Biomedical subjects

Makoto Shiota

Publications and source records attributed to Makoto Shiota.

9 recordsLinked to original sources

PubMed2007

Histological and histomorphometrical comparative study of the degradation and osteoconductive characteristics of alpha- and beta-tricalcium phosphate in block grafts.

The purpose of the present study was to compare alpha- and beta-tricalcium phosphate (TCP) as bone graft material for augmenting highly resorbed alveolar ridges. The cranial bones of 15 rabbits were used. Three titanium chambers filled with porous blocks of alpha-TCP, beta-TCP, or blood clots were placed in each slit. The two TCP blocks had similar inner/outer structures and purities. Animals were sacrificed after 2, 4, and 8 weeks. Specimens were embedded in polyester resin as nondecalcified specimens, and evaluated both histologically and histomorphometrically. In both TCP groups, blocks had hardly degraded at 2 weeks while in the alpha-TCP group, the block had notably started degrading after 4 weeks. In the beta-TCP group, degradation began at 4 weeks and this degradation had increased just slightly after 8 weeks. The alpha-TCP block degraded significantly more than the beta-TCP block. Residual alpha-TCP particles surrounded by newly formed bone decreased over time, and both particles and newly formed bone were simultaneously absorbed by osteoclast-like cells. These observations suggest that residual alpha-TCP particles surrounded by newly formed bone may disappear progressively from bone and could be incorporated into the bone remodeling cycle in combination with newly formed bone.

Absorbable Implants↗

PubMed2006

Biodegradation process of alpha-TCP particles and new bone formation in a rabbit cranial defect model.

The purpose of the present study was to observe the biodegradation process of pure alpha-tricalcium phosphate (alpha-TCP) particles and to determine the efficacy of alpha-TCP as a space maintainer in a bone defect. We used 14 rabbits and prepared two cranial bone defects in each rabbit. One defect was left empty as a control, whereas the other was filled with alpha-TCP particles about 300 mum in diameter. Animals were sacrificed at 1 week, 4 weeks, and 8 weeks. The cranial bone was then embedded either in paraffin wax for the preparation of decalcified specimens, or in polyester resin for the preparation of nondecalcified specimens. All specimens were evaluated histologically and histomorphometrically. As a consequence of the degradation of alpha-TCP, a "reticulate structure" appeared in the particles at 1 week and new bone was observed in this structure at 8 weeks. The amount of new bone between the control and experimental groups was not significantly different at any of the time points. However, in the experimental group, new bone at the surface of alpha-TCP was evident even in the center of the defect whereas fibrous connective tissue was dominant in the control group. These results indicate that alpha-TCP is a degradable osteoconductive material that is able to act as a space maintainer for bone regeneration when applied to a bone defect. While there was no significant difference in total bone formation between the experimental and negative control groups, the space-maintaining and osteoconductive properties of the particles may result in more complete bone formation in longer-term studies.

Absorbable Implants↗

PubMed2005

Basic evaluation of cast joining for electroformed coping using multi-purpose alloys.

The purpose of this study was to evaluate the bonding interface and bonding strength of electroformed coping when cast joining was used with a multi-purpose alloy. The multi-purpose alloy was cast at a mold temperature of 700, 750 or 800 degrees C. A high noble alloy tab was also soldered onto an electroformed coping as a control. Sectioned surfaces of cast joining and soldered specimens were observed using a scanning electron microscope and analyzed using an electron probe micro analyzer. Shear bonding strength of specimens cast at 750 degrees C and that of soldered specimens were determined. The edge of the cast joining alloy was round, but this improved as temperature increased. Diffusion of elements from the cast joining alloy and electroformed coping was detected at the interface, which contributed to a significantly higher bonding strength in the cast joining specimen than in the soldered specimen. These results suggested that the cast joining could be potentially employed for electroformed copings.

Dental Abutments↗

PubMed2004

The influence of implant location and length on stress distribution for three-unit implant-supported posterior cantilever fixed partial dentures.

STATEMENT OF THE PROBLEM: The influence of implant location for an implant-supported cantilever fixed partial denture (FPD) on stress distribution in the bone has not been sufficiently assessed. PURPOSE: This study examined the influence of location and length of implants on stress distribution for 3-unit posterior FPDs in the posterior mandibular bone. MATERIAL AND METHODS: Each 3-D finite element model included an FPD, mesial and distal implants, and supporting bone. The mesial implant with a length of 10 mm or 12 mm was placed in locations where its long axis was 3 mm to 11 mm posterior to the remaining first premolar. The distal implant with a length of 10 mm was fixed at the same distance from the premolar on each model. A buccally-oriented oblique occlusal force of 100 N was placed on each occlusal surface of the FPD. RESULTS: The maximum equivalent stresses were shown at the cervical region in the cortical bone adjacent to the mesial or the distal implants. Relatively high stresses of up to 73 MPa were shown adjacent to the mesial implant located 9 mm or more posterior to the first premolar. The use of a 12-mm-long mesial implant demonstrated a relatively weak influence on stress reduction. CONCLUSION: The implant location in the cantilever FPDs was a significant factor influencing the stress created in the bone.

Bite Force↗

PubMed2003

[Fit of electroformed porcelain-fused-to-metal crown on implant abutment].

