Bio-Medical Materials and Engineering - Volume 15, issue 4

Authors: Hashemi, Z.K. | Oshida, Y. | Deely, J.J. | Ki, Y.

Article Type: Research Article

Abstract: Background: A new approach called “minimum intervention” has been introduced for restoration of carious lesions to preserve tooth structure. This approach suggests that perhaps caries need not always be removed completely from deeper portions of the cavity. It is, therefore, important to characterize caries-affected dentin structures, because of the potential changes in bonding quality when using different dentinal substrates. Materials and method: Ninety teeth (30 teeth each group) were studied. The first group (CF) consisted of 30 caries-free teeth. The second group (CC) consisted of 30 teeth, for which caries-free dentin teeth was chemically demineralized. The third group (ND) consisted …of 30 extracted human molars with coronal carious lesions. After all tooth samples were water-polished with grit #600 SiC paper, they were tested by surface contact angle measurements and the electron-probe microanalyzer to measure Ca/P mol ratio. Results: Contact angles were CF=60.07°; CC=30.8°; ND=26.11°, p<0.05. Ca/P mol ratios were as follows; CF=1.549 (±0.0435); CC=1.324 (±0.2305); ND=1.568 (±0.0523), p<0.05. Weibull analyses for Ca/P mol ratio indicated shape parameter (m) of CF was 13.3; it was 12.8 for ND and 11.8 for CC. Above the δ point (=1.65 in Ca/P ratio), for both groups m=3.4. Conclusion: Caries-affected dentin surfaces (naturally-developed and chemically created) were statistically more chemically active than caries-free dentin surface. Ca/P mol ratio of chemically created caries was less than other two groups. Show more

Keywords: Minimum intervention, caries-affected dentin, caries-free dentin, characterization, Ca/P ratio

Citation: Bio-Medical Materials and Engineering, vol. 15, no. 4, pp. 251-260, 2005

Authors: Sonobe, Masato | Hattori, Koji | Tomita, Naohide | Yoshikawa, Takafumi | Aoki, Hideyuki | Takakura, Yoshinori | Suguro, Toru

Article Type: Research Article

Abstract: Recent studies have reported that statins, inhibitors of hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase, increase bone formation in osteoblasts in vitro, suggesting that statins may have a new therapeutic application in the treatment of osteoporosis. During the reparative phase of healing of bone fractures, bone marrow-derived mesenchymal stem cells differentiate into osteoblasts or chondrocytes to form callus. If statins also stimulate bone formation in bone marrow-derived mesenchymal stem cells they may have beneficial effects in the treatment of bone fractures. In this study, we assessed the effect of statins on bone formation in rat bone marrow-derived mesenchymal stem cells in vitro. The …statins fluvastatin, simvastatin and pravastatin did not significantly enhance mineralization, alkaline phosphatase (ALP) activity and bone gra protein (BGP, osteocalcin). These findings suggest that statins do not increase bone formation in bone marrow-derived mesenchymal stem cells. Show more

Keywords: Statins, bone marrow-derived mesenchymal stem cell, bone formation

Citation: Bio-Medical Materials and Engineering, vol. 15, no. 4, pp. 261-267, 2005

Authors: Mifsud, S. | Lagneau, C. | Lissac, M. | Grosgogeat, B.

Article Type: Research Article

Abstract: Objectives: The aim of this study is to compare the efficiency of two polymerization techniques (halogen curing – Astralis® 7 and plasma curing – Flipo® ), with two orthodontic adhesive materials (Enlight® , a composite resin, and Fuji OrthoTM LC, a glass ionomer cement). Methods: The efficiency of the polymerization techniques was shown by two mechanical tests. The hardness test was carried out on the exposed and non-exposed surfaces using 10×4×3-mm samples, polymerized either by halogen curing (40 seconds) or by plasma curing (5 seconds). The three-point bending tests were carried out on 2×2×25-mm samples polymerized as above. …The samples were kept 1 hr at room temperature, then for 24 hrs in distilled water at 37°C. Results: Whatever the polymerization technique used, the results are similar for hardness and flexion, with the exception of the hardness tests carried out after polymerization with the Flipo® light on the surface not directly exposed. Conclusion: In orthodontic practice, both polymerization techniques can be used. But a multibracket session can be long, and the reduction of time spent in the chair obtained by using plasma lamps seems to make this technique preferable. Show more

Keywords: Dental material, composite resin, glass ionomer cement, light curing

Citation: Bio-Medical Materials and Engineering, vol. 15, no. 4, pp. 269-277, 2005

Authors: Yoo, Je Young | Kim, Jong Min | Seo, Kwang Su | Jeong, Yong Kyun | Lee, Hai Bang | Khang, Gilson

Article Type: Research Article

Abstract: The aim of this study was to detect the amount of lactic acid (LA) and glycolic acid (GA) in poly(D,L-lactide-co-glycolide) (PLGA) by development a simple HPLC method and to determine the pH of media, which can influence on degradation of PLGA and drug release. Analysis of in vitro degradation behavior of PLGA with two different molecular weights as 8000 and 33,000 g/mol were performed in various media conditions (pH 3.0, 5.0, 7.0, and 9.0 of PBS and distilled water (approx. pH 5.8)). Also, effect of some additives on PLGA degradation was also investigated in pH 7.0 of PBS. GA and …LA were easily detected by a simple HPLC method (retention time: 6.5 min and 10.2 min, respectively). The result showed that GA was released larger amount than that of LA considering the initial sample weight of polymers, due to the higher hydrophilic property. In the lower pH of media conditions, the PLGA was faster degraded generally. The presence of various additives, moreover, affected decrease of pH and slight acceleration of LA and GA detection. Show more

Keywords: Poly(lactide-co-glyciolide), lactic acid, glycolic acid, HPLC, pH variation

Citation: Bio-Medical Materials and Engineering, vol. 15, no. 4, pp. 279-288, 2005

Authors: Peña, J. | Solano, E. | Mendoza, A. | Casals, J. | Planell, J.A. | Gil, F.J.

