Apical Forces Research Articles

Assessment of Vertical Force Generated with Single File Systems during Shaping of Constricted Root Canals.

This study aimed to evaluate the shaping force generated with OneShape (OS) and HyFlex EDM (HEDM) systems designed for single file shaping, in comparison with ProTaper Next (PTN). Maxillary premolar teeth received access cavity preparation and their canals were shaped with OS, HEDM, or PTN to size 25 according to manufacturer's instructions with consistent pressure on the files to give a gentle "in-and-out" movements of 2 mm amplitude. The canal shaping was completed with a total of three insertions. After each insertion, 1% NaOCl irrigation and recapitulation with K-file size 15 were performed. The vertical shaping force was measured using a force gauge (M5-20 Advanced Digital Force Gauge; Mark-10 Corporation, NY). The shaping time was analyzed by using a one-way analysis of variance (ANOVA) test and differences between the mean apical and coronal maximum force values were analyzed using the Kruskal-Wallis and Mann-Whitney U tests. The level of significance was set as 0.05. The magnitude of the vertical forces increased with successive advancements of the instruments within the canal. During canal shaping procedures in all groups, the apical and coronal maximum force values of the OS and HEDM ranged from 2.5 to 7.2 N and 1.3 to 2.9 N, respectively. PTN generated the lowest maximum apical forces during the second and third insertions (p < 0.05). HEDM generated significantly less maximum coronal forces than both OS and PTN during the first insertion while the use of OS was associated with the highest amount of force values in the second and third insertions (p < 0.05). In terms of shaping time, no significant differences were detected among the three tested systems (p = 0.606). The tested single file systems were associated with higher shaping forces in the apical direction that were significant in the second and third insertions.

Micro-CT evaluation of frozen and embalmed human cadavers on the effect of root canal preparation on microcrack formation in old dentin.

The aim of this study was to evaluate the existence of preoperative dentinal defects among differently preserved dentoalveolar bone-blocks (frozen vs. embalmed) and to investigate the effect of varying apical forces (low: <4 N, high: 4-8 N) during root canal preparation on microcrack formation using micro-computed tomography (micro-CT). Thirteen embalmed and seven frozen bone-blocks containing 1-3 single rooted teeth were collected. The teeth were evenly divided into three groups (n = 10): FLow (frozen, <4 N), ELow (embalmed, <4 N), EHigh (embalmed, 4-8 N). After working length determination all specimens were scanned preoperatively. Root canal preparation was performed using nickel-titanium instruments sizes 25/.06 and 40/.06 (F6 SkyTaper; Komet, Lemgo, Germany). A postoperative scan was performed and image stacks were co-registered. All cross-sectional images were screened to identify the presence of dentinal defects. The results were expressed as the percentage of teeth/slices presenting dentinal defects. The statistical analyses were performed with Kruskal-Wallis-Test and Mann-Whitney-U-Test (α = 5%). Embalmed specimens presented a significantly higher percentage of slices with preoperative microcracks (p<0.05) than frozen specimens. No significant difference between groups was observed regarding the induction of microcracks (p>0.05). Root canal preparation does not induce microcracks in dentoalveolar bone-blocks from donors of old age, irrespective of the preservation method and the apically directed forces.

Effect of Periodic Changes in Rotation Speed on Torsional Stress and Screw-in Force by Alternative Rotation Technique

IntroductionThis study evaluated the effect of periodic changes in rotation speed on torsional stress and screw-in force using the dedicated alternative rotation technique (ART) motion of the EQ-M (Metabiomed, Cheongju, Korea) endodontic motor. MethodsTwo ART modes of the EQ-M motor in 2 alternative techniques (ART30 and ART50) and continuous rotation were compared using ProTaper Next X2 (Dentsply Sirona, Charlotte, NC) files and simulated resin blocks (n = 12 per group). ART30 and ART50 were operated by continuous rotation of 350 rpm for 360° and then rotated at 30% increased speed from the base speed for 180° and at 50% increased speed for 180°, respectively. Before the test, the simulated resin blocks were pre-enlarged using ProTaper Gold S1 and S2 (Dentsply Sirona) and fixed on a metal stage connected to the force- and torque-measuring unit. During shaping the simulated canal in an automatic up-and-down manner, the parameters of maximum torque, sum of torque, maximum screw-in force, and maximum apical force were measured. The data were statistically analyzed using 1-way analysis of variance and the Tukey post hoc comparison test at the 95% significance level. ResultsThe ART30 and ART50 groups showed a lower maximum torque, sum of torques, screw-in force, and apical drive force than the continuous rotation group. There was no significant difference between the ART30 and ART50 groups (P > .05). When the screw-in force increased suddenly, the torque correspondently increased. ConclusionsUnder the limitations of this study, the ART mode could reduce the torsional stress and apical forces of the screw-in during instrumentation in comparison with continuous rotation.

Differential Cellular Stiffness Contributes to Tissue Elongation on an Expanding Surface.

