back from the tissues behind
the film and hitting the film again from the backside.
That backscatter would cause fog and reduce the image clarity.
It also reduces some dose to the tissues behind the film.
Speaker 3 (15:59):
Clever and there's that little bump on the film packet,
the identification dot, a small raised bump usually found near
one corner of the film, crucial for orienting the film
correctly later when you mount it.
Speaker 1 (16:09):
Okay. Types of intral films, we use three main ones.
Speaker 2 (16:12):
Routinely correct First, the periapical or PA shows the entire
tooth from the crown down to the root tip and
the surrounding bone, used for diagnosing abscesses, cysts, bone loss
around the root trauma. Comes in different sizes zero for
small kids, one for narrow interior areas, and two is
the standard adult size.
Speaker 1 (16:31):
Then the bite wing bw.
Speaker 2 (16:33):
By wings are essential. They show the crowns of both
the upper and lower teeth together when the patient bites
down on a tab, perfect for detecting interproximal carries, cavities
between the teeth and assessing the height of the alveolar
bone crest for pyidontal disease. And the big one, the
occlusal film. It's much larger, about four times the size
of a standard PA. The patient bites directly on it.
(16:55):
Used to show a large area of the maxilla or
mandible looking for impacted teeth For objects, fractures, salivary stones
or large lesions.
Speaker 1 (17:03):
Okay, so we have our processed pas and bite wings.
Now comes Mounting seems simple but critical for interpretation.
Speaker 2 (17:10):
Absolutely critical. Mounting means arranging the radiographs in a holder
and their correct anatomical position. It prevents confusion and allows
for systematic viewing. You usually use cardboard or plastic mounts,
and opaque ones are better because they block out extraneous light,
improving contrast.
Speaker 1 (17:26):
And the standard way to orient them. There's a convention, right, yes.
Speaker 2 (17:29):
The universal standard is labial mounting. You mount the films
as if you are outside the patient looking in the key.
Is that identification dot we mentioned the raised bump. With
labial mounting, the convex or raise side of that dot
on each film should be facing you the viewer.
Speaker 1 (17:44):
Okay, dot facing out and that means it means.
Speaker 2 (17:47):
The patient's left side will be on your right side
as you look at the mound, and their right side
will be on your left, just like looking at the
patient face to face.
Speaker 1 (17:56):
Got it. Labial mounting, dot raised towards you, and then
view them systematically.
Speaker 2 (18:00):
Always don't just jump around start say with the maxillary
anterior PAS. Move posteriorly on the maxilla, then view the
bite wings left to right, then move to the mandibular
films anterior to posterior. Look for everything underrupted teeth carries,
pulp chambers, bone levels, root tips, lesions follow a pattern
every time.
Speaker 1 (18:21):
We've definitely covered a lot of ground from electrons boiling
off a filament to exactly how that little dot tells
you left from right on the final image.
Speaker 2 (18:28):
It's quite a journey, isn't it. But what I find
fascinating is how interconnected it all is. Like how using
rectangular collimation isn't just about alori and patient safety.
Speaker 1 (18:37):
Right It directly improves the image quality by cutting down scatter.
Speaker 2 (18:41):
Exactly. Understanding the basic physics, the interactions, the biology, it
all feeds directly into making you a better, safer, and
more diagnostically accurate clinician. It's not just rules to memorize,
it's understanding the system.
Speaker 1 (18:54):
So for everyone listening, mastering these fundamentals, the machine, the science,
the safety really is step one for reliable diagnosis using radiographs.
Speaker 2 (19:03):
Coodn't agree more. And to help make some of this stick,
maybe a quick review scenario, let's do it? Okay, imagine this.
You've just processed a full mouth series of intro oral
films for an adult patient, but uh oh, the assistant
who mounted them used lingual mounting by mistake instead of
the standard labial mounting. What's the immediate critical interpretation error
this creates? And how could you quickly figure out the
(19:26):
correct left right orientation without taking all the films out
and remounting the entire set. Think about that identification dot,
where would it be facing in lingual mounting
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