INTRODUCTION:

Diagnosis “is the determination of the nature of a diseased condition, by careful investigation of its symptoms and history”.

Arriving at a correct diagnosis requires knowledge, skill and art; knowledge of the disease and their symptoms, skill to apply proper test procedures and the art of synthesizing impressions, facts and experience into understanding.

Symptoms are the units of information sought in clinical diagnosis.

They are defined as phenomena or signs of a departure from the normal and indicative of il lness.

They are classified accordingly.

Subjective symptoms – those experienced and reported by patients.

Objective symptoms – those ascertained by the clinician through various tests.

It thus follows that the corners or pillars of a correct clinical diagnosis are

A. Good case history. B. A thorough clinical examination. C. Relevant investigations / diagnostic tests.

In order to obtain a good case history, record of substantial data with relation to the patient’s medical and dental history is of great importance.

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HISTORY:Medical history:

Although the only systemic contraindications to endodontic therapy are uncontrolled diabetes or a very recent myocardial infarcation, only the patients medical history enables the clinician to determine the need for a medical consultation or premedication of the patient.

Additional barrier protection can be provided to all clinical personnel if the patients history reveals infection with communicable disease such as AIDS, hepatitis-B, TB etc.

Before rendering endodontic therapy the clinician must know what drugs the patient is using to identify possible adverse drug reaction. Dental history:

The primary aim in recording the patient’s dental history is to obtain complete information data of the patient’s chief complaint. Most common chief complaints range from - Pain- Swelling- Loss of function- Aesthetics

Pain is one of the most common chief complaints encountered. Pain:

When patients present with a history of pain careful attention is paid to their description.

In order to attain a detailed knowledge regarding pain following questions may be necessary 1) Type of pain:

Grossman has stated pulpal pain to be of the following two varieties i.e. a) Sharp, piercing and lancinating – A painful

response usually associated with the excitation of A-2

Delta nerve fibres. This pain usually reflects reversible state.

b) Dull, boring, gnawing and excruciating – a painful response usually associated with the excitation of C-nerve fibres. This pain usually reflects an irreversible state of pulpitis.

2) The duration of pain:When the pain is of a shorter duration (1 minute), it

is considered to be reversible pulpitis, whereas when the pain is of a longer duration it is considered to be irreversible pulpitis. 3) The localization of pain:

Sharp piercing pain can usually be localized and responds to cold.

Dull pain usually referred / spreads over a larger area and responds more abnormally to heat.

4) Factors which provoke / relieve pain (Int. Endo. J. 1990).

On assessment of pulp vitality by A.H. Rowe response to a provoking factor (e.g. on mastication) indicates pulp vitality, but stimulation causing extended severe pain suggests irreversible pulpitis. Different diagnosis of reversible and irreversible pulpitis

Reversible pulpitis

Irreversible pulpitis

1. HistorySlight sensitivity or occasional pain

Constant or intermittent pain

2. Pain Momentary and immediate, sharp in nature and quickly dissipates after.

Continuous, delayed onset, troubling persists for minutes to hours after removal of

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stimulus.

3. Location of pain

May be localized and is not referred

Pain is not localized. If it is localized only after periapical inv. pain is referred.

4. Lying down (change of posture)

No difference Marked prolonged

5. EPT Early response Early, delayed or mixed response.

6. Thermal test (Heat and cold) Responds Marked

prolonged

7. Percussion NegativeNegative in early stages, later positive when periapex is inv

8. Radiography NegativeMay show widening of PL space.

Clinical examination:This phase can be divided asA) Extraoral examinationB) Intra oral examination

The extra oral clinical examination begins with a patient’s dental history, while talking to the patient, the clinician should look for facial asymmetry or distensions, which would indicate a swelling of odontogenic origin or a systemic ailment. INTRA ORAL EXAMINATION:

This begins with a general evaluation of the oral structures. Several tests have been stated in order to

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determine the condition of teeth and supporting structures. Commonly used methods are

1) Visual and tactile and inspection2) Percussion3) Palpation4) Mobility and depressibility tests5) Periodontal tests6) Thermal tests7) Anaesthetic tests8) Test cavity9) Transillumination10) Biting11) Staining12) Gutta-percha point tracing13) Electric pulp testing14) Radiographs

Special methods:1) Xero-radiography2) Pulse-oximetry3) Laser Doppler flowmetry 4) Computerised tomography5) Digital subtraction radiography6) MRI7) RVG8) Computerized expert system9) Thermographic imaging10) Tact

Commonly used methods

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Visual and tactile perceptionThe simplest clinical test is visual examination. A

thorough visual and tactile examination of hard and soft tissues relies on checking the 3 C’s. Colour Contour Consistency

The visual and tactile inspections is usually carried out with a mouth mirror, explorer, and a periodontal probe under dry conditions with a good illumination source.

