Which property is affected negatively due to the filler percentage in flowable resins?

The property that is negatively affected by the filler percentage in flowable resins is strength. Flowable resins typically contain a higher percentage of resin and a lower percentage of filler compared to other composites. While this formulation allows for better flowability and adaptability to cavity shapes, it results in a decreased mechanical strength. A higher filler content usually enhances the strength of dental materials, but in flowable resins, the balance is skewed toward maintaining flow over strength, which makes them less robust compared to denser materials.

The other properties mentioned—radio-opacity, color stability, and bond strength—are either not directly affected by the filler percentage in a detrimental manner or can sometimes even improve with the right balance of filler. Hence, strength reduction in flowable resins is a known trade-off due to the priorities of being more fluid and adaptable in clinical applications.