Flexibility and fracture properties determine the performance of NiTi rotary instruments. The purpose of this study was to evaluate how geometrical differences between three NiTi instruments affect the deformation and stress distributions under bending and torsional conditions using finite element analysis.

Three NiTi files (ProFile .06 / #30, F3 of ProTaper and ProTaper Universal) were scanned using a Micro-CT. The obtained structural geometries were meshed with linear, eight-noded hexahedral elements. The mechanical behavior (deformation and von Mises equivalent stress) of the three endodontic instruments were analyzed under four bending and rotational conditions using ABAQUS finite element analysis software. The nonlinear mechanical behavior of the NiTi was taken into account.

The U-shaped cross sectional geometry of ProFile showed the highest flexibility of the three file models. The ProTaper, which has a convex triangular cross-section, was the most stiff file model. For the same deflection, the ProTaper required more force to reach the same deflection as the other models, and needed more torque than other models for the same amount of rotation. The highest von Mises stress value was found at the groove area in the cross-section of the ProTaper Universal.

Under torsion, all files showed highest stresses at their groove area. The ProFile showed highest von Mises stress value under the same torsional moment while the ProTaper Universal showed the highest value under same rotational angle.

Citations

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• Effect of internal stress on cyclic fatigue failure in .06 taper ProFile
  Hye-Rim Jung, Jin-Woo Kim, Kyung-Mo Cho, Se-Hee Park
  Restorative Dentistry & Endodontics.2012; 37(2): 79.     CrossRef

The purpose of this study was to evaluate the viability of periodontal ligament cell in rat teeth using slow cryopreservation method with magnetic field through MTT assay and TUNEL test. For each group, 12 teeth of 4 weeks old white female Sprague-Dawley rat were used for MTT assay, and 6 teeth in TUNEL test. The Maxillary left and right, first and second molars were extracted as atraumatically as possible under tiletamine anesthesia. The experimental groups were group1 (immediately extraction), group 2 (cold preservation at 4℃ for 1 week), group 3 (rapid cryopreservation in liquid nitrogen), group 4 (slow cryopreservation with magnetic field of 1 G), and group 5 (slow cryopreservation). F medium was used as preservation medium and 10% DMSO as cryoprotectant. After preservation and thawing, the MTT assay and TUNEL test were processed. One way ANOVA and Scheffe method were performed at the 95% level of confidence. The value of optical density obtained after MTT analysis was divided by the value of eosin staining for tissue volume standardization. In both MTT assay and TUNEL test, it had showed no significant difference among group 3, 4, and 5. And group 3 had showed higher viability of periodontal ligament cell than group 2.

From this study, slow cryopreservation method with magnetic field can be used as one of cryopreservation methods.

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• The evaluation of periodontal ligament cells of rat teeth after low-temperature preservation under high pressure
  Jin-Ho Chung, Jin Kim, Seong-Ho Choi, Eui-Seong Kim, Jiyong Park, Seung-Jong Lee
  Journal of Korean Academy of Conservative Dentistry.2010; 35(4): 285.     CrossRef
• Comparison of viability of oral epithelial cells stored by different freezing methods
  Do-Young Baek, Seung-Jong Lee, Han-Sung Jung, EuiSeong Kim
  Journal of Korean Academy of Conservative Dentistry.2009; 34(6): 491.     CrossRef
• The efficacy of programmed cryo-preservation under pressure in rat periodontal ligament cells
  Young-Eun Lee, Eui-Seong Kim, Jin Kim, Seung-Hoon Han, Seung-Jong Lee
  Journal of Korean Academy of Conservative Dentistry.2009; 34(4): 356.     CrossRef

This study investigated the effect of intermittent polymerization on the rate of polymerization shrinkage and cuspal deflection in composite resins.

