Tomas Bata University Zlin, Czech Republic February 2nd, 2012 Curing Kinetics of Reactive Photo-polymeric Dental Materials Prof. Dr.-Ing. Bernhard Möginger Hochschule Bonn-Rhein-Sieg Bonn-Rhein-Sieg University of Applied Sciences Folie 1
Depth Dependent Curing Behaviour of Dental Composites using DEA Outlook 1. Introduction and Scope 2. Experimental and Materials 3. Consideration of Photo-curing Process and Reaction Kinetics 4. Results 5. Conclusion Acknowledgement Folie 2
Introduction Application of Photo-polymeric Dental Fillings Classification of dental fillings in cavity classes I to IV The application defines the requirements of the filling materials. Ref: http://www.zahnwissen.de/images/kav_klassen.jpg Folie 3
Introduction Application of Photo-polymeric Dental Fillings Ref:: Voco GmbH Folie 4
Introduction Types of Modern Dental Fillings Photo-polymeric composites Glass ionomer cements Compomers Ormocers (organically modified ceramics) Folie 5
Introduction Composition of Photo-polymeric Dental Fillings Polymer resin composed of a mixture of several monomers mainly dimethacrylates (DMA) (12 to 40 weight%) Silanised glass fillers of micro and nano-scale (60 to 88 weight%) Additives e.g. light sensitive initiator system, accelerators, stabilizerss, inhibitor, pigments etc. (approximately 1 weight%) Folie 6
Structure monomers Introduction Composition of the polymer resin (Bisphenol-A-Glycidyl-Dimethacrylat) Folie 7
Introduction Composition of the polymer resin Comonomers (TEGDMA, DEGDMA, HEMA TEGDMA = 3 DEGDMA = 2 HEMA Hydroxyethylmethacrylat Folie 8
Introduction Composition of the polymer resin Properties of structure monomers Monomer M W Viscosity shrinkage g/mol mpa*s % BisGMA 512,6 800,000 6 UDMA 470,6 10,000 6,1 TEGDMA 286,3 10 14,5 Folie 9
Folie 10 Introduction Anorganic Fillers Glass based fillers Pyrogene SiO 2 (<100nm, spherically shaped) Refe: Report Nr.18 aus Forschung und Entwicklung, August 2007, Ivoclar Vivadent AG, Liechtenstein Folie 10
Folie 10 Introduction Anorganic Fillers Glass based fillers Pyrogene SiO 2 (<100nm, spherically shaped) Milled glass (>500nm, irregularly shaped) Ref: Report Nr.18 aus Forschung und Entwicklung, August 2007, Ivoclar Vivadent AG, Liechtenstein Folie 11
Folie 10 Introduction Anorganic Fillers Glass based fillers Pyrogene SiO 2 (<100nm, spherically shaped) Milled glass (>500nm, irregularly shaped) Mixed oxides e.g. ZrO 2 -SiO 2 ( spherically shaped, size and refraction index well adjustable) Ref: Report Nr.18 aus Forschung und Entwicklung, August 2007, Ivoclar Vivadent AG, Liechtenstein Folie 12
Folie 10 Introduction Anorganic Fillers Glass based fillers Pyrogene SiO 2 (<100nm, spherically shaped) Milled glass (>500nm, irregularly shaped) Mixed oxides e.g. ZrO 2 -SiO 2 ( spherically shaped, size and refraction index well adjustable) special X-ray opaque fillers, Ref: Report Nr.18 aus Forschung und Entwicklung, August 2007, Ivoclar Vivadent AG, Liechtenstein e.g.ybf 3 Glass ionomer cements Folie 13
Folie 10 Introduction Additives Initiation system Ref: Report Nr.18 aus Forschung und Entwicklung, August 2007, Ivoclar Vivadent AG, Liechtenstein Additive: Light absorbing initiator (blue range: 380-500nm) Accelerator mostly an amine Inhibitor, eg. BHT Pigments (opacity and color Folie 14
Introduction Basic Requirements of Dental Fillings Mechanical performance similar to the teeth No internal stresses Minimal volume shrinkage, best around 0.5% Good adhesion to the tooth Same colour like teeth X-ray opacity Folie 15
Experimental Methods to trace the curing reaction Shrinkage ATR FT-IR spectroscopy Poor initial time resolution Global curing behavior Good time resolution Maximum penetration depth of 10 µm Dielectric Analysis (DEA) Good time resolution Sensor dependent penetration depth form 30 to 120 µm Folie 16
Introduction Measuring principle of the DEA The dielektric material in the capacitor represents the sample.. Time scale: 10 ms to some days Ref: Grüner, M., Vortrag auf der Analytika 2004, Fa. Netzsch (frequency dependent) Folie 17
Introduction Measuring principle of the DEA lines of the E-field penetrating the dental material dental material polyimide foil + - d = distance of electrodes Comb capacitor Penetration depth of the E-field is determined by d. Folie 18
