ABSTRACT
Aim. This paper presents a simple, versatile in vitro methodology that enables indirect quantification of shrinkage and expansion stresses under clinically relevant conditions without the need for a dedicated instrument. Methods. For shrinkage effects, resulting cusp deformation of aluminum blocks with MOD type cavity, filled with novel filling compositions and commercial cements, has been measured using a bench-top micrometer and a Linear Variable Differential Transformer (LVDT, a displacement transducer) based instrument. Results. The results demonstrated the validity of the proposed simple methodology. The technique was successfully used in longer-term measurements of shrinkage and expansion stress for several dental compositions. Conclusions. In contrast to in situ techniques where a measuring instrument is dedicated to the sample and its data collection, the proposed simple methodology allows for transfer of the samples to the environment of choice for storage and conditioning. The presented technique can be reliably used to quantify stress development of curing materials under clinically relevant (oral) conditions. This enables direct examination and comparison of structural properties corresponding to the final stage of formed networks. The proposed methodology is directly applicable to the study of self-curing systems as they require mouth-type conditions (temperature and humidity) to achieve their designed kinetics and reactions.
ABSTRACT
OBJECTIVES: Visible light cure oxirane/polyol resins of Cyracure UVR-6105 with pTHF-250 has been previously shown useful for development of dental composites. This oxirane/polyol (4016) in combination with other oxiranes were formulated into composites (4016E, 4016G and 4016GB) containing 72.9-74.9% quartz filler. The main objective of the study was to evaluate some of the physical properties and the biocompatibility of the composites. RESULTS: PhotoDSC analysis of composites demonstrated twice the enthalphy values of Z100 (31J/g). Composites 4016E and 4016G showed compressive strengths similar to Z100 (337+/-35Mpa), P>0.05. Discs of composite 4016E, containing Epon 825 oxirane (E), and composite 4016G containing Araldite GY 281 oxirane (G) were non-cytotoxic (-) while the composite 4016GB, containing G and Ebecryl 1830 (B), was mildly (+) cytotoxic to L929 cells in the agar diffusion assay. Seven-day extracts of 4016GB composite were cytotoxic while extracts of 4016E and 4016G were less cytotoxic to L929 cells in the MTT assay. Extracts were obtained from 7 day incubations of composite (3 cm(2) surface area/ml) in acetone or ethanol/saline (1:20) at 37 degrees C. All composite extracts were non-mutagenic to Ames strains TA100, TA98, TA97a and TA1535. The overall results with composite 4016GB suggest that leachable components were cytotoxic but non-mutagenic. With the exception of oxirane components, G and E, the oxirane Cyracure UVR-6105 and other components were non-mutagenic. From cytotoxicity studies, the photoinitiator, Sarcat CD 1012, was the most cytotoxic (TC(50)=14 microM) component. Components G (TC(50)=17 microM), E (TC(50)=50 microM) and B (TC(50)=151 microM) were significantly (p < 0.05) more cytotoxic than Cyracure UVR-6105 (1488 microM) and the polyol, pTHF-250 (TC(50)=6072 microM). SIGNIFICANCE: Favorable results obtained with composites 4016G and 4016E indicates that suitable oxirane/polyol formulations can be designed and optimized for development of dental composites with acceptable mechanical properties and biocompatibility. However, leachable analysis of extracts obtained from longer incubation periods is needed before final conclusions could be drawn about the leachability of oxirane components.