The teeth and the soft tissues adjacent to the involved tooth must also be examined for detection of any related swelling and pathologic conditions.

Preparation

Palpation is a tactile skill acquired through practice and repetition. Before incipient swelling becomes clinically evident, it may be detected by gentle palpation with the index finger.

This simple test is done with the fingertip using light pressure to examine tissue consistency and pain response. Its value lies in locating the swelling over the involved tooth and determining the following.

i) Whether the tissue is enlarged sufficiently for incision and drainage and is fluctuant.

ii) The presence, intensity and location of pain.

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iii) The presence and location of adenopathy.

iv) The presence of bone crepitus.

Percussion:This test enables one to evaluate the status of the

periosteum surrounding the tooth. The tooth is struck a quick moderate blow initially with the finger and then by the handle of the mouth mirror.

A positive response to percussion indicates not only the presence of inflammation of the PL but also the degree of inflammation.

The degree of response is directly proportion to the degree of inflammation. Responses to percussion:

Positive response to percussion is indicative of periodontitis, which could be due to- Teeth underlying rapid orthodontic movement. - High points in resent restoration. - Lateral periodontal abscess. - Partial / tooth pulpal necrosis.

Negative response to percussion may be seen in cases of- Chronic periapical inflammation – it has been stated

that percussion sounds offer diagnostic clues. - Dull Note signifies abscess formation sharpt Note

denotes inflammation. Mobility – Depressibility test:

The rationale of mobility test is to evaluate the integrity of the attachment apparatus surrounding the tooth.

The test essentially consists of moving the involved tooth laterally in the socket using handles of 2 instruments or more preferably using two index fingers.

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The test for depressibility is similar and is performed by applying pressure in an apical direction on the occlusal / incisal aspect of tooth and observing vertical movement in any.

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Grades of mobility (Cohen) (Grossman):1st degree – less than 1mm horizontal movement. 2nd degree – 1mm of horizontal movement. 3 rd degree – greater than 1mm of horizontal

movement accompanied by vertical depressibility. Grades of mobility (Miller) 0 – No mobility within physiologic limits1 – Mobility within the range of 0-5mm. 2 – Mobility within the range of 0.5 to 1.5mm with

lateral movement. 3 – Mobility more than 1.5mm with lateral movements

and can be intruded / depressed into the socket. Mobilometers:

These are electronic devices / gadgets, which and in determining tooth mobility. Periodontal examination:

No clinical examination is complete without careful evaluation of the tooth’s periodontal support. Multirooted teeth should be carefully evaluated to determine whether there is any evidence of furcation involvement.

A lateral canal exposed to the oral cavity through a periodontal disease may become the portal of entry for toxins, which may cause pulpal degeneration. Thermal tests:

Thermal tests are especially valuable diagnostic aids because in certain types of inflammed pulps pain may be induced or relieved by applying cold or warm stimuli.

Reliable response to pulp vitality testing are critical and depend on the teeth being dry.

Grossman has stated that a response to cold reflects a vital pulp regardless of whether it is normal or abnormal. A heat test does not confirm vitality. An abnormal response to a heat test however exhibits

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presence of a pulpal or periapical disorder requiring endodontic treatment.

Another diagnostic difference as pointed out by Grossman is that when a reaction to cold occurs the patient can quickly point out to the painful tooth. Unlike in a heat test situation where the response can be localized diffused or even referred to different site.

Heat test:

The heat test can be performed using different techniques, which deliver different degrees of temperature.

The preferred temperature for performing a heat test (according to Cohen) is 65.5°C or 150F.

Heat test may produce a temperature as high as 150 degree centigrade at the surface of the tooth according to AHR Rowe et al (in an article on assessment of pulpal vitality) (Int End J. 1990 V-23), where temperature upto 150°C according to him are necessary for conducting thermal tests on teeth which are 1 st

coated with Vaseline to avoid gutta-percha sticking to the tooth.

