G. Palaghias

Interaction of calcium hydroxide with zinc oxide-eugenol type sealers: A potential clinical problem

When a ZnOE type sealer was placed in root canals treated previously with calcium hydroxide dressing, an accelerated sealer setting rate occasionally occurred. This clinical observation led to the present experimental design aiming to investigate the effect of calcium hydroxide on a ZnOE cement and ZnOE type sealers and to preliminarily assess the removal efficiency of a calcium hydroxide preparation from root canal systems. Micro-MIR FTIR spectroscopy was used to quantify the effect of calcium hydroxide on the setting reactions of a ZnOE cement and two ZnOE type sealers. The removal efficiency of calcium hydroxide from root canal systems was evaluated after treatment with NaOCl; NaOCl and filing; and NaOCl plus EDTA and filing. Calcium hydroxide preferentially interacted with eugenol inhibiting the ZnO-eugenol chelate formation. The Ca(OH)2-eugenol interaction was rapid, and kinetically dependent, leading to residual eugenol in the set product. The set ZnOE cement and the ZnOE type sealers in contact with calcium hydroxide were brittle in consistency and granular in structure. Although none of the treatments tested completely removed calcium hydroxide from root canals, treatment with EDTA significantly reduced the extent of residual calcium hydroxide.

Effect of acidic conditioners on dentin morphology, molecular composition and collagen conformation in situ.

OBJECTIVE The aim of the study was to evaluate the effect of some acidic conditioners on dentin morphology, molecular composition and collagen conformation in situ. METHODS Smear layer-covered dentin specimens prepared from third molars immediately after extraction were imaged by tapping made AFM and analyzed by MIR-FTIR spectroscopy. The same specimens were subjected to conditioning treatments with CA Agent (Kuraray), Scotchbond Etchant (3M Dental Products) and Scotchbond MP Etchant (3M Dental Products) gels and then imaged and analyzed again. The extent of dentin decalcification at the uppermost 2 microns region was calculated from the percentage reduction in the-PO4/amide I peak area ratio of conditioned specimens relative to their individual smear layer-covered references. These results were compared by ANOVA and Scheffé statistical analyses. The conformational changes of dentin type I collagen at the region were studied qualitatively by deconvoluting the amide I bands of MIR-FTIR spectra and assigning the band components to carbonyl hydrogen bonding states related to the alpha-helix structure. RESULTS All the conditioners removed the smear layer, funneled the tubules, increased the intertubular roughness and contaminated the dentin surfaces with residues from irreversibly adsorbed thickening agents. Conditioned dentin surfaces showed a reduction in orthophosphates and carbonates and an increase in amide I, II and III groups. CA Agent manifested a significantly lower extent of dentin decalcification than Scotchbond etchants (p < 0.05). Collagen conformational changes involved a decrease in intermolecular hydrogen bonded amide I carbonyls associated with the alpha-helix structure and enhancement of imide carbonyls hydrogen bonded to water, which suggest collagen denaturation. SIGNIFICANCE Apart from dentin decalcification, the acidic conditioners induced considerable changes on dentin collagen conformation mostly associated with denaturation processes. In addition, irreversibly adsorbed residual thickeners substantially modified the morphology and composition of dentin surfaces. These findings show the complex interaction pathways between conditioners and dentin surfaces and the great potential of modern in situ imaging and analysis techniques in probing these interactions.

Surface reactions of adhesives on dentin

The purpose of this study was to characterize changes in the surface chemistry of dentin following various adhesive treatments. The coronal parts of sound freshly extracted third molars were cross-sectioned over the pulp chambers, each producing a pair of dentin samples which were polished to 600 grit and cleaned with 3% H2O2. The first sample of each pair was used as a control, while the second one was subjected to one of the following adhesive treatments: (a) Gluma Cleanser, (b) Tenure Conditioner, (c) Scotchprep, (d) Gluma Cleanser/Gluma Primer, (e) Tenure Conditioner/Tenure Solution A&B, or (f) Scotchprep/Scotchbond 2 Adhesive. The treated samples paired with their respective controls were studied by small-area ESCA spectroscopy. Three areas of 1.0 mm in diameter randomly chosen on each sample were analyzed by survey and C1s, O1s, N1s high-resolution spectra. The samples from groups d, e, and f were additionally subjected to argon-ion-depth profiling of the uppermost 2-nm layer at 0.5-nm intervals. According to the results, treatment modes a, b, and c caused the reduction of carbonates and increased the -NH/NH2 ratio. Treatments a and c increased the alcohol groups, while treatments b and c increased the carbonyl and ether groups. All these changes were in comparison to the reference dentin specimens. Dentin treatment with d, e, and f induced a complex in depth distribution of the C, N, O binding states. The energy shifts detected do not indicate primary bonding of the tested adhesives to the dental substrate.