Pattern formation and morphogenesis of cell populations is essential for successful embryogenesis. Steinberg proposed the differential adhesion hypothesis, and differences in cell–cell adhesion and interfacial tension have proven to be critical for cell sorting. Standard theoretical models such as the vertex model consider not only cell–cell adhesion/tension but also area elasticity of apical cell surfaces and viscous friction forces. However, the potential contributions of the latter two parameters to pattern formation and morphogenesis remain to be determined. In this theoretical study, we analyzed the effect of both area elasticity and the coefficient of friction on pattern formation and morphogenesis. We assumed the presence of two cell populations, one population of which is surrounded by the other. Both populations were placed on the surface of a uniformly expanding environment analogous to growing embryos, in which friction forces are exerted between cell populations and their expanding environment. When the area elasticity or friction coefficient in the cell cluster was increased relative to that of the surrounding cell population, the cell cluster was elongated. In comparison with experimental observations, elongation of the notochord in mice is consistent with the hypothesis based on the difference in area elasticity but not the difference in friction coefficient. Because area elasticity is an index of cellular stiffness, we propose that differential cellular stiffness may contribute to tissue elongation within an expanding environment.

Comparative analysis of torque and apical force to assess the cutting behaviour of ProTaper Next and ProTaper Universal endodontic instruments.

This study assessed the cutting properties of two Nickel Titanium file systems with different designs and manufacturing materials. ProTaper Next X1 and X2 (PTN; Dentsply Sirona) and ProTaper Universal S2 and F1 (PTU; Dentsply Sirona) instruments were employed. The cutting parameters, that is torque and apical forces, were determined using a specially designed bench-testing machine. Dimensional and geometric parameters were considered to evaluate the results. The average maximum torque values showed statistically significant differences (P<0.05) among all instruments. Apical force for PTN X2 and PTU F1 instruments initially decreased and then experienced a rapid increase in the last 2mm of the canal. For PTN X1 and PTU S2, apical force increased during the entire test. When compared to PTU files, PTN required higher torque and apical forces during the shaping procedure. The results lead us to conclude that PTN instruments demonstrated a lower cutting efficiency than PTU.

In vivo quantification of the apical fixation forces of different mitral valved stent designs in the beating heart.

The aim of this study was the quantification of the apical fixation forces of mitral valved stents for the first time. A test set-up was developed to measure the forces acting on the apical fixation of mitral valved stents. Twenty pigs received a self-expanding valved stent in the mitral position via a transapical approach in an off-pump procedure. Following stent deployment in the beating heart, the apical fixation forces were recorded following a standardized protocol and normalized. The apical fixation force of two different valved stent designs (AP: sole apical fixation, n=10; SA: additional sub-annular fixation, n=10) was compared to quantify the impact of the design change. Force measurement was successfully conducted in 18 of 20 animals (design AP: n=10; design SA: n=8). Evaluation showed higher mean forces and amplitude in the group with sole apical fixation (p=0.046; Table1). The impact of the additional sub-annular fixation was shown by a significant reduction of the force acting upon the apex of the heart. Quantification of these in vivo forces provides important information about the impact of different stent designs and might provide an objective parameter for stent performance evaluation in clinical application.

ProTaperによる根管形成の力学的解析 : 垂直荷重・トルクの観察

ProTaperによる根管形成の力学的解析 : 垂直荷重・トルクの観察

Mechanisms of Abnormal Q Waves in Hypertrophic Cardiomyopathy Assessed by Intracoronary Electrocardiography

To clarify the mechanisms of abnormal Q waves in hypertrophic cardiomyopathy (HCM), local epicardial electrical activities were assessed by intracoronary electrocardiography (ECG). Unipolar intracoronary ECG was recorded by introducing a guide wire for angioplasty into the left anterior descending artery (LAD) in 20 patients with HCM and 10 control subjects. Intracoronary ECG showed no Q waves in any control subjects. Intracoronary ECG showed no Q waves in 8 HCM patients without abnormal Q waves on surface ECG. In 12 HCM patients with abnormal Q waves on surface ECG, 4 showed Q waves on intracoronary ECG associated with regional wall-motion abnormalities, suggesting Q waves are formed by loss of electrical forces due to transmural myocardial fibrosis. The remaining 8 patients, who did not have Q waves on intracoronary ECG, showed greater thickening of the basal free wall than the apical free wall, with no wall-motion abnormalities. Intracoronary ECG was characterized by increased R or R' waves and prolonged R peak times at the proximal LAD, suggesting Q waves are formed by increased electrical forces of hypertrophied basal septal and/or ventricular free wall, unopposed by apical forces. The study findings provide evidence for two mechanisms of abnormal Q waves in HCM: (1) loss of electrical forces due to transmural myocardial fibrosis, and (2) altered direction of resultant initial QRS vector due to increased electrical forces of disproportionate hypertrophy of the basal septal and/or ventricular free wall, unopposed by apical forces.

Engine-driven preparation of curved root canals: measuring cyclic fatigue and other physical parameters.

