Ashraf A. Eid

In vitro osteogenic/dentinogenic potential of an experimental calcium aluminosilicate cement.

INTRODUCTION Calcium aluminosilicate cements are fast-setting, acid-resistant, bioactive cements that may be used as root-repair materials. This study examined the osteogenic/dentinogenic potential of an experimental calcium aluminosilicate cement (Quick-Set) by using a murine odontoblast-like cell model. METHODS Quick-Set and white ProRoot MTA (WMTA) were mixed with the proprietary gel or deionized water, allowed to set completely in 100% relative humidity, and aged in complete growth medium for 2 weeks until rendered non-cytotoxic. Similarly aged Teflon disks were used as negative control. The MDPC-23 cell line was used for evaluating changes in mRNA expressions of genes associated with osteogenic/dentinogenic differentiation and mineralization (quantitative reverse transcription polymerase chain reaction), alkaline phosphatase enzyme production, and extracellular matrix mineralization (alizarin red S staining). RESULTS After MDPC-23 cells were incubated with the materials in osteogenic differentiation medium for 1 week, both cements showed up-regulation in ALP and DSPP expression. Fold increases in these 2 genes were not significantly different between Quick-Set and WMTA. Both cements showed no statistically significant up-regulation/down-regulation in RUNX2, OCN, BSP, and DMP1 gene expression compared with Teflon. Alkaline phosphatase activity of cells cultured on Quick-Set and WMTA were not significantly different at 1 week or 2 weeks but were significantly higher (P < .05) than Teflon in both weeks. Both cements showed significantly higher calcium deposition compared with Teflon after 3 weeks of incubation in mineralizing medium (P < .001). Differences between Quick-Set and WMTA were not statistically significant. CONCLUSIONS The experimental calcium aluminosilicate cement exhibits similar osteogenic/dentinogenic properties to WMTA and may be a potential substitute for commercially available tricalcium silicate cements.

Ability of new obturation materials to improve the seal of the root canal system: A review

New obturation biomaterials have been introduced over the past decade to improve the seal of the root canal system. However, it is not clear whether they have really produced a three-dimensional impervious seal that is important for reducing diseases associated with root canal treatment. A review of the literature was performed to identify models that have been employed for evaluating the seal of the root canal system. In vitro and in vivo models are not totally adept at quantifying the seal of root canals obturated with classic materials. Thus, one has to resort to clinical outcomes to examine whether there are real benefits associated with the use of recently introduced materials for obturating root canals. However, there is no simple answer because endodontic treatment outcomes are influenced by a host of other predictors that are more likely to take precedence over the influence of obturation materials. From the perspective of clinical performance, classic root filling materials have stood the test of time. Because many of the recently introduced materials are so new, there is not enough evidence yet to support their ability to improve clinical performance. This emphasizes the need to translate anecdotal information into clinically relevant research data on new biomaterials.

Wall shear stress effects of different endodontic irrigation techniques and systems

OBJECTIVES This study examined débridement efficacy as a result of wall shear stresses created by different irrigant delivery/agitation techniques in an inaccessible recess of a curved root canal model. METHODS A reusable, curved canal cavity containing a simulated canal fin was milled into mirrored titanium blocks. Calcium hydroxide (Ca(OH)2) paste was used as debris and loaded into the canal fin. The titanium blocks were bolted together to provide a fluid-tight seal. Sodium hypochlorite was delivered at a previously-determined flow rate of 1 mL/min that produced either negligible or no irrigant extrusion pressure into the periapex for all the techniques examined. Nine irrigation delivery/agitation techniques were examined: NaviTip passive irrigation control, Max-i-Probe(®) side-vented needle passive irrigation, manual dynamic agitation (MDA) using non-fitting and well-fitting gutta-percha points, EndoActivator™ sonic agitation with medium and large points, VPro™ EndoSafe™ irrigation system, VPro™ StreamClean™ continuous ultrasonic irrigation and EndoVac apical negative pressure irrigation. Débridement efficacies were analysed with Kruskal-Wallis ANOVA and Dunns multiple comparisons tests (α=0.05). RESULTS EndoVac was the only technique that removed more than 99% calcium hydroxide debris from the canal fin at the predefined flow rate. This group was significantly different (p<0.05) from the other groups that exhibited incomplete Ca(OH)2 removal. CONCLUSIONS The ability of the EndoVac system to significantly clean more debris from a mechanically inaccessible recess of the model curved root canal may be caused by robust bubble formation during irrigant delivery, creating higher wall shear stresses by a two-phase air-liquid flow phenomenon that is well known in other industrial débridement systems.

