Investigators consider plaque to be an early stage of calculus. The plaque matrix may contain a modified protein on which the calculus crystals may form. Another view is that lowering of the pH to 5 or 6 may cause a protein to precipitate on which the calcium crystals deposit. Others are of the opinion that some bacteria may produce a polysaccharide that forms the sticky bulk of the plaque which favors adhesion of bacteria together with acid formation which initiates the formation of calculi. In bone mineralizatipn the crystals are first found to be approximately 300-1500A in length and about 15-75A thick. These grow larger as calcification proceeds.