250 J. Dent. 1990; 18: 250-253

Measurement of facial skin temperature

S. Ariyaratnam and J. P. Rood Department of Oral and Maxi/lo-facial Surgery, University of Manchester Dental Hospital, Manchester, UK

ABSTRACT It is essential to know the pattern of facial skin temperatures in normal subjects to be able to objectively assess differences in cases of nerve injury. Thirty healthy adults were selected at random to investigate the pattern of facial temperature using liquid crystal thermography and an electronic thermocouple system. The highest temperature of the face was in the forehead area (c. 34°C) and the lowest (c. 32 “C) in the cheek area. If ambient temperature and humidity are controlled in a draught-free environment, symmetry of the facial skin temperature can be maintained. It is concluded that measurements of facial skin temperature may be used to investigate and assess lesions of peripheral branches of cranial nerves supplying the face.

KEY WORDS: Facial skin temperature

.I. Dent. 1990; 18: 250-253 (Received 20 March 1989; reviewed 26 April 1989; accepted 5 June 1990)

Correspondence should be addressed to: Mr S. Ariyaratnam, Department of Oral and Maxillo-facial Surgery, University Dental Hospital, Higher Cambridge Street, Manchester Ml 5 6FH. UK.

INTRODUCTION

It is widely accepted that injuries of the peripheral nervous system result in disturbance of sympathetic innervation, causing changes in cutaneous blood flow, surface temperature, sweat secretion and pilorection. Studies in the lower and upper limbs have shown a positive relationship between temperature changes and nerve injuries (Nakano, 1984; Uematsu, 1985).

Thermometry and thermographic studies have been used infrequently in the facial region in the objective assessment of nerve injury, although these methods have been successfully used in other parts of the body (Nakano, 1984; Uematsu, 1985). However, the validity of skin thermography and thermometry for the evaluation of lesions of peripheral branches of cranial nerves supplying the face depends on the stability and symmetry of facial tom*\~r~+,.m ;n rrn-01 o,.h;nntn I~I.Ip4aLul~ 111 II”llIlal JU”JtitiLJ.

It was the aim of the present study to establish baseline data of temperature patterns in the face of normal individuals using liquid crystal thermography (LCT) and an electronic thermocouple system (TC) and to assess the validity of LCT and TC in measuring temperature differences in facial skin.

MATERIALS AND METHODS

Thirty healthy individuals volunteered to participate in

the study. None of the subjects suffered from skin disorders and none was taking any form of medication. This sample comprised 15 males and 15 females with an age range from 18 to 30 years (mean age 23.7 years).

Two systems were employed for measuring skin temperature.

Liquid crystal thermography

The system used was the Novatherm LCT system (Novamedix Ltd, Hampshire, UK). This system consists of a thermal detector supported by a fixed distance metal frame attached to a Polaroid camera with a flash attachment (Fig. I).

The thermal detectors have micro-encapsulated liquid crystals which change colour reproducibly with tempera- ture. They are embedded in a latex membrane which is mounted on a transparent plastic frame. When the air- filled flexible detectors contact the body surface, an image appears on the box which represents the heat pattern in that area, and high resolution instant colour photographs record the images which can be documented. There are eight thermal detectors ranging from 22°C to 36°C. Each detector has a 4°C temperature span. For example the ‘Novatherm 30’ responds from 28°C to 32°C and overlaps the next detector by 50 per cent of the temperature scale for accurate assessment.

0 1990 Butterworth-Heinemann Ltd. 0300-57 12/90/050250-04

Ariyaratnam and Rood: Facial skin temperature 251

Fig. 7. The Novatherm Liquid Crystal Thermographic system.

Electronic thermocouple

A Comark electronic thermocouple (Comark Electronics I td. Cussex. IJKl. a multinle thermocounle svstem of the -_-, L-&C---, ___, _. ----.---~-_ ._._ _.__ -_--=__ L,L_____ -. ____ CUKUNi type TC, with 10 different thermocouples attached to the system (Fig. 2) was employed. By changing the switch position, it was possible to read each of the thermocouples on the electronic temperature scale. The accuracy of the system at 23°C is + 0S”C.

Skin temperature is affected by such factors as ambient temperature, humidity, air movement, and whether the subject has been exercising recently. All measurements were carried out in a closed room with minimal air movement as skin temperature is affected by such factors and the mhiwtc harl hw.n inrlnntc fnt at hart A< m;n Ull.. .&I” YYVJ’WCV Al.... “WILL IILU”“IY *“I UL AYUYL T., 111111.

A maximum of 10 min preparation time was required for each individual, so that the face was exposed to air at the ‘steady rate’ room temperature (Crandell and Hill, 1966). The mean ambient temperature was maintained at 22°C. A thermohygrograph (Negreti-Zambra Ltd, London, UK) was used to measure environmental temperature and humidity to ensure identical conditions for all measurements.

