Soram Oh

A comparison of nickel-titanium rotary instruments manufactured using different methods and cross-sectional areas: ability to resist cyclic fatigue

OBJECTIVEnThis study examined the effect of the manufacturing methods (ground, electropolished, and twisted) and the cross-sectional area (CSA) of nickel-titanium (NiTi) rotary instruments on their cyclic fatigue resistance.nnnSTUDY DESIGNnA total of 80 NiTi rotary instruments (ISO 25/.06 taper) from 4 brands (K3, ProFile, RaCe, and TF) were rotated in a simulated root canal with pecking motion until fracture. The number of cycles to failure (NCF) was calculated. The CSA at 3 mm from the tip of new instruments of each brand was calculated. The correlation between the CSA and NCF was evaluated. All fractured surfaces were analyzed using a scanning electron microscope to determine the fracture mode.nnnRESULTSnThe TF instruments were the most resistant to fatigue failure. The resistance to cyclic failure increased with decreasing CSA. All fractured surfaces showed the coexistence of ductile and brittle properties.nnnCONCLUSIONnThe CSA had a significant effect on the fatigue resistance of NiTi rotary instruments.

Comparison of mandibular first molar mesial root canal morphology using micro-computed tomography and clearing technique

Abstract Objective. Micro-computed tomography (MCT) with alternative image reformatting techniques shows complex and detailed root canal anatomy. This study compared two-dimensional (2D) and 3D MCT image reformatting with standard tooth clearing for studying mandibular first molar mesial root canal morphology. Materials and methods. Extracted human mandibular first molar mesial roots (n = 31) were scanned by MCT (Skyscan 1172). 2D thin-slab minimum intensity projection (TS-MinIP) and 3D volume rendered images were constructed. The same teeth were then processed by clearing and staining. For each root, images obtained from clearing, 2D, 3D and combined 2D and 3D techniques were examined independently by four endodontists and categorized according to Vertucci’s classification. Fine anatomical structures such as accessory canals, intercanal communications and loops were also identified. Results. Agreement among the four techniques for Vertucci’s classification was 45.2% (14/31). The most frequent were Vertucci’s type IV and then type II, although many had complex configurations that were non-classifiable. Generally, complex canal systems were more clearly visible in MCT images than with standard clearing and staining. Fine anatomical structures such as intercanal communications, accessory canals and loops were mostly detected with a combination of 2D TS-MinIP and 3D volume-rendering MCT images. Conclusions. Canal configurations and fine anatomic structures were more clearly observed in the combined 2D and 3D MCT images than the clearing technique. The frequency of non-classifiable configurations demonstrated the complexity of mandibular first molar mesial root canal anatomy.

Three‐dimensional modelling and concurrent measurements of root anatomy in mandibular first molar mesial roots using micro‐computed tomography

AIMnTo obtain concurrent radicular measurements in the mesiobuccal (MB) and mesiolingual (ML) canals of mandibular first molars using scanned data of micro-computed tomography (μCT) with novel software.nnnMETHODOLOGYnThe scanned data from 37 mandibular first molar mesial roots were reconstructed and analysed with custom-developed software (Kappa2). For each canal, three-dimensional (3D) surface models were re-sliced at 0.1-mm intervals perpendicular to the central axis. Dentine thicknesses, canal widths and 3D curvatures were measured automatically on each slice. Measurements were analysed statistically with anova for differences at each direction and at different levels of both canals.nnnRESULTSnLateral dentine thicknesses were significantly higher than mesial and distal thicknesses, at all the levels of both canals (Pxa0<xa00.001). Mesial thicknesses were significantly higher than distal thicknesses in the coronal third of both canals (Pxa0<xa00.001). Thinnest dentine thicknesses were mainly located on the disto-inside of both canals. Narrowest canal widths were 0.24xa0±xa00.10 and 0.22xa0±xa00.09xa0mm in MB and ML canals, respectively. Canal curvatures were greatest in the apical third of both canals (Pxa0<xa00.001), and they were greater in the MB canals than in the ML canals (Pxa0<xa00.05).nnnCONCLUSIONSnMicro-computed tomography with novel software provided valuable anatomical information for optimizing instrumentation and minimizing mishaps in nonsurgical root canal treatment.

