Narrow diameter and short dental implants DO work. I have been using them for the last 10 years! In some cases you can avoid bone grafting by using them.
They just need to be used with caution, especially if you have a strong bite. Short and or narrow implants are best for the front of the mouth where the bite force is less.
They will work better for you in the lower jaw than in the upper because the lower jaw bone is more dense than the upper.
In this post I am not talking about "mini dental implants."
This video reviews some of my thoughts on using them.
Here is an x-ray of short, wide implants with tall teeth replacing back teeth. If I have to place a short implant, I prefer to make it a wide diameter implant.
Here is an x-ray of one narrow, long implant replacing a front tooth.