The Why, When, and How of Small Animal Dental Radiology

The Why, When, and How of Small Animal Dental Radiology

"Be not afraid of growing slowly, be afraid only of standing still" - Chinese proverb

What is the first diagnostic tool you choose when presented with an animal that has broken a leg? You take a radiograph (x-ray). Why? To see what is hidden under the skin. The same premise must hold true for veterinary dentistry. In order to diagnose and create a patient’s dental treatment plan, the complete extent of existing pathology must be known. Radiology is essential in accessing this information.

Why Radiology?

To see pathology hiding below the gingiva or inside the tooth

Evaluate an area where the teeth appear to be missing

To document the obvious - supporting treatment decisions

For client communication

Medical/legal documentation

Postoperative confirmation of proper extraction

Preoperative, intraoperative, and postoperative endodontics

Follow progression of pulpal pathology and/or periodontal disease

For prepurchase exams on show dogs to see if the proper number of teeth exist

Documentation

Normal gingiva

Periodontal disease is the most common ailment in small animals. Frequently, patients presented for "routine teeth cleaning and examination" have mobile teeth. The decision to extract, perform flap surgery, or provide only medical therapy, is aided by radiographs, probing depths, and visual examination. The visual exam and probing depths are subjective and give different results based on the examiner. Radiographs document the problem in black and white. The degree of bone loss can be measured, and permanently used to document lesions.

The x-ray shows lesions above and below the gum line. What an opportunity to inform your pet owners about dental disease. Its one thing to hear that pathology exists, a procedure should be performed, and quite another to show your client areas of bone loss around the tooth, or a resorption that has "eaten away" the tooth’s root. Seeing is believing.

Legal uses of radiographs to support treatment decisions prove invaluable. Without proof of bone loss below the gingiva or endodontic disease, a dispute may ensue which pits the feelings of a client against the veterinarian, concerning the need for dental extractions due to advanced periodontal or endodontic disease. Radiograph show graphically that therapy is indicated, due to greater than 50% supporting bone loss.

X-ray of periodontal disease

The dental radiograph becomes part of your patient’s permanent medical record. Examining serial radiographs of periodontal or endodontic cases taken at three to six-month intervals provides invaluable information concerning progression or resolution of disease.

When to Take a Radiograph

When a tooth is mobile

When gingiva bleeds with or without probing

When a tooth is fractured (either enamel, dentin, or pulpal exposure)

When a tooth is discolored (pulpitis)

When furcation exposure is present (periodontal disease)

When teeth are missing without explanation

When a feline ondoclastic resorptive lesion (FORL) is noted.

Prior to extraction for anatomical orientation and documentation

When should full mouth (six views) radiographs be taken?

Where periodontal disease is preset anywhere in the mouth

When Feline Ondoclastic Resorptive Lesions (FORLs) are diagnosed

If there are fractured teeth of unknown origin

When evaluating the number of secondary teeth in a puppy or kitten as part of a soundness examination prior to purchase

To evaluate oral and facial swellings

How to Take an Intraoral Radiograph

The Radiograph Machine

Dental x-ray machine

Although the veterinarian has a choice to use his or her, standard full body radiograph machine, delivery of efficient dental care necessitates the use of dental machines. A dental radiology unit, is a must in your dental operatory.

From a dollars and cents standpoint, the dental x-ray machine is a profit center for the hospital. At least half of all teeth-cleaning patients need radiographic surveys. When radiographs are taken on all periodontal cases to evaluate degrees of bone loss, and where you respond by treating those cases with >50% bone loss, the dental x-ray machine generates additional practice income. When used routinely, $3000-$4000.00 invested in a dental machine will be paid back well within six months of purchase.

