Glass science behind lithium silicate glass-ceramics.

OBJECTIVES: Lithium silicate-based glass ceramics have evolved as a paramount restorative material in restorative and prosthetic dentistry, exhibiting outstanding esthetic and mechanical performance. Along with subtractive machining techniques, this material class has conquered the market and satisfied the patients' needs for a long-lasting, excellent, and metal-free alternative for single tooth replacements and even smaller bridgework. Despite the popularity, not much is known about the material chemistry, microstructure and terminal behaviour. METHODS: This article combines a set of own experimental data with extensive review of data from literature and other resources. Starting at manufacturer claims on unique selling propositions, properties, and microstructural features, the aim is to validate those claims, based on glass science. Deep knowledge is mandatory for understanding the microstructure evolution during the glass ceramic process. RESULTS: Fundamental glass characteristics have been addressed, leading to formation of time-temperature-transformation (TTT) diagrams, which are the basis for kinetic description of the glass ceramic process. Nucleation and crystallization kinetics are outlined in this contribution as well as analytical methods to describe the crystalline fraction and composition qualitatively and quantitatively. In relation to microstructure, the mechanical performance of lithium silicate-based glass ceramics has been investigated with focus on fracture strength versus fracture toughness as relevant clinical predictors. CONCLUSION: Fracture toughness has been found to be a stronger link to initially outlined manufacturer claims, and to more precisely match ISO recommendations for clinical indications.

On the assignment of quartz-like LiAlSi2O6 - SiO2 solid solutions in dental lithium silicate glass-ceramics: Virgilite, high quartz, low quartz or stuffed quartz derivatives?

OBJECTIVES: Here we aim to provide a background on X-Ray Diffraction analysis of quartz-like crystal structures with varying amounts of Al3+ and Li+ substitution, existing confusions on their nomenclature and its implications for novel lithium silicate glass-ceramics. METHODS: We reviewed the literature dealing with modifications of the quartz crystal structure and their stuffed LiAlSi2O6 derivates, LiAlSi2O6 - SiO2 solid solutions, the terminology of such phases and criteria used to define the structure known as virgilite. Based on this information, we attempted to allocate the quartz-like phases found in CEREC TesseraTM, InitialTM LiSi Block and Amber® Mill in the range of LiAlO2 - SiO2 solid solutions. For this purpose, their lattice parameters obtained from Rietveld refinement were compared with the lattice parameters of members of the corresponding solid solutions with defined SiO2 molar fraction found in the literature. RESULTS: Based on the lattice parameters available for low quartz, high quartz and its stuffed derivatives, including LiAlSi2O6 and the mineral virgilite, a plot of the a- and c-parameters vs. the mol% SiO2 related to LiAlO2 was constructed with the literature data and the data found for the three dental lithium silicates. As per the definitions of virgilite as either LixAlxSi3-xO6, with 0.5 < x < 1 or especially as members of the LiAlSi2O6 - SiO2 solid-solution series with more than 50 mol% LiAlSi2O6, the crystal structures in CEREC TesseraTM, InitialTM LiSi Block and Amber® Mill failed to fall within the ranges of mol% SiO2 confined for virgilite. SIGNIFICANCE: Based on available literature and definitions, the quartz-like phases found in the three dental lithium silicates should be addressed as stuffed (probably low) quartz solid solutions instead of "virgilite". However determined by mineralogical practices, the term "virgilite" for parts of the LiAlSi2O6 - SiO2 solid solution is ambiguous and can be considered as arbitrary.

Scavenging of bacteria or bacterial products by magnetic particles functionalized with a broad-spectrum pathogen recognition receptor motif offers diagnostic and therapeutic applications.

