DEN 7127 Extraoral Projections and Anatomy (eliz)- mz

Extraoral projections

Why do them?

• Examine areas not fully covered by intraoral films

• Evaluate the cranium, face (Mx +Mn), cervical spine, trauma or pathology

• Evaluate the patient's complaints and clinical signs prior to prescribing individualized extraoral projections

Canthomeatal line:

lateral canthus of the eye to center of external auditory meatus. Forms 10-degree angle with the Frankfort plane

Frankfort plane:

superior border of external auditory canal to infraorbital rim

lateral CEPH

film parallel to midsagittal plane

SMV

canthomeatal line parallel to receptor

Waters

cantomeatal line 37 degrees with receptor

PA Ceph

canthomeatal line 10 degree with receptor

Reverse Towne Projection

canthomeatal line -30 degrees with receptor

Used to identify fractures of the condylar neck and ramus

Lateral Cephalometric Projection

The central beam is___________________ to the midsagittal plane of the patient.

perpendicular

Lateral Cephalometric Projection

Evaluate the anteroposterior (AP) relationships between_________, __________ and ___________

maxilla, mandible and cranial base

Lateral Cephalometric Projection

Assess ______________ and______________ relationship

skeletal and soft-tissue

Lateral Cephalometric Projection

Monitor progress of _______________ and ______________ out comes

treatment and treatment outcomes

Lateral Cephalometric Projection

A wedge filter absorbs some of the radiation to allow visualization of ________________________________

soft tissue of the face.

Lateral Cephalometric Projection

Exact superimposition is impossible due to ________________________________________________________________

magnification of the structures on the far side from the receptor

don't need to learn every single landmark

not soft tissue

just obvious boney landmark structures

Posteroranterior(PA) skull projection

Evaluation of

Why do you do this?

Evaluation of craniofacial asymmetry

it make the face more clear

Posteroranterior(PA) skull projection

Monitor progress of _____________ and ____________________________

treatment and treatment outcomes

Posteroranterior(PA) skull projection

Positioning:

• Frankfort plane = ___________

• Canthomeatal line = _____________________

floor

10 degree from the floor

Posteroranterior(PA) skull projection

Submentovertex projection

• Can be useful in

-evaluating fractures of the zygomatic arches

-aeration of sphenoid sinuses

-osseous changes from skull base tumors

Is this image over or under exposed?

underexposed

Submentovertex projection

Indications are largely achieved by _______

CT

Waters projection

Evaluation of

sinuses, predominantly the maxillary sinus and a lesser extent the frontal sinus and ethmoid air cells, midfacial fractures

Waters projection

Diagnostic objectives are accomplished by______

CT

Reverse-Towne projection

• Helpful to evaluate

condyle and condylar neck fractures

Reverse-Towne projection

Diagnostic objectives are achieved by ______

CT

radiation dose

amount of ionising radiation a person receives

Absorbed dose

• Total energy absorbed by ionizing radiation per unit mass of irradiated material

• Absorbed Dose = _______/___________

• Absorbed Dose = Energy/ Mass

Absorbed dose-SI unit:

Gray, where 1 Gy = 1 J/kg

Absorbed dose -Traditional unit:

rad (radiation absorbed dose)

Conversion

• 1 rad = _____Gy

• 1 Gy= _____ rad

0.01

100

Equivalent (radiation-weighted) dose

Not all types of ionizing radiation cause the same biological damage

1 Gy of alpha particles cause (more/less/the same) biologic damage than 1 Gy x-ray photon

more

Radiation weighting factor established by ________________________________________________________ to account for the relative effect of producing biologic damage

ICRP (International Commission on Radiological Protection)

Equivalent dose =

Absorbed dose * Radiation weighting factor

Equivalent dose SI unit : Sievert [Sv] = [J/kg]

Equivalent dose Traditional unit:

rem (roentgen equivalent man)

Conversion

• 1 rem = _______

• 1 Sv = _______

0.01 Sv

100 rem

Who causes more damage? Tyson (heavy charged alpha particle) or Mayweather (x ray photons)?

Tyson

Tyson is equivalent to alpha particle or x-ray photon?

alpha particle

Mayweather is equivalent to alpha particle or x-ray photon?

x-ray photon

Radiation weighting factor

X ray photons =___

Alpha particle (heavy charged particle) =___

1. 20

Biologic damage

10 mGy from alpha radiation =______mGy of x ray

200

Effective dose

Used to estimate...

estimate the risk in humans

- account for different radiosensitivity of different tissues

- in terms of the risk for stochastic effects (cancer induction and heritable effects)

Tissue weighting factors established by the ______

ICRP

Effective dose = sum of products of equivalent dose to each organ or tissue and the corresponding weighting factor =

= equivalent dose (Ht) * tissue weighting factor (Wt)

Effective dose

SI unit : Sievert [Sv] =_____________

[J/kg]

Effective dose

Traditional unit: ____________________________

rem (roentgen equivalent mam)

1 Sv = _____ rems

100

Tissue weighting factor established by

ICRP

Background radiation (United States)

Naturally occurring radiation exposure

_____ mSv = Average annual per capita effective dose in the US in 2006 (NCRPreport No. 160)

3.1

Background radiation sequence

Radon (73%) > Space (11%) > Internal radionuclides (9%) > Terrestrial (7%)

• Radon-222:

Naturally occurring radioactive elements in earth's crust.