The heat tests can be performed using different techniques such as

1. Hot air2. Hot water3. Hot burnisher4. Hot gutta-percha5. Hot compound6. Polishing of crown with rubber cup

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For teeth with crowns hot water is better. Here the tooth to be tested is isolated using a rubber dam and immersed in ‘Coffee hot’ water delivered from a syringe. Disadvantage – Limited only to the tooth which is tested. Cold test:

Cold application can be performed in any of the following ways (i.e.). A) A stream of cold air from a 3-way syringe directed

against the crown of previously dried tooth. B) Use of ethyl chloride spray (which evaporates

rapidly) absorbing heat and cooling the tooth surface.

C) Application of ice sticks (sticks of ice are seldom used because they may warm when applied to the tooth and leak onto the gingiva, causing a false positive response.

D) Cold water bath – They are more time consuming but are clearly superior in their accuracy. Even when the tooth has been restored with a full crown sufficient contact is made to allow cooling or warming of the pulp.

In addition the cold water bath prevent excessive temperature- change damage to the tooth. E) Carbon dioxide snow (77.7°C or –108°F)

(odontotest) and / orF) Refrigerant dichlor – diflour methane (-50°C Figen /

Frigident). According to Chambers (1982), the advantage of

CO2 show vitality testing are itsEase and speed of application and its reliability.

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The method has been reported to be more reliable than other methods for testing the vitality of immature developing permanent teeth and traumatically injured anterior teeth – Fulling and Anderson 1976 and Ehimann 1977.

The CO2 snow also produce a distinct vitality response in teeth covered with metal crowns precluding the use of test drills.

In addition, false positive vitality reactions have not been reported in teeth with liquefaction necrosis.

Ehrmann (1977) has claimed that the test is ineffective in teeth with calcified pulps or in those of elderly patients with large deposits of reparative dentin.

However Schroeder (1981) has claimed that even degenerative and atropic pulps will react to cold.

Augsburger and Peters (1981) found that intra pulpal temperature, as measured in vitro decreased only by a mean of 15.6°C for non carious teeth. In gold crowned teeth the decrease was 13.2°C after a 5 sec exposure. Their clinical studies indicated that a 2 second exposure produced a vital response. Histologic studies have indicated that the pulp is not damaged by the application of the CO2 snow test (Schiller 1937).

Fuss and associates in an in vivo study comparing tooth vitality, produced a positive vitality response of 98.7% with dichloro-difluoro methane, 97.4% CO 2 snow, 94.8% with electric pulp tester, 53.2% with ethyl chloride and 32.5% with ice.

CO2 dry ice sticks are extremely cold and may cause infarcation lines in enamel (Cohen) but Ehrmann

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has stated that if it does occur it will not be of clinical significance. Rickoff reported that CO 2 did not damage the surface of but does cause pitting of the surface porcelain or PFM. Responses to thermal tests:

The patient’s response to heat and cold test are identical because the neural fibres in the pulp transmit only the sensation of pain (Hydrodynamic theory – Brannstorm). There are 4 possible reactions that the patients may experience (Cohen)1. No response – maybe non-vital or vital but giving a

negative response due to excessive calcifications, immature apex, recent trauma, patient medication etc.

2. Mild to moderate degree of awareness of slight pain that subsides within 1 or 2 seconds after the stimulus has been remove – Normal limits.

3. Strong momentary painful response subsides when the stimulus in removed – reversible pulpitis.

4. Painful response, which lingers after removal of stimulus – irreversible pulpitis.

Modification of techniques for thermal tests:A modified technique for thermal tests is provided

by the analytical pulp tester, which has a hot probe tip and a cold probe tip. The heating of the hot probe tip and cooling of the cold probe tip are controlled separately by the membrane switches on the control panel.

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Selective anesthetic testing:Selective anesthetic refers to administration of a

local anesthetic to facilitate identification of the tooth causing a painful episode.

If the source of pain cannot be differentiated, maxillary block should be given (along with palatal). If the pain vanishes, the maxillary tooth is identified as the causative agent, otherwise the mandibular tooth is indicated as the source of the problem.

The maxillary tooth is selected for the initial injections because of the greater degree deep anesthesia is normally obtainable in the maxillary arch. The likelihood of missing a mandibular block inj is always present (Weine).

