How is the amount of bone needed for a dental implant determined?

Hello! I am 34, and have congenitally missing lateral incisors. I had 5 consultations and 4 out of the 5 said they would not be comfortable with the job. If I have this right, I only have .5mm of bone in each area. I went last week to a cosmetic dentist about a bridge and he called me today saying his periodontist can do the implants, and the cost was significantly less that what the one surgeon who was willing to do the job quoted me at. I also have root resorption on the two teeth next to one of my missing teeth (I guess sue to braces). My question is, this dentist did not do a ct scan, only xrays. I didn’t think the amount of bone present could be determined by just xrays. Am I wrong? Should I be getting a ct scan to show how much bone there is?