For adhesive root canal sealers released in recent years, there have been few studies on their physical properties based on the ISO standard. In particular, the properties of sealers containing adhesive monomer have not yet been studied. The purpose of this study was to evaluate the physical properties of the adhesive root canal sealers Super-Bond™ RC-Sealer (Sun Medical) and MetaSEAL™ (Parkell) containing 4-META. In addition, items that did not satisfy the ISO standard were also tested for other sealers. The experiments were performed in accordance with ISO6876 specifications (2001, Dental root canal sealing materials) for the seven items of Flow, Working time, Setting time, Film thickness, Dimensional change following setting, Solubility and Radiopacity. The results indicated that each sealer satisfied the physical properties of the ISO standard except the dimensional change following setting. Although the ISO standard for this item is shrinkage of less than 1.0% and expansion of less than 0.1%, the expansion values of both sealers were over the ISO standard. Additional experiments were carried out to evaluate the dimensional change of other endodontic sealers: Epiphany® (Pentron), Epiphany® SE™ (Pentron), Tubli-Seal™ (SybronEndo), AH Plus® (Dentsply DeTrey), Root Canal Sealer (Henry Schein) and Sealapex™ (SybronEndo), following the setting test. These values of all the sealers except Sealapex™, which did not set under this test condition, were over the ISO standard. Epiphany® showed the maximum value and Tubli-Seal™ the minimum value among all the samples. The findings suggested that there is a clear positive correlation between the percentage of hydrophilic monomer in the sealer matrix and the dimensional change. Although the dimensional change values of eugenol-based Tubli-Seal™ and Root Canal Sealer were less than those of sealers containing hydrophilic monomer, elution behavior from the eugenol-based sealer was observed when immersed in distilled water. Regarding the seven items in accordance with ISO6876 for RC-Sealer and MetaSEAL™ containing 4-META, each sealer satisfied the ISO standard for the six items except dimensional change and was suitable for use as an endodontic sealer. All other six endodontic sealers did not satisfy the ISO standard in terms of dimensional change.

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It is generally accepted that root canal preparation with stainless steel hand files is a basic skill training in dental school. Recently, skill training for the preparation with a rotary nickel titanium file system has become important because of its increased application in dental clinics today. However, it is difficult to allocate sufficient time for skill training in dental school because of the diverse content of dental education. In the present study, we compared the effects of different training methods for root canal preparation with the rotary nickel titanium file system on the motivation as well as acquired skills of dental students. Dental students were randomly assigned to three groups: one group prepared a root canal model in a dental mannequin simulator (mannequin group), another group prepared the model by holding it by hand (holding group), and a control group. The mannequin and holding groups performed five consecutive days of training. On the first and the last day of consecutive practical training, and at one month after the training, the root canal preparation time of the model in the dental mannequin simulator and the root canal shape after the preparation were evaluated. Our results suggest that the five consecutive days of training with the dental mannequin simulator was effective to acquire skills of the rotary nickel titanium file system, as well as to keep the motivation of students.

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The purpose of this study was to investigate the effect of 35% hydrogen-based office-whitening agent on enamel by using optical coherence tomography (OCT). Labial surfaces of bovine teeth stored in 37℃ artificial saliva or purified water were treated by the whitening agent. OCT and laser scope observation was done before and immediately after application of whitening agent for 4 weeks. Tomographic images were obtained by OCT and morphological changes of enamel surfaces were observed by a laser scanning microscope. The results were as follows: 1. For the whitening group, the OCT images obtained changed during the test period and these tendencies depended on the storage conditions. The signal intensity from the specimen surfaces was higher when stored in distilled water than when stored in saliva, and the surface roughness of the specimens was also higher when stored in distilled water than when stored in saliva. 2. For the control group, although the signal intensities of the specimens stored in artificial saliva tended to be higher than those stored in purified water, no significant difference was found between them. For the laser scanning microscope observation, the same tendency was observed, and the surface roughness of the specimens stored in saliva increased compared to those stored in water.

