[in Japanese]

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[in Japanese]

View full abstract

[in Japanese]

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A chemical approach to the treatment of the implant surface is critical to promote bone formation around the implant. The aim of this study was to examine and compare the biological responses of a titanium surface treated with various chemical solutions. Titanium disks and cylindrical rods were prepared from commercially-pure titanium with machine turning. Titanium surfaces were treated with NaCl, KCl, CaCl₂, and MgCl₂ solutions for 3 h. The capacity for protein adsorption and cell attachment was tested on the titanium surface after solution treatment, in vitro, and was examined for its bone-to-implant strength in vivo. In addition, the wettability of each treated titanium surface was examined, and the cell survival rates were verified. In all solution conditions, no significant difference in cell viability and wettability was found. The control solution (pure water) showed no significant differences compared with the treatment groups of NaCl and KCl in protein adsorption and cell attachment capacity. After treatment with CaCl₂ or MgCl₂ solutions, protein adsorption and cell attachment were increased compared with those achieved with NaCl or KCl solutions. The solution containing Ca or Mg showed better boneimplant strength in vivo. The present results suggest that the titanium surface treated with a solution containing Ca or Mg ions enhanced protein adsorption and cell attachment capacity early and more dramatically for the process of bone formation and increased bone-implant strength in vivo. The solution treatment with divalent cations of Ca or Mg was effective for fabricating titanium implants with enhanced bioactivity and osteoconductivity. Therefore, this chemical treatment of titanium surfaces is a simple and convenient method for improving osseointegration.

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Because implants frequently comprise two or three types of pieces which are composed of small parts, fracture is apt to occur. Therefore, to increase strength, implants fabricated of both JIS type-4 titanium (G4) and Ti-6Al-4V alloy (G5) combined are currently being used. However, when different metals are used in combination, it is important to clarify the release of metal ions due to galvanic action, and the strength of the implants.
In this study, implant bodies and abutments were produced using G4 and G5 by machining, and two-piece implants of G4 and G5 combined were fabricated. The maximum bending load at an inclination of 30° and amounts of titanium and vanadium released in 1% lactic acid solution were measured.
The tensile strength, elongation, yield strength, and hardness of G4 and G5 wires were measured. As a result, the tensile strength, yield strength, and hardness were higher for G5 than G4, and the elongation of G4 was greater than that of G5. The maximum bending load of implants fabricated in combination at the inclination of 30° was the highest with G5G5, and lowest with G4G4. No significant difference in the maximum bending load was noted between G4G5 and G5G4. The strain showed a similar tendency. The amount of titanium release was the lowest with G4G4 and G4G5, and highest with G5G5. The amount of vanadium release was the lowest with G4G5, second lowest with G5G4, and highest with G5G5. Furthermore, because galvanic action does not readily occur with the combined use of titanium and titanium alloy and there was no problem regarding the strength, it was suggested that the combined implants would have no problems in clinical use.

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To evaluate one aspect of osteoclastic resorbabilities of calcium phosphate bone substitutes, their dissolution behaviors were compared in a weak acid solution without strong agitation to mimic the subosteoclastic zone. Of calcium phosphate bone substitutes, β-tricalcium phosphate (β-TCP)-associated material of CERASORB (CS) , ArrowBone-β-Dental (AB) , SynthoGraft (SG) and OSferion (OS) , apatite-associated material of Geistlich Bio-Oss (BO) and sintered carbonate apatite (CA) were used as particulates. Particle sizes of OS and CA were adjusted to those of CS, AB and SG; the latter three materials had essentially the same particle size ranging from 300 μm to 500 μm. Reaction kinetics were followed by measuring proton activity and by analyzing solution calcium and inorganic phosphate, and further analyzed by chemical potential plots obtained based on the solution composition. At one week of dissolution, CS, AB, SG, OS and CA reached quasi equilibrium with thermodynamic solubility of β-TCP, and BO reached quasi equilibrium with thermodynamic solubility of hydroxyapatite (HA). Estimation of Gibbs free energy of the degree of supersaturation or undersaturation with respect to HA at 1 h dissolution, which could be used to estimate dissolution rate, clearly showed that CA was much more soluble than β-TCP-associated materials of CS, AB, SG and OS, which were more soluble than BO, indicating that CA was easily dissolved by hydrogen ions secreted by osteoclasts. This finding strongly suggests that CA would be superior as an osteoclast-mediated bioresorbable bone substitute to any other calcium phosphate bone substitutes commercially in use today.

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When most of the upper jaw is lost by ablative surgery for a malignant tumor, a dento-maxillary prosthesis combined with an obturator is usually applied in order to rehabilitate the function of both mastication and speech and to improve the facial deformities. We present a case of a fabricated dento-maxillary prosthesis supported by dental implant following subtotal maxillectomy. The patient was a 51-year-old female. She was referred to our clinic by a dentist for examination of her upper palatal swelling. A biopsy was carried out and the histological diagnosis determined an adenoma. Surgical operation was done under general anesthesia. However, a pathologist found malignant cells by serial sectioning of the surgical specimen and finally diagnosed adenocarcinoma. Therefore, subtotal maxillectomy was performed immediately. After the radical surgery, the patient had no recurrence for seven years. She had used a dento-maxillary prosthesis combined with an obturator supported by her upper remaining teeth and alveolar bone. Unfortunately, the prosthesis became unstable due to loss of her hinge teeth caused by chronic periodontitis. We designed an implantsupported dento-maxillary prosthesis with dolder-bar type attachment. The dolder bar attachment was supported by three osseointegrated implants in her maxilla. After applying the implant-supported dento-maxillary prosthesis, her oral functions including mastication, deglutition and speech have been considerably improved for six years and seven months. The patient is highly satisfied with the prosthesis.

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