Publications by authors named "Naohiko Iwasaki"

41 Publications

Effects of build orientation on adaptation of casting patterns for three-unit partial fixed dental prostheses fabricated by using digital light projection.

J Prosthet Dent 2021 Feb 26. Epub 2021 Feb 26.

Professor, Department of Oral Biomaterials Engineering, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan.

Statement Of Problem: The lost-wax technique is commonly used for fabricating partial fixed dental prostheses. The casting patterns can be fabricated by using vat photopolymerization (a type of additive manufacturing), but the adaptation of these casting patterns has not been elucidated.

Purpose: The purpose of this in vitro study was to evaluate the effect of build orientation on the adaptation of casting patterns fabricated by digital light projection (DLP).

Material And Methods: A 3-unit partial fixed dental prosthesis with mandibular left second premolar and second molar abutment teeth was scanned and virtually designed with a computer-aided design software program. The cement space was designed to be 30 μm. Specimens were fabricated with 3 build orientations: 0 degrees (with the occlusal surface parallel to the platform), 30 degrees, and 45 degrees (by rotating the file along the long axis). The casting patterns were fabricated by using DLP (Cara Print 4.0) with a photopolymerizable monomer (dima Print Cast Q). Photopolymerization, cleaning, and postpolymerization processes were performed according to the manufacturer's instructions. The adaptation of the specimens was examined by using a silicone replica method. The vertical marginal discrepancy and axial wall, occlusal, and marginal gaps were measured by using a digital measuring microscope. The effect of build orientation at each cross-sectional area was statistically analyzed by using the Kruskal-Wallis test followed by the pairwise Wilcoxon rank sum test with Bonferroni correction (α=.05).

Results: Excess polymerized resin was observed along the intaglio buccal wall at build orientations of 30 degrees and 45 degrees. Vertical marginal discrepancies in the buccolingual section ranged from -50 to 248 μm, while those in the mesiodistal section ranged from -25 to 182 μm. The gaps in the buccolingual section ranged from 0 to 236 μm, while those in the mesiodistal section ranged from 0 to 177 μm. According to the observation of vertical marginal discrepancies and gaps, the 30-degree specimens inclined during insertion, and the 45-degree specimens were not completely seated. However, the marginal gaps of the 0- and 30-degree specimens were within the clinically acceptable limit of 120 μm.

Conclusions: The limited data indicated that the build orientation influenced the adaptation of casting patterns for 3-unit partial fixed dental prostheses fabricated by using DLP. A build orientation of 0 degrees is recommended for fabricating casting patterns for 3-unit partial fixed dental prostheses because no excess polymerization of the intaglio buccal wall was observed.
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http://dx.doi.org/10.1016/j.prosdent.2021.01.006DOI Listing
February 2021

Application of Glass Fiber and Carbon Fiber-Reinforced Thermoplastics in Face Guards.

Polymers (Basel) 2020 Dec 23;13(1). Epub 2020 Dec 23.

Department of Advanced Biomaterials, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan.

Face guards (FGs) are protectors that allow for the rapid and safe return of athletes who are to play after sustaining traumatic facial injuries and orbital fractures. Current FGs require significant thickness to achieve sufficient shock absorption abilities. However, their weight and thickness render the FGs uncomfortable and reduce the field of vision of the athlete, thus hindering their performance. Therefore, thin and lightweight FGs are required. We fabricated FGs using commercial glass fiber-reinforced thermoplastic (GFRTP) and carbon fiber-reinforced thermoplastic (CFRTP) resins to achieve these requirements and investigated their shock absorption abilities through impact testing. The results showed that an FG composed of CFRTP is thinner and lighter than a conventional FG and has sufficient shock absorption ability. The fabrication method of an FG comprising CFRTP is similar to the conventional method. FGs composed of commercial FRTPs exhibit adequate shock absorption abilities and are thinner and lower in weight as compared to conventional FGs.
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http://dx.doi.org/10.3390/polym13010018DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7793102PMC
December 2020

Effects of build conditions and angle acuteness on edge reproducibility of casting patterns fabricated using digital light projection.

Dent Mater J 2020 Jan 2;39(1):135-140. Epub 2019 Oct 2.

Department of Oral Biomaterials Development Engineering, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University.

The aim of the present study was to evaluate the effects of build conditions and angle acuteness on edge reproducibility of the casting patterns fabricated using a digital light process. The prism-shaped patterns with various vertex angles were fabricated in three build orientations. The height from the base to the vertex angle point of the fabricated pattern was measured and the incomplete height was calculated as the discrepancy between the original and measured heights. Two-way ANOVA revealed that the vertex angle and build orientation and their interaction were significant (p<0.05). The incomplete height significantly decreased with an increase of the vertex angle. When the vertex angle was 20° and the build-up direction was parallel to the edge of vertex angle and perpendicular to the triangular base, the incomplete height was the smallest. Therefore, build orientation and angle acuteness influenced the edge reproducibility of the casting patterns fabricated using a digital light process.
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http://dx.doi.org/10.4012/dmj.2018-401DOI Listing
January 2020

Effect of fiberglass orientation on flexural properties of fiberglass-reinforced composite resin block for CAD/CAM.

Dent Mater J 2019 Oct 21;38(5):738-742. Epub 2019 Jun 21.

Oral Biomaterials Development Engineering, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University.

