Safe pseudoelastic limit range under torsional loading with Reciproc Blue.

AIM: To determine the distortional angle and torsional load at the pseudoelastic limit of Reciproc Blue instruments and to verify the safety of using pre-set dedicated motors designed for use with the original Reciproc instruments. METHODOLOGY: Two torsional conditions of Reciproc R25 and Reciproc Blue R25 were tested using a custom device. The first condition fixed the file tips at 3 mm and repetitively rotated them, with gradually increasing angles, from 10° to 270°, and the resulting torque was recorded (n = 15). The second test involved a single continuous rotation until fracture (n = 15). The pseudoelastic limits of the instruments were determined from their torque-rotation curves. For statistical analysis, two-way analysis of variance and t-tests were used, at a 95% significance level. Tested specimens were examined using field-emission scanning electron microscopy (FE-SEM). RESULTS: The angle at the pseudoelastic limit was significantly greater for Reciproc Blue than Reciproc, regardless of test mode (P < 0.05). When torsional loading was repeated, using gradually increasing rotational angles, the torsional resistance was significantly lower than for a single rotation (P < 0.05). However, under all test conditions, the pseudoelastic limit was below the pre-set 170° of the dedicated reciprocating motor. FE-SEM evaluation of the lateral aspects of the instruments revealed numerous longitudinal microcracks running along their long axis. For Reciproc Blue groups, the file shaft machining grooves were distorted after repetitive and continuous torsional tests. CONCLUSIONS: The 170° pre-set angle of the dedicated endodontic motors for the Reciproc system was safe for Reciproc Blue in single or time-restricted use.

Anatomical relationship of maxillary posterior teeth with the sinus floor and buccal cortex.

This study aimed to evaluate the possibility of root fenestration or oroantral communication by evaluating the distance from root apex to the sinus floor and buccal cortex in maxillary posterior teeth using cone-beam computed tomography (CBCT) images. The study included 2182 roots of the maxillary posterior teeth from 219 patients after reviewing CBCT images of 462 patients according to the location of roots by two endodontists. The distances from each root apex to the maxillary sinus floor and buccal and palatal cortices were evaluated according to sex and age, and the mean values were compared by one-way analysis of variance and Mann-Whitney U-test. The distance between root apex and maxillary sinus floor was the greatest in maxillary first premolars and shortest in the mesio-buccal roots of maxillary second molars. The distances from root apex to the buccal and palatal cortical bones were significantly greater in male patients than those in female patients (P < 0·05). The palatal roots of maxillary first molars exhibited the highest incidence as well as the greatest mean length (1·96 mm) of protrusion into the maxillary sinus. The distance from root apex to the sinus floor was found to increase with age, except in case of maxillary second premolars. Understanding the relationship of maxillary posterior teeth with the sinus floor and buccal cortex could provide clinicians valuable information to help reduce iatrogenic damage.

'Screw-in' tendency of rotary nickel-titanium files due to design geometry.

AIM: To examine the effect of several standard geometric characteristics of rotary instruments on the 'screw-in' forces and stresses generated on root dentine using 3D finite element analysis (FEA). METHODOLOGY: Four cross-sectional designs (triangular, slender-rectangular, rectangular and square) were evaluated. The area of the triangular cross-section and of the slender-rectangular model were the same. Another rectangular model had the same centre-core diameter as the triangular one. Each design was twisted into a file model with 5, 10 or 15 threads over its 16-mm-long working section. Three curved root canals were simulated as rigid surface models: θ = 15 degrees/R = 36 mm radius; θ = 30/R = 18; and θ = 45/R = 12. A commercial FEA package was used to simulate the file rotating in the canal to determine the 'screw-in' force and reaction torque on the instrument. RESULTS: Instruments of a square cross-section had the highest 'screw-in' force and reaction torsional stresses followed by the rectangle, the triangle design and the slender-rectangle design, respectively. The file with closer pitch generated lower stresses, compared with that with longer pitch. The greater the root canal curvature, the higher the 'screw-in' force and reaction torque generated. CONCLUSION: This study demonstrated that the 'screw-in' tendency depends on both the instrument geometry and canal curvature. Clinicians should be aware that certain instrument designs are prone to develop high 'screw-in' forces, requiring the operator to maintain control of the handpiece or to use a brushing action to prevent instruments being pulled into the canal.

Design and stability analysis of single-input fuzzy logic controller.

In existing fuzzy logic controllers (FLCs), input variables are mostly the error and the change-of-error regardless of complexity of controlled plants. Either control input u or the change of control input Deltau is commonly used as its output variable. A rule table is then constructed on a two-dimensional (2-D) space. This scheme naturally inherits from conventional proportional-derivative (PD) or proportional-integral (PI) controller. Observing that 1) rule tables of most FLCs have skew-symmetric property and 2) the absolute magnitude of the control input |u| or |Deltau| is proportional to the distance from its main diagonal line in the normalized input space, we derive a new variable called the signed distance, which is used as a sole fuzzy input variable in our simple FLC called single-input FLC (SFLC). The SFLC has many advantages: The total number of rules is greatly reduced compared to existing FLCs, and hence, generation and tuning of control rules are much easier. The proposed SFLC is proven to be absolutely stable using Popov criterion. Furthermore, the control performance is nearly the same as that of existing FLCs, which is revealed via computer simulations using two nonlinear plants.