FELINE-Dental Radio Graphic Technique in Cats

8/14/2019 FELINE-Dental Radio Graphic Technique in Cats

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Vol. 22, No. 2 February 2000

Refereed Peer Review

FOCAL POINT

KEY FACTS

#In cats, proper dentalradiographic technique is

essential to ensure accurate

imaging for detection of occult

pathologic conditions.

Dental RadiographicTechnique in CatsUniversity of California, Davis

Milinda J. Lommer, DVMFrank J. M. Verstraete, DrMedVetCheryl H. Terpak, RDH, MS

ABSTRACT: Dental radiography is a critical tool in the evaluation and treatment of feline oral

diseases. Although dental radiographs can be obtained using standard radiographic equip-

ment and film, a dental radiography unit and intraoral film provide superior images, easier pa-

tient positioning, and less radiation exposure. The problem of zygomatic arch superimposition

over the maxillary premolars and molars may be avoided by using the extraoral near-parallel

technique. Full-mouth radiographs are indicated in cats presented for dental treatment for the

first time because important conditions may be found.

Dental disease is prevalent among domestic cats, with approximately 70%of cats older than 3 years of age being affected.1 However, clients maybe unaware of a dental problem until the disease has reached an ad-

vanced stage. Oral inspection during annual physical examinations may revealevidence of periodontal disease, odontoclast resorption lesions, or endodonticdisease. Dental radiography is essential to more accurately diagnose these condi-tions, formulate a therapeutic plan, and evaluate the success of therapy after ex-tractions or endodontic obturation.

Although dental radiographs can be obtained using extraoral film and stan-dard radiographic equipment, intraoral radiographic film and a dental radiogra-phy unit provide superior images with minimal radiation exposure. Skull radio-graphs may be useful in trauma patients or patients with neoplasms or whenintraoral film cannot be placed into the oral cavity.1 One method describes usingintraoral films with a standard radiography unit.2 A radiography unit used fordentistry must have a movable, rotating head to allow proper positioning for thebisecting-angle technique. However, conventional radiographic techniques often

result in superimposition of anatomic structures and may result in unsatisfactoryviews of individual teeth. Cats present additional challenges because of the com-pact shape of their skulls and the difficulty in obtaining satisfactory views withsuperimposition of the zygomatic arch over the maxillary cheek teeth.3

Although several techniques for diagnostic dental radiography have beendescribed,1,49 obtaining consistently good radiographs of feline maxillary premo-lars can often be difficult.3,8 The extraoral near-parallel technique provides a re-peatable method for achieving high-quality radiographs of the maxillary premo-lars and molars.

CE

I Dental radiography is indicated

during routine periodontal

treatment and when oral disease

is suspected.

I The parallel technique is used

for the mandibular premolars

and molars, whereas the

bisecting-angle technique

must be used for maxillaryand mandibular occlusal views.

I The extraoral near-parallel

technique provides a repeatable

method for obtaining high-quality

radiographs of the maxillary

premolars.

I Standardization of radiographic

orientation allows rapid

recognition of the location of

pathologic conditions.


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INDICATIONSOnly the mucosa, gingiva,

and dental crowns can be in-spected visually; but inspec-tion may not reveal the extentof disease.3,4,10 Radiographs

allow evaluation of tooth roots,the surrounding periodontalligament, and bone and aretherefore essential for assess-ing oral disease (see Indica-tions for Dental Radiogra-phy in Cats). Because oralradiography requires generalanesthesia or heavy sedation,however, it may be contra-indicated in critically ill pa-tients that cannot tolerate an-esthesia.

In veterinary practice, den-tal radiographs are typicallytaken only on an as-indicat-ed basis (i.e., if a problem isdetected during the initialoral examination and peri-odontal probing). However,

whole-mouth radiographs canprovide useful informationand should perhaps be done on a routine basis, as ispracticed in human dentistry. In a recent study involving115 cats,10 radiographs of teeth without clinical lesionsrevealed important findingsin 41.7% of cases. Radio-graphs of teeth with clinicallesions yielded additionalinformation in 86.1% of thecases. Therefore, full-mouthradiographs of cats being pre-sented for dental treatmentfor the first time is justifiable.