A fiberglass-reinforced composite resin (FRP) block using a plain woven fiberglass sheet for CAD/CAM has been introduced in dental practice. The aim of the present study was to evaluate the effects of the fiberglass sheet orientation on the flexural properties of an FRP block. The flexural properties of five types of fiberglass sheet-assigned specimens were examined using a three-point bending test. A one-way analysis of variance revealed that the orientation of fiberglass sheet significantly influenced the flexural strength, 0.2% yield strength, and flexural modulus. The values of the flexural properties of the FRP were the largest when the fiberglass sheets were perpendicular to the applied force, and the smallest when the fiberglass was parallel to the same. The flexural properties of the FRP block were anisotropic and they were significantly influenced by the orientation of fiberglass sheet.
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http://dx.doi.org/10.4012/dmj.2018-249DOI Listing
October 2019

OSNC1: Effect of Direct Retainer Types of Dent-Maxillary Prosthesis in Maxillectomy Patients: An Study.

J Indian Prosthodont Soc 2018 Oct;18(Suppl 1):S29

Department of Maxillofacial Prosthetics, Graduated School of Medical and Dental Sciences, Tokyo Medical and Dental University (TMDU) Tokyo Japan.

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http://dx.doi.org/10.4103/0972-4052.244641DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6238529PMC
October 2018

Improvement of the Shock Absorption Ability of a Face Guard by Incorporating a Glass-Fiber-Reinforced Thermoplastic and Buffering Space.

Biomed Res Int 2018 8;2018:6503568. Epub 2018 May 8.

Department of Advanced Biomaterials, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan.

This study aimed to evaluate the shock absorption ability of trial face guards (FGs) incorporating a glass-fiber-reinforced thermoplastic (GF) and buffering space. The mechanical properties of 3.2 mm and 1.6 mm thick commercial medical splint materials (Aquaplast, AP) and experimental GF prepared from 1.6 mm thick AP and fiberglass cloth were determined by a three-point bending test. Shock absorption tests were conducted on APs with two different thicknesses and two types of experimental materials, both with a bottom material of 1.6 mm thick AP and a buffering space of 30 mm in diameter (APS) and with either (i) 1.6 mm thick AP (AP-APS) or (ii)  1.6 mm thick GF (GF-APS) covering the APS. The GF exhibited significantly higher flexural strength (64.4 MPa) and flexural modulus (7.53 GPa) than the commercial specimens. The maximum load of GF-APS was 75% that of 3.2 mm AP, which is widely used clinically. The maximum stress of the GF-APS only could not be determined as its maximum stress is below the limits of the analysis materials used (<0.5 MPa). Incorporating a GF and buffering space would enhance the shock absorption ability; thus, the shock absorption ability increased while the total thickness and weight decreased.
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http://dx.doi.org/10.1155/2018/6503568DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5964619PMC
October 2018

Effect of incorporation of surface pre-reacted glass ionomer filler in tissue conditioner on the inhibition of Candida albicans adhesion.

Dent Mater J 2018 Jun 8;37(3):453-459. Epub 2018 Feb 8.

Removable Partial Prosthodontics, Tokyo Medical and Dental University (TMDU).

We investigated the effects of incorporation of surface pre-reacted glass ionomer (S-PRG) filler in tissue conditioner (TC) on Candida albicans adhesion. We prepared specimens containing 0, 5, 10, or 20 wt% of S-PRG filler, and measured the amount of C. albicans on the surface using a colony forming unit (CFU) assay and scanning electron microscopic images. In addition, we measured the consistency, penetration depth, and surface roughness (Ra). CFU values for 10 and 20 wt% were significantly lower than that for the control (p<0.05). Hyphal density on the surface was greater in the control. The 10 and 20 wt% specimens showed significantly higher consistency and Ra, lower penetration depth ratio than control (p<0.05). These results suggest that incorporation of S-PRG filler may reduce C. albicans adhesion onto TC surface; however, the optimal amount of filler is dictated by the influence of filler incorporation on mechanical and surface characters of TC.
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http://dx.doi.org/10.4012/dmj.2017-171DOI Listing
June 2018

Evaluation of the flexural properties of a new temporary splint material for use in dental trauma splints.

J Dent Sci 2017 Sep 1;12(3):308-310. Epub 2017 Apr 1.

Department of Sports Medicine/Dentistry, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan.

The present study evaluated the flexural properties of a new temporary splint material, G-Fix, for use in dental trauma splints in comparison with other resin materials. Four types of resin materials were considered in the present study: MI Flow II, light-cured composite resin (MI); G-Fix, light-cured resin for splinting teeth (GF); Super-Bond C&B, adhesive resin cement (SB); and Unifast III, self-cured methyl-methacrylate resin (UF). The flexural properties of these four materials were tested according to ISO 4049. The flexural strength significantly increased in the order of UF (64.9 MPa) < SB (76.5 MPa) < GF (94.3 MPa) < MI (161.2 MPa). The elastic modulus significantly increased in the order of UF (2.11 GPa) ≒ SB (2.23 GPa) < GF (2.62 GPa) < MI (7.39 GPa). A splint made of GF may be more flexible than a composite splint, which is categorized as a rigid splint.
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http://dx.doi.org/10.1016/j.jds.2017.02.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6399998PMC
September 2017

Effect of long-time immersion of soft denture liners in water on viscoelastic properties.

Dent Mater J 2017 Sep 26;36(5):584-589. Epub 2017 Apr 26.

Department of Oral Prosthetic Engineering, Division of Oral Health Sciences, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University (TMDU).