If teeth in the same arch are to be identified inject the posterior most tooth in the suspected zone. If the pain still persists after tooth has been completely anesthetized, then anesthetize the next tooth mesial to it and continue to do so until the pain disappears. Test cavity:

This test allows one to determine pulp vitality. It is performed when other methods of diagnosis have failed. The test cavity is made by drilling through the enamel – dentin junction of an unanesthetized toth. The drill ing should be done at slow speed and without a water coolant. Sensitivity or pain felt by the patient is an indication of pulp vitality; no endodontic treatment is indicated. If no pain is felt, cavity preparation may be continued until pulp chamber is reached. If the pulp is completely necrotic endodontic treatment can be continued painlessly in many cases without anesthesia. Transillumination test:

Emergence of the fibreoptic as a dental instrument has been a great aid in the use of transillumination for diagnosis. The test requires shining a bright light from

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the lingual or palatal surface of a tooth, with viewing in a darkened room.

In teeth with necrotic pulps the shadow of the pulp canal space appears darker than the rest of the tooth because of the breakdown of the blood cells.

Periapical tissue may be similarly transilluminated if the plates of bone are clone to each other as in mandibular anterior teeth. Teeth with radiolucencies reveal a shadow around the apex, whereas normal teeth show no difference.

Transillumination may be helpful in diagnosing the presence of a vertical fracture. With the fiber optic shining at right angles to the fracture line, the segment of the tooth on the side of the crack illuminates whereas the segment on the far side remains dark (Weine). Occlusal pressure test (Ingle) (Biting test):

A frequent complaint is pain on biting or chewing. A clinical test that stimulates the chief complaint is the occlusal pressure test (or biting test). Different methods are - Orange wood stick- Tooth slooth - Burlew disk (rubber- Wet cotton roll

The 1 st 3 allow to pin point testing of individual cusp areas while the wet cotton roll has the advantage of adapting to the occlusal surface allowing for pressure over entire occlusal table. This test is useful in identifying teeth with symptoms of apical periodontitis abscess or cracks.

An interesting clinical observation in patients with tooth infarcation (cracked tooth syndrome) is pain is often experienced when biting force is released rather than during the downward chewing motion.

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Staining:There are 2 methods to stain a tooth1) Remove the filling from the suspected tooth and

place 2% iodine in the cavity preparation. The iodine stains the fracture line dark.

2) Mix a dye with ZnOE and place it in the cavity preparation after filling has been removed. The dye will seep out and colour the fracture line.

3) Have a patient chew a disclosing tablet after taking out the filling in the suspected fractured tooth. The line will be stained. Purpose of staining is to detect cracked tooth syndrome.

Gutta-percha point tracing with a radiograph:Purpose: Can localize the endodontic lesion to the

specific tooth. In addition, this test aids in the differential diagnosis between a periodontal and an endodontic lesion. Electric pulp testing:

The EPT is a valuable tool in differential diagnosis. Historically, the E.P. tester has been used in

dentistry as early as 1867 and has evolved over the years into the present electronic digital pulp tester.

The electric pulp tester is designed to stimulate a response by electrical excition of the neural elements within the pulp.

According to Cohen, it is the real determinant of vitality.

According to Seltzer, pain elicited by the electric pulp tester is a poor indicator of the status of the pulp.

According to Cooley and Robinson 1980 the pulp tester actually helps to determine the pulp vitality or non-vitality and not the condition of the pulp.

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Advantages of EPT:1) Intensity of stimulus is comfortable to the patients. 2) The digital display of many EP testers provide

instant, easy and reliable information. 3) In some GP testers, a red indicator flashes on and

off when maximum stimulus is reached. 4) Gives a quantitative reading and can be compared

with the normal reading on the control group.Disadvantages:

1) Cannot be used on patients having Cardiac pace maker.

2) Usually cannot be used when gloves are work.

3) Some EPT equipments are very expensive.

4) EPT is not useful for recently erupted teeth with immature apex. This may be because the relationship between the odontoblasts and the nerve fibres of the pulp has yet to develop (Nicholls).

5) Recently traumatized teeth cannot be tested.

6) The probe tips of some EP tester is removable and falls out easily.

7) No indication is given regarding state of vascular supply which would give a more reliable measure of the vitality of the pulp.

8) Readings from posterior teeth with partially vital pulps may be misleading.

The results obtained from EPT could be misleading and these could be grouped as

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A) False positive response – when the pulp is necrotic but patient gives a positive response.

B) False negative - when the pulp is vital, but the patient is unresponsive to the EPT.

Reasons for false positive:

1) Conductor / electrode in contact with a metallic restoration or gingiva along with the current to reach the attachment apparatus.

2) Patient anxiety.

3) Liquefaction necrosis.

4) Failure to isolate or dry the tooth.

