Shozo Tsuruta

Release of mercury from dental amalgam fillings in pregnant rats and distribution of mercury in maternal and fetal tissues.

Mercury vapor released from a single amalgam restoration in pregnant rats and mercury concentrations in maternal and fetal rat tissues were studied. Dental treatment was given on day 2 of pregnancy. Mercury concentration in air sample drawn from the metabolism chamber with the rat was measured serially for 24 h on days 2, 8 and 15 of pregnancy. An average mercury concentration in the air samples from the rats given amalgam restorations was 678.6+/-167.5 ng/day on day 2. The average mercury concentration in the air samples tended to decline as time elapsed but a marked amount (423.2+/-121.5 ng/day) was observed even on day 15. The amount of mercury in the air samples increased 7--20-fold after chewing. The placement of the single amalgam restoration (3.8--5.5 mg in weight) increased the levels of mercury approximately three to 6 times in the maternal brain, liver, lung, placenta and 20 times in the kidneys. The highest mercury concentration among fetal organs was found in the liver, followed by the kidneys and brain. Mercury concentrations in maternal organs and fetal liver were significantly higher than those of the controls, and concentrations in maternal whole blood, erythrocytes and plasma, and in fetal whole blood were also significantly higher. Mercury concentrations in the fetal brain, liver, kidneys and whole blood were lower than those of the maternal tissues.

Placental transfer of mercury in pregnant rats which received dental amalgam restorations.

Mercury vapor released from one, two and four amalgam restorations in pregnant rats and mercury concentrations in maternal and fetal organs were studied. Dental treatment was given on day 2 of pregnancy. Mercury concentration in air samples drawn from each metabolism chamber with a rat were measured serially for 24 h on days 2, 8 and 15 of pregnancy. On each day of pregnancy, the amount of mercury in 24 h air samples was in proportion to the amalgam surface areas. Linear regression analysis showed relatively high correlation coefficients between the mercury content and amalgam surface areas, and the coefficients were statistically significant. A highly significant correlation was also found between the number of amalgam fillings and their surface areas. Mercury concentrations in major maternal organs with one, two and four amalgam fillings tended to increase with the increasing amalgam surface areas. Spearmans rank correlation test revealed significant correlations in the brain, liver, kidneys and placenta but not in the lung. Furthermore, significant correlations were also found between the mercury concentrations in all maternal organs and the amount of mercury in 24 h air samples on day 15 of pregnancy. Mercury concentrations in fetal brain, liver and kidneys were much lower than those of the dams but liver and kidneys showed positive correlations between the mercury content and maternal amalgam surface areas. Similar correlations were observed between the mercury concentrations in fetal organs and the amount of mercury in 24 h air samples on day 15 of pregnancy. In fetal brain, no significant correlations were found between either maternal amalgam surface areas or the amount of mercury in 24 h samples on day 15 of pregnancy but significant uptake of mercury was found in the samples from the dams given four amalgam fillings. The results of the present study demonstrated that mercury vapor released from the amalgam fillings in pregnant rats was distributed to maternal and fetal organs in dose-dependent amounts of the amalgam fillings.

The effect of zinc levels in a gold-based alloy on porcelain–metal bonding

OBJECTIVES The purpose of this study was to ascertain whether the amount of Zn in gold alloys contributes to porcelain-metal bonding. METHODS Experiments were carried out using a commercial Pd-free gold alloy with a nominal composition of 88.7 wt% Au, 9.49 wt% Pt, 1.5 wt% Zn, 0.1 wt% Mn, 0.2 wt% Rh, and 0.1 wt% Ir, which contains Zn and no other elements (In, Sn, Fe) known to affect porcelain-metal bond strength. To establish the effect of oxidation of the metal surface, porcelain was applied both to preoxidized and to non-preoxidized metal specimens. The bond strength was evaluated by means of the ISO 9693: 1999 crack initiation test. A conventional gold alloy was used as a control. The elemental distributions at the porcelain/alloy interfaces were analyzed in cross section by electron probe microanalysis. Additionally, after the bond strength test, cross-sections of the interfaces of the debonded specimens were microscopically analyzed to characterize the fracture mode. RESULTS The Pd-free gold alloy joints showed significantly higher bond strength values than joints made with conventional gold alloy. Preoxidation treatment significantly increases the bond strength, in the preoxidized joints Zn was highly localized at the interface and diffused into the porcelain up to about 10 μm from the interface, and the joint failed by cohesive fracture in the porcelain. In contrast, the non-preoxidized joint showed mainly adhesive fracture at the porcelain/alloy interface. SIGNIFICANCE The presence of Zn in gold alloys plays a part in establishing chemical bonding thus improving the bond strength between porcelain and alloy.

