This was the third summer since the COVID-19 infection was confirmed in Japan. Many people may not have expected it to last this long. At the beginning of the outbreak, there was much confusing information that made the public and dental professionals feel nervous. At such times, the prompt dissemination of information by academic societies and organizational bodies such as dental associations can have an enormous impact in reaching out to society. We believe that the most important role of an organization is to ensure the healthy lives of the public and to protect the lives of dental professionals. Close collaboration among academic societies, dental associations, and governments to build relationships of trust so that both the public and dental professionals can provide dental care safely and securely will help improve the value of dental treatment, thus raising the public health of the nation.

Half a century has passed since the establishment of the current predecessor of the Japanese Society of Oral Implantology, and the society has grown to become the largest dental society in Japan, and continues to be active as a leading society responsible for the clinical practice of implant dentistry in Japan. In dentistry, dental materials that are classified as medical devices by the Pharmaceutical and Medical Device Act have been frequently used. Implant treatment frequently uses implant bodies and bone graft materials that are classified into high-risk classes 3 and 4 in the risk classification, so it is necessary to control biological reactions. The surface of the implant body has been modified as a scaffold for bone formation, and it is expected to be connected with regenerative therapies such as the use of growth factors and cultured cells in the future. In addition, further utilization of digital technology is expected from treatment planning to surgery and prosthetic procedures. On the other hand, in Japan, which has entered a super-aging society, it is important to manage implants throughout patients' lives so that they not only maintain their health but also respond to health risks. The Society will continue to work with the goal of extending the healthy life expectancy of people by revising treatment guidelines, enhancing lifelong training programs, training specialists, and providing information to people.

The structure of disease in Japan is changing drastically with the declining birthrate and aging population, and the medical community is faced with the great challenge of caring for and nurturing newborns and extending healthy life expectancy. The Japan Prosthodontic Society has been preparing for the super-aging society with the slogan “healthy longevity created by occlusion and mastication”, and at the 129th Annual Meeting held in 2020, a symposium “Extending healthy life spans by improving eating power: significance of prosthodontics” was held to discuss the ideal prosthodontics treatment for those requiring support and nursing care. The symposium was co-sponsored by the Science Council of Japan and the Japan Psychogeriatric Society. Subsequently, in collaboration with the Japan Psychogeriatric Society, the Japan Prosthodontic Society have been tackling the socially important issues of recovery of masticatory function, food support, and measures against dementia through nutritional intake.

At the same time, the Japan Prosthodontic Society have also been working on the ideal of prosthetic dentistry for patients who require nursing care and support due to the onset of dementia or other systemic diseases, that is, the rational long-term management of patients after prosthetic treatment. In this context, the authors have proposed the selection of dental prostheses for long-term management, and the rationalization and labor-saving of prosthetic treatment, including post treatment management, which is called database-driven prosthodontics using a three-dimensional digital morphological database.

In this paper, the authors will discuss the role and potential of prosthetic dentistry in a super-aging society, focusing on its role in preventing cognitive decline or the onset of dementia, and the role of digital dentistry in long-term post-treatment management.

In 2011, “Problems related to dental implant treatment ─ focusing on physical problems ─” was announced by the National Life Center, and related academic societies and other organizations took measures to promote appropriate implant treatment. In 2019, we announced “Is your dental implant okay? ─ Consultations regarding dental implants that will not disappear ─”. The Japanese Society of Periodontology and the Japanese Academy of Clinical Periodontology responded to this presentation by saying, “Both societies will continue to be responsible for appropriately promoting implant treatment, which is becoming more important as part of periodontal treatment. We will listen to the voices of our patients and make sincere efforts to establish periodontal treatment and oral implant treatment that are trusted by the public.”

It goes without saying that dental implant treatment is an indispensable and important treatment for restoring oral function. Specialists in dental implant treatment must meet the expectations and gain trust from the nation. The training of dental implant specialists who are trusted both in name and practice and the setting of strict qualifications for authorizing specialists are necessary for society. As President of the Japanese Society of Oral and Maxillofacial Surgeons, I hope that implant dentists wil1 be certified as dental implant specia1ists who are truly trusted by the public as soon as possible.

Implant superstructure materials can be broadly divided into resin-based, ceramic-based, and metal-based materials, and there are many options. Ceramic-based materials are further divided into glass-ceramic-based and zirconia-based. On the other hand, advances in digital technology have made it possible to manufacture implant superstructures with high fitting accuracy using CAD/CAM systems. As CAD/CAM systems are diversifying year by year, the types of materials that can be used are increasing, which makes it difficult to select a material. For example, metallic materials are satisfactory in terms of mechanical properties, but their use is limited due to problems of esthetics and allergies. Although super-engineering plastics such as PEEK and PEKK have excellent chemical properties, they are used as frames (cores) due to their low hardness. Glass ceramics and composite resins have a microscopically heterogeneous structure, and their mechanical and chemical properties differ in each microstructural part, and so the surface may become rough when used as a superstructure in the oral cavity for a long period of time, causing the wear of the opposing teeth to increase. On the other hand, zirconia has a homogeneous structure and is the most chemically durable, strong and hard of all superstructure materials. With a mirror-polished surface finish, it can be determined that the wear on the opposing teeth is minimal. Therefore, from a material science standpoint, it is considered that zirconia has the best properties as an implant superstructure among various dental restorative materials.

