The condition of implant placement varies for each patient. In addition, the implant body is placed not only vertically against the biting force but also at various angles. Fracture loading reduces as the tilt angle increases. It has been reported that an implant body tilted by 45° fractured at one-tenth of the vertical compression stress.It has also been reported that the bending strength of Ti-6Al-4V alloy decreased with a tilt angle of 30°. The objective of this study was to evaluate the mechanical properties (proof stress, strain and hardness) of Ti-6Al-4V alloy subjected to heat treatment at 515, 535, and 555℃ and different heating times and cooling methods.
Regarding heating time, the highest proof stress was achieved at 90 min and 535℃. Regarding cooling method, furnace-cooling showed the highest proof stress compared to air-cooling and quenching. The proof stress of the furnace-cooled samples was higher than those of the air-cooled and quenched samples. The proof stress was independent of heating time, and the strain was independent of heat treatment. The hardness was independent of heating time and heating temperature. A faster cooling rate decreased the hardness.
Based on observations of the structure, the α and β phase were not changed by heating.
Recently, β-tricalcium phosphate (β-TCP) has been used in clinical implant treatment as a bio-absorbable material. We conducted an experimental histological investigation of the absorption process of small β-TCP granules and new bone formed in extraction sockets.The 4 maxillary incisors on both sides of the maxilla were extracted from 4 adult male Crab-eating Macaques. The extraction sockets on the right side were immediately filled with small β-TCP granules (50-150 μm) to form the experimental group, while those on the left side were unfilled, constituting the control group. At 4, 8, 12, and 16 weeks after surgery, the animals were euthanized and histomorphometric observations were performed. After 4 weeks, newly formed bone was observed from the apex to the middle region of the sockets in both groups, while β-TCP granules were also observed in the experimental group. After 8 weeks, the sockets were filled with newly formed bone in both groups, while βTCP granules remained in the experimental group. After 12 weeks, the findings in both groups were similar to those after 8 weeks, while trabecular bone in all sockets was thicker than after 8 weeks. In addition, small β-TCP granules were observed embedded in the trabecular bone in the experimental group. After 16 weeks, trabecular bone in both groups was thicker and denser than after 12 weeks, with a few β-TCP granules remaining in the trabecular bone of the experimental group. Image analysis showed that the amount of new bone formed in the sockets increased in both groups throughout the experimental period. In addition, the ratio of small β-TCP granules to new bone in the sockets of the experimental group decreased over time. Furthermore, after 4 and 8 weeks, the total amount of hard tissue in the experimental group (new bone and remaining β-TCP granules) was larger than in the control group (new bone).Our results revealed that absorption of small β-TCP granules required more than 16 weeks and that the remaining granules enclosed in the new trabecular bone did not inhibit new bone formation. These results indicate that small β-TCP granule materials are useful for extraction socket preservation.
Poly(ethylene terephthalate)(PET)sheet coated with a double layer of gelatin and calcium phosphate, which was proved to assist the proliferation of MC3T3-E1 cells and deposition of calcium salts in vitro, was examined for its efficacy in promoting new bone formation in vivo. Extraction cavities of beagle dogs were surrounded by the sheet for 14 and 30 days in a similar way that a non-resorbable membrane is used in guided bone regeneration (GBR). Histological observation revealed noticeable new bone formation in the extraction cavities covered with the sheet, and gingiva was regenerated on the newly formed bone. New bone formation was also recognized in the space between the sheet and the existing bones. The hardness, flexibility, and shape recovery ability inherent to PET were also favorable characteristics for a space-making membrane. The sheet did not cause any adverse effects on the living body. Even when a part of the sheet was exposed to the outside due to minor divulsion, no infection was found. The results of this study suggest that the present sheet may be a highly promising material for non-resorbable membrane used in GBR.
Biomimetic calcium phosphate ceramics with excellent bio-absorption and osteoinduction were designed by the partial dissolution-precipitation (PDP) treatment. Beta-tricalcium phosphate (β-TCP) ceramics with a single phase were transformed into monetite, hydroxyapatite (HAp) and β-TCP phases by the PDP treatment. The PDP-β-TCP ceramics had a specific surface area of 22.5 m2/g and porosities of 60-80%. Changes in microstructure of the ceramics before and after the PDP treatment influenced body fluid permeation, release characteristics of bone morphogenetic protein (BMP)-2 and osteoinduction.125I-labeled BMP-2 was loaded on two different ceramics, such as β-TCP and PDP-β-TCP. The two kinds of ceramics were implanted into the back region of subcutaneous tissue in rats and the in vivo release profiles of 125I-labeled BMP-2 and dose-responses of bone formation were investigated. In the PDP-β-TCP/BMP-2 system, the release time corresponding to the half amount (t1/2) of BMP-2 were prolonged about 7 times compared to the ceramics before adding the PDP treatment. BMP-2 dose-response of bone formation study showed the areas of bone tissues were significant higher in the PDP-β-TCP/BMP-2 (0.5 μg) system compared to the ceramics before adding the treatment. Furthermore, regions of body fluid permeation were observed as densely stained areas in the PDP-β-TCP/BMP-2 system. These results indicated the PDP treatment enhanced BMP-2 release, body fluid permeation and osteoinduction.
