Saliva-mediated Mechanisms of Post-Eruptive Enamel Mineralization

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Enamel hypomineralization, specifically molar-incisor hypomineralization (MIH), is diagnosed in the permanent dentition of up to 40% of children worldwide, and increases the risk of caries, attrition and reduced durability of fillings. A critical barrier to improving treatment of enamel hypomineralization is the gap in understanding how to amplify the processes of crystal growth and posteruptive enamel maturation. The goal of this project is to take advantage of the porcine model to determine how and how fast pig enamel acquires the hardness to last a lifespan although at eruption it has a mineral density similar to hypomineralized human enamel. Our working hypothesis is that during enamel maturation, mineral content, hardness, and acid resistance increase over time, whereas organic matrix content decreases. The objective of this proposal is to elucidate the mechanisms of naturally occurring posteruptive enamel mineralization in the porcine model system. Our central hypotheses are that 1) pig enamel erupts hypomineralized into the oral cavity with retained organic matrix that arrests crystal growth and results in incomplete mineralization; and 2) after eruption, whole saliva and the dental pellicle forming the interface with the enamel surface mediate the controlled removal of residual organic matrix and ion exchange to effectively continue the maturation process. Because fluoride treatments cannot remove the retained organic matrix that causes enamel softness, the rationale for the proposed studies is that determining how posteruptive mineralization can occur in pig teeth at a much faster rate than in human teeth will allow us to develop biomimetic approaches for enamel repair of MIH-affected human teeth. A follow-up (R01) study will then focus on strategies to improve enamel properties, specifically hardness and chemical resistance, to achieve a rate that is clinically meaningful. To attain these goals, we will test our central hypotheses in two Specific Aims. 1. Elucidate the kinetics of posteruptive enamel maturation in pig teeth by characterizing and quantifying changes in mineral and organic phases of both deciduous and permanent pig enamel at three-month intervals. 2. Characterize the composition of pig whole saliva and dental pellicle to determine if saliva/pellicle constituents facilitate continued mineralization in the absence of ameloblasts. Our results will increase knowledge of the mechanisms of enamel maturation, provide new insights on posteruptive enamel mineralization, and open a new perspective on treatment options. This is significant because retained organic matrix arrests crystal growth and maturation resulting in soft, hypomineralized enamel, which is more susceptible to caries and attrition, and to compromised bonding and durability of fillings. The proposed research is innovative because it 1) applies our unique expertise and research set-up to integrate the porcine model with novel analytical approaches to study the kinetics of enamel maturation and 2) challenges current paradigms that posteruptive enamel mineralization is a very gradual process with low efficiency and that enamel matrix proteases, rather than saliva constituents, facilitate the removal of enamel matrix proteins.