Physics of Dental Radiology (Very Important)

The physics of dental radiology is fundamental to the safe and effective use of imaging technologies in dentistry.

X-ray physics, particularly the principles of radiation generation, attenuation, and interaction with tissues, underpins the functioning of dental radiographic equipment. Understanding the physics behind image formation helps in optimizing exposure settings to minimize radiation dose while ensuring high-quality diagnostic images.

Concepts such as beam collimation, filtration, and the inverse square law are applied to protect both patients and practitioners from unnecessary radiation exposure.

Additionally, advancements in digital radiography and cone-beam computed tomography (CBCT) rely on the precise application of physics principles to produce detailed, three-dimensional images for accurate diagnosis and treatment planning in dental care.

1. Presented by: Nourhan M. Elsoudy
Certified Radiation Protection Officer

2. OutlineOutline

3. •Introduction
•Electromagnetic Radiation
•Ionizing and Non-ionizing Radiation
-Ionizing Radiations Biological Effects
•X-ray Production
-History of x-ray
-X-ray Tube
-Dental X-ray Machine
-Factors Controlling the X-ray Beam
-Dental X-ray Films
Outline

4. •Specialized Radiographic Techniques:
-Panoramic Imaging
-Computed Tomography
-Cone Beam Computed Tomography (CBCT)
-Magnetic Resonance Imaging
-Nuclear medicine
•Radiation Protection
-ALARA Principle
-Personal Dosimeters
-IAEA Recommendations
•References
Outline

5. IntroductionIntroduction

6. All of us are exposed to radiation
every day, from natural sources
such as minerals in the ground,
and man-made sources such as
medical x-ray.
Introduction

7. Introduction
Electromagnetic
Radiation

9. Introduction
Ionizing and Non-ionizing
Radiation

10. Ionizing Radiation:
•Ionizing radiation is radiation with enough energy so that during an interaction
with an atom, it can remove tightly bound electrons from the orbit of an atom,
causing the atom to become charged or ionized.
•Not all electromagnetic (EM) radiation is ionizing. Only the high frequency
portion of the electromagnetic spectrum which includes x-rays and gamma rays
is ionizing.
Ionizing and Non-ionizing Radiation

11. Non-ionizing Radiation:
•Non-ionizing radiation exists all around us from many sources. It is to the left of
ionizing radiation on the electromagnetic spectrum. It includes radio waves,
microwaves, infrared, ultraviolet and visible light.
•Non-ionizing radiation is the term given to radiation in the part of electromagnetic
spectrum where there is insufficient energy to cause radiation.
Ionizing and Non-ionizing Radiation

12. Ionizing Radiation Biological Effects:
Because living tissue is 70-90% water by weight,
the dividing line between radiation that excites
electrons and radiation that forms ions is often
assumed to be equal to the ionization of water.
Radiation that carries less energy can only excite
the water molecule. It is therefore called non-ionizing radiation.
Radiation that carries more energy can remove an electron from a water molecule,
and is therefore called ionizing radiation.
Ionizing and Non-ionizing Radiation

13. Ionizing Radiation Biological Effects:
•When ionizing radiation passes through living tissue, electrons are
removed from neutral water molecules to produce ??????
2??????
+
ions.
??????
2??????→??????
2??????
+
+??????
−
•The ??????
2??????
+
ion is an example of afree radical, which contains an unpaired
valence-shell electron. Free radicals are extremely reactive.
Ionizing and Non-ionizing Radiation

14. Ionizing Radiation Biological Effects:
•At the molecular level, these radicals destroy biologically active
molecules by either removing electrons or removing hydrogen atoms.
This often leads to damage to the membrane, nucleus, chromosomes,
or mitochondria of the cell that either inhibits cell division, results in
cell death, or produces a malignant cell.
•Most frequently ionizing-radiation induced cancers are: Leukemias,
thyroid, skin, breast, ovary, uterus, lung, myeloma and salivary glands.
Ionizing and Non-ionizing Radiation

15. Introduction
X-ray Production

16. History of X-ray:
•X-rays were discovered in 1895 by Wilhelm
Roentgen (1845-1923) who was a Professor at
WuerzburgUniversity in Germany. He won
a noble prize for his discovery of x-ray.
•Rontgen called them x-rays after the
mathematical symbol X for unknown.
X-ray Production

