milk has no observed regenerative properties for cells on knocked out teeth. it was discovered 30 years ago that milk was less damaging to knocked out teeth than water or saliva. it was recommended because it has a compatible osmolality (fluid pressure) to tooth root cells, and it is thought to be readily available. however, like physiologic saline, milk lacks the necessary metabolites and glucose necessary to maintain normal cell metabolism of the tooth root cells. the cells on knocked-out tooth roots in milk do not die immediately but are unable to replicate (mitosis) and so are less able to reform new cells when replanted. the most optimum storage media that are available have been shown to be ph balanced cell preserving solutions. the best known and most extensively tested is called hank’s balanced salt solution (hbss). it has all of the metabolites such as ca, phosphate ions, k+ and glucose that are necessary to maintain normal cell metabolism for long periods of time. hbss has been extensively tested in dental and medical research for the past twenty years. this research has shown that 90% of cells stored in hbss for 24 hours maintain their normal viability and after four days, still have 70%viable. in research studies, extracted dog’s teeth that have been placed in hbss for four days can still be replanted with little signs of resorption. hbss also has been shown to be capable of replacing lost cell metabolites. since a cell that has been cut off from its blood supply depletes its stored metabolites after fifteen minutes, a tooth that has been extra-oral for one hour has less vital cells to reconnect with the bone ligament cells. some studies in dental research have shown that knocked out teeth that have been dry for up to one hour will have less resorption if they are soaked in a hbss for 30 minutes prior to replantation. in these studies, dog’s teeth were extracted and left dry for 30, 45 and 60 minutes and then soaked in hbss for 30 minutes and then reimplanted. these teeth showed 50% less replacement resorption following reimplantation. it has also been shown that keeping the teeth cold while in the hbss does not affect success. many other types of storage liquids have been tested such as powdered milk, enfamil, gatorade, and contact lens solution. all of them have been shown to either be ineffective or damaging to avulsed tooth. prognosis despite the treatment provided, dental avulsion carries one of the poorest outcomes with 73-96% of the replanted teeth eventually being lost. there are three main factors which significantly influence the prognosis of the tooth. these include: the extent of damage to the periodontal ligament (pdl) at the time of injury the storage conditions of the avulsed tooth the duration prior to replantation dental trauma varies widely in complexity and usually there is little that lay people or professionals (excluding dentists) can do. however, avulsion is the one type of traumatic dental injury where lay people can play a critical role in determining the prognosis of the tooth. the tooth has the best prognosis if it is replanted within 15 minutes of the accident but also has an excellent prognosis if it has been stored in an optimal storage medium within one hour of the accident. pdl healing is the primary outcome measure when assessing interventions for tooth avulsion. when the healing of the pdl is unfavorable it means that there is no longer protection for the root from the surrounding alveolar bone. the bone that surrounds the tooth is continually undergoing physiological remodeling. over time, the root is gradually replaced by bone, which leads to the loss of tooth root and so the crown of the tooth fractures. the results of replanting permanent incisor teeth can be divided into short, medium and long-term survival of the tooth. if the tooth is replanted it acts in the short term to maintain space, maintain bone and provide good to excellent aesthetics. if unfavorable healing has occurred, the tooth can last into the medium term on 2-10+ years depending on the speed of bone turnover. long-term survival of the tooth only happens when favorable healing of the periodontal ligament has occurred. if this happens the tooth can be estimated to survive as long as any other tooth epidemiology research has shown that more than five million teeth are knocked-out each year in the united states. dental avulsion is a type of dental trauma, and the prevalence of dental trauma is estimated at 17.5% and can vary due to the geographical area. although dental trauma is relatively low, dental avulsion is the fourth most prevalent type of dental trauma. dental avulsion is more prevalent in males than females. males are three times more likely to suffer from dental avulsion than females. up to 25% of school-aged children and military trainees and fighters experience some kind of dental trauma each year. the incidence of dental avulsion in school aged children ranges from 0.5 to 16% of all dental trauma. many of these teeth are knocked-out during school activities or sporting events such as contact sports, football, basketball, and hockey. it is important for anyone whom is related, working, or witnessing sports that they be educated on this subject matter. being educated could aid in minimizing injuries that could do further harm to the victim. being informed and spreading awareness of dental avulsion in the state of knowledge, treatment, and prevention could make an impact. history the first reported cases of knocked-out teeth being replanted was by pare in 1593. in 1706, pierre fauchard also reported replanting knocked out teeth. wigoper in 1933 used a cast gold splint to hold reimplanted teeth in place. in 1959, lenstrup and skieller declared that the success rate of replanted knocked out teeth should be considered a temporary procedure because the success rate of less than 10% was so poor. in 1966 in a retrospective study, andresen theorized that 90% of avulsed teeth could be successfully retained if they were replanted within the first 30 minutes of the accident. in 1974, cvek showed that removal of the dental pulp following reimplantation was necessary to prevent resorption of the tooth root. in 1974, cvek showed that storage of knocked out teeth in saline could improve the success of replanted teeth. in 1977, lindskog et al. showed that the key to retention of the knocked-out teeth was to maintain the vitality of the periodontal ligament. in 1980, blomlof showed that storing the periodontal ligament cells in a biocompatible medium could extend the extra oral time to four hours or more. he found that the best storage medium was a medical research fluid called hank’s balanced solution. in this study, it was serendipitously discovered that milk could also maintain cell viability for two hours. in 1981, andreasen showed that crushing of cells on the tooth root could cause death of the cells and lead to resorption and reduction in prognosis. in 1983, matsson et al. showed that soaking in hank’s balanced solution for thirty minutes prior to reimplantation could revitalize extracted dog’s teeth that were dry for 60 minutes. in 1989, a systematic storage device was developed to optimally store and preserve knocked out teeth. in 1992, trope et al. showed that extracted dog’s teeth could be stored in hank’s balanced solution for up to 96 hours and still maintain significant vitality. in this study, milk was only able to maintain vitality for two hours. archaeology in ancient times, ritual dental avulsion was widespread among different cultures around the world. for example, it was common during the early holocene (from around 11,500 bp up to 5,000 bp) in north africa and was occasionally observed in the natufian culture (14,000 to 11,500 bp). such tooth avulsion was the intentional removal of one or more teeth, which was done for ritual or aesthetic reasons. it was also used to denote group affiliation. typically, the maxillary incisors were the teeth most often selected for removal. this practice is still common in parts of africa.