Oriented Needle-Like Apatite and Biodegradable Copolymer Composite Membranes

Needle-like apatites were formed on the pure titanium plate using a hydrothermal-electrochemical method. The solution of dichloromethane a nd poly-lactic acid / poly-glycolic acid copolymer (PLGA) was infiltrated to the de posited apatite and dried in air. After hardening of the film, the composite membrane was prepared b y elamination from the titanium plate. The deposited needle-like apatites were hexagonal bars 0.5~1 m in width and about 7 m in length. The apatite needles were well incorporated in the semitransparent copolymer film. The tips of the needles were exposed only on the side that contacted to the substrate. Introduction Ceramic materials are classified as bioinert, bioactive and bi oabsorbable ceramics. Bioactive ceramics such as tricalcium phosphate ( -TCP and -TCP ) and hydroxyapatite (HAp) are frequently used in clinical applications [1]. Because the osseous conduc ti and biocompatibility of the materials are required to restoration of bone defects, var ious morphology and size of these calcium phosphates have been used. HAp is most frequently applied as the filling material for bone defects [2]. When HAp is filled in such cases, HAp acts as s ame as natural bone. The osteoblast around the HAp are promoted their growth, adhesion and calcifica tion. Then, HAp is used as the alternative material for the hard tissue. Recently , bioactive ceramics are applied as the scaffold of tissue regeneration. On the other hand, synthetic polymers such as PLGA are frequently used as biodegradable membrane in dental and medical appli cations. The PLGA has been used as biodegradable sutures, hemostatic materials, bone fixat ion m terials and guided tissue regeneration (GTR) materials for dental and medical areas. When the polymer is used as scaffold in GTR and alternative materials, it is necessary that bi oabsorbable materials are compatible with mechanical properties of target tissue and its decomposition rate corr sponds to the regenerating speed of tissue. Several researchers [3] reported that these bioa bsorbable materials disintegrate via complicated process. In these polymers, for example, PLGA is dispos ed t be rapid decomposed for faster hydrolytic cleavage. Then PLGA is commonly used for purpose of faster decomposition. It has been reported that tricalcium phosphate, HAp and calcium hydrog en carbonate have been tried to improve the material strength. For example, apatite-c ollagen complex have many advantages and have been frequently used in the various applications. We have been studying on electrochemical deposition of apatite on titanium [4]. Our previous reports revealed that the electrochemical deposition of apatite promotes the bioactivity of i mplants [5]. Furthermore, the morphology of the deposited apatite could be easily controlled by the r egulation of the electrolytic conditions [6]. The purpose of this study was to develop a preparation method of a composite Key Engineering Materials Online: 2003-05-15 ISSN: 1662-9795, Vols. 240-242, pp 191-194 doi:10.4028/www.scientific.net/KEM.240-242.191

