Effect of surface treatment on the mechanical properties of nickel-titanium files with a similar cross-section

OBJECTIVES: The aim of this study was to compare the mechanical properties of various nickel-titanium (NiTi) files with similar tapers and cross-sectional areas depending on whether they were surface-treated. MATERIALS AND METHODS: Three NiTi file systems with a similar convex triangular cross-section and the same ISO #25 tip size were selected for this study: G6 (G6), ProTaper Universal (PTU), and Dia-PT (DPT). To test torsional resistance, 5 mm of the straightened file's tip was fixed between polycarbonate blocks (n = 15/group) and continuous clockwise rotation until fracture was conducted using a customized device. To evaluate cyclic fatigue resistance, files were rotated in an artificial curved canal until fracture in a dynamic mode (n = 15/group). The torsional data were analyzed using 1-way analysis of variance and the Tukey post-hoc comparison test, while the cyclic fatigue data were analyzed using the Mann-Whitney U test at a significance level of 95%. RESULTS: PTU showed significantly greater toughness, followed by DPT and G6 (p < 0.05). G6 showed the lowest resistance in ultimate torsional strength, while it showed a higher fracture angle than the other files (p < 0.05). In the cyclic fatigue test, DPT showed a significantly higher number of cycles to failure than PTU or G6 (p < 0.05). CONCLUSIONS: Within the limitations of this study, it can be concluded that the torsional resistance of NiTi files was affected by the cross-sectional area, while the cyclic fatigue resistance of NiTi files was influenced by the surface treatment.

Preference of undergraduate students after first experience on nickel-titanium endodontic instruments

OBJECTIVES: This study aimed to compare two nickel-titanium systems (rotary vs. reciprocating) for their acceptance by undergraduate students who experienced nickel-titanium (NiTi) instruments for the first time. MATERIALS AND METHODS: Eighty-one sophomore dental students were first taught on manual root canal preparation with stainless-steel files. After that, they were instructed on the use of ProTaper Universal system (PTU, Dentsply Maillefer), then the WaveOne (WO, Dentsply Maillefer). They practiced with each system on 2 extracted molars, before using those files to shape the buccal or mesial canals of additional first molars. A questionnaire was completed after using each file system, seeking students' perception about 'Ease of use', 'Flexibility', 'Cutting-efficiency', 'Screwing-effect', 'Feeling-safety', and 'Instrumentation-time' of the NiTi files, relative to stainless-steel instrumentation, on a 5-point Likert-type scale. They were also requested to indicate their preference between the two systems. Data was compared between groups using t-test, and with Chi-square test for correlation of each perception value with the preferred choice (p = 0.05). RESULTS: Among the 81 students, 55 indicated their preferred file system as WO and 22 as PTU. All scores were greater than 4 (better) for both systems, compared with stainless-steel files, except for 'Screwing-effect' for PTU. The scores for WO in the categories of 'Flexibility', 'Screwing-effect', and 'Feeling-safety' were significantly higher scores than those of PTU. A significant association between the 'Screwing-effect' and students' preference for WO was observed. CONCLUSIONS: Novice operators preferred nickel-titanium instruments to stainless-steel, and majority of them opted for reciprocating file instead of continuous rotating system.

Screw-in forces during instrumentation by various file systems

OBJECTIVES: The purpose of this study was to compare the maximum screw-in forces generated during the movement of various Nickel-Titanium (NiTi) file systems. MATERIALS AND METHODS: Forty simulated canals in resin blocks were randomly divided into 4 groups for the following instruments: Mtwo size 25/0.07 (MTW, VDW GmbH), Reciproc R25 (RPR, VDW GmbH), ProTaper Universal F2 (PTU, Dentsply Maillefer), and ProTaper Next X2 (PTN, Dentsply Maillefer, n = 10). All the artificial canals were prepared to obtain a standardized lumen by using ProTaper Universal F1. Screw-in forces were measured using a custom-made experimental device (AEndoS-k, DMJ system) during instrumentation with each NiTi file system using the designated movement. The rotation speed was set at 350 rpm with an automatic 4 mm pecking motion at a speed of 1 mm/sec. The pecking depth was increased by 1 mm for each pecking motion until the file reach the working length. Forces were recorded during file movement, and the maximum force was extracted from the data. Maximum screw-in forces were analyzed by one-way ANOVA and Tukey's post hoc comparison at a significance level of 95%. RESULTS: Reciproc and ProTaper Universal files generated the highest maximum screw-in forces among all the instruments while M-two and ProTaper Next showed the lowest (p < 0.05). CONCLUSIONS: Geometrical differences rather than shaping motion and alloys may affect the screw-in force during canal instrumentation. To reduce screw-in forces, the use of NiTi files with smaller cross-sectional area for higher flexibility is recommended.

