The possibility of dextran magnetite complex (DM) as a new hyperthermic material was examined in this study. DM suspension of 56 mg ml(-1) iron concentration was locally injected into the normal tongue of golden hamster. DM injected tongues were heated by 500 kHz alternating current (AC) magnetic field and its serial changes in temperature were recorded at 30-s intervals. The temperature of DM injected tongue was maintained at about 43.0-45.0 degrees C for 30 min by changing the AC magnetic field intensity. While temperature elevations of the contralateral tongue and the rectum were only of minor degree. In experiment on the extent of heating area, there was correlation between volume of black stain area and amount of the injected DM suspension (Y = - 18.1 + 1.94X, r = 0.931, P < 0.0001, n = 9 ). Histological examination after heating revealed brown uniform DM accumulation in the connective tissue between fibers of the tongue muscle. Except for vascular dilatations, no tissue damage was seen in the heated tongue. Thus, DM which has the possibility of selective and uniform heating in local hyperthermia might be useful for oral cancer therapy.

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These results strongly suggest the usefulness of this local hyperthermic system in the oral region that is accessible to this treatment.

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The time until the temperature in the pulp cavity reached 55.0 degrees C was 328 +/- 26 s (mean +/- s.d., n = 8) in the 56 mg as Fe ml(-1) of DM concentration. The temperature in the pulp cavity could be maintained at 53.5-59.0 degrees C for 1200 s by changing the magnetic field intensity safely, while temperature elevations of the dental surface on the coronal and apical sides were 4.9 degrees and 3.7 degrees C, respectively. Thus, this inductive heating system, which has the possibility of selective heating, might be useful for eliminating residues of pulp as a new ablation therapy.