Wataru Komada

Tokyo Medical and Dental University, Tokyo, Tokyo-to, Japan

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Publications (20)9.15 Total impact

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    ABSTRACT: The purpose of this study was to evaluate the surface strain of zirconia fixed partial denture frameworks and their abutment roots when restored with two types of post and core materials. Artificial mandibular first premolars and second molars were used as the abutment teeth. Posts and cores were of two types: resin composite with glass fiber posts (RC) and cast platinum gold alloy (MC). The cores and 4-unit zirconia frameworks were bonded to the specimens. Static loading was applied to the occlusal surfaces, and the surface strain of the frameworks and roots (distal premolar and mesial molar) was measured by strain gauge method. Premolar root showed a significantly higher magnitude of principal strain than molar root. RC showed a significantly higher magnitude of principal strain than MC. The results suggest that MC restrain the surface strain compared to RC when the missing teeth are replaced by a 4-unit zirconia framework.
    Dental Materials Journal 04/2014; · 0.81 Impact Factor
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    ABSTRACT: This study aimed to investigate the maximum depth imaging and optical properties of the dentin near the pulp by using optical coherence tomography (OCT) and to explore the possibility of measuring the remaining dentin thickness (RDT). Human third molars were used. In experiment 1, the cuspal dentin blocks (0.50-mm to 1.75-mm thickness) were prepared. Each specimen was scanned using OCT. OCT images could be obtained for all specimens with 1.00-mm or less thicknesses. In experiment 2, dentin-pulp complex slices (0.50-mm and 1.00-mm RDT) were prepared. Each specimen was scanned using OCT and micro-computed tomography, and compared. The resulting length change rates of OCT images for the 0.50-mm RDTs were significantly lower than those of the 1.00-mm RDTs. Within the limitations of this study, OCT was effective for measuring the 1.00-mm or less RDT and preventing pulpal injury, while considering the length change rate of OCT image as a variable.
    Dental Materials Journal 04/2014; · 0.81 Impact Factor
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    ABSTRACT: Objective: To compare the microtensile bond strength to dentin, water sorption and elastic modulus between two-step self-etch adhesives. Method: Mid-coronal flat dentin surfaces of human molars were prepared with 600-grit SiC paper. After the application of 2 two-step self-etch adhesives, Clearfil SE Bond (Kuraray Noritake Dental Inc. Tokyo, Japan) and KBV-100 (Kuraray Noritake Inc.) according to manufacturer’s instructions to the dentin surfaces, a resin composite (Clearfil AP-X, Kuraray Noritake Inc.) was built-up. After storage in 37 oC water for 24 h, the teeth were sectioned into beams (surface area: 0.7 x 0.7 mm), and then subjected to microtensile bond strength test at a cross-head speed of 1 mm/min (n=30). Water sorption (WS) of polymers of both adhesives were measured after water storage for one week (n=8). The elastic moduli of polymers of both adhesives in before/after one-week water-sorption (Dry/Wet) were also measured by three-point flexural bending test (n=8). Date were analyzed using student t-test (p<0.05). Result: The microtensile bond strength of KBV-100 (82.2±8.3MPa) was significantly higher than Clearfil SE Bond (71.3±10.1MP) (p<0.05). WS values of KBV-100 (3.83±0.20%) was less than Clearfil SE Bond (4.47±0.38%) (p<0.05). The elastic modulus of Clearfil SE Bond were 1345±93MPa (Dry) and 1098±127MPa (Wet) (p<0.05), while those of KBV-100 were 1568±191MPa (Dry) and 1451±200MPa (Wet) (p<0.05). The elastic modulus of KBV were significantly higher than those of Clearfil SE Bond in Dry and Wet states (p<0.05). Conclusion: KBV-100 showed higher microtensile bond strength, less WS and higher elastic modulus than Clearfil SE Bond.
