pH and carbonate levels in developing enamel

Our earlier studies showed that the surface of developing and calcifying en amel changes its pH alternatively along the tooth axis when stained with pH indicating dyes. Based on the pH conditions, the enamel at this stage was distinguished as neutral zone (N1 and N2) and acid zone (A1 and A2). The ai m of the present study was to correlate changes of pH with proteolytic acti vity and crystal size of the calcifying bovine enamel. Specimens of develop ing bovine enamel were separated into four maturing stages using pH stainin g methods. Crystal chemistry of the developing enamel was investigated usin g thermogravimetry (TGA), ICP emission spectrometry, X-ray diffractometry ( XRD) and infrared spectroscopy (IR). Previous biochemical analysis of prote olytic enzyme activity from enamel indicated that the optimal pH of the maj or protease was approximately pH 6.0, coinciding with the pH of the Al zone , IR, TGA and XRD analyses showed that most of the organic components of th e enamel decomposed at 580 degrees C. Higher levels of carbonate were obser ved in the secretory stages than in mature enamel, The Ca/P molar ratio of the enamel apatite was lower than the stoichiometric value of 1.67. These r esults suggest that growth and maturation of enamel apatite crystals is rel ated to a decrease in the carbonate level and appear to be related to the a lternative calcification and decomposition of enamel proteins.