Oral and Maxillofacial Radiology

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15 Νοε 2013 (πριν από 3 χρόνια και 10 μήνες)

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Oral and Maxillofacial Radiology

for the Child





Juan F. Yepes DDS, MD, MPH, MS, DrPH





Introduction

Radiation Safety and Protection

http://www.pedrad.org/associations/5364/ig/

Radiation….Who cares?

People in the Sun


(Edward Hopper 1882
-
1967)

Smithsonian American Art Museum


Radiation….Who cares?

Photos by


GEORGE STEINMETZ and Google images

Radiation….Who
cares?

www.webmd.com/melanoma
-
skin
-
cancer/slideshow


“374 CT scans in 1 year


992 mSv / year”

3.6 mSv annual dose

Antepartum dental radiography and

Infant low birth weight

Potential mothers


Chronic exposure to radiation

(stochastic)


Develop subclinical hypothyroidism


Got pregnant


Delivery babies with LBW

Radiation Worries For Children in Dentist’ Chairs


CBCT increases productive and generate more profit

http://video.nytimes.com/video/2010/11/22/us/1248069363524/the
-
price
-
of
-
a
-
smile.html

Dosimetry

Equivalent dose (Ht):

it is used to compare the biological effects of




different types of radiation to a tissue or organ.




It
is the sum of the products of the absorbed dose



(
Dt
) averaged over a tissue or organ and the



radiation
weighting factor (
Wr
)


depends on the



type
of radiation





Ht =
Σ

Wr

x
Dt



IS Unit


sievert (Sv)

Traditional unit


rem


1 Sv = 100 rem

Radiation Safety and Protection

Radiation Safety and Protection

Sources of Radiation Exposure

Natural Radiation


Cosmic Sources









Subatomic particles and photons from






the sun.







It is primarily a function of altitude






Sea level: 0.24 mSv / Year






Denver (Colorado): 0.50 mSv/Year







Exposure resulting from airline travel






5 hours flight: 25µSv


Radiation Safety and Protection

Natural Radiation




Cosmic





Terrestrial Sources






External Radiation
: Radioactive nuclides in





the soil, primarily potassium 40 and the





radioactive decay products of uranium 238,





and thorium 232 (0.5 mSv / year)






Radon
:
Radon is a decay product in the





uranium series. It is responsible of 52%





of the radiation exposure of the world’s





population (1.2 mSv/Year).





It is a GAS


attached to dust





particles


LUNGS






Other Internal
: Ingestion of uranium






Radiation Safety and Protection

Radiation Safety and Protection

Man
-
Made Radiation



Medical Diagnosis and Treatment










Well over one billion medical x
-
ray examinations





are performed annually worldwide.





Dentistry is responsible for less than 1% of the





man
-
made sources of radiation







Consumer and Industrial Products






Domestic water supply, tobacco products,





combustible fuels, dental porcelain, television





receivers, pocket watches, smoke alarms, and





airport inspection systems.

Sources of

Radiation

Exposure

Natural







Artificial

3.6
mSv / year

83% (3mSv / year)

17% (0.6mSv / year)

Cosmic


Terrestrial



Internal

radon

Ingestion

of food

2.4 mSv

Radiation Safety and Protection

From EPA website

Radiation Safety and Protection

Natural and Artificial Radiation
Terrestrial
Internal
Medical x-ray
Radon
Nuclear Medicine
Consumer Products
Cosmic
Other
3.6 mSv

2.4 mSv / Year

Medical x
-
ray


0.39 mSv (2.5% dental x
-
rays)

Radiation Safety and Protection

Radiation Safety and Protection

Dose and Risk in Radiology

Dose Limits

The NCRP and the ICRP established guidelines

for limitations on the amount of radiation

received by both occupationally exposed

Individuals and the public.


There are no limits on the exposure a patient

can receive from diagnostic or therapeutic

exposures.



Dentist and their staff are occupationally

e
xposed workers


no more than 50 mSv/Year

Radiation Safety and Protection

Effective
Dose from Diagnostic

Radiology and equivalent background

Examination

Effective

Dose
(mSv)

Equivalent
background
radiation (days)

Intraoral

Posterior

BW (F
-
speed)

(rectangular collimation)

0.005

0.6


FMX

(rectangular c.)

FMX (round collimation)

0.035

0.171

4

21

Extraoral

Panoramic

Cephalometric

0.009
-
0.026

0.003
-
0.066

1
-
3

0.5
-
1

CBCT

I
-
CAT®
(extended
view)

0.235

29

CT

Head

2

243

Background radiation: 3.6 mSv / year

Radiation Safety and Protection

Risk Estimates


The primary risk from dental radiography is radiation
-
induced cancer (stochastic )




The risk for cancer being induced in human as a result of exposure to low doses



of radiation is difficult to estimate for different reasons:



-

The data for the cancer risk from radiation exposure involve exposures



many times larger than dental radiology



-

Cancer is a common disease. It is difficult to detected the effect of



dental radiography



-

The time between the radiation exposure and the development of cancer



may be years to decades.