Periapical pressures developed by nonbinding irrigation needles at various irrigation delivery rates

INTRODUCTION Injection of sodium hypochlorite (NaOCl) from the root canal into periapical tissues may result in a NaOCl incident. The purpose of this study was to examine the fluid pressure generated by canal cleansing devices at the apical interface, when the tip of the irrigation device was not binding to the canal walls. METHODS Apical pressure was monitored in a closed-system root canal model, with NaOCl delivered by a syringe pump at 0.5-8 mL/min. Devices tested were VPro EndoSafe, Max-i-Probe, NaviTip, VPro StreamClean, and EndoVac Microcannula. Apical fluid pressure was recorded with a digital manometer (N = 20). The relationships between apical fluid pressure and fluid flow rate were modeled with polynomial regression and analyzed by using the Wald test. RESULTS EndoVac Microcannula was the only device that was capable of delivering negative apical fluid pressures, in the range of -35 mm Hg, at all fluid flow rates. All other devices generated positive apical pressures that increased nonlinearly with increasing fluid flow rates. These 4 positive pressure delivery devices were capable of generating pressures that exceeded the human central venous pressure (5.88 mm Hg). VPro EndoSafe differed from the other positive pressure delivery devices in that it generated significantly higher positive pressures at all flow rates (P < .0083). CONCLUSIONS Positive apical irrigation pressures in excess of the central venous pressure may be generated by some canal cleansing devices when irrigants are delivered at flow rates higher than 1 mL/min, even when the irrigation needle is not wedged into the canal walls.

Characterization of the Mineral Trioxide Aggregate–Resin Modified Glass Ionomer Cement Interface in Different Setting Conditions

INTRODUCTION Mineral trioxide aggregate (MTA) has been used successfully for perforation repair, vital pulpotomies, and direct pulp capping. However, little is known about the interactions between MTA and glass ionomer cement (GIC) in final restorations. In this study, 2 null hypotheses were tested: (1) GIC placement time does not affect the MTA-GIC structural interface and hardness and (2) moisture does not affect the MTA-GIC structural interface and hardness. METHODS Fifty cylinders were half filled with MTA and divided into 5 groups. The other half was filled with resin-modified GIC either immediately after MTA placement or after 1 or 7 days of temporization in the presence or absence of a wet cotton pellet. The specimens were then sectioned, carbon coated, and examined using a scanning electron microscope and an electron probe microanalyzer (SEM-EPMA) for interfacial adaptation, gap formation, and elemental analysis. The Vickers hardness numbers of the interfacial MTA were recorded 24 hours after GIC placement and 8 days after MTA placement and analyzed using the analysis of variance test. RESULTS Hardness testing 24 hours after GIC placement revealed a significant increase in hardness with an increase of temporization time but not with a change of moisture conditions (P < .05). Hardness testing 8 days after MTA placement indicated no significant differences among groups. SEM-EPMA showed interfacial adaptation to improve with temporization time and moisture. Observed changes were limited to the outermost layer of MTA. The 2 null hypotheses were not rejected. CONCLUSIONS GIC can be applied over freshly mixed MTA with minimal effects on the MTA, which seemed to decrease with time.

