Methodologies for measuring the setting times of mineral trioxide aggregate and Portland cement products used in dentistry

Impact of Particle Size on the Setting Behavior of Tricalcium Silicate: A Comparative Study Using ISO 6876 Indentation Testing and Isothermal Induction Calorimetry

This study examines the impact of particle size on the setting behavior of tricalcium silicate powders. The setting behavior was evaluated using ISO 6876 indentation testing and isothermal induction calorimetry techniques. The objective was to compare the outcomes obtained from these methods and establish a correlation between particle size and setting characteristics. The cement pastes were manually mixed with a water-to-solid ratio of 0.66 for conducting indentation tests according to ISO 6876, while calorimetry measurements were performed using isothermal (conduction) calorimetry at room temperature. The findings demonstrate a significant influence of smaller particle sizes on accelerating the hydration process of cement pastes, resulting in a reduction of setting time by up to 24%. Moreover, the final setting times obtained through the indentation method closely approximate the inflection points of the acceleration curves acquired by calorimetry, with time deviations of less than 12% regardless of particle size.

Rheological Properties and Setting Kinetics of Bioceramic Hydraulic Cements: ProRoot MTA versus RS

Hydraulic calcium silicate-based cements (HCSCs) have become a superior bioceramic alternative to epoxy-based root canal sealers in endodontics. A new generation of purified HCSCs formulations has emerged to address the several drawbacks of original Portland-based mineral trioxide aggregate (MTA). This study was designed to assess the physio-chemical properties of a ProRoot MTA and compare it with newly formulated RS+, a synthetic HCSC, by advanced characterisation techniques that allow for in situ analyses. Visco-elastic behaviour was monitored with rheometry, while phase transformation kinetics were followed by X-ray diffraction (XRD), attenuated total reflectance Fourier transform infrared (ATR-FTIR), and Raman spectroscopies. Scanning electron microscopy with energy-dispersive spectroscopy, SEM-EDS, and laser-diffraction analyses was performed to evaluate the compositional and morphological characteristics of both cements. While the kinetics of surface hydration of both powders, when mixed with water, were comparable, an order of magnitude finer particle size distribution of RS+ coupled with the modified biocompatible formulation proved pivotal in its ability to exert predictable viscous flow during working time, and it was more than two times faster in viscoelastic-to-elastic transition, reflecting improved handling and setting behaviour. Finally, RS+ could be completely transformed into hydration products, i.e., calcium silicate hydrate and calcium hydroxide, within 48 h, while hydration products were not yet detected by XRD in ProRoot MTA and were obviously bound to particulate surface in a thin film. Because of the favourable rheological and faster setting kinetics, synthetic, finer-grained HCSCs, such as RS+, represent a viable option as an alternative to conventional MTA-based HCSCs for endodontic treatments.

Multifactorial Analysis of Endodontic Microsurgery Using Finite Element Models

Background: The present study aimed to classify the relative contributions of four biomechanical factors—the root-end filling material, the apical preparation, the root resection length, and the bone height—on the root stresses of the resected premolar. Methods: A design of experiments approach based on a defined subset of factor combinations was conducted to calculate the influence of each factor and their interactions. Sixteen finite element models were created and analyzed using the von Mises stress criterion. The robustness of the design of experiments was evaluated with nine supplementary models. Results: The current study showed that the factors preparation and bone height had a high influence on root stresses. However, it also revealed that nearly half of the biomechanical impact was missed without considering interactions between factors, particularly between resection and preparation. Conclusions: Design of experiments appears to be a valuable strategy to classify the contributions of biomechanical factors related to endodontics. Imagining all possible interactions and their clinical impact is difficult and can require relying on one’s own experience. This study proposed a statistical method to quantify the mechanical risk when planning apicoectomy. A perspective could be to integrate the equation defined herein in future software to support decision-making.

Incorporation of amoxicillin-loaded microspheres in mineral trioxide aggregate cement: an in vitro study

Objectives

In this study, we investigated the potential of amoxicillin-loaded polymeric microspheres to be delivered to tooth root infection sites via a bioactive reparative cement.