The three sensory segments of the face corresponding to

Fig. 2. The Comark Multiple Thermocouple system in use.

the areas innervated by the three main branches of the trigeminal nerve were studied: the forehead, the cheek and the chin.

Two instant photographs for temperature analysis and documentation were taken with liquid crystal thermo- graphic detectors piaced iateraiiy on each side of the face. Excessive pressure was not exerted while placing the detectors on the face to prevent any disturbance in the normal blood flow to the area.

The area showing the highest temperature in each segment was picked up from the liquid thermographic picture. A site was selected from the relatively high temperature areas in each segment and symmetrically identified on the contralateral side for thermocouple measurements.

Each thermocouple was attached to the selected sites by adhesive tapes and left for 10 min to obtain steady recordings. A total of six thermocouple measurements was recorded from each individual.

RESULTS

The mean temperature measurements for the three anatomical sides in the 30 healthy adults were calculated I_.. _ - (laole 1). lne highest mean temperature on the face was

Table 1. Differences in temperature between right and left sides in the three anatomical areas

Variable

Mean temperature

f”C) Difference

(mean) T value Two-tail

probability

Right forehead 34.4 ..Y nq Left forehead 34.3 0.1 L.U.3 (j cj2*

Right cheek 32.2 Left cheek 32.3 0.1 1 .os 0.285*

Right chin 33.3 Left chin 33.3 0.04 0.47 0.644*

*Not significant.

252 J. Dent. 1990; 18: No. 5

Table II. Temperature differences between the three anatomical sites on the same side (right side)

Mean temperature Difference Two-tail

Variable (“Cl (mean) T value probability

Right forehead 34.4 Right cheek 32.2 2.2 10.65 o.ooo**

Right forehead 34.4 Right chin 33.3

1.1 9.92 o.ooo**

Right cheek 32.2 Right chin 33.3 1.1 5.93 o.ooo**

**Very significant (P < 0.001).

34.4”C on the forehead area. The lowest mean tempera- ture, on the cheek, was 32.2”C. The chin temperature, 33.42”C, lay between these two values.

The temperature differences between right and left sides were extremely small and stable throughout the face (Table I). For example, the mean temperature difference between right and left sides in the chin area was calculated as 0.036 (T = 0.47, P = 0.644). None of the differences was statistically significant.

The temperature differences were compared between the three segments on the same side (Table II). The temperature differences between these segments were statistically significant-for example, the right forehead area was warmer than the right cheek (T = 10.65, P = 0.0).

DISCUSSION

The results of this investigation have confirmed that a stable and reproducible skin temperature pattern of the face can be obtained in a thermally well maintained draught-free room (Berry and Yemm, 1971; Johanson, 1985). This study has also supported the view (Kirch et al., 1980) that the temperature of the human face varies from area to area. The probable reason for the temperature heterogenicity is that the skin of the face mainly lies over tissue with low metabolism (connective tissue, bone and tendon), so the heat transport by convection from the surface depends on the rate of blood flow through the skin, which can be particularly variable in these regions. In the trunk and thigh, however, the skin covers a large mass of metabolically active muscle, which produces large amounts of heat uniformly; thus in these areas the patterns shows homogenicity (Kirch et al., 1980).

The highest temperature was recorded in the forehead area, these results supporting studies done by others (Uematsu, 1985). This is probably due to the metabolic activity of the brain, separated from skin only by a thin layer of bone and muscle tissue (Kirch et al., 1980).

The lowest temperature on the cheek area may be due to the fat layers which act as insulators to heat conduction and also the other tissues underlying the skin being metabolically less active. This was demonstrated in our studies to be more prominent in females than in males.

Thermal symmetry in the different areas of the face can be expected in normal subjects; right and left facial temperature differences in normal subjects are statistic- ally insignificant. Although many studies show that the stability and reproducibility of the skin temperature can be obtained under controlled environments (Johanson, 1985; Uematsu, 1985), there was always a reluctance to accept the accuracy of the absolute skin temperature in the past, as any contact systems may alter blood flow and produce an inaccurate reading. However, the relative skin temperature difference between the normal side of the face and the affected side in individuals can be used for diagnostic purposes.

Many instruments have been described to measure the skin temperature including liquid thermometers, radio- meters, electric circuits and thermisters (Chase and Brierly, 1964), based on a variation of resistance and conductivity in metal with change of temperature. However the simplicity of the thermocouple principle has made it the most commonly adopted method (Richards, 1946).

In an attempt to assess the two systems used in the studies, both benefits and limitations were found. The Novatherm liquid crystal thermographic system is simple, portable and easy to manipulate. The main advantage of the system is its ability to provide graphic information and relative temperature distribution, even though it might not provide accurate temperature measurements, or even allow the examiner to locate and evaluate anatomical regions of the face which are showing different tempera- tures. It is difficult to place the thermal detectors on the front of the face, as these are not flexible enough to accommodate the prominent part of the nose, so that it was not possible to take a thermal picture of both sides of the face simultaneously. Once the areas of interest have been detected by liquid crystal thermography, the electronic thermocouple can be used to confirm the temperature.

