Cryopreservation of developing teeth

The orthodontic bonding properties of human enamel after cryopreservation

The aim was to investigate the effect of cryopreservation on the enamel bonding properties of orthodontic brackets. Sixty-six human premolars were randomly allocated to a control group or a cryopreserved group. Conventional stainless-steel orthodontic brackets were bonded with a light cure adhesive on the buccal side of the premolars. The shear bond strength (SBS) was determined at a crosshead speed of 1 mm/min. The SBS and adhesive remnant index (ARI) were evaluated respectively by an independent samples t test and Fisher's exact test (α≤0.05). The mean failure load was lower in the cryopreserved group. However, this difference in SBS was not significant (p=0.443). In both groups, the ARI mostly indicated a failure at the enamel-adhesive interface. The mean ARI scores for both groups were not significantly different (p=0.099). Within the limitations of this macro bond strength testing, it can be concluded that cryopreservation does not significantly affect the bonding properties of enamel.

An experimental study on periodontal regeneration after subcutaneous transplantation of rat molar with and without cryopreservation: an in vivo study

This study analysed the effects of cryopreservation on periodontal regeneration of autotransplanted rat molars. First and second maxillary molars (n=92) of 24 four-week-old Wistar rats were gently extracted and autotransplanted into the abdominal tissue immediately (control group n=44) or after cryopreservation in liquid nitrogen for 7 days (experimental group n=48). At 1, 2, 4 and 10 weeks after transplantation, the transplanted molars were excised and regeneration of the periodontal tissues was analysed on histological sections stained with routine H&E and Goldner method. Different tissue responses were scored on a tooth basis: inflammation, regeneration of the periodontal ligament, resorption/apposition of cementum, and alveolar bone formation. Sixty-two teeth were available for histological evaluation, including 30 experimental and 32 control samples. One week after transplantation, both control and test teeth were surrounded by granulation tissue and some areas of root resorption could be seen. After 2 weeks, signs of regeneration of the periodontal ligament, cementum apposition, and new bone formation roughly coincided in both groups, however markedly retarded in the experimental group. After 4 weeks, regeneration progressed equally in both groups, presenting fewer areas of cementum apposition in experimental samples. Finally, 10 weeks after baseline transplantation, no significant differences between both groups could be observed. Cryopreservation followed by autotransplantation of extracted teeth in rats appears to have minimal detrimental effects on regeneration of periodontal tissues after integration periods of 1-10 weeks. However, the present findings indicated that the regeneration process in general is retarded for cryopreserved teeth, as compared to their immediately transplanted homologues.

In vitro comparative analysis of cryopreservation of undifferentiated mesenchymal cells derived from human periodontal ligament

Cryopreservation aims to cease all biological functions of living tissues in a reversible and controlled manner, i.e., to permit the recovery of cells by maintaining a high degree of their viability and functional integrity. The objective of this study was to evaluate in vitro the influence of cryopreservation on undifferentiated mesenchymal cells derived from the periodontal ligament of human third molars. Mesenchymal cells were isolated from six healthy teeth and cultured in α-MEM medium supplemented with antibiotics and 15% FBS in a humid atmosphere with 5% CO(2) at 37°C. The cells isolated from each tooth were divided into two groups: group I (fresh, non-cryopreserved cells) was immediately cultured, and group II was submitted to cryopreservation for 30 days. The rates of cell adhesion and proliferation were analyzed in the two groups by counting the cells adhered to the wells at 24, 48 and 72 h after plating. The number of cells per well was obtained by counting viable cells in a hemocytometer using the Trypan blue exclusion method. Differences between groups at each time point were evaluated by the Wilcoxon test. The Friedman test was used to determine differences between time points and, if detected, the Wilcoxon test with Bonferroni correction was applied. The results showed no significant difference in the in vitro growth capacity of undifferentiated mesenchymal cells between the two groups. In conclusion, cryopreservation for 30 days had no influence on periodontal ligament mesenchymal cells.

Autotransplantation of 28 Premolar Donor Teeth in 24 Orthodontic Patients

Objective: To test the null hypothesis that premolar autotransplantation is not successful for orthodontic patients.

Materials and Methods: In the present study, 28 premolar transplants from 24 orthodontic patients were associated with orthodontic treatment. At a routine 3-month appointment, patients underwent a dental radiograph and a chair-side observation for periodontal problems. Three sets of dental radiographs were taken by one dental assistant using a custom holder at: preoperation (T0), 2 year postoperation (T1), and retention (T2) (4- to 14-year follow-up observation) stages. All transplants were conducted in a one-phase operation by one operator (Dr Inoue). Recipient sites were: ten for missing maxillary canines, nine for maxillary centrals and laterals, eight for lower second premolar, and five for other missing premolar sites. All recipients maintained the retained primary tooth with a socket.

Results: The success ratio of all 28 transplants was 100%, although four transplants shorter than a 4-year period of observation were omitted. Two transplant patients, one with a medical history of histiocytosis and the other with a history of osteomyelitis of the maxilla without a recipient socket, were also excluded from this study. Eleven of 22 premolar transplants had a root canal treatment (RCT), four of which had RCT within 2 years after the operation.

Conclusions: The null hypothesis was rejected. The success ratio of premolar transplants was 100%.

