What are the effects of biting forces on a three-unit bridge with implants positioned at 12 and 13?

The scenario presented indicates that a three-unit bridge has implants positioned at locations 12 and 13, which typically refers to the second and first molars in the dental arch. When a patient bites down, the forces transmitted through the bridge affect each implant differently based on their position and the biomechanical loading involved.

In a three-unit bridge, the force from biting is distributed between the supporting implants and the pontic (the artificial tooth that fills the gap). The implant at location 12, being distal to the load (usually biting forces are exerted posteriorly), will experience tension due to the lever arm effect; it is pulled upward as the bridge flexes under load. Conversely, the implant at location 13, which is located closer to where the bite occurs, will experience compression. This implant must withstand the downward force exerted by the occlusal load.

Thus, the situation results in tension on implant 12 because it is being lifted as stress is applied, while implant 13 undergoes compression since it is bearing the primary occlusal load directly. Understanding these biomechanical principles aids in implant placement and design of restorations for optimal function and durability.