Advantages of using the standard whole body veterinary radiology machine

No additional expense to purchase equipment

Can expose quality films

Advantages of using dental radiograph machine

Economical

Extension arms of various lengths allow vertical, horizontal, and rotational movement requiring less patient positioning necessary

Long arm can reach two closely located operatory areas

Radiographs can be taken in the dental operatory rather than moving the patient to radiology area

Shorter film focal length results in less scattered radiation

Anatomy of a dental x-ray unit

PID

Position Indicating Device (PID) - is an extension placed on the tube head at the collimator attachment. To minimize the amount of radiation exposure, the PID is lead lined. The shape of the PID may be circular or rectangular. Rectangular shaped PIDs limit the beam size to that of a number 2-periapical film.

The length of the PID provides an extension of 8, 12, or 16 inches from the x-ray tube to the animal’s skin. The operator needs to decide which extension to use. An 8" extension is referred to as short cone technique, longer extensions result in a long cone technique.

Short cone technique is preferable because it uses one-quarter the exposure, compared to the long cone technique, and is easier to position. Long cone technique produces films with increased detail.

Arm - the connection between the x-ray tube and control pannel.

Control Panel - contains timer, kilovoltage, and / or milliamperage regulators.

Electric timer-as a safety device, the timer operates only while the switch is being depressed and automatically cuts off electric current at the end of the exposure. The timer resets itself after each exposure.

Most dental units use 110V, 60Hz AC electricity. A separate dedicated electrical circuit is recommended.

Radiograph machine settings

Exposure variables considered in radiology include exposure time, peak killivoltage (kvp), and milliamperes (ma). Some machines allow the operator to modify each variable based on the size of patient and tooth type. Most machines have one or two variables preset allowing an operator to change exposure time.

Exposure factors affecting film quality:

kVp setting

MA setting

Exposure time setting

Film focus distance

Long or short cone

Killivoltage peak (kVp) determines the quality of x-radiation produced. The higher the kVp setting, the higher photon energy which strikes the tooth. Larger teeth require higher killivoltage to penetrate in order to get a diagnostic film. Most common killivolt settings are from 50-100 kVp.

Speed (exposure time) is either measured in fractions of a second or pulses. A pulse is 1/60 or .016 of a second.

Milliamperes, ma measures current. It directly affects the number of electrons. The milliampere number is set in most dental units between 7 and 15 mA. When using standard veterinary radiograph machines, 50 or 100 mA is commonly used. Changing the mA setting increases or decreases the intensity of the x-ray beam. Increasing the mA increases density of the radiograph.

Film focal distance (FFD) is another important variable. Moving the tube closer or farther away from the patient can affect intensity of the x-ray beam. As the distance from the patient is decreased (short cone technique), intensity of the radiation reaching the patient increases. As the distance is increased, intensity of the radiation reaching the patient is decreased (long cone technique).

Cone length

Dental radiograph machine cones come in variety of sizes from four to sixteen inches. Exposure adjustments must be made depending on the size used. For example, a four-inch cone would require one-quarter of the exposure compared to an eight-inch cone.

The patient indicator device (PID) is placed against the patient’s maxilla or mandible. This results in a FFD of 8,12, or 16 inches depending on the cone length. When using a standard veterinary radiograph machine the tube head (without a cone) is placed 12-16 inches away from the tooth.

Tooth film distance

When utilizing intraoral technique, film is placed parallel to the palatal or lingual tooth surface. Due to small animal oral anatomy this is not always possible. Instead, a bisecting angle technique is used resulting in a 20-50 degree angulation of the x-ray beam to the film plane, depending on which tooth is radiographed.

Rules for successful positioning

The closer the object being radiographed is to the film, the sharper and more accurate the image.

Use the longest film focal distance practical

Direct the central ray as close to a right angle (or bisecting angle) to the film as possible

Maintain as parallel interface between the film and object as possible

Digital imaging dental radiology

Digital imaging is a recent technical advancement in dental radiology. It will be as popular or even replace, film-based imaging in the future.

