|Year : 2017 | Volume
| Issue : 2 | Page : 87-92
Thermography: A newer diagnostic assessment tool in dentistry
Talla Harshavardhan, Nimma Vijayalaxmi, Mahesh Mudavath, Deepika Meesala
Department of Oral Medicine and Radiology, Meghna Institute of Dental Sciences, Nizamabad, Telangana, India
|Date of Web Publication||15-Sep-2017|
Department of Oral Medicine and Radiology, Meghna Institute of Dental Sciences, Mallaram, Nizamabad, Telangana
Source of Support: None, Conflict of Interest: None
Thermology is the study and application of bio-thermal process to assess health or disease while thermography is a technique of measurement of skin temperature distribution on the body over a given period of time. It is a noncontact, noninvasive method that utilizes the heat from an object to detect, display, and record thermal patterns and temperature across the surface of the object and it employs images and visually evaluates the thermal changes. The principle of thermography is based on the amount of blood circulation at different layers of the skin, as it varies, the temperature also changes accordingly. Consequently, disorders that affect the blood flow too result in abnormalities in temperature distribution and these when evaluated will provide valid diagnostic information. Thermography is being used to detect various pathological conditions in the medical and dental field. Various orofacial conditions in which thermography can be used are chronic orofacial pain, temporomandibular joint disorders, quantification of thermal insult to pulp, assessing inferior alveolar nerve deficit, and detection of herpes labialis in prodromal phase. Here, we discuss with the history, basics, and various applications of thermography in dentistry.
Keywords: Facial telethermography, infrared thermography, telethermography, thermography
|How to cite this article:|
Harshavardhan T, Vijayalaxmi N, Mudavath M, Meesala D. Thermography: A newer diagnostic assessment tool in dentistry. J Mahatma Gandhi Inst Med Sci 2017;22:87-92
|How to cite this URL:|
Harshavardhan T, Vijayalaxmi N, Mudavath M, Meesala D. Thermography: A newer diagnostic assessment tool in dentistry. J Mahatma Gandhi Inst Med Sci [serial online] 2017 [cited 2018 Jan 18];22:87-92. Available from: http://www.jmgims.co.in/text.asp?2017/22/2/87/214764
| Introduction|| |
Heat (or warmth) has a profound cognitive impact on humans. There are strong associations of life with warmth, of moderate body temperature with health, and of high body temperature with disease. Body heat is generated by metabolism and by muscular activity and keeps the core body temperature at a defined slightly oscillating level (about 37°C). The organisms heat loss depends on ambient factors and results of conduction, convection, infrared radiation (IR), and evaporation (sweating) from the surface of the skin despite breathing and other mechanisms. Thermology is the study and application of biothermal processes to assess health or disease and the word thermography employs imaging and visual evaluation of those thermal changes from an object to detect, display, and record thermal patterns across the surface of the object. Any tissues sufferance is accompanied by four signs: rubor, tumor, dolor, and calor. The last one can be measured today through thermography. Every warm bodies have moving Brownian movement More Detailss. They crush each other, resulting in thermic energy, measured with thermometer or thermograph. More interactive movements result in more thermic energy. Over the years, a variety of devices such as thermometers, thermistors, thermocouples, and liquid crystal imaging systems have been employed to measure the body temperature.
| History|| |
IR was first discovered by Sir William Herschel in 1800 and it was his son Sir John F. W. Herschel who recorded these spectra on the infra side of red around 1840. All objects including the human body emit radiation in the infrared spectrum, and according to Wien's law, the frequency at which the maximum energy is emitted is dependent on the temperature of the body. Therefore, by measuring the IR emitted by the skin surface, the temperature can be determined [Table 1] and [Table 2].
| Principle|| |
The thermography principle is as the amount of blood circulation at different layers of the skin varies, the temperature also changes accordingly. Consequently, disorders that affect the blood flow too result in abnormalities in temperature distribution and these when evaluated will provide valid diagnostic information.
