Dental amalgam has been a traditional restorative material for many years, known for its durability and strength. However, there is a growing trend towards the use of more aesthetic materials, such as composites and glass ionomers, which blend better with natural tooth structure.

To diagnose class III caries clinically, which is caries that involves the proximal surfaces of teeth, a good supplement to radiographs is to examine the proximal surfaces for any color changes, particularly at the contact points where two teeth touch. This is often done using a combination of visual inspection and the use of a dental explorer to detect cavities and softened enamel. However, the answer provided, "Caries activity tests," refers to methods used to assess the activity or inactivity of a caries lesion, not necessarily for diagnosis.

Annealing gold foil is the process of heating gold to remove impurities and restore its cohesion properties. 

Explanation: The lingual approach to the distal surface of a canine for Class III amalgam restoration is primarily related to aesthetics. This approach minimizes visibility of the restoration from the facial aspect, which is important for maintaining the natural appearance of the tooth. Aesthetic considerations are particularly significant in anterior teeth, where the visibility of restorations can impact the overall smile and facial aesthetics. While retention, outline form, and resistance are important factors in cavity preparation, the lingual approach is specifically chosen to enhance the aesthetic outcome.

Gingivally, the depth of a class V cavity is typically 0.75-1 mm. This depth is sufficient to provide a good bond with the tooth structure and prevent microleakage without causing significant gingival irritation or damage.