5) In multirooted teeth where the pulp may be partially necrotic.

Reasons for a false negative response:

1) Patients heavily premedicated with analgesics, narcotics, alcohol, tranquilizers.

2) Inadequate contact with enamel.

3) Recently traumatized tooth.

4) Excessive calcification in the canal.

5) Recently erupted tooth with an immature apex (Nicholls).

Types of pulp testers:

2 main verities are available (Nicholls)

i) Bi-polar

ii) Monopolar

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Mono polar pulp testers are most commonly employed for this purpose.

Another method of differentiating pulp testers (Nicholl)

1) Whether current is varied

2) Whether voltage is varied

The former is preferable since a given voltage may lead to different amounts of current due to variation in electrical resistance of tissues especially enamel.

The common commercially available pulp testers are;

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1) Analytic technology pulp tester:

In which the wave form has an output in the form of bursts of 10 high frequency pulses followed by a space. This is reportedly done to minimize the patient’s discomfort. The EPT is turned on automatically when the probe touches the tooth and is turned off when the tooth contact is broken (after a delay of 15 seconds).

The analytical pulp tester has a special end fitting probe design with which pulp testing of crowned teeth may be achieved.

- Digilog pulp tester- Green wood pulp tester- Pelton crane tester- Parkell pulp tester (Battery operated)

a) Digitest

b) Gentle pulse (Parkell product)

- Analytic technology

a) Vitality scannerb) Endonanalyzer

Evident / pulpdent- Trilite

Hygenic corp. - Pulppen

Sienmens AG- Sicotest

Mada equip Co.- Digipex IIAamdent- Neo otestDahlin - Dentometer

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RADIOGRAPHY:One of the most important diagnostic aids,

radiographs, permit visual examination of the oral structure that would otherwise be unseen by the naked eye.

In the sequence of examination radiographic evaluations should come last.

Radiograph is a 2 dimensional representation of a 3dimensional object.

Normal landmarks / information observed on radiographs. This includes - Crowns of each tooth. - Curvatures of root. - Lamina dura of each root. - Bony architecture. - Quick change of RC colour on the radiograph from

dark to light may indicate a bifurcation or trifurcation.

- Anatomic landmarks – mental and incisive foramina, mandibular canal maxillary sinus etc.

- Presence of caries, that involve or threaten to involve the pulp. While observing roots one should look for periapical

lesions and other root defects such asa) Fractures.b) External and internal resorption.c) Pulp stones.d) Linear calcifications.e) Open apices.f) Bony defects.

The radiographs have certain limitations. It has been stated that lesions of the cancellous bone are not

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discrenable on the radiograph until the cortical bone has been reached or penetrated.

This has been confirmed by studies by Bender, which state that such lesions are only visible on the radiograph when atleast 6.6% of the cortical bone in the direct path of the x-ray beam has been destroyed.

Also the periapical lesions are usually larger than that seen on radiographs.

Lesions within the tooth observable by radiographs:

a) Pulp death in a developing tooth is readily apparent as the root ceases to develop.

b) Pulp stones – inflammation

c) Internal resorption (after) seen following traumatic injury.

Lesions outside the tooth observable or radiographs:

a) Widening of PL space occurring due to

– Acute apical periodontitis. – Acute apical abscess. – Occlusal trauma.

b) Changes associated with chronic periapical abscess.

c) External root resorption.

Special diagnostic methods:

Because of the inadequacies of the electric pulp testers, other modalities have been tried in an effort of correlate some parameters of disease processes with clinical testing procedures.

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ULTRASONICS (SELTZERS):Attempts have been made to detect pulpitis by

ultrasonic means but with little success – (Krisoff and Sharpe 1966).

The problem is that little information is available relative to the acoustic properties of dental hard tissues, mainly because of the crudity of the instrumentation.

With an improved instrument, the transmission and reflection of sound from the DEJ and from the dentin pulp interface has been recorded (Barber et al 1969).

With continued improvement it is conceivable that an ultrasonic diagnostic tooth will be perfected. INFRARED THERMOGRAPHY:

Alterations in the temperatures of diseased bodily structures have been detected with sophisticated infrared thermographic equipment.

It has been assumed that teeth with vital pulps would have higher surface temperatures than those with necrotic pulps.

Crandell and Hill (1966) found that by the use of an infrared thermometer, there were no difference between the surface temperature of teeth with normal pulps and those of pulpless teeth. LIQUID CRYSTAL TESTING:

Howell et al 1970 have attempted to employ the colour of cholisteric liquid crystals applied to the surfaces of the teeth as a diagnostic modality.

