After placement of multiple dental implants, a radiograph is usually taken to demonstrate the implants' relative positions. The implants can be relatively parallel or not parallel. There may be a certain esthetic satisfaction in parallel placement. There may be prosthetic fabrication issues if the implants are extremely off from parallel. Nonetheless, from a biomedical engineering perspective, nonparallel placement may better resist occlusal loads.

True parallel placement may be impossible when implants are placed in the curved edentulous arch, especially when there is a facial concavity. The importance of parallel placement may be overrated since there are techniques to correct difficulties in prosthetic fabrication.2,3 

Nonparallel placement of multiple implants may increase the stability of a prosthesis when the implants are splinted in the prosthesis. Under load, this placement distributes stresses through more of the containing bone than parallel implants. In-line implants may induce screw loosening under...

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