Thermal conductivity through various restorative lining materials.

Abstract

OBJECTIVES: Traditional teaching has advocated the placement of insulating materials under restorations to protect against 'thermal shock'. Often this involves placement of a thick zinc-oxide eugenol cement lining. The purpose of this in vitro study was to assess the heat transfer through four lining materials and dentine and to relate these findings to the temperature exposures that may be experienced in the oral environment. METHODS: Two 'traditional' linings, zinc oxide eugenol cement (ZNOE) and calcium hydroxide paste (CAOH), and two more contemporary materials, a resin modified glass polyalkenoate (RMGP) and dentine bonding system (DBS) were studied in addition to dentine itself. Seven samples of each material were tested by utilising a Lees' Disc apparatus. Incorporation of thermocouples allowed heat transfer through the sample to be recorded. Thermal conductivity (J/m/s/ degrees C) was calculated for individual samples and a mean value obtained for each material. One way ANOVA and post hoc Tukey's tests were applied to the data obtained. RESULTS: In ascending order of thermal conductivity, DBS<CAOH<RMGP<DENTINE<ZNOE. Statistical analysis revealed that the thermal conductivity of DBS was significantly less than RMGP, DENTINE and ZNOE (p<0.05); CAOH was significantly less than DENTINE and ZNOE (p<0.05); RMGP was significantly higher than DBS and significantly less than DENTINE and ZNOE (p<0.05). CONCLUSIONS: Thermal insulation is not a major consideration in cavity lining and therefore other criteria for selection of a lining material should be applied.