Which one of the following is the usual retentive component present on a removable orthodontic appliance?

The Adams crib is a commonly used retentive component on removable orthodontic appliances, particularly in the context of holding the appliance securely in the patient's mouth. This component is specifically designed to engage with the anatomy of the teeth, providing stabilization and preventing the appliance from dislodging during normal oral functions.

The Adams crib typically wraps around the posterior teeth, allowing it to latch onto existing dental structures for retention. This feature is essential for ensuring that the orthodontic appliance remains in place while facilitating tooth movement or maintaining dental alignment.

While other components like bands can also have a role in orthodontic appliances, they are usually fixed components that are not integral to removable appliances. Canine retractors are typically used in fixed orthodontic systems and are not relevant in this context. Finger springs are used for specific movements and adjustments in orthodontic treatment but do not primarily serve as a retentive mechanism for removable appliances. Thus, the Adams crib is definitively the retentive component that is most commonly found in removable orthodontic appliances.