1468 Reduction in Polymerization Stress through Macro-initiator Particles
J.R. CONDON, Proto-tech, Portland, OR, USA, and J.A. SMITH, Proto-tech, Portland, OR, USA

Concentrated photo-initiator particles (macro-initiators) in composite can alter the spatial dynamics of polymerization in such a way that the generation of polymerization stress is affected. Objective: The level of polymerization and the reduction of polymerization stress achieved through macro-initiation was observed and compared to a control for resin and composite formulations. Method: Visible-light sensitive macro-initiators were prepared by synthesizing camphorquinone on the surface of aerosil silica particles. Macroinitiator powder was added to 50/50 wt% BisGMA/TEGDMA resin alone or resin with 50wt% filler particles (functionally silanated, 1 Fm ave size). The level of macroinitiator was varied to find the level necessary to produce cure equivalent to a control resin containing 0.5 wt% CQ after 20sec light curing, as measured by micro-FTIR (n=5). The polymerization stress was observed as the force generated by curing a layer of resin in a cylindrical geometry in a custom uni-axial testing machine (n=5). Results analyzed by ANOVA/Tukey's test (p<0.05). Results: ave.(s.d.)

                        Macroinitiator level, %                                                        

RESIN            7.5                   10                    12.5                15                    Control

D.C.                58.6 (1.5)a            64.1(2.1)b            60.5(1.6)ab            59.2(2.0)ab            62.1(1.7)b     

Force, N            28.0(1.0)a            39.2(2.8)b            50.5(0.8)c            47.9(0.6)c            66.0(1.0)d

COMPOSITE

D.C.                60.9 (2.2)a            62.5(0.6)ab            65.9(2.7)b            64.8(1.7)b            75.6(1.0)c     

Force, N            34.6(0.7)a            42.7(1.5)b            45.8(1.6)b            43.6(1.1)b            50.8(1.4)c

Conclusions: A level of 10 wt% was sufficient to achieve the same cure as the control in the resin. With 10% macroinitiator, the experimental resin produced significantly lower stress (40% reduction). For the composite, increased macro-initiator effected cure, but even at 15wt%, the experimental composite did not cure as well as the control. The use of macro-initiators in dental resins can lead to significant reductions in polymerization stress without compromising degree of cure. Supported by NIH/NIDCR SBIR A1420G1.            

Seq #180 - Polymers and composites
10:45 AM-12:45 PM, Friday, 11 March 2005 Baltimore Convention Center 338

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