I suspect the Soviets had an equivalent to the USA’s Dog tags, etc., though IIRC, some armies’ soldiers in WWII still had only paper identification. If this was paper, you can make your own guess as to it chances for being intact. As for dental records – I think you are projecting too much of “today” into the past. Even assuming the body was in Soviet hands, instead of German, when they made any assumed effort to identify him, dental records were neither as common or easily accessible as they are today – and even if they were, many people never saw a dentist until they REALLY needed one - i.e., preventative care was hardly a common practice, so I suspect there would be few soldiers who had records to check. Then, the Soviet Union would also be suffering a many casualties, and it probably didn’t have much infrastructure or other resources to spare from its war-prosecution effort. I could go on, but I think you ought to be getting the picture…