To examine the morphological changes of the mandibular alveolar ridge following mandibular ridge augmentation with artificial biological materials, serial rotational panoramic roentgenograms were analyzed using an X-ray image analyzing system.
Prior to the main experiment, the preliminary experiment using a head and neck phantom were performed to clarify the effect of head posture on the brightness of the X-ray images in this X-ray image analysis.
In the main experiment, 20 cases, 7 males and 13 females (average age of 66.7 years), underwent mandibular ridge augmentation with artificial biological materials and had a medical checkup at regular intervals up to 12 months after the operation.
The changes in area, length, height, and brightness of the mandibular alveolar ridge were evaluated quantitatively with the X-ray image analyzing system, and the results were as follows
1. The preliminary experiment demonstrated that the change of brightness in the X-ray images caused by the rotational change of head posture were significantly small, suggesting effective evaluation by the X-ray image analyzing system.
2. Although the area, length, and height of the augmented part of the alveolar ridge were reduced with the passage of time, their reduction ratio was small and long-term maintenance of the alveolar ridge shape after the insertion of dentures was suggested.
3. The brightness of the augmented alveolar ridge increases gradually, suggesting bone formation in this augmented portion.
4. In 13 cases with one-sided alveolar ridge formation, the area of the augmented part of the alveolar ridge correlated significantly with its height and length. In 7 cases with two-sided alveolar ridge formation, however, the area significantly correlated with its height only.
From the above results, there were few morphological changes in the augmented alveolar ridge with granular artificial biological materials, suggesting the long-term stability of the alveolar ridge shape and the clinical usefulness of this material.

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Partially purified bone morphogenetic protein (BMP) was mixed with either insoluble bone matrix (IBM) or collagen (COL) derived from IBM. The bone collagen fibers were treated by digesting with pepsin to remove the antigenesity. BMP composites were implanted into the dorsal subcutaneous tissue of 4-week-old male rats. Each composite was removed at 1 and 2 weeks after implantation, and the ectopic-induced hard tissues were observed by routine histology. In BMP-ISM, bone was induced in a process resembling an endo-chondral ossification mode with antigenesity. In BMP-COL, much chondro-osseous tissue and fibrous bone formation were observed at 2 weeks, and the amount of induced hard tissues was much more than that in BMP-IBM. The collagens did not cause remarkable immunogenic response. These results suggested that bone collagen is superior as a carrier of BMP.

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Dental implants have become an accepted form of permanent teeth replacement. The fixture can be implanted in the mandible and/or the maxilla. Diagnostic imaging can play an important role in evaluating such dental implant patients. Especially, computed tomography and computer-reformatted cross-sectional imaging are suitable for the measurement and diagnosis of the mandible and maxilla. However, the absorbed dose from computed tomography was higher than that from conventional tomography, including panoramic radiography.
Magnetic resonance imaging can produce high quality tomographic images with greater soft tissue contrast without ionizing radiation, anesthesia, and injection. The aim of this study was to evaluate the usefulness of magnetic resonance imaging for diagnosis of the preoperative condition of dental implant patients.
Five volunteers were examined by 0.5 T MR scanner, using 3 kinds of sequences-proton density and T1- and T2-weighted images. The detection of the mandibular canal and the maxillary alveolar bone were mainly investigated.
In T1-weighted images, mandibular canal and alveolar bone were detected in all five volunteers.
It was concluded that magnetic resonance imaging was very useful for evaluating the preoperative condition in dental implant patients without using radiation.

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In recent years, implants have been widely used in dental and oral fields. Many cases have been reported, and the indication of implants has been investigated. Many cases progressed well, but a few cases did not.
The unfavorable cases of dental implant were reexamined by clinical observation. The results were as follows
1. The number of unfavorable cases of dental implant increased until 1992 but decreased after 1993.
2. The patients were 20 males and 29 females, and 83.7% of them were 40-69 years of age.
3. Pain was the most common chief complaint of the patients, followed by swelling.
4. Systemic diseases, including hypertension and diabetes mellitus, were noted in 63.3% of the patients.
5. Only 24.5% of the patients who visited our department were referred to us by the dentists who performed the implantations.
6. Right after implantation, 26.5% of the patients showed symptoms.
7. Treatment at our department was removal of most of the implants.