Materials and Methods Materials 1. VOCO Arabesk Top OA2 77 weight.% anorganic fillers with particle sizes of 0,05μm and 0,7μm; 23 weight.% of acrylate based resin of the monomers BisGMA, TEGDMA and UDMA; 2. VOCO Grandio OA3 87 weight% anorganic fillers with partikle sizes of 20nm to 60nm and 1μm; 13 weight.% of acrylate based resin of the monomers BisGMA, TEGDMA and UDMA; Initiator system of both materials: Campherquinone initiator and dimethylene aminobenzoe acid ethyl accelerator, butylhydroxy toluene inhibitor, and further additives Experimental equipment 1. Netzsch Dielectric Analyser DEA 231/1 Epsilon with external steered oven 2. Netzsch mini IDEX sensor with Ni electrodes on polyimide foil electrode distance: 100 µm 2 mm 3. VOCO Celalux LED light source Folie 19
Methods Experimental setup Light guide to LED lamp Microscope slides Sample Sample support Double sided adhesive Sensor Folie 20
Methods Experimental setup LED lamp Light guide Sample Oven Oven Thermo couple Dielectric analyser (DEA) DEA sensor Folie 21
Consideration of the photo-curing process Occuring reactions Initiator activation Accelerator activation Start reaction of the polymerization Growth reaction of the polymer chain Cross-linking reaction of polymer chains Termination reactions Folie 22
Consideration of the photo-curing process Occuring initiation reactions singulet excitation triplet excitation triplet decay triplet degradation Accelerator activation Accelerator degradation Accelerator decay Ref: Cook, Photopolymerization kinetics, Polymer, 600-609 (1992), Vol. 33, Nr. 3 Folie 23
Consideration of the photo-curing process Initiation process and acceleration activation camphorquinone Ref: Report Nr.18 aus Forschung und Entwicklung, August 2007, Ivoclar Vivadent AG, Liechtenstein ion radicals radicals dimethyl amino benzoe acid ethyl ester (accelerator) Folie 24
Consideration of the photo-curing process Polymerization and cross-linking Start reaction k start A + DMA A (DMA) k start reaction constant of amine radicals Growth reaction A ( DMA) ( DMA ) + DMA A ( DMA) + 1 ( DMA ) n k ucg n k ucg reaction constant of undisturbed chain growth Folie 25
Consideration of the Reaction Kinetics The reaction rate depends on the concentrations of DMA and activated initiator molecules DMA dc ( t) = k dt ucg initiator DMA * c0 ( x) * c ( t) Solving yields: c DMA ( t) = c DMA 0 * e k ucg * c initiator 0 ( x) * t Transferring to the degree of conversion: α( t) = c DMA c c DMA 0 DMA ( t) c c DMA initiator 0 kucg * c0 = 1 DMA 0 ( t) = 1 e ( x) * t Folie 26
Consideration of the Reaction Kinetics The remaining relative amount of DMA molecules is given by ( 1 α ( t )) = e k ucg * c initiator 0 ( x ) * t The logarithm provides initiator ( 1 α( t) ) = k * c ( x) t log 0 ucg * This expression has to be connected to the ion viscosity signal measured with the DEA! Folie 27
Consideration of the Reaction Kinetics With the assumption that the degree of conversion is proportional to the measured ion viscosity follows: η t t init ( ion ion ) τ reac η η e ion ion ( t) η 0, init With the boundary conditions: = * For t = t init η ion ( t = tinit ) = η0, ion init α( t = t init ) = 0 For t η ion ( t ) = η ion α( t ) = 1 Folie 28
Consideration of the Reaction Kinetics Rearranging and taking to the logarithm yields Evaluation 1: ion ion t η η ( ) 1 log ion ion = * t tinit init 14 η η 44 24 0, 44 3 τ { reac experimental data slope b 144244 3 fit function ( ) Expanding the exponential in a Taylor series yields Evaluation 2: η ion ion ion initiator ( t tinit ) = η0, init + Δηmax * kucg * c0 ( x) * 144 44 24444 3 slope B ( t t ) init Folie 29
Results time dependent log(ion viscosity) Arabesk OA2 lg ion viscosity η ion of uncured material chain growth scatter due to matrix filler interactions diffusion controlled chain growth and cross-linking lg ion viscosity points of the raw data curve illumination initiation of radicals time in s Folie 30
Results Comparison to FT-IR degree of conversion Arabesk OA2 Folie 31
Results reproducibility of log(ion viscosity) Arabesk OA2 10 Primary curing log (ion viscosity) 9,5 9 8,5 curve #1 curve #2 curve #3 8 0 5 10 15 20 25 30 35 40 illumination time in s thickness d = 1mm Folie 32
Results ion viscosity Arabesk OA2 8 ion viscosity in 10 9 ohm*cm 6 4 2 0 0 25 50 75 100 125 150 time in s Folie 33