Computer image capturing and image enhancement has many advantages compared to the traditional film systems. With digital imaging, the dental radiograph machine is still used to expose the lesion, but instead of film, a sensor pad is placed inside the mouth, accepts the image, and transfers it to the computer screen. Advantages over the traditional film based systems include:

75-90% reduction in radiation used to produce an image

instant image production-no processing chemicals

can retake film immediately if not pleased with the image

able to enlarge the entire image or certain section, adjust contrast, brightness, enhance the margins, rotate images

can measure distances between two points-helps in estimating endodontic working file lengths

can measure tooth densities for evaluation of areas of decreased density (class one or two feline oral resorptive lesions).

Radiation Safety

The ALARA principle

ALARA stands for as low as reasonably achievable. This concept endorses the use of the lowest possible exposure of the patient (and operator) to x-radiation to produce a diagnostically acceptable radiograph.

Staff of the veterinary facility must be protected against radiation exposure.

Shielding of the x-ray beam in the machine greatly reduces occupational exposure. X-ray aprons must be worn at all times when taking films.

Veterinarian responsibilities

Prescribe only those radiographs that are diagnostically necessary

Install and maintain radiographic equipment in safe working condition

Use of minimum exposure "E" speed film if possible, however the "D" Ultraspeed is most commonly used in veterinary medicine.

All personnel who expose radiographs are adequately trained, supervised, and monitored.

General anesthesia is mandatory for any animal receiving x-rays. Total immobilization allows the technician to position x-ray film in the patient’s mouth without exposing his or her hands to radiation.

There are three types of radiation-primary, secondary, and leakage.

Primary radiation comes from direct exposure from the x-ray beam. The operator must always keep away from the primary beam of the x-ray machine. The veterinarian or staff should never hold films in the patient’s mouth with bare or gloved fingers. Devices must be used to position the film in the mouth without operator exposure.

Secondary (scatter) radiation comes from areas that have been irradiated by the primary beam. Protective aprons must be worn to help shield the body from this type.

Leakage radiation comes from the tube housing and not the primary beam. Neither the tube housing nor the cone should be held during exposure.

Personnel monitoring

A film badge monitoring service is used to provide radiation monitoring for all members of the office staff functioning near film exposure. The dosimeter badge is worn at all times in the veterinary office. It measures the amount and type of radiation an individual is exposed to in the working environment. The badge should not be worn outside of the office.

A monthly report on radiation monitoring becomes a permanent record for the office staff and should be saved indefinitely.

Film

Small intraoral film is used in dental radiography. It is inexpensive, flexible, and provides great detail. Non-screen film is preferable due to the high definition necessary to interpret dental lesions. Dental film is conveniently used for intra or extra-oral placement.

Dental film

Individual dental films are packaged in a light tight packet that is made of either plastic or paper. Inside the packet, film is positioned between an inner lining of two sheets of black paper. A sheet of lead foil is located at the "back" of the packet, next to the tab opening. Lead foil protects the film from secondary radiation, which may cause the film to fog.

Back of packet

The back of the packet has a tab opening used to remove film for processing. This side is placed next to the tongue or palate.

Intraoral dental film is packaged singly or with two films per packet. When two films are exposed, the practitioner may use the second film to give to the client or referring veterinarian. Film packets are color-coded—green indicates a single film packet, gray a two-film packet.

Film speed

Commonly used dental film is available as speed D (ultra speed) and speed E (ekta speed). Speed E film is rated at twice the speed of D film, requiring half the exposure, with small loss of quality. Ultra speed is used predominantly in veterinary dentistry.

Film sizes

Three sizes of dental film are frequently used in veterinary dentistry:

child periapical size 0 measures 7/8 x 1 5/8 inches-used mostly in cats, exotics, and small dogs

Adult periapical size 2, also called standard size measures 1 ¼ x 1-9/16 inches. Size 2 is the most popular size used.

Occlusal size 4 measures 2 ¼ x 3 inches. Occlusal film used to radiograph larger teeth and survey studies.

Film Dot

Dental film is embossed with a raised dot in one of the corners. The convex side of the dot indicates front side of the film. The dot is used to identify right from left. The convex (raised) dot is placed at the occlusal edge and toward the x-ray tube. The concave (depressed) dot is placed toward the tongue or palate.

