In Kaneko et al. Their findings were positive but the thermal properties of the mineralized tissue were not considered. These values were obtained from the use of thermocouples, a thermometer, a thermistor, a pulse-laser and infra-red thermography Lisanti and Zander, ; Phillips et al. Table 1. Thermal diffusivity and thermal conductivity values of human enamel and dentin.
A map provides spatial information from co-ordinates on two axes, such as X and Y. The use of a thermal value for each co-ordinate corresponding to a pixel of tooth-tissue could be represented from a grayscale, producing a thermal map specific to that tooth-tissue.
This could show the spatial relationship of the thermal properties of the tooth-tissue as an image, rather than a series of numerical values. This may be more clearly understood from the map providing a 2-dimensional relationship of the thermal properties across the whole surface of the tooth-tissue. The thermal properties of enamel and dentin may be sufficiently different to visually distinguish enamel from dentin.
Demineralized areas within both tissues may also have different thermal properties due to tissue-changes, such as mineral loss from caries, which may be seen in the thermal map. The primary aim of this study was to produce a thermal map of a sound, human tooth-slice to visually characterize human enamel and dentin. The secondary aim was to map a human tooth-slice with demineralized enamel and dentin to consider future diagnostic potential of thermal maps in caries-detection.
Both teeth were cut bucco-lingually with an Accutom-5 Struers, Copenhagen, Denmark into 1 mm-thick tooth-slices and then polished with an grit abrasive sheet, with the addition of distilled water as needed. Slice-thickness was measured with a digimatic micrometer IP65 Quantumike Mitutoyo. Photographs and radiographs of each tooth-slice were taken. A period of 35 min stabilization was allowed prior to commencing data-collection.
Figure 1. Thermal cube with hotplate and heating-mat green in position, with camera secured on the cube by a fixed-mounting normal to the samples.
The parameters used with the camera were: Emissivity 0. The carrier was manually transferred to the aluminum hotplate. Data-capture by the thermal camera commenced prior to transfer of the carrier. Figure 2.
Thermograph of Sample 1—Sound tooth-slice, with circular areas-of-interest shown to enable calculation of the characteristic-time-to-relaxation used in the computation of the thermal diffusivity of the tissues. Once the value of thermal diffusivity was known, thermal conductivity could be calculated:.
The thickness of the sound tooth-slice measured less than a millimeter in all areas, with the greatest enamel-thickness in the middle at 0. The carious tooth-slice was thicker in all areas, with the maximum thickness of enamel at 1.
Table 2. Dimensions of tooth-slices as recorded with a calibrated digimatic micrometer. The initial rewarming temperatures for the sound tooth-slice in both crown- and root-dentin green and pink broken-lines were lower than the two areas of enamel purple and blue broken-lines.
It took circa 30 s to reach thermal equilibrium of all tissues Figure 3. The rate of rewarming in both regions of enamel are the same and marginally quicker i. The results for the right-hand side enamel and crown-dentin respectively, show differences in characteristic-times-to-relaxation: enamel at 3.
The results indicate from the sound tooth-slice that enamel has a higher value of thermal diffusivity 3. All values are provided in Table 3. These values fall mainly within the accepted range for thermal diffusivity of enamel at 2. Figure 3. Table 3. Within the carious tooth-slice, the rate of rewarming in the two sound enamel areas-of-interest purple and blue broken-lines are similar, whereas the enamel carious lesion is slower red solid-line Figure 4.
Carious enamel fails to reach equilibrium in the 30 s time-period. Crown-dentin green broken-line warms quicker than root-dentin pink broken-line. The carious dentin mustard solid-line is the slowest of all tissues to rewarm and fails to reach equilibrium within the time-frame.
The characteristic-time-to-relaxation for carious enamel is 5. This is the only occassion where enamel has a slower characteristic-time-to-relaxation than dentin. All other values give enamel 4. The enamel has a lower value of thermal diffusivity, ranging from 1. Thermal diffusivity shows the crown-dentin 0. The carious area of dentin has an increased value of 1. The thermal conductivity of carious enamel 0. All other values of thermal conductivity for enamel and dentin within the carious tooth-slice are lower than others' findings.
Figure 4. The two thermal maps distinguish the mineralized tissues of enamel, dentin and the carious areas of both tissues using the thermal properties of characteristic-time-to-relaxation and heat-exchange during rewarming Figure 5.
Figure 5. Sample 1- Sound tooth-slice and Sample 2 - Carious tooth-slice. Initially, a photograph is shown, followed by an X-ray, then the characteristic-time-to-relaxation thermal map and, finally, the heat-exchange thermal map depicting enamel, dentin and carious areas of enamel and dentin. Infra-red thermal imaging is a technique which is yet to be maximized within the field-of-medicine and its subsidiary specialty - dentistry.
Published work for determining the thermal properties of tooth-tissue Panas et al. Tooth-slice thicknesses of 2. Lin et al. Simultaneous heat-application to the irregular occlusal surface would be unlikely, compared to the application of vertical heat to the flat surface of the samples within this study and Panas et al.
The tooth-slices within this study were viewed directly—unlike Lin et al. They were also heated directly—unlike Panas et al. Neither of these additional layers was considered in their final calculations. Despite these variations, a single-sample Lin et al. Multiple samples from different teeth have not previously been reported from this technique, nor have areas of demineralization or caries.
