When I talked with some of the dental schools earlier this cycle, they said that since everything is started to be stored electronically now, they will have your DAT scores on file for 2 years. The majority of the schools I applied to this year still had my DAT score on file from last year, so it just depends on the school. A few schools will still require you to request the ADA to send them again though, so you will have to call each school up and see what they say.