Effect of dentin primers on the morphology, molecular composition and collagen conformation of acid-demineralized dentin in situ

OBJECTIVES The purpose of this study was to assess the effect of two commercial primers and distilled water on the morphology, molecular composition and collagen conformation of acid-demineralized dentin in situ. METHODS Dentin specimens etched with Scotchbond Etchant were imaged by tapping mode AFM and analyzed by MIR-FTIR spectroscopy. They were then primed with Scotchbond Multi-Purpose Plus Primer, Scotchbond 1 Adhesive or distilled water and imaged and analyzed again. The chemical modifications induced on the uppermost 2 microns of primed dentin were studied after water and original primer subtraction. The conformational changes of type I collagen at this region were evaluated by deconvoluting the amide I band components. The absorbance ratio An(1655/1627) was used to semiquantitatively assess, on a relative basis, the extent of collagen denaturation. RESULTS All the priming treatments swelled the collapsed dentin collagen left after etching. No evidence of primary bonding was found after priming treatments, while approximately 50% of the conditioned dentin collagen appeared denatured. Treatment with distilled water did not change the status of denatured collagen, however, application of the commercial primers refolded the alpha-helix to approximately 95% of the extent found on the native reference dentin. SIGNIFICANCE The dynamic response of dentin collagen to demineralization and priming treatments reveals the critical role of some primers in rapidly restoring the conformational status of acid-denatured collagen. Implementation of reactive adhesive groups in alpha-helix recovery may provide an associative means of modifying the mechanical properties of the demineralized collagen based on the extent of their intermolecular bonding.

Effects of Dentin Bonding Agents on the Cell Cycle of Fibroblasts

The aim of this study was to evaluate the effects of 3 dentin bonding agents on cell survival and proliferation and on cell cycle progression of cultured cells. The experiments were performed on RPC-C2A and L929 cells. Specimens of the 3 dentin bonding agents (Clearfil Tri-S, AdheSE, and XP BOND) were placed in culture medium, and the extraction media were applied to cells as experimental material. The effect of the bonding materials on cell survival and proliferation was assessed by a modified sulforhodamine B staining assay, and the effect on DNA synthesis was assessed by bromodeoxyuridine uptake. Flow cytometry was used for cell cycle analysis. Cell viability and proliferation decreased in a dose-dependent manner after exposure of cells to the tested materials. XP BOND expressed the highest activity of all tested bonding agents (P < .05). The self-etch bonding agents tested did not produce any significant effects on cell cycle distribution. However, exposure of cells to the total-etch agent XP BOND induced a G(2)-phase arrest in both cell lines, and this effect was more evident in L929 cells than in RPC-C2A cells.

Corrosion pattern of silver points in vivo

The purpose of this study was to examine the electrochemical behavior of silver points in vivo. The apices of silver points removed from teeth with successful or failed endodontic treatments were subjected to complete surface characterization by small-area ESCA, scanning electron microscopy, and electron probe microanalyzer. Cross-sections of the points near the apex were examined with scanning electron microscopy and electron probe microanalyzer to identify the depth of corrosion involvement. According to the results, all silver points manifested evidence of corrosion attack. Electron probe microanalyzer showed no difference in the elemental distribution found on the points. ESCA analysis of the uppermost 5-nm point layer revealed the presence of N on silver points removed from failed treatments. The examination of cross-sections manifested deep S penetration in the bulk of the points removed from failed treatments. Considering the results of this study, no direct association seems to exist between the extent of the corrosion involvement and the prognosis of the treatment. Handling factors and the presence of bacteria are probably the parameters determining the outcome of a treatment.

DEVELOPMENT AND VALIDATION OF AN ISOCRATIC HPLC METHOD FOR THE SIMULTANEOUS DETERMINATION OF RESIDUAL MONOMERS RELEASED FROM DENTAL POLYMERIC MATERIALS IN ARTIFICIAL SALIVA

A simple and rapid method for the simultaneous determination of Bisphenol-A (BPA), Triethylene glycol dimethacrylate (TEGDMA), Bisphenol A glycerolate dimethacrylate (BIS-GMA), and Urethane dimethacrylate (UDMA) from dental polymeric materials in artificial saliva is described. Chromatographic analysis was performed isocratically on a Kromasil 100-C18 analytical column (25 cm × 4.6 mm id, 5 µm) with CH3CN:H2O, 75:25%, v/v as mobile phase within 6 min. The developed method was validated in terms of selectivity, linearity, accuracy, precision, and sensitivity. Accuracy and precision were examined at three concentration levels. Repeatability and between-day precision was examined over a period of five days and revealed RSD values lower than 11.2%. The relative errors ranged from −13.8% to 3.9%. In artificial saliva the limit of quantification (LOQ) was calculated as 1.2–3.6 ng/µL. No interference was observed under described experimental conditions. Residual monomers released from dental materials were quantified after exposure of specimens to different solvent ratios.

