In my archives I have a copy of 1.7.. ot_ticket & ot_thread are the tables. ot_thread is joined to ot_ticket on ticket_id. If you trace class.ticket.php create function it inserts into TICKET_TABLE (ot_ticket), then the message body get's appended as a Message, which is a ThreadEntry (class.thread.php), which eventually calls the create function, which inserts into the TICKET_THREAD_TABLE (ot_thread). This becomes hideously complicated in later versions, where even the Subject is a "dynamic form field"..