It's impossible to perform an implant or place an All-on-4 in a single visit, as it's a two-stage procedure that includes a mandatory minimum healing time of at least 3 months between the two steps (this is osseointegration).
The dental implant is placed under local anaesthetic. The dental surgeon makes an incision in the gum to gain access to the bone. He drills a hole, inserts the implant and then sutures the gum. Once the operation is complete, you'll have to wait several months for the implant to heal. During the 2nd visit, the dental surgeon screws an abutment onto the implant, which is now well integrated with the bone. A ceramic or zirconium crown can then be added. These prostheses are custom-made from an impression taken during the initial visit. Perfectly matching your natural teeth, they are imperceptible. The dental surgeon ensures that the result suits you both aesthetically (shade, shape) and in terms of comfort (chewing).