Aim of this study was to investigate the effect of long-time immersion of soft denture liners in 37°C water on viscoelastic properties. Six silicone-based and two acrylic resin-based soft denture liners were selected. Cylindrical specimens were stored in distilled water at 37°C for 6 months. Viscoelastic properties, which were instantaneous and delayed elastic displacements, viscous flow, and residual displacement, were determined using a creep meter, and analyzed with 2-way analysis of variance and Tukey's comparison (α=0.05). Viscoelastic properties and their time-dependent changes were varied among materials examined. The observed viscoelastic properties of three from six silicone-based liners did not significantly change after 6-month immersion, but those of two acrylic resin-based liners significantly changed with the increase of immersion time. However, the sum of initial instantaneous elastic displacement and delayed elastic displacement of two acrylic resin-based liners during 6-month immersion changed less than 10%, which might indicate clinically sufficient elastic performance.
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http://dx.doi.org/10.4012/dmj.2016-320DOI Listing
September 2017

Discoloration of various CAD/CAM blocks after immersion in coffee.

Restor Dent Endod 2017 Feb 8;42(1):9-18. Epub 2016 Dec 8.

Department of Prosthodontics, Faculty of Dentistry, Chulalongkorn University, Bangkok, Thailand.

Objectives: This study evaluated color differences (Δs) and translucency parameter changes (Δs) of various computer-aided design/computer-aided manufacturing (CAD/CAM) blocks after immersion in coffee.

Materials And Methods: Eight CAD/CAM blocks and four restorative composite resins were evaluated. The CIE values of 2.0 mm thick disk-shaped specimens were measured using the spectrophotometer on white and black backgrounds ( = 6). The Δs and Δs of one day, one week, and one month immersion in coffee or water were calculated. The values of each material were analyzed by two-way ANOVA and Tukey's multiple comparisons (α = 0.05). The Δs after prophylaxis paste polishing of 1 month coffee immersion specimens, water sorption and solubility were also evaluated.

Results: After one month in coffee, Δs of CAD/CAM composite resin blocks and restorative composites ranged from 1.6 to 3.7 and from 2.1 to 7.9, respectively, and Δs decreased. The ANOVA of Δs and Δs revealed significant differences in two main factors, immersion periods and media, and their interaction except for Δs of TEL (Telio CAD, Ivoclar Vivadent). The Δs significantly decreased after prophylaxis polishing except GRA (Gradia Block, GC). There was no significant correlation between Δs and water sorption or solubility in water.

Conclusions: The Δs of CAD/CAM blocks after immersion in coffee varied among products and were comparable to those of restorative composite resins. The discoloration of CAD/CAM composite resin blocks could be effectively removed with prophylaxis paste polishing, while that of some restorative composites could not be removed.
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http://dx.doi.org/10.5395/rde.2017.42.1.9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5299759PMC
February 2017

Mechanical properties of composite resin blocks for CAD/CAM.

Dent Mater J 2014 ;33(5):705-10

Oral Biomaterials Engineering, Department of Oral Materials Sciences and Technology, Course for Oral Health Engineering, School of Oral Health Care Sciences, Faculty of Dentistry, Tokyo Medical and Dental University.

This study compared commercial composite resin blocks with one ceramic block for use in computer-aided design/computer aided manufacturing (CAD/CAM). Four composite resins, one composite ceramic, and one feldspar-ceramic block were investigated. Flexural strength (FS), flexural modulus (FM), and Vickers hardness (VH) were determined under three conditions: dry storage; immersion in water at 37°C for 7 days; and immersion in water at 37°C for 7 days followed by 10,000 thermocycles. After dry storage, FS ranged from 127 to 242 MPa, FM from 9.6 to 51.5 GPa, and VH from 64 to 455. Two-way ANOVA was performed for FS, FM and VH followed by Tukey's multiple comparison (α<0.05). Results demonstrated that the materials degraded after water immersion and thermocycling, but their properties were within the acceptable range for fabrication of single restorations according to the ISO standard for ceramics (ISO 6872:2008).
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http://dx.doi.org/10.4012/dmj.2014-208DOI Listing
September 2016

Effect of immersion time of restorative glass ionomer cements and immersion duration in calcium chloride solution on surface hardness.

Dent Mater 2014 Dec 2;30(12):e377-83. Epub 2014 Sep 2.

Advanced Biomaterials, Department of Restorative Sciences, Division of Oral Health Sciences, Graduate School, Tokyo Medical and Dental University, Tokyo, Japan.

Objectives: The objective of this study was to evaluate the effect of immersion time of restorative glass ionomer cements (GICs) and immersion duration in calcium chloride (CaCl2) solution on the surface hardness.

Methods: Two high-viscosity GICs, Fuji IX GP and GlasIonomer FX-II, were selected. Forty-eight specimens were randomly divided into two groups. Sixty minutes after being mixed, half of them were immersed in a 42.7wt% CaCl2 solution for 10, 30, or 60min (Group 1); the remaining specimens were immersed after an additional 1-week of storage (Group 2). The surface hardness of the specimens was measured and analyzed with two-way ANOVA and the Tukey HSD test (α=0.05). The surface compositions were examined using energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy.

Results: The surface hardness of Group 1 significantly increased as the immersion duration in CaCl2 increased; that of Group 2 significantly increased only after 60-minute CaCl2 immersion. After CaCl2 immersion, the amounts of Ca increased as the immersion duration increased. The surface hardness after CaCl2 immersion significantly correlated with the amount of Ca in Group 1, but not in Group 2. The binding energy of the Ca2p peak was similar to that of calcium polyalkenoate. These findings indicated that the Ca ions from the CaCl2 solution created chemical bonds with the carboxylic acid groups in the cement matrix.

Significance: Immersion of GICs in CaCl2 solution at the early stage of setting was considered to enhance the formation of the polyacid salt matrix; as a result, the surface hardness increased.
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http://dx.doi.org/10.1016/j.dental.2014.08.366DOI Listing
December 2014

Texture of composite resins exposed to two- and three-body wear in vitro.