Autotransplantation of mesiodens for missing maxillary lateral incisor with cone‐beam CT‐fabricated model and orthodontics

AIMnAutotransplantation is a viable treatment option for a missing tooth when there is a suitable donor, especially in adolescents with remaining facial growth. This report presents the aesthetic restoration of a missing maxillary lateral incisor through orthodontic treatment and autotransplantation of a mesiodens using a CBCT-fabricated rapid-prototyping model.nnnSUMMARYnA 14-year-old male patient with a congenitally missing maxillary lateral incisor was referred from the Department of Orthodontics. The teeth were moved orthodontically to regain space for the missing lateral incisor and to close the space of the mesiodens after transplantation. A replica of the donor tooth was fabricated from a cone-beam computed tomography scan through a rapid-prototyping machine before autotransplantation surgery. The model was used to create a socket for the graft tooth, thereby shortening the extra-oral time and minimizing the damage to the root surface. After transplantation and orthodontic tooth movement, the mesiodens was finally restored with an aesthetic laminate restoration. Over 3 years, the aesthetics remained excellent, and the transplant functioned normally without any signs or symptoms of root resorption.nnnKEY LEARNING POINTnMissing anterior teeth may be replaced through a combination of orthodontics, autotransplantation with a rapid-prototyping model and prosthodontic restoration, in growing patients.

Fracture Resistance of K3 Nickel-Titanium Files Made from Different Thermal Treatments

The purpose of this study was to compare fracture resistances of K3 nickel-titanium files made from different thermal treatments. K3 (SybronEndo, Orange, CA), K3XF (SybronEndo), and experimentally heat treated K3 (K3H) were used. For the cyclic fatigue test, the samples were rotated with up-and-down motion in the artificial canal with the curvature of 60 degrees until the fracture occurred. The number of cycles to fracture (NCF) was measured. For the torsional fracture test, the samples were tightly bound and rotated until the fracture occurred. Elastic modulus (EM), ultimate torsional strength (UTS), and angle of rotation to fracture (ARF) were measured. The results were statistically analyzed by one-way ANOVA. The NCF of K3H was higher than those of K3 and K3XF (P < 0.05). The EM of K3XF and K3H was lower than that of K3 (P < 0.05). There was no significant difference in UTS. The ARF of K3XF was higher than that of K3 (P < 0.05). K3XF and K3H showed more flexibility than K3. The maximum torsional angle of K3XF was higher than that of K3, but there was no significant difference on the UTS in all three groups.

Evaluation of three obturation techniques in the apical third of mandibular first molar mesial root canals using micro-computed tomography

Background/purpose Recent studies have demonstrated a high incidence of isthmuses in mandibular first molar mesial roots, and intratubular mineralization following mineral trioxide aggregate obturation. This study assessed the filling quality of three obturation techniques in the apical 5 mm of mandibular first molar mesial root canals. Materials and methods Sixty extracted human mandibular first molar mesial roots with two separate canals that had interconnecting isthmuses, were prepared to an apical size of 40/0.06. They were allocated to three groups of 20 roots for obturation by either cold lateral compaction (CLC) or the continuous wave of condensation (CW) that used gutta-percha and AH Plus sealer, or by an orthograde canal obturation using OrthoMTA. The obturated roots were scanned by micro-computed tomography and assessed for the volumetric ratio (%) of gutta-percha, sealer, and OrthoMTA within the main canals or isthmuses in the apical 5 mm area. Measurements were analyzed statistically for differences among three obturation techniques. Results In the main canals, filled volume ratios were not significantly different among groups. Within isthmuses, the filled volume ratio for CLC was lower than in CW (P = 0.025) or OrthoMTA (P = 0.002). In isthmuses, the gutta-percha volume ratio in CLC was lower than in CW (P = 0.005), although the sealer volume ratio was higher than in CW (P = 0.049). Conclusion CLC demonstrated lower filling densities in isthmuses in the apical region than either CW or OrthoMTA. Orthograde MTA obturation showed comparable filling quality to gutta-percha with sealer.

Clinical assessment of whitening efficacy and safety of in-office tooth whitening system containing 15% hydrogen peroxide with or without light activation

Objectives: This clinical study evaluated the effect of light activation on the whitening efficacy and safety of in-office bleaching system containing 15% hydrogen peroxide gel. Materials and Methods: Thirty-three volunteers were randomly treated with (n = 17, experimental group) or without light activation (n = 16, control group), using Zoom2 white gel (15% , Discus Dental) for a total treatment time of 45 min. Visual and instrumental color measurements were obtained using Vitapan Classical shade guide and Shadepilot (DeguDent) at screening test, after bleaching, and 1 month and 3 month after bleaching. Data were analyzed using t-test, repeated measure ANOVA, and chi-squared test. Results: Zoom2 white gel produced significant shade changes in both experimental and control group when pre-treatment shade was compared with that after bleaching. However, shade difference between two groups was not statistically significant (p > 0.05). Tooth shade relapse was not detected at 3 months after bleaching. The incidence of transient tooth sensitivity was 39.4%, with being no differences between two groups. Conclusions: The application of light activation with Zoom2 white gel system neither achieved additional whitening effects nor showed more detrimental influences.