To determine whether a film is on the right or left side, imagine where the convex dot is located, and identify the progression of teeth from incisors to molars. Hint: mentally place the film in your mouth imagining dot orientation and progression of premolars to molars to help determine if the film is from the right or left sides of the mouth.

Film mounting

After you have processed radiographs, mount the finished films in cardboard or plastic holders. Mounting makes films easy to view, allows patient identification, and protects film from damage.

Mounts are labeled with the patient’s name and date of the study. The films are laid out so the embossed dots are located in the upper left corner. Maxillary films are positioned above the mandibular films. Mount the films with the raised portion of the dot toward you. Read films as if you were facing your patient, with the right side of the animal on your left.

Radiographic Landmarks

It is important to be able to look at a film and identify the area exposed.

Maxillary incisors will show a large radiodense (white area) distal to the teeth, with two ovals representing the nasal area. All incisor teeth have one root

Mandibular incisors - look for a black space separating mandibular rami

Maxillary premolars and molars - look for a fine while line representing the maxillary recess apical to the roots

Mandibular premolars and molars - look for radiolucent (black areas) above and below the jaw. Other than the first premolar (in the dog) and third premolar (in the cat), all mandibular premolars and molars have two roots

Positioning the film and patient

Place film inside the mouth, parallel to the teeth to be examined. Film is held in position by the endotracheal tube, waded up newspaper, lead x-ray gloves (without fingers inside), sponges, clay encased in a plastic bag, or commercial holding devices. The operator must not use their fingers to hold film to be exposed

Immobilization: Elimination of patient movement is essential to image sharpness. Movement of the film packet or the patient’s head must be avoided during exposure. Vibration and other movement of the x-ray tube will cause a blurred image

Bisecting angle technique is used in most exposures. Lay film far enough inside the animal’s mouth so that its root structure will be projected on the film. Imaginary lines are drawn along the long axis of the tooth and the plane of the film. The point where these two lines meet will create an angle. Instead of aiming the central beam perpendicular to the film as in the parallel technique, the central beam is aimed perpendicular to the line bisecting the angle created between the line of the tooth and line of the film

Angulation of the primary beam is dependent on which area is being radiographed.

Anterior maxilla: PID aimed at the apex of the first premolar at 45 degrees angle rostral to the hard palate

Maxillary cheek teeth: PID aimed at apex of the fourth premolar at 45 degrees pointing toward the palate

Anterior mandible: PID aimed at the apex of the first premolar at 20 degrees to the ventral border of the mandible

Mandibular cheek teeth:

Anterior - PID aimed at the apex of the first premolar at 45 degrees

Posterior - PID aimed at 90 degrees to the tooth

Vertical angulation refers to the up and down movement of the PID. Vertical angulation will determine how accurately the length of the object being radiographed is reproduced

Foreshortened image: changes in vertical angulation are similar to those changes in shadows caused as the sun moves in the sky. At noon, when the sun is directly overhead, a shadow is foreshortened (shorter). Foreshortened images appear shorter than they really are, caused by too much vertical angulation. To reduce a foreshortened image, the vertical angulation is reduced

Elongated image: in late afternoon as the sun moves toward the horizon, shadows are elongated (lengthened). Elongated images, appear longer than the actual tooth, are caused by too little vertical angulation. The tooth will appear longer than the anatomical length. To correct an elongated image, vertical angulation increased

Horizontal angulation refers to back and forth movements on a plane that is parallel with the floor. Proper horizontal angulation produces normal interproximal anatomic representation of the teeth without overlapping

Horizontal (paralleling) technique directs the central ray at right angles to tooth and film. When radiographing a single tooth, the film packet is placed parallel to the long axis of the tooth. With paralleling technique, the central beam is projected at a right angle to the film packet. In the dog and cat, this is accomplished best when radiographing mandibular cheek teeth

SLOB rule - when two roots of a triple rooted tooth are superimposed on the radiograph; it is difficult to evaluate both roots. In order to visualize the roots, two radiographs are taken at oblique angles. Vertical position is fixed and the tube is moved horizontally. Horizontal tube shift will result in a film with the overlapped roots moved apart. When the root "moves" in an opposite direction to the horizontal shift of the tube, then the root is labial or buccal. If the root "moves" in the same direction as tube, it is labial or palatal. SLOB stands for same lingual, opposite buccal

Film Processing

Proper exposure of film is only part of the of process in producing quality dental radiographs. Processing the film completes the procedure.

