The potential of magnesium phosphate cements in regenerative dentistry

In regenerative dentistry, the use of calcium phosphate cements (CPC) and MTA remains limited by prolonged setting times, low initial mechanical strength, and a lack of antimicrobial activity. These constraints hinder the effectiveness of treatments in endodontics and oral surgery requiring immediate stability. The authors of this review evaluate the potential of magnesium phosphate cements (MPC), fast-setting materials (5-10 min) offering a mechanically more robust alternative, with compressive strengths exceeding 50 to 100 MPa at 24 hours.

The objective of this work is to synthesize the chemical and biological properties and clinical applications of MPCs, while identifying the technological barriers to their clinical transfer. The authors examine the hypothesis that the controlled release of Mg²⁺ ions stimulates osteoblastic differentiation via the activation of RUNX2 and the Wnt/β-catenin pathway, while exerting an intrinsic antimicrobial action superior to MTA. A critical point of the analysis focuses on the management of exothermic setting reactions (>42-47 °C), potentially iatrogenic for pulp vitality, and on the replacement of ammonium phosphate with potassium to improve systemic biocompatibility.

Review methodology

This study is a critical Mini Review synthesizing current data on magnesium phosphate cements (MPC) compared to calcium phosphate cements (CPC) and MTA. The analysis focuses on the physicochemical and biological properties documented in the scientific literature.

The reported evaluation parameters and protocols include:

• Chemical synthesis: Analysis of the acid-base reaction between magnesium oxide (MgO) and phosphate salts (ammonium or potassium dihydrogen phosphate) producing a struvite matrix.
• Setting kinetics: Comparison of clinical setting times, established between 5 and 10 minutes for MPCs versus 15 to 60 minutes for CPCs.
• Mechanical tests: Measurement of compressive strength at 1 hour (~30 MPa) and at 24 hours (from 50 MPa to over 100 MPa for potassium-optimized systems).
• Thermal safety: Monitoring of the exothermic reaction with identification of a tissue risk threshold between 42 and 47 °C.
• Cellular response: Evaluation of alkaline phosphatase activity and RUNX2 expression under the influence of Mg²⁺ ion concentrations between 1 and 10 mM.

The review also lists strategies for modulating the reaction through the addition of specific adjuvants such as glucose, borax, boric acid, trimagnesium phosphate, calcium silicate, or chitosan.

Mechanical properties and setting kinetics

The authors of this review highlight a major difference in kinetics between magnesium phosphate cements (MPC) and conventional calcium phosphate cements (CPC). MPCs exhibit a clinical setting time of 5 to 10 minutes, compared to 15 to 60 minutes for CPCs, thus optimizing the surgical workflow.

*Values exceeding 100 MPa are achieved with optimized potassium phosphate-based formulations.

Biological response and cell signaling

The osteogenic potential of MPCs is primarily mediated by the sustained release of Mg²⁺ ions. Compiled data indicate that concentrations between 1 and 10 mM induce an upregulation of the RUNX2 gene and alkaline phosphatase (ALP). This biological activity is based on several intracellular signaling cascades identified in the synthesis:

• Activation of ion transport via TRPM7.
• Signalisation mediated by α5β1 integrin.
• Stimulation of IGFBP5.
• Activation of the Wnt/β-catenin pathway.

Thermal safety and antimicrobial activity

The setting reaction of MPCs is exothermic. The review reports a risk of irreversible thermal damage to the dental pulp and surrounding tissues if the temperature exceeds the critical threshold of 42–47 °C. The incorporation of retarders (borax) or substitution with potassium phosphate (KH₂PO₄) allows for moderating this exothermic profile and eliminating ammonia release.

From a microbiological perspective, MPCs exhibit superior intrinsic activity compared to MTA and calcium hydroxide (Ca(OH)₂) in planktonic models. This efficacy is attributed to pH alkalinity, high osmotic stress, and the disruption of bacterial membranes by Mg²⁺ ions.

Clinical analysis: unprecedented reactivity and mechanical resistance

This review highlights a technological breakthrough compared to conventional calcium phosphate cements (CPC). The major clinical benefit of these magnesium phosphate cements (MPC) lies in their fast setting kinetics (5 to 10 minutes) and their initial compressive strength, reaching 30 to 100 MPa within 24 hours. For the practitioner, these figures significantly outperform apatitic CPCs, which often only exhibit a strength of 1 MPa after one hour of setting.

Beyond mechanics, the bioactivity of MPCs is intrinsic. The release of Mg2+ ions activates key signaling pathways (RUNX2, Wnt/β-catenin, TRPM7) stimulating osteogenesis and angiogenesis via the upregulation of HIF-1α and VEGF. Unlike passive materials, MPCs act as dynamic scaffolds. Furthermore, their natural antimicrobial capacity — linked to alkaline pH and osmotic stress — proves superior to that of MTA and calcium hydroxide in reported study models.

Technical limits and clinical constraints

Despite these performances, the authors highlight critical limitations. The setting reaction is exothermic: without the addition of retarders (borax, boric acid), the temperature can exceed the tissue safety threshold (42–47 °C), posing a risk of necrosis in cases of direct pulp capping. Furthermore, formulations containing ammonium release ammonia vapors, making potassium-based systems clinically safer.

Finally, although preclinical evidence (in vitro on pulp stem cells and in vivo on animal models) is encouraging, the synthesis highlights a glaring lack of data from robust multicenter clinical trials in humans, which currently hinders their widespread adoption.

Summary of key results

This review highlights the mechanical superiority of magnesium phosphate cements (MPC), reaching 50 to over 100 MPa at 24h compared to only ~35 MPa for conventional CPCs. Their rapid setting kinetics (5-10 min) and bioactivity, mediated by the activation of RUNX2 and TRPM7 pathways by Mg²⁺ ions, promote early osteogenesis and vascularization.

In concrete terms, for the practitioner:

• Operating time savings: the complete setting in 5 to 10 minutes simplifies your surgical and endodontic procedures compared to the setting times of traditional cements (15-60 min).
• Immediate structural stability: their compressive strength exceeding that of cancellous bone makes them a choice option for filling defects requiring rapid mechanical support.
• Thermal caution: for pulp vitality, opt exclusively for potassium-based formulations or those with retardants, in order to avoid the risk of irreversible thermal injury related to the exothermic reactions of ammonium systems (>42°C).

Technical lexicon of magnesium phosphate cements (MPC)

Struvite: Crystalline matrix (NH₄MgPO₄·6H₂O) resulting from the acid-base reaction between magnesium oxide and ammonium phosphate, ensuring the initial structural cohesion of the cement.

TRPM7: Ion channel and membrane transporter whose activation by Mg²⁺ ions released by the material triggers the signaling cascades necessary for osteoblastic differentiation.

IGFBP5: Insulin-like growth factor binding protein whose activation is induced by MPCs, playing a key role in the osteogenic potential of the scaffold during tissue regeneration.

RUNX2: Essential transcription factor for the osteoblastic lineage, positively regulated by the magnesium concentration (1–10 mM) resulting from the controlled degradation of the cement.

Exothermic reaction: Critical heat release during cement setting (potentially exceeding 42–47 °C), requiring the incorporation of retarders such as borax to preserve the vitality of the dental pulp.

Potassium struvite: Alternative crystalline phase (KMgPO₄·6H₂O) formed in potassium-based systems, allowing the elimination of ammonia release and moderating the thermal profile of the reaction.

Bacterial plasmolysis: Intrinsic antimicrobial mechanism of action of MPCs caused by high osmolarity, leading to a disruption of the bacterial membrane without the use of exogenous antibiotics.

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