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Keiko NAKATA, Toru NIKAIDO, Masaomi IKEDA, Richard M. FOXTON, Junji TA ...
2009 Volume 28 Issue 5 Pages
523-529
Published: 2009
Released on J-STAGE: October 13, 2009
JOURNAL
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The purpose of this study was to assess the relationship between quantitative light-induced fluorescence (QLF) values and demineralization depths in an enamel erosion model
in vitro.
Flat labial enamel surfaces of bovine incisors were ground with 800-grit SiC and coated with nail varnish, but also leaving rectangular windows of enamel uncoated. Subsequently, they were immersed in a lactic acid gel (pH 5.0) for 0 to 7 weeks to make an enamel erosion model. Carious lesions thus induced were analyzed by QLF and the demineralization depths measured using SEM/ EDS method at the end of each period. A wide range of erosive lesions were produced with a steady increase in both demineralizing depth and fluorescence loss (Δ
F) over time. With this model, a good correlation was exhibited between each Δ
F value and the demineralization depth. Results of this study indicated that QLF could detect and quantify mineral loss under the eroded surface of the enamel erosion model.
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Suha TURKASLAN, Arzu TEZVERGIL-MUTLUAY, Bora BAGIS, Pekka K. VALLITTU, ...
2009 Volume 28 Issue 5 Pages
530-536
Published: 2009
Released on J-STAGE: October 13, 2009
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This study compared the initial and final failure loads and failure modes of indirect resin composite laminate veneers with and without fiber reinforcement. Forty intact lower canines received standard laminate preparations and were randomly assigned into four test groups (
n=10). In Group 1, indirect resin composite veneers were repaired with two layers of preimpregnated bidirectional glass fiber weave and a restorative composite; in Group 2, with a layer of preimpregnated unidirectional glass fibers and a restorative composite; and in Group 3, with an experimental semi-IPN matrix composed of multidirectional short glass fibers. Indirect resin composite veneers without any fiber reinforcement were used as control (Group 4). All specimens were thermocycled and tested with a universal testing machine. On the final failure load, there were no statistically significant differences (
p>0.05) among the test groups. Within each group, pairwise comparison of initial and final failure loads revealed statistically significant differences (
p<0.05), except for Group 4 (
p>0.05). On failure mode, unreinforced specimens showed instantaneous failure, whereas reinforced specimens mostly demonstrated elongated failure.
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Takashi KONO, Masao YOSHINARI, Shinji TAKEMOTO, Masayuki HATTORI, Eiji ...
2009 Volume 28 Issue 5 Pages
537-543
Published: 2009
Released on J-STAGE: October 13, 2009
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This study examined the mechanical properties of roots combined with prefabricated fiber post. Three types of specimens were evaluated: (1) prefabricated fiber post alone (FP); (2) core composite resin with FP (CFP); and (3) root with CFP (RCFP). The volume fractions of the prefabricated fiber post in the core composite resin (FP/CFP ratio) were set to 0, 0.16, 0.22, 0.28, and 0.48. Bending test for FP and CFP, and diametral compression test for FP, CFP, and RCFP were carried out. The FP/CFP ratio showed no effect on the diametral tensile strength (DTS) of RCFP; and there were no significant differences in DTS with/without FP. The flexural strength of CFP increased with increase in FP/CFP ratio. The DTS of CFP declined in comparison with that of core composite resin only.
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Taira MIYASAKA, Hiroyuki OKAMURA
2009 Volume 28 Issue 5 Pages
544-551
Published: 2009
Released on J-STAGE: October 13, 2009
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The polymerization shrinkage values of commercial flowable and conventional composites were measured with a newly developed laser displacement sensor. Compressive strength and filler content were also measured. Compared to conventional composites, the flowable composites required a longer time — not exceeding 4 minutes — to reach a constant polymerization shrinkage rate. In terms of shrinkage ratio, it was less than 1.5% for conventional composites at 90 minutes, which was lower than that of flowable composites,
i.e. more than 2.0%. The compressive strength of conventional composites was higher than that of flowable composites. A highly significant correlation between filler content and polymerization shrinkage at 90 minutes was observed, and polymerization shrinkage tended to decrease as filler content increased. In light of the results obtained in this study, the newly developed displacement meter with a laser displacement sensor proved to be effective for in-depth investigation of the polymerization shrinkage of dental composites.