TECHNIQUESTo obtain viable images

on dental radiographs, the

central x-ray beam must bedirected at a specific anglerelative to the tooth rootand the film. Otherwise, theresultant image will be dis-torted. The parallel and bi-secting-angle techniques arethe two primary techniquesused in veterinary dentistry.

ParallelWith the film placed par-

allel to the long axis of thetooth, the primary x-ray beamshould be directed perpendic-ular to the film and the long

axis of the tooth (Figure 1).The film must be adjacent tothe tooth to prevent distor-tion or magnification of theimage. This technique isused for radiographs of themandibular premolars andmolars.

Bisecting AngleBecause of interference by

the palate and mandibularsymphysis, film cannot be po-

sitioned parallel to the longaxis of the maxillary teeth ormandibular canines and in-cisors. Therefore, the bisect-ing-angle technique is usedbecause the film can be placedat an angle to the long axis ofthe tooth without distortingthe image. This technique is

based on the geometric principle of isometric triangles:If two triangles have an equal angle at the apex and oneshared side, the opposite sides are equal in length (Fig-

ure 2).The film should be placed

as close as possible to the toothwithout bending the film; do-ing so bisects the angle be-tween the long axis of thetooth and the film, therebycreating a shared side betweentwo isometric triangles. Theprimary x-ray beam should bedirected perpendicular to thebisecting line rather than tothe long axis of the tooth.

When this technique is fol-lowed correctly, it results in alinearly accurate image. Theportion of the film farthestfrom the tooth may, however,be slightly distorted.

DENTAL FILMBoth D- and E-speed films

Small Animal/Exotics Compendium February 2000

D E N T A L E V A L U A T I O N I V I A B L E I M A G E S I W H O L E - M O U T H R A D I O G R A P H Y

Figure 1Illustration of the parallel technique, which is used toradiograph the mandibular premolars and molars.

I Routine dental prophylaxis (to assess bone level or

detect occult pathologic conditions)10

I Periodontal pockets detected on probing

I Odontoclastic resorptive lesions (to determine

extent)

I Fractured teeth

I Draining tracts or jaw swelling

I Jaw fractures

I Unerupted teeth in young patients (to determine

status)

I Chronic gingivitis, faucitis, or stomatitis

I Suspected neoplasia

I Missing teeth or supernumerary teeth9

I Endodontic treatment

I Dental extractions (to determine individual

morphologic tooth characteristics or whether root

fractures occur during extraction)

I Treatment of pathologic conditions (to evaluate

treatment progress)

I Bony changes in the mandible or maxilla caused by

renal or nutritional secondary hyperparathyroidism

Indications for Dental Radiography in Cats

Dental radiography unit

X-ray beam

Long axis

of the tooth

Mandibularfirst molar


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are routinely used in veteri-nary dentistry. D-speed filmprovides high contrast andfine detail, whereas E-speedfilm reduces the patients ex-posure to radiation by 50%

but has slightly less contrastthan does D-speed film. Fivesizes of dental film are avail-able; the most common usedin feline dentistry are 0, 2,and 4. Sizes 0 and 2 are peri-apical films, and size 4 is oc-clusal film (Table I).

STANDARD VIEWSSix views are adequate for

visualizing the entire felinedentition. At the University

of California VeterinaryMedical Teaching Hospital,an inexperienced student as-sisted by an experienced vet-erinary dental technician orclinician can take a com-plete set of radiographs in approximately 30 minutes.10

With practice, a complete set of radiographs of con-sistent quality can be obtained in approximately 15

minutes. Table II summa-rizes recommended views, po-sitions, techniques, film sizes,and lengths of exposure.

