RNA isolation from alveolar bone and gene expression analysis of RANK, RANKL and OPG : a new tool to monitor bone remodeling and healing in different bone substitutes used for prosthetic rehabilitation

OBJECTIVE: (i) To validate a simple and efficient method for extracting high quality RNA from small samples of bone tissue, (ii) to test its application on limited amounts of grafted oral bone and (iii) to analyze the gene expression of the OPG/RANK/RANKL system and IL-6 in "spontaneous healing" and grafted tissue. DESIGN: 26 patients in need of extraction of one lower molar tooth were divided in 3 groups. In group A (8 patients) the alveolar socket was left for spontaneous healing, in group B (8 patients) it was filled with a hydroxyapatite scaffold while in group C (10 patients) it was filled with hydroxyapatite granules. A small amount of bone was scraped from the alveolar site and sent for analysis. Four months later a new bone specimen was harvested during implant bed preparation. RESULTS: IL-6 increased over time in all groups and in particular to the grafted groups. RANK, RANKL and OPG increased over time in all groups, except for RANK in group B. The RANKL/OPG ratio showed a negative value in group A and even more in group B, while it was positive in group C. CONCLUSIONS: The alveolar site grafted with a granular biomaterial behaved similar to the physiological healing group but displayed a slow remodeling process. RANK, RANKL, OPG and the RANKL/OPG ratio might be able to distinguish among different biomaterials and represent different healing patterns according to different clinical conditions.