Degree of conversion and flexure strength of preheated resin composite with different curing times / Ahmed Esmat Abdelftah ; Supervised Mona Ismail Riad , Iman Ibrahim Elsayad

Thesis (M.Sc.) - Cairo University - Faculty of Oral and Dental Medicine - Department of Operative Dentistry

The present study was carried out to investigate the effect of preheating resin composite that cured at different curing times on its degree of conversion and also the flexure strength. A total of 180 resin composite specimens were prepared. They were divided into 3 main groups of 60 specimens each according to the pre-curing temperature used either 5o C (cooled in the refrigerator), 37o C or 54o C .Each group was subdivided into 3 subgroups of 20 specimens each according to the curing time used for 10, 20 or 40 seconds. 10 specimens used for degree of conversion test and the other 10 for the flexure strength test. A sensitive electronic balance was used in weighting an amount of 2 mg of uncured composite that was carried with a Teflon tweezers and placed in a porcelain mortar with 0.198 gm of potassium bromide powder, which gives neutral spectra, to be ground together and held under a hydraulic pressure device to form and shape a composite disc specimen with standardized dimensions. The composite disc was placed into an attachment in the optical compartment of the FTIR apparatus to test the uncured specimen. The spectra of the uncured sample were scanned in the transmission mode in infra red spectrum from 4000-400 cm-1. The steel mold with the composite disc inside was placed either in the oven, adjusted to the previously planned temperature either 37o C or 54o C, or in a refrigerator at 5o C. The disc was then light cured immediately after gaining the wanted temperature with a light curing unit for either 10, 20 or 40 seconds. The steel mold with the cured disc was then replaced again into the FTIR apparatus

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