The linear polymerization shrinkage of each composite was measured using the custom-made linometer along with the light shutter specially devised to block the light at the previously determined interval. Samples were divided into 4 groups by light curing method; Group 1) continuous light (60s with light on); Group 2) intermittent light (cycles of 3s with 2s light on & 1s with light off for 90s); Group 3) intermittent light (cycles of 2s with 1s light on & 1s with light off for 120s); Group 4) intermittent light (cycles of 3s with 1s light on & 2s with light off for 180s). The amount of linear polymerization shrinkage was measured and its maximum rate (Rmax) and peak time (PT) in the first 15 seconds were calculated. For the measurement of cuspal deflection of teeth, MOD cavities were prepared in 10 extracted maxillary premolars. Reduction in the intercuspal distance was measured by the custom-made cuspal deflection measuring machine. ANOVA analysis was used for the comparison of the light curing groups and t-test was used to determine significant difference between the composite resins.

Pyramid showed the greater amount of polymerization shrinkage than Heliomolar (p < 0.05). There was no significant difference in the linear polymerization shrinkage among the groups. The Rmax was group 4 < 3, 2 < 1 in Heliomolar and group 3 < 4 < 2, 1 in Pyramid (p < 0.05). Pyramid demonstrated greater cuspal deflection than Heliomolar. The cuspal deflection in Heliomolar was group 4 < 3 < 2, 1 and group 4, 3 < 2, 1 in Pyramid (p < 0.05).

It was concluded that the reduced rate of polymerization shrinkage by intermittent polymerization can help to decrease the cuspal deflection.

This study was done to evaluate the reliability of the digital color analysis system (ShadeScan, CYNOVAD, Montreal, Canada) for dentistry.

Sixteen tooth models were made by injecting the A2 shade chemical cured resin for temporary crown into the impression acquired from 16 adults. Surfaces of the model teeth were polished with resin polishing cloth. The window of the ShadeScan handpiece was placed on the labial surface of tooth and tooth images were captured, and each tooth shade was analyzed with the ShadeScan software. Captured images were selected in groups, and compared one another.

Two models were selected to evaluate repeatability of ShadeScan, and shade analysis was performed 10 times for each tooth.

And, to ascertain the color difference of same shade code analyzed by ShadeScan, CIE L^*a^*b^*values of shade guide of Gradia Direct (GC, Tokyo, Japan) were measured on the white and black background using the Spectrolino (GretagMacbeth, USA), and Shade map of each shade guide was captured using the ShadeScan.

There were no teeth that were analyzed as A2 shade and unique shade. And shade mapping analyses of the same tooth revealed similar shade and distribution except incisal third.

Color difference (ΔE^*) among the Shade map which analyzed as same shade by ShadeScan were above 3.

Within the limits of this study, digital color analysis instrument for dentistry has relatively high repeatability, but has controversial in accuracy.

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• Development of polarization dental imaging modality and evaluation of its clinical feasibility
  Eunji Kim, Taeyoon Son, Yoon Lee, Byungjo Jung
  Journal of Dentistry.2012; 40: e18.     CrossRef

The aim of this study was to compare the compositions and cytotoxicity of white ProRoot MTA (white mineral trioxide aggregate) and 3 kinds of Portland cements. The elements, simple oxides and phase compositions of white MTA (WMTA), gray Portland cement (GPC), white Portland cement (WPC) and fast setting cement (FSC) were measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), X-ray fluorescence spectrometry (XRF) and X-ray diffractometry (XRD). Agar diffusion test was carried out to evaluate the cytotoxicity of WMTA and 3 kinds of Portland cements.

The results showed that WMTA and WPC contained far less magnesium (Mg), iron (Fe), manganese (Mn), and zinc (Zn) than GPC and FSC. FSC contained far more aluminum oxide (Al₂O₃) than WMTA, GPC, and WPC. WMTA, GPC, WPC and FSC were composed of main phases, such as tricalcicium silicate (3CaO·SiO₂), dicalcium silicate (2CaO·SiO₂), tricalcium aluminate (3CaO·Al₂O₃), and tetracalcium aluminoferrite (4CaO·Al₂O₃·Fe₂O₃). The significance of the differences in cellular response between WMTA, GPC, WPC and FSC was statistically analyzed by Kruskal-Wallis Exact test with Bonferroni's correction. The result showed no statistically significant difference (p > 0.05).

WMTA, GPC, WPC and FSC showed similar compositions. However there were notable differences in the content of minor elements, such as aluminum (Al), magnesium, iron, manganese, and zinc. These differences might influence the physical properties of cements.