Materials and Methods

Amoxicillin-loaded microspheres were synthesized by a spray-dray method and incorporated at 2.5% and 5% into a mineral trioxide aggregate cement clinically used to induce a mineralized barrier at the root tip of young permanent teeth with incomplete root development and necrotic pulp. The formulations were modified in liquid:powder ratios and in composition by the microspheres. The optimized formulations were evaluated in vitro for physical and mechanical eligibility. The morphology of microspheres was observed under scanning electron microscopy.

Results

The optimized cement formulation containing microspheres at 5% exhibited a delayed-release response and maintained its fundamental functional properties. When mixed with amoxicillin-loaded microspheres, the setting times of both test materials significantly increased. The diametral tensile strength of cement containing microspheres at 5% was similar to control. However, phytic acid had no effect on this outcome (p > 0.05). When mixed with modified liquid:powder ratio, the setting time was significantly longer than that original liquid:powder ratio (p < 0.05).

Conclusions

Lack of optimal concentrations of antibiotics at anatomical sites of the dental tissues is a hallmark of recurrent endodontic infections. Therefore, targeting the controlled release of broad-spectrum antibiotics may improve the therapeutic outcomes of current treatments. Overall, these results indicate that the carry of amoxicillin by microspheres could provide an alternative strategy for the local delivery of antibiotics for the management of tooth infections.

Manoeuvrability and biocompatibility of endodontic tricalcium silicate-based putties

OBJECTIVES

The present study evaluated the indentation depth, storage modulus and biocompatibility of an experimental endodontic putty designed for endodontic perforation repair and direct pulp-capping (NeoPutty). The results were compared with the properties associated with the commercially available EndoSequence BC RRM Putty (ES Putty).

METHODS

Indentation depth was measured by a profilometer following indentation with the 1/4 lb Gilmore needle. Elastic modulus was evaluated using a strain-controlled rheometer. The effects of eluents derived from these two putties were examined on the viability and proliferation of human dental pulp stem cells (hDPSCs) and human periodontal ligament fibroblasts (hPDLFs), before (1 st testing cycle) and after complete setting (2nd testing cycle).

RESULTS

The ES Putty became more difficult to ident and acquired a larger storage modulus after exposure to atmospheric moisture. Biocompatibility results indicated that both putties were relatively more cytotoxic than the bioinert Teflon negative control, but much less cytotoxic than the zinc oxide-eugenol cement negative control. NeoPutty was less cytotoxic than ES putty in the 1st testing cycle, particularly with hDPSCs. Both putties exhibited more favourable cytotoxicity profiles after complete setting.

CONCLUSIONS

NeoPutty has a better window of maneuverability after exposure to atmospheric moisture. From an in vitro cytotoxicity perspective, the NeoPutty may be considered more biocompatible than ES putty.

CLINICAL SIGNIFICANCE

The experimental NeoPutty is biocompatible and is capable of reducing the frustration of shortened shelf life when jar-stored endodontic putties are exposed to atmospheric moisture during repeated opening of the lid for clinical retrieval.

Rheological Characterization as an Alternative Method to Indentation for Determining the Setting Time of Restorative and Endodontic Cements

This study explored an alternative approach using rheology to assess setting time. The following cements were tested: ProRoot^® MTA (Dentsply, Tulsa, OK, USA), Biodentine^® (Septodont, Saint Maur des Fosses, France), Fuji VII^®, FujiVII^® EP, and Fuji IX^® (from GC Corporation, Tokyo, Japan), RealSeal SE™ Sealer (SybronEndo, Amersfoort, The Netherlands), AH 26^® and AH Plus (both from Dentsply DeTrey, Konstanz, Germany). Freshly mixed cements were placed into a strain-controlled rheometer (1 rad·s^-1 with an applied strain of 0.01%). From measurements of elastic modulus over time, the time taken to reach 90% of the plateau elastic modulus (designated as the setting time) was determined for each cement. In increasing order, the setting times were as follows: Fuji VII EP 3.3 min, Fuji VII 3.6 min, Fuji IX 3.7 min, ProRoot MTA 5.1 min, Biodentine 15.9 min, RealSeal 22.2 min, AH Plus 5933 min, and AH 26 5067 min. However, ProRoot MTA did not yield reliable results. The time to reach the 90% plateau elastic modulus correlates well with the setting time of glass ionomer cements and Biodentine. Using this approach gives much longer setting times for endodontic sealers than previously recognized.

