Influence of rotational speed on the cyclic fatigue of Mtwo instruments.

AIM: To evaluate the effect of rotational speed on cyclic fatigue of Mtwo nickel-titanium files. METHODOLOGY: A total of 120 new Mtwo rotary instruments sizes 10, 0.04 taper; 15, 0.05 taper; 20, 0.05 taper; and 25, 0.06 taper were randomly divided into three groups on the basis of the rotational speed used to shape nine standardized simulated canals: group A = 350 rpm; group B = 250 rpm; group C = 150 rpm. Each group consisted of 40 instruments, 10 for every size. The average preparation time (in seconds) and the average correlated numbers of cycles to instrument (NCI) the nine standardized canals were recorded for each file. The resistance to cyclic fatigue was determined by counting numbers of cycles to failure (NCF) with a rotational speed of 300 rpm in a 60° curve with a 5-mm radius. Data were analysed by two-way anova. RESULTS: Preparation time was significantly longer at 150 rpm than at 250 or 350 rpm. The average number of cycles needed for each file to instrument nine standardized canals was significantly higher at 350 and 250 rpm, than at 150 rpm. There were no significant differences in the NCF (P > 0.05) between A, B and C groups for instruments of the same size. CONCLUSIONS: Speed did not affect the cyclic fatigue of Mtwo instruments with the same size and taper. Preparation time was shorter at 350 or 250 rpm rather than at 150 rpm. However, there was no significant difference between 350 and 250 rpm rotational speed, neither in the preparation time of simulated canals nor in the resistance to fatigue fracture.

El sistema rotatorio Mtwo NiTi para preparación de conductos / Mtwo Niti rotary system for root canal preparation

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Pulp-dissolving ability of several endodontic irrigants: a spectrophotometric evaluation.

The aim of this study is to test the dissolving action of different concentrations of NaOCl (0.5%, 2.5% and 5%) and EDTA 17% on bovine pulp tissue, testing solutions at three different times (1, 5, 10 minutes), 100 mg.of dental pulp placed into a becker with 20 ml of solution was evaluated using a spectrophotometer. A solution of NaOCl 5% showed the highest solubility value. Samples treated with 2.5% NaOCl showed solubility values of 0.98 in one minute, 29.1 in five minutes and 57 in ten minutes. Groups treated with NaOCl 0.5% showed small dissolving modifications. 17% EDTA showed the lowest values of solubility. 5% NaOCl solution showed highest pulp dissolving ability, even a 2.5% solution showed high dissolving ability but in longer times.

Influence of a brushing working motion on the fatigue life of NiTi rotary instruments.

AIM: To evaluate the cyclic fatigue resistance of Mtwo NiTi rotary instruments when used with a brushing or no-brushing action in oval root canals. METHODOLOGY: Cyclic fatigue testing of instruments was performed in tapered artificial canals with a 5 mm radius of curvature and an angle of curvature of 60 degrees. Twenty Mtwo instruments for each size were selected and divided into two groups: group A = 10 instruments used with a no-brushing motion (control group); group B = 10 instruments used with a brushing-milling action. Each Mtwo instrument was used for cleaning and shaping 10 oval root canals. In all 80 instruments were rotated until fracture occurred and the number of cycles to failure (NCF) recorded. Data were analysed by one-way ANOVA, Tukey HSD test and independent sample t-test to determine any statistical difference; the significance was determined at the 95% confidence level. RESULTS: No statistically significant reduction of NCF between instruments used with a no-brushing motion (group A) and instruments used with a brushing motion (group B) were apparent except for size 25, 0.06 taper. Mtwo size 10, 0.04 taper, size 15, 0.05 taper, size 20, 0.06 taper, size 25, 0.06 taper instruments had a decrease in life span of 1%, 0.5%, 8% and 19%, respectively. CONCLUSIONS: Fatigue life of instruments of larger size could be reduced by using them with a lateral brushing or pressing movement. However, each file was successfully operated without intracanal failure, demonstrating that Mtwo rotary instruments can be used safely in a brushing action in simulated clinical conditions up to 10 times in oval canals.

Cyclic fatigue resistance and three-dimensional analysis of instruments from two nickel-titanium rotary systems.

AIM: To determine how instrument design affects the fatigue life of two nickel-titanium (Ni-Ti) rotary systems (Mtwo and ProTaper) under cyclic fatigue stress in simulated root canals. METHODOLOGY: Cyclic fatigue testing of instruments was performed in stainless steel artificial canals with radii of curvature of 2 or 5 mm and an angle of curvature of 60 degrees . A total of 260 instruments were rotated until fracture occurred and the number of cycles to failure were recorded. The morphology of Ni-Ti rotary instruments was investigated by measuring the volume of millimetre slices of each instrument size starting from the tip to the shank by means of microCT analysis. The fracture surface of three representative samples of each size was analysed by scanning electron microscopy (SEM). Data were analysed by one-way anova, Holm t-test, paired t-test and linear regression; the significance was determined at the 95% confidence level. RESULTS: Cycles to failure significantly decreased as the instrument volume increased for both the radii of curvature tested (P < 0.01). The radius of curvature had a statistically significant influence on the fatigue life of the instruments (P < 0.05). Larger instruments underwent fracture in less time under cyclic stress than smaller ones. SEM evaluation showed typical features of fracture through fatigue failure. CONCLUSIONS: The metal volume in the point of maximum stress during a cyclic fatigue test could affect the fatigue life of Ni-Ti rotary instruments. The larger the metal volume, the lower the fatigue resistance.

A comparison of cyclic fatigue between used and new Mtwo Ni-Ti rotary instruments.

