Oral and maxillofacial surgeon Donald Adams said the marks on the knuckles of Robin's right hand were consistent with striking the teeth of a teenage boy, the Christchurch Court News website reported. Robin's son Stephen, 14, fought his killer before being shot dead along with four other members of his family.
But Mr Adams also conceded that the marks could have been made by many things other than teeth.
He was giving evidence on the 52nd day of the trial of Robin Bain's son David Bain on five charges of murdering his parents and three siblings in the Every Street, Dunedin, family home in 1994.
The defence claims that Robin Bain shot dead his wife and three of his four children before turning the gun on himself.
Mr Adams said he obtained a cast of the upper jaw of a 16-year-old boy's natural teeth.
The photograph of Robin Bain's hand shows four marks in a curved arrangement, which could relate to a curve of natural teeth, he said.
In cross-examination by crown prosecutor Robin Bates he was asked if the marks could be made by other things encountered in our daily lives.
He agreed, and when told that Robin Bain had been fixing spouting during the weekend prior to his death, agreed that it was possible any work of that nature could cause marks of that type.
Grant Russell, a consultant urologist, said that nothing could be concluded from someone having 400mls of urine in his bladder, as Robin Bain had at the time of his death. For some people it would create urgency but with others it would not be a problem.
The Crown case is that Robin Bain could not have committed the murders with a full bladder, because whoever did had a long struggle with Stephen Bain, and cleaned up afterwards.
He said a man could wake up, urinate and still be left with 400mls in his bladder.
Adrenaline, excitement and distraction could also decrease urine production and increase the ability to store urine.
Peter Ross, a forensic scientist at the Victorian police forensic scientist department in Australia, was asked to look at David Bain's sister Laniet's head wound.
He said it was an unusually large entry wound and the bullet that caused the damage had lost considerable energy. He said the bullet must have been damaged before it struck the skull, and that something had happened to the bullet to cause it to expand before it struck the skull.
Mr Ross, who will continue his evidence tomorrow, is the 53rd and final defence witness.
But cross-examination is still scheduled for another witness who will give his testimony by video link from Britain.
