What is the difference between a all on four dental implants and denture? Does the all on four show the gum line when you smile?

The
major difference between All on 4 and a denture is that the All on 4 is implant
supported and the denture is tissue supported.
The denture rests on the gums and retention is passive, relying on
“suction” created by the “fit” of the denture.
Therefore, depending on a person’s anatomy and the skill of the dentist,
the denture may be more secure or loose.
A denture is fabricated using an acrylic base and teeth made of various
materials. A denture also covers more surface area of the mouth which can affect the taste of food. 

The
All on 4 is more secure and mimics natural teeth as they are generally attached
to the implants using screws. They can
be removed by the dentist but not by the patient. The materials used for All on 4 are typically stronger as well.

The
gum line depends on the amount of bone loss experienced by the patient. Even with higher levels of bone loss,
excellent aesthetics can be achieved by the dentist and a quality dental lab.

Dentures are removable teeth and made of acrylic( plastic type ). All-on-4 dental implant technique gives fixed teeth, with out any acrylic flanges, can even replace lost gums and bone to an extend. The final prosthesis (Fixed teeth) of All-on-4 can give Zirconium (metal free) crown and bridges.

If the All-on-4 case is properly planned, the gumline should NOT be showing. It is important to address this issue before the dental implants are placed. When a patient presents to my office with a "gummy" smile and asks for an All-on-4, I have to do some modification to the underlying bone during the All-on-4 procedure in order to properly prepare it so that the gumline does not show. 

There are many differencesDenture - Plastic teeth rest on your gums and move when you chewAll on 4 - The teeth rest on the implants and there is no movement when you chewDenture - You continue to lose bone and the denture will become more loose over timeAll on 4 - The implants maintain the boneDenture - Covers a lot of the mouthAll on 4 - Minimal coverageDenture - Chewing efficiency not as goodAll on 4 - Chewing efficiency very good Denture - loss of bone causes loss of facial supportAll on 4 - maintains facial supportHope that answers your questions. Wish you all the best in your journey

All on four is a minimal option for fixed non-removable tooth replacement. It's very expensive for what you get and better off getting 2-3 implants with a denture on top (removable). The Esthetics are horrible, you will spit when you talk and hiss a lot of air when you try to enunciate certain words. It's a form of under treatment in hopes of saving money and not worth it! Not a fan based on the past 12 years of seeing results from my colleagues. Good luck!