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Atsufumi MANABE, Masafumi KANEHIRA, Werner J. FINGER, Hisashi HISAMITS ...
2009 Volume 28 Issue 5 Pages
552-557
Published: 2009
Released on J-STAGE: October 13, 2009
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The purpose of this
in vitro investigation was to study the effects on bond strength to primed human enamel stemming from opacity and polymerization inhibition by oxygen due to two coating resins. The coating resins and primers used were White Coat and an experimental material, SIR. The bond strengths on fine-ground enamel were evaluated for three shades of each of these coating resins after 24-hour storage in water. In addition, their degrees of opacity and oxygen inhibition depths were measured. The mild self-etch primer solutions produced very shallow but distinct etching patterns for micromechanical retention of the coating resin. Significant linear relationships between bond strength on the one hand and opacity and oxygen inhibition depth on the other were found for the three shades of each coating resin. Generally, the bond strength mediated on enamel is sufficiently high when these resins are combined with their proprietary adhesives. Therefore, the decrease in bond strength with increasing opacity of the coating resin shades has to be taken into account during application and light-curing.
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Kunio IKEMURA, Kensuke ICHIZAWA, Takeshi ENDO
2009 Volume 28 Issue 5 Pages
558-564
Published: 2009
Released on J-STAGE: October 13, 2009
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The effect of the pH value of single-bottle, self-etching 2-hydroxyethyl methacrylate (HEMA)-free adhesives on their shelf lives with bonding ability was investigated. Two experimental adhesives [SA-1 (pH=3.0); SA-2 (pH=2.1)] comprising 6-methacryloyloxyhexyl phosphonoacetate (6-MHPA), 4-acryloyloxyethyltrimellitic acid (4-AET), Bis-GMA, water, and acetone, in which the pH values were controlled with 1N NaOH, were stored for 6 weeks at 50°C in air. Shear bond strengths of aged adhesives to ground and unetched enamel and dentin were measured at a crosshead speed of 1.0 mm/min, and the data were analyzed by ANOVA. The resin-tooth bonding interfaces were further observed with SEM. With SA-1, the bond strengths to the tooth substrates were maintained throughout the 6 weeks. However, with SA-2, bond strength significantly degraded from weeks 4 to 6 (
p<0.05). Based on SEM observation, non-aged and 6-week-aged adhesive SA-1 appeared to be strongly adhered to both enamel and dentin. It was found that the stability of the self-etching adhesive was influenced by its pH value.
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Hiroyuki MINAMI, Shiro SUZUKI, Sadaaki MURAHARA, Yasukazu SAIMI, Yoshi ...
2009 Volume 28 Issue 5 Pages
565-570
Published: 2009
Released on J-STAGE: October 13, 2009
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This study evaluated the effect of a fiber-premixed indirect resin composite (FMC) substructure on the fracture resistance of mesialocclusal-distal (MOD) indirect composite restorations adhered to extracted human upper premolars. The teeth received a standardized MOD cavity preparation, and indirect composite inlays were fabricated with or without using the FMC. Inlays were cemented into the cavity preparations using either Super-Bond C&B or Panavia F2.0. A total of 28 specimens, namely seven specimens for four groups, were thus fabricated. Failure load and failure energy were determined after thermocycling (4–60°C for 5,000 cycles). In terms of failure load, no significant differences were found among the four groups. In terms of failure energy, FMC substructure exerted a significantly favorable effect on Super-Bond C&B-bonded group but a negative one on Panavia F2.0-bonded group. In conclusion, the failure energy of the group using FMC substructure and which was adhered using Super-Bond C&B was significantly higher than the other groups.