17. History of X-ray:
•Roentgen was experimenting with a vacuum tube covered in black
paper when suddenly he noticed that a piece of fluorescent paper was
glowing. Normally, such a glow would be caused by ultraviolet light,
but ultraviolet light would have been blocked by the black paper.
•If black paper didn’t block the rays, what would? He tried different
materials. Lead blocked the rays almost completely. Other materials
blocked them if they were thick enough, but water didn’t block them at all.
X-ray Production

18. History of X-ray:
•At one point, his hand passed between the tube and
the screen. He noticed that his hand created ashadow
on the screen and he saw the bones of his hands.
•He tested different materials to see if they were also
sensitive to the rays and discovered that photographic
plates were. He took anX-rayphotograph of his wife’s
hand that clearly showed the bones of her hand as well
as her wedding ring.
X-ray Production

19. History of X-ray:
14 days later the publication of Roentgen,
Dr. Otto Walkhoffmade the first picture of the teeth.
Walkhoffaskedthe physicist to take an X-ray of his
back teeth. Small pieces were cut from small
photographic plates wrapped in rubber dam and
exposed them for 25 minutes.
X-ray Production

20. X-ray Tube:
X-ray tube, also called Roentgen tube,
evacuated electron tube that produces
X-rays by accelerating electrons to a high
velocity with a high-voltage field and
causing them to collide with a target,
the anode plate.
X-ray tube used in dentistry is approximately
15 cm long and 1 inch in diameter.
X-ray Production

21. Dental X-ray Machine:
X-rays are an important diagnostic tool for the dentist.
Early detection and treatment of disease is the best way to
ensure a healthy mouth over a lifetime.
Any X-ray apparatus, even of the simplest type,
is an intricate and complicated piece of machinery
consisting of four main parts:
1-The X-ray tube 2-The control panel
3-The transformer 4-The tube stand
X-ray Production

22. Factors Controlling the X-ray Beam:
1-Exposure time
2-Tube current (mA) (The number of photons that reach the patient and the film)
3-The voltage (kVp) (The higher the kVpthe greater the penetrability of the beam through matter)
4-Filtration (Filtration of the x-ray beam removes lower energy x-ray photons from the beam)
5-Collimation (Used to reduce the size of the x-ray beam and reduce the volume of irradiated tissue)
X-ray Production

23. Factors Controlling the X-ray Beam:
6-Inverse square law (The radiation Intensity is inversely proportional to the square of the distance)
7-Cones (An open ended beam indicating device must be used)
8-Film speed (Faster image receptor systems result in decreased radiation exposure to the patient)
X-ray Production

24. Dental X-ray Films:
Dental film is a non-screen film. This means that it is
directly exposed by the x-ray and does not require
an intensifying screen. This gives much more detail than
standard radiographic film, but requires a higher amount
of exposure. It is packaged in its own paper or plastic sleeve,
to protect it from light and the oral environment.
The films that's placed inside patient's mouth composed of:
1. film base (0.18 mm thick) transparent base made of plastic(cellulose acetate).
2. adhesive layer: cause adhesions of the film emulsion to the film base.
3. film emulsion: record the x-ray image, sensitive to x-ray &visible light.
X-ray Production

25. Introduction
Specialized Radiographic
Techniques

26. Panoramic Imaging:
Panoramic dental x-ray uses a very small dose of
ionizing radiation to capture the entire mouth in one
image. It is commonly performed by dentists and oral
surgeons in everyday practice and may be used to plan
treatment for dentures, braces, extractions and implants.
Specialized Radiographic Techniques

27. Computed Tomography:
Three-dimensional (3D) radiographic imaging
of bony structures is an invaluable tool for
diagnostic and treatment planning purposes,
especially in oral and maxillofacial surgery
and implant dentistry.
Specialized Radiographic Techniques

28. Cone Beam Computed Tomography
(CBCT):
Dental cone beam computed tomography (CT)
is a special type of x-ray equipment used when
regular dental or facial x-rays are not sufficient.
Dentist may use this technology to produce three
dimensional (3-D) images of your teeth, soft
tissues, nerve pathways and bone in a single
scan.
Specialized Radiographic Techniques

29. Comparison Between CBCT and CT:
Specialized Radiographic Techniques

30. Magnetic Resonance Imaging:
Magnetic resonance imaging is a technique, which uses a combination of magnetic fields
and radio-frequency waves to generate images of the body. Instead of detecting tissues by
the x-ray, magnetic resonance detects the presence of hydrogen nuclei through their
resonance in a magnetic filed.
Specialized Radiographic Techniques