There are 3 types of liquid crystal, termed nematic, smectic and cholisteric according to their molecular arrangement, (Ferguson 1964).

The molecules of cholisteric crystals are arranged in layers. Changes in temperature or pressure alter the

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pitch and period of the helical structures, so that new colours are produced.

Cholisteric crystals can, therefore, serve as the active elements in devices that map the distribution of temperature.

LASER DOPPLER FLOWMETRY:

LDF was introduced (1972 – Riva, Ross, Benedek) as a non-invasive method to measure the blood flow.

The crux of LDF is based on the detection of movement of blood cells in the pulpal blood vessels (and not on neural responses) which thus gives a true picture regarding pulp vitality.

The technique consists of a laser at 632.8nm and is focused on the tissue study with a fiberoptic probe. As the light hits various components of the tissues it is partially absorbed and partially back scattered.

The back scattered light has 2 components

1) Light back-scattered from static tissue which has the same frequency as the light going in

2) The other component is the Doppler shifted light with a different frequency.

The back scattered light is processed and an output signal is produced (i.e.) both the shifted and unshifted light is transmitted to a detector by optical fibres where it is converted into electric current and processed.

The detected output signal can be fed into an analog printer, or be read from a digital board.

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Advantages of LDF:1. Non-invasive2. Simple to apply3. Provides a continuous record4. Useful to demonstrate establishment of vitality

of untreated teeth. Disadvantages:1. Impossible to calibrate the readings in

absolute units. 2. Output may not be linearly related to

blood flow. PULSE OXIMETRY:

Text relying on the passage of light through a tooth have been considered as a possible means of detecting pulp vitality with greater objectivity.

Pulse oximetry is a relatively recent advancement in non invasive monitoring. It is a non invasive oxygen saturation monitor that also provides continuous pulse rate readings.

The liquid crystal display (LCD) gives oxygen saturation pulse rate (and plethysmographic waves from readings).

Concept: Pulse oximetry uses red and infrared wavelengths in order to transilluminate a tissue and detects absorbance peaks due to pulsative circulation and uses this information to calculate the pulse rate and oxygen saturation.

The tooth being tested is sandwiched between a photoelectric detector and an LED (light emitting diodes) or red and infrared lights.

This method is clearly superior to other vitality testing methods since it does not rely on sensory nerve response.

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XERO-RADIOGRAPHY (MARCO 1984):

The term xero-radiography is derived from the Greek word XEROS which literally means dry which differentiates x’radiograhy from the conventional photochemical system.

Technique:

X’ radiography uses a rigid aluminium / selenium coated photoreceptor plate. The plate in electrically charged, placed in a water proof electric cassette, positioned in the mouth and exposed to the x-rays at a lower level of radiation. The entire process requires only 25 seconds for dry permanent image. The plates may be reconditioned, recharged and used repeatedly.

Advantages:

1. It produces sharper, clearer and finer details of the image.

2. Reduced radiation dose is required.

3. Pronounced edge enhancement is observed.

DIGITAL IMAGING:

Digital imaging in dentistry was 1 st introduced for intraoral imaging.

Despite the fundamentally different technology used in film-based imaging and in digital imaging, there are also many similarities between these 2 methods.

Instead of silver halide grains, a small number of light sensitive elements is used to record the image data from the x-ray shadow. To display the image, different shades of gray are produced by the amount of light emitted from the monitor screen.

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The difference between both methods is the fact that in analog radiographic image the silver grains are randomly dispersed in the emulsion, whereas the electronic elements of a digital sensor are arranged in a regular grid of rows and columns. The quantitative characteristics of the light-sensitive elements of the electronic sensor result in gray shades having discrete value.

What is a digital image?

The electric signal that is produced by the sensor is a voltage that is varying as a function of time.

The sensor is connected to a special board in the computer called a frame grabber. The function of this board is to sample the signals at short intervals, thus converting the analog signal into a digital signal. The output of the measurements is stored as numbers.

When the image is captured and digitized by means of an electronic sensor system, the radiation intensities are measured along a rectangular 2-dimensional grid of sensor elements called pixels (20-70mm).

The outcome of the measurements of each sensor elements is transformed to the computer and stored as a number between 0-255. To display the image, the numbers are readout and used to control the intensities of the pixels on the monitor screen.

