Effect of curing conditions on physical and chemical properties of MTA.

AIM: To evaluate setting time, pH, solubility and surface roughness of MTA+ and ProRoot MTA and characterize their hydration under several curing conditions. METHODOLOGY: Specimens were prepared to evaluate setting time (n = 6 for each group, specimen dimensions 10 × 8 × 5 mm), solubility (n = 6 for each group, specimen dimension 20 mm in diameter and 1.5 mm thick) after 1 and 28 days, pH (n = 10 for each group, specimen dimensions 10 mm in diameter and 1 mm thick) after 1, 7, 14, 21 and 28 days and surface roughness (n = 10 for each group, specimen dimensions 4 mm in diameter and 3 mm high) after 28 days when cements were cured at 95% humidity or immersed in saline or HBSS at 37 °C. The powder and liquid were mechanically mixed by an amalgamator. The set materials were characterized using X-ray diffraction analysis, scanning electron microscopy and X-ray energy-dispersive analysis. Statistical comparisons were employed using one-way anova. The level of significance was set at P = 0.05. RESULTS: Setting time was significantly shorter when cements were cured at 95% humidity compared to those in saline (P < 0.001) and HBSS (P < 0.001). Setting time of MTA+ was significantly shorter than that of ProRoot MTA (P < 0.001), which had a significantly higher pH than MTA+ (P < 0.05) for all periods and immersion liquids. After immersion in saline, MTA+ was significantly less soluble than ProRoot MTA (P < 0.001); when immersed in HBSS, no significant difference was found (P = 1.00). The surface roughness of both cements was affected when exposed to HBSS (P < 0.001 for both cements) and saline (P < 0.001 for both cements). Storage in HBSS created a homogenous surface; incubation in saline or humidity created a biphasic surface. The main crystalline phases in both cements were tricalcium silicate, bismuth oxide and calcium hydroxide. CONCLUSIONS: MTA+ had a shorter setting time than ProRoot MTA, promoted lower pH and had lower solubility in saline. Curing conditions affected the surface roughness and microstructure of the cements.

A new method for real-time quantification of irrigant extrusion during root canal irrigation ex vivo.

AIM: (i) To introduce a new method of quantifying extruded irrigant during root canal irrigation ex vivo. (ii) to evaluate the effect of periapical tissue simulation and pressure equalization and (iii) to determine the effect of needle type, apical preparation size and apical constriction diameter on irrigant extrusion. METHODOLOGY: Sixteen human single-rooted teeth were sequentially prepared to sizes 25-45, 0.06 taper and mounted on a plastic vial simulating a periapical lesion. The apical constriction diameter was standardized to 0.15-0.35 mm. The vial was filled with distilled water or air and was either open to the environment or closed. A point-conductivity probe was used to determine the volume of extruded irrigant into the vial. NaOCl was delivered by an open-ended or a closed-ended needle at 3 mm short of working length. Results were analysed by two 3-way repeated-measures ANOVAs. RESULTS: The open-ended needle extruded significantly more irrigant than the closed-ended in the majority of cases (P < 0.002). An increase in the apical size was related to decreased irrigant extrusion (P < 0.024). The effect of constriction diameter was not significant. The water-closed and water-open methods were related to less extrusion than the air-closed and air-open methods, respectively (P < 0.005). Open systems (water-open, air-open) allowed extrusion of larger amounts of irrigant than corresponding closed systems (water-closed, air-closed) (P < 0.005). CONCLUSIONS: The conductivity probe is a reliable method for real-time quantification of irrigant extrusion ex vivo. Not simulating tissue resistance in ex vivo experiments may lead to significant overestimation of irrigant extrusion.

Short- and long-term sealing ability of Gutta-flow and AH-Plus using an ex vivo fluid transport model.

AIM: To use the fluid transport model to evaluate the ex vivo short- and long-term microleakage along root canals filled with Gutta-flow or AH-Plus using the cold lateral compaction technique. METHODOLOGY: A total of 38 single-rooted human teeth were used for the assessment of microleakage. The crowns of the teeth were sectioned below their cemento-enamel junctions to adjust the length of the roots to approximately 15 mm. The root canals were instrumented using the step-back technique and filled using cold lateral condensation. The sealer employed was either Gutta-flow (Group A) or AH-Plus (Group B). Microleakage along the root canals was evaluated using a fluid transport model after periods of 1 week and 3 months. RESULTS: The microleakage values (microL h(-1)) for group A were 0.36 +/- 0.33 at 1 week and 0.41 +/- 0.36 at 3 months. Group B showed mean microleakage values 0.2 +/- 0.31 at 1 week and 0.28 +/- 0.38 at 3 months. Statistical analysis indicated no significant differences (P > 0.05) between the two groups after either 1 week or 3 months. CONCLUSIONS: There was no significant difference between AH-plus and Gutta-flow in terms of sealing ability.