    IADR Asia/Pacific Region (APR) Regional Meeting and Co-Annual Scientific Meeting of IADR Divisions 2013; 08/2013
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    ABSTRACT: The aim of the present study was to evaluate the fracture load and fracture mode of thin Ceria-stabilized tetragonal zirconia polycrystals/Al(2)O(3 )nanocomposites (Ce-TZP/A) and Yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) crown frameworks. Artificial maxillary second premolars were prepared for metal-ceramic crown and all-ceramic crown restorations and Co-Cr tooth analogs were duplicated. 10 standard (0.5 mm overall thickness) zirconia-ceramic crown frameworks (Y-TZPs) for all-ceramic crown preparation and 10 modified (a 0.3-mm-thick framework increased in thickness by adding a 1.0-mm-thick palatal margin with a height of 2.0 mm) zirconia-ceramic crown frameworks (Y-TZPm, Ce-TZP/Am) for metal-ceramic crown preparation were fabricated. The frameworks were cemented to the Co-Cr tooth analog and loaded vertically until fracture. The fracture load of Y-TZPs (180.0 N) and Ce-TZP/Am (183.7 N) were significantly higher than that of Y-TZPm (133.7 N). There was a significant difference in fracture mode between Y-TZPm and Ce-TZP/Am. Within the limitation of this study, Ce-TZP/Am provide sufficient strength for clinical application.
    Dental Materials Journal 01/2013; 32(1):189-194. · 0.81 Impact Factor
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    ABSTRACT: The purpose of this study was to evaluate the influence of flexural modulus of non-metal posts on the fracture strength and failure mode of composite resin cores. Thirty-two human premolars were divided into four groups: prefabricated glass fiber post with 1.0 mm diameter and composite resin core (Group PE1.0), that with 1.5 mm diameter and composite resin core (Group PE1.5), experimental post (flexural modulus; 4.25GPa) and composite resin core (Group EX), and preparation for abutment teeth only (Group NT). After a static loading test, the fracture strength and failure mode were recorded. Group NT (1670.81 N) showed higher fracture strength than Groups PE1.0 (866.44 N), PE1.5 (825.19 N) and EX (1075.63 N) (p<0.05). This study showed that the fracture strength of endodontically treated teeth restored with composite resin cores is not influenced by the flexural modulus of non-metal posts.
    Dental Materials Journal 02/2012; 31(1):113-9. · 0.81 Impact Factor
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    ABSTRACT: Objectives: Recently, the clinical applications of zirconia frameworks have expanded the range of indications of all ceramic restorations. Ceria-stabilized tetragonal zirconia polycrystal (Ce-TZP)/Alumina nanocomposite (NZ; Panasonic Healthcare Co., Ltd, Ehime, Japan) shows a very high toughness and a complete resistance to low temperature aging degradation compared with Yttria-stabilized tetragonal zirconia polycrystal. When the occlusal space is limited, the use of zirconia frameworks for occlusal surface might be an option for ceramic restorations. However, the wear behavior of human enamel opposed to NZ has not reported. The purpose of this study was to evaluate the wear of human enamel opposed to NZ. Methods: NZ and extracted human third molars were used. Wear of human enamel was evaluated as the volumetric loss of the specimens by three-body wear test. Hemispherical human enamel stylus with a 5 mm diameter was fabricated by grinding with a diamond bur and a 1000-grit silicon carbide paper. Flat NZ (with grinding; Ra=0.012m) and extracted human enamel specimens (without grinding; TO) were embedded into acrylic tubes with acrylic resin (n=3). A three-body wear test with PMMA slurry was performed (vertical load of 5kgf) for 50,000 cycles in distilled water at 37oC. After testing, the diameter of worn surface areas of the enamel specimens were measured by laser microscope (1LM15, Lasertec Co., Ltd, Kanagawa, Japan) and volumetric loss was calculated with mathematical formula. The data were statistically analyzed (t-test, p<0.05). Result: Volumetric loss of enamel opposed to NZ and TO were 1.82831.7584, 0.72741.1878 (mm3), respectively. There were no significantly difference between NZ and TO (p<0.05). Conclusions: In this study, NZ showed the similar wear of antagonistic enamel to TO./>/>/>/>/>/>/>/>/>/