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Junko TOKUNAGA, Tetsuya KOJIMA, Soichiro KINUTA, Kazumichi WAKABAYASHI ...
2009 Volume 28 Issue 5 Pages
571-577
Published: 2009
Released on J-STAGE: October 13, 2009
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Cast titanium is a known hard-to-polish material, and its final polishing step is a perpetual challenge. The best way to tackle this challenge lies in automatic and non-mechanical polishing methods. Against this background, the suitability of large-area electron beam (EB) irradiation was examined in this study. In parallel, the optimum condition for efficient surface polishing was investigated. Cast titanium specimens were prepared, whereby their surface glossiness, surface roughness, and corrosion resistance were measured before and after EB irradiation. After EB irradiation, favorable results were observed: the cast titanium surface became smooth, the glossiness increased, and corrosion resistance was enhanced. These results were attributed to the low heat conductivity of titanium. With mechanical polishing, this property results in temperature rise and burnout reaction of the titanium surface with oxygen and the abrasives. However, during EB irradiation, the low heat conductivity of titanium was an advantage in raising the surface temperature to the melting point, such that a smooth surface was yielded after solidification. Based on the results obtained, automatic polishing by EB seemed to be a suitable polishing method for metal frameworks of removable dentures, and an efficient one too by saving time and effort.
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Kenichi TAJIMA, Toru NIKAIDO, Go INOUE, Masaomi IKEDA, Junji TAGAMI
2009 Volume 28 Issue 5 Pages
578-586
Published: 2009
Released on J-STAGE: October 13, 2009
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The aim of this study was to evaluate the effects of coating root dentin surfaces with adhesives vis-à-vis the prevention of root dentin demineralization. Root dentin surface was ground with #600 SiC, and then either a single coat of Clearfil SE Bond (SE), Clearfil Tri-S Bond (TS), G-Bond (GB), Hybrid Bond (HB-1), or two coats of HB (HB-2) were applied. Specimens were immersed in an artificial demineralizing solution, then sectioned through the center of the root and polished. Thickness of the coating layer and depth of the demineralized dentin layer were observed under a confocal laser scanning microscope (CLSM). Nanohardness values of the coating layer and underlying dentin were measured using a nanoindentation tester. All obtained data were statistically analyzed. Dentin demineralization was not observed in the surface coating groups with the exception of HB-1, and nanohardness of the underlying dentin was comparable to that of normal dentin. Based on the results obtained, it seemed that coating root dentin surfaces with an adhesive material is a promising good practice to prevent demineralization.
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Marie KOIKE, David JACOBSON, Kwai S. CHAN, Toru OKABE
2009 Volume 28 Issue 5 Pages
587-594
Published: 2009
Released on J-STAGE: October 13, 2009
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The hardened alpha-case (α-case) layer inevitably forms on the surface of titanium castings when prepared by investment casting. Because the hardness of the α-case is incomparable to that of the interior structure, the perception exists that the α-case is difficult to remove during cutting, grinding and polishing. Grindability (ease of grinding) of cast cpTi and cast Ti-6Al-4V was evaluated by grinding cast specimens incrementally using a SiC abrasive wheel. The present study revealed that the presence of the brittle α-case with lower fracture toughness is beneficial in grinding titanium. The α-case on the ductile cpTi can be ground much easier than its bulk interior structure. In less ductile Ti-6Al-4V, the grinding rate is much higher than that of cpTi, and the α-case and its interior structure are at similar levels since the fracture toughness of its α-case and the bulk material is not large enough.
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Hiroshi TAKEUCHI, Motohiko NAGAYAMA, Yoshinori IMAIZUMI, Takashi TSUKA ...