Sepsis is a dysregulated host response of severe bloodstream infections, and given its frequency of occurrence and high mortality rate, therapeutic improvements are imperative. A reliable biomimetic strategy for the targeting and separation of bacterial pathogens in bloodstream infections involves the use of the broad-spectrum binding motif of human GP-340, a pattern-recognition receptor of the scavenger receptor cysteine rich (SRCR) superfamily that is expressed on epithelial surfaces but not found in blood. Here we show that these peptides, when conjugated to superparamagnetic iron oxide nanoparticles (SPIONs), can separate various bacterial endotoxins and intact microbes (E. coli, S. aureus, P. aeruginosa and S. marcescens) with high efficiency, especially at low and thus clinically relevant concentrations. This is accompanied by a subsequent strong depletion in cytokine release (TNF, IL-6, IL-1ß, Il-10 and IFN-γ), which could have a direct therapeutic impact since escalating immune responses complicates severe bloodstream infections and sepsis courses. SPIONs are coated with aminoalkylsilane and capture peptides are orthogonally ligated to this surface. The particles behave fully cyto- and hemocompatible and do not interfere with host structures. Thus, this approach additionally aims to dramatically reduce diagnostic times for patients with suspected bloodstream infections and accelerate targeted antibiotic therapy. STATEMENT OF SIGNIFICANCE: Sepsis is often associated with excessive release of cytokines. This aspect and slow diagnostic procedures are the major therapeutic obstacles. The use of magnetic particles conjugated with small peptides derived from the binding motif of a broad-spectrum mucosal pathogen recognition protein GP-340 provides a highly efficient scavenging platform. These peptides are not found in blood and therefore are not subject to inhibitory mechanisms like in other concepts (mannose binding lectine, aptamers, antibodies). In this work, data are shown on the broad bacterial binding spectrum, highly efficient toxin depletion, which directly reduces the release of cytokines. Host cells are not affected and antibiotics not adsorbed. The particle bound microbes can be recultured without restriction and thus be used directly for diagnostics.

Grasping the Lithium hype: Insights into modern dental Lithium Silicate glass-ceramics.

OBJECTIVES: Lithium-based glass-ceramics are currently dominating the landscape of dental restorative ceramic materials, with new products taking the market by storm in the last years. Though, the difference among all these new and old products is not readily accessible for the practitioner, who faces the dilemma of reaching a blind choice or trusting manufacturers' marketing brochures. To add confusion, new compositions tend to wear material terminologies inherited from vanguard dental lithium disilicates, disregarding accuracy. Here we aim to characterize such materials for their microstructure, crystalline fraction, glass chemistry and mechanical properties. METHODS: Eleven commercial dental lithium-based glass ceramics were evaluated: IPS e.max® CAD, IPS e.max® Press, Celtra® Duo, Suprinity® PC, Initial™ LiSi Press, Initial™ LiSi Block, Amber® Mill, Amber® Press, N!CE®, Obsidian® and CEREC Tessera™. The chemical composition of their base glasses was measured by X-Ray Fluorescence Spectroscopy (XRF) and Inductive Coupled Plasma Optical Emission Spectroscopy (ICP-OES), as well as the composition of their residual glass by subtracting the oxides bound in the crystallized fraction, characterized by X-Ray Diffraction (XRD) and Rietveld refinement, and quantified accurately using the G-factor method (QXRD). The crystallization behavior is revealed by differential scanning calorimetry (DSC) curves. Elastic constants are provided from Resonant Ultrasound Spectroscopy (RUS) and the fracture toughness measured by the Ball-on-Three-Balls method (B3B- K Ic). The microstructure is revealed by field-emission scanning electron microscopy (FE-SEM). RESULTS: The base glasses showed a wide range of SiO2 /Li2O ratios, from 1.5 to 3.0, with the degree of depolymerization dropping from ½ to 2/3 of the initial connectivity. Materials contained Li2SiO3+Li3PO4, Li2SiO3+Li3PO4+Li2Si2O5, Li2Si2O5+Li3PO4+ Cristobalite and/or Quartz and Li2Si2O5+Li3 PO4+LiAlSi2O6, in crystallinity degrees from 45 to 80 vol%. Crystalline phases could be traced to their crystallization peaks on the DSC curves. Pressable materials and IPS e.max® CAD were the only material showing micrometric phases, with N!CE® and Initial™ LiSi Block showing solely nanometric crystals, with the rest presenting a mixture of submicrometric and nanometric particles. Fracture toughness from 1.45 to 2.30 MPa√m were measured, with the linear correlation to crystalline fraction breaking down for submicrometric and nanometric crystal phases. SIGNIFICANCE: Dental lithium-based silicate glass-ceramics cannot be all put in the same bag, as differences exist in chemical composition, microstructure, crystallinity and mechanical properties. Pressable materials still perform better mechanically than CAM/CAM blocks, which loose resistance to fracture when crystal phases enter the submicrometric and nanometric range.

Toughening by revitrification of Li2SiO3 crystals in Obsidian® dental glass-ceramic.

