Intraoral Radiography Techniques Flashcards
What are the principles of radiation protection?
Justification, optimisation , limitation
What is optimisation in intraoral radiography?
•DC x-ray tube is more efficient and allows shorter exposure times
•Rectangular collimator for the majority of intraoral radiographs.
What is the aim for the penumbra to achieve the best quality image?
To be as small as possible with minimal magnification
Ideal situation is D
–Small focal spot
–Long distance between focal spot and object
–Short distance between object and image detector.
What steps should u take to get the best quality intraoral radiographs?
•Using a film holder with a bite block achieves:
–Film and tooth as close together as possible
–Film parallel to tooth
•Using a beam aiming device attached to the film holder achieves:
–X-ray beam perpendicular to tooth and film
•Using a long cone, rectangular colimator
–X-ray source to tooth distance as great as possible
–Good size match between the xray beam and the image detector.
Types of intraoral radiography
•Bitewings (BW)
•Periapicals (PA/IOPA)
•Occlusals
What do bitewings show?
• Show the crowns of premolars and molars of both jaws
•No or minimal overlap of enamel
–Up to half thickness of enamel is acceptable
Where should u see the bitewing?
Should see from contact point between canine and first premolar to the most distal contact point
Horizontal bitewings show superficial bone levels if bone loss is more than ..
6mm
Indications of bitewing radiographs
•Detection of approximal caries
•Detection of occlusal caries
•Detection of recurrent caries
•Assess depth of caries
•Monitor caries progression
•Check for overhangs
•Check for calculus deposits
•Assess superficial bone levels/architecture
•May see pins/perforations
What film size do we use for adults?
Size 2
What film size do we use for children?
Size 0 or 1
How to take bitewing radiograph
Use film holder with beam aligning devices
What is the horizontal bitewing technique?
•Long axis of film horizontal
•Bite block in middle of film
–Film held as close to the teeth as possible
–Film parallel to teeth
•Beam projects at right angles to the film (horizontally and vertically)
What is vertical bitewing technique?
•Long axis of film is vertical
•Each film covers fewer teeth but shows more alveolar bone
–Indicated if > 6mm bone loss
•Usually need at least 2 each side to cover the posterior teeth.
Advantages of film holders for bitewings
–Simple
–Film not displaced by tongue
–Beam always at right angles to film
–Less chance of cone cutting
–Reproducible technique
Disadvantages of film holders for bitewing
–More expensive initially
–May be uncomfortable
Incorrect technique for taking bitewings
- Open mouth= missed anatomy/ contact points
- Incorrect alignment of x-ray tube w the beam aiming ring = cone cutting (incomplete image)
- horizontal beam angulation error= overlapping contacts
Second type of technique for bitewings
•Original technique used sticky tab attached to the middle of the film
•Patient would bite on a wing which projects at right angles to the film
•Tab technique still useful for children who can’t cope with larger film holders in their mouths.
Advantages of adhesive tab technique
•Cheap
•Simple
•Good for small children
Disadvantages of adhesive tab technique
•Not reproducible
•More change of coning off
•Operator dependent
What does periapical radiographs include?
•Periapical radiographs should include
–All of tooth (crown and root)
–Periapical tissues (approximately 3 mm beyond the apex)
Indications for taking a periapical
•Apical pathology
–e.g. rarefying osteitis, cysts, root resorption
•Periodontal disease
•Endodontics
•Root morphology prior to extraction
•Impacted teeth
•Implant assessment
•Trauma
What is the periapical paralleling technique?
•Film holder and beam aiming ring
–Holds film parallel to tooth
–Aids correct alignment of beam with image detector
•Anterior periapicals
–Film size 0
–Blue bite block/ring
•Posterior periapicals
–Film size 2
–Yellow bite block/ring
Where is the cotton wool roll placed?
Cotton wool roll placed between bite block and OPPOSING teeth NOT the tooth being x-rayed
Advantages of paralleling technique
•Conforms to 3.36 of Guidance notes for Dental Practitioners on the Safe Use of X-ray Equipment
•Higher chance of reproducible radiographs
–Geometric accuracy with minimal magnification
–Less foreshortening or elongation
–Less likelihood of distortion due to film bending
•Less superimposition of zygoma over roots of maxillary molars
•Localising ring minimises cone cutting
–Fewer repeats and therefore lower dose.
Disadvantages of paralleling technique
•Expensive in first instance due to purchase of film holders
•Holders need to be sterilised
•Careful and accurate placement required
•Some patients find it uncomfortable
•Longer to perform a full mouth survey as smaller films used anteriorly.
Alternative periapical technique- bisecting angle technique
•The original periapical technique
•Not routinely used in LDI
•Film must be as close to tooth as possible
•Crown edge touching film and root diverging away
Steps in bisecting angle technique
•Diagram
–Line A-B = long axis of tooth
–Line A-C = film plane
–Line A-D = bisecting plane
•Bisecting plane
–Located at the midpoint of the angle between the long axis of the tooth and the film plane.
•X-ray beam aligned perpendicular to the bisecting plane.
How are films used in bisecting angle technique?
•Film holders can be used but more common for patient to hold film in place with finger
•Use largest periapical film anteriorly to reduce risk of cone cutting.
When can bisecting angle technique be useful?
Occasionally can be useful if can’t view a very long root on paralleling periapical film
How can bisecting angle technique be useful?
–Change the angle of the tube (i.e. no longer paralleling)
•Intentionally cause foreshortening
•Can project all of tooth and periapical tissues
–BUT not geometrically accurate so cannot take measurements.