J Contemp Dent Pract 2014 Mar 1;15(2):232-41. Epub 2014 Mar 1.

Professor and Chair, Department of Oral Function and Morphology, Tohoku University Graduate School of Dentistry, Sendai, Japan.

Purpose: To analyze on scanning electron microscopy (SEM) pictures from eight composite resins, taken in the centers of the initial, the middle and the terminal thirds of in vitro produced wear tracks morphological features to explain causative mechanisms for the material wear observed under two- and three-body wear.

Materials And Methods: In vitro wear behavior of eight composite resins, three conventional and five nanofiller containing marketed products was evaluated using a custom-made Zr-ball-on-disk sliding device. The composite specimens were subjected to 50,000 one-way sliding cycles (1.2 Hz, 50 N load), either simulating two-body wear with water as the intermediate medium or three-body wear using aqueous suspensions of polymethyl methacrylate (PMMA) beads and poppy seeds, respectively. Volume loss of the materials was determined in previous study. Representative specimens were selected for inspection by scanning electron microscopy at 500-fold magnification. From each of the 24 wear tracks microphotographs were taken in the central deepest parts of the initial, middle and terminal thirds of the tracks.

Results: For most materials morphological differences were detected depending on the location within the wear track. As a rule, the surface deterioration found increased toward the final part of the wear scar. According to common classification in tribology abrasive wear and fatigue wear, or a combination of both mechanisms were found for all materials tested. Wear was dependent both on the testing mode and on the composition of the individual composite resin material.

Conclusion: The morphological assessment of wear tracks refects the nature of the abrasive and reveals insight into the mechanism generating wear patterns. Morphological details confirmed abrasive and fatigue-related wear as main failure mechanisms. Selection of food-like slurries as third-body media, such as poppy seed suspension is mandatory to simulate wear of composite restorations in occlusal cavities where three-body wear is the dominating determinant of loss of substance and surface deterioration.
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http://dx.doi.org/10.5005/jp-journals-10024-1521DOI Listing
March 2014

Effect of ultraviolet light irradiation and sandblasting treatment on bond strengths between polyamide and chemical-cured resin.

Dent Mater J 2014 ;33(4):557-64

Advanced Biomaterials, Oral Health Sciences, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University.

The aim of this study was to evaluate the effects of ultraviolet light (UV) irradiation and sandblasting treatment on the shear bond strength between polyamide and chemical-cured resin. Three types of commercial polyamides were treated using UV irradiation, sandblasting treatment, and a combining sandblasting and UV irradiation. The shear bond strength was measured and analyzed using the Kruskal-Wallis test (α=0.05). Comparing shear bond strengths without surface treatment, from 4.1 to 5.7 MPa, the UV irradiation significantly increased the shear bond strengths except for Valplast, whose shear bond strengths ranged from 5.2 to 9.3 MPa. The sandblasting treatment also significantly increased the shear bond strengths (8.0 to 11.4 MPa). The combining sandblasting and UV irradiation significantly increased the shear bond strengths (15.2 to 18.3 MPa) comparing without surface treatment. This combined treatment was considered the most effective at improving the shear bond strength between polyamide and chemical-cured resin.
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http://dx.doi.org/10.4012/dmj.2014-016DOI Listing
July 2016

Color stability of adhesive resin cements after immersion in coffee.

Clin Oral Investig 2015 Mar 21;19(2):309-17. Epub 2014 Jun 21.

Removable Partial Prosthodontics, Department of Masticatory Function Rehabilitation, Division of Oral Health Sciences, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo, 113-8549, Japan.

Objectives: Marginal discoloration of luting cement may affect the appearance of esthetic restorations. This study evaluated the color stability of current adhesive resin cements after immersion in coffee.

Materials And Methods: Four dual-cured resin cements (Clearfil SA cement Automix Universal, Maxcem Elite Clear, Maxcem Elite Yellow, and RelyX Unicem2 Automix A2) and two chemical-cured resin cements (Super-Bond C&B Clear and Super-Bond C&B Esthetic) were examined. The CIE L*a*b* of 2.0-mm-thick disc-shaped specimens was measured using a spectrophotometer on a white background (n = 6). The color differences (∆E) after 1-day and 1-week immersion in 37 °C water or coffee were analyzed by two-way ANOVA by selecting immersion solution and product as main factors, followed by Tukey's HSD test (α = 0.05). Water sorption and solubility were also evaluated.

Results: The two-way ANOVA of the ∆Es suggested that the two main factors and their interaction were significant. The ∆Es after coffee immersion were significantly greater than those after water immersion, except for Super-Bond C&B Esthetic. The ∆Es after water immersion were not significantly different among the products; those of Maxcem Elite Clear and Maxcem Elite Yellow after coffee immersion were significantly greater than the others. The water sorption and solubility significantly correlated with the ∆Es.

Conclusions: The ∆Es of the adhesive resin cements examined after 1-week coffee immersion were significantly different among the products. The product showing greater water sorption and solubility displayed greater color change.

Clinical Relevance: Adhesive resin cements should be carefully selected when the marginal appearance of the ceramic restoration is important.
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http://dx.doi.org/10.1007/s00784-014-1272-8DOI Listing
March 2015

Effect of ultraviolet light irradiation period on bond strengths between fiber-reinforced composite post and core build-up composite resin.

Dent Mater J 2014 ;33(1):133-40

Advanced Biomaterials, Department of Restorative Sciences, Division of Oral Health Sciences, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University.

