Evaluation of condensation silicone dental impression materials modified with diatomaceous Earth and zinc oxide fillers

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Abstract
Condensation silicones are widely used for dental impressions due to their handling ease and affordability but have limitations like shrinkage, suboptimal rheology, and bacterial contamination risk. This study investigated the effects of incorporating microsized diatomaceous earth (DE) and zinc oxide (ZnO) on the physical, mechanical, rheological, and antibacterial properties of condensation silicone dental impression material. DE/ZnO powders were ball-milled with silica and calcium carbonate, then mixed with hydroxy-terminated polydimethylsiloxane and tetraethyl orthosilicate. The resulting pastes, including a control, were evaluated. Microstructural analysis was conducted via SEM, EDAX, and XRD. SEM/EDAX confirmed filler incorporation: dispersed needle-like ZnO and localized DE aggregates in the silicone matrix. XRD verified ZnO crystalline wurtzite structure and DE cristobalite phase. Incorporating of DE/ZnO extended the setting time and improved the flowability. Compared to the control, ZnO incorporation significantly enhanced dimensional stability, extended working time, slightly decreased hardness, exhibited a lower elastic modulus with significantly higher elongation, and moderately improved wettability. DE incorporation shortened working time, did not improve dimensional stability, slightly decreased hardness, showed similar elastic modulus to the control but with higher elongation, and significantly improved wettability. Antibacterial tests against E. coli and S. mutans revealed significant activity for the ZnO-containing samples but no effects for the DE-containing samples. No significant differences were found in the mixing times among the samples. Results show distinct filler roles: ZnO improves functional properties (stability, antibacterial) and DE modifies surface characteristics (wettability), highlighting potential for targeted property tailoring through filler choice.

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