In British English full stops are uncommon after abbreviations that contain the first and last letters of the full expression. Examples are: Dr and Mr
In American English, full stops are common, and Mr. and Dr. are preferred.
An abbreviation usually does not have a distinct pronunciation of its own: we pronounce Mr as ‘mister’ and ‘Dr’ as ‘doctor’. There are, nevertheless, a few exceptions to this rule. For example, the abbreviation p. for pence is sometimes pronounced as ‘pee’.