As a predominantly lithium-metasilicate-containing glass-ceramic, Obsidian® (Glidewell Laboratories, USA) has a peculiar composition and microstructure among other dental lithium silicates, warranting an evaluation of the crystallization process to establish relationships between microstructural evolution and mechanical properties. Blocks of the pre-crystallized material were processed into slices measuring 12 × 12 × 1.5 mm3 and subjected to the mandatory crystallization firing by interruption the heating ramp at temperatures between 700 °C and 820 °C (dwell time between 0 min and 10 min). The crystallization peaks of the base and the pre-crystallized glass were obtained by differential scanning calorimetry (DSC). The coefficient of thermal expansion and the glass transition temperature were derived from differential thermal analysis (DTA). X-ray diffraction (XRD) was performed to quantify and characterize the crystal phase fraction, whose microstructural changes were visualised using FE-SEM. The ball-on-three-balls surface crack in flexure method was used to track the evolution of fracture toughness. The microstructural evolution during crystallization firing was characterized by two regimes of growth: (i) the progressive revitrification (dissolution) of the 5 µm-sized Li2SiO3 polycrystals manifested at the boundaries of nanometric single coherent scattering domains (CSDs); (ii) the non-isothermal period is marked by an Ostwald ripening process characterized by the growth of the single crystalline structures into 0.5 µm polycrystals. The decrease in the crystal fraction of Li2SiO3 crystals from 41 vol.% to 37 vol.% is accompanied by the formation of a small amount of Li3PO4 (6 vol.%), maintaining the total crystal phase fraction mostly constant. The KIc accompanied the reverse trend of crystallinity, departing from 1.63 ± 0.02 MPa√m at the pre-crystallized stage to 1.84 ± 0.06 MPa√m after 10 min at 820 °C in a linear trend. Toughening appeared counter-intuitive in view of the decreasing crystal fraction and size, to rather relate to the relaxation of the residual stresses in the interstitial glass due to the spheroidization of the initially anisotropic, elongated Li2SiO3 crystals into round, nearly equiaxed particles, as let suggest from the disappearance of the extensive microcracking.

Synthesis, Characterization, Antibacterial Properties, and In Vitro Studies of Selenium and Strontium Co-Substituted Hydroxyapatite.

In this study, as a measure to enhance the antimicrobial activity of biomaterials, the selenium ions have been substituted into hydroxyapatite (HA) at different concentration levels. To balance the potential cytotoxic effects of selenite ions (SeO32-) in HA, strontium (Sr2+) was co-substituted at the same concentration. Selenium and strontium-substituted hydroxyapatites (Se-Sr-HA) at equal molar ratios of x Se/(Se + P) and x Sr/(Sr + Ca) at (x = 0, 0.01, 0.03, 0.05, 0.1, and 0.2) were synthesized via the wet precipitation route and sintered at 900 °C. The effect of the two-ion concentration on morphology, surface charge, composition, antibacterial ability, and cell viability were studied. X-ray diffraction verified the phase purity and confirmed the substitution of selenium and strontium ions. Acellular in vitro bioactivity tests revealed that Se-Sr-HA was highly bioactive compared to pure HA. Se-Sr-HA samples showed excellent antibacterial activity against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus carnosus) bacterial strains. In vitro cell-material interaction, using human osteosarcoma cells MG-63 studied by WST-8 assay, showed that Se-HA has a cytotoxic effect; however, the co-substitution of strontium in Se-HA offsets the negative impact of selenium and enhanced the biological properties of HA. Hence, the prepared samples are a suitable choice for antibacterial coatings and bone filler applications.

Effect of sintering parameters on phase evolution and strength of dental lithium silicate glass-ceramics.

