Influence Of Photopolymerization And Stratification On Immediate Hardness Of Three Dental Materials B. Pelissier*, P. Tramini, E. Castany And F. Duret (UFR d'Odontologie Montpellier I, France) According to the principles of adhesive dentistry, the dental composite restoration must be realized by stratification. Moreover, the hardness of photocured composite is directly linked to the luminous intensity and to the time of exposure by lightcured lamp. The aim of our work is to evaluate the impact of photopolymerization and stratification on immediate hardness of three dental materials. Disk-shaped samples (starting thickness = 2 mm, plus 1 mm at each step of stratification) were cured with two lamps (ESPE "ELIPAR HIGHLIGHT" 2 phase polymerization lamp and DMDS "APOLLO 95 E" plasma lamp) during different times. Analyses of the Vickers hardness by microdurimeter "LEICA VHMT 30" were performed on opposite side with a 50 g load, during 5 seconds of load- maintenance. Ten measures have been realized for each step of stratification of the same sample (2 mm, 3 mm and 4 rnm), in order to determinate an analyzable and valid mean.   All the measures have been suitable in a same area to avoid hardness disparities existing on the surface of the sample. Four-way analysis of variance (type of material / stratification effect /exposure time / type of lamp) with statements of hardness as variables, provided a significant difference between materials. For each material the stratification and the time of exposure have a significant influence on immediate hardness, with an increase between 15% and 50%. In conclusion, we can demonstrate that the photopolymerization by stratification does improve the immediate hardness of the three dental materials which have been studied, thus their polymerization in depht is more complete.