Types of thermography
Based on the method of application, thermography can be classified into the following types:
- Semi-quantitative contact method – liquid crystal thermography
- Quantitative infrared-detecting noncontact methods which are categorized as follows.
- Infrared telethermography
- Dynamic telethermography
- Facial telethermography.
Liquid crystal thermography
A liquid crystal thermography uses a thermometer consisting of flexible rubber sheets and cholesteric crystals [Figure 1] which are arranged in several layers and are mounted in a frame. These sheets also have the provision for inflation so that the heat-sensitive surface conforms better to the body's contour. To measure the thermal changes, the crystal sheets are placed over the surfaces to be examined. After placement, the crystals change from their neutral color into different color in response to the surface temperature. The resultant color display is then photographed using polaroid photography [Figure 2] which gives an instant hard copy of the image.
- Less expensive
- Portable compared to electronic tele-thermography units.
- They are technique sensitive
- Requires timed skin contact to record a reproducible temperature distribution
- Moreover, the temperatures recorded are not accurate due to the contact of the crystal sheet with the body surface which can cause compensatory warming/cooling of the contact area.
Infrared telethermography (infrared thermograph, telethermography, telethermometry, electronic thermography, or digital infrared telethermographic imaging)
It is a noncontact method of temperature measurement where the detector is kept remotely at a single spot. This method consists of an infrared detector, amplifier-digitizer, a micro-computer, and a video display. The infrared detectors used here are of different types as follows:
- Single-element infrared detector
- Linear array infrared detectors
- Two-dimensional array detectors.
Single-element infrared detectors consist of a set of rapidly rotating mirrors and a germanium lens which focus the infrared flux. As the IR emitted by the face enters the germanium lens, it passes through the mirrors that are placed perpendicular to each other. These set of mirrors rotate rapidly on a vertical and horizontal axis simultaneously so that every point on the field of view is scanned and reflected onto the detector which converts them into electrical signals. An amplifier then converts these electric signals into digital values which are then fed into a computer which reconstructs a digitized thermal image.
Linear array infrared detectors consist of an infrared camera with a linear array of detectors that require just one mirror. The mirror generally rotates around a vertical axis to scan the field of view and hence its vertical resolution is limited.
Two-dimensional array detectorsor focal plane arrays consist of a germanium lens and a plate of miniature detectors. The germanium lens functions in the same way as in single detector system and helps in focusing the infrared influxes directly on to the detectors.
Advantages: They have higher speed (allowing to obtain >100 images/s), reliability, and maintenance-free performance since they require no moving parts.
Disadvantages: They have limited spatial resolution.
Dynamic area telethermometry
It is advancement in infrared imaging in which quantitative assessment of temperature changes (temporal thermal behavior) over a non-uniform temperature area is measured. To record the temporal thermal behavior, a series of thermal images are taken from each subarea. The values of each subarea unit constitute a time series of temperatures, the dynamics of which can be quantitatively analyzed using fast Fourier transform (FFT). The characteristic feature of dynamic area telethermometry (DAT) is that the FFT spectra can project the underlying temporal thermal behavior in terms of thermoregulatory frequencies. Another additional quality of DAT is the possibility to determine the microspatial homogeneity of skin temperature which is the representation of temporal behavior of cutaneous perfusion.
Heat emissions from the human face have been shown to be physiologic indicators of the underlying health or disease. Heat emission is directly related to cutaneous vascular activity, yielding enhanced heat output on vasodilatation and reduced heat output on vasoconstriction. Infrared telethermography of the face may serve, therefore, as an utterly harmless, noninvasive diagnostic technique that can help to differentiate selected clinical problems. The pattern of radiative heat dissipation over the human body is normally symmetrical. It has been shown that, in normal controls, differences in skin temperature on selected 10 points from side to side are small (about 0.28°C). The significant difference between the absolute facial temperature of men versus women has also been observed. Men were found to have higher temperatures over the 25 anatomic zones measured on the face (e.g., orbit, upper lip, lower lip, chin, cheek, etc.) than women. The rationale behind this is that men have more basal metabolic rate than women and men's skin dissipates more heat per unit area of the body surface. Similarly, age and ethnicity variations in facial temperature can also occur.