Creep and dynamic viscoelastic behavior of endodontic fiber-reinforced composite posts

PURPOSE Fiber-reinforced composite (FRC) posts have gained much interest recently and understanding of their viscoelastic properties is important as they can be used in stress-bearing posterior restorations. The aim of this study was to evaluate the creep behavior and the viscoelastic properties of four commercial FRC posts under different temperatures and different storage conditions. METHODS The FRC posts tested were Glassix, C-Post, Carbonite and Snowlight. For the creep measurements a constant load below the proportional limit of the posts was applied and the angular deformation of the specimens was recorded. The viscoelastic parameters were determined by using dynamic torsional loading under four different conditions. RESULTS All materials were susceptible to creep and exhibited linear viscoelastic behavior. Residual strain was observed in all FRC posts. The viscoelastic properties were affected by the increase of temperature and water storage (p<0.001) resulting in their decline. Carbon fiber posts exhibited better performance than glass fiber posts. CONCLUSIONS FRC posts exhibit permanent strains under regular masticatory stresses that can be generated in the oral cavity. Their properties are susceptible to changes in temperature, while direct contact with water also affects them deleteriously.

A Simple Isocratic HPLC Method for the Simultaneous Determination of the Five Most Common Residual Monomers Released from Resin-Based Dental Restorative Materials

Resin-based dental restorative materials bonded to tooth structure have become one of the most important groups of dental materials nowadays. The presence of un-reacted monomers, as well as the degradation of resins, caused by hydrolysis and/or enzyme catalysis from saliva and oral environment, can lead to the continuous leaching of monomers with potentially cytotoxic and genotoxic effects for the human organism. A simple and rapid method for the determination of 2-hydroxyethyl methacrylate, bisphenol A, triethylene glycol dimethacrylate, urethane dimethacrylate, and bisphenol A glycerolate dimethacrylate monomers released from dental polymeric materials is described. Chromatographic separation was achieved isocratically, within 11 min, using a Kromasil 100-C18 column (25 cm × 4.6 mm, 5 µM) with CH3OH:CH3CN:H2O, 60:15:25%, v/v, at a flow rate of 1.5 mL/min. The developed method was validated in terms of selectivity, linearity, accuracy, precision, and sensitivity. Within-day repeatability and between-day precision revealed RSD values lower than 11%. The limits of detection ranged from 0.17–0.33 ng/µL. No interference was observed under the described experimental conditions. The method was applied to the study of the monomers released from resin cements through human dentine. All, except for bisphenol A, were found to be released from resin cements through human dentin into the pulp space.

A Simple and Rapid HPLC Method for the Direct Determination of Residual Monomers Released From Dental Polymeric Materials in Blood Serum and Urine

Bisphenol-A (BPA), Triethylene glycol dimethacrylate (TEGDMA), Bisphenol A glycerolatedimethacrylate (Bis-GMA), and Urethane dimethacrylate (UDMA) are organic monomers that can be released from dental composites and, depending on their concentration in biological fluids, can cause adverse reactions and toxic or other effects. Herein, a simple and rapid method has been developed for the simultaneous determination of the aforementioned monomers in human blood serum and urine. Chromatographic analysis was performed isocratically on a Perfect Sil 120 ODS-2 analytical column (250 mm × 4.0 mm, 5 µm) with CH3CN:H2O, 70:30%, v/v as mobile phase within 6 min. The developed method was validated in terms of selectivity, linearity, accuracy, precision, and sensitivity in spiked matrices. Repeatability and between-day precision over a period of five days revealed Relative Standard Deviation (RSD) values lower than 13.1% for blood serum samples and lower than 6.6% for urine samples. Recovery of the examined analytes ranged from 92.6% to 106.1% in blood serum samples and from 95.0% to 106.9% in urine samples. The stability of the four monomers in blood serum and urine samples was studied in terms of long-term storage (at 4°C and −18°C), short-term storage (room temperature), and during sequential freeze-thaw cycles.