The amount and distribution of sclerotic human root dentine.

In low-power photomicrographs of ground sections of canine teeth, the amount of sclerosis increased with age linearly and was not markedly affected by the function of the tooth or external stimuli encountered during life. The pattern of distribution was similar in all teeth. Sclerosis started in the apical dentine adjacent to the cementum and extended coronally and towards the root canal, with increasing age. In the plane transverse to the long axis of the root, sclerosis appeared first at the mesial and distal sides so that the sclerotic zones formed a butterfly shape.

The histology of sclerotic human root dentine.

Studies by optical microscopy, microradiography and SEM suggested that sclerosis is the result of occlusion of the dentinal tubules by a mineral substance with a refractive index similar to that of the rest of the dentine. Translucence appeared before the majority of the tubules were completely occluded. The deposition of the occluding mineral took place initially in individual tubules or in groups of tubules. The occluding material and the peritubular dentine were almost indistinguishable under SEM. Both were smooth and densely mineralized. The process of deposition of occluding mineral appeared to be more like that of in-vitro mineralization and thus different from that of peritubular dentine.

Clinical relevance of standardization of endodontic irrigation needle dimensions according to the ISO 9,626:1991 and 9,626:1991/Amd 1:2001 specification.

AIM: To examine the current status of standardization of endodontic irrigation needles produced by different manufacturers. METHODOLOGY: Measurements of needle internal and external diameter were conducted under scanning electron microscopy and stereoscopic microscopy to determine the incidence and degree of deviation from ISO 9,626:1991 and ISO 9,626:1991/Amd 1:2001 specification. RESULTS: None of the needles examined complied with the ISO nominal size. All SS needles were within the ISO tolerance limits. A Ni-Ti needle, which is not included in the specification, was found to exceed ISO external diameter limits. CONCLUSIONS: Exact knowledge of the tip's external diameter is crucial for the selection of the appropriate size irrigation probe during endodontic treatment. Units of the widely used 'gauge' system cannot be directly extrapolated to clinical practice. Adoption of millimetre as the standard metric unit, already recommended by ISO, should be accelerated. A colour-coding of needles corresponding to endodontic instruments would also be beneficial.

Effect of heat sterilization on surface characteristics and microstructure of Mani NRT rotary nickel-titanium instruments.

AIM: To evaluate the effect of repeated dry heat sterilization on surface characteristics and microstructure of Mani nickel-titanium rotary instruments. METHODOLOGY: Thirty-three new Mani NRT instruments, size 30, taper 0.04 and 25 mm in length were examined. Twenty-seven instruments were divided into three groups for surface characterization by scanning electron microscopy (SEM). In the first group (n = 3), instruments were examined in the 'as-received' condition and after they had been subjected to 11 sterilization cycles. In the second and third subgroups (n = 12), 12 instruments were prepared for cross-section and a further 12 for longitudinal sectional analysis and evaluated in subgroups of three, after 0, 1, 6 and 11 sterilization cycles. The remaining six instruments were analysed with differential scanning calorimetry (DSC), three in the 'as-received' condition and three after being subjected to 11 cycles of sterilization. RESULTS: Scanning electron microscopy observations indicated the presence of debris, pitting and deep milling marks in both new and sterilized files. After 11 sterilization cycles, debris remained and surface roughness was increased significantly (P = 0.05). DSC analyses showed that the specimens in the 'as-received' condition and after 11 sterilization cycles were in the austenite phase or a mixture of austenite and R-phase at 37 degrees C. CONCLUSIONS: The machining defects and structural imperfections of new Mani instruments are indicative of the difficulty in manufacturing nickel-titanium endodontic instruments. DSC measurements suggest that Mani instruments are capable of superelastic behaviour under clinical conditions.

[Examination of side dentinal tubules by the use of S.E.M]. / Exetase diakladoses odontinosolenarion me sarotiko elektroniko mikroskopio (S.E.M.).

This research was undertaken in order to find information about the number and the fine structure of the side dentinal tubules and their junction area with the main dentinal tubules. Frozen structure dentine specimens from 60 human canines examined with S.E.M. was the material used in the present investigation.