OBJECTIVE: With the establishment of CAD/CAM technology, competing lithium silicate based formulations have been introduced for clinical use, but little is known about their phase composition. Here we investigate a commercially available SiO2-Al2O3-K2O-Li2O-P2O5-ZrO2 system to evaluate the crystal phase evolution during the second heat treatment by changing the main crystallization parameters. METHODS: With a focus on the final stage of crystallization, we characterized the dimensional changes in the crystallographic structure of the residual Li2SiO3 and the lithium orthophosphate (Li3PO4) phases with variations in crystallization parameters, i.e. time, temperature and cooling rate over the range of the glass transition temperature Tg. The phase fractions (crystalline and glass) and the sizes of coherent scattering domains (CSDs) were resolved by means of quantitative X-Ray Diffraction using Rietveld refinement combined with an external standard method (G-factor). Biaxial flexure testing was conducted to evaluate the influence of crystallization parameters on the characteristic strength and natural defect distribution. RESULTS: An increase in crystallization temperature from 840 to 880°C resulted in a significant reduction of the Li2Si2O5 content, which indicated a reversion of the Li2SiO3 to Li2Si2O5 phase transformation. Reduction to 800°C had no significant effect. Furthermore, the CSD sizes of Li2SiO3 and Li3PO4 continuously increased with increasing temperature, which was accompanied by an increase in strength parameters. Reducing the cooling rate over the range of Tg resulted in an increased strength at low failure probabilities. SIGNIFICANCE: These findings help to establish recommendations for adjustment of the crystallization protocol, which has potential to increase the clinical reliability of the material investigated.

Setting Mechanism of a CDHA Forming α-TCP Cement Modified with Sodium Phytate for Improved Injectability.

A calcium deficient hydroxyapatite (CDHA) forming cement with a bimodal grain size distribution, composed of α-TCP and fine grained CDHA at a weight ratio of 9:1, was modified by the addition of sodium phytate (IP6) in variable amounts ranging from 0.25 to 2 wt.%, related to the powder content. The injectability of the cement paste was drastically increased by the IP6 addition, independent of the amount of added IP6. Additionally, the cement paste viscosity during the first minutes decreased. These effects could be clearly related to a slightly more negative zeta potential. Furthermore, IP6 was shown to strongly retard the setting reaction, as can be seen both in the calorimetry and X-ray diffraction measurements. In addition, octacalcium phosphate (OCP) was identified as a further setting product. All measurements were performed at 23 °C and 37 °C to assess the effect of temperature on the setting reaction for both clinical handling by the surgeon and the final hardening in the bone defect.

Crack-healing during two-stage crystallization of biomedical lithium (di)silicate glass-ceramics.

OBJECTIVE: The study is aimed to evaluate the two single commercially available two-step lithium-(di)silicate systems by analyzing their parent glass composition and studying the quantitative crystalline and glass phase evolution during the second stage heat-treatment. The mechanical repercussions of the crystallization firing were evaluated using strength and fracture toughness tests. METHODS: XRF and ICP-OES were used to determine the oxide composition of the parent glasses in Suprinity PC (Vita Zahnfabrik) and IPS e.max CAD (Ivoclar-Vivadent). The crystalline phase of both materials was determined by quantitative XRD and the G-factor method in the partially and post-crystallization states. The oxide composition of the residual glass phase was derived by subtracting the chemistry of the crystalline phase fractions from the parent glass composition. Mechanical testing of biaxial flexural strength and fracture toughness were used to demonstrate how crack-like defects behave during crystallization. RESULTS: The two tested lithium (di)silicate systems showed strong differences in oxide composition of the parent glass. This showed to influence the transformation of lithium metasilicate in lithium disilicate, with the former remaining in high vol.% fraction in the post-crystallization Suprinity PC. In IPS e.max CAD cristobalite precipitated at the surface during the second-heat treatment. Strength and fracture toughness tests revealed that crack in both materials, whether introduced by grinding or indentation, heal during the crystallization firing. Cristobalite seemed to have contributed to a surface strengthening effect in IPS e.max CAD. SIGNIFICANCE: Accurate crystalline phase quantification aids in the determination of the residual glass composition in dental glass-ceramics. For both systems crystallization firing induced healing of cracks generated by CAM grinding.

Phase-specific bioactivity and altered Ostwald ripening pathways of calcium carbonate polymorphs in simulated body fluid.

Calcium carbonate is an abundant biomineral, and already archeological records demonstrate its bioactivity and applicability for osseo-integrative implants. Its solubility, which is generally higher than those of calcium phosphates, depends on its polymorph turning calcium carbonate into a promising biomaterial with tunable bioresorption rate. However, the phase-dependent bioactivity of calcium carbonate, i.e., its osteoconductivity, is still insufficiently characterized. In this study, we address this issue by monitoring the behavior of the four most important calcium carbonate phases, i.e., calcite, aragonite, vaterite, and amorphous calcium carbonate, in simulated body fluid solution at 37 °C. Our results demonstrate that the thermodynamically stable calcite phase is essentially inert. In contrast, the metastable phases aragonite and vaterite are bioactive, thus promoting the formation of calcium phosphate. Amorphous calcium carbonate (ACC) shows prominent bioactivity accompanied by pronounced redissolution processes. Mg-stabilized ACC was additionally tested since its increased stability eases formulation and handling in future applications. It is highly bioactive and, moreover, the additional release of Mg promotes cell viability. Overall, our results demonstrate that bioactivity of calcium carbonate is phase-dependent, allowing tailored response and bioactivity of future calcareous biomaterials. Our results also reveal that phosphate ions strongly interfere with Ostwald-Lussac step ripening of calcium carbonate, kinetically stabilizing metastable polymorphs such as vaterite and aragonite; this is a distinctive feature of the calcium carbonate mineral system which clearly has to be considered in future applications of calcium carbonate as a bioceramic.

