What do the different DDs mean in dentistry?

I'm told I'm either a DD1 or DD2 and I get the impression that if you are a DD4 your mouth is going to be a challage. So what does it all mean?

What do the different DDs mean in dentistry?
At my school we refer to the amount of hard deposits (calculus/tarter) on a persons teeth as classes. For example;





Class 1: has minimal deposits, up to Class 4: which has deposits on every tooth and every surface (mesial, cervical, and distal a.k.a. towards the mid line, on the neck, and away from the mid line).





I am guessing that you are referring to the same thing. Maybe the DD stands for Dental Deposits.
Reply:its the size of the dental assistant's chest
Reply:I may b d size of impression trays which fits ur mouth.... as trays r available in diff. sizes 4 taking impressions.......