Dosimetry

Dose Limits


NCRP and ICRP
(private nonprofit organizations)

ALARA:
As low As Reasonable Achievable

Maximum Permissible Dose

(MPD)

for occupationally exposed workers

NCRP:

50 mSv/yr

ICRP:

50 mSv/yr



Radiation Safety and Protection

Thyroid




Intraoral


full mouth survey with round collimation is 0.94 mSv;


the same study with rectangular collimation results in a dose of


0.26 mSv




Panoramic Radiograph


0.11 mSv

Radiation Safety and Protection

Radiation Safety and Protection

Reducing Dental Exposure

Patient Selection Criteria



Little evidence to support radiographic exposure of all edentulous


areas of the oral
cavity.




Clinical evaluation

+
Combined selected periapical radiographs

can


result in a
43% reduction

in the number of films without a clinical


consequential increase in the rate of undiagnosed disease.




ADA and FDA developed guidelines for the selection of patients for


dental radiographic
examination.

Radiation Safety and Protection

Patient Selection Criteria

Radiographs must be limited to the areas required for

adequate diagnosis and treatment based on professional

judgment

Dentist should not prescribe routine radiographs at
preset

intervals

for all patients

For new or referred patients, clinicians should obtain recent

dental radiographs from the patient’s previous dental health

care provider

Dental radiographs my be prescribed for pregnant patients with

careful adherence to the radiation safety protocols

Dentist should prescribe dental radiographs
ONLY

after clinical evaluation

Radiation Safety and Protection

Patient Protective Equipment



Leaded aprons and thyroid shields that contain lead or other materials


are patient


protective equipment.




If all the NCRP recommendations are followed rigorously, the use


of lead apron on patients is not required.
(1)





Thyroid shielding with a leaded thyroid shield or collar is
strongly


recommended

for children and pregnant women.
(2)





Thyroid collars are also recommended for adults when it will not interfere


with the exposure.
(1)




To prevent cracks in the leaded shield, practitioners should enforce


that leaded aprons and collars are hung and not folded

(1)
National Council for Radiation Protection & Measurements; 2003


(2)
US Department of Health and Human Services, Public Health Service, FDA and American Dental Association Council of


Scientific Affairs, 2004

Patient Protective Equipment

Protection of the Personnel

ADA: Council of Scientific Affairs
2006

Radiation Safety Procedures



If leaving the room or making use of some other barrier is


impossible, strict adherence to POSITION DISTANCE RULE is


mandatory

6 feet

6 feet

Except: New Mexico

Radiation Safety and Protection

Selection Criteria


-
Exposing radiographs in asymptomatic children


-
Development of the dentition as criterion


-
Risk of caries as criterion


-
Radiographic examination

Selection Criteria



The stage of dentition development




The risk of dental caries

Selection Criteria


Exposing radiographs in asymptomatic children

Selection Criteria


Exposing radiographs in asymptomatic children

Selection Criteria


Development of the dentition as criterion


Selection Criteria


Risk of caries as criterion


Selection Criteria


Risk of caries as criterion


Guidelines for prescribing dental radiographs

New Patient



Child with primary dentition

(prior to the eruption of first permanent tooth)


-
Individualized radiographic exam

-
Selected periapicals / occlusal views or posterior bitewings


** Patients without evidence of disease and with open proximal contacts


may not require a radiographic examination at this time

ADA, December 2004

Selection Criteria


Guidelines for prescribing dental radiographs

New Patient


Child with
transitional
dentition

(After eruption of first permanent tooth)


-
Individualized radiographic exam consisting of posterior


bitewings with panoramic exam or posterior bitewings and


selected periapical images.

ADA, December 2004

Guidelines for prescribing dental radiographs

New Patient


Adolescent with permanent dentition / Adult dentate or partially edentulous

(prior to the eruption of third molars)


Individualized radiographic exam consisting of posterior bitewings with

Panoramic exam or posterior bitewings and selected periapicals


A full mouth intraoral radiographic exam is preferred when the patient

has clinical evidence of generalized dental disease or history of

extensive dental treatment

ADA, December 2004

Commonly used radiographic techniques in Pediatric

Dentistry



Bitewing



Paralleling



Bisecting


Projection Geometry

Photons (x
-
rays) originating

at different places on the

focal spot result in a zone of

unsharpness on the radiograph


The larger the focal spot area,

the greater the loss of clarity


Three methods to improve the quality of

the radiograph:


1.
Use as small an effective focal spot as


practical (1.0 mm or less)


2.

