Effect of TiO2 doping on the structure and properties of lithium silicate-based glass-ceramics for potential dental applications

A series of glass samples with the nominal composition 65SiO₂ - (22.5-x) Li₂O - 12.5Al₂O₃ - xTiO₂, where x varies as 2.5, 5, 7.5, and 10 mol%, were synthesized using the conventional melt-quenching technique. Differential scanning calorimetry (DSC) was utilized to identify crucial thermal transitions, which informed the process of fabricating corresponding glass-ceramic derivatives. X-ray diffraction (XRD) analysis confirmed the formation of three primary crystalline phases in the glass-ceramics: lithium disilicate (Li₂Si₂O₅), lithium aluminosilicate (LiAlSiO₄), and brookite (TiO₂). Scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDAX) demonstrated that crystal growth increased in size and developed well-defined morphologies. Vickers microhardness testing indicated that TiO₂-doped lithium silicate glasses and their glass-ceramic counterparts exhibit mechanical properties compatible with dental application requirements. Differential scanning calorimetry (DSC) analysis revealed that increasing TiO₂ content (2.5-10 mol%) shifted thermal transitions to higher temperatures, indicating improved thermal stability and a stronger glass network. Higher TiO₂ also enhanced microhardness (5.02-5.93 GPa) and compressive strength (440-542 MPa), with further gains after heat treatment due to TiO₂-induced crystallization of hard phases. Corresponding glass-ceramics showed increased hardness (5.51-7.27 GPa), compressive strength (492-583 MPa), and density (2.478-3.441 g/cm³), confirming the reinforcing and densifying effects of TiO₂. Fourier transform infrared spectroscopy (FTIR) results suggested that modifiers such as Li₂O and TiO₂ disrupt the SiO₄ tetrahedral network by introducing non-bridging oxygens (NBOs) and weakening some bonds, thereby affecting network polymerization and structural rigidity. TiO₂ incorporation enhanced thermal stability, hardness, and compressive strength, with further gains after heat treatment due to TiO₂-induced crystallization. FTIR analysis confirmed structural modifications promoting a stronger glass network. These improvements yield glass-ceramics with mechanical and thermal properties comparable to dental enamel, enhancing their suitability for restorative applications.