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In recent years, implants have been widely used in dental and oral fields. Many investigators have reported the indication of implants. Most of these cases progressed well, but the others did not.
To investigate the patient's awareness of dental treatments for removal of dental implants, we mailed a questionnaire to 33 patients.
1. The rate of collected questionnaires was 81.8%.
2. 92.6% of the patients underwent treatments such as partial dentures after removal of the implants, but only 40% of the patients were satisfied with these treatments.
3. This investigation clarified that informed consent between the dentists and the patients was insufficient.

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The mobility of 8 one-piece bridges with osseointegrated implant (ITI K type) and 2 natural teeth abutments were examined by Periotest^® (SIEMENS A.G.). The implant of 1 case was removed due to its bad condition after 2 years, but those of 7 other cases were good in clinical findings after about 7 years, and Periotest values (PTVs) were not changed.
Therefore, the significant difference between PTVs of bone remodeling and steady phases is not recognised, and joining of natural teeth and implant is not always contraindicated.

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The efficiency of imaging the anterior teeth of panoramic radiography was investigated and compared with that of zonography on SCANORA^® using the model of steel balls arranged in lines, and clinical application was attempted.
From the results of this experiment, it was concluded that zonography reproduces shape and position better than dental panorama does.
As a result of applying zonography to a patient that had several buried incisor implants, it not only showed a better result in shape and position but also enabled avoidance of a bad effect of trauma shadows of cervical vertebrae.

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Osseointegrated implant prosthesis has become an imperative part in the recent prosthodontic treatment. Since implants have direct bone contact without a periodontal membrane, the occlusal force against the implant prosthesis is directly transmitted to supporting bone around implants. The purpose of this study was to analyze stress distribution during chewing movement in supporting bone around implants and natural teeth. Three-dimensional finite element models of a lower first molar and a titanium implant were constructed.The average angles of closing pathways of the mandible during chewing movement were calculated both in chopping and grinding type patterns.The direction of forced variation of the mandible simulated the calculated angles of closing pathways.
The results were as follows
1. Determination of the direction of displacement constraints by calculating the angles of closing pathways during chewing movement enable analyzing stress distributions during functional movement.
2. The implant model has a high stress concentration in supporting bone around the neck of the implant, while the natural tooth model has sufficient stress distribution in supporting bone. It would suggest that much attention should be paid to occlusion of implant prosthesis.
3. C-type and G-type models showed different stress values for food. It was considered that the occlusal form corresponding to the chewing pattern should be given for implant prosthesis.

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For a long time, gold alloys have been used as metalic materials in dentistry, because they have good chemical and physical properties.
In the field of dermatology, it has been reported that the metal allergies are caused by dental materials and cosmetics.
Gold alloys are basically resistant to corrosion,releasing only minute amounts of ions.
An exposed titanium surface reacts with oxygen to form a tough and tenacious oxide film. It is believed this oxide film is responsible for excellent bio-compatibility of titanium alloy.
We developed Au-1.5%Ti alloy, which can form the oxide film. An oxide titanium layer was formed on the surface of this alloy, which was observed by X-ray microanalyser, after heat treatment.
This fact improved the bio-compatibility of the Au-1.5%Ti alloy.

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Measures to promote osteogenesis during bone repair after the placement of endosseous implants may shorten the period required for initial implant fixation and thereby permit early seating of the superstructure. Prosthodontically, this may provide significant benefits by promoting early restoration of the patient's occlusion. A capacitively coupled electric field (CCEF) was used to promote osseointegration around titanium alloy implants placed in the distal end of the femur of adult rabbits to investigate how effective CCEF stimulation was on peri-implant osteogenesis.
The results were as follows
1. Observation by fluorescent labeling, basic fuchsin-methylene blue double-stain and CMR revealed more newly-formed bone in drilled holes in the stimulated group than in the control group.
2. Fluorescence labeling studies indicated that with time new bone was formed in the direction from the existing bone towards the implant surface in both groups.
3. The results of CMR image analysis demonstrated that the rate of contact between bone and the implant surface was significantly higher in the stimulated group than in the control group (p＜0.001).
4. CMR image analysis also indicated that the level of osteogenesis in the drilled holes was significantly higher in the stimulated group than in the control group.
The results suggested that CCEF may be therapeutically useful in oral implantology.