    03/2011
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    ABSTRACT: Objective: Recently, composite resin core is often used with various kinds of glass fiber posts. However, it is not clear yet what kind of glass fiber post is most suitable for the post. The aim of this study was to evaluate the influence of the material properties of glass fiber posts on the stress distributions in the abutment tooth restored with composite resin by 3-dimensional finite element methods. Methods: Three types of 3-dimensional finite element models of endodonticaly treated premolar were made. In these three models, posts and cores were built up with composite resin and three types of glass fiber posts. That is, these models simulated restored teeth with composite resin and high Young's modulus (45 GPa) glass fiber post (HF), moderate Young's modulus (29 GPa) glass fiber post (MF) and low Young's modulus (3 GPa) glass fiber post (LF). In all models, same occlusal force, which were measured with a small 3-dimensional occlusal force meter during chewing beef jerky in vivo, were applied to the center of occlusal surface (lingual direction:24N,distal direction:29N, apical direction:164N). Then Von Mises stress distribution within the root was calculated. Results: In all models, there were same distributions of stress concentrations at the cervical area. The magnitude of stress at this area for HF, MF and LF were 14.2 Mpa, 14.3 MPa and 14.6 MPa respectively. However, at the dentin of root around the end of glass fiber posts, there were differences of stress concentrations. The magnitude of stress at this area for HF, MF and LF were 11.8 Mpa, 9.6 MPa and 4.9 MPa respectively. Conclusion: Within the limitation of this experiment, LF thought to be most suitable since this model showed lower stress value, which means less possibility of root fracture.
    IADR General Session 2011; 03/2011
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    ABSTRACT: Objectives: In recent years, metal free restorations have been focused on for many reasons, especially, esthetics and reduced allergic potential. The clinical applications of zirconium oxide have expanded the range of indications of all ceramic restorations. But abutment tooth reductions for all ceramic restorations are larger than those of metal ceramic restorations. Ceria-stabilized tetragonal zirconia polycrystal (Ce-TZP)/Alumina nanocomposite shows a very high toughness compared with Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP). The aim of this study was to evaluate the relation between the fracture strength and the material of the zirconia crown framework. Methods: Master dies made by cobalt-chrome alloy were fabricated to sumilate upper second premolar abutment tooth for porcelain fused to metal (PFM) crown. 5 Ce-TZP/Alumina nanocomposite crown frameworks (P-NanoZR, Panasonic healthcare, Japan) and 5 Y-TZP crown frameworks (cercon, DeguDent, Germany) were fabricated. The thickensses of the frameworks were 0.3mm like PFM crown frameworks. A load (1mm/min) was applied using a universal testing machine (AUTOGRAPH AGS-H, Shimadzu, Japan) on the center of the occlusal surface of the crown frameworks and measured the fracture strength. The t-test was used for the statistical analysis of fracture strength. Results: The fracture loads of Ce-TZP/Alumina nanocomposite frameworks were 174.331.9N. Those of Y-TZP frameworks were 107.911.4N. The fracture strength of the Ce-TZP/Alumina nanocomposite framework was significantly higher than that of the Y-TZP framework (p<0.05). Conclusion: The results suggested that we can reduce the amount of abutment tooth reduction using Ce-TZP/Alumina nanocomposite crown frameworks.
