Aim of the study: evaluate the in vivo pulp response and the intra-pulpal temperature change of refrigerated and pre-heated resin composite restored in class V cavities with different depths (superficial and deep), and to compare responses and measure the time needed for pulp temperature to return to starting point.Material and methods:a-Evaluation of pulp response to refrigerated and preheated composites:Two hundreds and fifty two teeth in twelve dogs were used in assessment of pulp response. (20 teeth in each dog) and 1 tooth in each dog randomly chosen from teeth other than tested, used as control group without any cavity preparation or restoration. The study was divided into three classes of 80 teeth each according to the selected observation period: 1 day, 7 days and 45 days. Teeth were divided into four main groups according to resin composite temperature. In the first group, the composite used was refrigerated at 5 ºC. For the other three groups the composite was pre-heated either (37 ºC, 54 ºC or 68 ºC). Each group was subdivided into two subgroups according to cavity depth either superficial or deep.A standardized round class V cavity was prepared in the buccal surfaces. The prepared cavities were restored by the resin composite at different temperatures.After observation periods of 1, 7 and 45 days dogs were sacrificed. The teeth were separated. Teeth were decalcified. Serial sections of 6-8 um thicknesses were cut longitudinally and examined for histo-pathological features in comparison to control groups, at x40, x100 and x200. These features were graded and scores were recorded, tabulated and statistically analyzed.b-Intrapulpal temperature change measurements:A total of forty teeth in two dogs were used. The teeth were divided into four main groups of 10 teeth each according to the resin composite temperature used. The first group was refrigerated at 5 ºC, and the other three groups were pre-heated either (37 ºC, 54 ºC or 68 ºC). Each group was subdivided into two subgroups of 5 teeth each according to the cavity depth either superficial or deep.A standardized round class V cavity was prepared in the middle of buccal surfaces. From the lingual surface of each tooth, a small deep cavity was prepared till pulp exposure was performed. The cavities prepared on buccal surfaces were restored with resin composite. A K type thermocouple probe was used to measure temperature changes. Three readings were taken, inside the buccal cavity to measure composite temperature just when it was applied in class V buccal cavity, starting intra-pulpal temperature before composite application and the changed intrapulpal temperature and when the intrapulpal temperature returned to normal to figure out the time needed for the pulp to return to the starting normal temperature. Data were collected, recorded, tabulated and statistically analyzed.Results:1.No pulpal tissue changes appeared after one day and 7 days testing periods with superficial cavity filled with either refrigerated or pre-heated resin composite, except with resin composite pre-heated to 68 ºC, the pulp tissue showed moderate inflammation , and severe inflammation in deep cavities. The pulp tissue retained to its normal condition after 45 days in both cavity depths.2.The highest increase in intra-pulpal temperature was with pre-heated resin composite to 68 ºC, followed by 54 ºC and 37 ºC ,while the intra-pulpal temperature decreased with refrigerated resin composite .3.The time taken to the pulp to return to its normal temperature was less than one minute with all tested resin composite temperatures. The resin composite pre-heated to 68 ºC, takes more time than all other tested temperature. Conclusions:1.Refrigerated or even pre-heated resin composite to 54 ºC does not adversely affect the pulp tissue.2.Pulpal tissue changes with pre-heated resin composite to 68 ºC return to normality with time.3.Tissue changes become obvious with decreased dentin thickness.4.Intrapulpal temperature changes are resin composite temperature and cavity depth dependent.5. Time to return to normal intra- pulpal temperature with either refrigerated or pre - heated resin composite was not critical to pulp tissue health.