Analysis of para-chloroaniline after chemical interaction between alexidine and sodium hypochlorite using mass spectrometry: A preliminary study

The purposes of this study were firstly to investigate the any formation of precipitate after interaction between ALX and NaOCL and secondarily to analyze the PCA formation by using time of flight secondary ion mass (TOF-SIM) spectrometry. Mass spectrometry analysis was performed for the mixture of 0.5% ALX and 5.25% NaOCl. As controls, 2.5% CHX with 5.25% NaOCl and 1% PCA solutions were used. Any for- mation of precipitates in 10 tested solutions was evaluated by naked eye. Results of mass spectrum showed that the typical peak of PCA was not detected in mixed solution of ALX and NaOCl, whereas CHX/NaOCl mixture showed the same peak that found in the PCA spectrum. Precipitate formation was only observed in CHX/NaOCL mixture. The present TOF-SIM spectrometry results indicated that ALX can be a useful root canal irrigant combined with NaOCl during canal instrumentation. Further study is necessary to confirm the antimicrobial effect of ALX against endodontic pathogen before its clinical application as an endodontic irrigant.

Mechanical and Metallurgical Properties of Various Nickel-Titanium Rotary Instruments

The aim of this study was to investigate the effect of thermomechanical treatment on mechanical and metallurgical properties of nickel-titanium (NiTi) rotary instruments. Eight kinds of NiTi rotary instruments with sizes of ISO #25 were selected: ProFile, K3, and One Shape for the conventional alloy; ProTaper NEXT, Reciproc, and WaveOne for the M-wire alloy; HyFlex CM for the controlled memory- (CM-) wire; and TF for the R-phase alloy. Torsional fracture and cyclic fatigue fracture tests were performed. Products underwent a differential scanning calorimetry (DSC) analysis. The CM-wire and R-phase groups had the lowest elastic modulus, followed by the M-wire group. The maximum torque of the M-wire instrument was comparable to that of a conventional instrument, while those of the CM-wire and R-phase instruments were lower. The angular displacement at failure (ADF) for the CM-wire and R-phase instruments was higher than that of conventional instruments, and ADF of the M-wire instruments was lower. The cyclic fatigue resistance of the thermomechanically treated NiTi instruments was higher. DSC plots revealed that NiTi instruments made with the conventional alloy were primarily composed of austenite at room temperature; stable martensite and R-phase were found in thermomechanically treated instruments.

Effect of acidic solutions on the microhardness of dentin and set OrthoMTA and their cytotoxicity on murine macrophage.

Objectives To evaluate the effects of three acids on the microhardness of set mineral trioxide aggregate (MTA) and root dentin, and cytotoxicity on murine macrophage. Materials and Methods OrthoMTA (BioMTA) was mixed and packed into the human root dentin blocks of 1.5 mm diameter and 5 mm height. Four groups, each of ten roots, were exposed to 10% citric acid (CA), 5% glycolic acid (GA), 17% ethylenediaminetetraacetic acid (EDTA), and saline for five minutes after setting of the OrthoMTA. Vickers surface microhardness of set MTA and dentin was measured before and after exposure to solutions, and compared between groups using one-way ANOVA with Tukey test. The microhardness value of each group was analyzed using student t test. Acid-treated OrthoMTA and dentin was examined by scanning electron microscope (SEM). Cell viability of tested solutions was assessed using WST-8 assay and murine macrophage. Results Three test solutions reduced microhardness of dentin. 17% EDTA demonstrated severe dentinal erosion, significantly reduced the dentinal microhardness compared to 10% CA (p = 0.034) or 5% GA (p = 0.006). 10% CA or 5% GA significantly reduced the surface microhardness of set MTA compared to 17% EDTA and saline (p < 0.001). Acid-treated OrthoMTA demonstrated microporous structure with destruction of globular crystal. EDTA exhibited significantly more cellular toxicity than the other acidic solutions at diluted concentrations (0.2, 0.5, 1.0%). Conclusions Tested acidic solutions reduced microhardness of root dentin. Five minutes application of 10% CA and 5% GA significantly reduced the microhardness of set OrthoMTA with lower cellular cytotoxicity compared to 17% EDTA.