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Two case treated with GTAM barriers alone to facilitate bone tissue repair for bone defect were reported. The GTAM barrier technique effectively facilitated bone tissue repair, but GTAM barrier alone required more than 1 year for bone tissue filling. Therefore, GTAM barrier with autologous bone graft may be desired to shorten the healing period and to improve bone quality.

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Patients with loss of molar teeth in upper jaw often exhibit restricted endosseous implant due to insufficient vertical bone mass to secure implant between the floor of maxillary sinus and the top of alveolar bone.
Endosseous implant in patients without sufficient vertical bone mass is generally carried out by embedding granules or block of hydroxyapatite, or reconstruction of bone in maxillary sinus floor. However, these methods require considerable surgical invasions and their prognosis have not been thoroughly evaluated¹⁾.
A simple small-scale technique with less surgical invasion was tried by hammering the formed channel floor or drilled floor of hole to make a hypostosis without injuring mucosa of the sinus floor. The floor was lifted, and the resultant space was filled with crushed deciduous teeth or hydroxyapatite granules to secure the vertical bone mass. Then a fixture was embedded in the bone mass. During the procedure, several interesting findings were observed.

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Transplantation of a lower unerupted third molor to a socket of a first or second molor, which was extracted for dental caries, is not rare.
A case of odontogenic sinusitis caused by homoplastic transplantation was experienced, and homoplastic transplantation was considered not to be a better treatment.
This report raised the question of whether or not homoplastic transplantation was a better treatment.

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In the severely atrophic maxilla, prosthetic rehabilitation is difficult. However, rehabilitation using osseointegrated implants with bone grafting can resolve this problem. Among the various methods of bone graft to the maxilla, sinus lift is commonly used.
This report presents two cases of oral rehabilitation using osseointegrated implants with the sinus lift. In case 1, grafted bone was harvested from the mental region of the mandible, and implantation was performed at the same time as the autogenous corticocancellous bone block graft. In case 2, grafted bone was harvested from the alveolar bone in the anterior region of the mandible, and implantation was performed secondarily after the autogenous particulate bone graft.
Bone biopsy for histological analysis was performed in the above two cases.
In both cases, new trabecular bone was observed in the augmented sinus floor. However, the trabeculae were more dense on the alveolar side than in the central area. In the case with splintered bone, empty bone lacunae were seen in the grafted region.

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Swift, accurate impression taking of the bone surface is an indispensable requirement for a successful subperiosteal implant. Therefore, the operability and features of various individual tray materials in combination with precision rubber impression materials were compared to establish an ideal impression taking method of the bone surface. The materials and methods employed for the cases were as follows:
1) Materials for individual tray
(1) Room temperature curing resin: Ostron 100 (GC)
(2) Light-activated resin: Eporex Rebase (Nippon Oil＆ Fats Co., Ltd.)
(3) Thermoplastic resin 1: Erkoplast (Erkodent)
(4) Thermoplastic resin 2: heat forming (Shofu Inc.)
2) Precision Impression Materials
(1) Polysulfide rubber impression materials (Surflex, GC)
(2) Vinyl silicone rubber impression materials (Coltex, Yoshida, Exaflex, GC; Express,3M)
Four subperiosteal implant impression materials (Ostron 100, Eporex Rebase, Erkoplast and heat forming) were applied to the individual tray. As a result, it was found that heat forming was the ideal material from a clinical perspective. This is supported by superior operability without irritation or foul odor, and heat forming properties that allowed for even, sufficient thickness when compared to the other three materials mentioned above.

