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978-3-319-68195-5 107

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Infrared Thermography. An in Vitro Study
on Its Use as Diagnostic Test in Dentistry
Ana Mª Paredes1(&), Leopoldo Forner1, Rosa Cibrián2,
José Ignacio Priego2,3, Rosario Salvador Palmer2,
Leonor del Castillo1, and Carmen Llena1
1
Departament of Stomatology, Universitat de València, C/Jose Capuz, 11 B,
Paiporta, 46200 Valencia, Spain
anaparedesfos@hotmail.com
2
Biophysics and Medical Physics Group, Department of Physiology,
Universitat de València, Valencia, Spain
3
Research Group in Sports Biomechanics (GIBD), Department of Physical
Education and Sports, Universitat de València, Valencia, Spain
1 Introduction
Pulp tissue consists of richly vascularized and innervated tissue with a very small
circulatory access zone (the apical foramen) [1]. The amount and quality of pulp tissue
can only be determined using histological techniques, which imply necrosis of the
tissue [2].
“Pulp vitality tests” are currently available that induce a neurological reaction in
response to a stimulus (thermal or electrical), though they are unable to determine the
presence or absence of pulp tissue blood flow [3–5].
New techniques that do determine the presence of pulp tissue blood flow have been
evaluated, such as laser Doppler flowmetry and oximetry. However, these techniques
are difficult to apply in daily practice and at present are not normally used [5].
Infrared thermography is another technology that could be used as a pulp vitality
test. The present study was carried out to evaluate the capacity of this technique to
differentiate between teeth with and without simulated pulp irrigation on applying a
cold stimulus, and to develop a protocol for its clinical use.
2 Material and Methods
2.1
Samples
Forty extracted maxillary teeth were used: central incisors (N = 10), lateral incisors
(N = 10), canines (N = 10) and first premolars (N = 10). The study was approved by
the Ethics Committee of the University (Ref. H1448443121595).
© Springer International Publishing AG 2018
J.M.R.S. Tavares and R.M. Natal Jorge (eds.), VipIMAGE 2017,
Lecture Notes in Computational Vision and Biomechanics 27,
DOI 10.1007/978-3-319-68195-5_107
Infrared Thermography. An in Vitro Study
2.2
979
Protocol
The teeth were sectioned at the middle third of the root using an 881 drill (Komet,
Lemgo, Germany). The canal was then widened to reach the pulp chamber, followed
by insertion of an irrigation needle (injecting water at 37 °C) and a thermocouple
(Digital Multimeter DB 2000, Xindar, Mendaro, Spain) to allow continuous monitoring
of the water temperature. A lateral perforation was moreover made in the root for the
placement of another needle to keep the water in continuous circulation.
Since no previous study had determined enamel emissivity, three measurements
were made, and the resulting emissivity was found to be 0.98.
The laboratory was kept at a temperature of 20 ± 1 °C, without air currents, and
with working illumination positioned at a distance of 45−55 cm from the samples.
Thermal images were obtained from each specimen under two conditions: with and
without water irrigation at 37 °C, using a thermographic camera (FLIR E60, FLIR,
Luxemburgstraat, Belgium) positioned at a distance of one meter from the tooth.
Thermal stress was induced using a propane/butane nebulizer at −50 °C (Endo
Frost, Roeko, Cuyahoga Falls, USA). The camera was used to obtained 13 min videos,
recording the baseline condition of each specimen, the thermal change and subsequent
recovery (Figs. 1 and 2).
Fig. 1. Thermographic image of tooth recovery without simulated irrigation 30 s after
application of the stimulus.
980
A.M. Paredes et al.
Fig. 2. Thermographic image of tooth recovery with simulated irrigation 30 s after application
of the stimulus.
In order to determine whether mineralized dental tissue thickness could influence
the measurements, we carried out two radiological studies using a dental cone beam
computed tomography (CBCT) system (Master 3D, Vatech, Hwaseong, Korea), followed by measurement of the thickness of each tooth using Dental 3D software.
2.3
Statistical Analysis
The data were analyzed using analysis of variance (ANOVA), with a level of significance of p < 0.05.
3 Results
The model obtained was able to differentiate teeth with and without simulated pulp
circulation. Recovery following thermal stress showed significant differences between
the two dental simulations, and these differences persisted 5 min after thermal stress. In
addition, the thickness of the mineralized dental tissues did not affect the thermographic
measurements.
