Screw tightening of the superstructure of osseointegrated implants often produces unsuitable strain on the prosthesis and surrounding bone． The purpose of this study was to investigate the effects of screw tightening on surrounding bone in several conditions．
　Three Steri-oss® implants were placed in an acrylic resin experimental model， and a three-unit framework was fabricated on the implants． The fit of the framework was judged excellent by laboratory microscopy． Ten strain gauges were attached on the experimental model surface around the implants． The strain was measured after every screw was tightened by a custom-designed torque controller． Static and dynamic strain was recorded． Each test was repeated five times under the same conditions．
　The results were as follows：
　1．The order of screw tightening affected stress distribution． The distribution was unequal and asymmetrical to the implants．
　2．Staged tightening of the screws decreased the sum of all strains．
　3．Tightening torque does not affect stress distribution．
　4．Misfit of the abutment／superstructure joint increased the sum of all strains．
　5．Strain induced by tightening of the second or third implant was greater than that by tightening the first one．

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It is known that the success of tooth transplantation depends on the preservation of the periodontal ligament. The purpose of this study was to investigate the effect of long-term cryopreservation of the tooth with periodontal ligament in terms of cell activity in vitro.
The teeth with periodontal ligament were obtained from beagle dog and cryopreserved for 6 months,1 year and 2 years in the liquid nitrogen.Cryopreserved teeth for each period were thawed in a water bath at 37℃, and periodontal ligament tissues were cultured in α-MEM supplemented with 10%FBS and antibiotic solution. In the control group, periodontal ligament tissues were cultured immediately after the tooth extraction. After subculture, cells were plated in 35 mm cell culture dishes at a concentration of 1 × 10⁵ cells per dish.Either cell transmigration or confluent periods at the primary culture were investigated. Proliferation ratio, alkaline phosphatase(ALPase)activity and the positive ratio of proliferating cell nuclear antigen(PCNA)were also examined.
Either cell transmigration or confluent periods were prolonged in the experimental groups compared to those of control group(p＜0.05), However, no statistical difference was found in either the cell proliferation ratio or ALPase activity of any time period of the experimental groups compared to those of the control group. Furthermore, there was no significant difference in the PCNA positive cell ratio in all groups.
The results suggested that cryopreservation delayed the cell transmigration period from the tissues because the cells received damage to tissue or DNA in the cryopreserved environment and it took time to repair the damage. However, after repairing the cells, there was no significant difference between experimental and control groups in terms of cell proliferation and differentiation. In this study, it can be considered that there is no effect of long-term cryopreservation on periodontal healing in the case of tooth transplantation or replantation.

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In determining long-term prognosis of dental implant treatments, control of inflammation in peri-implant tissue is an important factor. The level of inflammation in peri-implant tissues was investigated by evaluating 1)plaque accumulation,2)volume of implant crevicular fluid, and 3)marginal bone resorption around implants. Screw-retained superstructures and cemented superstructures were compared in terms of inflammatory conditions in surrounding tissues. As for statistical analysis,Mann-Whitney U-test was used for inter-group comparison. A possible correlation was evaluated by regression analysis.
The results are as follows:
1. The measurement of implant crevicular fluid volume was larger in the screw-retained prosthesis group,18 to 85(mean 42.6±6.3), than in the cemented prosthesis group,4 to 26(mean 16.3±2.3)with statistical significance(p＜0.001).
2.With screw-retained prostheses, a correlation was confirmed between disclosing staining of outer crowns and volume of implant crevicular fluid(r=0.883).
3. Three years after the delivery of superstructures, marginal bone resorption around implants was 0 to 0.80mm(0.40±0.70mm on the mesial sides,0.39±0.08mm on the distal sides, mean 0.40±0.74mm)for screw-retained prostheses and 0 to 0.80mm(0.31±0.77mm on the mesial sides,0.35±0.06mm on the distal sides, mean 0.33±0.07mm)for cemented prostheses, indicating no statistical difference between the two groups.
4. A correlation was not found between marginal bone resorption around implants and disclosing staining of outer crowns as well as volume of implant crevicular fluid.
Peri-implant inflammation was more significant around screw-retained superstructures, which suggests that it is largely affected by plaque accumulated in slight gaps between inner crowns and outer crowns.

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Bone quality and quantity distribution of 415 jaws in 371 dental implant patients who were treated in Implant Clinic, Hospital of Nippon Dental University were studied following the classification proposed by Lekholm and Zarb(1985);the following results were obtained.
1. The cases of bone quality “1” were significantly less in number than other bone qualities.
2.The anterior edentulism(incisor/canine)showed significantly less soft in quality and significantly less massive in quantity than posterior (premolar/molar)edentulism.
3.The maxillae showed significantly less hard in quality and significantly more massive in quantity than the mandibles.
4.Females showed significantly less hard in quality and significantly less massive in quantity than males.
5. Bone quantity showed the inclination to reduce as the age of patients increased.
6. The second decade patients(youngest patients in this study)showed significantly less hard in bone quality than others.