All samples are from different donors with inherent anomalies in the tissue-types, as previously described. Investigation of a point location or a single line of a single tissue-sample with any temperature-recording-method, e.
The larger the area-of-interest used for each tissue and the greater the sample-size, the more valid and reliable any inference from the findings. Within this study, two samples, one sound and one carious with a demineralized area, were investigated with multiple areas-of-interest for each tissue.
Enamel values of thermal diffusivity and conductivity fall within proximity of known-ranges for the sound tooth-slice but do differ slightly between the two sides examined. Greater variation is seen within the demineralized enamel, where the carious area-of-interest returns the lowest values.
This could be explained by the loss rajeunir photo en ligne journal mineral, but caution is needed as the range of values for the sound areas-of-interest differ by a similar proportion within the same sample.
These findings appear appropriate to the nature of the tissues being investigated and a more general outcome as described by Panas et al. That is, following the application of heat and analysis with thermal imaging, a difference between the thermal response of enamel and dentin was detectable, with enamel tending to conduct heat quicker than dentin. The data from this study agrees with that baseline principle and within the two samples presented - sound and demineralized - the thermal properties indicate that enamel conducts heat quicker than dentin within each sample.
Two exceptions are seen - one for carious enamel and one for the root-dentin outlier. The carious lesion will have a reduced mineral content - not quantified in this study - and returns a thermal conductivity which lies between the crown-dentin and carious dentin of the same tooth-slice. Comparison between sample-values does not agree with this principle and may be due to the natural variation of the samples from different people, the age of the teeth, the orientation of enamel prisms and dentinal tubules or the carious process.
Further work is needed to investigate these relationships. The purpose of this study was to see if enamel and dentin could be visualized from their individual thermal properties within a map. A thermal map provides a 2-dimensional diagram of the spatial relationship of every thermal value per pixel calculated across the whole tooth-slice. This advances the techniques previously described and adds to the information of an optical image. The thermal maps are produced from the gradient of the rewarming curve - characteristic-time-to-relaxation - and the integral of the curve - heat-exchange.
As seen in Figure 5the two types of thermal map do characterize enamel and dentin.
Congrès de l'Association Dentaire Française | PARIS | Palais des Congrès
The characteristic-time-to-relaxation map of sample one, the sound tooth-slice, shows a diffuse boundary between enamel and dentin and is sensitive to the tissue-thickness, as shown from the sloping-sides of the tooth-slice in the root-area. This is radiolucent on the X-ray. The heat-exchange thermal map shows distinct contrast between enamel and dentin and the carious change within the enamel and dentin is clearly visible, compared to the characteristic-time-to-relaxation thermal map, where there is less contrast of the carious lesion within enamel and diffuse change is seen in dentin.
All the advantages of the characteristic-time-to-relaxation thermal map are retained by the heat-exchange thermal map. The spatial resolution defines the ability to distinguish two separate points but this does not necessarily transfer to diagnostic ability for the human operator. The lesion shown within the demineralized tooth-slice is large, and the minimum size and level of demineralization detectable with this system is currently unknown and requires additional work with suitable test-objects.
Spatial resolution can be limited due to equipment and the infra-red wavelength nm to 1 mm which will always be less than that of X-rays 0. This study has viewed slices of teeth in-vitronot a whole tooth, and the findings can underpin future models on whole teeth. Two studies have investigated carious lesions in whole human teeth in-vitro - one looking at artificially-created lesions on the smooth labial surface of incisors Kaneko et al. The theory of a thermal difference between sound tooth-tissue and carious tissue was based on evaporative cooling due to an increase in moisture-content within the micro-pores of the carious lesion.
This was found to provide a positive outcome in both studies. Consideration of the thermal properties of the tissues, as seen in this study, were not presented in either of the whole-tooth studies, but their outcomes positively reinforce the need for further work. This is being investigated for comfort and time-of-application.
The use of thermal imaging to detect approximal caries is unlikely as it cannot penetrate tissues in the way X-rays do.
However, detection of early smooth-surface lesions and occlusal lesions would allow preventive measures to be prescribed. X-rays have limitations, as previously mentioned, as do optical detection methods. Thermal imaging may complement our current armamentarium.
Detection of active and arrested caries remains uninvestigated with thermal imaging and consideration botox advantages and disadvantages wikipedia be needed for other potential causes of difference in tooth structure and composition, e. The enamel and dentin of tooth-slices can be characterized in-vitro from their thermal properties, as seen in the thermal maps of heat-exchange and characteristic-time-to-relaxation.
The heat-exchange map produces better contrast between enamel and dentin than the characteristic-time-to-relaxation map. Within enamel and dentin, demineralized tissue can be detected in both maps, with heat-exchange providing the greatest contrast within both tissues. These thermal maps support further investigation of thermal imaging to complement diagnosis of caries. PL, DB, designed the Study, undertook the acquisition, analysis and interpretation of data, wrote the first draft of the manuscript, provided contribution to revision and final approval of the manuscript and are accountable for the work presented.
FC, VC, were involved with conception of the design, revision and approval of the manuscript. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Some data within this manuscript was presented at the Enamel 9 Conference, 30th October to 3rd November, and PL's attendance at the Conference was supported by an Early Career Research Award from Enamel 9, which was gratefully received. Bader, J. The evidence supporting alternative management strategies for early occlusal caries and suspected occlusal dentinal caries. Based Dent. A systematic review of the performance of methods for identifying carious lesions.
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