The effectiveness of newly developed photocurable bonding agents in creating adhesion between composite resin and polished dentin without any pretreatment was investigated. Methacryloyl tyrosine amide (MTYA) and glyceryl methacrylate (GM) were used as an adhesive monomer and a water soluble methacrylate monomer, respectively. A water soluble photoinitiator, 2-hydroxy-3-(3, 4-dimethyl-9-oxo-9H-thioxanthen-2-yloxy)-N, N, N-trimethyl-1-propanaminium chloride (QTX) was used in combination with 2-(N, N-dimethylamino)ethyl methacrylate (DMAEMA) and benzene sulfinic acid sodium salt (BSNa).
Fresh bovine dentin was prepared by wet grinding with #1000 stones. The two parts of photocurable bonding agents were mixed well before application. After application of photocurable bonding agents to the polished surface, polymerization was performed for one min irradiation. Then Protect Liner (Kuraray Co.) was applied and polymerized by one min irradiation. The tensile bond strengths were measured after one day of immersion in 37℃ water.
The one min application of photocurable bonding agent (A1: 6% MTYA+70% GM+4% DMAEMA+1% BSNa aqueous solution, BSu3: 3% succinic acid+5% glutaraldehyde+2% QTX aqueous solution) gave a mean bond strength of 6 MPa, while 5 min application gave 11 MPa. The incorporation of acidic monomers, such as acrylamido glycolic acid or phenyl-p, was not very effective in increasing bond strengths. SEM observation showed the formation of a hybrid layer 2 μm thick by applying mixtures of A1 and BSu3 for 5 min.

View full abstract

Three different mixed silanes, (1) 3-mercaptopropyltrimethoxysilane (3-SH) and 3-methacryloxypropyltrimethoxysilane (3-MPS), (2) 3-SH, 3-MPS and 1, 6-bis(trimethoxysilyl)hexane, (3) 3-SH and N, N-bis(3-trimethoxysilylpropyl)methacrylamide, were used as primers for adhesion of poly(methyl methacrylate) to various dental precious metal alloys, base metal alloys and porcelain teeth.
After the thermo-cycle test, the bond strengths of precious metal alloys and porcelain teeth specimens treated with 3-SH/3-MPS primer were excellent. All 3-SH mixed primers to Ag alloy showed better water-resistance adhesion. There was no effect of three mixed primers on base metal alloy specimens.

View full abstract

Corrosion of dental alloys is usually evaluated by the uniform corrosion test. However, in dental clinics, localized corrosion is widely observed at the cervical and proximal area of metal restorations or at the interface between restoration and cavity wall. This study evaluated the crevice and galvanic corrosion of dental alloys using models simulating, the oral enviroment to understand localized corrosion behavior of metal restorations.
Two dental commercial alloys, Au-Pd-Ag-Cu and Ag-Sn-Zn were used as the specimen electrode. For the uniform corrosion test, the usual model was used, for the crevice corrosion test, a model with a 50 μm space between the metal surface and glass plate was designed and for the galvanic corrosion test, a model coupling both alloys by a copper wire was designed. The models were immersed in 0.9% NaCl solution adjusted at pH2. The natural potential (Evs. Ag/AgCl) and polarization resistance (Rp) were measured every 2 days for 60 days by the coulostatic method. Galvanic current between P and M was measured. The potential sweep method was also applied to the models to determine the rate of reaction of the crevice and uniform corrosion. After 60 days, the specimens were elementally analyzed by ESCA (Electron Spectroscopy for Chemical Analysis). The following results were obtained:
In crevice corrosion, the E and Rp values of Au-Pd-Ag-Cu were low compared with those in uniform corrosion and the rate of reaction decreased. The E value of Ag-Sn-Zn markedly decreased compared with that in uniform corrosion. However, in the crevice corrosion both the Rp and the rate of reaction showed values similar to those in the uniform corrosion.
In the galvanic corrosion, the E and Rp values of Au-Pd-Ag-Cu decreased compared with those uniform corrosion. On ESCA, a marked amount of Sn was found on the surface of the alloy which contained no Sn.
The E and Rp of Ag-Sn-Zn were similar to the uniform corrosion. On ESCA, a Sn rich surface layer was detected. Even on the 60th day, galvanic current was still detected indicating that the galvanic corrosion may continue for long period.
The results suggest that the corrosion rate of precious alloys depends on enviromental conditions.