Preparation of a Composite Membrane Containing Biologically Active Materials

Oriented needle-like apatite was formed on a pure titanium plat e with the hydrothermal electrochemical method. BMP was applied on the titanium plate. Poly-lactic acid/poly-glycolic acid (PLGA) dissolved in dichloromethane was dropped on the titanium subst rate. The dried and delaminated PLGA layer containing apatite with BMP was the biologically active membrane. The composite membrane was easy to bend along the shape of the bone defect. Introduction Biologically active materials, stem cells and their scaffol ds are required to promote new bone formation. Especially in case of dental applications, various diseas e such as periodontal disease and severe apical legion cause bone defect. Guided Bone Regeneration and Guided Tissue Regeneration are techniques for the treatment of the bone defects [1, 2]. Biodegradable membranes have been successfully applied to these treatments [3]. Generally, poly-lactic acid, poly-glycolic acid and PLGA are known as materials of biodegradable membranes. The biodegradable membranes are useful materials because of their r esorption, usability, and retention property. On the other hand, it is well known that bone morphogenetic protein (BMP) induces bone format ion. PLGA and gelatin are frequently used as the carriers of BMP. W e have reported the preparation of biodegradable PLGA membrane containing oriented needle-like apatite [4]. In the present study, BMP was extracted from bovine cortical bone. Oriented needl e-like apatite was formed on the titanium plate and biodegradable composite membrane containing oriented needle-like apatite with BMP was prepared. Materials and Methods Preparation of BMP BMP was prepared with the method of Urist [5] and Mizutani [6]. One hundred pieces of the bovine cortical bones removed soft tissue were washed in cold water, froz n in liquid nitrogen and grinded to a particle size of 1 mm . The particles of bone were defatted in chloroform and methanol (1:1) for 2 h (chloroform and methanol were evaporated for 12 h after defatted) and decalcified in 0.6 M HCl for 72 h. The decalcified particles of b ne were exposed to 2 M CaCl 2· 2H2O solution for 1 h, 0.5 M EDTA for 1 h and extracted in 6 M urea containi g 0.5 M CaCl 2· 2H2O and 1 mM n-ethyl maleimide (n-EM) for 48 h. Extracted solution without particles of bone was dialyzed against distilled water for 72 h. Dialyzed solution w as centrifuged for 20 min. The precipitate was dissolved in 1 L of 6 M urea containing 0.5 M CaCl 2· 2H2O (without 1 mM n-EM). Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 1115-1118 doi:10.4028/www.scientific.net/KEM.254-256.1115

Micro-CT Analysis of New Bone Formation Around Implant with Electrochemically Deposited Apatite

Micro-CT was employed to determine the volume of new bone formed ar ound the implants with and without the electrochemically deposited apatite. With the accumulation of new bone area in the 2-dimensional images, the volumes of new bone around implants were deriv d. Linear regression analysis revealed a correlation ( r=0.704) between the pull-out bonding strengths and the volume of new bone of rabbit femora around the implants. Introduction We reported that the electrochemical deposition of apatite have som advantages: i.e. it can easily create a homogeneous apatite coating on substrates having complicate d sh pes such as dental implants, and requires only simple and small devices. Furthermore , varying the electrochemical conditions can easily control the morphology of deposited apatite [1-6]. The bonding strength of the implant with the electrochemically deposited apatite depended on the morphology of apatite [7, 8]. The apatite deposited at 100 ̊C showed the best bioactivity in vitro [6, 8]. At 3-week implantation, the boundary of the implant coated at 100 ̊C was completely fill d with new bone, whereas that at 200 ̊C was not filled with it [9]. On the other hand, micro-computed tomography (CT) recently is applied to osteology [10-12]. The purpose of the pres ent tudy was to quantitatively determine the volume of new bone formed around the implants with and without the electrochemical apatite coating using micro-CT and to discuss the relation between the amount of new-bone and their bonding strengths. Materials and Methods The electrolyte was heated in stainless steel-autoclave asse mbled two electrodes, a stirring screw, a pressure gauge, a pressure valve, a thermo-couple and an electric hea ter. A platinum plate, 20 x 20 x 0.5 mm, was used as the counter electrode and commercially pur e titanium bars, 2 x 12 mm, were employed as the working electrode. The electrolyte was prepared by dissolving given amounts of reagent-grade chemicals of 137.8 mM of NaCl, 1.67 mM of K 2HPO4, and 2.5 mM of CaCl2·2H2O into distilled water. The solution was buffered to pH value of 7.2 wi th 50 mM tris(hydroxymethyl)aminomethane [(CH 2OH)3CNH2] and an adequate amount of hydrochloric acid. The electrolyte was heated at 100, 150, and 200 ̊C using electric heater and agitated by a stainless screw. The current was maintained at 12.5 mA/cm 2 by DC power supply for 1 hr. After loading of the constant current, the titanium bars loaded as cathodes were r insed with distilled water and dried at 37 ̊C in air. These titanium bars with and without the electrochemically depos it d apatite were implanted into the femora of Japanese white rabbit. The rabbits were sacrific ed at 3 weeks after implantation and the femora were taken out from the bodies. Immediately, the fem ora were used for radiographic Key Engineering Materials Online: 2003-05-15 ISSN: 1662-9795, Vols. 240-242, pp 611-614 doi:10.4028/www.scientific.net/KEM.240-242.611

