Can delayed grafting of frozen teeth achieve periodontal ligament healing?

Autologous teeth transplanted technology is putting healthy teeth into empty alveolar socket and waiting to be fixed by newly formed alveolar bone and periodontal membrane, to perform chewing function. Vigorous donor teeth are usually impacted teeth or orthodontic excess teeth that are often extracted and discarded during adolescence. However, they should have more potential function that repairing dentition defects due to caries, apical periodontitis, cysts, and other causes after being an adult. Therefore, once the preserved technical is skilled, utilization of dental tissues extracted early in life would create new possibilities. The problem is whether cryopreservation reduces tissue regeneration. Scholars who emphasize periodontal ligament (PDL) healing firmly believe it can avoid pathological reaction and ensure the success of transplantation. Nowadays, the ideal success rate can reach 80.0 % - 91.1%, but the classic transplantation procedure is time-dependent, which requires the donor tooth to be extracted and transplanted immediately. Freezing is a recognized effective way to make physiological and biochemical activities quiescent, and to maintain the potential of cells to relive after rewarming in the same medium. During cells cryopreservation, the challenge is in the inappropriate freezing and thawing condition, intracellular freezing would break cells' physical structure, spoil normal PDL and increase resorption of root. So even though delay in freezing autotransplantation would greatly expand procedure in-dications, it has not yet become a mainstream treatment. Slow freezing and vitrification technology are main cryopreservation ways certified effective that essentially prevent ice crystals from damaging cells. To some extent, none of them is perfect considering cell cytotoxicity from cryoprotectants or controlling of freezing rate. Now, with the modified freezing method, we firstly put forward Antifreeze proteins (AFPs) to tooth cryopres-ervation, and assume that low concentration AFPs combined with vitrification may yield better results in PDL healing of delayed autotransplanted tooth. Based on analyzing the freezing mechanism, cell studies, animal experiments and individual case reports, we propose a procedural freezing method and summarized how to reduce cryogenic injury of cryopreserved tooth for potential use in tooth transplantation. However, more studies and data are needed about masticatory function and long-term prognosis observation.