Mineral Trioxide Aggregate-A Review of Properties and Testing Methodologies

Mineral trioxide aggregate (MTA) restoratives and MTA sealers are commonly used in endodontics. Commonly referenced standards for testing of MTA are ISO 6876, 9917-1 and 10993. A PubMed search was performed relating to the relevant tests within each ISO and "mineral trioxide aggregate". MTA restoratives are typically tested with a mixture of tests from multiple standards. As the setting of MTA is dependent upon hydration, the results of various MTA restoratives and sealers are dependent upon the curing methodology. This includes physical properties after mixing, physical properties after setting and biocompatibility. The tests of flow, film thickness, working time and setting time can be superseded by rheology as it details how MTA hydrates. Physical property tests should replicate physiological conditions, i.e. 37 °C and submerged in physiological solution. Biocompatibility tests should involve immediate placement of samples immediately after mixing rather than being cured prior to placement as this does not replicate clinical usage. Biocompatibility tests should seek to replicate physiological conditions with MTA tested immediately after mixing.

Classification and Nomenclature of Commercial Hygroscopic Dental Cements

Objective

Under the Global Medical Device Nomenclature (GMDN) system, the newly introduced term 'hygroscopic dental cement' (HDC) encompasses MTA as well as cements based on bioceramics, calcium silicate or calcium sulphate. Many HDCs have a long history of use in dentistry. There is a need for a consistent, logical and informed approach to the nomenclature of traditional and novel HDCs.

Methods

Commercial manufacturers of HDC were contacted requesting information on the compositions of products. Manufacturers that were unknown to the authors, that were unable to be contacted, that wished to be excluded from this paper, or that did not send their information on compositions in due time were not included.

Results

The compositions of commercial HDCs include various hybrids of calcium silicates, calcium aluminates, calcium phosphates, calcium sulphate as well as zinc sulphates. Furthermore, there are variations in the radiopacifier as well as additives that change the handling or setting processes.

Conclusion

The inclusion of different additives to HDCs enables variation in handling properties such that they now exist as distinct putties and sealers as well as cements.

The influence of particle size and curing conditions on testing mineral trioxide aggregate cement

Objectives: To assess the effects on curing conditions (dry versus submerged curing) and particle size on the compressive strength (CS) and flexural strength (FS) of set MTA cement.

Materials and methods: Two different Portland cements were created, P1 and P2, with P1 < P2 in particle size. These were then used to create two experimental MTA products, M1 and M2, with M1 < M2 in particle size. Particle size analysis was performed according to ISO 13320. The particle size at the 90th percentile (i.e. the larger particles) was P1: 15.2 μm, P2: 29.1 μm, M1: 16.5 μm, and M2: 37.1 μm. M2 was cured exposed to air, or submerged in fluids of pH 5.0, 7.2 (PBS), or 7.5 for 1 week. CS and FS of the set cement were determined using a modified ISO 9917-1 and ISO 4049 methods, respectively. P1, P2, M1 and M2 were cured in PBS at physiological pH (7.2) and likewise tested for CS and FS.

Results: Curing under dry conditions gave a significantly lower CS than when cured in PBS. There was a trend for lower FS for dry versus wet curing. However, this did not reach statistical significance. Cements with smaller particle sizes showed greater CS and FS at 1 day than those with larger particle sizes. However, this advantage was lost over the following 1–3 weeks.

Conclusions: Experiments that test the properties of MTA should cure the MTA under wet conditions and at physiological pH.