EFFECT OF COMPOSITE TYPE, LIGHT-INTENSITY, CONFIGURATION FACTOR AND LASER POLYMERIZATION ON POLYMERIZATION CONTRACTION FORCES

Purpose: To investigate the effect of composite type, light intensity, configuration factor and laser polymerization on polymerization contr action force. Materials and Methods: Glass rods (10 pairs/group) were etched with HF acid, silanated, unfilled resin applied and light cured for 20 s. Rods were held vertically in chucks on a Zwick machine. A c ylindrical matrix was filled with Silar chemical cure, Silux Plus micr ofill or Z-100 hybrid composite and the crosshead of the UTM positione d at an inter-rod distance corresponding to a specific ratio of bound to unbound composite surface area (configuration factor or C). Exposur e time with the Demetron 401 conventional visible light curing unit (D 401) was 40 s/side (80 s total). Exposure times for the ILT Model D550 0 air cooled laser (LAC) and Model 5500ABL water cooled laser (LWC) wa s 20 s/side (40 s total). Experimental groups, n = 10 with constant fa ctors in parentheses, included: (1) Silar chemical-cured (C=3); (2) 2- 100 hybrid (C=3, D401, 100% intensity); (3) Silux Plus microfill (C=3, D401, 100% intensity); (4) D401 100% light intensity =476 mW (2-100, C=3, D401); (5) D401 50% intensity =238mW (Z-100, C=3, D401); (6) D401 25% intensity =119 mW (2-100, C=3, D401); (7-9) C=5, 3 & 1 respective ly (2-100, D401, 100% intensity); (10) D401 with 13 mm tip =391 mW/cm( 2) (2-100, C=3; D401); (11) D401 with Turbo Tip =811 mW/cm(2) (2-100, C=3; D401); (12) LAC =265 mW, 689 mW/cm(2) (2-100, C=3); (13) LWC =365 mW, 1100 mW/cm(2) (2-100, C=3). One Way ANOVA and Duncan's Multiple R ange Test (alpha=0.05) were performed separately for each variable. Re sults: Homogeneous subsets by variable were: composite type Group 1 (2 5N) < Group 3 (65.8N) < Group 2 (90.4N); intensity Group 6 (73.9N) =Gr oup 5 (77.7N) < Group 4 (90.4N); C-Factor Group 7 (81.8N) < Group 8 (9 0.4N) < Group 9 (103.4N); light source Group 12 (77.4N) = Group 13 (79 .1N) < Group 10 (90.3N) = Group 11.(89.4N). The chemical-cured composi te had the lowest maximum polymerization contraction force, the microf ill was intermediate and the hybrid composite had the highest recorded force. Increases in light intensity increased the maximum force on th e force/time curve. Maximum forces were inversely related to C-factor (C5 < C3 < C1) and directly related to composite volume in a non-rigid system which allowed compliance. Maximum force was not significantly different with the two tips tested on the conventional curing light. F orces obtained with laser polymerization were similar for the two lase r groups, which were both statistically lower than the conventional li ght tested.