    IADR General Session 2011; 03/2011
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    ABSTRACT: To compare the fracture strengths of pulpless teeth restored using resin cores with and without fiber posts, and with and without bonding adhesive in the post cavity. Human extracted roots were prepared with post cavities and divided into four experimental groups: Groups 1 and 2--after application of adhesive to both the top surface of the root and the inner surface of the post cavity, DC core Automix was injected into the post space with or without fiber-post placement; Groups 3 and 4--adhesive was applied to the top surface of the root only, with or without post placement. Resin-cores were then built-up. Teeth prepared for full crowns served as controls. After water storage at 37 degrees C for 24 hours, the all specimens were embedded in acrylic resin at 2 mm below CEJ, and loaded at 45 degrees to the long axis of the tooth using a universal testing machine until fracture. The data were analyzed by one-way ANOVA (alpha = 0.05). The fracture loads were, Group 1: 1832 +/- 240 N, Group 2: 1815 +/- 347 N, Group 3: 1626 +/- 396 N, Group 4: 1810 +/- 332 N, Control Group: 1622 +/- 274 N. There were no significant differences among all the groups (P > 0.05).
    American journal of dentistry 12/2010; 23(6):300-4. · 1.06 Impact Factor
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    ABSTRACT: Objectives: The aim of this study was to evaluate the influence of water immersion on the flexural strengths and elastic modulus of three kinds of glass fiber posts. Methods: Two commercially available glass fiber posts (FIBER POST, GC, Japan (GP) and FibreKor Tapered Post, Pentron, U.S.A. (PP) and a newly developed glass fiber post CLEARFIL FIBERPOST, Kuraray medical, Japan (KP)) were used for this study. Each fiber post was divided into two groups; a control (GPC, PPC and KPC) and a water immersion group (GP30, PP30 and KP30). In the water immersion group, the specimens were stored in deionized water for 30 days at 37 C in darkness. Flexural strengths and elastic modulus were determined using a universal testing machine (Auto Graph AGS-H, Shimadzu, Japan) at crosshead speed of 1.0 mm/min. The data were analyzed by two-way ANOVA and t-test with Bonferroni correction (p<0.05). After the test of mechanical strength, glassfiber-matrix resin interface of specimens were observed using SEM (FE SEM XL30S, PHLIPS, U.S.A). Results: In the flexural strength, GP30 (657.5 94.7 MPa) showed significant lower value than GPC (885.1 49.5 MPa). PP30 (775.8 41.7 MPa) showed significant lower value than PPC (885.7 37.3 MPa). KP30 (723.1 53.5 MPa) and KPC (770.5 51.9 MPa) showed no significant difference. In the elastic modulus, GP30 (10.9 0.31 GPa) showed significant lower value than GPC (11.7 0.14 GPa). PP30 (12.3 0.17 GPa) showed significant lower value than PPC (12.5 0.27 GPa). KP30 (10.2 0.20 GPa) and KPC (10.4 0.23 GPa) showed no significant difference. In water immersion groups, some glassfiber-matrix resin interfacial gaps were observed by SEM. Conclusion: The results suggested that water immersion had little influence on the mechanical properties of KP.
    IADR General Session 2010; 07/2010
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    ABSTRACT: Objective: To evaluate the bond strengths of six resin cements to Ce-TZP/Alumina nano-composite. Methods: Six resin cements were used for this study; Resicem/AZ Primer, Multilink Automix/Monobond Plus, Clearfil Esthetic Cement/Clearfil Ceramic Primer, PanaviaF2.0/Clearfil Porcelain Bond Activator and Clearfil SE Bond Primer, Bistite II and G-Luting. The surfaces of Ce-TZP/Alumina nano-composite were polished with 600 grit SiC paper, blasted, treated and devided into 12 groups of eight each. Stainless steel rods were bonded to the Ce-TZP/Alumina nano-composite surfaces using one of the six resin cements. The tensile bond strengths were tested after 24h water storage (37C) and after thermocycling(5C - 55C, 30sec dwell time for 10,000 cycles) using an universal testing machine. These specimens were fractured under tension at a crosshead speed of 1 mm/min, and the maximum load at fracture was recorded. The data were analyzed by two-way ANOVA and t-test(p<0.05). Results: The results are presented in the table below. The bond strengths of PanaviaF2.0 and G-Luting after 24h were significantly higher than those of the other resin cements(p<0.05). On the other hand, the bond strength of PanaviaF2.0 after thermocycling was significantly higher than those of the other resin cements except G-Luting(p<0.05). The bond strengths of PanaviaF2.0 and G-Luting after 24h were significantly higher than those after thermocycling. Conclusions: A combination of the primer and resin cement containing a phosphate ester monomer(Clearfil SE Bond Primer and PanaviaF2.0) was effective in bonding to Ce-TZP/Alumina nano-composite after 24h and after thermocycling. Table. Tensile bond strengths (MPa) to Ce-TZP/Alumina nano-composite. N=8 in each group. Same superscript letter indicate no statistically significant differences.