Recently, with the development of CAD/CAM technology, the use of prosthetic devices made with zirconia has been increasing, in view of the material's fracture strength, biocompatibility, and esthetics. However, there are few reports on its long-term prognosis. There are three considerations regarding the effective use of zirconia to overcome the complications of implant prostheses. Firstly, zirconia should be used for the stress-bearing area to reduce the risk of fracture. Secondly, the prosthesis should be a screw-retained or frictional-retained type. Thirdly, the intraoral luting technique should be used to achieve the best passive fit.

As there is little data on the use of zirconia, it is important to use zirconia correctly based on both physiological and theoretical properties. This article examines the effective use of zirconia implant prostheses.

Objective : Mandibular bone width is an extremely important consideration when conducting implant treatment, but no study has examined its association with occlusal status. The objective of this study was therefore to identify factors associated with mandibular bone width, including occlusal status.

Subjects and Methods : The bone width at the midline of the mandible, the bone width at the anterior margin of the mandibular ramus, and the maximum masseter width were measured in two groups of patients who had undergone computed tomography scanning for a condition unrelated to implant surgery, one group with normal occlusion and the other with reversed occlusion.

Results : Statistical analysis showed that, in women, the minimum bone width at the midline of the mandible and the minimum bone width at the anterior margin of the mandibular ramus were significantly narrower in individuals with reversed occlusion. In both men and women, the maximum masseter width was significantly narrower in individuals with reversed occlusion. An investigation of the correlation between maximum masseter width and mandibular bone width identified significant correlations between the maximum masseter width and the minimum bone width at the midline of the mandible (r＝0.429, p＝0.014) and the minimum bone width at the anterior margin of the mandibular ramus (r＝0.354, p＝0.047) in women. Regression analysis of factors related to the minimum bone width of the mandible found that occlusion was the only factor significantly associated with bone width at the midline of the mandible (β＝－0.244, p＝0.042) and bone width at the anterior margin of the mandibular ramus (β＝－0.267, p＝0.026).

Conclusions : The results of this study demonstrated that the occlusal relationship contributes to mandibular bone width and masseter width, and that the mandibular bone of patients with mandibular prognathism tends to be comparatively thinner than that of individuals with normal occlusion.

Objective : This study examined the incidence of peri-implantitis based on the frequency of regular maintenance visits without excluding smokers or patients with mild systemic diseases or periodontitis.

Methods : The participants were patients of a single dental clinic who had completed treatment with implant prostheses at least three years earlier. The participants were divided into two groups : regular compliers (RC), who visited the clinic for maintenance at least four times between January 2019 and December 2020;and irregular compliers (IC), who visited the clinic fewer than four times. These two groups were compared in terms of prevalence of peri-implant mucositis and peri implantitis.

Results : The implant survival rate was 99.76% (post-prosthesis mean ± SD : 75.21 ± 30.53 months). Peri-implantitis occurred in 93 of 263 implants (35.5%) in the RC group and 79 of 126 implants (62.7%) in the IC group ; the difference between the groups was statistically significant (p＜0.001). Peri-implantitis occurred in 26.2% of RC patients who did not have periodontitis. The odds ratios of peri-implantitis for peri-implant mucositis, periodontitis, and regular checkup visits were 4.825, 4.290, and 3.054, respectively.

Discussion and Conclusion : The results of this study suggest that regular implant maintenance combined with maintenance therapy (supportive periodontal therapy) are important for preventing peri-implantitis.

Purpose : The aim of this retrospective multi-center study was to determine the survival rate of implants that support mandibular overdentures (IOD), marginal bone loss of the implants, and events and complications during the follow-up period. Materials and

Methods : Data were collected from 64 patients with edentulous mandibles who were treated with IOD at eight clinics by dentists belonging to the Fukuoka Oral Implant Research Association. Sixty-four patients with 183 implants were followed for a mean duration of 8.7 ± 4.0 years. Four kinds of attachments (32 locators, 15 bar attachments, 7 magnetattachments, and 10 ball attachments) were used.

Results : Ten of 183 implants (5.5%) in six patients were lost. Therefore, the implant survival rate was 94.5%. In the 10 failed implants of six patients, six locators, two magnets, and two ball attachments were used, respectively ; there were no failed implants in bar attachments. The bone loss was measured around 156 implants that did not fail. Nearly all bone loss was 0-2 mm among almost all follow-up periods. Five of 110 implants were followed for 5-15 years, exhibiting more than 3 mm of peri-implant bone loss. Changes in the retention discs of locators and the clips of bar attachments were often carried out. Denture base re-linings and repair of fractured dentures were performed infrequently.

Conclusion : The majority of IOD in this study were stable for a long time.

Questionnaire surveys on the Consultation Desk for Oral Implant Treatment have been conducted five times (2015, 2017, 2018, 2019, 2021) since it was launched in March 2013. Based on these surveys, the eight-year results were examined to analyze the activities of the Consultation Desk. The average response rate of Consultation Desk facilities was 81.6%, showing the high awareness of each facility. The average rate of facilities that received consultations was 17.7%, the average number of consultations was 94.8 and the number of consultations of each facility was mostly one to five. The main contents of consultations were dental implant treatments at other clinics. On the other hand, the facilities' respondents expressed the need for disseminating the Consultation Desk system. The Consultation Desk for Oral Implant Treatment is important to maintain the reliability of implant treatment and needs to be strengthened systematically.