What is an important requisite for fillers in dental composite restorative resins used in load bearing areas?

High filler content is essential for dental composite restorative resins, particularly in load-bearing areas, because it significantly enhances the mechanical properties of the material. Fillers play a crucial role in increasing the strength, durability, and wear resistance of composites. In applications where high strength is required, such as in load-bearing restorations, having a higher filler content ensures that the material can withstand occlusal forces without deforming or fracturing. This characteristic allows the composite to maintain its integrity over time and ensures that it performs effectively in function and aesthetics.

Other options do not adequately meet the requirements for load-bearing restorations. For example, while sub-micro sized particles can improve certain properties, their mere size does not guarantee the strength and durability associated with high filler content. A high coefficient of thermal expansion can lead to issues with bonding and durability as it may result in stress at the interface with tooth structure over time. Low viscosity is more desirable for ease of manipulation and placement but may not provide the strength needed for high-stress areas, particularly if it corresponds to lower filler content. Thus, high filler content is paramount for optimizing the performance of the composite in demanding clinical situations.