My dentist told me i have two mild loss in the back but no danger in losing them. he suggested a deep cleaning should to the job. is this true.

Bone loss: When periodontal (gum) disease is not treated, it gets worse over time leading to loss of teeth. Listen to your dentist and do what he\she recommends. Early intervention is better than waiting until the problem is more serious, the treatment more intensive, and the likelihood of success diminished. Be grateful your dentist caught this early and wants to improve your dental health.

Yes: Not sure what is meant by "two mild loss" and where but I am assuming it is a gum or periodontal problem. In a mild case a dental hygienist will do a "deep" cleaning, sometimes with local anesthetic. Several months later the results of the treatment will be evaluated. Most of the time that does it and back to regular cleanings. If it doesn't then a referral to a gum specialist is indicated.

Unsure: Unsure what you're asking. If you mean that your gums are inflamed and therefore you have pockets that are 2 millimeters too deep, a deep cleaning coupled with appropriate oral hygiene should resolve the issue. If not successful, evaluation by a Periodontist, a gum specialist, would be in order.

Perhaps: You could always try the deep cleaning and if the issue is not resolved then alternative therapies can be considered. Seems like you're asking for a guarantee, and none can really be given.