My lower 6 was extracted and 7, 8are present can ortho treatment close the space or i need to fix it either with bridge or implant and why?

Possibly: An orthodontist or dentist can tell you the best option for your specific case. X-rays will be needed to assess the positioning of the roots of the back teeth. It will depend on many factors, including your "occlusion", or bite. If you plan to replace the tooth with an implant or bridge, a space maintainer may be necessary to keep the back teeth from tipping into the space. See a dentist soon.

Lower 6: Hard to say without seeing your teeth. I would see an orthodontist, the space can be closed however the question is what is best in your particular case over the long haul (20+yrs). If they can close the space that is the best option. If not then i would suggest the implant.

Complex question: Don't know the condition of your second or third molars, or how much bone is left after the extraction of the first molar, so any advice is hypothetical. Moving those two teeth will take a lot of time and effort (and cost), so much so that it may be easier and less expensive to place an implant and crown. Consult with an orthodontist ; oral surgeon in your town to get a better idea...

Orthodontic opinion: See an orthodontic specialist who can help you make the move-teeth or implant-crown decision. Depending on your occlusion, bone contours, gum health, position and angulation of teeth, orthodontist can help close space or optimize space for the best restoration. Ask your dentist which orthodontist does this best for his patients.