The purpose of an x-ray image is to provide radiographic information. The small pixels provide enough resolution to satisfy this requirement.

The various methods to acquire a digital image.

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1. Conventional radiograph digitized using a flatbed scanner and transparency adapter.

2. Conventional radiograph digitized using a charged coupled device camera.

3. Semidirect digital image, acquire using photostimulable phosphor plates.

4. Direct digital image, acquired using a CCD, complementory metal oxide semiconductor or other electronic device.

Advantages:

1. Lower dose

2. Gain of time

3. Image processing – (Makes information more easily accessible for human eye).

4. Reconstruction (used to produce 3-D information.

5. Teleradiology which is not easily available from conventional radiographs.

Teleradiology – Is also a good example of the advantage offered by digital imaging.

Transmission of an electronic image over a phone line or over the internet is much faster than the traditional way of sending the radiograph by mail.

Image compression:

Digital image can be compressed to reduce transmission time or storage requirements.

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Extraoral digital imaging:Nowadays extra oral digital imaging systems are

also available. Similar to the intra oral sensor system, direct and semidirect sensor technology is applied for panaromic and skull radiography.

Tomography is possible only using a semidirect photostimulable phosphor plate system, because the image data are collected over an area that is much larger.

The 1 st commercialized digital panaromic system was the Digipan, which was a modification of OPG 100 (CCD).

The 1 st FDA approved photostimulable phosphor system (PSP) available in US was Denoptix system. Selected application for digital imagine in dentistry:Contrast processing:

To detect differences in structures in a radiograph. When contrast is not sufficient it may be possible to enhance digital images to disclose pathology that would be undetected e.g. More accurate determination of size of PA radiolucency.

For detection of simulated DC under orthodontic brackets. Automated diagnosis:

The movement toward artificial interlligence for automated diagnosis has taken a huge step forward with the FDA’s approval of Logicon caries detector.

The probability of a true positive for enamel and dentin lesions is indicated. Three dimensional imaging:

3D imaging is not limited to CT or magnetic resonance imaging Webber has developed a new method

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of producing 3D images from series of 2D images. This system is termed as TACT.Disadvantages:- Expensive.- Rate of change in the operating platforms and

processing software. Photostimulable phosphor radiography PPR:

A new radiographic digital imaging technology (PPR) has potential to improve dental radiography and is likely to become common.

The technique is variously referred to as digital luminescence radiography, storage phosphate radiography, computed radiography and radio luminography.

In 1994 the first dental PPR system become available commercially (Digora). It is used for- Caries detection- Alveolar bone imaging- PPR system provided reliable endodontic

measurements even at low exposure. PPR measurements were more accurate for

assessing trial file length than were film based measurements. SUBTRACTION RADIOGRAPHY:

It is a procedure in which a time –1 digital image of a specific anatomic area is subtracted from a time – 2 image of the same anatomic area. What remains are the anatomic features that changed between time 1 and time 2.

This is an image enhancement method, resulting in the area under focus being clearly displayed against a neutral gray background.

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It may be used to detect caries, success of RCT and condition of PA lesions. Advantages of PPR:1. Storage phosphor plates can be reused indefinitely. 2. Can be used with existing x-ray sources. 3. Linear response to radiation is available. 4. Wide exposure rage and fewer retakes. 5. Less radiation requirement. 6. No chemical processing. 7. Can be processed to enhance features of interest

and suppress interfering anatomic structures. 8. Can be transferred to other site. 9. Can be easily and inexpensively stored. 10. Computer – aided diagnosis. Disadvantages:

1. Phosphor plates must be packed in sterile envelopes.

2. Images may initially appear different from film based images.

3. Display method is not optimal. 4. Expensive5. They are at present time – intensive and may

include the time need to make diagnosis. Tomosynthesis:

The principle of tomosynthesis is based on selective focusing of an arbitrary slice through the object by shifting and adding a set of basis projections.

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LOCALISED COMPUTED TOMOGRAPHY:Localized CT (Micro-CT, radiograph

micotomography) is base on the principle of CT, however, sampling volume and reconstruction of cross-sections are more relevant to dental applications. TELERADIOGRAPHY:

Definition – In 1994 the American college of radiology defined teleradiology as the electronic transmission of radiologic images from one location to another for the purpose of interpretation, consultation or both.