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• Development of Multi-functional Composite Cement with Strength Improvement Using Disposable Waste Masks
  Jong-Won Chung, Hyun-Kyoung Yang
  Journal of Power System Engineering.2022; 26(3): 31.     CrossRef
• The effects of mineral trioxide aggregate on osteo/odontogenic potential of mesenchymal stem cells: a comprehensive and systematic literature review
  Danial Babaki, Sanam Yaghoubi, Maryam M. Matin
  Biomaterial Investigations in Dentistry.2020; 7(1): 175.     CrossRef
• Remineralization of demineralized dentin using a dual analog system
  Neha Saxena, Stefan Habelitz, Grayson W. Marshall, Laurie B. Gower
  Orthodontics & Craniofacial Research.2019; 22(S1): 76.     CrossRef
• Chemical analysis and biological properties of two different formulations of white portland cements
  Hany Mohamed Aly Ahmed, Norhayati Luddin, Thirumulu Ponnuraj Kannan, Khairani Idah Mokhtar, Azlina Ahmad
  Scanning.2016; 38(4): 303.     CrossRef
• In vitrocytotoxicity of four calcium silicate-based endodontic cements on human monocytes, a colorimetric MTT assay
  Sedigheh Khedmat, Somayyeh Dehghan, Jamshid Hadjati, Farimah Masoumi, Mohammad Hossein Nekoofar, Paul Michael Howell Dummer
  Restorative Dentistry & Endodontics.2014; 39(3): 149.     CrossRef
• Conservative approach of a symptomatic carious immature permanent tooth using a tricalcium silicate cement (Biodentine): a case report
  Cyril Villat, Brigitte Grosgogeat, Dominique Seux, Pierre Farge
  Restorative Dentistry & Endodontics.2013; 38(4): 258.     CrossRef
• Chemical characteristics of mineral trioxide aggregate and its hydration reaction
  Seok-Woo Chang
  Restorative Dentistry & Endodontics.2012; 37(4): 188.     CrossRef
• Physical and chemical properties of experimental mixture of mineral trioxide aggregate and glass ionomer cement
  Yu-Na Jeong, So-Young Yang, Bum-Jun Park, Yeong-Joon Park, Yun-Chan Hwang, In-Nam Hwang, Won-Mann Oh
  Journal of Korean Academy of Conservative Dentistry.2010; 35(5): 344.     CrossRef
• Biocompatibility of bioaggregate cement on human pulp and periodontal ligament (PDL) derived cells
  Choo-Ryung Chung, Euiseong Kim, Su-Jung Shin
  Journal of Korean Academy of Conservative Dentistry.2010; 35(6): 473.     CrossRef
• Physical properties of novel composite using Portland cement for retro-filling material
  Sang-Jin Lee, Ok-In Cho, Jiwan Yum, Jeong-Kil Park, Bock Hur, Hyeon-Cheol Kim
  Journal of Korean Academy of Conservative Dentistry.2010; 35(6): 445.     CrossRef
• A bioactivity study of Portland cement mixed with β-glycerophosphosphate on human pulp cell
  Young-Hwan Oh, Young-Joo Jang, Yong-Bum Cho
  Journal of Korean Academy of Conservative Dentistry.2009; 34(5): 415.     CrossRef
• Comparison of biocompatibility of four root perforation repair materials
  Min-Kyung Kang, In-Ho Bae, Jeong-Tae Koh, Yun-Chan Hwang, In-Nam Hwang, Won-Mann Oh
  Journal of Korean Academy of Conservative Dentistry.2009; 34(3): 192.     CrossRef
• Effects of condensation techniques and canal sizes on the microleakage of orthograde MTA apical plug in simulated canals
  Deuk-Lim Nam, Jeong-Kil Park, Bock Hur, Hyeon-Cheol Kim
  Journal of Korean Academy of Conservative Dentistry.2009; 34(3): 208.     CrossRef

