what are the chances of bone regeneration when implants are placed without any Bone Graft?

Placing an implant without a bone graft is a normal variant of the procedure. Depending on your bony structure it may not have been needed. The fact that you had a membrane placed indicates that some sort of regeneration was trying to be achieved. 

What you are seeing may be one of two things

1)Cover screw: if it is a cover screw then you lost a lot of tissue and may have some issues in the future if you are not careful with oral hygiene. 

2) Healing abutment: if it is a healing abutment you have nothing to worry about as your implant is 3mm deeper then that. The function of the healing abutment is for the tissue to grow around it and not on top of it so that the implant can be acessed in the future.

 

Based on your description, I'm thinking that since you had your implants placed by a trained clinician, a bone graft was not necessary.  Perhaps what you are seeing in your mouth are the cover screws of the implant.  When gum tissue heals, it may recede somewhat.  When this happens, the top part of the implant which will connect it to the fake tooth may start to show.  Once your tooth is connected to the implant, you will not see this cover screw since it is taken out to have an abutment placed into the implant.  The abutment connects the implant to a fake tooth.

If this is not the case and the implant threads are actually exposed, then after an appropriate amount of healing, your periodontist may be able to expose the implants and graft bone and/or soft-tissue at that time.  If this is unsuccessful, then explantation of the implant and placement of a bone graft prior to re-implantation may be your only option.  Good luck!

If the margins of the implants show very little and the implants are not loose-the dentist should check that-

you should not be concerned.

If they show a lot and they are loose than the implants failed.

They need to be removed, place bone graft and wait 4 to 6 months for bone regeneration, than attempt to replace the implants.

Dr Barba

It sounds like there was already a bone deficiency at time of implant placement. What he may have done is place the implants and noticing that there is some parts of it exposed and not covered by bone. Then he may have placed the 'membrane' over it, perhaps with some bone particles, to hope to cover it.

Usually it's best to augment the bone first and develop the right width before placing the implant. In situations where there is a slight exposure (implant not covered by bone), grafting  can be done to regenerate missing bone. The succes depends on how much exposure, type of bone graft, and health of overlying gum tissue.

If you are noticing that the implant is showing, that means there is no bone over it. This can be problematic, both from aesthetic stand poiint as well as longevity and success of implant. Regrafting at this time maybe unpredictable. Removing the implant, grafting the site properly, and then replacement with a new implant later is another option.

Bone grafts are needed with there are defects or inadequate amount of bone, but it is very often needed.  If the periodontist did not place one, then they were able to get them placed without on.  If they are starting to show, then an onlay graft may be needed.  You may also be seeing the healing collar or cover screw.  Not likely a very big deal.

I would certainly return to your periodontist and express concern, but things are likely doing just fine.