It does not matter what tooth it is.
The fact is in the Basenji standard, the teeth are to be a scissors bite.
If the tooth is NOT there, it will not be part of the bite that is being looked at anyways.
If the dog is getting consistently last in his class, I would have to speculate that are far more serious faults than a missing tooth.
And I would not consider one missing tooth to be as serious as a totally undershot or wry bite.
Of course, this is only my opinion as breeder, exhibitor and a judge.