Maxillary

Incisors and CaninesTo radiograph the maxil-lary incisors and canines, catsshould be positioned in ster-nal recumbency. With the

white side up, size 4 intraoralfilm should be inserted intothe mouth toward the palate.Ideally, both canine cuspsshould touch the film. Formore efficient use of the film,it can be placed in the mouthdiagonally. The films em-

bossed bubble (or dot) mustbe outside the mouth (seeFilm Positioning and Orien-tation section). A tongue de-pressor can be used to pre-vent the film from bending

over the endotracheal tube (Figure 3).The cats head can be adjusted so that the film is lev-

el with the cone of the radiographic tube head. The

Compendium February 2000 Small Animal/Exotics

P E R I A P I C A L A N D O C C L U S A L F I L M I R E C O M M E N D E D V I E W S I P O S I T I O N I N G

Figure 2Illustrations of(top)the bisecting-angle technique,which is used to radiograph the maxillary incisors and canineteeth and (bottom) the principle of isometric triangles: Thelength of the tooth and the projected image are equal inlength. (A= angle; BSA= bisecting-angle technique)

TABLE IDental Film Used in Cats

Kodak Kodak Dimensions Size Ultra-speed Ektaspeed Plus (mm) View

0 DF-54 EP-01P 22 35 Mandibular P3M1

2 DF-58 EP-21P 31 41 Maxillary P2M1, mandibular occlusal

4 DF-50 EO-41P 57 76 Maxillary occlusal

M1 = first molar; P2= second premolar; P3= third premolar.

TABLE IIRecommendations for Standardizing Radiography in Cats

Exposure Time at 60 kV and 7 mAView Position Technique Film Size (seconds)

Maxillary I and C Intraoral (occlusal) Bisecting angle (C) 4 0.16

Maxilla P2M1 Extraoral Near parallel 2 0.20

Mandibular I and C Intraoral (occlusal) Bisecting angle (C) 2 0.12

Mandible P3M1 Intraoral Parallel 0 or 2 0.12

C= canine; I= incisor; P2= second premolar; P3= third premolar.


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root of a maxillary canineshould be palpated to deter-mine the direction of its plane;placing a cotton-tipped ap-plicator on the plane mayhelp to visualize its direction.

The angle between theplane of the root and theplane of the film should bedetermined and bisected ac-cordingly (Figure 2). Usingthe applicator may help tovisualize this angle. Thecone of the tube head shouldbe positioned so that thecentral x-ray beam is per-pendicular to the bisectingangle and situated as close as possible over the cats noseand head.

Premolars and MolarsBecause the zygomatic

arch overlies the maxillarypremolars in cats, the imagesof these two structures oftenoverlap on radiographs. To

avoid this problem, the extra-oral near-parallel technique(Figure 4A) is recommend-ed. Extraoral film must belabeled to distinguish it fromintraoral film and to ensureproper orientation duringprocessing.

Cats should be positionedin lateral recumbency withtheir mouth propped open.

Size 2 intraoral film, white side up, is placed under theside to be radiographed (Figure 4B). The tips of the pre-


B I S E C T I N G - A N G L E T E C H N I Q U E I N E A R - P A R A L L E L T E C H N I Q U E I L A T E R A L R E C U M B E N C Y

Figure 4A

Figure 4(A) Illustration and (B) clinical setup showingproper positioning for the extraoral near-parallel view of themaxillary premolars and molars. (C) Radiograph of the rightmaxilla. Note the position of the opposite arcade, embossedbubble (dot), and endotracheal tube. The x-ray beam is an-gled from the distal direction, allowing identification of themesial roots of the fourth premolar. The lettering ULT(ul-tra-speed) is reversed because the radiograph is being viewed

with the bubble facing down.

Figure 4B

Figure 4C

Figure 3Clinical setup showing proper positioning for theocclusal view of the maxillary incisors and canines using thebisecting-angle technique.


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molar cusps should be near thelower edge of the film to ensurethat most of the film is underthe maxilla and zygomaticarch. The film should then besituated with the bubble along

the lower edge (Figure 4C).The cats head should be ro-tated so that the plane of theroots of the premolars to beradiographed is parallel to thefilm. A 1-inch roll of adhesivetape can be placed under thepatients chin to secure thehead in the proper position(Figure 4B). The endotrachealtube should be gently guidedtoward the mandible so that itdoes not interfere with the

image of the maxillary teeth(Figure 4C). The cone shouldbe positioned so that the cen-tral x-ray beam is directedpast the opposite arcade andfalls precisely on the roots ofthe premolars near the filmand situated as close as possi-ble to the cats head to ensurethat the circumference of thecone covers the film.