Article Type: Research Article

Abstract: The main objective of this work has been the characterisation and correlation of the wear behaviour of the NiTi shape memory alloys in their different phases. The weight losses for the different alloys in function of the present phase, and of the Ms transformation temperature are studied. Adhesive wear tests, Pin-on-Disk, according to the ASTM-G99 standard have been carried out. The thermoelastic martensitic transformations that cause the superelastic effect, the reorientation and coalescence of martensitic plates and the damping effect promotes a high ability to accommodate large deformations without generating permanent damages that causes the wear. The resulting plastic …deformation may be accumulated during wear process without generating fracture. The results show that the wear resistance is mainly dependent of the Ms transformation temperature for both alloys. For the NiTi alloys also the Ni atomic percentage and the hardness of the alloys are important parameters in the wear behavior. Show more

Keywords: Shape memory alloys, wear, NiTi, superelasticity, articular prosthesis

Citation: Bio-Medical Materials and Engineering, vol. 15, no. 4, pp. 289-293, 2005

Authors: Fukui, Tomohiro | Matsumoto, Takeo | Tanaka, Toshihiro | Ohashi, Toshiro | Kumagai, Kiichiro | Akimoto, Hiroji | Tabayashi, Koichi | Sato, Masaaki

Article Type: Research Article

Abstract: To investigate the mechanism of aneurysm rupture, it is necessary to examine the mechanical properties of aneurysm tissues in vivo. A new approach to evaluate in vivo mechanical properties of aortic aneurysmal tissues has been proposed in this study. The shape of the aneurysm was modeled as a sphere, and equi-biaxial stress in the in vivo state was estimated from the diameter and the wall thickness of each aneurysm and mean blood pressure of each patient. The mechanical properties of the aneurysm at the in vivo stress were estimated from its in vitro biaxial tensile properties. There were no significant …correlations among maximum diameter D, wall thickness t, and mean infinitesimal strain in the in vivo state εm . This indicates the wall deformation during aneurysm development was not elastic but plastic. The mean incremental elastic modulus Hm , an index of tissue stiffness, had a significant positive correlation with elastic modulus anisotropy index KH . This indicates the aneurysmal wall got more anisotropic in vivo as it becomes stiffer. Show more

Keywords: Aortic aneurysm, anisotropy, equibiaxial property

Citation: Bio-Medical Materials and Engineering, vol. 15, no. 4, pp. 295-305, 2005

Authors: Al-Ali, S. | Oshida, Y. | Andres, C.J. | Barco, M.T. | Brown, D.T. | Hovijitra, S. | Ito, M. | Nagasawa, S. | Yoshida, T.

Article Type: Research Article

Abstract: Background: When a dissimilar couple is exposed to corrosive environment, it will normally exhibit a galvanic corrosion. The galvanic corrosion might be influenced by various factors, including type and concentration of electrolyte, surface area ratio between anode and cathode, type of coupling material, and coupling manner. Purpose: The purpose of this study was to investigate and compare the galvanic corrosion behavior of commercially pure titanium when coupled with type IV Au alloy, Au–Ag–Pt alloy, and Ag–Au–Pd alloy by different coupling methods. Materials and methods: Couples were prepared by a laser welding or a mechanical adhering method. Electrochemical corrosion studies were …conducted in a Ringer's solution at a scanning rate of 0.1 mV/sec in a range from −250 mV to +250 mV with respect to EOCP . Corrosion parameters (EOCP , ICORR , ECORR ) were obtained. Results: It was found that (i) there was a significant difference between LWC and AJC for three couples (p<0.05), (ii) the crevice line caused all three couples more corrosive than weld joint line, (iii) for both joint, it was found that type (IV) Au alloy exhibited discoloration to some extent. Conclusions: It is concluded that among the three couples with two different coupling methods, Ti/Ag–Au–Pd couple exhibited best corrosion resistance in a room temperature Ringer's solution. Show more

Keywords: Galvanic corrosion, crevice corrosion, coupling mode, titanium, dental precious alloys, discoloration

Citation: Bio-Medical Materials and Engineering, vol. 15, no. 4, pp. 307-316, 2005

Authors: Dargahi, Javad | Najarian, Siamak | Talebi, Mehdi

Article Type: Research Article

Abstract: In this study, design optimization of a tooth implant-supported fixed prosthesis was investigated theoretically. A three-dimensional finite element analysis was utilized to simulate the stress distribution and deformation, with an emphasis on the material selection for various parts of the prosthesis. This mandibular prosthesis was supported by six implants. The properties of 3 different materials for implants and 4 different materials for framework were incorporated into 12 different models. For the loading conditions used, it was found that the largest displacements occurred at the far ends of the framework and that the resulting deflection was highly dependent on the material …properties of the framework. The simulations showed that the stress in the framework was mainly concentrated near the holes in the lower surface and that the highest values of von Mises stresses occurred in the lingual part of the prosthesis. Furthermore, the modeling results revealed that more rigid frameworks led to a corresponding decreased stress in the retaining screws and that high-stress concentration areas moved from the neck of the implant towards the base of it, as the value of Young's modulus increased. It was concluded that the first best model was the Cr–Co alloy for the framework and the Ti alloy for the implant and the second best choice was the Cr–Co alloy for both the framework and the implant. Show more

Keywords: Fixed prosthesis, FEA, dental implant, modeling, three-dimensional

Citation: Bio-Medical Materials and Engineering, vol. 15, no. 4, pp. 317-331, 2005