Komoriyama et al. in their study showed that there were differences in temperature within the oral cavity between teeth, free gingiva, attached gingiva, and alveolar mucosa by identification of these tissues on thermal images.
| Clinical Requirements|| |
Thermography is a painless, noninvasive procedure that can be done within minutes and requires the following:
A trained telethermographer and a high-quality telethermography system consisting of infrared camera, thermal control unit, and image analysis software.
Room requirements for thermography
- The examining room should be of approximately 8 feet × 10 feet to maintain a uniform temperature
- The room must be free from drafts, carpeted, and curtains should be used to prevent outside IR from entering the room
- Windows and doors should be adequately sealed to prevent airflow in the area where the patient is positioned
- The examining room must have a thermometer to evaluate the temperature of the room
- The room temperature should be maintained between 18°C and 23°C and should not vary more than 1°C during the course of the study
- The humidity of the room should also be controlled (30%–70%) such that there is no moisture build up on the skin, perspiration, or vapor levels that can interact with radiant infrared energy
- Standard fluorescent lighting is adequate and incandescent lighting should not be used during the examination due to the amount of IR it produces.
- During the examination, the patient should be positioned relatively equidistant and adequately spaced from each wall
- Prior to examination, patients with minor infections in and around the face should be recorded like those occurring with pimples, razor nicks, etc. as they can interfere with the diagnosis and can appear as hyperthermic artifacts
- Similarly before the examination, the patients' face must be cleared from lotions, creams, powders, deodorants, or antiperspirants on the area to be imaged as it can have an effect on skin reflectivity.
- No physical therapy, ultrasound treatment, acupuncture, or hot/cold pack should be used 24 h prior to the examination'
- The examining body area should not be shaved for 4 hours and patient should not bathe for an hour before examination'
- Before the commencement of the procedure, the hair must be pulled back from the face with an elastic head band, all clothing and jewelry at the site of examination should be removed
- The patient should be allowed to sit in a relaxed position for a minimum of 15 min ahead of examination to allow for a stable physiologic behavior
- A handheld electric fan can be used for 25 s to cool the face before initiation of the procedure.
| Contraindications|| |
- Patients with fever and with sunburn are not eligible for accurate thermal image analysis, in such cases, it is advisable to defer telethermographic facial studies until the acute phase subsides
- Similarly, facial scars can appear as pathological hypothermic lesions.
| Clinical Applications of Thermography in Dentistry|| |
Chronic oro-facial pain
Grattet et al. in 1996 developed a classification system using telethermographs for patients with chronic pain.[Table 3] They classified them as normal when selected anatomic area (ΔT) values range from 0.0 to +0.250C, hot when it is >0.350C, and cold when it is <0.350C. When a selected anatomic area value is 0.26–0.350C, the finding is classified as equivocal.
This new system of thermal classification resulted in 92% agreement in classifying pain patients, making it as an important diagnostic parameter [Figure 3].
|Figure 3: Thermographic image in orofacial pain (myofacial pain dysfunction syndrome)|
Click here to view
Normal temporomandibular joint (TMJ) examination using thermography had showed symmetrical thermal patterns with a mean ΔT value of 0.10C. On the other hand, patients affected with internal derangement and TMJ osteoarthritis showed ΔT values of +0.40C. Beth and Gratt in 1996 conducted a double-blinded clinical study to compare the ΔT values among active orthodontic patients, TMD patients, and asymptomatic TMJ controls [Figure 4]. The results showed the average TMJ area ΔT values as +0.20C, +0.40C, and +0.10C in these groups, respectively. The above findings suggest that telethermography can distinguish between patients undergoing active orthodontic treatment and patients with TMD.