The Comark thermocouple system is simpler to use and its adaptability to multi-thermocouple measurement is a great advantage. However, the limitations are related to fixing the thermocouples to the skin and that a single thermocouple provides a reading of temperature from a very small area.

Ariyaratnam and Rood: Facial skin temperature 253

CONCLUSIONS References

Thermal symmetry of the skin temperature of the face can be maintained in a controlled environment. This justifies clinical investigations of the type which involves com- parison of an affected area with a homologous unaffected area on the opposite side and thus temperature measure- ments may be of use in the assessment of nerve injuries.

Berry D. C. and Yemm R. (1971) Variations in skin temperature of the face in normal subjects and in patients with mandibular dysfunction. Br. J. Oral Surg. 8, 242-241.

Chase G. 0. and Brierly J. N. (1964) Transducers In: Norman D. W. (ed.), Instrumental Methods of Experimental Biology. New York, MacMillan, p. 458.

Crandell C. E. and Hill R. P. (1966) Thermography in dentistry: a pilot study. Oral Surg. Oral Med. Oral Pathol. 21, 316-320.

Of the sites tested the warmest area on the face was the forehead and the coldest area was the cheek. Liquid crystal thermography can be used to obtain graphic information on relative temperature distribution. Once the area of interest has been detected, the thermocouple can be used to measure accurately the temperature- relative to the normal contralateral site. These methods of measuring skin temperature should be of value in assessing the severity of nerve injuries and could possibly be helpful in monitoring recovery.

Johanson A. (1985) Reproducibility and variation of skin temperature over the temporomandibular joint and masseter muscle in normal individuals. Acta Odonfol. Stand. 43, 309-313.

Kirch K. A, Merke J., Hinghofer-Szalkay H. et al. (1980) A new plethysmograph to measure volume changes in small circumscribed tissue area. PZIugers Arch. Physiol. 189-197.

Nakano K. K. (1984) Liquid crystal contact thermography (LCT) in the evaluation of patients with upper limb entrapment neuropathies. Neural. Orfhop. J. Med. Surg. 5, 97-102.

Richards R. L. (1946) Methods of study-with particular reference to the recording of skin temperatures. In: Richards R. L. (ed.), The Peripheral Circulation in Health and Disease. Edinburgh, E. and S. Livingstone, pp. 22-28.

Uematsu S. (1985) Thermographic imaging of cutaneous sensory segments in patients with peripheral nerve injury. Skin temperature stability between sides of the body. .Z. Neurosurg. 62, 716-720.

Acknowledgements

The authors wish to thank Dr D. G. Waste11 for statistical advice and Mr C. M. Atack for preparing the photo- graphic illustrations.

Book Review

Clinical Oral Microbiology. T. W. MacFarlane and L. P. Samaranayake. Pp. 284. 1989. London, Wright. Softback, f 14.95.

This excellent new textbook provides, for the first time, an authoritative account of oral microbiology in relation to clinical diseases of the mouth and general dental practice. It is inexpensive and well produced. The few spelling errors and misprints are not likely to cause confusion, except for that on page 213 (para 3, line 2) where a list of Gram-positive ‘anaerobes’ is defined as ‘aerobes’. The text is commendably terse, and there is an avoidance of excess technical information. The pure microbiological aspects of the book are difficult to fault. A larger section on the atypical mycobacteria may be more appropriate for a dental readership. An explanatory note relating to the API Strep identification system (p. 104) would have been useful for students and clinicians. It would also be helpful to stress the need for unfixed tissue for mycobacterial culture (p. 1 14). and conversely to fix smears taken from the oral cavity (p. 198). The tables and figures are generally clear and concise, although I had some difficulty in interpreting figure 5.2 on p. 59. The integration of

microbiology with clinical dentistry is excellent. There are a few key clinical points which could usefully have been added. The risk groups for tuberculosis are not defined, although these are important as an aid to selecting those patients for further investigation. The significance of thrush as a clinical sign has been underplayed, except in relation to AIDS. Oral candidosis in patients on steroid inhalers is discussed, but the simple prophylactic measure of washing excess steroid powder off the mucosa with a drink of water is not mentioned. The possibility of immunosuppression (e.g. lymphoma) as a cause of recurrent attacks of shingles in particular is not discussed, although clinically important, nor has the relatively lower susceptibility to acyclovir of herpes zoster compared with herpes simplex. Cross-infection control is dealt with expertly; only the need for plasters to cover cuts and abrasions on the hands, even when wearing latex gloves, has not been adequately stressed. All these are minor points for the next edition. Meanwhile, this is an excellent book which deserves to become the standard text in many, if not all, dental schools. J. Wg