Histopathological observation of dense particulate hydroxyapatite consolidated in the frontal sinus of dogs.

Dense particles of hydroxyapatite (HAP) were consolidated in the frontal sinus of dogs, and bone formation with time was observed in undecalcified ground sections using Cole's HE stain. In the HAP mass on the experimental side, a small amount of newly generated bone was seen around the inner wall of the sinus after 3 months. Even after 12 months, bone formation was still limited to the surrounding region and did not extend to the central region of the sinus. In the sinus opened area, bone formation was seen from both ends of the bone along the HAP particles, and ossiferous closing was observed without leaving a recess at 12 months. On the control side, yellow bone marrow tissue, pneumatic spaces or cyst formation were seen, and a recess was left in the sinus opened area in all cases.