Biomedical subjects

Junro Yamashita

Publications and source records attributed to Junro Yamashita.

4 recordsLinked to original sources

PubMed2006

Biomechanical effects of fixed partial denture therapy on strain patterns of the mandible.

STATEMENT OF PROBLEM: The mandibular posterior 3-unit fixed partial denture (FPD) is a conventional prosthodontic therapy and presumably has an effect on the direction and magnitude of occlusal forces and, thus, on the biomechanical environment of the mandible, which may in turn affect bone structure. However, the impact of FPD therapy on mandibular biomechanics is unknown. PURPOSE: The purpose of this study was to test the hypothesis that 3-unit FPD therapy alters strain patterns in the mandible during loading. MATERIAL AND METHODS: Four human cadaver mandibles missing first molars were bilaterally fixed and artificially loaded on each tooth individually. Surface cortical bone strains were measured with multiple strain gauges during loading of up to 250 N. Next, 3-unit FPDs with a chamfer finish line were fabricated using Type IV gold alloy. Strain measurements were conducted in the same manner to assess differences in strain patterns before and after therapy. Paired-sample tests for metric and angular data were used to assess difference in strain pattern before and after therapies (alpha=.05). RESULTS: When loading was applied on the teeth not involved in FPD therapy, no differences were found before and after FPD placement. When the posterior retainers were loaded, the strain distribution differed (P=.01); on the buccal cortices, strain levels increased posteriorly but decreased significantly anteriorly. However, these differences were less than 100 muepsilon, and the overall deformation pattern of the mandible after the FPD therapy was similar to that before FPD therapy. Strain distributions when the pontic was loaded were similar to those when the posterior retainer was loaded. CONCLUSION: Three-unit FPD therapy did not alter the overall deformation pattern of the mandible during loading.

Analysis of Variance↗

PubMed2006

The comparison of provisional luting agents and abutment surface roughness on the retention of provisional implant-supported crowns.

STATEMENT OF PROBLEM: In immediate implant loading, it is important to keep provisional restorations in place during early-phase healing. Current luting agents for provisional restorations may provide inadequate retention, creating a clinical challenge. PURPOSE: This study compared the retention of provisional autopolymerizing acrylic resin implant-supported single restorations with combinations of different implant abutment surface conditions and provisional luting agents. MATERIAL AND METHODS: Thirty solid titanium implant abutments (ITI), 4 mm high, were divided into 3 groups. Ten abutments were unaltered, 10 were airborne-particle abraded with 50-microm aluminum oxide, and 10 were roughened with a medium-roughness diamond rotary cutting instrument. Thirty implant analogs (ITI) were mounted in autopolymerizing acrylic resin blocks. A solid titanium implant abutment was placed in each implant analog and torqued to 35 N.cm. After fabrication of 4 provisional acrylic resin crowns for each abutment, provisional luting agents TempBond, TempBond NE, Life, and Zone were used to secure the provisional crowns to the respective abutments. All specimens were luted with one of the provisional luting agents for a given test. After ultrasonic cleaning of the abutments, another provisional crown was luted with another luting agent. All specimens were stored in 100% humidity environment for 1 day at 37 degrees C prior to testing. Each provisional acrylic resin crown was pulled from the abutment with a 500-kg load cell in a universal testing machine at a crosshead speed of 0.5 cm/minute, and tensile strength was recorded (N). Data were analyzed using analysis of variance (ANOVA) and the Scheffe test (alpha=.05). RESULTS: Tensile strength was significantly higher for Life and TempBond NE than for TempBond and Zone, regardless of the surface conditions (P=.0001). The result of the 2-way ANOVA indicated that a significant interaction existed between the provisional luting agents and surface conditions (P=.0039). TempBond NE showed significantly higher tensile strength when combined with airborne-particle-abraded surfaces compared to other combinations (P=.011). However, no difference was found in tensile strength of Life and Zone between different combinations. The tensile strength of TempBond was lower when used with the unaltered surface compared to other combinations (P=.001). CONCLUSION: Surface modification of an implant abutment by airborne-particle abrasion or diamond rotary cutting instrument did not improve retention of a provisional acrylic crown when Life or Zone was used as the luting agent. Airborne-particle abrasion may be an effective method to increase retention of a provisional acrylic crown when TempBond NE is used.

Acrylic Resins↗

PubMed2004

The zinc finger mutation C417R of I-kappa B kinase gamma impairs lipopolysaccharide- and TNF-mediated NF-kappa B activation through inhibiting phosphorylation of the I-kappa B kinase beta activation loop.

The activation of the I-kappaB kinase (IKK) complex by TNF or LPS stimulates phosphorylation and degradation of I-kappaBalpha, leading to the nuclear translocation of NF-kappaB. The IKK complex is mainly composed of two catalytic subunits, IKKalpha and IKKbeta, and a chaperon subunit IKKgamma. Although IKKgamma does not have catalytic activity, it is essential for IKK activation induced by multiple stimuli. Importantly, the key residue cysteine 417 at the zinc finger domain of IKKgamma has been found to be mutated to arginine (IKKgammaC417R) in a human genetic disorder called the anhydrotic ectodermal dysplasia with immunodeficiency. To understand the underlying mechanisms of immunodeficiency, we examined whether the IKKgammaC417R mutant modified IKK activation and NF-kappaB transcription stimulated by LPS or TNF in human monocytes. We found that overexpression of IKKgammaC417R severely impaired LPS- and TNF-induced I-kappaBalpha phosphorylation and degradation in a dominant-negative fashion. Also, LPS- and TNF-induced NF-kappaB transcription was inhibited by IKKgammaC417R. The reconstitution of IKKgamma, but not IKKgammaC417R, in IKKgamma-deficient cells restored NF-kappaB signaling, indicating the zinc finger structure of IKKgamma plays a key role in IKK activation. Moreover, C417R mutation in IKKgamma abolished both LPS- and TNF-induced phosphorylation of the activation loop of IKKbeta. Collectively, our results indicated that the zinc finger structure of IKKgamma plays a key role in LPS- and TNF-induced NF-kappaB activation. The anhydrotic ectodermal dysplasia with immunodeficiency patients' immunodeficiency may be associated with NF-kappaB defect in response to bacterial stimulation.

Active Transport, Cell Nucleus↗

PubMed2002

Collagen and bone viscoelasticity: a dynamic mechanical analysis.

The purpose of this study was to explore the effects of changes in Type I collagen on the viscoelasticity of bone. Bone coupons were heated at either 100 or 200 degrees C to induce the thermal denaturation of Type I collagen. Half of these specimens were rehydrated after heat treatment; the other half were tested in a dry condition. The degree of denatured collagen (DC%) was analyzed by a selective digestion technique with the use of alpha-chymotrypsin. Isothermal (37 degrees C) and variable temperature tests (scans from 35 to 200 degrees C) were performed with the use of a dynamic mechanical analyzer to evaluate changes in bone viscoelastic properties as a function of collagen damage, specifically, changes in the loss factor (tan delta) and storage modulus (E') were assessed. Significant collagen denaturation occurred only when bone was heated at 200 degrees C irrespective of the hydration condition. Also, DC% did not show a significant effect on tan delta. However, higher values of tan delta were observed in wet samples compared to dry specimens. The temperature-scan tests revealed that the hydration condition, but not DC%, significantly affected the behavior of tan delta. However, E' was not strongly influenced either by DC% or by water content. These results suggest that at a constant frequency the denaturation of collagen triple-helical molecules may have few effects on the viscoelasticity of bone, but moisture may play a prominent role in determining this property.

Biomechanical Phenomena↗