    IADR General Session 2010; 07/2010
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    ABSTRACT: Objectives:Recently, hybrid resin composite is used for inlays or crowns in the molar region because of its high esthetic performance and mechanical properties. It is important that hybrid resin composite has high wear resistant properties for preventing the fractures or the loss of stable occlusal relationships of restorations.The purpose of this study is to evaluate the wear resistance of four hybrid resin composites opposed to human enamel. Methods:Four types of hybrid resin composite, EsteniaC&B (KURARAY MEDICAL INC, ES), PEARLESTE (Tokuyama Dental Co, PE), CERAMAGE (SHOFU INC, CM), GRADIA FORTE (GC Co, GF) were investigated. Wear resistance of these materials was evaluated as the volumetric loss of the specimens by three-body wear test. Hemispherical hybrid resin composite specimens with a 5mm diameter were fabricated according to the manufacturer's direction(n=3). As a control, hemispherical human enamel with a 5mm diameter (TO) was fabricated by grinding with a diamond bur and a 1500-grit silicon carbide paper. Flat enamel antagonist specimens were fabricated by grinding extracted human third molars with a 1500-grit silicon carbide paper. A three-body wear test using PMMA slurry was performed for 50,000 cycles in distilled water at 37C. After testing, the diameter of worn surface areas of the specimens were measured by laser microscope (1LM15, Lasertec Co) and volumetric loss was calculated with mathematical formula. The data were statistically analyzed (one-way ANOVA, Scheffe's, p<0.05). Results: Volumetric loss of ES, PE, CM, GF, and TO were 0.04640.0293, 0.05440.0276, 0.84820.4885, 0.04070.0321, 0.00150.0004(mm3),respectively. The volumetric loss of CM was significantly higher than three other types of hybrid resin composite and human enamel(p<0.05). There were no significantly difference among ES, PE, GF and TO(p<0.05). Conclusions:In this study, ES, PE, GF showed higher wear resistant properties than CM.
    IADR General Session 2010; 07/2010
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    ABSTRACT: Objective: The objective of this investigation was to evaluate the bond strengths of six resin cements to zirconia ceramic. Methods: 96 Zirconia ceramic specimens were ground flat with #600-grit SiC paper. The surfaces were airborne-particle abraded and then divided into 12 groups of eight each; and conditioned with primer recommended by manufacturer recommended as follows: Resicem/AZ Primer, Multilink Automix/Monobond Plus, Clearfil Esthetic Cement/Clearfil Ceramic Primer, Panavia F2.0/Clearfil Porcelain Bond Activator and Clearfil SE Bond Primer. Bistite II and G-Luting were untreated with primer. Stainless steel rods were bonded to the ceramic surfaces using one of the six resin cements. The tensile bond strengths were tested after 24h (37C) water storage and after thermocycling(5C55C, 30sec dwell time for 10,000 cycles) using a universal testing machine. Data were analyzed by two-way ANOVA and t-test (p<0.05). Results: The results are presented in the table below. The bond strengths of Panavia F2.0 and Resicem after 24h were significantly higher than those of Multilink Automix, Clearfil Esthetic Cement and Bistite II (p<0.05). However there were no significant differences among them after thermocycling (p>0.05). On the other hand, the bond strengths of Panavia F2.0 and Resicem after 24h were significantly higher than those after thermocycling. Conclusions: The primer containing a phosphonic acid monomer(AZ Primer) or with a combination of the primer and resin cement containing a phosphate ester monomer(Clearfil SE Bond Primer and Panavia F2.0) was effective in bonding to zirconia ceramic after 24h. Table. Tensile bond strengths (MPa) to zirconia ceramic. Same superscript letter indicate no statistically significant differences.