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The purpose of this study was to investigate periodontal tissue healing of autotransplanted teeth.Ten Japanese dogs were used for this study. Prior to the transplantation, lower premolar and molars were extracted under general anesthesia. Three months later, the lower third incisors were extracted and autotransplanted into the newly prepared bone cavities in the mandibular extracted area.Evaluations were made at 1,2,4 and 8 weeks after transplantation. At these observation times, the dogs were sacrificed under general anesthesia.Block sections containing teeth and their surrounding tissues were removed and fixed by immersion in Karnovsky's fixative solution. Each specimen was decalcified in 10%EDTA, sectioned, stained with hematoxylin and eosin and examined under the light microscope, and a few specimens were examined under the transmission electron microscope.
The results were as follows:
One week after transplantation, degenerated periodontal ligaments were found around the transplanted teeth. Four weeks later newly formed bone trabeculae were observed in the alveolar bone cavity. Eight weeks after transplantation, alveolar bone proper was formed around the transplanted teeth. However, most specimens showed that functional arrangements of periodontal ligaments were not seen in this period. Only a few specimens at 8 weeks showed functional arrangements of periodontal ligaments.
It may be concluded that the prognosis for transplanted teeth depends on the viability of periodontal ligaments, and newly induced periodontal ligaments surround the transplanted teeth.

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Single standing implants that had been functioning more than 5-years were examined. They were checked from various aspects including some periodontal parameters.
Twenty-three patients and 30 implants were selected for this study. All implants were ITI Bonefit® and were placed in molar or premolar position.
Result:The most common implant site was the lower molar position, and the most common implant size was 4.1 mm in diameter and 12 mm in length.As for complication, loosening screw and peri-implant-mucositis were observed.
Severe complications such as like loss of osseointegration or loss of attachment were not observed.
Periodontal parameters of single standing implants did not show any significant difference from the reported data of splinting implants.
Moreover edentulous type, free end or bound, did not effect the prognosis of single standing implant.
Conclusion:If patient selection and follow-up are proper, single standing implant would be a safe and predictable treatment.

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PRP (platelet rich plasma) has a beneficial effect on wound healing due to growth factors.When the bone graft was performed combination to PRP, the outcomes brought about a favorable condition in the graft area soon after operation. Early reports about PRP, the preparation of PRP dissociated from 400～500 whole blood as autologous blood. The procedure was complex and must return to transfusion of remaining blood after surgery. Recently, the importance of PRP is recognizing in bone graft and the opportunity to use PRP is increasing. Therefore, it is required to obtain a little quantity of PRP more easily. Thus, a method of a little PRP preparation was examined, and the optimal centrifugation method was selected.In this time, twice centrifuging separated 1 ml PRP from 8 ml whole blood was used for 20 volunteers, and the centrifugation method was prepared for four centrifugation groups.
As for the results, the group which contained the highest concentration of platelets was 2,400 rpm 7minutes/3,000rpm-10minutes(1st/2nd). The mean of platelet level was 119.3(±29.7)×10⁴/μl and magnification was 4.9 in the group. It was found that the 1 ml PRP which separated from 8 ml whole blood contained either equivalent or more platelets compared with another techniques. Therefore, it was suspected that the 1 ml PRP also has a beneficial effect on wound and bone healing.

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Successful application of osseointegrated dental implants for functional reconstruction of edentulous and partially edentulous jaws has been well documented in many clinical studies. However, most of the studies have focused on implant survival after insertion of the superstructures.
The purpose of this follow-up study was to separately investigate acquisition and maintenance of osseointegration in relation to the risk factors for osseodisintegration. The subjects were a consecutive series of patients in whom osseointegrated dental implants had been installed at Okayama University Dental Hospital from February 1990 to September 2000. Acquisition and maintenance of osseointegration were clinically assessed by 4 calibrated examiners in a follow-up period (from April to September 2000) using the criteria described by Zarb and Albrektsson(1988). Troubles of the superstructures were also assessed by oral examination and/or clinical record inspection in the follow-up period.
Two hundred sixty-two implants (82 maxillary and 180 mandibular implants) had been placed in 98 patients (46 males and 52 females, mean age 54.7 years). Among them,89 superstructures supported by 188 dental implants (55 maxillary and 133 mandibular implants) were installed in 74 patients (35 males and 39 females, mean age 56.0 years) at the time of follow-up. The mean functional time of the superstructures was 3.2＋/-2.8 years (1 month to 10 years).
Rate of successful acquisition of osseointegration in the consecutively installed maxillary implants (81.7%)was significantly lower than that in the mandible implants(96.1%)(chi-square test:p＜0.01).On the other hand, Kaplan-Meier analyses with an intention-to-treat concept revealed no significant difference in the cumulative survival rates between maxilla and mandible as 96.4 and 94.0%, respectively (Log-rank test:p=0.99). Older age and smoking behavior significantly contributed to the unsuccessful acquisition of osseointegration, while length and diameter of implants, age, sex, smoking and diabetes had no statistically significant influence on the cumulative survival rates of the dental implants after installation of the super structures (e.g., after acquisition of osseointegration). These results reconfirm the previously reported finding that implants placed in the mandible can acquire osseointegration more easily than those in the maxilla. Meanwhile, once the implants acquire osseointegration, prognosis of the implants is relatively promising regardless of the placement location.

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