This study compared the adaptation of a conventional and an electroformed porcelain-fused-to-metal crown. A master model was selected from an ITI implant with a solid abutment (height: 4 mm). Conventional cast metal frameworks of 0.7 mm thickness were prepared with a high noble metal alloy (Degudent U, Degussa) for porcelain fusing (n = 5). Electroformed frameworks of 0.2 mm thickness were determined using pure gold deposition on the abutment using the Auro-Galva-Crown system (AGC, Wieland) (n = 5). Subsequently, a porcelain (Super Porcelain AAA, Noritake) was fused to each framework. Internal gaps between the framework and its abutment were determined using the thickness of a silicone fit checking material. The gaps were measured both before and after porcelain fusing. The thicknesses of the silicone layer of the electroformed and the conventional porcelain-fused-to-metal crown were 34.6 and 38.5 microns at the margin, 33.2 and 39.6 microns at the internal slope, 22.0 and 33.0 microns at the axial, 58.6 and 65.1 microns at the occlusal, respectively. Three-way analysis of variance revealed that the mean gaps in the electroformed porcelain-fused-to-metal crown were significantly thinner than those in the conventional porcelain-fused-to-metal crown (p < 0.05). The electroformed porcelain-fused-to-metal crown showed better adaptability than the conventional porcelain-fused-to-metal crown regardless of porcelain fusing.

Crowns↗

PubMed2003

[A clinical study on unfavorable cases of dental implant].

The clinical analysis of 462 patients (154 men and 308 women) with problems of implant therapy done at other clinics is reported. They visited the clinic for oral implant of the Tokyo Medical and Dental University Hospital during the period from January 1996 to March 2002. The results were as follows: 1) The majority of the patients (76.6%) were 40 to 69 years of age. 2) Of the total patients, 26.8% had been referred from the other outpatient clinics in our hospital, 14.7% from private dental offices and 2.6% from attending doctors. 3) There were 361 patients with complications related to the implant therapy. Seventy-six patients asked for second opinions concerned about a diagnosis or treatment recommendation. Thirty patients required maintenance of the implants. 4) The most common complications observed were peri-implantitis (184 cases). Prosthodontic complications (72 cases) included framework/resin/veneering material fractures, screw loosening and fractures. There were implant fractures in 21 cases, sensory disturbance in 20 cases, problems related to sinus in 13 cases, problems of connected teeth in 30 cases and phonetic/esthetic complications in 10 cases. 5) The types of problem implants were osseointegrated implants (196 cases), alumina-ceramic implants (74 cases), metallic blade-type implants (35 cases), pin-type implants (10 cases), subperiosteal implants (6 cases) and other implants.

Adult↗

PubMed2002

[The influence of medial implant location in three-unit posterior cantilever fixed partial dentures on stress distribution in surrounding mandibular bone].

This study examined the influence of medial implant location in three-unit posterior cantilever fixed partial dentures (FPDs) on stress distribution in mandibular bone surrounding two implants. A three-dimensional finite element model that included three-unit FPD and two cylindrical-type implants (4 mm in diameter and 10 mm in length) osseointegrated in the posterior mandible, was digitized. Five different models were created according to the medial implant location between the missing second premolar and the first molar location. The distal implant was fixed at the missing second molar location. Oblique bite force of 100 N at 30 degrees buccal to the vertical direction was directed on each of three artificial teeth, respectively and simultaneously, while the lower surface of the mandible was fixed. The maximum equivalent stress in the cortical and the trabecular bone generally increased as the medial implant shifted to a distal position. Under the simultaneous bite force, relatively low maximum stresses within the cortical bone: between 55 MPa and 57 MPa, were shown in the models with the medial implant placed within the range of one implant diameter from the most medial position, while higher maximum stresses: between 64 MPa and 73 MPa, were demonstrated with more distally placed medial implants. The results suggest that reasonably low mechanical stress in the surrounding bone may be assured when the medial implant is placed in the range between the missing second premolar position and one implant diameter distal from that location.

Dental Implants↗

PubMed2002

[Clinical study of risk management for dental implant treatment--changes of blood pressure and pulse rate during implant surgery under local anesthesia].

The changes of systolic blood pressure (SBP), diastolic blood pressure (DBP), and pulse rate (PR) during implant surgery under local anesthesia were analyzed in 38 normal healthy patients. The results were as follows: 1. SBP significantly increased compared with the preoperative control throughout surgery. 2. DBP did not change significantly compared with the preoperative control throughout surgery. 3. PR increased just after the local anesthesia, and lowered afterward. 4. Both SBP and DBP increased in correlation with age. 5. SBP, DBP, and PR increased in correlation with surgical procedure time. 6. SBP, DBP, and PR increased in correlation with number of implantation. From these results, it was indicated that implant surgery might be accompanied by a risk, even in healthy patients.

Age Factors↗

PubMedDate not supplied

Stress analysis in edentulous mandibular bone supporting implant-retained 1-piece or multiple superstructures.

PURPOSE: The aim of this study was to investigate the stress distribution in mandibular bone supporting a single or separate multiple implant-retained superstructures. MATERIALS AND METHODS: Three-dimensional finite element models consisting of the mandibular bone, 8 implants, and 1 or more superstructures were created. Vertical and oblique loads were directed onto the occlusal areas of the superstructures to simulate the maximum intercuspal contacts and working contacts, such as the canine-protected and group function occlusion. RESULTS: The unseparated 1-piece superstructure generated the lowest maximum equivalent stresses in the peri-implant bone, followed by the 2-piece superstructure separated at the midline. For the 3-piece superstructure, which was separated between the canine and the premolar, the maximum stress was lower when the canine on the working side was loaded than when the posterior teeth were loaded. DISCUSSION: Separating the 1-piece superstructure into 2- to 4-piece superstructures increased the mechanical stress around supporting implants. Canine load on the working side is distributed well in 1-piece and 3-piece superstructures. CONCLUSION: Based on the results of this finite element model study, canine protected occlusion is recommended for 1-piece and 3-piece superstructures. The unseparated superstructure was more effective in relieving stress concentration in the edentulous mandibular bone than the separated superstructures.

Bite Force↗