MandibularIncisors and Canines

Cats should be positionedin dorsal recumbency and gentle pressure exerted onthe lingual frenulum of the tongue to relax any tension.

With the white side up, size 2 film should be insertedover the tongue. The bubble on the film should be out-side the mouth. Ideally, both canine cusps should touchthe film. Gauze can be placed under the film to secureit (Figure 5). The cats head can be adjusted so that thefilm is level with the plane of cone of the radiographictube head. The root of a mandibular canine should bepalpated to determine the direction of its plane.

The angle between the plane of the canine root andthat of the film should be determined and then bisect-ed. The cone of the tube head should be positioned sothat the central x-ray beam is perpendicular to the bi-secting angle and situated as close as possible over thecats chin.

Premolars and MolarsWith the cat in lateral recumbency, size 0 or 2 film

should be placed on the floorof the mouth near the premo-lars. The white side shouldbe near the teeth to be radio-graphed, and the bubble shouldbe caudal to the mandibular

ramus. Gauze can be gentlyplaced above the film to holdit firmly on the floor of themouth. The cone of the tubehead should be positionedclose to the mandible so thatthe central x-ray beam is per-pendicular to the film. Thefilm must be within the cir-cumference of the cone (Fig-ure 6).

SPECIAL VIEWS

Occlusal views of the maxil-lary and mandibular caninesand incisors are satisfactory forroutine evaluation. However,if pathologic conditions of thecanine teeth are suspected,these views are inadequate be-cause superimposition of thecanines and premolars ob-scures the apices of the ca-nines. The lateral-oblique view(Figure 7) is recommended forevaluating the periapical re-gion of the maxillary canines.This view is obtained using

the bisecting-angle technique: The angle of the long axisof the canine tooth as viewed from the front of the cat(Figure 7) and the plane of the film should be bisected.The same technique can be used for the mandibular ca-nines. Size 2 film should be used for the mandible andsize 4 for the maxilla; the film should be placed squarelyin the mouth, with the bubble in front. The recom-mended exposure time is 0.16 seconds for the maxillaand 0.12 seconds for the mandible.

To separate the mesialbuccal and lingual (palatal)

roots of the maxillary fourth premolars, the central x-ray beam should be directed at a slight angle from thecaudodistal or rostromesial direction while maintainingthe proper vertical angle with the film to prevent imagedistortion. When the intraoral technique is being used,the following rule, known as the SLOB rule, helpsidentify these roots on developed film: samelingual,oppositebuccal.8 Same refers to the horizontal direc-tion of the beam; if the beam is angled from the distal


C O N E P O S I T I O N I N G I C E N T R A L B E A M I O C C L U S A L V I E W S I I N T R A O R A L T E C H N I Q U E

Figure 5Clinical setup showing proper positioning forthe occlusal view of the mandibular incisors and caninesusing the bisecting-angle technique.

Figure 6Clinical setup showing proper positioning forradiographing the mandibular premolars and molars us-

ing the parallel technique.


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Compendium February 2000 Small Animal/Exotics

direction, the root most distal on the film is the lingualroot and the opposite, or mesial, root is the buccal root.However, because the extraoral near-parallel techniqueis recommended for cats, the reverse applies: If thebeam is angled from the distal direction, the root mostdistal on the film is the buccal root and the opposite, ormesial, root is the lingual root (Figure 4C).

FILM POSITIONINGAND ORIENTATION

The most common problem withintraoral radiography is improp-er positioning of the film or theprimary beam. The film must beplaced far enough in the mouth toobtain images of the molars andpositioned so that the apices of theteeth are visible on the film. Whenthe bisecting-angle technique isused, accurate determination ofthe long axis of the tooth and cor-rect bisection of its angle with thefilm are important. Otherwise,

elongation or foreshortening mayoccur. The extraoral near-paralleltechnique used for maxillarycheek teeth may result in elonga-tion, foreshortening, or superim-position of anatomic structuresover the tooth roots if not doneproperly.

