At times we need bone grafts to make sure the implants stay firm, strong, and longer. Bone grafts are bioresorbable mineral reservoirs which induce the formation of new bones. When the available bone width or height is not enough to support the implant, bone grafts become necessary. Posterior maxillary implants mostly need bone grafts as they have a close proximity to the sinus wall.

Bone grafts do not make way for antigen-antibody reaction be it autograft or allograft. However, bone grafts have certain disadvantages:

They increase the cost of implants.
They increase the time required for placing implants and also extend the time of surgery needed for placing implants. The bone grafts need a few months to integrate well with your jaws and be ready for the implants.
Also, there is a need for another surgery to take out some of the healthy bone from some other part of the body (autograft) and place it in the place needed for the implants. Although composite materials or bone substitutes are available for bone grafts, autologous bone grafts are the gold standards. Only autografts provide the best:
Osteoconduction: A phenomenon in which the bone graft serves as a scaffold over which the new bone grows.

Osteoinduction: It’s a property which stimulates the formation of new bone by inducing the conversion of osteoprogenitor cells to osteoblasts.

Osteogenesis: A process wherein the osteoblasts present in the bone graft generate new bone.

It’s an intervention which puts the patient at some additional risk as any surgery is risky. Complications to anesthesia, infection at the site of the wound, injury to the adjacent nerves, etc. are few of the complications of surgery though rare.
Bone grafts for implants also carry risks such as resorption of graft, exposure of graft, infection of graft, and dislodgment of graft during implant placement states a study published in 2005 in the International Journal of Periodontics and Restorative Dentistry.
 

Thus, we can logically conclude that bone graft is not needed always and should be considered only when it’s an absolute necessity!