Buckling resistance, bending stiffness, and torsional resistance of various instruments for canal exploration and glide path preparation

OBJECTIVES: This study compared the mechanical properties of various instruments for canal exploration and glide-path preparations. MATERIALS AND METHODS: The buckling resistance, bending stiffness, ultimate torsional strength, and fracture angle under torsional load were compared for C+ file (CP, Dentsply Maillefer), M access K-file (MA, Dentsply Maillefer), Mani K-file (MN, Mani), and NiTiFlex K-file (NT, Dentsply Maillefer). The files of ISO size #15 and a shaft length of 25 mm were selected. For measuring buckling resistance (n = 10), the files were loaded in the axial direction of the shaft, and the maximum load was measured during the files' deflection. The files (n = 10) were fixed at 3-mm from the tip and then bent 45degrees with respect to their long axis, while the bending force was recorded by a load cell. For measuring the torsional properties, the files (n = 10) were also fixed at 3-mm, and clockwise rotations (2-rpm) were applied to the files in a straight state. The torsional load and the distortion angle were recorded until the files succumbed to the torque. RESULTS: The CP was shown to require the highest load to buckle and bend the files, and the NT showed the least. While MA and MN showed similar buckling resistances, MN showed higher bending stiffness than MA. The NT had the lowest bending stiffness and ultimate torsional strength (p < 0.05). CONCLUSIONS: The tested instruments showed different mechanical properties depending on the evaluated parameters. CP and NT files were revealed to be the stiffest and the most flexible instruments, respectively.

Cutting efficiency of apical preparation using ultrasonic tips with microprojections: confocal laser scanning microscopy study

OBJECTIVES: The purpose of this study was to compare the cutting efficiency of a newly developed microprojection tip and a diamond-coated tip under two different engine powers. MATERIALS AND METHODS: The apical 3-mm of each root was resected, and root-end preparation was performed with upward and downward pressure using one of the ultrasonic tips, KIS-1D (Obtura Spartan) or JT-5B (B&L Biotech Ltd.). The ultrasonic engine was set to power-1 or -4. Forty teeth were randomly divided into four groups: K1 (KIS-1D / Power-1), J1 (JT-5B / Power-1), K4 (KIS-1D / Power-4), and J4 (JT-5B / Power-4). The total time required for root-end preparation was recorded. All teeth were resected and the apical parts were evaluated for the number and length of cracks using a confocal scanning micrscope. The size of the root-end cavity and the width of the remaining dentin were recorded. The data were statistically analyzed using two-way analysis of variance and a Mann-Whitney test. RESULTS: There was no significant difference in the time required between the instrument groups, but the power-4 groups showed reduced preparation time for both instrument groups (p < 0.05). The K4 and J4 groups with a power-4 showed a significantly higher crack formation and a longer crack irrespective of the instruments. There was no significant difference in the remaining dentin thickness or any of the parameters after preparation. CONCLUSIONS: Ultrasonic tips with microprojections would be an option to substitute for the conventional ultrasonic tips with a diamond coating with the same clinical efficiency.

Clinicopathologic Observation of Odontogenic Sinus Tracts Draining to the Skin / 대한피부과학회지

BACKGROUND: An odontogenic sinus tract draining to the skin is the most common type of cutaneous fistula that occurs on the face. This lesion can be a diagnostic challenge to clinicians who are not familiar with cutaneous fistula since many patients with an odontogenic sinus tract draining to the skin do not have any symptom such as toothache. OBJECTIVE: Our purpose was to determine the characteristic features of an odontogenic sinus tract draining to the skin. METHODS: Eleven patients who presented with an odontogenic sinus tract draining to the skin at the Dermatologic Department of Pusan National University Hospital during the last ten years were enrolled in this study. We reviewed all the medical records of the patients. RESULTS: The mean age was 51.8 years. The male to female ratio was 1.2:1. Nine patients (82%) had lesions on their chins or the mandibular region. The most common tooth with endodontic infection was the lower first premolar tooth (36%), and the most common clinical feature was pyogenic granuloma-like solitary papule (64%). The panoramic view showed radiolucent periapical abscesses in all the patients. Skin biopsy showed chronic granulomatous inflammation, and fistular tracts were present in three patients. Only 1 of 11 patients (9%) had toothache, and two patients had prior therapies for prosthetic dentures or caries, respectively. Nine patients (82%) were treated ineffectively, and their first visit was to adermatologic clinic (91%) or an otolaryngologic clinic (9%). After the diagnosis of odontogenic sinus tract draining to the skin, eight patients (73%) were treated completely by root canal therapy or extraction of teeth. CONCLUSION: In this study, most patients had no toothache or history of dental disease, and they were treated inappropriately, even in dermatologic clinics. The results of this study will help reduce the incidence of inappropriate management for odontogenic sinus tract draining to the skin at dermatologic departments.

Cranial subdural hematoma developing after spinal anesthesia: A case report / 대한마취과학회지

Intracranial subdural hematoma is an exceptionally rare complication of spinal anesthesia. An 88-year-old female patient diagnosed with grade V uterine prolapse with rectocystocele received a vaginal hysterectomy and anteroposterior repair under spinal anesthesia. At 4 days postoperatively, she appeared to have decreased orientation, inappropriate behavior, and right side weakness grade III. Brain MR diffusion and CT revealed a bilateral subdural hematoma. She was improved after burr hole drainage. We report a case of intracranial subdural hematoma developing after spinal anesthesia, a rare complication.

Transesophageal Echocardiographic Diagnosis of Pulmonary Thromboembolism during Cesarean Delivery: A case report / 대한마취과학회지

Acute pulmonary thromboembolism (PTE) is life-threatening and difficult to diagnose. However, echocardiography can help diagnose and monitor PTE by visualizing the thrombus and assessing hemodynamic changes. Here we report the usefulness of transesophageal echocardiography (TEE) in a diagnosis of maternal PTE during cesarean delivery by showing a thromboembolus in pulmonary artery. In addition, TEE also prompted effective cardiopulmonary resuscitation for recurrent hemodynamic collapse due to a massive PTE, as well as rapid introduction of an extracorporeal membrane oxygenator to treat maternal hypoxia.