Effects of Tricalcium Silicate Cements on Osteogenic Differentiation of Human Bone Marrow-Derived Mesenchymal Stem Cells In Vitro

Tricalcium silicate cements have been successfully employed in the biomedical field as bioactive bone and dentin substitutes, with widely acclaimed osteoactive properties. This research analyzed the effects of different tricalcium silicate cement formulations on the temporal osteoactivity profile of human bone marrow-derived mesenchymal stem cells (hMW-MSCs). These cells were exposed to four commercially available tricalcium silicate cement formulations in osteogenic differentiation medium. After 1, 3, 7 and 10 days, quantitative real-time polymerase chain reaction and Western blotting were performed to detect expression of the target osteogenic markers ALP, RUNX2, OSX, OPN, MSX2 and OCN. After 3, 7, 14 and 21 days, alkaline phosphatase assay was performed to detect changes in intracellular enzyme level. An Alizarin Red S assay was performed after 28 days to detect extracellular matrix mineralization. In the presence of tricalcium silicate cements, target osteogenic markers were downregulated at the mRNA and protein levels at all time points. Intracellular alkaline phosphatase enzyme levels and extracellular mineralization of the experimental groups were not significantly different from the untreated control. Quantitative polymerase chain reaction results showed increases in downregulation of RUNX2, OSX, MSX2 and OCN with increasing time of exposure to the tricalcium silicate cements, while ALP showed peak downregulation at day 7. For Western blotting, OSX, OPN, MSX2 and OCN showed increased downregulation with increased exposure time to the tested cements. Alkaline phosphatase enzyme levels generally declined after day 7. Based on these results, it is concluded that tricalcium silicate cements do not induce osteogenic differentiation of hBM-MSCs in vitro.

In Vitro Biocompatibility and Oxidative Stress Profiles of Different Hydraulic Calcium Silicate Cements

INTRODUCTION MTA Plus is a new calcium silicate cement with unknown cytotoxicity characteristics. The objectives of this study were to examine the effect of MTA Plus on the viability, apoptosis/necrosis profile, and oxidative stress levels of rat odontoblast-like cells. METHODS MDPC-23 cells were exposed to gray and white MTA Plus (GMTAP, WMTAP), gray and white ProRoot MTA (GMTA, WMTA) cements, or their eluents. The cells were evaluated for (1) cell viability by using XTT assay, (2) apoptosis/necrosis by using flow cytometry and confocal laser scanning microscopy, and (3) oxidative stress by measuring reactive oxygen species. RESULTS XTT assay showed that all test cements exhibited marked initial cytotoxicity that decreased with time. By the end of the third week, GMTAP and GMTA were comparable to untreated cells (negative control) in terms of cell viability, whereas WMTAP and WMTA were significantly lower than the untreated cells. Apoptosis/necrosis profiles of cells exposed to WMTAP and GMTAP were not significantly different from untreated cells, whereas cells exposed to WMTA and GMTA showed significantly less viable cells. All experimental groups exhibited reduction of intracellular reactive oxygen species formation compared with untreated cells, although cells exposed to WMTA were not significantly different from untreated cells. CONCLUSIONS Both the gray and white versions of MTA Plus possess negligible in vitro cytotoxic risks that are time and dilution dependent. They enrich the spectrum of hydraulic calcium silicate cements currently available to clinicians for endodontic applications.

Quality of obturation achieved by an endodontic core-carrier system with crosslinked gutta-percha carrier in single-rooted canals

