The Effect of Cantilever Length and Implant Tilt on the Prosthetic and Supporting Structures in Screw Retained Full Arch Prostheses [A combined in-vitro and in-vivo study]

Abstract

The restoration of the edentulous arch with an implant-retained prosthesis results in preservation of the alveolar ridge height, better masticatory performance and better patient acceptance when compared to complete dentures.

The lower jaw anatomy usually favours inter-foraminal implant placement which results in a posterior cantilever that causes mechanical overload due to the increased bending moment. Mechanical overload can result in biological complications manifested mainly with bone loss at the most distal implant. Bending moments has been also blamed for many prosthetic complications as screw loosening, screw fracture, prosthesis fracture and in few cases fracture of the implant body.

The magnitude of the detrimental stresses resulting from such cantilever depends on many factors; namely, the cantilever length, quality of bone, opposing occlusion, antero-posterior implant (AP) spread, geometry, number and tilt of the implants and height and design of the prosthesis. The increase in the cantilever length has been regarded as a major force magnifier. The "All-On-4" strategy shortens the cantilever length by directing the collar of the most posterior implant distally to emerge at the second premolar region instead of the first premolar while 1 keeping the implant apex away from the inferior alveolar nerve •