The aim of this study was to test four hypotheses, divided into two parts:In the 1st Part of the study, the flexural properties (flexure- strength (FS) and flexuralmodulus(FM)) of 4 different groups of tooth-colored core-buildup materials (glassionomers:conventional-and metal-modified, resin-modified glass-ionomers, polyacidmodifiedcomposite resins (compomers) and composite resins: self-, light- and dualcured,were investigated, testing the effect of different variables (material type, storagetime and condition, and the curing mode) on flexural properties. Moreover, the effect ofthe light-curing step on 3 dual-cured materials (a resin-modified glass-ionomer and 2composite resins) was investigated, comparing their flexural properties with and withoutlight-curing.A total of 850 bar-shaped specimens (25 mm x 2mm x 2mm) were tested in a 3-pointbendingtest device, after storage under 5 different conditions (10 min dry in an incubator(baseline) to be additionally stored for either 2h,24h and 7d in deionized water (37°C/7dthermocycling with 5000 cycles at 5-55°C).From the results it can be concluded that several variables influence the flexuralproperties of the 4 groups of tooth-colored core-buildup materials. The type of material(glass-ionomer or resin-based), storage condition, as well as light-curing, significantlyinfluences flexural properties of the 4 groups of tooth-colored restorative materials,showing higher flexural properties (FS and FM) for resin-based materials and lightcured-types compared to chemically-cured types.In the 2nd Part of the study the relationship between the flexural properties (FS and FM)and the degree of conversion as well as the influence of storage condition on the degreeof conversion of 7 different composite resin materials were assessed.A total of 280 bar-shaped specimens were tested. The degree of conversion wasdetermined by calculating the percentage of reacted C=C bonds using an FTIR analysis(baseline method) on the fractured bar-shaped specimens immediately after recording theflexural properties. Prior to testing, the specimens were subjected to 8 different storageconditions (5 min and 10 min dry storage in an incubator at 37°C, in distilled water at37°C for 1h, 4h, 24h, 2d, 7d and 7d thermocycling after being stored for 10 min asbaseline in an incubator at 37°C).The bivariate correlation analysis revealed a significant relationship (p<0.05) between% DC and flexural properties (FS and FM) for 3 materials: 2 self-cured compositeresins (Luxa Core Automix and Clearfil Core New Bond) as well as Rebilda DC, thedual-cured composite resin, while the rest of composite resins revealed no correlationbetween both parameters.For the influence of storage condition on the degree of conversion, a significant (p <0.05) yet weak (r2 < 0.25) correlation between both parameters was recorded for allcomposite resins, except for Luxa Core Automix Dual, the dual-cured composite resin,which revealed no correlation between both parameters (p > 0.05).From the results it can be concluded that degree of conversion does not reflect themechanical properties for all composite resins equally, and that in contrast to the 7 daystorage period in distilled water, which obviously influenced both flexural properties,the thermocycling period revealed no influence on the DC values for all compositeresins tested.
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