Cryopreservation before replantation of mature teeth in monkeys

The effect of cryopreservation in liquid nitrogen at −196°C for 1 week was studied by histometric analysis of 60 mature teeth replanted in 10 green Vervet monkeys. The effect of preincubation in enriched tissue culture medium was also investigated. 2 different freezing rates were compared, and the effect of stepwise equilibration of DMSO was studied as well as the effect of root canal treatment. The histometric analysis carried out 8 weeks after replantation revealed that if the cryoprotectant was equilibrated stepwise at room temperature, 10% DMSO had an even better cryoprotecting effect than previously shown by 5% DMSO equilibrated at 0°C. When this procedure was combined with a slow freezing rate of 0.3°C/min from −4°C to −35°C followed by plunging in liquid nitrogen, and supplemented by endodontic treatment before replantation, the amount of normal periodontal healing was almost similar to unfrozen and immediately replanted control teeth. Furthermore, this cryoprofile induced replacement resorption equal to the replanted control teeth. Preincubation in enriched medium for 24 h did not reduce resorption activity of the periodontal ligament. Endodontic treatment reduced the inflammatory resorption, demasking, however, hereby limited amount of ankylosis, that could be reduced by the above-mentioned cryoprofile.

An optimal cryoprofile for mature teeth seemed to be (i) slow equilibration at room temperature to a final concentration of 10% DMSO, (ii) slow freezing rates (0.3°C/mm) and plunging in liquid nitrogen at −35°C combined with fast thawing after storage at −196°C, and followed by (iii) endodontic treatment after thawing.