- produced in the uranium-238 decay chain

emits alpha particles, which can be inhaled.

• Space/cosmic radiation:

comes from sun or cosmic rays. Composed of protons, helium nuclei, and nuclei of heavier elements. Function of altitude, doubling with each 2000m increase in elevation. Sea level 0.33 vs Denver 0.5 mSv/yr

Internal radionuclides:

Ingestion of food and water containing radioactive material such as uranium and thorium and etc.

Terrestrial:

radioactive materials in the soil. Potassium-40, thorium-232, uranium-238, radium. In brick, concrete, granite

medical, and consumer products _____ mSv/year

3.1

CT: Computed tomography

Nuclear medicine

Interventional radiography and fluoroscopy

Conventional radiography and fluoroscopy

Consumer products and other: Cigarette smoking, Air travel, Mining, agriculture, and combustion of fossil fuels e.g., flight of 5 hours cruising at an altitude of 12km results in an exposure of 25 microSv

_____ billions x-ray and nuclear medicine exams done annually worldwide. ___% of these are dental radiographic exams.

3.6, 14

• Daily background dose = _____ microSv

8.5

Does 3D image have more radiation than 2D?

yes, but it's not that much different.

Communicating radiation risk to patients

Allow the patient to

fully express his/her thoughts. Acknowledge their concerns

Explain the patient

why you need radiographs as part of the patient's personal diagnosis (caries, extent of bone loss, periapical infection and information that can only be obtained by radiographic examination)

Reassure the patient

you make efforts to minimize the radiation (digital sensor, thyroid collar, rectangular collimation, individualized imaging parameters)

Convey the relative magnitude of the dose that the patient is likely to receive (compare to _________________________________________)

natural background radiation or airline flight

Rectangular collimation

the area of patients skin surface exposed by 50% to 65% over round

Dose Limit (NCRP: National Council on Radiation Protection)

is there a limit?

no

ALARA____________________________________________

(As Low As Reasonably Achievable)

ALADA _________________________________________

(As Low As Diagnostically Acceptable),

Pregnant or potentially pregnant patient

• Follow the same principle of _______________, ADA selection criteria for dental radiographs

• Estimated fetal dose from dentomaxilofacial radiography is ________________ fold lower than the threshold dose for deterministic effects on embryo and fetus.

ALARA, 42,000

Dosimeter

The ADA recommends who should wear a dosimeter

• the workers who may receive an annual dose greater than 1 mSv should wear personal dosimeters to monitor their exposure levels.

• Pregnant dental personnel operating x-ray machine, regardless of anticipated exposure levels.

The requirement to use personnel dosimeters is specified by ____________________________________

state and national regulations

• In US, the code of federal regulations requires that personnel likely to receive more than _______ of the annual dose limit be monitored.

10%

NCRP:

National Council on Radiation Protection and Measurement

ICRP:

International Commission on Radiological Protection

If you can't stand behind a wall, were can you stand? Minimum distance?

6 feet/2 meters

Don't stand behind or in front where there is likely to be rebounding scattered radiation

Radiographic prescription

Follow the principle of ALARA (As Low As Reasonably Achievable)

• Least amount of radiation exposure necessary to generate diagnostically acceptable images

• Prescribe individualized radiographs only after a clinical examination

• Attempt to acquire previous radiographs from patient's previous dentist.

• Progression of caries, periodontal disease and pathology

CHILD WITH PRIMARY DENTITION (PRIOR TO ERUPTION OF FIRST PERMANENT TOOTH)

NEW PATIENT

Selected PA's/Occlusal+ BWX

CHILD WITH PRIMARY DENTITION (PRIOR TO ERUPTION OF FIRST PERMANENT TOOTH)

RECALL PATIENT

Caries High Risk

BWXevery6-12months if not visualized or probed

CHILD WITH PRIMARY DENTITION(PRIOR TO ERUPTION OF FIRST PERMANENT TOOTH)

RECALL PATIENT

Monitoring of growth and development

Clinical judgment

CHILD WITH PRIMARY DENTITION(PRIOR TO ERUPTION OF FIRST PERMANENT TOOTH)

RECALL PATIENT

Other circumstances

Clinical judgment

When is FMS first recommended?

ADOLESCENT W/ PERMANENT DENTITION (PRIOR TO ERUPTION OF THIRD MOLARS; 12~18)

New patient

ADULT DENTATE AND PARTIALLY EDENTULOUS

RECALL PATIENT

Caries Low Risk

BWX every 24-36 months

Every patient should have a FMX every 12 months T/F

False! there should not be a rule for every patient. It should depend on the patient and their risk