2009 Volume 28 Issue 5 Pages
595-601
Published: 2009
Released on J-STAGE: October 13, 2009
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The feature of osteoconductivity, and expression of inductive BMP and transcription factors (Runx2 and Osterix) for osteoblast differentiation, which was related to conductive bone formation, were observed in experimentally created defects in rat femoral and parietal bones filled with
β-tricalcium phosphate (
β-TCP) or carbonate apatite (CAP). Femoral cortical bone defects were repaired by conductive bone formed by osteoblasts differentiated around
β-TCP and CAP, and immunohistochemical observation revealed that the osteoblasts expressed BMPs, Runx2, and Osterix. However, the repair in parietal bone defects was incomplete despite the
β-TCP and CAP filling. Only cells, which differentiated around
β-TCP or CAP, and formed conductive bone expressed BMPs, Runx2, and Osterix. These findings revealed that the osteoconductivity of calcium phosphate materials required the expression of BMPs as the prerequisite for Runx2 and Osterix expression. Therefore, it is suggested that when calcium phosphate ceramics are used as bone substitute materials, BMPs are essential for osteoconductivity.
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Yuji FUKUI, Wataru KOMADA, Keiichi YOSHIDA, Shiho OTAKE, Daizo OKADA, ...
2009 Volume 28 Issue 5 Pages
602-609
Published: 2009
Released on J-STAGE: October 13, 2009
JOURNAL
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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.
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Kenichi IIYAMA, Hisashi DOI, Takao HANAWA
2009 Volume 28 Issue 5 Pages
610-619
Published: 2009
Released on J-STAGE: October 13, 2009
JOURNAL
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Titanium is widely used in dental applications. This study investigated the effects of casting conditions on the mechanical characteristics of cast titanium, with a special focus on mold temperature. As such, the mechanical characteristics of specimens prepared at various mold temperatures of 23, 200, 400, 600 and 800°C were compared. On tensile strength, a significant decrease was observed at mold temperatures above 400°C as well as an increase in the scattering of the measured values at higher mold temperatures. On the durability of cast titanium which was assessed by simulating the actual clasp movement during cyclic flexural test, it was found to decrease as the mold temperature increased. When compared with Type 4 dental gold alloy, titanium which was cast at room temperature exhibited equivalent or better durability. Based on the results of this study, it is recommended to perform casting at lower mold temperatures in order to produce highly fatigue-proof cast titanium clasps.
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Ali Riza CETIN, Nimet UNLU
2009 Volume 28 Issue 5 Pages
620-626
Published: 2009
Released on J-STAGE: October 13, 2009
JOURNAL
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The aim of this study was to assess the clinical performance of three direct composite resins and two indirect inlay systems in posterior teeth using the modified USPHS criteria. A total of 100 restorations were placed in the molars of 54 patients by one operator. All restorations were directly evaluated by two examiners at baseline, 6 months, and 12 months. Statistical analysis was conducted using McNemar chi-square test at a significance level of 5% (
p<0.05). Recall rate was 100% at 6 and 12 months, and all the restorations evaluated (
i.e., 100%) received Alpha rating for the criteria of retention and gingival adaptation. At 12 months for the surface texture criterion, 80% of Filtek Supreme XT received Alpha rating while it was 95% for Tetric EvoCeram and AELITE Aesthetic. For marginal discoloration, 85% of Tescera ATL and Filtek Supreme XT received Alpha rating while it was 95% for Tetric EvoCeram and AELITE Aesthetic. Further, none of the restorative systems received a Charlie rating for any of the criteria at all evaluation periods. In summary, all the restorations demonstrated clinically satisfactory performance with no significant differences detected among them.
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Ryoji SHIMOGORYO, Toru EGURO, Eiichiro KIMURA, Michito MARUTA, Shigeki ...
