Oreibi, who objected to the informality of the term, said: "I warned your colleagues yesterday twice to respect the court and its officials."
Aref insisted that the information he wanted to give was more important than the form of address and then used the word "brothers" again to refer to the prosecutors.
The judge then ordered him to be removed. Aref protested and Oreibi said: "You are arrested for 24 hours for violating professional conduct."
Aref was released shortly afterwards after the judge said that he "wanted the sessions to continue normally".
After the stormy start, the court on Wednesday heard two expert witnesses testify against the accused before the session was adjourned to Thursday.
Physician Asfandiar Shukri, a US citizen, said that during a series of examinations of Kurdish refugees near the Turkish border he had determined that mustard gas was used on them in 1988.
"This mustard gas was similar to what was used by the Nazis in the Second World War," Shukri told the court, adding that it appeared that "nerve gas" was also used.
In evidence given on Tuesday, a US forensics expert took the stand to tell in detail how he unearthed the remains of 27 people from a mass grave in northern Iraq.
Clyde Snow was the first such expert to testify in the trial, which prosecutors have previously said would rely heavily on forensic evidence to show how thousands of Kurds were killed during the Anfal - or Spoils of War - campaign in 1988.