Influence of cryopreservation on human periodontal ligament cells in vitro

Cryopreservation of teeth before autotransplantation may create new possibilities in dentistry. The purpose of this study was to examine the effect of a standardised cryopreservation procedure on human periodontal ligament (PDL) cell cultures. Human PDL fibroblasts obtained from immature third molars of 11 patients were cultured and divided into two groups. The experimental group was cryopreserved and cultured after thawing. The control group was cultured without cryopreservation. A comparison was made between cryopreserved and control cells. To evaluate possible differences in the characteristics of the fibroblasts, the cells in both groups were tested for viability (membrane integrity), growth capacity and alkaline phosphatase (ALP) expression. The Wilcoxon test for paired comparison between cryopreserved and non-cryopreserved cells was performed for each characteristic. The results showed that membrane integrity of cells was not influenced by cryopreservation. There was no statistically significant difference in growth capacity between cryopreserved and control cells. Non-cryopreserved cells were slightly stronger positive for ALP, but the difference was not statistically significant. From these experiments it can be concluded that the observed parameters are not influenced by cryopreservation.

Tooth transplantation and cryopreservation: State of the art

Autotransplantation of teeth is useful and has many indications in dentistry. Cryopreservation of teeth creates new possibilities--eg, when autotransplantation is needed, but the recipient site is too small and orthodontic treatment is needed to gain space for the transplant. This review article examines the reactions of various dental tissues after autotransplantation vs after autotransplantation with cryopreservation. Various subjects will be discussed, including periodontal healing, pulp reactions, and root development after autotransplantation with and without cryopreservation.

Revascularization after cryopreservation and autotransplantation of immature and mature apicoectomized teeth

Autotransplantation of immature teeth can have a success rate of almost 98% if the tooth is atraumatically transplanted from the donor site to a suitable acceptor site and the extraoral time is kept to a minimum. When the tooth cannot be transplanted immediately, cryopreservation and storage in a tooth bank offer new possibilities for autotransplantation. However, the effect of cryopreservation on the revascularization of transplanted teeth is still unknown. The purpose of this study was to examine revascularization in immature teeth that have an open apex and in mature teeth that have had the apex cut. The study was carried out on 16 teeth in 2 dogs; 8 teeth were removed and immediately transplanted to the contralateral position and 8 teeth were cryopreserved and transplanted 1 week later. The results show that: (1) teeth can revascularize after autotransplantation if the original pulp tissue is removed at the time of extraction, (2) there is no significant difference in the amount of revascularization between teeth stored in a tooth bank for 7 days and those immediately transplanted without freezing, and (3) there is no difference in the ingrowth of new pulpal tissue between mature apicoectomized teeth and immature teeth.

Cryopreservation as long-term storage of teeth for transplantation or replantation

A method is presented which for the first time demonstrates the possibility of storing a human tooth over a period of 18 months in a frozen state with the periodontal membrane preserved viable, enabling the thawed tooth to heal with a normal periodontal ligament evaluated 2 years after autotransplantation. The cryopreservation technique included equilibration of the extracted tooth into 10% DMSO (dimethylsulphoxide) at room temperature in tissue culture medium including 10% human serum, freezing with a controlled rate of 1.2 degrees C/min to -40 degrees C and 6 degrees C/min to -100 degrees C, followed by transfer to and storage in liquid nitrogen at -196 degrees C. The tooth was thawed at a fast rate of approximately 100 degrees C/min, and DMSO was removed by slow equilibration at room temperature. A mature human bicuspid was autotransplanted after cryopreservation. Endodontic treatment was initiated 4 weeks after transplantation. 2 years after transplantation, the grafted tooth showed clinically and radiographically normal periodontal healing without signs of root resorption or marginal bone loss.

Cryopreservation before replantation of mature teeth in monkeys. (II). Effect of preincubation, different freezing and equilibration rates and endodontic treatment upon periodontal healing

The effect of cryopreservation in liquid nitrogen at -196 degrees 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 degree C. When this procedure was combined with a slow freezing rate of 0.3 degree C/min from -4 degrees C to -35 degrees 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 slow equilibration at room temperature to a final concentration of 10% DMSO, slow freezing rates (0.3 degree C/min) and plunging in liquid nitrogen at -35 degrees C combined with fast thawing after storage at -196 degrees C, and followed by endodontic treatment after thawing.

Cryopreservation of mature teeth before replantation in monkeys (I). Effect of different cryoprotective agents and freezing devices

Cryopreservation is clinically relevant in storage of teeth for transplantation or replantation. The effect of cryopreservation was studied by histometric analysis of 60 teeth replanted in 10 green Vervet monkeys. The following cryopreserving agents were examined: 5% and 10% dimethylsulfoxide (DMSO) and 10% glycerol. Furthermore, 2 types of freezing method were compared: automatic biological freezing (Cryoson) and a simplified freezing device of Sperling. Cryopreserved teeth were stored for 1 week at - 196 degrees before replantation. The histometric analysis carried out 8 weeks after replantation showed that 5% DMSO had the best effects in protecting the periodontal ligament (PDL) during cryopreservation. This medium induced no replacement resorption and secured a considerable extent of normal periodontal ligament compared to the control teeth replanted immediately without cryopreservation. 10% DMSO and 10% glycerol also preserved the PDL but with a lower degree of survival and a higher degree of ankylosis. 10% DMSO exposed at 0 degree C followed by immediate replantation did not induce any pathological effect on the PDL. All cryopreserved teeth showed some degree of inflammatory resorption. However, this could be due to the expected necrosis of the pulp tissues of the frozen teeth because of the lack of diffusion of cryoprotectant agent into the pulp of mature teeth.