The correct answer is Gold.

- Among the dental materials listed, gold exhibits the highest resistance to corrosion.
- This is primarily due to gold's noble metal characteristics, meaning it is chemically inert and does not easily react with the oral environment.
- Gold forms a stable surface that prevents the formation of oxides or other corrosion products.

- Titanium, while highly biocompatible and resistant to corrosion due to its protective oxide layer, is more susceptible to mechanical wear and chemical attack compared to gold.

- Stainless steel has a protective chromium oxide layer that confers good corrosion resistance, but it is still prone to pitting and crevice corrosion, especially in the chloride-rich environment of the mouth.

- Cobalt-chromium alloys are corrosion resistant due to their chromium content; however, their corrosion resistance does not surpass that of pure gold.

In clinical dentistry, gold has been used extensively as a restorative material owing to its durability, corrosion resistance, and biocompatibility. This makes it a preferred choice for long-lasting restorations without degradation caused by oral fluids.

Reference: Craig's Restorative Dental Materials, 13th Edition, Chapter 3: Physical and Chemical Properties of Dental Materials, Page 85