Specirnens were collected from 26 cadavers (18 males, 8 females; 40～90 years old, mean 75.6 years old), which had no injuries to alveolar bone. Five types (type 1, dentious jaw; type 2, molar teeth loss; type 3, first molar or premolar teeth loss; type 4, edentulous jaw, thick jaw body; type 5, edentulous jaw, thin jaw body) were observed by microscopy and scanning electron microscopy.
Microscopy: Compacted alveolar crests (ACs) were found in type 1. Some of them formed vortexlike structures in the spongy bone. In contrast, thin ACs were found in other types. The level of density of the alveolar crest was decreased in types 4 and 5.
Scanning microscopy: Type 1; Regularly arranged bone matrices formed a compact and dense layer in the dental bone. Many small mineralized matrices were found in the cortical bone around Haversian systems.
Types 2 and 3; lrregularly spreading fibrous networks and collagenous bundles were found.
Types 4 and 5; Spreading bone matrices and irregularly arranged fine collagenous bundles were found.
Our observation of existing teeth was concerned with the structure of dental bone in the human mandible, which suggested useful information for implantation. Type 2 is a good condition for implantation in clinical treatment compared with types 4 and 5.
A screw-retained prosthesis on an osseointegrated implant requires high accuracy, through so-called “ passive fit.” Two tests are proposed to evaluate the fit of an abutment/superstructure joint:the one-screw test (Sheffield's test), and the angular change with tightening the screw. The purpose of this study was to experimentally reconsider both passive fit tests.
1. The required force was measured when waxes prepared were pressed down on the digital force gauge. Influence of the manufacture and shape of wax, and room temperature at measurement,on the force was examined. The results suggest that pressing of wax is an unstable procedure to make a 200-g load, and the load was influenced by the manufacture and shape of wax,and room temperature.
2. The influence of the 200-g load of the Sheffield's test on the stress distribution of the implant and bone was evaluated by a three-dimensional liner static stress analysis. A 25-mm cantilever model was constructed for a 3-dimensional finite element model, and the apex of the cantilever was loaded in 200 gf. The maximum equivalence stress of 4 MPa was observed at the implant.
3. A custom-designed apparatus was constructed to measure the torque and angular change with the screw tightening. The relationship between required torque and angular change with the screwing was examined. The PME and conical abutment of a Steri-oss implant system were used for the sample materials. The results suggest that measuring the angular change with the screw tightening is useful for the fit test, and the angular change is different in each abutment.
Only a few studies have been performed on the relationship between tooth loss or aging and changes of artery distributions in the maxilla.
A total of 55 maxilla, obtained from Japanese cadavers, were used, and the running and distribution patterns of the arteries around and inside of the dentulous and edentulous maxilla were observed in this study.
Vertical and horizontal distances of the posterior superior alveolar artery were measured based on Frankfurt and midsagittal planes, and then the artery's running patterns were classified. The inside diameters of the posterior superior alveolar artery, the branch distributed to the maxilla from the foramina alveolar, and the bucco-gingival branch were measured. The minute vessels distributed inside the bone were also observed using vessel mold specimens.
The posterior superior alveolar artery in the edentulous maxilla ran closely to the bottom of the maxillary sinus. The inside diameter of the branch distributed to the maxillary from the foramina alveolar was smaller in the edentulous maxilla than in the dentulous maxilla. But there were no significant differences between the other two vessels. Furthermore, no age-related change was evident in these three arteries. Scanning electron microscopic observations of vessel mold specimens showed that the vessels were smaller and their distributions were more rough in the edentulous maxilla than in the dentulous maxilla.
These may imply that the differences observed between the dentulous maxilla and the edentulous maxilla are caused by the absorption of alveolar bone following the loss of teeth, morphological changes of the maxillary sinus, and decreased demand for arterial blood.
As a means to recovering occlusal functions in prosthetic treatment for lost teeth, osseointegrated implants have been popularly accepted as a highly reliable method, supported by a large amount of research data. However, an excessively large load resulting from occlusal force may be concentrated at the interface between the implant surface and the bone, and it may break the osseointegration. One factor that can lead to age of break up this osseointegration is the surrounding bone thickness that supports the implant. Various type of mechanical effects created in the sirrounding bone thickness to the implant have been investigated by experimental sumulation studies, but no investigation has ficused on the relationship between the bone thickness surrounding the fuxture and the strain created in the bone. Therefore, in order to clarify this issue, fixtures were embedded in a human dry skull with a deficiency of the maxillary incisors. The experiments were carried out with a static load applied, and the distributions of strains on the bone surfaces were elucidated.
The edentulous incisor portion of the human dry skull was installed with four Brånemark system implant® fixtures.These were classified into two groups: one was the group of the same fixtures with the same installation angle, and the other was a different installation angle group. These were connected to the abutment, and a tentative occlusal plane was established from the remaining teeth cusp top; then, a superstructure was fabricated and connected to be parallel to the plane of occlusion. The load was applied to an access hole, and a 10-kgf static load was applied to each access hole. For strain measurement of the bone surface around each fixture, a strain gauge method was employed. At first the strain on the bone surface was measured using a one-piece superstructure, in order to measure the strain difference caused by differences in surrounding bone thickness and the fixture installation angle. Finally, the superstructure was cut at the mesiodistal center of each access hole, and a load was applied in the same manner as a single tooth setting implant, and the strain was measured.