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The physical and handling properties of flowable resin composites have been improved by modifying the materials. Furthermore, nano-fill and nano-hybrid flowable resin composites designed to combine high mechanical properties and superior polishing surfaces have been developed and have recently become commercially available. The purpose of this study was to investigate the toothbrush abrasion of flowable resin composites including nano-fill and nano-hybrid materials. The relationships between toothbrush abrasion and the following material properties were also investigated: surface hardness, surface roughness and filler content. Nine flowable resin composites and a paste type of a resin composite were used. Toothbrush abrasion was conducted in a toothbrush simulator using calcium carbonate slurry for 50,000 cycles. The maximum wear depth was measured with a profilometer after each 10,000 brushing cycles. Vickers hardness numbers were determined after grinding the surface with SiC paper, grit #1000. Surface roughness (Ra) was determined on the ground surface and on the brushed surface. The surface texture of the worn samples was examined by SEM. The wear depth of every material increased linearly with the number of brushing cycles. After 50,000 brushing cycles, the wear depth of Tetric® N-Flow was the highest of 9 flowable resin composites, followed by Palfique Estelite LV High Flow. The wear depth of Clearfil® Majesty® LV was the lowest, followed by Filtek™ Supreme XT Flowable Restorative. Surface hardness, surface roughness before brushing and filler content obtained from the manufacturer's information had no impact on the toothbrush abrasion of the flowable resin composites. However, the materials with low wear depth showed much higher surface roughness after brushing. From the SEM observations, the materials with larger particles including glass fillers and nanoclusters showed low wear depth.

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The suck-back phenomenon of dental air turbine handpieces causes the intake of saliva, blood and cut shavings from the oral cavity, contaminating not only the air turbine handpiece, but also the tube connector and the unit. Cross infection can occur even if the air turbine handpiece is changed for each patient. This study evaluated the anti-suck-back effect of four new air turbine handpieces models produced by different companies. 1. Measuring suck-back pressure: The suck-back pressure from the front face of the air turbine handpiece, back face and whole head of the air turbine handpiece were measured. The air turbine handpiece was allowed to rotate within a sealed flask. Then rotation was stopped and the amount of colored water drawn from the beaker into a glass tube was examined by maximum water height. 2. Verification of suck-back: The air turbine was started and then stopped in a floating flask under fluorescent mist caused by another air turbine handpiece (mist condition), fluorescent nebulization with an ultrasonic nebulizer (fume condition) and full immersion of the head of the air turbine handpiece in fluorescent stain solution. The cycle of starting for 2 seconds and stopping for 5 seconds was repeated 1, 2, 3, 5, 10, 30, 50, 100, 200, 300, 400 and 500 times until fluorescent stains on a gauze pad covered at the exhaust vent became visible in fluorescence microscopy images under each condition. The exhaust vent parts on the coupling as well as on the air turbine handpiece head were observed by fluorescence microscopy for the existence of fluorescent stains. As a result, the water height for each part of one air turbine handpiece was below 0 mm. Except for under full immersion, this model did not have any visible penetration of fluorescence to the exhaust vent even after 500 cycles under mist/fume conditions. Conversely, the other air turbine handpieces showed suck-back phenomena. In full immersion of the whole head of the air turbine handpiece, all handpieces showed suck-back phenomena immediately. As the handpiece heads are not completely sealed, full immersion must be avoided to prevent liquid intake. In conclusion, one air turbine handpiece showed the possibility avoiding suck-back.

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The purpose of this study was to evaluate the effect of the method of removing carious dentin on resin-composite bond strengths to dentin using three self-etching adhesive systems: G-Bond (GC), One-up Bond F (Tokuyama Dental) or Clearfil Mega Bond (Kuraray Medical). The bur-cut, Er: YAG-lased and ultrasonic vibrated dentin was subjected to micro-tensile bond testing and observation of ultra-structure by scanning electron microscopy. A smear layer was not formed on the dentin surface after removing carious dentin in the case of Er: YAG-lased and ultrasonic vibrated dentin. Clearfil Mega Bond showed significantly higher micro-tensile bond strength to bur-cut and ultrasonic vibrated dentin compared with Er: YAG-lased dentin (p<0.05). One-up Bond F showed significantly higher micro-tensile bond strength to ultrasonic vibrated dentin compared with bur-cut and Er: YAG-lased dentin (p<0.05). It is suggested that the method of removing carious dentin by an ultrasonic vibration device is useful for dentin adhesion when using self-etching adhesive systems.

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