Processing fundamentals

Active fresh solutions

Standardized method of processing

Light secured area

Film may be developed:

By hand with regular or rapid dental processing solutions in the darkroom

With Chairside developer - a portable light safe box with developer, fixer, and water in small containers. Putting your hands through two diaphragms in a lighted room accesses the solutions. The box’s top, an orange or red Plexiglas safety filter, enables you to see inside. The whole process from opening the film packet to examination of a rinsed film takes approximately one minute

Automatically Film is placed into one end of the automatic dental processor and comes out fully developed, fixed, and dried in 2 to 7 minutes. Using standard veterinary automatic processors are discouraged because small dental films may become lost in the processor, and tape used to attach to larger films, may harm the processor’s rollers

Instant dental x-ray film (Veterinary dental film system VDFS-Hawaii Mega-cor, Inc. Aiea, Hawaii) develops in 30 seconds within the film packet after infusion of developer and fix solutions

Steps for manually processing dental x-rays

Once the film packet is in a light secured area, open the packet tab on the packet and slide forward the paper liner and film. This will present film to be processed. Only touch the sides of the film with your fingers

A film hanger is attached to the film. Film should extend horizontally from the clip. Give the film a gentle tug to make certain it is firmly attached to the clip

Place the film into the developing solution for 10-30 seconds (depending on room temperature - longer time if less than 68 degrees)

The film is rinsed in distilled water for 10 seconds

Place the film in the fixing solution for 30 seconds

Rinse for 30 seconds in distilled water

After viewing, the film is placed in the fixer for 5 minutes and a distilled water rinse for 20 minutes

When rinsing is complete, hang the radiograph on a rack to dry or use a hair drier for rapid drying

Processing solutions must be fresh for developing quality films. Solution containers are covered at all times to minimize evaporation. The maximum effective lifetime of the processing solutions varies with use. One rule is to change solutions every other week with routine use. If many films are processed, solutions become exhausted and need replacement more often.

Quality Control

A good radiograph is useless unless it is read accurately, and a poor radiograph cannot be read properly.

A quality assurance film is exposed daily to verify that all parts of the dental radiography system are working properly. The use of a step wedge helps accomplish this goal. The step wedge is an object composed of several graduated pieces of aluminum placed so that each successive piece is shorter, thus producing a step effect.

Use of the step wedge to establish a control radiograph

Dental film is laid tab side down on a flat surface

A step wedge is placed over the film

Expose using medium dog technique

Process using new chemicals

The processed image ideally shows ten shades of varying densities from light gray to black. If not all ten steps are apparent, adjust exposure up or down until all can be distinctly seen. If the lightest steps (from the thickest part of the wedge) are indistinct, increase the exposure. If the darkest steps (from the thinnest part of the wedge) are indistinct, decrease the exposure. Once the correct exposure is determined, this becomes the control film. Expose twenty-thirty films.

Daily quality control using step wedged developed radiographs

Mount the control film processed with new solutions next to the view box. Every two or three days, processes a test film and compare it to the control film. If they are not identical, verify that the processing time and temperature are correct. If more than two steps are lighter than the control film, the processing solutions are exhausted and need changing.

