The osseointegrated implant is recognized as one of the most reliable means of therapy for prosthetic treatment of missing teeth. However, bone resorption sometimes occurs by concentrating stress at the interface between the fixture surface and the surrounding bone, due to lack of the buffer system provided by the periodontal membrane of the natural tooth. The resulting discordance between the functional long axis and occlusal force of the fixture is the main factor responsible for the loss of osseointegration. In many cases, bone resorption is seen over a wide area, especially on the side of inclination of a tilted fixture.
The present experiment using the strain gauge method was therefore conducted in order to clarify the mechanical effects of the mesiodistal angle of tilt of a fixture on the strain distribution in an implant structure and surrounding bone.
The second, third, and fourth mandibular premolars were extracted from beagle dogs, and 4 months after tooth extraction, two fixtures were installed in the premolar area on each side. At this time, by changing the mesiodistal installation tilt angles of the two fixtures, six placement modality patterns were set up. Four months after fixture installation, at the osseointegration stage, the dogs were sacrificed and their mandibles were removed.Test specimens were prepared by attaching the abutment and superstructure to the fixture. Strain gauges were bonded to the abutment surface, the bone around the connection between the abutment and the fixture, and the buccolingual alveolar bone. A load of 10 kgf was applied vertically to the horizontal plane of the superstructure, and the strain distribution was analyzed chronologically.
The experimental results and conclusions were as follows:
1. The best dynamic stability was achieved when the two fixtures were set up parallel to the functional axis of the occlusal force.
2. When the two fixtures were installed with a tilt in the same direction, there appeared to be a risk of loading in a single direction, thus inviting microfracture of the surrounding bone.
3. When one of the two fixtures was installed in a tilted position, it appeared possible to disperse the stress by installing the other fixture with a tilt in the opposite direction.
We designed a new implant to prevent the downward growth of epithelium and to achieve a more rigid initial fixation. As this implant system has dead space in the cervical portion, we studied histologically the bone regeneration in the dead space and also the possibility of preventing the downward growth of epithelium in dog.
This new implant has a sword-guard form on the superior fixture and three projections on the inferior sword-guard. The implant was made of Ti-II,the surface of which was processed by wire electric discharge. We installed two new implants and one IAT FIT II® into the mandibule of dog. The new implants were inserted in two ways:only malleting, or malleting after making a countersink.
The results showed that the bone was regenerated in the dead space and we also confirmed the prevention of downward growth of epithelium.
Therefore, we consider that wide tissue integration can be achieved by this stronger initial fixation due to the effect of prevention of downward growth of epithelium.
It was previously reported that when hydroxyapatite having a high molar ratio of Ca/P was heated,CaO crystals precipitated in the matrix phase of hydroxyapatite. In this study using spherical hydroxyapatite (HAP) with a Ca/P molar ratio of 3.5, six different pre-heated samples were prepared. They included HAP samples heated at 800℃ for 60 min, 300 min, 720 min, and 1,440 min, and HAP samples heated at 900℃ for 60 min, 300 min, 720 min, and 1,440 min, respectively. These pre-heated HAP samples were subjected to immersion tests in a physiological salt solution for one week and the immersion tests were repeated for four weeks. Such pre-heated samples after immersion tests were further investigated by x-ray diffraction analysis, and dissolved amounts of Ca and P, changes in pH values and cell culture were studied.
Within the limitations of this in vitro study, the following conclusions were obtained.
1. After the first one-week immersion test, the HAP sample heated at 800 and 900℃ showed pH values of 11-12. The pH values of both sample groups decreased in a range of 9.1-9.7 after the subsequent immersion tests.
2. The dissolved amount of Ca after the fourth-week immersion tended to decrease, compared to those after the first-week immersion tests. On the other hand, the dissolved amount of P was not affected by either the temperature or duration of heating.
3. Some heat treatments obstructed cell multiplication as a result of performing cell cultivation for seven days. As cell multiplication was hardly obstructed by the heat treatment of this research, the treatment was effective. The living body reaction will be examined in future studies.
Bone augmentation has been used to restorer bone resorption in implant treatment. In general, bone grafts are used for bone augmentation. However, the bone newly formed by bone graft would cause bone resorption by remodeling. Similarly, bone resorption occurs in the sinus lift technique, but there is a difference of resorption volume depending on the type of graft bone. In this study, we investigated the volume of resorption after sinus lift using iliac bone. The subjects were 33 sinuses of 21 cases, and included two forms: the block and particular bone (block group), and particular bone only (particular group). The criterion for choosing the graft bone type was the alveolar bone height measured from dental CT images. In the case of under 5.0 mm, the combination of block and particular bone type was used, and only the particular bone type was used for other cases. The volume of bone resorption was measured by panorama CT images as vertical bone height at preoperative, 1 month after, and 6 months after, and the resorption ratio was calculated. The results were as follows.
1. The measured bone height at 1 month after in the block group was 21.1±3.3 (range of 16.4-25.4)mm, and in the particle group was 19.8±3.9 (range of 14.2-24.8) mm.
2. The measured bone height at 6 months after in the block group was 19.1±1.1 (range of 14.5-24.5) mm, and in the particle group was 14.0±2.6 (range of 10.4-16.4) mm.
3. The calculated value of bone resorption in the block group was 2.0±1.1 (range of 0.8-4.8)mm, and in the particle group was 5.8±1.9 (range of 3.6-8.4) mm.
4. The resorption ratio in the block group was 13.0±5.8 (range of 3.6-24.7)%, and in the particle group was 43.8±5.5 (range of 36.1-53.6)%.
5. In the block group, there was no significant difference in resorption ratio between genders.
6. In both groups, there was no significant difference in resorption ratio between presence and absence of perforation of the maxillary sinus membrane.
In the present results, the block group showed less bone resorption than the particle group considered from the variation of vertical bone height. Bone resorption was definitely prevented in the block group in comparison with the particle group. We consider that the bone block which was established upward of the sinus was useful for sinus lift because of less bone resorption.
In this study, we performed a pull-out strength test using an ultrathin HA coated implant by the thermal decomposition method (HA type) and pure titanium implant (Ti type).
Prior to the experiment, surface quality was analyzed using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) for the HA type.
Each screw was embedded in the rabbit femur and pull-out strength was examined using a load cell type omnipotent testing device.
1. The surface of the HA type was observed by SEM and EDS, and the HA layer coated on the Ti surface was detected by SEM. Moreover, a coating layer of calcium was observed on the surface by EDS and the thickness was found to be 2-5μm.
2. In the pull-out strength test, at 2, 4, 8 and 12 weeks, the strength of the HA type was 1.38, 1.33, 1.27 and 1.14 times that of the Ti type, suggesting that bone joint power is developed at an early stage.
Therefore, even if an HA coated implant by the thermal decomposition method is ultrathin, its bone conduction ability is good. Hence, this biomechanical material is useful for biological combinations.