Results evaluation 2 of ion viscosity Arabesk OA2 After the initiation the ion viscosity depends linearly on time before the slope decreases and reaches saturation. ion viscosity * 10^8 ohm*cm 30 25 20 15 10 5 0-5 thickness d = 1mm curve#2 fit#2, 3 to 9 s 0 2 4 6 8 10 12 14 time in s Assumption: ion α( t) η ( t) ion viscosity degree of conversion The slope of ion viscosity corresponds to curing rate. Folie 34
Results evaluation 1 of ion viscosity Arabesk OA2 After the initiation the ion viscosity depends linearly on time before the slope decreases and goes slowly to infinity. 0,05 log(δη ion (t)/δη ion max) 0,00-0,05-0,10-0,15-0,20 0 5 10 15 20 time in s Folie 35
Results depth dependency of ion viscosity Arabesk OA2 10 log (ion viscosity) 9,5 9 8,5 8 2 nd illumination log (ion viscosity), depth = 0,5mm log (ion viscosity), depth = 1,0mm log (ion viscosity), depth = 1,5mm log (ion viscosity), depth = 2,0mm 0 10 20 30 40 50 60 70 80 time in s Folie 36
Results evaluation of ion viscosity Arabesk OA2 After the initiation the ion viscosity depends linearly on time before the slope decreases and reaches saturation. ion viscosity * 10^8 ohm*cm 30 25 20 15 10 5 0-5 thickness d = 1mm curve#2 fit#2, 3 to 9 s 0 2 4 6 8 10 12 14 time in s Assumption: ion α( t) η ( t) ion viscosity degree of conversion The slope of ion viscosity corresponds to curing rate. Folie 37
Results evaluation of ion viscosity Arabesk OA2 With increasing depth the range of constant initial slope is extended and still increases for larger times. ion viscosity * 10^8 in ohm*cm 20,0 16,0 12,0 8,0 4,0 0,0 curve#2 fit#2, 4 to 20 s thickness d = 2mm Something changes in the initiation mechanism if only few initiator radicals are generated. 0 5 10 15 20 25 30 time in s Folie 38
Results depth dependent initial slope of ion viscosity 5 Fit function: Grandio - experimental mean values initial slope of ion viscosity in 10^8 ohm*cm/s 4 3 2 1 Grandio - fit mean values Arabesk - experimental mean values Arabesk - fit mean values ion ion µ d & =η& * e 0 0 η Fit parameter Arabesk OA2 Grandio OA2 η ion 0 [ohm*cm] 6,66 3,92 µ [mm -1 ] 1,16 0,99 d [mm] 0,87 1,01 0 0 0,5 1 1,5 2 2,5 depth in mm Folie 39
Conclusions for photo-polymeric dental materials Results: 1. The curing rate increases with light intensity. 2. The range of linear time dependency increases with decreasing light intensity. 3. After the range of linear time dependency of the ion viscosity the curing rate exhibits an increasing curing rate for very low light intensities. 1. For very high light intensities the concentration of activated initiator molecules is depth dependent but constant. 2. At low light intensities the generation of activated initiator molecules becomes time dependent leading to an increasing number of starter radicals. Folie 40
Conclusions for photo-polymeric dental materials Activation of initiator system irradiation of light curing unit 0.5 1.0 2.0 4.0 sample irradiation depth [mm] Folie 41
Conclusions for photo-polymeric dental materials Starting of the chain growth irradiation of light curing unit 0.5 1.0 2.0 4.0 sample irradiation depth [mm] Folie 42
Chain growth Conclusions for photo-polymeric dental materials irradiation of light curing unit 0.5 1.0 2.0 4.0 sample irradiation depth [mm] Folie 43
Chain growth Conclusions for photo-polymeric dental materials irradiation of light curing unit 0.5 1.0 2.0 4.0 sample irradiation depth [mm] Folie 44
Conclusions for photo-polymeric dental materials Chain growth and activation of the initiator system in deep depths irradiation of light curing unit 0.5 1.0 2.0 4.0 sample irradiation depth [mm] Folie 45
Conclusions for photo-polymeric dental materials Chain growth and cross-linking irradiation of light curing unit 0.5 1.0 2.0 4.0 sample irradiation depth [mm] Folie 46
Conclusions for photo-polymeric dental materials DEA is an appropriate method to determine the curing behaviour. The curing process is strongly depth dependent due to the available light for initiation reactions. Between the surface and the penetration depth µ -1 the ion viscosity depends degressively on time. For depths exceeding the penetration depth the ion viscosity exhibits a progressive behaviour before turning to saturation. initiation rate becomes time dependent If the composition is known the reaction constant can be determined. Folie 47
Acknowledgement Thanks to Johannes Steinhaus, Mandy Großgarten Prof. Matthias Frentzen, Dental Clinic of University of Bonn Stephan Knappe, Netzsch Gerätebau GmbH BMBF-FHProfUnt grant no. 17081X10 Folie 48