Film quality encompasses many variables:

Density is the degree of blackness created on the x-ray film. Density is controlled by milliampere-seconds (mAs). 10 to 12.5 mAs will provide good detail

Contrast is the relative difference between densities. High contrast film would include areas of white and black. Low contrast films may appear gray. Contrast is controlled by kVp (normally between 50-90), and processing variables (temperature, development time, light leaks)

The range of development times is related to solution temperature recommended by the manufacturer are designed to provide acceptable contrast. Underdevelopment (caused by weak, exhausted, cold solutions, or by too short a development time) results in poor contrast. Overdevelopment causes fog and overall darkening of the image

Troubleshooting Reasons for Poor Film Quality

Faulty radiographs are commonly caused by incorrect:

positioning of the film packet or tube head

processing procedures

kilovoltage

movement of the patient or tube head during the exposure

Film fogging appears as a gray or dark film

Causes of film fogging

film was not placed in fixer long enough (most common reason)-easy to diagnose and repair--immerse the film into the fixer for another five minutes and see if the image improves

exhausted processing chemicals

outdated film

Light leaks from film packet or processing area

Over processing (placing the film in the developer too long, or in too hot developing solution)

Film processed in fixer contaminated developer

Film exposed to stray radiation, excessive heat, or light leaking into processing area

No image

the film was immersed in the fixer before the developer

If the film is completely clear, it was not exposed at all

Light film

not enough exposure time

not enough kilovoltage

weak developer

or too short time in developer solution

Dark film

too much exposure

too high kilovoltage,

too much exposure time

too long in developing solution

developing solution too warm (ideal temp 68 degrees)

Blurred images result from motion during exposure. The patient, film, or x-ray head moved.

Partial image

film partially immersed in developer

while in the developer, the film came into contact with other films or the side of the tank

The film or tube head was incorrectly positioned.

Fingersprints come from poor handling. Film must be touched only by the edges.

Frosty-appearing films - normally, finished dry film will be smooth and shiny. When film is not washed thoroughly, or rinsed in water mixed with fixer, fixer will dry on the film leaving a frosty finish. Using fresh distilled water with each study easily prevents this common problem.

Streaked film - the film was insufficiently developed, fixed, rinsed, or processing solutions were contaminated.

Crescent-shaped lines - film packet sharply bent, damaging the film

Common causes for repeated films

Incorrect film positioning

Movement of tube head or patient during exposure

Incorrect exposure setting

Placing film in mouth backwards

Exposing film twice

Poor processing

The dental technician should be able to expose and process a full set (6) intraoral film within fifteen minutes.

Interpreting Dental Radiographs

The radiograph, when correlated with case history and clinical examination, is one of the most important diagnostic aids available to the veterinarian. When examined under proper conditions, dental radiographs of diagnostic quality reveal evidence of disease that cannot be found in any other way.

Some normal anatomical structures may be confused as pathology.

Middle mental foramen - opening in the mandible through which the mental nerve passes-- located ventral to the mandibular first or second premolar near the apex of the canine tooth

Posterior mental foramen - located ventral to the mandibular third premolar. At times can be confused with a periapical lesion. If in doubt, radiograph the tooth in an oblique angle, which will show the foramen not connected to the tooth’s apex

Mandibular canal - located on the ventral border of the mandible, may be superimposed on apices of mandibular cheek teeth and appear as periapical disease

Radiology of periodontal disease

The most common disease in small animals older than five years is periodontal disease. Treatment may include supragingival and subgingival scaling, periodontal surgery, tooth resection, or extraction. Radiography plays an important role in determining the extent of periodontal disease and helps dictate therapy. When evaluating periodontal disease, radiographs are evaluated for:

alveolar bone changes

interdental bone height

presence of the lamina dura

trabecular patterns

size of periodontal ligament space

degree of bone loss

Radiographs show two-dimensional representation of three-dimensional structures, and may not adequately represent severity of disease. Early destructive bone lesions sometimes are not radiographically observable. Buccal and lingual alveolar bone are particularly difficult to evaluate because they are superimposed. In addition to radiographic findings, the clinician must rely on clinical examination, including sulcular depths, tooth mobility, and appearance of attached gingiva in order to decide on the diagnosis and treatment plan.

