Tapered style (conical) implants were also known as root-shaped implants, as they were modified to mimic the root form of the tooth. These implants tend to have more aggressive threads and provide better initial stability by widening the osteotomy at insertion and compressing the bone.
Parallel walled (cylindrical) implants are less aggressive, but offer more bone-implant contact, as they have more surface area than a cone of the same length. This assists in secondary stability, as the tip of the implant does the cutting, and the remaining portion of the threads and implant body follows without further cutting or compressing the bone.