Just had cbct for tooth implants. he said i just qualified due to bone height. i asked about bone quality. he left to come back to say he cannot.(?)

Ask why not?: Only the dentist who examined you and saw the cbct can answer your questions accurately. Simply ask for a more thorough explanation as to why he gave you the answer that he did. If necessary, get a copy of the cbct and take them to another periodontist or oral surgeon or prosthodontist for a second opinion.

Poor bone quality?: Your question is unclear. Bone is often categorized into four types ie type i-iv. Type i being the most dense, type IV most porous. If you have adequate height and width but insufficient density bone compaction techniques allow for implant placement in type IV bone. Often the implant is staged (submerged) in such cases.

CB measures quantiy: Cone beam ct scans measure bone volume/quantity. The quality of bone is based primarily upon location (maxillary bone typically is not as dense as mandibular bone) and overall health. If you do not smoke, are not a diabetic and you have an adequate quantity of bone as measured by a cbct scan, you are likely a great candidate for implants ... Which will likely have an excellent long term prognosis.

Hard to tell...: Dental implants require sufficient bone height, width, and to a lesser extent quality. Cbct is very good at looking at the physical dimensions of the receptor bone/ridge, and to some extent the quality. Sometimes, however, the quality is determined during the procedure and not entirely by the review of the imaging.