Normal, healthy alveolar bone has characteristic appearance on radiographs. The alveolar crest is situated approximately 2 to 3 mm apical to the cementoenamel junction of the teeth. The shape of the alveolar crest may vary from rounded to flat. The alveolar crest normally lies 1-2 millimeters below the cementoenamel junction (CEJ). Between incisor teeth, the alveolar crest will usually appear pointed. Between premolar and molar teeth, the crest will be parallel to a line between the adjacent CEJs where the enamel thins and disappears.

The alveolar crest is continuous with lamina dura of adjacent teeth. When viewing lamina dura and periodontal ligaments, only interproximal portions are visible. Buccal and lingual areas are not seen in the radiograph.

Radiographic bone changes in periodontal disease

Crestal Lamina Dura: Normally a radiopaque line appears to cover the alveolar socket and extends on top of interdental bone. Because the facial and lingual bony plates are obscured by dense root structure, radiographic evaluation of bone changes in periodontal disease is based mainly on the interdental septa. With marked periodontal disease, crestal lamina dura is indistinct, irregular, fuzzy, and radiolucent. Widening of the periodontal ligament space and loss of lamina dura is due to resorption of the alveolar bone secondary to periodontal disease.

Bone level: Normally the crest of interdental bone appears 1-2 millimeters below the cementoenamel junction. Bone level in periodontal disease is lowered as inflammation extends and bone resorbed. The overall height of alveolar crestal bone in relationship to the cementoenamel junction is used to evaluate bone loss. Distribution of bone loss is classified as either localized or generalized depending on the number of areas affected. Localized bone loss occurs in isolated areas, generalized bone loss involves the majority of the crestal bone. Initially, periodontitis develops as localized erosion of the alveolar crest. Bony changes cannot be radiographically detected until they are advanced. As the severity of periodontitis increases, more alveolar bone is destroyed and the process becomes generalized.

Periodontal ligament space: The periodontal ligament is composed of connective tissue. It normally appears as a fine radiolucent line next to the root surface. On its outer side is lamina dura, bone lining the tooth socket, which appears radiopaque. When examining a radiograph for periodontal disease, the lamina dura of each tooth is inspected to see if it is continuous or breached, indicating pathology. Absence of the lamina dura and lack of continuity are indicative of periodontal disease. With disease, the periodontal ligament space may appear of varying thickness, indicating disease involvement is not consistent around the entire root. . Usually teeth with very wide periodontal spaces are mobile.

Patterns of bone loss: The interdental septa may be reduced in height with the crest horizontal and perpendicular to the long axis of the adjacent teeth, or there may be vertical (angular) bone loss. A reduction of only 1.0 mm in the thickness of the cortical plate is sufficient to permit radiographic visualization.

Amount of bone loss: Radiography is an indirect method for determining the amount of bone loss in periodontal disease. It shows the amount of remaining bone rather than the amount lost.

Stages of periodontal disease

Gingivitis: Periodontal disease is classified from stages 1 to 4 based on the severity of radiographic and clinical signs. Stage 1 is referred to as gingivitis. Clinically, the gingiva appears swollen and inflamed. In stage 1 disease, there is no bone loss.

Early periodontitis: Stage 2 disease is early periodontitis and signifies the first appearance of radiographic abnormalities. The loss of alveolar bone is accompanied by an apical migration of gingival fiber apparatus and junctional epithelium. The loss of osseous support can occur either as generalized horizontal loss involving some or all surfaces of the teeth, or as localized vertical bone loss.

The earliest radiographic sign of periodontitis is a loss of definition in the crestal bone. The alveolar crest loses its distinct sharp appearance and becomes blunted. Bony margins become diffuse and irregular and may show areas of localized erosion. In the incisor regions there is blunting of the alveolar crests. In the premolar and molar regions, there may also be loss of normally sharp angles between the lamina dura and the alveolar crests.

Established periodontitis: Stage 3 periodontal disease is typified by pocket formation. Radiographically, bony destruction extends to the buccal and/or lingual alveolar plates. There may also be horizontal or vertical defects.