The distribution of stress in the jawbone during mastication is highlighted in this paper as an important index of the mechanical performance of dental implants. The objective of this paper is twofold. The first objective was to demonstrate the importance of considering the heterogeneity (spatial distribution) of the mechanical properties of jawbone in stress analysis. Next, the influence of the alignments of the implants on the peri-implant bone stress was examined using a finite element method (FEM) and numerical analysis model which reproduced the heterogeneity of the jawbone based on the spatial distribution of the bone density measured as CT data. For the former objective, numerical analyses of a finite element model of the mandible of a patient were conducted. Using CT data of this patient and taking into account the non-uniformity (spatial distribution) of bone density, we reproduced a patient-specific geometry and mechanical properties of the jawbone. In-vivo three-dimensional loads measured by instruments attached to the implants were used in the numerical analyses. As for the material properties of jawbone, we employed two models: a multi-value model that considers the inhomogeneity and spatial variability of mechanical properties of the bone, and a binary model with two discrete mechanical properties for cortical bone and cancellous bone. In the numerical analyses, a large difference in the stress distributions was observed between these two models. This demonstrates the insufficiency of the over-simplified binary model and the validity of the multi-value model that is closer to reality. The effects of the alignments of the implants were analyzed against the maximal voluntary clenching (MVC) load measured in the patient. As a result, peri-implant bone stress was found to be greatly reduced when the alignments of the implants were changed to match the direction of MVC load. It is suggested that such alignments are optimal. As more realistic loads, the loads measured while chewing peanuts were used for implants aligned in such optimal directions. For those loads, stress reduction was observed, especially when the loads had large magnitudes. Thus, we demonstrated the importance of accurate modeling of bone material properties and the alignments of implants in terms of the distribution of peri-implant bone stress.
Objective: Superstructures can be placed immediately to restore masticatory function or in the early period after implant placement. Another method involves the use of transitional mini-implants to enhance the support of provisional dentures and to restore masticatory function in the early period after surgery. However, there have not been many reports on the clinical course or success rate of transitional mini-dental implants. In this study, transitional mini-implants were placed in the anterior regions of edentulous patients at the Division of Oral Implantology at our university hospital. These implants were clinically examined until their removal, and their usefulness was evaluated. Methods: The subjects were 10 patients (4 men and 6 women, mean age: 65.3±12.16 years). They underwent implant placement surgery in their mandibles and simultaneous transitional mini-implant placement in the anterior mandibles between February 2007 and October 2011 at the Division of Oral Implantology. The items examined included duration of the loading period, complications, implant survival rate, and bone quality. Results: A total of 21 transitional mini-implants were placed in 10 patients. The mean duration of the loading period was 117±17.64 days. Some patients had complications of implant mobility, pain, and suppuration. These complications caused 3 implant bodies to be removed during the non-loading period and relief was needed in two implant bodies. The survival rate of transitional mini-implants was 85.7% (18/21 implants) during the non-loading period. The survival rate of implant bodies was 100% (44/44 implants). The bone quality ranged from D2 to D3. Discussion and Conclusion: In this study of 10 patients, the results suggest that the complications were more likely to occur when there was strong occlusal force on the transitional mini-implants rather than poor bone density at the implant site. The survival rate of implant bodies was 100% during the non-loading period, and masticatory function was restored in the early period after surgery. These results show that treatment with a transitional mini-implant is effective. In determining the implant placement site, complications would be less likely to occur if the occlusal force on the transitional mini-implants is decreased.
Purpose: We report a case of bisphosphonate-related osteonecrosis of the jaw (BRONJ) around implants placed in the mandible diagnosed by histopathological findings. The patient was a 58-year-old female who visited our department on 10th April 2010 due to gingival swelling and a feeling of discomfort around an implant placed in the left mandibular molar area. She had been treated by intravenous administration of bisphosphonate preparations (BPs) for vestibular bone metastasis due to breast cancer from October 2002 to March 2009. Based on the clinical findings, BRONJ was strongly suggested, so necrotic bone including the implant was resected under general anesthesia. Non-decalcified specimens of the resected bone were prepared and stained with toluidine blue. Results: She could start cancer chemotherapy because no recurrence of inflammation was noted postoperatively. However, she died from multiple metastasis one year postoperatively. Histopathological examination of marginally excised bone showed extensive contact without connective tissue between bone and the implant surface and also bone necrosis without osteocytes in lacunae of the bone. Discussion: At present, conservative medical treatment is recommended for BRONJ. However, we think it is acceptable to perform surgical treatment for BRONJ patients who need cancer chemotherapy as soon as possible.