Increase the distance between the focal spot


and the object by using a long, open
-
ended


cylinder


3.
Minimize the distance between the object and


the film

Commonly used radiographic techniques in Pediatric Dentistry

Projection Geometry

Image Size Distortion



Image size distortion (magnification) is the increase in size of the image on the



radiograph compared with the actual size of the object.




Image size distortion results from the relative distance of the focal spot
-
to
-
film and



object
-
to film




Increasing the focal spot
-
to film distance and decreasing the object
-
to
-
film distance



minimizes image magnification

Commonly used radiographic techniques in Pediatric Dentistry

Projection Geometry

Image Shape Distortion



Image shape distortion is the result of unequal magnification of different parts



of the SAME object.




This situation arises when
not all the parts of an object are at the same focal



spot
-
to
-
object distance.

10 cm

8 cm

Commonly used radiographic techniques in Pediatric Dentistry

Projection Geometry

Image Shape Distortion



To minimize shape distortion, the practitioner should make an effort to align the



tube, object, and film carefully according to the following guidelines:



-

Position the film PARALLEL to the long axis of the object



-

Orient the central x
-
ray perpendicular to the object and film: Image



shape distortion occurs if the object and film are parallel BUT the central



x
-
ray is not directed at right angles to each. This is most evident



on maxillary molar projections.

Copyright permission from Oral Radiology, White
-
Pharoah

Commonly used radiographic techniques in Pediatric Dentistry

Projection Geometry

Copyright permission from Oral Radiology, White
-
Pharoah

Paralleling and Bisecting
-
Angle Techniques



An early method for aligning the x
-
ray beam and the film with the teeth and jaws



was the
bisecting
-
angle
-
technique.



-

The film is placed as close to the teeth as possible without deforming it.


-

However, when the film is in that position , it is not parallel to the



long axes of the teeth


-

Imaginary plane that bisects the angle between the teeth and the film.

Commonly used radiographic techniques in Pediatric Dentistry

Projection Geometry

Copyright permission from Oral Radiology, White
-
Pharoah

Paralleling and Bisecting
-
Angle Techniques



The
paralleling technique is the preferred method for making intra
-
oral radiographs
.




It derives its name as the result of placing the film parallel to the long axis of the tooth.




This procedure minimizes image distortion and best incorporates the principles of



image geometry.




To achieve this parallel orientation, the practitioner often must position the film towards



the middle of the oral cavity, away from the teeth
(image magnification and loss of



definition)




Use of film holders

Commonly used radiographic techniques in Pediatric Dentistry


Specific Dental Projections in Pediatric Dentistry





periapical



occlusal



panoramic

Occlusal Projections

Occlusal Techniques


-
Occlusal radiographs are named for the fact that the film


is placed upon the occlusal surface for exposure


-
Usually # 4 size films, also called occlusal films


-
Standardized projections

Maxillary Occlusal Projections





Mandibular Occlusal Projections

Occlusal

2. Standard Occlusal View



Bridge of the nose


Similar to anterior occlusal view


Film long axis: Side to side (cross)


70 degrees

Maxillary Occlusal Views

Standard

Occlusal

Views

70
°

Film

Glabellum

Standard occlusal view

Mandibular Occlusal Views


1.
Anterior Occlusal View



Film placed on the occlusal surfaces


Long axis: antero
-
posterior direction


The film extends ¼ inch labial


In pediatric patients


# 2


Beam: Just above the chin point


60 degrees

Anterior

Occlusal

Views

60
°

Film

Chin point



Panoramic Imaging

Panoramic Imaging

Principal Advantages:



Broad coverage of the facial bones and teeth



Low patient radiation dose



Ability to use in patients unable to open their mouths



Short time required to make panoramic image : 3


4 minutes (including patient






positioning)


Panoramic Imaging


Basic Principles


Panoramic imaging is most useful clinically for the diagnostic


problems requiring broad coverage of the jaws:





Trauma





Location of third molars





Extensive disease





Tooth development

Panoramic Imaging


Basic Principles

Disadvantages



The images do not display the fine anatomic detail available on


intra
-
oral periapical radiographs.



Unequal magnification



Geometric distortion across the image



Overlapping structures


cervical spine in the anterior region

Panoramic Imaging


Basic Principles

Interpreting the Panoramic Image


Recognizing normal anatomy structures


MOST IMPORTANT




-

Complex of the anatomy of the mid
-
face



-

Superimposition of anatomical structures



-

Changing projection orientation

Absence of a normal anatomic structure

maybe the MOST IMPORTANT finding

on the image.

Panoramic Imaging

Anatomic Landmarks

CBCT