The aim of the present study is to compare the corrosion tendency using two kinds of NiTi files in the various environmental conditions through the visual examination and electrochemical analysis. ProTaper Universal S2, 21 mm (Dentsply Maillefer, Ballaigues, Switzerland) and Hero 642, 0.06 tapers, size 25, 21 mm (Micromega, Besancon, France) rotary instruments were tested. The instruments were randomly divided into eighteen groups (n = 5) by the immersion temperature, the type of solution, the brand of NiTi rotary instrument and the presence of mechanical loading. Each file was examined at various magnifications using Scanning Electron Microscope (JEOL, Akishima, Tokyo, Japan) equipped with energy dispersive X-ray microanalysis (EDX). EDX was used to determine the components of the endodontic file alloy in corroded and noncorroded areas. The corrosion resistance of unused and used NiTi files after repeated uses in the human teeth was evaluated electrochemically by potentiodynamic polarization test using a potentiostat (Applied Corrosion Monitoring, Cark-in-Cartmel, UK).

Solution temperature and chloride ion concentration may affect on passivity of NiTi files. Under the conditions of this in vitro study, the corrosion resistance is slightly increased after clinical use.

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• Comparing Cyclic Fatigue Resistance and Free Recovery Transformation Temperature of NiTi Endodontic Single-File Systems Using a Novel Testing Setup
  Emad Youssef, Holger Jungbluth, Søren Jepsen, Manfred Gruener, Christoph Bourauel
  Materials.2024; 17(3): 566.     CrossRef
• The Determination of the Corrosion Rates of Rotary Ni-Ti Instruments in Various Irrigation Solutions
  Tolga Özcan, Bade Sonat, Meltem Dartar Öztan, Fatma Basmaci, Umut Aksoy
  Cyprus Journal of Medical Sciences.2023; 8(2): 136.     CrossRef
• A Nonlinear Probabilistic Pitting Corrosion Model of Ni–Ti Alloy Immersed in Shallow Seawater
  Špiro Ivošević, Gyöngyi Vastag, Nataša Kovač, Peter Majerič, Rebeka Rudolf
  Micromachines.2022; 13(7): 1031.     CrossRef
• Corrosion resistance assessment of nickel-titanium endodontic files with and without heat treatment
  Tatiana Dias Costa, Elison da Fonseca e Silva, Paula Liparini Caetano, Marcio José da Silva Campos, Leandro Marques Resende, André Guimarães Machado, Antônio Márcio Resende do Carmo
  Restorative Dentistry & Endodontics.2021;[Epub]     CrossRef
• Effect of Sodium Hypochlorite, EDTA, and Chitosan Solution on Corrosion and Quantity of Extruded Nickel Ions Using Two Rotary Instruments (In Vitro)
  Eltica Oktavia, Trimurni Abidin
  World Journal of Dentistry.2019; 10(3): 207.     CrossRef

The purpose of this study was to evaluate the color stability of resin cements with accelerated test. Four dual curing resin cements: Panavia-F (KURARAY), Duolink (BISCO), Variolink-II (Ivoclar Vivadent), and RelyX Unicem (3M ESPE) and 1 self curing resin cement: Resiment CE (j. l. Blosser) were used in this study. In control group, Gradia Anterior (GC) composite resin and Tescera Dentin (Bisco) indirect composite were used. Ten disk shape specimens were made from each resin cement. The specimens were subjected to an accelerated aging process in a refrigerated bath circulator at 60℃ for 15 and 30 days. Spectrophotometric analyses were made before and after 15 days and 30 days of accelerated aging time.

The color characteristics (L^*, a^*, b^*) and the color difference (ΔE^*) of the specimens before and after immersion were measured and computed.

Regardless of type of the resin cements, L^* value was decreased and a^* value was increased, but there were no significant difference. But b^* value was increased significantly (p < 0.05). Tescera inlay showed least color change (p < 0.05), but Gradia showed notable color change after 15 days.

After 30 days on accelerated aging, ΔE^* value was increased (Panavia-F < Variolink-II < Resiment CE < Duolink < Unicem) (p < 0.05), but there were no significant difference among Panavia-F, Variolink-II, and Resiment CE groups. After 30 days of accelerated aging, ΔE^* value of all resin cements were greater than 3.0 and could be perceived by the human eye.