The aim of the present study was to characterize the effects of the ultraviolet light (UV) irradiation period on the bond strength of fiber-reinforced composite (FRC) posts to core build-up resin. Three types of FRC posts were prepared using polymethyl methacrylate, urethane dimethacrylate, and epoxy resin. The surfaces of these posts were treated using UV irradiation at a distance of 15 mm for 0 to 600 s. The pull-out bond strength was measured and analyzed with the Dunnett's comparison test (α=0.05). The bond strengths of the post surfaces without irradiation were 6.9 to 7.4 MPa; those after irradiation were 4.2 to 26.1 MPa. The bond strengths significantly increased after 15 to 120-s irradiation. UV irradiation on the FRC posts improved the bond strengths between the FRC posts and core build-up resin regardless of the type of matrix resin.
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http://dx.doi.org/10.4012/dmj.2013-175DOI Listing
October 2015

Effect of fabrication process on the bond strength between silicone elastomer and acrylic resin for maxillofacial prosthesis.

Dent Mater J 2014 ;33(1):16-20

Clinics for Oral and Maxillofacial Rehabilitation, University Hospital, Tokyo Medical and Dental University.

This study evaluated the effects of the fabrication process on tensile bond strength between maxillofacial silicone elastomer and acrylic resin. A common maxillofacial silicone elastomer (VST-50), two primers (Sofreliner primer and R-SI-LINE Plasticbond), and two acrylic resins (Unifast III and Palapress Vario) were selected. Silicone elastomer between primed acrylic resin plates were polymerized using a metal flask mold or a flaskless stone mold. Bond strength of the specimens was measured by a tensile test and analyzed using two-way analysis of variance (ANOVA) with Tukey's honest significant difference test. All fracture surfaces showed interfacial fracture. Both the fabrication process and the primer-acrylic resin combination affected bond strength, and two-way ANOVA indicated a significant interaction. Bond strength was generally greater when silicone elastomer was polymerized using a flaskless stone mold.
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http://dx.doi.org/10.4012/dmj.2013-225DOI Listing
October 2015

Quantitative wear and wear damage analysis of composite resins in vitro.

J Mech Behav Biomed Mater 2014 Jan 20;29:508-16. Epub 2013 Oct 20.

Advanced Biomaterials, Department of Restorative Sciences, Division of Oral Health Sciences, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan. Electronic address:

The aim of this study was to investigate volume loss and worn surfaces' morphologies of eight composite resins: Durafill VS (DUR), Clearfil AP-X (APX), Filtek Z250 (Z250), Filtek Supreme XT (FIL), Kalore (KAL), MI Flow (MFL), Venus Diamond (VED) and Venus Pearl (VEP). Disc-shaped specimens were fabricated and mounted in a ball-on-disc wear testing machine and abraded in water or with the third-body media, poppy seed slurry and polymethyl methacrylate (PMMA) slurry. Volume loss (n=5) was determined after 50k sliding cycles, and analyzed using two-way ANOVA (α=0.05). The worn surfaces were examined with SEM. Two-way ANOVA suggested significant interaction between composite and wear condition. DUR, KAL and MFL showed low wear in water. DUR, Z250 and FIL showed moderate wear with PMMA slurry, whereas APX, KAL and MFL were deeper abraded. Under the action of poppy seed slurry DUR proved high volume loss. SEM showed that Z250, FIL and MFL were uniformly abraded in water. KAL and MFL with poppy seed were heavily destructed, whereas VED and VEP appeared very smooth. KAL and MFL abraded with PMMA slurry showed many cracks, but VEP remained crack-free and smooth. Volume loss and worn surfaces' morphologies varied with type of composite and third-body media used.
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http://dx.doi.org/10.1016/j.jmbbm.2013.10.003DOI Listing
January 2014

Flexural impact force absorption of mouthguard materials using film sensor system.

Dent Traumatol 2014 Jun 18;30(3):193-7. Epub 2013 Sep 18.

Dental Biomaterials and Prosthodontics Unit, School of Dental Sciences, Universiti Sains Malaysia, Kubang Kerian, Malaysia.

Purpose: Several methods have been used to measure the impact force absorption capacities of mouthguard materials; however, the relationships among these measurement systems have not been clearly determined. The purpose of the present study was to evaluate the impact force-absorbing capability of materials using a drop-ball system with film sensors and load cells to clarify the relationship between these two sensor systems.

Materials And Methods: Disk-shaped specimens (1, 2, and 3 mm thick) were prepared using three commercial thermoplastic mouthguard materials (Bioplast, Impact Guard, MG 21) and one experimental mouthguard material [mixture of Poly (ethyl methacrylate)]. Impact force was applied by letting a stainless steel ball drop free-fall onto the specimens and then measuring the impact load under each specimen using a film sensor system and a load cell sensor system.

Results: The total load measured with the film sensor system decreased with an increase in mouthguard thickness, while almost none of the transmitted impact forces measured with the load cell system were statistically different.

Conclusions: The film sensor system was considered to be superior to the load cell system because the maximum stress and stress area could be determined.
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http://dx.doi.org/10.1111/edt.12068DOI Listing
June 2014

Effect of calcium chloride solution immersion on surface hardness of restorative glass ionomer cements.

Dent Mater J 2013 ;32(5):828-33

Advanced Biomaterials, Department of Restorative Sciences, Division of Oral Health Sciences, Graduate School, Tokyo Medical and Dental University.

