Crystallization-controlled glass-ceramics for modified glass ionomer cements: Structural evolution and mechanical enhancement

Despite over four decades of innovation, the mechanical performance of conventional glass ionomer cements (GICs) remains limited by the reactivity and structural instability of their glass fillers. In particular, alumino-silicate-fluoride (ASF) glass-ceramics derived from waste resources remain largely unexplored for GIC fabrication, despite their strong potential for sustainable dental materials. In this study, ASF-based glass-ceramics were synthesized from clam shell (CS) and soda-lime-silica (SLS) glass waste and systematically crystallized to tailor their structures for GIC applications. Thermal analysis revealed a glass transition temperature of ∼764 °C and crystallization onset at ∼918 °C. XRD confirmed fluorapatite (Ca5(PO4)3F) as the dominant phase up to 800 °C, while excessive crystallization at higher temperatures (≥1000 °C) produced mullite (Al5SiO9.5) and anorthite (CaAl2Si2O8). Incorporation of optimally crystallized glass-ceramic fillers (800 °C) into GIC significantly enhanced densification (2.46 g cm−3) and compressive strength, reaching 82.03 MPa after 28 days of ageing, exceeding ISO 9917 requirements (≥70 MPa). However, over-crystallization resulted in grain coarsening and reduced cement reactivity, leading to strength degradation. Overall, this work demonstrates that waste-derived ASF glass-ceramics with controlled crystallization provide a viable route toward high-strength, sustainable GICs for dental applications.