Horizontal bone loss radiographically appears as decreased alveolar bone around several adjacent teeth. Crestal bone is normally located 1.0 mm apical to the cementoenamel junction. With horizontal bone loss, both the buccal and lingual plates of bone as well as interdental bone have been resorbed. A suprabony pocket exists where the epithelial attachment is above the bony defect and is associated with horizontal bone loss.

Horizontal bone loss may be classified as localized or generalized, depending on the regions involved, and as mild (less than 10% bone loss), moderate (10-30%), or severe (>30%), depending on the extent of bone loss.

Vertical bone defects are also called infrabony (or intrabony) defects. The epithelial attachment on the root surface is below the crest of bone. The number of walls remaining classifies Infrabony lesions. The defect extends apically from the alveolar crest and is initially surrounded by three walls of bone: two marginal (lingual or palatal and facial) and a hemisepta (the bone of the interdental septum that remains on the root of the uninvolved adjacent tooth). As disease progresses, two, one, and no (cup)-walled defects may occur.

Radiographically, a vertical bone defect is generally V shaped and sharply outlined. It is immediately adjacent to the root surface of the affected tooth, and the adjacent bone has normal radiographic appearance. Infrabony defects may not be identified on the radiograph if the defect is relatively small. Radiography of a gutta-percha point inserted into the pocket may be helpful to evaluate the extent of the defect.

Advanced periodontal lesions: Stage 4 disease is represented by deep pockets, tooth mobility, gingival bleeding, and pustular discharge. Bone loss is extensive.

Furcation exposure results from bone loss at the root junction of multirooted teeth. Furcation exposure indicates advanced periodontal disease. It is sometimes difficult to determine radiographically whether the interadicular space is involved unless there is a radiolucent area in the region of the furcation. Advanced furcation exposures where both cortical plates are gone are easily recognized on radiographs.

Alveolar dehiscence exists when alveolar cortical bone is resorbed along the entire length of the root. Radiographically there will be radiolucency surrounding the effected root.

Radiographic interpretation of endodontic disease

The 40% rule

40% of the bone has to be destroyed before you can visualize periapical lucency. When examining radiographs, just because you may not see lesions, does not mean they are not present. Radiology is only one tool in your diagnostic toolbox.

External resorption begins on the surface of the tooth. The resorption may result from periapical inflammation, excessive occlusal forces, or from unknown stimuli.

Internal resorption arises from within the pulp. The cause is unknown but trauma is believed to be a contributing factor. Often, it is difficult to determine if the lesion is due to internal or external resorption. If you visualize a normal appearing root canal through the resorption then the lesion is external in origin.

Periapical abscesses usually appear as a slight thickening of the apical periodontal ligament and minimal alveolar bone resorption. Most cases do not reveal extensive bone loss due to the short time period between pulp death and the formation of the periapical abscess.

A chronic purulent periapical abscess radiographically presents as a homogeneous radiolucency at the root tip, and a dark halo in the periapical tissues.

A dental granuloma appears as a radiolucent lesion with a circumscribed outline revealing a wall of compact cancellous bone. The apex of the tooth projects into the lesion.

A radicular cyst-is a fluid filled sac at the apex of a nonvital tooth. Radiographically it will appear as a rounded, circumscribed, radiolucency bounded by an unbroken line of sclerotic bone.

Condensing osteitis occurs in response to low-grade infection. It appears as a small radiodense area around the apex of a tooth circumscribed by a large area of denser bone. The tooth is nonvital.

Miscellaneous conditions

Ankylosed tooth - a tooth is ankylosed when there is union between the tooth root and alveolar bone. The union may be with either cementum or bone. Causes of ankylosed teeth include traumatic injury, occlusal trauma, and periapical inflammation.

Metabolic disease - renal secondary hyperparathyroidism radiographically is portrayed as a generalized loss of bone support of all the teeth.

Neoplasia - Radiographically look for destruction of all tissues around the tooth.

Foreign bodies - in all cases of oral swellings, or nasal discharge, radiographs must be taken.

As you can see, radiology is a vital diagnostic tool to diagnose dental pathology. Essential therapy decisions are based on radiographic findings.