Why is porcelain not used in long span bridge works?

The correct answer highlights a crucial property of porcelain that affects its suitability for long-span bridge works—its high casting shrinkage. When materials are cast, they undergo a shrinking process as they cool, which can lead to warping or structural weaknesses. This is particularly important in the context of dental bridgeworks, where precision in fit and form is vital for both aesthetics and functionality.

Materials used in long-span bridges need to maintain dimensional stability to ensure longevity and performance. Because of porcelain's susceptibility to high casting shrinkage, it may not maintain the integrity of its shape over time when subjected to the stresses of being part of a larger structure. As a result, this characteristic significantly limits its application in situations requiring robust and reliable materials, such as dental bridges designed to cover larger spans.

While considerations like low strength and durability, high cost, or discoloration can impact material choice in dental applications, the critical nature of casting shrinkage directly affects the structural integrity essential for longer spans. Thus, porcelain's high casting shrinkage makes it a less viable option for bridgeworks compared to other materials designed to withstand these demands.