Environmental mineral content and fluorine exposure emerged as central determinants of enamel resistance and caries prevalence, linking endemic fluorosis with caries risk and enamel chemistry under environmental exposure. Developmental histology and hereditary defects in dentin and enamel revealed ontogenetic and genetic bases for dental variability, with enamel development observed in rats and humans. Biomechanics, physiology, and innervation described the functional biology of teeth: dentin physiologic changes, tooth innervation, and responses to systemic alteration, linking structure and neural control to clinical outcomes. Caries etiology and experimental caries frameworks showed how laboratory experiments and environmental contexts shape understanding of caries causation, enamel/dentin responses, and public-health influences. Enamel, dentin, and dentoalveolar tissue chemistry and materials science focused on composition, surface reactivity, and adsorption phenomena, informing restorative interfaces and tissue behavior. Historical Significance: This period established foundational links among environment, development, and pathology of dental hard tissues, guiding early preventive strategies and fluoride public-health policy considerations. It contributed systematic maps of eruption timing and morphogenesis, informing pediatric dentistry and orthodontics, and augmented dentition-focused anthropology.