OBJECTIVES The present study examined the quality of obturation in root canals obturated by GuttaCore, a gutta-percha-based core-carrier system with a cross-linked thermoset gutta-percha carrier, by comparing the incidence of gaps and voids identified from similar canals obturated by cold lateral compaction or warm vertical compaction. METHODS Thirty single-rooted premolars with oval-shaped canals were shaped and cleaned, and obturated with one of the three obturation techniques (N=10): GuttaCore, warm vertical compaction or cold lateral compaction. Filled canals were scanned with micro-computed tomography (micro-CT); reconstructed images were analysed for the volumetric percentage of gaps and voids at three canal levels (0-4mm, 4-8mm and 8-12mm from working length). The roots were subsequently sectioned at the 4-mm, 8-mm and 12-mm levels for analyses of the percentage of interfacial gaps, and area percentage of interfacial and intracanal voids, using scanning electron microscopy (SEM) to examine negative replicas of root sections. Data were analysed with parametric or non-parametric statistical methods at α=0.05. RESULTS Both micro-CT and SEM data indicated that canals obturated with GuttaCore core-carriers had the lowest incidence of interfacial gaps and voids, although the results were not significantly different from canals obturated by warm vertical compaction. Both the GuttaCore and the warm vertical compaction groups, in turn, had significantly lower incidences of gaps and voids than the cold lateral compaction group. CONCLUSIONS Because of the similarity in obturation quality between GuttaCore and warm vertical compaction, practitioners may find the GuttaCore core-carrier technique a valuable alternative for obturation of oval-shaped canals. CLINICAL SIGNIFICANCE The quality of obturation achieved by GuttaCore in single-rooted canals is not significantly different from that achieved by warm vertical compaction.

Synthesis of antimicrobial silsesquioxane–silica hybrids by hydrolytic co-condensation of alkoxysilanes

Organically modified silicates represent an excellent example of organic–inorganic hybrids in materials science. The routes to achieve incorporation of organic functionalities include grafting and co-condensation (one-pot synthesis). Compared with the grafting method, the advantage of one-pot synthesis manifests as the tunability of both mechanical and biological properties. Herein, we report a silsesquioxane–silica hybrid (SqSH) with dual functional groups (alkylammonium and methacrylate chains) synthesized by the hydrolytic co-condensation of one tetraethoxysilane and two alkoxysilanes. Successful co-condensation is validated by attenuated total reflection-Fourier transform infrared (ATR-FTIR), 29Si nuclear magnetic resonance (29Si NMR), and thermogravimetric analysis (TGA). 3-(Trimethoxysilyl)propyldimethyloctadecyl ammonium chloride (SiQAC), one of the three precursors, simultaneously serves as a structure-directing agent in the modified Stober reaction, resulting in SqSH particles with structural hierarchy of both ordered lamellar structure and spherical morphology, as revealed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The SqSH particles bear tunable mechanical properties and, when incorporated into bis-GMA/TEGDMA resin, antimicrobial activities against Streptococcus mutans, Actinomyces naeslundii, and Candida albicans.

Time-based lateral hygroscopic expansion of a water-expandable endodontic obturation point

OBJECTIVES This study compared the time-based lateral expansion of two sizes and two batches of water-expandable obturation points (CPoint, EndoTechnologies, LLC) and a similar-sized gutta-percha point (control) at various distances from the point apex: 5, 10, and 15mm. METHODS Two batches of sizes 25 and 40 (0.06 taper) CPoints and a single lot of size 40 (0.06 taper) gutta-percha were tested (N=5). Points were fixed to the bottom of a Petri dish, and digital images of each point location were obtained under 50× magnification, which also captured a calibrated linear scale reticule. After imaging each dry cone location, 10mL of water was added, and images were obtained at various time points: 20 and 40min, 1, 2, 3, 4, 5, 6, 7, 8, and 24h. Between measurements, dishes were stored at 37°C. Side-to-side dimension of each point was determined using imaging software RESULTS No significant differences (p>0.05) in lateral dimension at each tip distance between batches of similar-sized CPoint samples were found (2-tailed unpaired Students t-test). Changes in CPoint dimension were significantly higher (p<0.05) for both sizes at each tip distance after 20min of water immersion (one-factor repeated-measures ANOVA; Tukey test). Gutta-percha did not significantly change from the dry value during water immersion (p>0.05). CONCLUSIONS When exposed to water, the lateral expansion of a new hydrophilic endodontic obturation point significantly increases in dimension within 20min, whereas a conventional gutta-percha point does not.