Hydration mechanism of a calcium phosphate cement modified with phytic acid.

Calcium phosphate cements composed of ß-tricalcium phosphate (ß-TCP) and phosphoric acid were modified by addition of 5, 10, 12.5, 15 and 20 wt% phytic acid (IP6) related to the ß-TCP content and compared to a reference containing 0.5 M citric acid monohydrate solution as setting regulator. The hydration reaction of these cements was investigated by isothermal calorimetry and in-situ X-ray diffraction at 23 °C and 37 °C. The cements were further characterized with respect to their injectability, rheology, zeta potential and time-resolved compressive strength development. Injectability was strongly improved by IP6 addition, while the maximum effect was already reached by the addition of 5 wt% IP6. This could be clearly related to an increase of the negative zeta potential leading to a mutual repulsion of cement particles. A further increase of the IP6 content had a detrimental effect on initial paste viscosity and shifted the gelation point to earlier time points. IP6 was further proven to act as a retarder for the cement setting reaction, whereas the effect was stronger for higher IP6 concentrations. Additionally, IP6 favoured the formation of monetite instead of brushite and a better mechanical performance compared to the IP6 free reference cement. STATEMENT OF SIGNIFICANCE: Calcium phosphate cements (CPCs) are clinically applied for bone repair due to their excellent biocompatibility and bone regeneration capacity. A deep understanding of the setting mechanism is the prerequisite for the targeted fabrication and application of such bone cements, whereas setting characteristics are usually adjusted by additives. Here, novel injectable CPC formulations were developed by modifying a cement composed of ß-tricalcium phosphate and phosphoric acid with phytic acid (IP6). A detailed investigation of the setting mechanism of the IP6 modified CPCs is provided, which demonstrated the effectiveness of IP6 as setting regulator to adjust the reaction time and kind of setting product. Additionally, the high surface charge of cement particles after IP6 addition was effective in dispersing cement particles leading to low viscous cement pastes, which can be directly applied through a syringe for minimal invasive surgery.

Hydration mechanism of partially amorphized ß-tricalcium phosphate.

Calcium phosphate cements (CPCs) are applied as bone cements due to their excellent biocompatibility. In the present study, the quantitative phase content development during hydration of partially amorphized ß-tricalcium phosphate (ß-TCP) within the first 24h was investigated by in-situ X-ray diffraction (XRD) combined with the G-factor method, an external standard method. The quantity of amorphous phase (ATCP) in the powders was determined by the G-factor method. The hydration model established for partially amorphized ß-TCP indicates that ATCP reacted first, followed by the hydration of a small fraction of crystalline ß-TCP starting after some h. Consequently, hydration resulted in biphasic samples composed of calcium deficient hydroxyapatite (CDHA) and crystalline ß-TCP. The ratio wt%(CDHA)/wt%(ß-TCP) after 24h hydration was adjustable by the initial ATCP content. The crystallinity of CDHA was nearly independent of the ATCP content. Since the biological degradability of CDHA and ß-TCP differ, the degradation performance of the set cements is expected to be adjustable by varying the ATCP content. The present study provided a basic understanding of the hydration mechanism of partially amorphized ß-TCP, which is the prerequisite for the development of applicable CPC formulations. STATEMENT OF SIGNIFICANCE: Calcium phosphate cements (CPCs) are medically applied for bone repair due to their excellent biocompatibility. ß-Tricalcium phosphate (ß-TCP), which is hardly reactive in water in its crystalline state, was previously shown to be activatable by partial amorphization. This provides potential for the development of new CPCs setting to biphasic samples composed of ß-TCP and calcium deficient hydroxyapatite (CDHA). The degradation performance of these cements is expected to be adjustable by varying the ratio of CDHA to ß-TCP. In the present study, the so far unknown setting mechanism of partially amorphized ß-TCP was investigated in detail. The results contribute to the basic understanding of the hydration of partially amorphized ß-TCP, which is important for the targeted development of new cement formulations.