View full abstract

Two testing methods were designed to quantitatively evaluate the chipping beh\avior of dental stones. One method measured the average and maximum widths of the chipped area along the edges of a groove that was cut with the rotating saw of a microcutter in a flat surface of a board-shaped specimen of dental stone. A CCD camera connected to a personal computer was used to record the chipped area, and the resulting graphic data were analyzed using a personally developed software. The other method measured the minimum thickness of a thin unbroken piece sliced with the rotating saw from a cylinder-shaped specimen of dental stone. The minimum thickness was determined statistically using the staircase method.
The two testing methods were employed to study the effects of the rotation speed and the cutting load of the saw on the values of the widths and the thickness using a dental stone and a high-strength dental stone. The average and maximum widths increased generally as the rotation speed increased and as the cutting load decreased. The minimum thickness increased with increasing rotational speed, but was almost independent of the cutting load. The two testing methods appeared to be useful in quantitatively evaluating the chipping behavior of dental stone.

View full abstract

One of the determining factors governing the titanium flow in a mold cavity is the intensity of the casting force, including its direction. Actual casting force is the pressure applied to the narrow orifice of the cavity even in the case of the centrifugal casting. The filling areas and flow nature were observed by X-ray radiographs and flow patterns became apparent on tracer (Pd) distribution maps. The results of these experiments proved that the most significant factor influencing flow behavior in the mold cavity is the intensity of the body force, the gravity or the centifugal force. Furthermore, external and internal defects in the titanium castings are also influenced by this factor.

View full abstract

Chitosan is polysaccharide which can be extracted from crustacea and absorbed in vivo. Sintered bovine bone and synthesized hydroxyapatite are considered biocompatible and osteoconductive substances. In this study, chitosan and these osteoconductive materials were composited. A chitosan film was formed by mixing its sol with apatite materials, followed by neutralizing a CaO solution or a sodium by polyphospate solution. The chitosan sol was prepared by mixing chitosan with Malic acid or Malonic acid. The effect of neutralization on these solutions was investigated.
The following results were obtained;
The pH of chitosan sol prepared with Malic acid with was higher than that of chitosan sol prepared Malonic acid.
The pH value of chitosan sol mixed with hydroxyapatite was higher than that of chitosan sol mixed with bovine bone.
The viscosity of chitosan mixed with Malonic acid was higher than that of chitosan mixed with Malic acid.
The hardness of chitosan film prepared with Malonic acid exhibited a higher value than that of chitosan film prepared with Malic acid.
No significant differences in hardness were found between chitosan film neutralized by CaO solution and that neutralized by sodium polyphosphate solution.
Tensile strength of chitosan film neutralized by a CaO solution was higher than that neutralized by a sodium polyphosphate solution.
The elongation of chitosan film neutralized by sodium polyphosphate solution had higher value than that neutralized by a CaO solution.

View full abstract

In the edgewise technique, we use an archwire to produce orthodontic force. The magnitude and distribution of force are not completely known due to difficulties arising from factors such as friction between the archwire and bracket and the clearance at the bracket slot, although this knowledge is important for proper control of tooth movement. Hence, we developed an experimental model to analyze the force produced by an archwire and coil spring. Assuming that a case of maxillary protrusion is being treated by retraction of the maxillary incisors, following the extraction of the first premolar and the retraction of the canine, force and torque in the bracket and the momentum at the center of resistance of the incisors are measured enabling us to analyze the incisor movement quantitatively.

View full abstract

The influence of oral temperature on the orthodontic force of a super-elastic Ni-Ti alloy wire was investigated by three-point bending test. The temperature change at the wire slot of the bracket on the upper first molar ranges between 7 and 52℃. Therefore, force change was measured under conditions of temperature change between 3 and 60℃. The load was measured at the point of 1.0 mm deflection. The load in the loading process decreased slightly through the temperature change of 37-60-37℃ and 37-3-37℃. The load in the unloading process increased considerably through the temperature change. Thermal cycling affected the load alternately both in the loading and unloading process. It was proven that the orthodontic force of the super-elastic Ni-Ti alloy wire changes in a complicated manner by the temperature change in mouth, and that the load changes even after the temperature recovers.

View full abstract

Solubility and tissue reaction of α-tricalcium phosphate (α-TCP) plasma-coated layers on titanium were examined by subcutaneous implantation tests. The α-TCP plasma-coated layers were prepared by plasma spraying of β-TCP powder on titanium. Hydroxyapatite (HAp) plasma-coated layers on titanium were used as control samples. An in vivo solubility test was carried out, as follows: Thirty-six samples, 10×10×1 mm, were implanted in subcutaneous tissue of a mongrel dog's back. At 1, 2, and 3 months after implantation, the coated layers were investigated by X-ray diffractometry (XRD) and SEM observation, weight-loss measurement, and histological estimation.
The transformation of the surface of the α-TCP coated layers into HAp was detected by the XRD more than 1 month after implantation. Weight loss of the α-TCP coated layers 2 months after implantation was 1.5 times greater than that of the HAp coated layers, and at 3 months, 1.6 times greater than previously. Histological examinations showed that connective tissues surrounded the α-TCP and HAp coated samples. Slight inflammatory reaction was observed in the connective tissue on the α-TCP coated layers as well as on the HAp coated layers.

View full abstract