Is it possible to install dental implants without stitches? I got 3 lower implants yesterday but not any stitches. Is it normal?

Yes it is possible to have no stitches after having implants placed. Usually in this case, a punch incision is made. After the implant is placed, a healing abutment is used to shape the surrounding gum tissue. 

When there is adequate keratinized tissue, an implant can be placed flapless with no stitches, and when an implant is placed immediately with tooth extraction no stitches are required.

It is possible to do a little punch through the gums to place an implant. With that, you don't need an incision meaning you don't need stitches to close the incision.