Mastication behavior is regulated in a coordinated fashion by stomatognathic organs. Oral sensation including periodontal sensation is related to quality of mastication. While many experiments on implant sensation have been reported, the perception of osseointegrated implants is unclear. In this study, a literature review was conducted using the databases of PubMed and the Japan Medical Abstracts Society to survey the evidence relating to the difference of sensation by occlusal stress between endosseous dental implants and natural teeth. We searched the Pubmed database by using the keywords: "perception", "dental implants", and "sensation";and the Japan Medical Abstracts Society website by using the keywords:"dental implant (shika-inpuranto in Japanese)", "sensation (kankaku in Japanese)", and "perception (chikaku in Japanese)". 28 articles (20 English and 8 Japanese papers) were found in total in the two databases. Of these, 17 papers were on pressure perception and 7 on occlusal perception (appreciable thickness to bite), 1 on touch perception, 2 on vibration perception, 1 on response time, and 1 on hardness perception. Overall reports suggested that the perception thresholds of osseointegrated implants were significantly higher than those of natural teeth. More detailed experiments are required for a systematic review on implant perception.
A clinical survey was conducted in new patients who visited the Dental Implant Clinic in the Dental Hospital of Tokyo Medical and Dental University at five-year intervals from April 1996 to March 2011. The total number of new patients, gender distribution, age distribution and reasons for their visit each year were calculated and analyzed. The following results were obtained. The number of new patients increased markedly from 275 in 1996 to 1644 in 2011, although the growth rate has showed a decline in recent years. The male-female ratio was 1 to 2 almost every year. By age bracket, the largest number of new patients in each year was those in their 40s and 50s in 1996, 50s in 2001, 50s and 60s in 2006 and 60s in 2011. This trend of aging in new patients may be attributed to the yearly decrease of the number of missing teeth and the difference of consumer propensity by age group. Regarding reasons for their visit, about 80% of the patients sought dental implant treatment. The number of patients who had complaints about previous implant therapy increased year by year, although its proportion to the total number of new patients remained approximately constant. Appropriate measures for such patients with complaints should be established and implemented.
Objective: Implant therapeutics is a field of comprehensive dentistry requiring various dental knowledge, techniques, and experience. Although it is currently taught as an undergraduate program in many educational institutions, its content varies. Postgraduate clinical training should incorporate this program. We conducted an attitude survey on implant treatment training involving residents to promote the program and provide residents with appropriate knowledge and understanding of implant treatment. Methods: All 134 postgraduate residents between 2006 and 2011 at Kanagawa Dental University Yokohama Clinic participated in this study. On the first day, a lecture was given on implant surgery, and the subjects watched a video on implant surgery and a live operation using a monitor television. Implantation procedures were explained, implantation procedures were practiced using defect models, and individual trays were produced using implantation models. On the second day, a lecture was given on implant prosthetics, and impression-taking using the open- and closed-tray methods was performed using the individual trays. The questionnaire consisted of 15 items, including the degree of difficulty, necessity, and introduction of implant treatment, as well as opinions, selection reasons, and impressions. Questionnaires were filled in before and after the training, and statistical analysis was performed using the Wilcoxon rank sum test. Results: Regarding the question “What do you think of implant treatment compared to partial dentures and bridges?”, subjects answered that implant treatment was better than bridges requiring tooth grinding after the training. To the question “Would you recommend implant treatment to your family?”, the number of subjects who answered “yes” increased after the training. When asked “Is implant treatment more difficult than other treatment methods?”, the number of subjects who answered “yes” decreased after the training. To the question “If patients ask, can you explain about implants?”, the number of subjects who answered “yes” increased after the training.All subjects answered “yes” to “Is this training necessary?”. The question on time allocation revealed that the training time was short. Significant differences were observed between before and after training, which revealed that further education on implant therapeutics for postgraduate residents is needed. Conclusions: The number of residents who could explain implant treatment increased after the training; however, the influence of undergraduate education in recent years was reflected in these results. A systematic educational program that connects enrichment of the core curriculum in undergraduate education with postgraduate clinical training is needed. Our aim is to conduct further training including observation of treatment at our single training institution to maximize educational effects.