In Vitro Assessment Of The Light-Tip Polymerization Device. A Clinical Application H. Tassery *, E. Toca, A. Raskin (1), A. J. Faucher (Faculté D’Odontologie Marseille. Université De La Méditerrané. France (1)Université U.C.L Belgique) Previous studies, (Ericson et al., 1894 ; Neiva et al., 1897) in order to reduce the negative effects of the polymerization contraction, adviced the use of a light tip polymerization device.   The purpose of this study was   (1) to compare, using dye penetration, the sealing efficiency of Tetric Ceram (TC) applied with four different filling procedures in class II restoration versus Bisfil 2B (self-cured),   (2) to analyse using FTIR device the effects of these procedures on the conversion degree of the TC versus Bisfil 2B (B2B) versus soft-polymerization.   (1) Fifty teeth were randomly divided into 5 groups.   G1 : TC 100% (500mW/cm² x 40-3 Ic x 2mm). G2 : G1-Light-tip. G3 : Plasma (1,5W/cm² -3 Ic x 2mm). G4 : B2B. G5 : G1 (-1 Ic x 4mm).   After thermocycling the tracer penetration was evaluated with Episcope Wild 420 (8 measures by restoration)   (2) FTIR analysis was achieved on the same groups except G5 replaced by G’5/G’6 (soft and soft light-tip). Classe II samples were made on a ceramic mould in order to ovoid any kind of embbeded material. Ultra thin samples (3µm) were achieved using an ultra-microtome and analysed by FTIR.   Quantitative values and FTIR area units were statistically analysed with a Kruskall-Wallis test. (p: 0.05). Groups with the same superscript did not differ (1) a#b ( p : 0.01);(2) a#b#c (p : 0.001).   Results were summarized in the table 1 and 2. The benefits of the light tip device associated with the soft procedure in term of microleakage and conversion degree valided its clinical use.   Ic: increment     Mean logarithmique leakage mm (SD) G1 0.24 (0.27) a G2 0.416 (0.14) a G3 unpolymerized G4 0.41 (0.18) a G5 0.01 (0.01) b   Groups Area units ratio vynil double bond / aromatic double bond (SD)   1 mm 4 mm G1 0.41 (0.09) b 0.37 (0.067) b G2 0.34 (0.018) a 0.53 (0.04) c G3 0.04 (0.02) b unpolymerized G4 0.34 (0.06) a 0.29 (0.06) a G*5 0.32 (0.04) a 0.37 (0.05) b G*6 0.27 (0.08) a 0.32 (0.05) a