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• Influence of light-curing on the translucence change and color stability of amine-free dual-cured resin cements
  Sung-Hyeon Choi, Bo-Ram Lee, Bin-Na Lee, Hoon-Sang Chang, Yun-Chan Hwang, Won-Mann Oh, In-Nam Hwang
  Korean Journal of Dental Materials.2019; 46(3): 165.     CrossRef
• Effect of Accelerated Aging on the Color Stability of Dual-Cured Self-Adhesive Resin Cements
  Ah-Rang Kim, Yong-Chan Jeon, Chang-Mo Jeong, Mi-Jung Yun, Jung-Bo Huh
  Journal of Korean Dental Science.2015; 8(2): 49.     CrossRef

The purpose of this study was to evaluate the effects of MTAD, EDTA and sodium hypochlorite(NaOCl) as final irrigants on coronal leakage resistance to Enterococcus faecalis. Forty extracted human maxillary molars were used in this experiment. The teeth were randomly divided into positive control group (Group 1; n = 5), negative control group (Group 2; n = 5) and three experimental groups (n = 30). In Group 3 (n = 10), the root canals were irrigated with sodium hypochlorite. In Group 4 (n = 10) and 5 (n = 10), the root canals were irrigated with sodium hypochlorite and rinsed with EDTA and MTAD, respectively. The teeth in each group were cleaned and shaped to #40 profile with .04 taper, and obturated with gutta-percha and AH-26 root canal sealer. The coronal portion of each tooth was placed in contact with inoculum of Enterococcus faecalis in Brain Heart Infusion (BHI) culture media. Each root tip was placed in a vial containing sterile culture media. The vials were placed in anaerobic chamber and observed everyday for turbidity for 180 days. Statistical analysis was performed using Fisher's Exact Test. After 180 days, Group 3, 4, and 5 showed 7, 4 and 5 leaking samples respectively. The differences in leakage resistance were not statistically significant among Group 3, 4 and 5.

This study was aimed to investigate whether an oxygen inhibition layer (OIL) is essential for the interfacial bonding between resin composite layers or not.

A composite (Z-250, 3M ESPE) was filled in two layers using two aluminum plate molds with a hole of 3.7 mm diameter. The surface of first layer of cured composite was prepared by one of five methods as followings, thereafter second layer of composite was filled and cured: Group 1 - OIL is allowed to remain on the surface of cured composite; Group 2 - OIL was removed by rubbing with acetone-soaked cotton; Group 3 - formation of the OIL was inhibited using a Mylar strip; Group 4 - OIL was covered with glycerin and light-cured; Group 5 (control) - composite was bulk-filled in a layer. The interfacial shear bond strength between two layers was tested and the fracture modes were observed. To investigate the propagation of polymerization reaction from active area having a photo-initiator to inactive area without the initiator, a flowable composite (Aelite Flow) or an adhesive resin (Adhesive of ScotchBond Multipurpose) was placed over an experimental composite (Exp_Com) which does not include a photoinitiator and light-cured. After sectioning the specimen, the cured thickness of the Exp_Com was measured.

The bond strength of group 2, 3 and 4 did not show statistically significant difference with group 1. Groups 3 and 4 were not statistically significant different with control group 5. The cured thicknesses of Exp_Com under the flowable resin and adhesive resin were 20.95 (0.90) um and 42.13 (2.09), respectively.

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• Finishing and Polishing of Composite Restoration: Assessment of Knowledge, Attitude and Practice Among Various Dental Professionals in India
  Sankar Vishwanath, Sadasiva Kadandale, Senthil kumar Kumarappan, Anupama Ramachandran, Manu Unnikrishnan, Honap manjiri Nagesh
  Cureus.2022;[Epub]     CrossRef
• Evaluation of Surface Roughness of Composite, Compomer and Carbomer After Curing Through Mylar Strip and Glycerin: A Comparative Study
  Asli Topaloglu-Ak, Dilara Çayırgan, Melisa Uslu
  Journal of Advanced Oral Research.2020; 11(1): 12.     CrossRef
• Effect of glycerin on the surface hardness of composites after curing
  Hyun-Hee Park, In-Bog Lee
  Journal of Korean Academy of Conservative Dentistry.2011; 36(6): 483.     CrossRef