    IADR General Session 2010; 07/2010
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    ABSTRACT: This study was aimed at evaluating the fracture resistance of structurally compromised roots restored with four different post and core systems. Thirty-two bovine roots were uniformly shaped to simulate human mandibular premolar roots. The roots were divided into four groups based on the type of restoration: cemented cast post and core (Group MC), resin composite build-up (Group CR), resin composite and prefabricated glass fiber post build-up (Group FRC), and thick-layer dual-cured resin composite-reinforced small-diameter tapered cast post and core (Group CRM). After a static loading test, the failure mode and fracture resistance were recorded. Group CRM (719.38+/-196.73 N) exhibited a significantly high fracture resistance compared with the other groups (Group MC: 429.56+/-82.43 N; Group CR: 349.56+/-66.21 N; Group FRC: 398.94+/-112.71 N; p<0.05). In conclusion, Group CRM exhibited better mechanical properties for structurally compromised roots with no ferrules, although all types of restorations showed non-restorable fracture modes.
    Dental Materials Journal 09/2009; 28(5):602-9. · 0.81 Impact Factor
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    ABSTRACT: Objective: Ceria-stabilized tetragonal zirconia/alumina nanocomposite (Ce-TZP/ Al2O3 nanocomposite) has recently been developed by Panasonic Electric Works Ltd. This new material exhibits very high toughness and complete resistance to low temperature aging degradation compared to yttria-stabilized tetragonal zirconia (Y-TZP). The objective of this in-vitro study was to investigate the bond strength of four ceramics bonded to Ce-TZP/ Al2O3nanocomposite frameworks. Material and Method: Thirty-six Ce-TZP/ Al2O3 nanocomposite frameworks (25x3x0.5 mm) were fabricated and divided into four groups. The surfaces of the Ce-TZP/ Al2O3 nanocomposite frameworks were polished with 600 grit SiC paper. The framework surfaces were sandblasted with 50 m alumina particles. Four types of ceramics specially developed for zirconium oxide, Cercon Ceram Kiss (Degudent), Cerabien ZR (Noritake), Vintage ZR (Shofu) and Vita VM9 (Vita) were applied and adjusted to a final thickness of 1.5mm including the Ce-TZP/ Al2O3 nanocomposite frameworks according to ISO 9693. The specimens were subjected to a three-point bending test using a universal testing machine (AUTOGRAPH AGS-H, Shimadzu). The data (mean SD, MPa) were analyzed by one-way ANOVA and Tukey HSD test (p<0.05). Results: The surface roughness of the Ce-TZP/ Al2O3 nanocomposite frameworks were Ra 0.13 0.02m. The bond strengths of Cercon Ceram Kiss, Cerabien ZR, Vintage ZR and Vita VM9 to Ce-TZP/ Al2O3 nanocomposite frameworks were 30.4 1.52, 29.3 1.44, 28.2 2.21 and 28.4 1.76 MPa respectively. There were no significant differences among these four ceramics (p<0.05). The bond strengths of four tested ceramics were higher than the standard strength of ISO 9693 (25MPa). Conclusion: The results showed that these four tested ceramics were suitable ceramics for Ce-TZP/ Al2O3 nanocomposite.
    IADR General Session 2009; 04/2009
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    ABSTRACT: The purpose of this study was to identify crown materials to decrease the stress concentrated at the cervical area of endodontically treated teeth. To this end, 14 extracted human mandibular premolars were divided into two groups for this study: complete cast crowns versus polymer-based crown and bridge material crowns. Both complete cast crowns (MC) and polymer-based crown and bridge material crowns (HC) were cemented with a glycidyl methacrylate-based resin cement (RC) to composite resin cores with glass fiber posts. Static loading was applied and distortion was measured with four pieces of strain gages attached to the marginal area. Findings showed that there was a large difference in distortion between crown and root in MC. On the other hand, distortions at the cervical area of crown and root were similar in HC.