They have not been used as extensively in dentistry. RADIOVISIOGRAPHY (DR. FANCOIS MOYER):

RVG digitizes ionizing radiation and provides an instantaneous image on a videomonitor thereby reducing radiation exposure by 80%. RVG equipment has a fiberoptic intraoral sensor (with a selemium coated plate). Advantages:

1. Elimination of X-ray film. 2. Significant reduction in exposure time. 3. Instantaneous image display.

The RVG has 3 components- The ‘radio’ component x-ray unit. - The ‘visio’ portion. - The ‘graphy’ component.

a) The RADIO component consists of a hypersensitive intraoral sensor and a conventional x-ray unit.

b) The VISIO portion consists of a video monitor and display processing unit.

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c) The GRAPHY component is a high resolution video printer that instantly provides a hard copy of the screen image using the same video signal.

The RVG system appears to be promising for the future of endodontics. But, the resolution of RVG is slightly lower than that produced with conventional terms, which can however be improved through enhancement procedures. MAGNETIC RESONANCE IMAGING:

Recently MRI has been tried out as a diagnostic tool in endodontics. Magnetic fields and radiographic waves are used fields and radiographic waves are used to generate high quality cross-sectioned images of the body. MRI works on electromagnetic energy. X-rays involve ionization. MRI can distinguish blood vessels and nerves from surrounding soft tissues. However this needs very large equipment. The high electromagnetic waves which are needed have not been approved of for use in scanners. It is believed that MRI machines will be developed for evaluation of odontogenic problems. Disadvantages – Not to be used in patients with cardiac pace makers metallic restoration orthodontic appliances aneurysms. COMPUTERISED TOMOGRAPHY:

CT is a radiographic technique that blends the concept of thin laser radiography with the computer image.

Techibana has reported about the used of CT in endodontics. It is possible to determine the buccolingual and mesiodistal widths of teeth and the presence or absence of root canal filling materials and metal posts. Also observable are the carious lesions, extent of the maxillary sinus and its proximity to the root apices.

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Advantages:Observation of structure which are difficult to

visualize with conventional x-ray. Provides images for 3D reconstruction of roots, root

canals and teeth. Disadvantages:- Expensive- Skin dose is large- Time consuming.

Digital subtraction radiography:The progress of caries from an incipient lesion

through the DEJ is often difficult to detect. Likewise the assessment of healing or expansion of the periapical lesion after RC therapy is a challenge because the subtle changes in the density of the lesion may not be detectable with the naked eye.

Subtraction radiography offers a remedy for these problems. This is an image enhancement method, resulting in the area under focus being clearly displayed against a neutral gray black background or it is super imposed on the radiograph itself (i.e.) required areas are enlarged against the entire background. The DSR may be used to assess the successfulness of RCT and also periapical lesions improved through enhancement procedures. COMPUTERISED EXPERT SYSTEM – JOHN FIRRIOLA:

The COMENDEX (CES) was used for the diagnosis of selected pulpal pathosis (i.e.)- Normal pulps- Reversible pulpitis- Irreversible pulpitis due to hyper occlusion. - Irreversible pulpitis.

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- Necrotic pulp. - Infection due to endodontic failure.

Appropriate diagnostic case facts are obtained and this data is entered into the computer. The computer checks and gives out the diagnosis. With rapid advances being made in the field of computers, we may get many more programmes for efficient endodontic diagnosis.

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TACT – (TUNED APERTURE COMPUTED TOMOGRAPHY):

This is a relatively new type of imaging device that may have advantage over current radiographic modalities in viewing an object while decreasing the superimposition of the overlying anatomical structures.

The TACT system uses digital radiographic images and the TACT software correlates the individual images of a subject into a layering of images that can be viewed into slices.

The ‘TACT’ image is composed of a series of 8 digital radiographs that are assimilated into are reconstructed TACT image. Preliminary studies have shown that TACT has advantages over conventional film in the visualization of canals in the human molar.

The TACT system of imaging has also been proved to be an effective diagnostic tool for evaluating primary simulated recurrent dental caries and simulated osseous defects.

With the advent of this new technology the practitioners has a new tool to diagnose external root resorption earlier than previous modalities and therefore include the likelihood of a favorable prognosis. REFERENCES:01. Endodontic Practice – Grossman.02. Endodontics – Ingle.03. Endodontic Therapy – Weine.04. Pathways of Pulp – Cohen, 7 th Edition.05. Digital Radiography, DCNA - 06. Recent Advances in Diagnostic methods for

endodontic treatment – R.Nageswar Rao.07. The Dental pulp – Seltzer.

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