Quantification of thermal insult to pulp
Dental pulpal tissue is exposed to a variety of thermal insults during various dental treatment modalities. Debonding of orthodontic brackets, electrothermaldebonding (ETD) method, is widely used, this technique although has many advantages than the conventional mechanical method can pose serious thermal damage to pulp. Cummings et al. in 1999 performed an in-vitro study on extracted human premolar teeth applying ETD. Thermal imaging analysis was done using mercury cadmium telluride detector which showed that the pulpal temperature increased from 16.8°C to 45.6°C, which can pose serious threat to pulpal vitality.
Similarly, the use of ultra-high speed air-driven instrumentation during cavity preparation can result in serious thermal insult to the pulp. Carson et al. in 1979 performed a study employing thermography to determine the pattern of heat distribution and dissipation during ultra-speed cavity preparation using both an air–water spray and air-only coolants to determine if a point heat source is generated. This study stated that the mean magnitude of temperature increases with both types of coolant, 2.80C and 3.670C, probably does not exceed the physiologic limits of the pulp [Figure 5].
Assessing inferior alveolar nerve deficit
Numerous studies have shown that thermal imaging technique can play a vital role in effective assessment of inferior alveolar nerve deficit. Gratt et al. in 1994 stated that patients with inferior alveolar nerve deficit when examined showed ΔT values of +0.50C on the affected side, whereas patients with no inferior alveolar nerve deficit showed a symmetrical thermal ΔT value of +0.10C. The authors stated that the changes are due to blockage of the vascular neuronal vasoconstriction.
Detection of herpes labialis in prodromal phase
During the prodromal phase, all patients showed an increase in temperature with the mean localized change in temperature (Dt°C) being 1.1°C ± 0.3°C over a mean. When the patient was asymptomatic.thermographically positive area of 126 mm ± 34 mm is seen. After 72 h of treatment with acyclovir cream, majority of the patients returned to normal with no clinical or thermographical evidence of infection [Figure 6].
Other applications of thermography
- Evaluation of craniomandibular disorders
- Detection of carotid occlusal disease
- Quantification of the effects of postsurgical inflammation
- Quantification of the effects of analgesics, anti-inflammatory drugs, etc.
- In the diagnosis of myofascial symptoms
- In the diagnosis of nerve and bone disorders
- Joint pains, osteoarthritis, rheumatoid arthritis
- Hyper- or hypo-tonic muscular pain reactions
- Endodontic treatments can monitored
- To assess the reaction of tissue to a new dental material
- Diagnosis of any kind of orofacial inflammation
- Acute and chronic periodontitis
- Cancers in orofacial region
- Myofacial pain dysfunction syndrome.
- Noninvasive technique
- Easy seating examination
- Minimal examination time (2–3 min)
- Obvious difference in color changes (gradient: −0.05°C)
- Its real-time application enables very fast scanning of stationary targets and capturing fast-changing thermal patterns 
- To store thermograms, we can use many methods:
- Printing on paper, Xerox paper, or coated with a material that changes color on heating; this is the thermal printing
- Magnetic devices (compact disc [CD] or computer database archive).
- Quality cameras often have a high price range
- Images are difficult to interpret accurately when based on certain objects, specifically objects with erratic temperatures
- Most cameras have ±2% accuracy or worse in measurement
- Unable to detect the inside temperature if the medium is separated by glass/polythene material, etc. Only able to detect surface temperatures
- There must be a temperature difference for certain surveys
- Sensitivity and resolution reduce with distance and angle of view
- Training and staying proficient is time-consuming.
| Conclusion|| |
In dentistry, thermography can become an important diagnostic tool, because of accurate measurement of regional temperature and differentiation of minor temperature difference with or without any invasive procedural involvement (0.05°C difference). Thermography may be useful in elaborating a right diagnosis on an inflammatory reaction from maxillofacial territory. After treatment, thermograms can give important reaction about that treatment methods and their efficiency. Thermograms can be saved in a database, on CD, or printed on a special or regular paper. It is a method that utilizes the thermal images to detect, display, and record thermal pattern and temperature across the surface of the object.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1], [Table 2], [Table 3]