Adhesive bonding of various materials to hard tooth tissues. XX. Calcium-to-calcium distances in hydroxyapatite.

Distributions of Ca-to Ca distances have been obtained from the crystal structure of hydroxyapatite for all biologically significant planes. Most frequently, calcium ions are separated by about 4, 6.3, 7.9, and 9.0 to 9.6 A. Frequent occurrence of distances at 10.4, 11.8, and 12.6 A result from a Ca ion in one repeating unit being paired with a Ca in another unit cell.