Is D7951 a quadrant code?

This can be reported twice if both upper quadrants are augmented. I would recommend sending documentation to support both the UL and UR quadrants so there is no question as to overbilling the procedure.
See Coding Companion 2022, Clinical Coding Scenario #3 on page 215 for verification.

This procedure is performed to increase the alveolar height when reconstructing portions of the maxilla usually to support dental implants. There are several ways in which the procedure may be performed. Regardless of the method used the provider makes an incision into the gum exposing the lateral boney wall of the sinus. A window is cut into the thin membrane that covers the sinus and bone graft material is placed into the space. Bone substitutes may also be used. During a less invasive technique, the sinus membranes are lifted by gentle tapping of the sinus floor with the use of osteotomes. The amount of augmentation achieved with the osteotome technique is usually less than what can be achieved with the lateral window. The goal of this procedure is to stimulate bone growth and form a thicker sinus floor, in order to support dental implants.