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The major factor for a successful subperiosteal implant depends on sufficient membrane peeling and precision impression taking. However, it must be noted that perfect impression taking is a requirement that must be fulfilled within a period of limited effective time of anesthesia and intermittent treatment of the subject. Therefore, in the prior study, the operability and features of various individual tray materials in combination with precision rubber impression materials were compared to establish an ideal impression taking method of the bone surface. In this study, the individual tray materials, applied in various cases to gain insight into some subperiosteal implant impression methods, were as follows
(1) Room temperature curing resin: Ostron 100 (GC)
(2) Light-activated resin: Eporex Rebase (Nippon Oil＆ Fats Co., Ltd.)
(3) Thermoplastic resin 1: Erkoplast (Erko-dent)
(4) Thermoplastic resin 2: heat forming (Shofu Inc.)
Since impression taking of the bone surface is conducted within a limited period of time and operating field, corrective performance of the individual tray becomes a major issue. Among the four types of impression materials it was found that heat forming was the most ideal material in this respect, because it was capable of correction in warm water, being a thermoplastic resin. By combining it with the express system, that is, a machine mixed type-hydrophilic vinyl silicone impression material, it was found that the impression taking time could be shortened or lengthened almost in accordance with the operator's intentions.

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Intraalveolar transplantation by simple extraction of a tooth was performed in two cases of deep root caries, which extended to the alveolar margin and displaced tooth. Remodeling of the marginal bone adjusted to the root and normal periodontal membrane-like structure were present three months after autotransplantations in both cases. Sign of apparent root resorption was not seen one and a half year after the operation in both cases.
These findings indicated that this method would be useful when an orthodontic procedure is desirable but not available for deep root caries, displaced teeth, and so on.

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The alveolar ridge, when left untreated after extraction of teeth, tends to cause alveolar bone resorption, and difficulty is often experienced during implant surgery.
In such cases, implantology at the new socket of the donor site, using blocking membrane or autogenous bone grafting, or implant placement combined with guided bone regeneration method, is being practiced although there are unknown factors in its predictability.
Andreasen reported that, in autotransplantation of teeth, the adaptation of the tooth transplanted to the donor site will not affect the healing of a healthy periodontal ligament.
Therefore, it is considered that significant bone regeneration can be expected even if there are some bone defects around the transplanted tooth if there is a healthy periodontal ligament.
This is a report about two cases in which autotransplantation of teeth was carried out at the site of large bone defect caused after extraction and at the site of bone defect after extirpation of comparatively large radicular cyst.
Good results were obtained in both cases.

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Up to now, replantation and transplantation of teeth has been common treatments in oral surgery. Replantation of teeth is a fundamental method which oral surgeons should learn for the preservation of injured teeth. It is not rare that a lower unerupted third molar is transplanted to a socket of alower first molar which was extracted for dental caries in early age. In the oral surgery field, it has been believed that the average life of replanted teeth is 4 to 6 years and that it is a temporary treatment.
Recently, some investigators reported far better results of replantation and transplantation of teeth than that had been reported in the past. It has been revealed that the key points of this technique is to preserve periodontal membrane, and to perform adequate root canal treatment.
In this paper, the history of this technique, the biological principle to success, the enlarging indication of this technique, and the relation with dental implant are reviewed. In conclusion, this technique will become more important to dentistry and will have an important influence on the development of the dental implantology in the future.

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Monthly explanation meetings on dental implant treatment for patients are held at the Dental Hospital of Nihon University, School of Dentistry, Matsudo. In the meetings, questionnaires are handed out to investigate the patients' knowledge of dental implants who desire implants. In this paper, the outline of the meetings and the results of the questionnaires are reported. The results were as follows
1. Patients had usually obtained information on dental implants through mass media and from acquaintances and/or their families.
2. Patients, when not satisfied with their dentures, showed a tendency to place their hope on the implant.
3. Patients did not have much knowledge of indication and/or contraindication.
4. Most of the patients expected the implant to be more durable than the doctors did.
Patients' knowledge of implant treatment was generally low. The explanation meeting itself was very effective to educate those patients. It was reconfirmed that the operators themselves should give the patients sufficient explanation about the treatment and as a matter of course should operate with sufficient “informed consent.”

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