AIM: To evaluate the cyclic fatigue of Mtwo Ni-Ti rotary instruments after controlled clinical use in molar teeth. METHODOLOGY: Twenty Mtwo instruments of each size were selected and divided into two groups: group A consisted of 10 new instruments (control group); group B consisted of 10 used instruments. Each instrument in group B was used to clean and shape 10 root canals of molar teeth in patients. Cyclic fatigue testing of instruments was performed in tapered artificial canals with a 5-mm radius of curvature and a 60 degrees angle of curvature. In all 140, instruments were rotated until fracture and the number of cycles to failure was recorded. Data were analysed using one-way anova, Tukey's HSD test and independent sample t-test to determine any statistical difference; the significance was determined at the 95% confidence level. RESULTS: A reduction of cycles to failure between new (group A) and used (group B) instruments was apparent. A statistically significant difference (P < 0.05) was noted between instruments of groups A and B in all sizes with the exception of size 40, 0.04 taper. CONCLUSIONS: Clinical use significantly reduced cyclic fatigue resistance of Mtwo rotary instruments when compared with an unused control group. However, all the instruments had minimal instrument fatigue when discarded after controlled clinical use.

SEM evaluation of canal wall dentine following use of Mtwo and ProTaper NiTi rotary instruments.

AIM: To compare using scanning electron microscopy (SEM) root canal walls following instrumentation in vitro with two different rotary NiTi instruments. The hypothesis was that no difference should be observable between the experimental groups in terms of debris on canal walls and surface morphology. METHODOLOGY: Twenty-four single-rooted human teeth were selected. Two types of NiTi instruments were used, Mtwo (Sweden & Martina, Padova, Italy) and ProTaper (Dentsply Maillefer, Ballaigues, Switzerland). Irrigation for both groups was performed after each instrument change with 5% NaOCl, 3% H2O2 and 17% EDTA solutions. Three different areas (coronal, middle and apical thirds) of the root canal were evaluated using SEM. The canal wall of each sample was assessed and compared using a predefined scale of four parameters, namely, smear layer, pulpal debris, inorganic dentine debris, surface profile. Data were analysed statistically using the Kruskal-Wallis test (anova). RESULTS: A statistically significant difference (P < 0.01) was found between the apical third and the middle and coronal thirds for both groups. No difference was observable between instrumentation groups. In the apical third canal walls were often contaminated by inorganic debris and by smear layer. In the apical third, the surface profile was affected by uninstrumented regions, comprising dentine depressions and grooves in which predentine was still visible. CONCLUSION: Both instruments produced a clean and debris-free dentine surfaces in the coronal and middle thirds, but were unable to produce a dentine surfaces free from smear layer and debris in the apical third. The presence of deep grooves and depression on dentine walls in the apical third may well explain the presence of less-instrumented areas.

[Today's trends in endodontics]. / Gli attuali orientamenti in endodonzia.

Some new means and innovative operative techniques in the field of endodontics are presented that have been developed and perfected over time. Instruments such as the operative microscope, ultrasonography, miniaturised tools for surgery, new materials such as mineral trioxide aggregate (MTA) should become part of the daily routine of the endodontist. For example, the operative microscope plays a role in diagnosing pulp damage after removal of deep caries; in orthograde endodontics in diagnosing perforations; alongside ultrasonography in the search for calcified canals, removal of pins (screw-type, fibre, etc.) and also in positioning MTA. In all these cases, the operative microscope is used discontinuously, alternating working and observation phases. In endodontic surgery, the operative microscope is on the contrary used continuously, enabling the surgeon to observe details of anatomy of the root apex at high magnification, and above all enabling positioning of canal obturation with perfect seal. It is clear that the operative microscope used in all surgical phases will enable complete management of the operation and facilitate the endodontist in observing the operative field, otherwise very difficult to control.

[Immunological phenomena in pulpal-periapical lesions]. / Fenomeni immunitari nelle lesioni pulpo-periapicali.

Based on an extensive review of the literature, the authors examine immunological reactions in pulpal and periapical lesions. Although it has been known for some time that bacterial infection causes this pathology, attention has been recently focused on immunological factors in the ambit of the phlogistic process. The present study examines the correlation between the latter and the type of extent of antigenic response, focusing attention on their important role in the phenomena of osteoclastic activation and inhibition of bone repair. From a physiological point of view there are few inflammatory cells in dental pulp, like macrophages and T lymphocytes. When the pulp comes into contact with the antigenic substance it activates a specific and aspecific immune response: the form through the activation of B and T lymphocytes, and the latter through the action of LPS, PMN and complement. An important role in the immune response is played by the cytokines which are able to regulate the intensity and duration of the immune response against potential pathogenic agents. It was initially thought that these were only produced by lymphocytes and as a result they were known as lymphokines. Later it was observed that other cell populations were also able to produce them. Phlogosis of the periapex starts before the pulp is fully necrotic. Tissue detritus and products of bacterial derivation escape through the numerous endoparadontal communication pathways and stimulate an inflammatory response by the vascular system of the parodontal ligament. The concomitant immune reaction occurs due to the tendency to block and restrict the inflammation to the radicular channels, thus preventing its diffusion.(ABSTRACT TRUNCATED AT 250 WORDS)

[Morphological characteristics of spreaders]. / Indagine sulle caratteristiche morfologiche degli spreaders.

Different kinds of spreaders can be used in the lateral condensation technique. Selection of condensation instruments must not be empirical because the quality of the filling partly depends on the compatibility between the spreader and the prepared root canal. The shape of the instrument should allow for easy insertion to the proper length without any interference. On these bases the Authors evaluated and compared the morphology of some spreaders, and gave data and directions how to rationally use these instruments in clinical practice.