Brachycephalic cats present a

radiographic challenge because of the increased difficul-ty in preventing superimposition of the zygomatic archover the maxillary premolars and molars. The extraoralnear-parallel technique can be used for brachycephaliccats, but considerable patience and several attempts maybe required to position cats for maxillary views.

After the film has been developed, the identification

S L O B R U L E I C O M M O N P R O B L E M S I B R A C H Y C E P H A L I C C A T S

Figure 8Recommended orientation of standard radiographic views on the view box. Thepatients right side is on the left of the view box. (A, B, and C= maxillary teeth; D, E, andF= mandibular teeth)

Figure 7A

Figure 7B

Figure 7(A) Illustration showing the bisecting-angle tech-nique. (B) Radiograph of the right maxillary canine tooth.Note the superimposition of the zygomatic arch over the fourthpremolar. (A= angle)

Patients Right Side

A

D

B

C

F

E


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bubble distorts a small portion of the image directlyunderneath it (Figure 4C). Thus it is important to po-sition the bubble away from the teeth that are beingradiographed. For example, when radiographing themandibular premolars and molars, the bubble must bepositioned caudally near the mandibular ramus to pre-

vent it from distorting the image of the apices of themandibular third premolars.Because of their small size, intraoral radiographs cannot

be designated as leftor right. However, the bubble can as-sist in orientation. When the film is correctly positioned,the bubble is convex toward the beam and concave to-

ward the inside of the mouth. After processing, the film isoriented with the bubble convex toward the interpreter(bubble up). For extraoral film, the bubble is convex to-

ward both the beam and the inside of the mouth. There-fore, the film is oriented with the bubble concave towardthe interpreter (bubble down; Figure 4C). These em-bossed bubbles, along with a basic knowledge of dental

anatomy, enable the interpreter to determine the positionof the film during exposure.

When viewing full-mouth radiographs, it is helpful toorient them on the view box exactly as the dental chart isorganized: The patients right side is on the left side ofthe view box, the last molar is on the periphery, the firstincisor is on the midline, the maxillary teeth point down,and the mandibular teeth point up (Figure 8). This ori-entation allows rapid recognition of the location of ab-normalities seen on the radiographs and facilitates com-parison with the clinical findings noted on the chart.

About the AuthorsDr. Lommer and Ms. Terpak are affiliated with the Veteri-

nary Medical Teaching Hospital and Dr. Verstraete is with

the Department of Surgical and Radiological Sciences,

School of Veterinary Medicine, University of California,

Davis, California.

REFERENCES1. Wiggs RB, Lobprise HB: Veterinary Dentistry Principles and

Practice. Philadelphia, LippincottRaven, 1997.2. Mills AW: Oraldental disease in cats. A feline practitioners

perspective. Vet Clin North Am Small Anim Pract22:12971307, 1992.

3. Harvey CE: What are the questions [Editorial]?J Vet Dent11:86, 1994.

4. Bellows J: Radiographic signs and diagnosis of dental dis-ease. Semin Vet Med Surg (Small Anim)8:138145, 1993.

5. Emily P, Penman S: Handbook of Small Animal Dentistry, ed

2. New York, Pergamon Press, 1994.6. Harvey CE, Flax BM: Feline oraldental radiographic exam-

ination and interpretation. Vet Clin North Am Small Pract22:12791295, 1992.

7. Zontine WJ: Dental radiographic technique and interpreta-tion. Vet Clin North Am4:741762, 1974.

8. Holmstrom SE, Frost P, Eisner ER: Veterinary Dental Tech-niques, ed 2. Philadelphia, WB Saunders Co, 1998.

9. Harvey CE, Emily PP: Small Animal Dentistry. St. Louis,Mosby Yearbook, 1993.

10. Verstraete FJM, Kass PH, Terpak CH: Diagnostic value offull-mouth radiography in cats. Am J Vet Res59:692695,1998.


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FELINE-Dental Radio Graphic Technique in Cats

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