2009 Volume 28 Issue 5 Pages
627-633
Published: 2009
Released on J-STAGE: October 13, 2009
JOURNAL
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Apatite cement containing porogen can be a useful material for the fabrication of biporous (macro- and microporous) apatite, which has gained much attention as a bone substitute material because of its large surface area and that it improves cell penetration. In the present study, the effects of added mannitol on the setting reaction and mechanical strength of apatite cement were evaluated. Apatite cements containing 0–40 wt% of mannitol were prepared and allowed to set in 0.9% saline kept at 37°C for 1–7 days. Although the diametral tensile strength (DTS) value increased with time, it decreased with the amount of added mannitol. SEM observation and XRD analysis revealed that mannitol had no inhibitory effect on the transformation reaction of apatite cement to apatite. It was thus concluded that mannitol was a good candidate for the fabrication of biporous apatite because it is biocompatible, exhibits satisfactory dissolution behavior, and that it caused no inhibitory effects on the compositional transformation to apatitic material.
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Masanori HASHIMOTO, Shinichi FUJITA, Kazuhiko ENDO, Hiroki OHNO
2009 Volume 28 Issue 5 Pages
634-641
Published: 2009
Released on J-STAGE: October 13, 2009
JOURNAL
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This study examined the effect of dentinal water on bonding, comparing one-bottle and two-step self-etching adhesives using microtensile bond test and scanning electron microscope. The bond strength of resin to dentin was measured for wet dentin (control) and dry dentin substrates. Wet dentin is the normal substrate for bond testing, whereas dry dentin was dehydrated in a desiccator at different drying times (5 to 60 min) before bonding. After bond testing, the fractured surfaces were examined. Although no correlation was found for two-step self-etching adhesives, the bond strength of the dry-dentin was significantly increased with the increase in the drying-time for one-bottle adhesives. With increased drying-time, the amount of water-bubbles was decreased for one-bottle adhesives; however, no bubble formation was seen in two-step adhesives in any group. The hydrophilic resin adhesive may entrap the water from dentin by osmosis during and after bonding. This effect may depend on the “hydrophilicity” of adhesives.
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Yoshinori KADOMA, Yoh TAMAKI
2009 Volume 28 Issue 5 Pages
642-648
Published: 2009
Released on J-STAGE: October 13, 2009
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In order to clarify the effect of fluorination of an adhesive resin on the durability of the resin bond to precious metal alloys, 2,2,2-trifluoroethyl methacrylate (TFEMA)-poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA)/TBBO adhesive resin was prepared. The tensile bond strength of this resin to precious metal alloys treated with 9,10-epithiodecyl methacrylate (EP8MA) generally increased in the order Ag alloy<Pd alloy<Au alloy after thermal cycling; bond strength was decreased by thermal cycling. The water sorption of TFEMA-PTFEMA/TBBO resin was much higher than that of MMA-PMMA/TBBO resin because of phase separation. For Au alloy, the bonding durability of TFEMA-PTFEMA/TBBO resin against penetration of water was comparable to that of MMA-PMMA/TBBO resin; however, for Pd and Ag alloys the performance of the fluorinated resin was markedly inferior to that of MMA-PMMA/TBBO resin. These reduced tensile bond strengths were considered to be caused by insufficient copolymerization with EP8MA molecules adsorbed on the precious metal alloys.
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Kohji NAGATA, Hidekazu TAKAHASHI, Masahiro ONA, Hiroyasu HOSOMI, Noriy ...
2009 Volume 28 Issue 5 Pages
649-656
Published: 2009
Released on J-STAGE: October 13, 2009
JOURNAL
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The purpose of this study was to evaluate the reinforcing effect of fiberglass on composite resin retainers of the telescopic dentures. A finite element method was used to assess the effect of the abutment height and the embedment of the fiberglass on the stress distributions of the retainers. The experimental retainers of Poly(methylmethacrylate), composite resin (CR) and the fiber-reinforced composite resin (FRC) were used in the fracture test. The fracture load of the FRC retainers were significantly greater than those of the other retainers. The embedment of the fiberglass reduced the stress at the upper surface of the CR retainers. The fracture origin in the CR retainers was seen on the upper surface, while that of the FRC was at the cervical region near the abutment. These results suggest that the change in the fracture pass by the fiberglass increased the fracture resistance of the CR retainer.
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