The objective of this study was to evaluate the effect of the concentration of calcium chloride (CaCl2) solution on the surface hardness of restorative glass ionomer cements (GICs). Two high-viscosity GICs, Fuji IX GP and GlasIonomer FX-II, were immersed in several concentrations of CaCl2 solution for 1 day and 1 week. The immersed specimen surfaces were evaluated using microhardness testing, grazing incidence X-ray diffraction, and energy-dispersive X-ray spectroscopy. Immersion in a higher concentration of CaCl2 solution produced a greater increase in the surface hardness. No crystalline substance was observed on the immersed surface. Calcium ions were selectively absorbed in the matrix of the GIC surface after immersion. They reacted with the non-reacted carboxylic acid groups remaining in the cement matrix. These reactions were considered to cause an increase in the surface hardness of the GICs.
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http://dx.doi.org/10.4012/dmj.2013-143DOI Listing
September 2015

Fluoride release and mechanical properties after 1-year water storage of recent restorative glass ionomer cements.

Clin Oral Investig 2014 May 22;18(4):1053-1060. Epub 2013 Aug 22.

Oral Biomaterials Engineering, Course of Oral Health Engineering, School of Oral Health Care Sciences, Faculty of Dentistry, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo, 113-8549, Japan.

Objectives: The objective of this study was to evaluate the relationships between fluoride release and mechanical properties after 1-year water storage of five recent restorative glass ionomer cements (GICs).

Materials And Methods: Five GICs, FujiIX GP EXTRA (FEX), FujiIX GP (FIX), GlasIonomer FX-II (GFX), Ketac Molar Easymix (KME), and Riva Self Cure (RSC), were examined. Cumulative fluoride release, compressive strength, and surface hardness were measured up to 1-year storage (n = 5), and analyzed with one-way or two-way ANOVA and Tukey HSD test (α = 0.05). Elemental compositions before and after 1-year storage were also examined (n = 3).

Results: The amounts of fluoride release were significantly different among the products. The highest amount of fluoride release occurred during the first day. Then, the amount of fluoride release rapidly decreased and still continued until 1-year storage. Compressive strengths indicated that two main factors were significant (GFX < FEX = RSC < FIX < KME; 1 day < 1 week = 1 month = 3 months = 6 months = 1 year), but surface hardness showed a slightly different tendency (GFX = RSC < FEX = FIX = KME; 1 year < 1 day < 1 week = 1 month = 3 months = 6 months). Significant correlation was found between decrease of silicon and decrease rate of the surface hardness.

Conclusions: Fluoride releases were detected up to 1-year storage, but the mechanical properties slightly decreased due to decrease of Si after 1-year storage. Elution of Si instead of fluoride release was considered more critical to deteriorate the mechanical properties of GICs.

Clinical Relevance: Fluoride released for 1-year water storage will contribute to secondary caries prevention. The amount of fluoride release did not affect these mechanical properties. These results indicate the usefulness of these GICs.
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http://dx.doi.org/10.1007/s00784-013-1074-4DOI Listing
May 2014

Translucency of dental ceramics with different thicknesses.

J Prosthet Dent 2013 Jul;110(1):14-20

Department of Prosthodontics, School of Stomatology, Fourth Military Medical University, Xi'an, China.

Statement Of Problem: The increased use of esthetic restorations requires an improved understanding of the translucent characteristics of ceramic materials. Ceramic translucency has been considered to be dependent on composition and thickness, but less information is available about the translucent characteristics of these materials, especially at different thicknesses.

Purpose: The purpose of this study was to investigate the relationship between translucency and the thickness of different dental ceramics.

Material And Methods: Six disk-shaped specimens of 8 glass ceramics (IPS e.max Press HO, MO, LT, HT, IPS e.max CAD LT, MO, AvanteZ Dentin, and Trans) and 5 specimens of 5 zirconia ceramics (Cercon Base, Zenotec Zr Bridge, Lava Standard, Lava Standard FS3, and Lava Plus High Translucency) were prepared following the manufacturers' instructions and ground to a predetermined thickness with a grinding machine. A spectrophotometer was used to measure the translucency parameters (TP) of the glass ceramics, which ranged from 2.0 to 0.6 mm, and of the zirconia ceramics, which ranged from 1.0 to 0.4 mm. The relationship between the thickness and TP of each material was evaluated using a regression analysis (α=.05).

Results: The TP values of the glass ceramics ranged from 2.2 to 25.3 and the zirconia ceramics from 5.5 to 15.1. There was an increase in the TP with a decrease in thickness, but the amount of change was material dependent. An exponential relationship with statistical significance (P<.05) between the TP and thickness was found for both glass ceramics and zirconia ceramics.

Conclusions: The translucency of dental ceramics was significantly influenced by both material and thickness. The translucency of all materials increased exponentially as the thickness decreased. All of the zirconia ceramics evaluated in the present study showed some degree of translucency, which was less sensitive to thickness compared to that of the glass ceramics.
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http://dx.doi.org/10.1016/S0022-3913(13)60333-9DOI Listing
July 2013

Effect of components and surface treatments of fiber-reinforced composite posts on bond strength to composite resin.

J Mech Behav Biomed Mater 2013 Oct 30;26:23-33. Epub 2013 May 30.

Advanced Biomaterials, Department of Restorative Sciences, Division of Oral Health Sciences, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan.

