Nader Salib, DDS

You can potentially go to an All-on-4 from a snap on denture if:1. Implants are stable long term2. Implants are in the correct position. If your smile is high, you may be able to see the transition of your teeth and natural gums. 
A dental exam, CT scan and proper facial cosmetic evaluation by a qualified oral & maxillofacial surgeon is needed to determine these answers

There are many conditions that may affect dental implants. 

Diabetes and and smoking are 2 of the most critical. Regarding diabetes, if left uncontrolled, your ability to heal and integrate an implant with sufficient bone will be compromised. 

Diabetes if it is controlled should not have an adverse effect on your healing. 

your smile will depend on many factors. 

How high and wide your lips move when you smile are the most important factors when evaluating your smile. 

Ideally, a proper pre-operative evaluation would have occurred with photos and a discussion with both patient and Doctor. 

At this point, you should critically evaluate not only the amount of teeth showing but the possibility of "black triangles". 

The he laboratory may be able to fabricate better looking teeth but also consider a hybrid prosthesis if possible. This will depend on impact placement and may require additional work. 

Excellent question. Our teeth help to keep bon by stimulating it. Whenever you chew, the vibrations from the crown travel to the roots and to the surrounding bone stimulating it, keeping it alive.  

When teeth are removed, your bone will shrink. To determine if you're eligible for implants, a proper clinical and radiographic exam should be performed. 

A CBCT (come beam CT) will allow you to visualize your available bone and even help plan implant placement!

Excellent question-

it's important to remember that implants are medical decides. They should NOT move and there should NOT be any sensation around them. 

Soreness may may indicate inflammation or infection around gums. It may also point to a more serious problem. 

Looseness is a clear sign the implant has failed. 

It it should be removed immediately to prevent infection from spreading to other teeth and implants. a course of antibiotics may help but ultimately the implant is the source printed ruin and should be dealt with immediately.