    Dental Materials Journal 04/2009; 28(2):142-52. · 0.81 Impact Factor
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    ABSTRACT: The aim of this study was to compare three types of post and core systems by analyzing the stress magnitude within the root. To this end, two-dimensional photoelastic simulation models of endodontically treated maxillary central incisors were fabricated. Three different types of post and core systems were selected for this study: composite resin post and core, composite resin core in combination with a glass fiber post, and conventional cast metal post and core. The fabricated models were observed in a transmission polariscope with the same loading force (400 N) on 45 degrees palatal direction and the fringe orders registered were thereby analyzed. Results obtained in this study suggested that abutment build-up using composite resin core in combination with a glass fiber post model produced the lowest stress concentration and is hence effective in preventing stress concentration in the case of restored endodontically treated teeth.
    Dental Materials Journal 04/2009; 28(2):204-11. · 0.81 Impact Factor
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    ABSTRACT: Although composite resin core is used with various types of prefabricated posts, it remains unclear which kind of material is most suitable for the post. The aim of this study was to evaluate the influence of prefabricated posts on the stress distribution within the root by finite element analysis. Posts and cores were built up with composite resin and four types of prefabricated posts: two types of glass fiber posts (GFP1, GFP2) with low and high Young's moduli, a titanium post (TIP), and a stainless steel post (SSP). In all models, stress distribution during function was calculated. There were differences in stress concentration at the root around the end of posts. The magnitudes of stress for GFP1, GFP2, TIP, and STP were 8.7, 9.3, 11.7, and 13.9 MPa respectively. Given the results obtained, GFP1 was the most suitable material for post fabrication since this model showed a lower stress value. It would therefore mean a lower possibility of root fracture.
    Dental Materials Journal 08/2008; 27(4):605-11. · 0.81 Impact Factor
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    ABSTRACT: The purpose of this study was to identify crown materials and luting agents that would decrease the stress concentrated at the roots of endodontically treated teeth. To this end, natural tooth model (NT), full cast crown model (gold-silver-palladium alloy; MC), polymer-based restorative material crown model (HCC), and all-ceramic crown model (ACC) were constructed. In each model, methyl methacrylate-based resin cement (MMA) and composite cement (CC) were used as luting agents. The magnitudes of von Mises stress of the roots during function were compared. When the luting agent was changed from MMA to CC, von Mises stress in the cervical area decreased by 37.8% for MC, 27.1% for HCC, and 37.0% for ACC. Within the limitations of this study, the combination of HCC and CC gave rise to the lowest stress concentration at the cervical area.
    Dental Materials Journal 04/2008; 27(2):229-36. · 0.81 Impact Factor
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    ABSTRACT: This study evaluated the influence of alveolar bone level on the fracture resistance of root restored with post and core. Forty-eight extracted human mandibular premolars were divided into six groups. Cast posts and cores were cemented (MN8 and MP8) or resin cores were built up with fiber posts and composite resin (FN8, FP8, FN4, and FP4). Post length was 8 mm (MN8, MP8, FN8, and FP8) or 4 mm (FN4 and FP4). Specimens were embedded 2 mm (MN8, FN8 and FN4) or 5 mm (MP8, FP8 and FP4) below cement-enamel junction. All specimens were loaded at 45 degrees to the long axis until fracture. With normal bone model, cast post and core (MN8) showed the highest fracture resistance (2262.4 N). However, in the resorbed bone model, there were no significant differences in fracture resistance between cast post and core and fiber post with composite resin.
    Dental Materials Journal 04/2006; 25(1):177-82. · 0.81 Impact Factor