WARD ET AL 6. Smith DC. The acrylic denture-mechanical evaluation mid-line frac- ture. Br Dent J 1961;110:257-67. 7. Ware AL, Docking AR. The strength of acrylic repairs. Aust J Dent 1950;54:27-32. 8. McCrorle JW, Anderson JN. Transverse strength repairs with self-cur- ing resins. Br Dent J 1960,109:364-66. 9. Sanford JW, Burns CL, Paffenharger GC. Self-curing resin for repair- ing dentures: some physical properties. J Am Dent Assoc 1955;51:301- 15. 10. Osborne J. Transverse tests on denture base materials. Br Dent J 1949;86:64-7. 11. Peyton FA, Anthony DH. Evaluation of dentures processed by differ- ent iechnics. J PROSTHET DENT 1963;13:269-82. Reprint requests to: DR. JOHN E. WARD VIRGINIA COMMONWEALTH UNIVERSITY SCHOOL OF DENTISTRY 521 N. 11~~ ST. ROOM 301, Box 566 RICHMOND, VA 23298-0566 The knife-edge tendency in mandibular residual ridges in women Ichiro Nishimura, DDS, DMSC,~ Ryuji Hosokawa, DDS, PhD,b and Douglas A. Atwood, MD, DMDC Harvard School of Dental Medicine, Boston, Mass. To investigate the bone resorption pattern of the residual alveolar bone, the morphologic change that occurred in mandibles was analyzed with standardized lateral cephalographs of 30 edentulous patients (15 women and 15 men). The longitudinal morphologic changes were measured at the sagittal sections of the mandibular bony contour at the symphysis area on superimposed cephalographic tracings. To quantify the morphologic change, a knife-edge index (KEI) was developed as the area change divided by the height change. Geometrically, the higher value of KEI represents the greater tendency to become a narrow residual ridge. The KEI values were statistically higher in the women than in the men (p < 0.002). In addition, the value of KEI seems to correlate with osteopenic change at the center point of the body of the second vertebra @ < 0.01). The continuous bone resorption activity in the edentulous mandible of women seems to be empha- sized at the labial and lingual surfaces of the residual alveolar bone, resulting in a knife-edge type of residual ridge. (J PROSTAET DENT 1992;67:820-6.) F ollowing the extraction of teeth, the bony socket and adjacent soft tissue undergo a series of tissue repair reactions including acute inflammation, rapid restoration of epithelial integration, and connective tissue remodeling. Histologic evidence of active bone formation in the bottom of the socket and bone resorption at the edge of the socket are seen as early as 2 weeks after the tooth extraction, and the socket is progressively filled with newly formed bone in about 6 m0nths.l Rapid bone remodeling subsides by this Presented in part at the International Association for Dental Re- search meeting, Montreal, Quebec, Canada. aAssistant Professor of Prosthetic Dentistry. bResearch Associate in Prosthetic Dentistry and Recipient of the fellowship for Japanese Junior Scientist, Japan Society for Pro- motion of Science. CProfessor Emeritus of Prosthetic Dentistry. 10/l/35085 time but continuous bone resorption may persist at the ex- ternal surface of the crestal area of the residual alveolar bone, resulting in considerable morphologic changes of bone and overlying soft tissues over the years.2 This phe- nomenon has been described as the reduction of residual ridges (RRR).3 The patients with severe RRR experience significant alteration in mid to lower facial contour,4 and have much difficulty in accepting the subsequent prosth- odontic treatments.5 To document RRR by means of a standardized method, the lateral cephalometric radiograph has shown that there are significant individual variations in the rate and amount of bone resorption and in the morphologic changes of the residual alveolar bone.6-s Despite recent efforts to explain the significant differences in the rate of RRR observed in different patients, no etiologic factors are proven to date.g In most previous studies, the rate of RRR or the degree of residual alveolar bone atrophy was measured as the linear 820 JUNE 1992 VOLUME 67 NUMBER 6