DESCRIPTION (provided by applicant): The morphology of a dental crown is controlled by a strictly regulated spatio-temporal expression of ameloblast specific genes encoding for enamel matrix proteins. Once ameloblasts enter the differentiation stage along the dentino-enamel junction (DEJ) and begin to secrete enamel matrix proteins, they also start moving away from the DEJ and toward the outer enamel surface (OES) whilst forming enamel prisms. Once ameloblasts reach the OES, appositional growth terminates locally and this transition spreads to the cells located farther down the cusp until it reaches the cells at the cervical margin (CM). As the enamel thickens due to appositional growth, it also broadens (as more ameloblasts differentiate and extend the DEJ down the slopes of the crown). This extension eventually slows down and finally stops as the last ring of ameloblasts enter secretory stage, also at the CM. Enamel formation is subjected to rhythmical molecular signals that occur on short (24 hour) periods and give rise to cross-striations, or lines perpendicular to each prism. Another, more marked disturbance, occurs over longer periods (once every 6-10 days depending upon the individual), and induces the formation of striae of Retzius (SR), which are long-period growth markers. Little is known about the mechanisms regulating enamel formation, but careful analysis of short- and long-period growth lines should permit quantification of the critical parameters that determine crown shape during development. We hypothesize that these developmental events are best understood within a conceptual framework that envisions enamel crown shape to be determined by the biological regulation of five parameters: 1) appositional growth rate, 2) duration of appositional growth, 3) extension rate, 4) the duration of ameloblast extension, and 5) spreading rate of appositional termination. We also hypothesize that because a record of enamel formation can be identified by cross- striations and SR lines, obtaining accurate numerical values for the five parameters governing the shape of the ameloblast layer is feasible and might improve our understanding of how enamel forms. Our specific aims are: (1) To measure the distances between enamel growth lines representative of the apposition, extension, and termination processes and to identify landmarks documenting daily enamel formation; and (2) To develop a mathematical model that generates a 3D computerized reconstruction of the crown by accurately simulating dental enamel growth based upon measurements of the growth and developmental parameters that actually determine crown form. This information will fill critical gaps in our knowledge of enamel development, improve understanding pathological enamel formation and may also provide a mathematical foundation for dental tissue engineering. PUBLIC HEALTH RELEVANCE: Teeth form incrementally with characteristic short- and long-period growth markings in enamel. We hypothesize that these markings can be accurately measured using a combination of microscopic techniques. We also believe that the values obtained can be represented mathematically and used to generate a 3D model of enamel formation with the aim of increasing our understanding of development and of diseases affecting enamel.

Teeth form incrementally with characteristic short- and long-period growth markings in enamel. We hypothesize that these markings can be accurately measured using a combination of microscopic techniques. We also believe that the values obtained can be represented mathematically and used to generate a 3D model of enamel formation with the aim of increasing our understanding of development and of diseases affecting enamel.