Reaction kinetics of dual setting α-tricalcium phosphate cements.

Addition of ductile polymers to calcium-deficient hydroxyapatite (CDHA)-forming bone cements based on α-tricalcium phosphate (α-TCP) is a promising approach to improve the mechanical performance of α-TCP cements and extend their application to load-bearing defects, which is else impeded by the brittleness of the hardened cement. One suitable polymer is poly-(2-hydroxyethylmethacrylate) (p-HEMA), which forms during cement setting by radical polymerisation of the monomer. In this study the hydration kinetics and the mechanical performance of α-TCP cements modified with addition of different HEMA concentrations (0-50 wt% in the cement liquid) was investigated by quantitative in situ XRD and four-point bending tests. Morphology of CDHA crystals was monitored by scanning electron microscopy. The hydration of α-TCP to CDHA was increasingly impeded and the visible crystal size of CDHA increasingly reduced with increasing HEMA concentration. Modification of the cements by adding 50 wt% HEMA to the cement liquid changed the brittle performance of the hardened cement to a pseudoplastic behaviour, reduced the flexural modulus and increased the work of fracture, while lower HEMA concentrations had no significant effect on these parameters. In such a composite, the extent of CDHA formation was considerably reduced (34.0 ± 1.8 wt% CDHA with 50 % HEMA compared to 54.1 ± 2.4 wt% CDHA in the reference formed after 48 h), while the general reaction kinetics were not changed. In conclusion, while the extent of CDHA formation was decreased, the mechanical properties were noticeably improved by addition of HEMA. Hence, α-TCP/HEMA composites might be suitable for application in some load-bearing defects and have adequate properties for mechanical treatment after implantation, like insertion of screws.

Calorimetry investigations of milled α-tricalcium phosphate (α-TCP) powders to determine the formation enthalpies of α-TCP and X-ray amorphous tricalcium phosphate.

One α-tricalcium phosphate (α-TCP) powder was either calcined at 500°C to obtain fully crystalline α-TCP or milled for different durations to obtain α-TCP powders containing various amounts of X-ray amorphous tricalcium phosphate (ATCP). These powders containing between 0 and 71wt.% ATCP and up to 2.0±0.1wt.% ß-TCP as minor phase were then hydrated in 0.1M Na2HPO4 aqueous solution and the resulting heat flows were measured by isothermal calorimetry. Additionally, the evolution of the phase composition during hydration was determined by in situ XRD combined with the G-factor method, an external standard method which facilitates the indirect quantification of amorphous phases. Maximum ATCP hydration was reached after about 1h, while that of crystalline α-TCP hydration occurred between 4 and 11h, depending on the ATCP content. An enthalpy of formation of -4065±6kJ/mol (T=23°C) was calculated for ATCP (Ca3(PO4)2), while for crystalline α-TCP (α-Ca3(PO4)2) a value of -4113±6kJ/mol (T=23°C) was determined.

Effect of amorphous phases during the hydraulic conversion of α-TCP into calcium-deficient hydroxyapatite.

Powders of α-tricalcium phosphate (α-TCP), which readily react with water to form calcium-deficient hydroxyapatite (CDHA), are frequently used in bone cements. As, for clinical applications, it is important to adjust the setting reaction of the cements to a reasonable reaction time, exact knowledge of the hydration mechanism is essential. It is known that prolonged milling results in partial amorphization of α-TCP powders and that dissolution of the amorphous phase significantly accelerates the hydration, but it is not clear yet when the amorphous phase reacts in comparison to the crystalline α-TCP. Therefore the aim of this study was to investigate the development of quantitative phase content of α-TCP samples during hydration. For this purpose, three α-TCP powders, containing 0, 16 and 71wt.% of amorphous phase (ATCP), were mixed with either deionized water or a 0.1M Na2HPO4 aqueous solution. The crystalline evolution of the paste was assessed quantitatively during the first 48h of hydration at 23°C by G-factor quantification. The present investigations demonstrate that ATCP reacted earlier than crystalline α-TCP. The results also suggest the formation of an X-ray amorphous phase during the hydraulic conversion formation of α-TCP into CDHA.