The experimental results and conclusions are as follows:
1. For the coupling with the same fixture installation angle, the loading direction was made unidirectional to each fixture.
2. A large reactin force was generated against the moment that used the fixture abutment connective portion as a rotation axis, and the stress was assumed to be dispersed because of the different installation angle.
3. It was therefore suggested that stress might be concentrated on the labial side with a thinner bone wall,when the bone thickness was compared between the labial and palatal sides.
4. It was suggested that it would be rational to increase the number of connected fixtures from the viewpoint of dispersion of occlusal force, and the dynamic burden on the fixture could be alleviated.
5. The fixture was installed with a larger angle, suggesting that the strain concentrated in the apical portion.
6. It was suggested that the labial side at the portion with a thin bone wall of less than 1 mm often developed bone resorption or microfracture of the surrounding bone.
Since metal welding by a laser features a narrow heat-affected zone and accurate joining of a prosthesis, it has been used for increasingly more dental applications.
However, such metal welding can be accomplished by using a high-power laser unit for prosthetics, and as yet there are no reports on metal welding in the mouth using a dental laser unit.
In order to improve the superstructural accuracy of an implant, thermal influences on tooth metal and its strength were investigated, using an Nd:YAG laser designed to provide a high peak power value per pulse.
Twelve percent gold-silver-palladium alloy, high-carat gold alloy,and gold alloy for burning ceramics were used as metal samples. Ten samples of each alloy were prepared for tensile tests and thermal influence tests.
For tensile tests, each sample was cut at the center, welded all around under an irradiating condition of 900 mJ, 15 pps, and at a distance of 0.1 mm, and then measured by a tensile tester.
For thermal influence tests,the variation in temperature of each irradiated sample was measured using a thermograph.
The results of these tests showed that the tensile strength of each sample was about 80 MPa.
The strength of resin for picking up at the time of trying was approximately 60 MPa, and the variation in temperature of each sample subjected to the thermal influence test was less than 4℃, proving an extremely small thermal influence.
As a result of this investigation, the possible use of metal welding in the mouth was suggested.
We investigated the dynamic effects of varying the fixture insertion angles and various methods of occlusion on the nature of occlusal force conduction through implants that were attached to human edentulous dried mandibles, and the effects on the surrounding alveoli and the mandibular bone itself while applying static loads to these mandibles.
Fifteen dry human edentulous mandibular bones were used. Five Branemark system implants (tianium screw type, Nobel Biocare) were inserted between the bilateral mental foramens of the mandibular bone (implants R2, R1, M, L1, and L2, from the right). In these specimens, a tentative occlusion plane was established at a site that was parallel to the lower marginal plane of the mandible and 20 mm from the alveolar crest in the median area. The implants were inserted at right angles to this tentative plane (vertical implant group), at a tilt of 10° toward the labial side (labially tilted implant group), or at a tilt of 10°toward the lingual side (lingually tilted implant group). Each of the 3 groups consisted of 5 specimens. After insertion of the fixture, a superstructure and a complete maxillary denture were produced. As the mode of occlusion, central occlusion and edge-to-edge occlusion were used. A static load (10 kgf) was applied to the central area of the dental arch,the anterior teeth area, and the left molar area. Microstrain occurring in the mandibular surface and the abutment surface of the implant was measured by attaching a stress concentration gauge to the bone surface (labial and lingual sides) and a uniaxial gauge to the abutment surface (labia, lingual, mesial, distal sides). In addition, the axial force occurring in each abutment was calculated by Hook's law, from the amount of strain on the abutment surface.
The results of transmission and dispersion of occlusal force in this study suggested that compression force tends to concentrate on the distal implant in the labially tilted implant group when a load is applied on the central area of the dental arch, which corresponds to the state of occlusion of the entire dental arch,when a load is applied on the molar area, which corresponds to chewing in the molar area.Insertion of a fixture tilted in this direction may be disadvantageous for load bearing. The results of me a surement of strain on the bone surface also showed more marked strain in the labially tilted implant group than in the other two groups. This indicates that labially tilted implants carry a high risk for destruction of osseointegration.
From July 1992 to December 1998, maxillary sinus floor augmentations using autogenous bone grafts combined with simultaneous implant installation were performed on 14 sinuses from eight patients at the First Department of Oral and Maxillofacial Surgery of Tsurumi University.
The eight patients, including three males and five females, ranged from 38 to 64 years of age, with a mean of 52 years old. The surgical procedure performed was bilateral sinus floor augmentation in six patients, and unilateral sinus floor augmentation in two. The grafted bone was obtained from the iliac crest in seven patients, and from the mentum in one. ITI Bonefit solid screw implants were used in seven cases, and Branemark standard fixtures were used in one case. In total, 55 fixtures were applied, with 45 of these being implanted in the maxillary molar region,
One fixture was removed at a secondary operation due to failure to achieve osseointegration, and another one was kept under sleeping condition because of an undesirable position for prosthodontic treatment. The remaining 43 fixtures have been still in place.
CT image findings revealed that the grafted bone of the upper part of the fixture apex disappeared within one year. However, minimum resorption was observed, and sufficient bone contact was maintained around the fixture body in cases after a lapse of from five to two years. In our first case, machine surfaced fixtures were used,with the result that relatively remarkable bone resorption was observable around the fixtures seven years postoperatively.