Advantages of bisecting angle technique
–Cheap
–Quick
–More comfortable for patient
Disadvantages of bisecting angle technique
–Difficult to assess line of bisection- operator dependent
–Dose to finger
–Not reproducible
–Increased likelihood of cone cutting
–Not geometrically accurate
–Superimposition of structures e.g zygoma.
Further way of optimising technique of taking radiographs
Paralleling technique using film holders with beam aligning devices
–Reduces chances of non diagnostic films
What is the difference between bisecting angle and paralleling technique?
Bisecting - xray beam high, angles inferiorly, zygoma thru roots, no cant see periapical tissues
Paralleling- film parallel to tissue, xray beam perpendicular to film and long axis of tooth, xray beam lower to zygoma, projects superiorly. See roots + periapical tissue.
What are occlusals similar to?
bisecting angle periapical
Indications for occlusals
–Pathology not fully covered by periapical
–Assess impacted teeth such as maxillary canines
–Used in localisation in conjunction with other films (parallax principle)
–Trauma
–Bony expansion of mandible
–Submandibular duct stones
Occlusal technique
•Uses a larger film size
•Use circular collimator
•Film held between the teeth, parallel to occlusal plane
–Raised dot/sensitive surface of the receptor towards the arch being imaged i.e. up for maxillary teeth.
Where’s the Occlusal planes in maxillary and mandibular
•Maxillary
–Alar-tragus line
–White line in photograph
•Mandibular
–Corner of mouth to tragus
–Red line in photograph
What’s a true radiograph ? (Occlusal)
X-ray beam perpendicular to film from all directions
What’s a oblique radiograph? (Occlusal)
X-ray beam angled other than right angles to film from at least one direction
Why is Maxillary true virtually a useless film?
•Xray beam along line C in diagram
•Inclination of maxillary incisors does not allow a cross sectional view
•Unclear view of the incisors
–Superimposition of the bones of face and skull.
What is a upper standard occlusal? Or anterior oblique (AO) or maxillary midline
Maxillary oblique occlusal at the midline
What is the beam angulation of the maxillary oblique occlusal?
60 degrees to the occlusal plane, through tip of nose.
Other than the midline what may be known as lateral maxillary occlusal?
upper oblique occlusal of whichever tooth centred over
Why is maxillary vertex no longer used in LDI
Projects down through the vertex of skull along long axis of incisors, resulting in cross sectional view
Not ‘true’ occlusal
Beam angle is more than 90° to film
Mini cassettes with intensifying screens used due to the volume of bone that needs to be penetrated
X-ray beam angled towards abdomen so use of lead apron is prudent
Does not give a detailed image, teeth look like “a string of pearls”
What is mandibular true occlusal also known as? And at what degrees is the beam to the film?
lower 90o occlusal
X-ray beam is 90o to the film
Why is a cross sectional view achieved in mandibular true occlusal?
As the teeth in the mandible are more upright a cross sectional view is obtained
How are mandibular true occlusals positioned?
Mounted as if looking into the patients mouth
–Raised dot away from examiner
–Digital images require a ‘vertical flip’ and rotation
Why can you be confident that both teeth are on the palatal surface in the maxillary vertex occlusal and not upper standard occlusal
Upper standard occlusal angulation doesn’t come thru long axis of tooth
Maxillary vertex occlusal has a correct beam angulation
Where can mandibular true occlusal be?
Midline or to one side or the other
Indications of mandibular true occlusal
–Detection of calculi in the submandibular ducts
–Assessment of bucco-lingual position of unerupted mandibular teeth
–Evaluation of bucco-lingual expansion of body of mandible lesions
–Assessment of fracture displacement of the anterior mandible
–Assessment of mandibular width for implants.
What does lower anterior occlusal look like?
Big bisecting angle periapical
Indications of lower anterior occlusal
–Periapical assessment o flower incisors in patients unable to tolerate film holder
–Evaluation of larger lesions in the anterior mandible.
In lower anterior occlusal, what is the midline also known as?
Standard
What is beam angulation in lower anterior occlusal
Approx 45 degrees thru the chin point
Howe often is lower oblique occlusal used?
Rarely
Indications for lower oblique occlusal
–Radiopaque calculi in the submandibular gland
–Assessment of bucco-lingual position of unerupted lower third molars
–Evaluation of bucco-lingual expansion of lesions in posterior mandible.
How is the xray tube aimed in lower oblique occlusal?
X-ray tube aimed upwards and forwards from below and behind the angle of the mandible.
Why do we use localisation?
Localise impacted teeth or foreign bodies
–Orthodontist may wish to know whether a tooth is positioned such that it will interfere with tooth movement
–Surgeons may need to know whether a tooth is better approached buccally or palatally
Parallax technique of localisation
•2 views at an angle to each other
–Vertical shift e.g. paralleling periapical and oblique occlusal
–Horizontal shift e.g. 2 periapicals at different horizontal angulations
•Object further away moves in the same direction as the x-ray source
•SLOB rule
–Same lingual, opposite buccal
What radiograph would u use for caries?
bitewings best choice; slight bone loss also can be seen on horizontal bitewings
What is the slob rule
Same lingual, opposite buccal
If object move in same direction of xray source, positioned lingually
If object moves in opposite direction of xray source, positioned buccally
Why do we justify radiographs
Risk to patient outweighed by net benefit of that particular radiographic examination
