Biomedical subjects

Tetsuo Ichikawa

Publications and source records attributed to Tetsuo Ichikawa.

6 recordsLinked to original sources

PubMed2002

Fracture mechanisms of retrieved titanium screw thread in dental implant.

Titanium and its alloy are increasingly attracting attention for use as biomaterials. However, delayed fracture of titanium dental implants has been reported, and factors affecting the acceleration of corrosion and fatigue have to be determined. The fractured surface of a retrieved titanium screw and metallurgical structures of a dental implant system were analyzed. The outer surface of the retrieved screw had a structure different from that of the as-received screw. It was confirmed that a shear crack initiated at the root of the thread and propagated into the inner section of the screw. Gas chromatography revealed that the retrieved screw had absorbed a higher amount of hydrogen than the as-received sample. The grain structure of a titanium screw, immersed in a solution known to induce hydrogen absorption, showed features similar to those of the retrieved screw. It was concluded that titanium in a biological environment absorbs hydrogen and this may be the reason for delayed fracture of a titanium implant.

Biocompatible Materials↗

PubMed2002

Dynamics of bone marrow pressure with tapping of titanium and hydroxyapatite implants in rabbits.

The purpose of the present study was to evaluate the difference in stress transfer between titanium (Ti) and hydroxyapatite (HA) by the measurement of bone marrow pressure using a catheter pressure transducer. Ti and HA implants were inserted in the tibiae of rabbits. A hole of 1 mm in diameter was drilled in the bone and a fine catheter pressure transducer was placed in the bone marrow through a tube. The top of the abutment was vertically tapped with an impulse hammer, and the acceleration signal from the hammer and pressure signal from the catheter pressure transducer were examined. The time of contact (impulse duration) recorded in the impulse with Ti and HA was 166+/-17 micro sec and 164 +/- 17 micro sec, respectively. Maximum bone marrow pressure (BMP) with Ti and HA was 54.2 +/- 32.6 and 47.5 +/- 10.0 mmHg, respectively. Variation of the BMP with Ti was significantly larger than that with HA (P < 0.05). A negative correlation coefficient between impulse duration and BMP was found. The results of the present study suggest that the stress transfer is different between Ti and HA implants using dynamics of the bone marrow pressure.

Acceleration↗

PubMed2002

Installing magnetic keepers using LASER welding.

Magnetic overdenture attachments can provide useful denture retention. A technique is proposed that involves installing the magnetic keeper in the overdenture abutment coping using laser welding. Compared with the conventional cast-to technique, the new technique provides a suitable contour to the abutment coping with the magnetic keeper and ensures proper mounting in the abutment coping, installing the magnetic keeper easily and effectively.

Dental Abutments↗

PubMed2002

Complete denture with a removable palatal lift prosthesis: a case report and clinical evaluation.

The palatal lift prosthesis is used to alleviate rhinopharyngeal closure dysfunction. It is generally problematical to use in edentulous patients, because the palatal lift prosthesis requires secure retention of the denture base and is difficult for the patient to retain while eating. This article describes the fabrication of a complete denture with a removable palatal lift prosthesis and a clinical evaluation of the denture's stability. A sprue pin and tube were used as a connecting attachment between the removable palatal lift prosthesis and the denture base. The force required for lifting the soft palate and the denture's stability were measured in the clinical evaluation. The prosthesis required an average retentive force of 0.26 N for each 1 mm of soft palate lift. The force required to dislodge the denture was measured with and without the palatal lift prosthesis in place. The force required to dislodge the conventional complete dentures of five healthy individuals was also measured as a reference. The denture was 24.4% less stable when the palatal lift prosthesis was in place and was generally easier to dislodge than were conventional dentures. This denture with a removable palatal lift prosthesis is useful for patients with dysfunction of the soft palate involving hypernasal speech who have difficulty in retaining the prosthesis while eating.

Adult↗

PubMedDate not supplied

Shock absorbability and hardness of commercially available denture teeth.

PURPOSE: Composite resin teeth are more widely used than porcelain or acrylic resin teeth in the fabrication of removable dentures because of their high fracture toughness and high abrasion resistance. The purpose of this study was to evaluate the shock absorbability of commercially available artificial posterior teeth by the free drop-ball test with an accelerometer and to evaluate the Vickers hardness at the surface. MATERIALS AND METHODS: The tested artificial teeth included seven composite resin teeth, one acrylic resin tooth, and one porcelain tooth. Specimens were tested 50 hours after immersion in distilled water at 37 degrees C. The impact value and Vickers hardness were measured. A one-way analysis of variance was used to analyzed the data (P = .05). RESULTS: The composite resin teeth showed an intermediate impact value between that of the acrylic resin tooth and the porcelain tooth. Among the artificial teeth investigated, the porcelain tooth showed the highest impact value. A significant difference in the impact value was observed between the porcelain tooth and the composite resin and acrylic resin teeth. However, no significant difference was observed among the composite resin teeth tested. A significant correlation was found between the impact values and the Vickers hardness of the artificial teeth. CONCLUSION: The present findings suggest that composite resin teeth and acrylic resin teeth have a higher shock absorbability than porcelain teeth.

Absorption↗

PubMedDate not supplied

Immediate implant-supported oral rehabilitation using a photocurable plastic skull model and laser welding. A technical note on the screw-retained type: Part 1.

PURPOSE: This article describes a new procedure for immediate implant-supported oral rehabilitation using a photocurable resin skull model and a laser-welding apparatus. MATERIALS AND METHODS: Preoperatively, the framework was fabricated on a photocurable resin skull model produced from a CT scan and individually designed guide template. The implants were immediately placed using the guide template; laser welding connected the components of framework. RESULTS: Despite the custom-made prosthesis, the total treatment from implant placement to superstructure placement can be completed within only 1 day. CONCLUSION: This procedure for immediate implant-supported oral rehabilitation using a photocurable resin skull model and a laser-welding apparatus may be useful for any implant system and patient.

Dental Articulators↗