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The purpose of the present study was to compare the properties required for the clinical application of soft lining materials containing a fluorinated monomer versus that of conventional materials in an effort to develop a new soft lining material with long-term stable viscoelastic properties. Four soft lining materials were examined. Two experimental materials containing dodecafluoroheptyl methacrylate (SR12F) or tridecafluorooctyl methacrylate (SR13F) were prepared. Two commercial soft lining materials, one acrylicbased and one silicone rubber-based, were selected as reference materials. Shore A hardness, viscoelastic properties, water sorption, solubility, and staining resistance were evaluated. The Shore A hardness and the displacements were analyzed with two-way analysis of variance (ANOVA) and Tukey's HSD test. The water sorption, the solubility and the color change were analyzed with one-way ANOVA and Tukey's HSD test. The significance level was set at 0.05. SR12F and SR13F showed greater viscous flow, low water sorption, low solubility, and good staining resistance compared to the commercial products. The results indicate that the soft lining materials containing fluorinated monomers might have a potentially long-term stable viscoelastic behavior.

Soft denture lining materials are required to be minimally contaminated from the viewpoint of oral hygiene. The experimental materials containing fluorinated monomers showed high flexibility and high contamination resistance. The use of monomers with a large number of fluorine atoms could give clinically-useful properties to these materials. AbstractPurpose: To develop a new fluorine-containing soft denture lining material, the influences of fluorinated monomers on physical properties and contamination resistance were examined. Methods:Five experimental materials of different chemical compositions in fluorinated monomer and two plasticized acrylics (Supersoft, VertexSoft) were used to evaluate water sorption, solubility, staining resistance, Shore A hardness, and contact angle. Five specimens for each test were fabricated. The results were analyzed with one-way analysis of variance (ANOVA) and Tukey's HSD test using statistical software at p = 0.05. Results: The amount of water sorption tended to decrease as the number of the fluorine atoms in fluorinated monomers increased. Similar solubility was shown regardless of the type of fluorinated monomer. The use of fluorinated monomers for immersion in coffee allowed suppression of discoloration. In b-carotene, there were no significant differences in color changes among four experimental materials with fluorinated monomer. Shore A hardness was decreased and the contact angles tended to increase as the number of fluorine atoms in fluorinated monomers increased. When comparing the experimental materials and commercially available materials, the experimental materials containing fluorinated monomers with large numbers of fluorine atoms showed adequate clinical properties except for staining test of b-carotene. Conclusion:Monomers with a large number of fluorine atoms can be used to develop applicable soft denture lining materials in clinical practice.

Aim To evaluate how different rotational speeds affect the torque/force generation and shaping ability of rotary root canal instrumentation using JIZAI (MANI, Utsunomiya, Japan) nickel‐titanium instruments in continuous rotation and optimum torque reverse (OTR) motion. Methodology Mesial root canals of extracted mandibular molars were instrumented up to size 25, 0.04 taper using JIZAI instruments, and anatomically matched canals were selected based on geometric features of the canal [canal volume (mm3), surface area (mm2), length, 15°–20° curvature and radius of curvature (4–8 mm)] after micro‐computed tomographic scanning. An automated root canal instrumentation and torque/force analysing device was programmed to permit a simulated pecking motion (2 s downward and 1 s upward at 50 mm min−1). The selected canals were prepared with size 25, 0.06 taper JIZAI instruments using continuous rotation or OTR motion and further subdivided according to the rotational speed (300 or 500 rpm, n = 10 each). Real‐time clockwise/counterclockwise torque and downward/upward force were recorded using a custom‐made torque/force analysing device. Then, the registered pre‐ and post‐operative micro‐computed tomographic datasets were examined to evaluate the canal volume changes and centring ratios at 1, 3, 5 and 7 mm from the apical foramen. Data were analysed using two‐way analysis of variance or the Kruskal–Wallis test and Mann–Whitney U test with Bonferroni correction (α = 5%). Results Maximum upward force and clockwise torque were significantly smaller in 500 rpm groups than in 300 rpm groups (P < .05); however, no significant difference was found between continuous rotation and OTR motion (P > .05). OTR motion developed higher maximum counterclockwise torque than continuous rotation (P < .05). Maximum downward force, canal volume changes and centring ratios were not significantly different among all groups (P > .05). There was no file fracture in any of the groups. Conclusions Under laboratory conditions using JIZAI instruments, a rotational speed of 500 rpm generated significantly lower maximum screw‐in forces and torque values than rotational speed of 300 rpm. Continuous rotation and OTR motion performed similarly in shaping the canals.

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Selection of an appropriate nickel–titanium (NiTi) rotary system is important for minimally invasive endodontic treatment, which aims to preserve as much root canal dentin as possible. This study aimed to evaluate selected mechanical properties and the root canal shaping ability of TruNatomy (TRN), a NiTi rotary system designed for minimally invasive endodontic shaping, in comparison with existing instruments: HyFlex EDM (HEDM), ProTaper Next (PTN), and WaveOne Gold (WOG). Load values measured with a cantilever bending test were ranked as TRN < HEDM < WOG < PTN (p < 0.05). A dynamic cyclic fatigue test revealed that the number of cycles to fracture was ranked as HEDM > WOG > TRN > PTN (p < 0.05). Torque and vertical force generated during instrumentation of J-shaped artificial resin canals were measured using an automated instrumentation device connected to a torque and vertical force measuring system; TRN exhibited smaller torque and vertical force values in most comparisons with the other instruments. The canal centering ratio for TRN was smaller than or comparable to that for the other instruments except for WOG at the apex level. Under the present experimental conditions, TRN showed higher flexibility and lower torque and vertical force values than the other instruments.

This study aimed to evaluate how various rotational modes influence the torque/force production and shaping ability of ProTaper Universal (PTU; non-heat-treated) and ProTaper Gold (PTG; heat-treated) nickel–titanium instruments. J-shaped resin canals were instrumented with PTU or PTG using an automated instrumentation device operated with reciprocating rotation [150° clockwise and 30° counterclockwise (R150/30) or 240° clockwise and 120° counterclockwise (R240/120)], optimum torque reverse motion (OTR), or continuous rotation (CR) (n = 10 each). Maximum force and torque were recorded, and canal centering ratios were calculated. Statistical analysis was performed with two-way ANOVA and a Bonferroni test (α = 0.05). The results were considered with reference to previous studies on the microstructure of the instruments. The upward force generated by R240/120 and OTR was smaller than that generated by R150/30 and CR in PTG (p < 0.05). The clockwise torque produced by OTR was lower than that produced by R150/30 in PTU and R240/120 and CR in PTG (p < 0.05). R240/120 and OTR induced less canal deviation compared to CR in PTU at 0 mm from the apex (p < 0.05). In conclusion, R240/120 and OTR reduced the screw-in force in PTG and improved the canal centering ability in PTU, which may be associated with the heat treatment-induced microstructural difference of the two instruments.