How do you find what type of implant was done ? Can X-ray help?

The implant brand is an important information needed to be able to order parts necessary to make new denture/ restoration.....if your doctor does not have this info recorded, you can try : whatimplantisthat website. the have an extensive catalog of implant shape/ xray. This could be compared to the xray taken from your implant you can also post your xray and ask them to identify good luck 

X-rays tell us about
the style of an implant, but don’t always let us know the brand and model. In
order for a proper abutment to be made, your dentist will need to know exactly
which model the implant was, otherwise they cannot accommodate for the
prosthesis being able to be put onto it correctly.

Your dentist is correct. It is important to know the size and manufacturer of the implant being restored. The easiest way to find this out is to ask the dentist that surgically placed the implant for the records which you have already done. If the records cannot be retrieved, it can be tricky to identify the implant. Without records, the best way for the dentist to identify the implant is to compare the patient's radiographs to a catalog of implant radiographs. If an obscure implant was used it may require a consultation with a specialist known as a prosthodontist. Good luck and best wishes. 

To make a new crown, bridge or secure a denture to an existing implant a perfect impression is needed.  If records are lost, an xray may help.  You need to know brand, width and hex style.