For the most predictable results when making a removable prosthesis, what type of impression should be used?

Using a custom tray with tooth stops for making a removable prosthesis is the best choice for achieving predictable results. Custom trays are specifically designed to fit the unique anatomy of a patient's mouth, which allows for better control over the impression material and improves accuracy in capturing the details of the oral structures.

Tooth stops are additional features added to the custom tray that help to engage specific teeth, providing a stable reference point during the impression process. This ensures that the tray remains in the correct position and reduces the likelihood of movement, which can lead to inaccuracies in the impression. By having a resilient and precisely fitting tray, along with the tooth stops, the final impression reflects the soft and hard tissues more accurately, leading to an optimal fit for the removable prosthesis.

Other options, such as stock trays, do not offer the same level of adaptability and precision, as they are generic and may not conform well to the individual patient's anatomy. Modified stock trays may provide some improvement but generally lack the tailored fit and control of a fully custom tray. Digital impressions, while innovative and providing certain advantages, may not yet offer the reliability and established protocols necessary for all scenarios in removable prosthodontics, particularly in situations where tactile feedback and material properties are crucial for capturing details.