Save cells before tooth replantation- A Review
Avulsion is one of the most complex traumatic injury affecting both teeth and children. Avulsed teeth can be replanted. Management protocols for avulsed teeth should include management of the pulp and periodontal ligament (PDL) cells in order to improve the long-term prognosis and survival of these teeth. If immediate replantation is not possible, the clonicity and progenicity of the viable PDL cells can be maintained with aid of suitable storage medium at the place of trauma. The incorrect use of a storage medium potentially increases the risk of PDL cell necrosis, which can result in ankylosis and replacement resorption of the tooth root. Considering the importance of the storage media, an informed choice of a media is essential for a favourable outcome. This review discusses the common storage media that are available and some of the unique features of each media along with the problems associated.
Avulsion, Replantation, Storage media
According to WHO classification, Avulsion or ex-articulation is complete displacement of the teeth from its alveolar socket. [1, 2] Avulsion of permanent teeth is seen in 0.5- 3% of all dental injuries. Andreasen &Andreasen predicted that the incidence of these injuries may eventually surpass the incidence of dental caries. Numerous studies show that this injury is one of the most serious dental injuries, and the prognosis is very much dependent on the actions taken at the place of accident and promptly after the avulsion. The immediate replantation of teeth is the ideal treatment of choice for the avulsed teeth to prevent post replantation complications such as inflammatory resorption, ankylosis or replacement resorption. If immediate replantation is not possible, the clonicity and progenicity of the viable PDL cells can be maintained with aid of suitable storage medium at the place of trauma. The lack of first aid knowledge about the avulsion among the public and health care centers delays immediate replantation and limits the prognosis of the avulsed tooth. Various storage media are available maintain the progenicity and clonicity of PDL cells to improve the outcome of the replantation. The purpose of this article is to, review the current storage media with their pros and cons and to provide an insight about the efficacy of newer storage media available.
Cvek  showed that storage of knocked out teeth in saline could improve the success of replanted teeth. Lindskog et al  reported that the key to retention of the knocked-out teeth was to maintain the vitality of the periodontal ligament. Andreasen  also mentioned that crushing of cells on the tooth root could cause death of the cells and lead to resorption and reduction in prognosis. Blomlof , mentioned that the best storage medium was a medical research fluid called Hank’s Balanced Salt Solution maintained the cell viability for two hours. Matsson et al  showed that soaking in Hank’s Balanced Solution for thirty minutes prior to reimplantation could revitalize extracted dog’s teeth which were dry for 60 minutes. Blomlof L  recommended milk as a storage media prior to reimplantation when immediate replantation is not possible. Krasner et al  reported that the systematic storage device “Save-A-Tooth” was developed to optimally store and preserve knocked out teeth. Layug et al  quoted that milk packed in ice seems to be best alternative, due to its wide availability and minimum detrimental effect. Marino T G et al  showed that long shelf life milk is more effective than Save A Tooth. Pearson et al  mentioned that Baby Milk formula (Enfamil) is more effective storage media than pasteurised milk for atleast 4 hrs. Al-Shaher et al  reported that 75% PDL cells had been kept viable after 20 hr maintenance in propolis solution. Sonoda CK et al  mentioned that saliva can be storage medium for avulsed tooth when no medium is present at accidental site. Khademi et al  introduced egg albumin as a storage medium for up to 10 hrs. Gopal K et al  reported that coconut water can be used as a storage medium due to its readily acceptable by the body and sterile in nature. Ji Young Hwang et al  invented green tea extract as a suitable, alternative storage media for avulsed teeth. Likewise there are many storage media available for the success of replanted tooth [Table-1].
Factors considered for storage media
The prognosis of the tooth re-implantation depends on the existence of feasible cells in the periodontal ligament and also depends on those which are able to proliferate on the damaged areas of the root.[17,18] Therefore either immediate replantation or storage of the tooth should be done in an appropriate storage media.