31. Nuclear Medicine:
Nuclear medicine and radioactive tracers
have considerable application in dental field,
because they provide one of the few
practical methods for studying the limited
metabolic activities of bones and teeth.
They are useful in studying many problems
of calcification and mineral exchange.
Specialized Radiographic Techniques

32. Introduction
Radiation protection

33. Radiation Protection:
Dentist should take several steps to ensure the least amount
of exposure possible when X-rays are taken.
1-No one but the patient should be in the exam room during
x-ray exposures.
2-Place a leaded shield (Lead apron’s) over the patient’s body
(Especially pregnant patients)
3-Use the fastest type of film (E/F) or digital sensors.
Radiation Protection

34. Radiation Protection:
Dentist should take several steps to ensure the least amount of exposure
possible when X-rays are taken.
4-Use a collimator, collimators limit the size and shape of the useful x-ray
beam reaching the patient.
5-Use a personal dosimeter for himself.
Radiation Protection
On the left is a rectangular collimator.
On the right the collimator is being used.

35. ALARA Principle:
There are three factors that control the amount, or dose, of radiation received
from a resource:
1-Time: Reducing the time of an exposure reduces the effective dose proportionally.
2-Distance: Increasing distance reduces dose due to the inverse square law.
3-Shielding: The term “Biological shield” refers to
a mass of absorbing material placed around radiation
source, to reduce the radiation to a level safe for humans.
Radiation Protection

36. Personal Dosimeters:
There are three main devices for monitoring and measuring radiation dose:
1-Film badge
2-Thermoluminescent dosimeter
3-Pocket dosimeter (Ionizing chambers)
Radiation Protection

37. IAEA Recommendations:
•The patient dose for each x-ray examination should be optimized so that it is
As Low As Reasonably Achievable (ALARA).
•The accumulated effect of the radiation exposure should be taken into consideration.
The salivary and the thyroid glands are among the organs at risk in dental radiology.
•Employees performing dental radiography should not normally receive significant
radiation dose provided normal radiation protection measures are employed, such as
distance and shielding. A report from UK estimates a mean level of less than 0.1 mSv
per year, in the practice conditions that prevail there. In the USA the mean dose
received by dental workers is reported to be 0.2 mSv.
Radiation Protection

38. IAEA Recommendations:
•Given the low doses received by staff involved in dental radiography, routine
personnel monitoring is generally considered to be desirable but not necessary.
•It is unusual for any member of staff in dentistry to get the foetaldose limit of 1 mSv
from work. A female staff member should understand the importance of notifying her
employer if she becomes pregnant.
•Film should not be hand held by a member of the dental practice staff. If necessary it
should be held by the patient, but only when it cannot otherwise be kept in position.
If the patient can not hold it, and a comforter/carermust be involved, then this should
be done using forceps or other device (eg., a specifically designed dental film holder)
so that fingers are not in primary beam.
Radiation Protection

39. IAEA Recommendations:
•Typical effective doses are for:
-intraoral dental X ray imaging procedure 1–8 μSv;
-panoramic examinations 4-30 μSv;
-cephalometric examinations 2-3 μSv,
-CBCT procedures (based on median values from literature): 50 μSvor below
for small-or medium-sized scanning volumes, and 100 μSvfor large volumes.
•Professional societies in collaboration with national authorities often recommend
that users make regular image quality performance checks on X-ray equipment
(and viewing screens where relevant). To enable users to do this, manufacturers
should provide details of the test procedures and the expected results in the
equipment’s instruction manual.
Radiation Protection

40. Introduction
References

41. References
1.JuditForrai, et al. History of X-ray in Dentistry. 2007, 3(3):205-211.
2. Spencer, James N.;Bodner, George M.;Rickard, Lyman H., et al. Chemistry structure and
dynamics 5
th
edition. 2010.
3. Ahmed Ghoneima, EmanAllam, Katherine Kula and L. Jack Windsor, et al. Three-Dimension
al Imaging and Software Advances in Orthodontics. 2012, DOI:10.5772/32037.
4. Vinita Boloor, et al. Nuclear medicine in dentistry revisited: New avenues to explore. 2013, D
OI:10.4103/2278-0513.119253.
5. Andy Wai Kan Yeung, YuxiongSu, Michael M. Bornstein, et al. CT scan vs. Cone Beam CT:
an overview. 2020.
6. IAEA official website: https://www.iaea.org/

42. Thanks