If you were being treated for dentures, why would the dentist do bone grafting on the teeth being pulled?

Bone grafting is not something that is required for dentures, but it is strongly recommended.  Bone grafting will provide a better base for the denture to sit upon.  Without the bone grafting, your denture may be loose.  An alternative to bone grafting is getting some implants, which will secure the denture even better.  Implants are typically more expensive than bone grafting.  I hope this helps, but you can follow me on RealSelf if you have more questions.

When a patient is at the point they need extractions and dentures, they have likely had a significant amount of bone loss from periodontal disease. A denture must rest on a uniform, smooth ridge in order to have proper retention without any underlying, sharp bony areas which could cause pain when it compresses against the gum during chewing.  During surgery, bone may be reduced and smoothed in some areas while other areas may need grafting in order to preserve the bone ridge in those areas.  Please see your dentist annually after receiving your dentures to ensure that they fit well. Have periodic relines to re-establish balance so that the bone does not resorb as quickly as it can.  It is best to consider some kind of implant retention to stabilize your dentures, and this will preserve bone for the long term and establish excellent retention of your dentures.

It is always recommended to do bone grafting after extraction to help preserve your ridge.  For implants, I would definitely suggest getting a bone graft.  For denture or pontic, it is not required but still useful to get bone grafting to help preserve your ridge.  There's also different type bone grafting material.   For example, I would recommend using xenograft for denture or pontic due to its resorption characteristics.  

bone grafting has become the standard of care after dental extractions. Although , some patients may not want to replace the extracted teeth immediately.    Over the years we have learned without proper ridge preservation after extractions , the jaw will lose height, width and density once the tooth is removed . If a patient does not elect to have the grafting done,  and their desires to replace the missing teeth changes  later it becomes a more difficult procedure for implants , aesthetics in bridges Ext.    No dentist wants you to lose your teeth, but if you do bone grafting will help ensure you have a healthier jaw and more choices if you later desire to place an implant or bridge.  Good luck bone grafting is important 

Bone grafting in the extracted socket site is very important to preserve the surrounding bone height. No mater what procedure you are getting, denture or bridge, bone grafting will make sure that you are set up for a positive outcome.