The aim of this study was to clarify the effect of the components and surface treatments of fiber-reinforced composite (FRC) posts on the durable bonding to core build-up resin evaluated using the pull-out and microtensile tests. Four types of experimental FRC posts, combinations of two types of matrix resins (polymethyl methacrylate and urethane dimethacrylate) and two types of fiberglass (E-glass and zirconia-containing glass) were examined. The FRC posts were subjected to one of three surface treatments (cleaned with ethanol, dichloromethane, or sandblasting). The bond strength between the FRC posts and core build-up resin were measured using the pull-out and microtensile tests before and after thermal cycling. The bond strengths obtained by each test before and after thermal cycling were statistically analyzed by three-way ANOVA and Tukey's multiple comparisons test (p<0.05). The bond strengths except for UDMA by the pull-out test decreased after thermal cycling. Regardless the test method and thermal cycling, matrix resins, the surface treatment and their interaction were statistically significant, but fiberglass did not. Dichloromethane treatment was effective for the PMMA-based FRC posts by the pull-out test, but not by the microtensile test. Sandblasting was effective for both PMMA- and UDMA-based FRC posts, regardless of the test method. The bond strengths were influenced by the matrix resin of the FRC post and the surface treatment. The bond strengths of the pull-out test showed a similar tendency of those of the microtensile test, but the value obtained by these test were different.
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http://dx.doi.org/10.1016/j.jmbbm.2013.05.022DOI Listing
October 2013

Effects of the space for wash materials on sulcus depth reproduction with addition-curing silicone using two-step putty-wash technique.

Dent Mater J 2013 ;32(1):150-5

Advanced Biomaterials, Department of Restorative Sciences, Division of Oral Health Sciences, Graduate School, Tokyo Medical and Dental University, Tokyo, Japan.

Aim of this study was to investigate effects of space thickness and consistency of wash materials on sulcus depth reproduction with silicone impressions, low (L), medium (M), and very high consistency (VH), using two-step putty-wash technique. Impressions were taken from truncated cones with 50-, 100-, or 200-μm-wide sulci, using the combinations L+VH or M+VH and different space thickness for wash materials: 2 mm (ST2), 1 mm (ST1), and approximately 25 μm (ST0.025). Sulcus depth reproduction tended to increase with increasing sulcus width. Sulcus reproduction of ST0.025 was deeper than those of the other groups. At 100- and 200-μm sulcus widths, sulcus reproductions of ST1 and ST2 with L+HV were deeper than with M+HV. Regardless of consistency, the thin spacer produced deep reproduction. Adequate 0.5 mm sulcus reproductions were obtained with 100 and 200 μm wide sulci and 1- and 2-mm spacer widths, combined with low consistency impression material.
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http://dx.doi.org/10.4012/dmj.2012-228DOI Listing
January 2014

Two- and three-body wear of composite resins.

Dent Mater 2012 Dec 17;28(12):1261-70. Epub 2012 Oct 17.

Advanced Biomaterials, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan.

Objective: The aim of the present study was to investigate two- and three-body wear of microfilled, micro-hybrid and nano-hybrid composite resins using a ball-on-disc sliding device.

Methods: One microfilled (Durafill VS), one micro-hybrid (Filtek Z250), one hybrid (Clearfil AP-X), one nanofilled (Filtek Supreme XT), and two nano-hybrid (MI Flow, Venus Diamond) composite resins were examined. The composites were filled in a cylindrical cavity, and light polymerized. After storage in 37°C distilled water for 7days, all specimens were tested with a custom-made ball-on-disc sliding device with a zirconia ball as antagonist (50N loads, 1.2Hz, 10,000 cycles) immersed in water, poppy seed slurry and polymethyl methacrylate slurry, respectively. Maximum wear depth and volume loss of worn surfaces were quantified by a digital CCD microscope and analyzed with two-way analysis of variance.

Results: The interactions between composite resin and condition of their maximum wear depth and volume loss were significant (p<0.01). The abrasive wear produced at three-body loading with poppy seed slurry was very large for the microfilled composite, and small for all other composites tested. In contrast, two-body wear of the microfilled composite, and one nano-hybrid composite was very low.

Significance: The ball-on-disc sliding device used is considered suitable to simulate sliding of an antagonist cusp on an opposing occlusal composite restoration, either in the two- or the three-body wear mode. All tested materials except for the microfilled composite showed low surface wear when exposed to poppy seed as the third-body medium.
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http://dx.doi.org/10.1016/j.dental.2012.09.008DOI Listing
December 2012

Flexural properties and shock-absorbing capabilities of new face guard materials reinforced with fiberglass cloth.

Dent Traumatol 2013 Feb 28;29(1):23-8. Epub 2012 Mar 28.

Sports Medicine/Dentistry, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan.

Aim:  Experimental materials incorporating fiberglass cloth were used to develop a thin and lightweight face guard (FG). This study aims to evaluate the effect of fiberglass reinforcement on the flexural and shock absorption properties compared with conventional thermoplastic materials.

Material And Method:  Four commercial 3.2-mm and 1.6-mm medical splint materials (Aquaplast, Polyform, Co-polymer, and Erkodur) and two experimental materials were examined for use in FGs. The experimental materials were prepared by embedding two or four sheets of a plain woven fiberglass cloth on both surfaces of 1.5-mm Aquaplast. The flexural strength and flexural modulus were determined using a three-point bending test. The shock absorption properties were evaluated for a 5200-N impact load using the first peak intensity with a load cell system and the maximum stress with a film sensor system.

Results And Conclusions:  The flexural strength (74.6 MPa) and flexural modulus (6.3 GPa) of the experimental material with four sheets were significantly greater than those of the 3.2-mm commercial specimens, except for the flexural strength of one product. The first peak intensity (515 N) and maximum stress (2.2 MPa) of the experimental material with four sheets were significantly lower than those of the commercial 3.2-mm specimens, except for one product for each property. These results suggest that the thickness and weight of the FG can be reduced using the experimental fiber-reinforced material.
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http://dx.doi.org/10.1111/j.1600-9657.2012.01135.xDOI Listing
February 2013

Quantification of in vitro produced wear sites on composite resins using contact profilometry and CCD microscopy: a methodological investigation.

