What is a defining feature of a type 3 lesion in feline tooth resorption?

A type 3 lesion in feline tooth resorption is characterized by the presence of both type 1 and type 2 lesions within the same tooth. Type 1 lesions involve the resorption of the crown while maintaining periodontal attachment, whereas type 2 lesions involve the root resorption with concurrent loss of periodontal attachment. Therefore, the defining feature of a type 3 lesion is that it exhibits a combination of both resorptive processes, indicating a complex case that requires careful diagnosis and management.

The other options do not accurately describe a type 3 lesion. A situation where only the crown is affected points to a type 1 lesion rather than a combination of lesions. Similarly, the presence of normal periodontal integrity suggests that the tooth is not involved in any resorptive process, which contradicts the nature of type 3 lesions. Lastly, a condition solely involving retained roots would align more with type 2 lesions where the crown is absorbed and roots remain. Consequently, option C correctly encapsulates the complexity of type 3 lesions in feline tooth resorption.