Infrared Thermography. An in Vitro Study
981
4 Discussion
The few studies that have addressed this subject place emphasis on the environmental
conditions required for correct recording of the thermographic measurements [7–9].
Smith (2004) and Kells (2000) indicated that the environmental temperature should be
20 ± 1 °C, without air currents, and with working illumination positioned at a distance
of 45–55 cm from the sample.
We used 40 maxillary teeth prepared as described by Smith (2004), sectioning the
root at its middle third and widened the canal to allow the injection of water at 37 °C.
In our case we moreover inserted a thermocouple. Another difference of our study with
respect to the literature is that each tooth served as case and control, i.e., two measurements (with and without irrigation) were obtained from one same tooth. The
measurements were obtained by means of a video recording the 3 min prior to
application of thermal stress, the moment of cooling, and subsequent recovery during
10 min.
On the other hand, we analyzed the influence of the thickness of the mineralized
dental tissues upon the thermographic measurements, since no such evaluation had
been made in any previous study.
The conclusions drawn by the studies of tooth temperature variations using thermography are heterogeneous. It has been reported that temperature recovery is initially
very rapid and subsequently stabilizes [8, 9], though clinically it is difficult to confirm
whether a tooth presents blood flow (and is therefore vital), since tooth temperature is
affected by different environmental situations [8]. The present study confirms the initial
rapid tooth temperature recovery and subsequent stabilization, though recovery was
found to progress logarithmically. This means that thermographic recordings can be
made during the first 5 min after cooling - this time being sufficient from the clinical
perspective, with the avoidance of recordings immediately after triggering of the
thermal stimulus. According to Kells, valid tomographic images can only be obtained
during the first three minutes after cooling. This difference with respect to our own
study may be attributable to sample differences.
5 Conclusions
Low temperature thermal stimulation produces an immediate temperature drop in teeth
both with and without simulated irrigation. This is followed by logarithmically progressing recovery, with significant differences between the two simulations.
The thickness of the mineralized dental tissue does not affect the measurements of
thermal change.
In sum, thermographic recording within a period of 5 min is able to distinguish
between a tooth with a pulp temperature equivalent to that of a vital tooth and a tooth
with a temperature equivalent to that of a tooth with necrotic pulp tissue.
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A.M. Paredes et al.
References
1. Hargreaves, K.M., Cohen, S.: Vías de la pulpa, pp. 17–21. Elsevier Mosby, Maryland (2011)
2. Ring, E., Ammer, K.: The technique of infrared imaging in medicine. Thermology Int. 10, 1
(2000)
3. Gopikrishna, V., Pradeep, G., Venkateshbabu, N.: Assessment of pulp vitality: a review. Int.
J. Paediatr. Dent. 19(1), 3–15 (2009)
4. Sadique, M., Ravi, S.V., Thomas, K., Dhanapal, P., Simon, E., Shaheen, M.: Evaluation of
efficacy of a pulse oximeter to assess pulp vitality. J. Int. Oral Health 6(3), 70–72 (2014)
5. Zadik, D., Chosack, A., Eidelman, E.: The prognosis of traumatized permanent anterior teeth
with fracture of the enamel and dentin. Oral Surg. Oral Med. Oral Pathol. 47(2), 173–175
(1979)
6. Chandler, N.P., Pitt Ford, T.R., Monteith, B.D.: Laser light pasaje through restored and
carious posterior teeth. J. Oral Rehabil. 41(8), 630–634 (2014)
7. Kells, B.E., Kennedy, J.G., Biagioni, P.A., Lamey, P.J.: Computerized infrared thermographic imaging and pulpal blood flow: part 1. A protocol for termal imaging of human teeth.
Int. Endod. J. 33(5), 442–447 (2000)
8. Kells, B.E., Kennedy, J.G., Biagioni, P.A., Lamey, P.J.: Computerized infrared thermographic imaging and pulpal blood flow: part 2. Rewarming of healthy human teeth following a
controlled cold stimulus. Int. Endod. J. 33(5), 448–462 (2000)
9. Smith, E., Dickson, M., Evans, A.L., Smith, D., Murray, C.A.: An evaluation of the use of
tooth temperature to asses human pulp vitality. Int. Endod. J. 37(6), 374–380 (2004)
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