Clinical Application Of Thermography In Dentistry
Thermography measurement in the clinical set up can be done on a given spot or over an extended area of interest. Infrared telethermography of the face in normal subjects have shown that men have higher temperatures than females. The rationale behind this is that men have more basal metabolic than women and his skin dissipates more heat per unit area of body surface. Similarly age and ethnicity variations in facial temperature can also occur. [14-16]

In Chronic Orofacial pain patients 
Gratt and his colleagues in 1996 developed a classification system using telethermographs for patients with chronic pain. [17] 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. Moreover they also found that hot thermographs had the clinical diagnosis of (1) sympathetically maintained pain, (2) peripheral nerve mediated pain, (3) TMJ arthropathy, or (4) maxillary sinusitis. Subjects classified with cold subareas on their thermographs were found to have the clinical diagnosis of (1) peripheral nerve-mediated pain (2) sympathetically independent pain. Subjects classified with normal telethermographs included patients with the clinicaldiagnosis of (1) cracked tooth syndrome (2) trigeminal neuralgia (3) pretrigeminal neuralgia (4) psychogenic facial pain. This system of thermal classification resulted in 92% agreement in classifying pain patients making it as an important diagnostic parameter. [12,17]

In TMJ disorders 
Normal TMJ examination using thermography had showed symmetrical thermal patterns with a mean ΔT values of 0.10C. [12, 14, 18] On the other hand, patients affected with internal derangement and TMJ osteoarthritis showed ΔT values of +0.40C. [19, 20] Beth and Gratt in 1996 conducted a double-blinded clinical study to compare the ΔT values among active orthodontic patients, TMD patients and symptomatic TMJ controls. The results showed that the average TMJ area ΔT values as +0.20C, +0.40C, and +0.10C in these groups respectively.(21) The above findings suggest that tele-thermography can distinguish between patients undergoing active orthodontic treatment and patients with TMD. [12,21]

In quantification of thermal insult to pulp 
Dental pulpal tissue is exposed to variety of thermal insult during various dental treatment modalities. Of late for debonding of orthodontic brackets Eelectro Thermal Ddebonding (ETD) method is widely used, this technique although has many advantages than the conventional mechanical method can pose serious thermal damage to pulp. Cummings and his colleagues in 1999 performed an in-vitro study on extracted human premolar teeth applying ETD. Thermal imaging analysis was done using mercury cadmium terullide detector showed that the pulpal temperature increased from 16.80C- 45.60C, which can pose serious threat to pulpal vitality. It can be stated from the study that, ETD methods needs intermittent cooling of the teeth with simultaneous thermal imaging to prevent pulpal damage. [22] Similarly the use of ultra high speed air-driven instrumentation during cavity preparation can result in serious thermal insult to the pulp. To overcome this, it is believed that various coolants (air water spray or air/water alone) can be used to reduce the intrapulpal temperature and prevent subsequent damage to the pulp. It was only until 1979, when Carson and his colleagues 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. [23]
In assessing inferior alveolar nerve deficit
Over the years numerous studies have shown that thermal imaging technique can play a vital role in effective assessment of inferior alveolar nerve deficit. [12,24] Gratt and his colleagues in 1994 stated that patients with inferior alveolar nerve deficit when examined showed ΔT values of +0.50C on the affected side whereas subjects with no inferior alveolar nerve deficit showed a symmetrical thermal ΔT value of +0.10C. [25] The authors stated that the changes are due to blockage of the vascular neuronal vasoconstriction and this was confirmed by the same colleagues in the same year when similar thermological picture was obtained in normal subjects by temporary blockage of the inferior alveolar nerve using 2% lidocaine. [26]

Qualitative evaluation of N2O concentration
N2O is a highly insoluble gas which is rapidly absorbed and is eliminated swiftly by the lungs, thus it is used widely either alone or in combination with other anesthetic agents. [27] Results of various studies have shown that leakage of N2O into the workplace can lead to adverse health effects such as reproductive, hematologic and nervous dysfunctions. [28] Studies on acute and chronic occupational exposures have shown that N2O air concentration levels as low as 50 parts per million (ppm) can result in bone marrow depression, paresthesias, altered concentration, impaired visual effects, alterations in vitamin B12 and plasma homocysteine concentrations. [29-31]

In response to these findings and in order to effectively control exposures several guidelines have been published that define appropriate use and control criteria for N2O usage. The ADA made 10 recommendations that address the use of appropriate engineering controls for proper scavenging. [32] However, they are proved futile and health hazards secondary to N2O exposure is still on the rise. Rademaker et al in 2009 conducted a study using infrared thermography to determine the effectiveness of two N2O scavenging systems- The Safe Sedate Dental Mask (Airgas, Radnor, Pa.) system (System I) and Porter Nitrous Oxide Sedation System (Porter Instrument, Hatfield, Pa.) (System II). The results suggested that neither of the system was able to control occupational exposure of N2O oxide below the NIOSH REL. [33]

Additional applications of telethermography
- Evaluation of cranio mandibular disorders. [34]
- Detection of carotid occlusal disease. [35]
- Quantification of the effects of post-surgical inflammation. [36]
- Quantification of the effects of analgesics, anti-inflammatory drugs, etc.
- In the diagnosis of myofacial symptoms.

Conclusion
Thermography aids in the assessment and staging of various dysfunctions of the head and neck region. The unique significance of thermography is both qualitative and quantitative assessment which helps in estimation of progression of the disease in a systematic manner. With the innovation of novel equipments and the state of the art facility, thermography in the near future will certainly re-emerge as a unique research tool in dentistry.

References
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[19] Gratt BM, Sickles EA, Ross JB. Thermographic characterization of an intemal derangement of the temporomandibular joint. J Orofacial Pain. 1994; 8: 197-206.
[20] Gratt BM, Sickles EA, Wexler CA. Thermographic characterization of osteoarthrosis of the temporomandibular joint. J Orofacial Pain. 1993; 7: 345-353.
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Infrared thermography: Experience from a decade of pediatric imaging.

Eur J Pediatr. 2007 Aug 30;
Infrared thermography: Experience from a decade of pediatric imaging.
Saxena AK, Willital GH.

Department of Pediatric Surgery, Medical University of Graz, Auenbruggerplatz 34, Graz, A-8036, Austria

The aim of this study was to evaluate the feasibility of clinical application of infrared thermography (IRT) in the pediatric population and to identify pathological states that can be diagnosed as well as followed up using this non-invasive technique. In real time computer-assisted IRT, 483 examinations were performed over a period of 10 years from 1990-2000 on 285 patients in the pediatric age group (range 1 week-16 years) presenting with a wide range of pathologies. The temperature was measured in centigrade (degrees C), and color images obtained were computer analyzed and stored on floppy discs. IRT was found to be an excellent noninvasive tool in the follow-up of hemangiomas, vascular
malformations and digit amputations related to reimplantation, burns as well as skin and vascular
growth after biomaterial implants in newborns with gastroschisis and giant omphaloceles. In the
emergency room, it was a valuable tool for rapid diagnosis of extremity thrombosis, varicoceles,
inflammation, abscesses, gangrene and wound infections. In conclusion, IRT can be performed in
the pediatric age group, is non-invasive, without any biological side effects, requires no sedation or
anesthesia and can be repeated as desired for follow-ups, with objective results that can demonstrated as colored images. Periodic thermographic studies to follow progression of lesions seem to be a
useful and reproducible method.