Mechanical Properties of Newly Developed Root Canal Sealers Containing Titanium Oxide

Titanium oxide (TiO2) has lately attracted considerable attention as a new material in dentistry because of its catalytic activity and biocompatibility. In the present study, we developed a novel root canal sealer consisting of TiO2 and evaluated its mechanical properties in vitro. The newly developed root canal sealer containing TiO2 has satisfied the requirement of ISO formulation 6876. Our results suggest that the newly developed root canal sealer has excellent physical characteristics, which may make it suitable for clinical use as a root canal sealer material.

Reciprocal Tribocontact of Biomedical Alloys

Reciprocal Tribocontact has been manifested to be responsible for the certain attrition of artificial components in dental fields. But confusion on the aspects of friction and wear pattern was found between fretting and sliding, the two items often emerging in reports about friction and wear of biomaterials, due to the ambiguity on definition. By refining the definition of fretting with partial slip concept, this work compared friction and wear behaviors of three dental alloys under fretting and sliding conditions. Results indicate that friction force waveform and surface damage topography created by fretting quite differs from by sliding. The curve of friction force vs time under fretting is of nearly perfect sine waveform; some micro disturbance occurs on the peaks and valleys of the waveform while the amplitude is big enough. Wear patterns from fretting consist of a central stick region, a surrounding slip region and sometimes crack between the two regions, but wear patterns from sliding are of linear tracks running through the entire scar, scraped trace or severe surface deformation.

Rheological approach for determining yield stresses in flowable resin composites prior to setting

The purpose of this study is to develop a method for quantifying the fluidity of flowable resin composites using determinations of yield stress. Five commercially available composites (AliteFlo LV, Flow-it ALC, Venus flow, Tetric N-flow, Revolution Formula2) were investigated. Yield stress values were obtained by plotting shear stresses for a range of shear rates, followed by fitting of Casson fluid models to flow curve data and extrapolation to the stress axis. To confirm that yield stress reflected fluidity, apparent viscosity at the lower shear rate (0.2 s-1) was calculated from flow curves. Yield stresses ranged from 5.4 to 43.1 Pa, and were found to capture differences in the fluidity of composites that were not captured by viscosity measurement at the low shear rate. Yield stress is directly proportional to fluidity, and could serve as a simple and precise indicator for selecting flowable resin composites for use in various clinical applications.

Comparison of the Physical Properties of Dental Restorative Materials Used in Endodontics

There is little information concerning the physical properties of various commercialized water-based temporary filling materials. In this study, the setting characteristics of 5 water-based temporary filling cements, i.e., Caviton, HY-seal, Lumicon, Cavit-G, and Cavit-W, were examined. Reinforced plastic pipes were filled with the test materials, and the specimens were then immersed in distilled water at 37°C. Setting time of each specimen was determined by a penetration test using a Vicat penetrometer; and setting layer depth was measured with micrometer calipers. Cavit-W exhibited the fastest setting time, whereas Caviton and HY-seal demonstrated the slowest setting time. These results indicate that the setting properties of these materials used in this study were significantly different for each material, which showed some changes on the surface and the internal part after the start of water absorption.