Comparing the effects of mineral trioxide aggregate and calcium enriched mixture on neuronal cells using an electrophysiological approach

Abstract

Introduction: The main goal of this ex vivo study was to assess and compare the cellular and electrophysiological effects of two dental biomaterials, white mineral trioxide aggregate (WMTA) and calcium enriched mixture (CEM) cement, on neuronal cell excitability and electrical properties.

Materials and methods: A conventional intracellular current clamp technique was used to study the cellular effects of WMTA and CEM on the excitability, firing and the shape of action potential of neuronal soma membrane of F(1) nerve cells. The dental biomaterials were prepared according to the manufacturers' directions and were applied to the bathing media and 0.05 mL of total mixture of each dental material at a distance of 3 mm from the cells.

Results: Findings indicated that exposure to both dental biomaterials shifted the irregular high frequency firing type observed in control conditions to a more regular low frequency firing pattern. Neuronal exposure to WMTA, but not CEM, significantly hyperpolarized the cell resting membrane potential. Both treatments significantly influenced the duration and the amplitude of action potentials. Extracellular application of either CEM or WMTA caused a significant increase in the after hyperpolarization (AHP) amplitude and AHP area, but the potentiating effect of WMTA was more effective than CEM.

Conclusion: Treatment with WMTA or CEM resulted in a profound alteration in the firing behaviour of F(1) cells and changed the AP characteristics. Both dental biomaterials reduced the neuronal activity possibly through enhancement of K(+) outward current. This may possibly explain the positive mechanisms of these biomaterials in regenerative endodontics, though further research is needed for such a conclusion.

Keywords: Action Potential; CEM Cement; Calcium Enriched Mixture; Helix Aspersa; Intracellular Recording; MTA; Neuronal; White Mineral Trioxide Aggregate.

Figure 1

Measurements of action potential properties; RMP, resting membrane potential; AP Amplitude, Action potential and duration; AHP, after hyperpolarizations amplitude and area under the AHP

Figure 2

Effect of WMTA and CEM on firing pattern of F₁ neurons; Intracellular recordings from F₁ neurons show firing pattern in control condition (upper panel) and after extracellular application of CEM (middle panel) and WMTA (lower panel)

Figure 3

Effects of bath applications of CEM and MTA on action potential characteristics. Average data (mean ± SEM) showing the effect of CEM and WMTA on firing frequency; A) resting membrane potential; B) action potential duration; C) action potential amplitude; D) after hyperpolarizations (AHP) amplitude; E) and AHP area; F) One-way ANOVA was used to analyze the data. *,**,*** = significantly different (P<0.05, P<0.01, P<0.001, respectively) from the control; ‡‡ = significant difference (P<0.01) between CEM and WMTA

Figure 4

Effect of CEM and WMTA on the AHP amplitude recorded in low Ca²⁺ Ringer solution; A) Superimposed action potentials (truncated) recorded in normal Ringer and in low Ca²⁺ Ringer solution (left panel) and in the presence of CEM and WMTA application (right panel) into the bating solution containing low Ca²⁺ concentration; B) Bar graph summarising the effects of CEM and WMTA on the AHP amplitude measured in low Ca²⁺ concentration Ringer)