Effect of benchtop compared to simulated clinical light-curing on microhardness of a bulk-fill restoration using...

To evaluate the influence of the curing environment (benchtop vs. a simulated clinical technique) and light-curing unit (LCU) type (budget gun-style vs. a high-quality Valo Cordless pen-style) on the microhardness of a bulk-fill resin-based composite (RBC) placed in standardized Class II MOD cavities.

Standardized MOD cavities were prepared in typodont teeth and restored with one bulk-fill RBC. Restorations were photocured on the benchtop or in a simulated clinical technique using either a budget gun-style LCU with a small tip or a high-quality pen-style LCU that has a wider tip. The Vickers microhardness was measured at the top, bottom, and longitudinal sections across mesial, central, and distal boxes of the RBCs. Bottom-to-top (B/T) microhardness ratios were calculated to evaluate curing adequacy. Data were analyzed using multivariate quantile regression (⍺=0.05).

Benchtop curing with the Valo Cordless LCU produced significantly higher microhardness values than the simulated intraoral curing. Simulated conditions produced lower hardness values, particularly in the distal boxes, where the budget LCU often failed to achieve a clinically acceptable 80% B/T hardness ratio. The hardness values were greater in the central regions, while they were lower in the peripheral regions that received less energy due to access issues and tip angulation. Longitudinal analysis confirmed reduced curing depth at the bottom surfaces in all groups.

Photocuring RBCs under standardized laboratory conditions produces better results than what can be achieved clinically. Polymerization efficiency is strongly affected by access to the RBC and by the LCU type. When used under simulated conditions in the posterior regions, budget LCUs with smaller tips produced inadequate curing. Thus, results reported from laboratory bench studies are unlikely to be achieved clinically. The results highlight the importance of testing products under patient simulator-based conditions to improve the clinical relevancy of in vitro studies.