Two important factors considered for storage medium are Hydrogen ionic potential/ pH and Osmolality. According to Marino et al, the pH and the osmolality of the storing environments must be physiologic, for both interfere in the surviving of cells of the periodontal ligament. Each storage media has different pH and osmolality based on which the survival of PDL cells is assessed [Table-2]. Authors have reported that the cellular growth may occur between 290 and 330mOsm/kg. The pH must be between 7.2 and 7.4, but growth may occur between pH 6.6 and 7.8.
Ideal requirements of storage media
An ideal storage media should have the osmolality and pH closer to physiological conditions to maintain the viability, clonogenic capacity and mitogenicity of the Pdl cells. It should be readily available at the site of accident  so that, the tooth can be immediately placed into it, should have a longer shelf life, should have anti-inflammatory and anti-microbial properties which reduces inflammation and replacement resorption.[21,22] It should also have an antioxidant property which will protect the cells from oxygen radical mediated damage. Finally last but not the least the storage media should be economical. Not a single storage media fulfill all the ideal requirements, so various comparable studies been conducted to evaluate the efficiency in maintaining the cell viability of PDL cells of replanted teeth.
Container for the transport of avulsed teeth along with the medium must be unbreakable, nontoxic to the cells of PDL, should be leaking proof, easy handling, should be sterile as well the internal walls must be made of soft material. Some of the commercially available are “tooth rescue box” (Dentosafe) containing a culture medium, salts, amino acids, glucose and vitamins  and “Save A Tooth” system, a 6-part system containing HBSS media, that was designed to prevent damage to the PDL cells of an avulsed teeth.
Newer Medias in Research
Ascorbic acid: Addition of ascorbic acid to osteoblastic cell lines can stimulate type 1 collagen production, followed by expression of specific markers associated with osteoblastic phenotypes such as alkaline phosphates (ALP) and osteocalcin. Ishikawa et al  studied the effect of ascorbic acid on PDL cells and observed that ascorbic acid increased the ALP activity which is required for binding of PDL cells to type 1 collagen via ?2?1 integrin whose expression is again increased by ascorbic acid, so it may serve as potential storage media.
L-DOPA (Levodopa; Sigma chemical, Perth, WA, Australia): is drug with possible mitogenic effect. It stimulates secretion of growth hormone from pituitary gland which aids in healing process. Mandana et al  observed the effect of levodopa on human PDL fibroblasts and stated that it can also have local effect on growth of cells and can act as preserving medium for avulsed teeth.
Cryoprotective agents: The effect of low temperature storage on clinical success of reimplantation has been studied. Schwatz and Andreasen  studied the effects of the cryopreserving agents, 5% and 10% dimethyl sulphoxide (DSMO) and 10% glycerol on PDL. They observed that use of different cryoprotectives, combined with controlled freezing rates can preserve the PDL of reimplanted teeth.
The success of dental reimplantation depends on the existence of viable cells on the periodontal ligament, which are able to proliferate on the denuded areas of the root surface. This can be reached through immediate reimplantations taking place within up to 30 minutes or transporting the tooth in an adequate storage medium for dental reimplantation.
Tap water, saliva and saline must be avoided for the storage of avulsed teeth, because they do not offer any benefit to the healing. Contact lens solutions and Emdogain also do not offer any good results over other media. Propolis and egg white needs additional studies where propolis is not easily available in emergency situations whereas egg white is a promising media considering its availability. Milk is significantly better than other storage media, but it is not so efficient as Hank’s balanced salt solution, viaspan and eagle’s medium as storage medium for avulsed teeth for the maintenance of vitality and proliferative capacities of periodontal ligament cells. Although HBSS, ViaSpan and Eagle’s medium have great potential to maintain the PDL cells in a viable state of avulsed teeth, lack of ready availability to the general public as well the cost makes them less than ideal for developing countries like India. Milk remains the most convenient, cheapest and readily available solution in most situations, also being capable of keeping PDL cells alive.