Objective. This study evaluated temperature rise of low-shrinkage (LS) self-etch primer (P), LS self-etch adhesive (A), and P90 silorane-based composite resin systems, photopolymerized under normal and artificially demineralized dentin. Methods. Forty 1.5？mm-thick dentin discs were prepared from sound human molars, half of which were demineralized. Temperature rise was measured during photopolymerization using a K-type thermocouple under the discs: 10？s and 40？s irradiation of the discs (controls/groups 1 and 2); 10？s irradiation of primer (P), 10？s irradiation of adhesive (A), 40？s irradiation of P90 without P and A, and 40？s irradiation of P90 with P and A (groups 3 to 6, resp.). The samples were photopolymerized using an LED unit under 550？mW/cm2 light intensity. Data was analyzed using repeated measures ANOVA and paired-sample -test ( ). Results. There were no significant differences in temperature rise means between the two dentin samples for each irradiation duration ( ), with significant differences between the two irradiation durations ( ). Temperature rise measured with 40？s irradiation was significantly higher than that of 10？s duration for undemineralized and demineralized dentin ). Conclusions. Light polymerization of P90 low-shrinkage composite resin resulted in temperature rise approaching threshold value under artificially demineralized and undemineralized dentin. 1. Introduction Exothermic photopolymerization reaction of resin-based restorative materials and the heat produced by light-curing units (LCUs) might irritate the pulp due to an increase in temperature in the tooth cavity [1, 2]. Various factors, including the intensity of the light [3], the chemical composition of the restorative material [4, 5], heat conduction properties of composite resins [6], the depth of the cavity or the thickness of the restoration [6, 7], and irradiation duration [8, 9], might influence the extent of temperature rise during photopolymerization. Studies have shown that the heat generated during restorative procedures might have a detrimental effect on dental pulp. There is still controversy over the 5.5°C threshold temperature rise for irreversible changes in the dental pulp [10, 11]. Dentin has been reported to have a low thermal conductivity; however, the risk of irreversible pulp damage is greater in deep cavities with minimal residual dentin thickness, in which there is a concomitant increase in tubular surface area [12]. A large number of in vitro studies have been carried out to determine temperature rise during light-curing procedures of
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