An increasing number of engine-driven rotary systems are marketed to shape root canals. Although these systems may improve the quality of canal preparations, the risk for instrument fracture is also increased. Unfortunately, the stresses generated in rotary instruments when shaping curved root canals have not been adequately studied. Consequently, the aim of an ongoing project was to develop a measurement platform that could more accurately detail physical parameters generated in a simulated clinical situation. Such a platform was constructed by fitting a torque-measuring device between the rotating endodontic instrument and the motor driving it. Apically directed force and instrument insertion depth were also recorded. Additional devices were constructed to assess cyclic fatigue and static fracture loads. The current pilot study evaluated GT rotary instruments during the shaping of curved canals in plastic blocks as well as "ISO 3630-1 torque to fracture" and number of rotations required for fatigue fracture. Results indicated that torques in excess of 40 Nmm were generated by rotary GT-Files, a significantly higher figure than static fracture loads (less than 13 Nmm for the size 20. 12 GT-File). Furthermore, the number of rotations needed to shape simulated canals with a 5 mm radius of curvature in plastic blocks was 10 times lower than the number of rotations needed to fracture instruments in a "cyclic fatigue test". Apical forces were always greater than 1 N, and in some specimens, scores of 8 N or more were recorded. Further studies are required using extracted natural teeth, with their wide anatomical variation, in order to reduce the incidence of fracture of rotary instruments. In this way, the clinical potential of engine-driven rotary instruments to safely prepare curved canals can be fully appreciated.

Dynamic torque and apical forces of ProFile.04 rotary instruments during preparation of curved canals.

To analyse torque and force generated whilst shaping curved canals using rotary instruments. A specially designed computer-controlled testing platform was used to record events during the shaping of straight and curved canals in plastic blocks and in extracted human teeth using ProFile.04 instruments. Size 40 apical stops were prepared using crown-down, apical preparation and step-back procedures. Maximum torque, apically directed force and the numbers of revolutions were recorded at a resolution of 100 samples s-1. Load causing separation as required by the ISO 3630-1 test and cyclic fatigue was also recorded. Mean maximum scores were calculated and statistically tested using one- and two-way analyses of variance. Highest and lowest torque scores were recorded, respectively, in straight canals in plastic blocks at 25 Nmm and in natural canals at 14 Nmm. Significant differences were recorded for canal type and preparation phase (P < 0.0001). Loads causing separation varied from 3.7 to 32.3 Nmm. Apically directed forces ranged from 1 to 7.5 N. Again, there were significant differences depending on canal type and preparation phase (P < 0.0001). The number of revolutions during preparation ranged from 18 to 41. Size 15, 30 and 45 ProFile.04 instruments separated after 581, 430 and 402 revolutions, respectively, in a standard cyclic fatigue test. The new torque-testing platform details physical parameters during preparation of curved canals. To improve predictability, instrumentation sequences must be tested for excessively high torsional moments or forces. This study indicated that up to 10 curved canals could be safely prepared with a sequence of ProFile. 04 rotary instruments without separation due to cyclic fatigue. Efforts should continue to correlate root canal anatomy with torque and force generated during rotary root canal preparation.

Movement behavior of teeth and dental implants in periotest measurement in occlusion--an in vitro study

Early diagnosis of periodontal disease is essential for the planning of restorative, prosthetic and surgical treatment. The usual clinical methods are mostly subjective. Although the Periotest device has been specially developed for the diagnosis of periodontal disease, it can also be used to aid occlusal adjustment after insertion of inlays or artificial crowns. To investigate this application of the Periotest, a jaw model with idealized dental crowns incorporating motion and force sensors has been constructed. Motion and force are recorded during measurements with the Periotest. The maximum amplitudes in the apical (vertical) direction obtained with unpolished occlusal points increased with increasing occlusal load. With polished contact points, the maximum values in the apical direction revealed no dependence on occlusal load. The maximum amplitudes of movement and force in the oral (horizontal) direction decrease with increasing occlusal load both with polished and unpolished contact points. With the first, the teeth appear to slide one upon the other such that the overall distance between them remains unchanged, and no additional apical forces develop. In the case of rough contact points, additional forces develop, and falsify Periotest measurements.

OR 55 A comparative study of the compressive apical forces applied with Flex-R and Onix-R nickel titanium files used in the balanced force technique

OR 55 A comparative study of the compressive apical forces applied with Flex-R and Onix-R nickel titanium files used in the balanced force technique

Critical analysis of the balanced force technique in endodontics

The "balanced force" technique was introduced in 1985 and it was reported that the resistance of the dentin, as it circumferentially contacted the flutes of a file in a curved root canal, would be sufficient to override and mask any tendency of the file to straighten during rotational instrumentation. An alternative mechanism based on compressive force and file flexure is presented in this article. In a laboratory study, the apical force necessary to cause files of sizes #10 to #70 to bend and conform to an average canal curvature was determined. These measurements were then related to the apical forces applied to teeth when utilizing the Balanced Force technique in a simulated clinical setting. It was then proposed that the apically directed force necessary to prevent coronal movement of the file and to effect dentinal shearing during counterclockwise rotation placed the file in compression, flexing it to conform to the curvature of the canal. This explanation was consistent with the experimental data for the files used in this study up to size #60 for an average canal curvature and for average instrumentation forces.