J Med Dent Sci 2012 Jun 1;59(2):53-6. Epub 2012 Jun 1.

Advanced Biomaterials, Department of Restorative Sciences, Division of Oral Health Sciences, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo.

Background: Although attritive and abrasive wear of recent composite resins has been substantially reduced, in vitro wear testing with reasonably simulating devices and quantitative determination of resulting wear is still needed. Three-dimensional scanning methods are frequently used for this purpose. The aim of this trial was to compare maximum depth of wear and volume loss of composite samples, evaluated with a contact profilometer and a non-contact CCD camera imaging system, respectively.

Method: Twenty-three random composite specimens with wear traces produced in a ball-on-disc sliding device, using poppy seed slurry and PMMA suspension as third-body media, were evaluated with the contact profilometer (TalyScan 150, Taylor Hobson LTD, Leicester, UK) and with the digital CCD microscope (VHX1000, KEYENCE, Osaka, Japan). The target parameters were maximum depth of the wear and volume loss.Results - The individual time of measurement needed with the non-contact CCD method was almost three hours less than that with the contact method. Both, maximum depth of wear and volume loss data, recorded with the two methods were linearly correlated (r(2) > 0.97; p < 0.01).

Conclusion: The contact scanning method and the non-contact CCD method are equally suitable for determination of maximum depth of wear and volume loss of abraded composite resins.
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June 2012

Wear simulation effects on overdenture stud attachments.

Dent Mater J 2011 25;30(6):845-53. Epub 2011 Nov 25.

Division of Prosthodontics, Institute of Odontology, Faculty of Medicine, Vilnius University.

The aim of this study was to evaluate wear effects on overdenture resilient attachments. Six commercially available attachments were investigated: ERA orange and white (EO and EW), Locator pink, white and blue (LRP, LRW and LRB) and OP anchor (OP). Five specimens were used for wear simulation while other two specimens served as controls. Fifteen thousands insertion-removal cycles were simulated. Dimensional changes and surface characteristics were evaluated using light microscopy and SEM, respectively. Sudden decrease of retentive force was characteristic for EO and EW attachments. Retentive force of Locator attachments fluctuated throughout the wear simulation period. Dimensional changes and surface wear was more expressed on plastic cores than on plastic rings of attachment males. Based on SEM analysis, some of the specimens obtained smoother surface after wear simulation. Mechanism of retention loss of resilient overdenture attachments can be only partially explained by dimensional changes and surface alterations.
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http://dx.doi.org/10.4012/dmj.2011-057DOI Listing
February 2017

Effects of surface roughness and tapered angle of cone crown telescopic system on retentive force.

Dent Mater J 2011 23;30(5):635-41. Epub 2011 Sep 23.

Removal Partial Denture Prosthodontics, Department of Masticatory Function Rehabilitation, Division of Oral Health Sciences, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan.

This study evaluated the effect of surface roughness and tapered angle of cone crowns on retentive force (RF). Cone crowns from Ti-6Al-7Nb alloy with a tapered angle of 4, 5, or 6° were fabricated using a milling machine and a finishing machine to produce a smooth surface. Cone crowns of 6° with a rough surface were also prepared. The RF during 1,000 cycles of insertion/separation was recorded. The first RF of the 6° cone crowns was 24.2-27.7 N, and the surface roughness was not significant. The RF of all specimens decreased at 100 cycles, then those of inner and outer crowns with the same roughness remained unchanged, but those of different roughnesses increased with number of cycles. The RF of cone crowns with a smaller tapered angle was significantly greater than with a larger angle at any measured cycles.
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http://dx.doi.org/10.4012/dmj.2011-006DOI Listing
February 2012

Effects of investment type and casting system on permeability and castability of CP titanium.

J Prosthet Dent 2010 Aug;104(2):114-21

Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan.

Statement Of Problem: Several factors, such as casting systems and investment properties, are important to obtain a sound titanium casting. Although various casting systems and investments for titanium are commercially available, their effects on CP titanium castability are not clear.

Purpose: The purpose of this study was to determine permeability of investments and to evaluate the effects of investment type and casting system on titanium castability.

Material And Methods: Three investments for titanium (experimental gypsum-bonded investment, Selevest CB, and Speed Titan) and 4 titanium casting systems (Cyclarc, Ti-Cascom, Vulcan T, and Ticast Super R) were used. Permeability was measured using a flow meter and argon gas at 0.1, 0.2, and 0.3 MPa. Castability was calculated as the percentage of reproduced holes compared to a perforated wax pattern. Data for castability and permeability were analyzed separately with 2-way ANOVA and the Tukey HSD test (alpha=.05).

Results: The ANOVA for permeability and castability showed significant interaction (P<.001 and P=.004, respectively). Differences in permeability among the 3 investments increased with a higher gas pressure. Permeability of the experimental investment at each pressure level was significantly greater than that of the other investments, except for Speed Titan at 0.1 MPa (P<.05). The permeability of Selevest CB at each pressure level was significantly less than that of the other investments (P<.05). Cyclarc and Ti-Cascom specimens were not significantly different, in terms of castability, using the investments evaluated, but castability of Vulcan T and Ticast specimens varied significantly by the investment used (P<.05).

Conclusions: Within the limitations of this study, investment type, pressure level, and their combinations influenced permeability. Castability of titanium was influenced by investment type, casting system, and their combinations. The investment with the highest permeability did not demonstrate the best result for castability.
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http://dx.doi.org/10.1016/S0022-3913(10)60103-5DOI Listing
August 2010