1. 'Bone Research Branch, National Institute of Dental Research, Bldg. 30, Room 106, MSC-4320, National Institutes of Health, Bethesda, Maryland 20892
2. American Dental Association Health Foundation, Paffenbarger Research Center
3. Dental and Medical Materials Group, Polymers Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA