Which condition is a contraindication for using an all-ceramic inlay?

The use of an all-ceramic inlay can be contraindicated in cases of excessive functional loading forces due to the inherent material properties of ceramics. While all-ceramic restorations provide excellent aesthetics and are highly biocompatible, they can be more brittle than other materials, such as metal. When subjected to high stress and functional loading, ceramics are at a greater risk of fracture or insufficient retention.

In situations where the occlusion involves significant forces, such as a bruxism or patients with heavy occlusal wear, the durability of an all-ceramic inlay may not withstand the demands of the functional loading over time. This makes choosing a different material, such as a metal or a combination of ceramic and metal for strength, more favorable to ensure longevity and minimize the risk of restoration failure.

The other conditions presented do not directly lead to the same level of concern regarding the material properties under functional loading. Class II restorations can indeed use all-ceramic materials effectively; the conservative nature of a restoration refers more to cavity preparation style rather than a direct contraindication; and patient preference typically guides treatment planning but doesn't inherently compromise the material's effectiveness under stress.